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The definitive version is available at http://dx.doi.org/10.1016/j.vetpar.2011.07.016

Thompson, R.C.A. and Smith, A. (2011) Zoonotic enteric protozoa. Veterinary Parasitology, 182 (1). pp. 70-78.

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Accepted Manuscript

Title: Zoonotic Enteric Protozoa

Authors: R.C.A. Thompson, A. Smith

PII: S0304-4017(11)00485-7DOI: doi:10.1016/j.vetpar.2011.07.016Reference: VETPAR 5944

To appear in: Veterinary Parasitology

Please cite this article as: Thompson, R.C.A., Smith, A., Zoonotic Enteric Protozoa,Veterinary Parasitology (2010), doi:10.1016/j.vetpar.2011.07.016

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Zoonotic Enteric Protozoa1

2

R.C.A. Thompson*, A. Smith3

4

WHO Collaborating Centre for the Molecular Epidemiology of Parasitic Infections, 5

School of Veterinary and Biomedical Sciences, Murdoch University, South Street, 6

Murdoch, Western Australia 6150, Australia.7

8

*Corresponding Author: WHO Collaborating Centre for the Molecular Epidemiology 9

of Parasitic Infections and the State Agricultural Biotechnology Centre, School of 10

Veterinary and Biomedical Sciences, Murdoch University, South Street, Western 11

Australia 6150, Australia. Tel: 08 9360 2466. Email: a.thompson@murdoch.edu.au12

13

Abstract14

A growing number of enteric protozoan species are considered to have zoonotic 15

potential. Their clinical impact varies and in many cases is poorly defined. Similarly, 16

the epidemiology of infections, particularly the role of non-human hosts, requires 17

further study. In this review, new information on the life cycles and transmission of 18

Giardia, Cryptosporidium, Entamoeba, Blastocystis and Balantidium are examined in 19

the context of zoonotic potential, as well as polyparasitism and clinical significance.20

21

Keywords: Enteric protozoa, Zoonoses, Transmission, Foodborne, 22

Polyparasitism, Clinical significance, Giardia, Cryptosporidium, Entamoeba, 23

Blastocystis, Balantidium.24

25

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1. Introduction27

28

Humans are susceptible to infection with numerous species of protozoa that colonise 29

the intestinal tract. An increasing number of these protozoa are being shown to have 30

zoonotic potential although their clinical significance varies. Apart from Entamoeba 31

histolytica and Balantidium coli, they do not invade the mucosal tissues or other 32

organs. Cryptosporidium has an epicellular association with the host cell, principally 33

in the mucosal epithelium, but cannot be considered to be invasive. In most cases, the 34

pathogenesis of most enteric protozoa is poorly understood and with some species, 35

such as E. coli, opinions vary as to whether they should be considered as parasites.36

37

In this review, we update the latest information on individual species of enteric 38

protozoa, and then examine transmission, polyparasitism and clinical significance on 39

a broad scale.40

41

2. The parasites42

43

2.1. Giardia44

45

The molecular characterisation of Giardia isolates from different species of 46

mammalian hosts throughout the world has confirmed the existence of host specific 47

species and two species with broad host ranges and which are zoonotic (Table 1). A 48

revised taxonomy has consequently been proposed which largely reflects the species 49

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nomenclature reported by early workers in the field (Monis et al., 2009; Thompson 50

and Monis, 2011). 51

52

The application of multilocus genotyping to Giardia from human and other 53

mammalian hosts in different parts of the world has clearly demonstrated the 54

occurrence of zoonotic species in human and non-human hosts (dogs, cats, livestock 55

and wildlife) in the same geographical areas supporting the potential for zoonotic 56

transmission (rev. in Thompson, 2011; Leonhard et al., 2007). Although such studies 57

do not provide evidence of actual zoonotic transmission, a number of studies in 58

defined endemic foci have provided convincing evidence involving dogs and humans 59

(Traub et al., 2004; Inpankaew et al., 2007; Salb et al., 2008). Although the focus of 60

these studies has been on the dog as a reservoir of human infection, several reports 61

demonstrate that ‘reverse zoonotic transmission’ (zooanthroponotic) is an important 62

factor that must be considered in understanding the epidemiology of Giardia 63

infections. Humans are considered to be the source of infection in non-human 64

primates and painted dogs in Africa, marsupials in Australia, beavers and coyotes in 65

North America, muskoxen in the Canadian arctic, house mice on remote islands and 66

marine mammals in various parts of the world (Graczyk et al., 2002; Sulaiman et al 67

2003; Moro et al., 2003; Appelbee et al., 2005, 2010; Kutz et al., 2008; Dixon et al., 68

2008; Teichroeb et al., 2009 Thompson et al., 2009, 2010b, 2010; Ash et al., 2010; 69

Johnston et al., 2010). These reports raise important issues for conservation. This is 70

because we do not understand the impact Giardia may have on what are possibly 71

naïve hosts that may have been exposed to the parasite relatively recently as a 72

consequence of habitat disturbance and human encroachment (Thompson et al 2010a; 73

Johnston et al., 2010). In contrast, in Aboriginal communities in isolated regions of 74

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northern Australia, reverse zoonotic transmission undoubtedly occurs between 75

humans and dogs but the fact that the dogs are frequently infected with their own 76

host-adapted species of Giardia, G. canis, demonstrates that competitive interactions 77

likely limit opportunities for zoonotic species to establish in dogs (Hopkins et al.,78

1997, 1999; Thompson and Monis, 2004). However, the fact that dogs have contact79

with young children passing Giardia cysts, as well as discarded nappies/diapers, 80

means that dogs are likely to act as mechanical transmitters of zoonotic Giardia since 81

their coats are likely to be contaminated with cysts.82

83

Although competitive interactions between different species/assemblages of Giardia84

has been proposed to explain the predominance of single assemblage infections in 85

both dogs and cattle, this may reflect the consequences of mixed infections in 86

endemic foci where the frequency of transmission is very high. In other situations 87

where transmission is sporadic mixed infections may co-exist and have been 88

increasingly reported from multilocus studies in several countries in humans, dogs 89

and cattle (e.g., Hussein et al., 2009; Sprong et al., 2009; Dixon et al., 2011; Covacin 90

et al., 2011). 91

92

The two zoonotic species/assemblages of Giardia are geographically widespread and 93

as more isolates are genotyped some patterns are emerging on host occurrence. 94

Recent studies in dogs have shown that it is not possible to extrapolate from one 95

geographical region to another in terms of the prevalence or species/assemblage 96

composition of Giardia infections in dogs (Ballweber et al., 2010; Covacin et al., 97

2011). Until recently, comprehensive data on the assemblage distribution of Giardia 98

in dogs in the USA was not available, and studies in Europe had suggested that 99

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assemblage B has a predominantly human distribution (Sprong et al., 2009). 100

However, a recent study of dogs infected with Giardia in the USA found a higher 101

frequency of infections with assemblage B than assemblage A, which has not been 102

reported elsewhere (Covacin et al., 2011). This suggests that in North America at 103

least, we cannot assume that assemblage A is the most common of the zoonotic 104

assemblages found in non-human hosts. Indeed in wildlife, assemblage B often 105

predominates (e.g., Johnston et al., 2010) whereas in cattle, assemblage A is most 106

often reported (Sprong et al., 2009). However, there is extensive genetic sub-107

structuring within assemblage B, and it is possible that some subgroups are commonly 108

associated with zoonotic infections than others. As regards Giardia infections in 109

humans, there is some evidence of geographic sub-structuring (Wielinga et al., 2011) 110

and assemblage B may be more common in isolated and/or community settings where 111

the frequency of transmission is high (Thompson 2000). Under such circumstances, 112

the parasite is likely to be exposed to greater selection pressure in terms of exposure 113

to antigiardial drugs and competitive interactions which might explain why evidence 114

of recombination in Giardia is mostly confined to assemblage B isolates (Lasek-115

Nesselquist et al., 2009; Thompson and Monis 2011).116

117

It is still not yet clear whether the different species/assemblages of Giardia are 118

associated with differences in pathogenesis. Although differences have been reported 119

in human populations infected with assemblage A vs B, no clear picture has emerged 120

(Thompson and Monis 2011). This may be particularly relevant to the two main 121

disease syndromes of diarrheoa and failure to thrive. Similarly, it is not known 122

whether there is any difference in the clinical outcome in dogs infected with the 123

zoonotic assemblages or G. canis.124

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125

2.2. Cryptosporidium126

127

Current evidence indicates that the main reservoirs of zoonotic Cryptosporidium 128

remain livestock, with the potential transmission of C. parvum (= C. pestis [see 129

Slapeta 2011), including the so-called cervine genotype, to humans via contaminated 130

water or through direct contact with livestock (Robertson et al 2010; Gormley et al.,131

2011). Sub-genotyping continues to reveal genetic sub-structuring within C. parvum 132

but whether this is reflected in variation in host specificity and zoonotic potential 133

remains unclear. The recent demonstration of zoonotic transmission to humans in the 134

U.K of a newly described genotype of Cryptosporidium from rabbits (Chalmers et al.,135

2009) has raised concerns that humans may be at risk of Cryptosporidium infection 136

from rabbits in other geographical areas, as recently proposed in Australia where the 137

rabbit genotype has been identified (Nolan et al., 2010). Although given a new species 138

name, C. cuniculi, by Robinson et al (2010), it is genetically very close to C. parvum 139

and C. hominis and thus it may be prudent to reconsider the taxonomic status of all 140

three ‘species’ in the future, particularly given the intra-specific genetic variability 141

that has been described. In contrast, available evidence suggests that the evolving 142

nomenclature for what appear to be host specific forms in different species of 143

domestic and wild animals, is likely to be stable and largely reflective of the early 144

taxonomy (see O’Donoghue, 1995) proposed before the advent of molecular 145

characterisation.146

147

Phylogenetically, Cryptosporidium has been shown to have closer affinities to 148

gregarine protozoa than the coccidians (Barta and Thompson 1996; Borowski et al., 149

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2010). This is reflected in the life cycle, developmental biology, metabolism and host 150

parasite relationship of Cryptosporidium and will require a reappraisal of its biotic 151

potential, particularly in terms of survival, particularly in aquatic environments.152

153

2.3. Entamoeba154

155

Of the zoonotic amoebae, Entamoeba histolytica is undoubtedly of most clinical 156

significance and is considered by some authorities as the only amoeba parasitic in the 157

human intestine (Schuster and Visvesvara, 2004). However, the public health risk 158

from zoonotic transmission of E. histolytica would appear to be minimal. Dogs can be 159

a potential source of human infections following coprophagy of human faeces, 160

although this reverse zoonosis is unlikely to result in significant environmental 161

contamination since E. histolytica rarely encysts in dogs (Eyles et al., 1954; Barr, 162

1998). Similarly, E. histolytica is found in non-human primates (Schuster and 163

Visvesvara, 2004) but the risk to public health would appear to be minimal as such 164

infections appear to again reflect reverse zoonosis.165

166

A number of other potentially zoonotic species of Entamoeba have been reported in 167

humans including E. coli, E. polecki and E. hartmanni ( Meloni et al., 1993; Stensvold 168

et al., 2011). They have generally been considered to be ‘non-pathogenic’ and 169

‘commensals’ but increasing evidence of their widespread and common occurrence, 170

particularly as co-infections with other enteric protozoa and helminths, warrants a re-171

evaluation of their potential clinical significance. Of the three species, E. coli is one of 172

the most commonly reported enteric protozoa in human surveys (Chunge et al.,1991; 173

Ouattara et al., 2008; Youn, 2009; Boeke et al., 2010), and apart from non-human 174

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primates (e.g. Howells et al., 2011) has been recovered from dogs and marsupials 175

(Campos Filho et al., 2008; Youn, 2009). It also exhibits extensive genetic diversity 176

with at least two major subtypes. Although previous reports have considered E. 177

polecki to be zoonotic (Barnish and Ashford, 1989), recent molecular studies suggest 178

this species is restricted to humans whereas E. hartmanni is potentially zoonotic with 179

infections reported in non-human primates (Stensvold et al., 2011).180

181

2.4. Blastocystis182

183

Blastocystis is an emerging pathogen in terms of its association with disease and 184

zoonotic potential (Vassalos et al., 2008; Boorom et al., 2008; Parkar et al., 2010). 185

Now that robust molecular tools are available to detect and characterise Blastocystis, 186

it has been shown to be both more common and genetically diverse than previously 187

envisaged (Parkar et al., 2010). Blastocystis is a ubiquitous parasite of humans usually 188

associated with chronic infections, the prevalence of which increases with age. In 189

addition to humans, Blastocystis is common in numerous species of wild and 190

domestic animals (Parkar et al., 2007, 2010; Yoshikawa et al., 2008).191

192

As has been shown with Giardia and Cryptosporidium, Blastocystis comprises a 193

genetically variable complex of interspecific and intraspecific variants and a stable 194

taxonomy has yet to be established. Humans are susceptible to infection with a variety 195

of genetically distinct subtypes some of which have also been reported in domestic 196

and wild animals (Parkar et al., 2007, 2010; Yoshikawa et al., 2008). Studies in 197

defined endemic foci, such as zoos, have provided convincing evidence of zoonotic 198

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transmission (Parkar et al., 2010). However, the frequency of zoonotic transmission 199

and risk factors have still to be clearly defined.200

201

2.5. Balantidium202

203

This is the only ciliate known to cause infections in humans and is considered to be 204

zoonotic with pigs as the asymptomatic natural reservoir, although other domestic 205

livestock such as cattle may be infected in some areas (Bilal et al., 2009). Non-human 206

primates are also susceptible to infection (see Howells et al., 2011) but their role in 207

zoonotic transmission is likely to be minimal.208

209

Balantidium is most common in tropical and subtropical regions (Zaman, 1998; 210

Farthing et al., 2003; Owen, 2005) and the risk of infection in humans is in 211

communities that have a close association with pigs (Schuster and Ramirez-Avila 212

2008). However, infection in humans is rarely reported (Farthing et al. 2003; Schuster 213

and Visvesvara, 2004; Conlan et al. 2011). The parasite is invasive in humans and can 214

cause serious disease but cases are reported sporadically (Schuster and Visvesvara, 215

2004; Conlan et al., 2011). The low reported prevalences, even in pig rearing 216

communities (Owen 2005; Kirkoyun Uysal et al., 2009) would suggest that even if 217

cysts are ingested from the environment, the parasite rarely establishes ‘patent’ 218

infections. However, the only reported waterborne outbreak originating from 219

contaminated pig faeces, resulted in 110 people infected (Walzer et al., 1973 [in 220

Farthing]). This would suggest that sporadic and/or isolated infections usually go 221

unnoticed or that sojourn in water may enhance infectivity to humans in some way.222

223

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3. Transmission224

225

3.1. Pathways of transmission226

227

Specific transmission pathways for enteric protozoan parasites can be difficult to 228

determine though some routes are more common than others. Direct transmission via 229

the faecal/oral route is likely to be the most common form of transmission, whether 230

zonotic (see above) or direct person to person. However, indirect transmission, where 231

infection results through the mechanical transmission of oo/cysts on, for example, 232

flies (Szostakowska et al., 2004) or other animals such as dogs or livestock, or by the 233

contamination of food or water sources (Smith et al., 2007; Karanis et al., 2007; 234

Nyarango et al., 2008), poses a significant threat particularly in the developing world. 235

Quantifying the level of protozoan parasite infection using commonly applied metrics 236

such as the DALY (eg Pruss et al., 2002) is impractical unless gross non-specific 237

estimates are required as distinguishing between all possible sources of infection and 238

the confounding impact of polyparasitism is rarely if ever possible (Payne et al., 2009; 239

King 2010). Epidemiological analysis of focal point contaminations such as water or 240

specific food contamination events can provide good estimates of the spread and 241

impact of parasite infection, but on a global scale, due to the uncertainty caused by the 242

scarcity of data (Payne et al., 2009) the impact of these occurrences remains poorly 243

understood.244

245

3.2. Enhancing transmission246

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Children are a particularly high risk group for infection with enteric protozoan 248

parasites although the relative risk for infection with different parasites varies 249

between different geographic regions of the world (Figure 1). Interestingly, based on a 250

major review of the number of reports in the scientific literature (Smith and 251

Thompson, unpublished report, Food Safety, Zoonoses and Foodborne Diseases, 252

World Health Organization, Geneva) the risk of infection appears greater within rural 253

environments than within urban areas; presumably because of the increased 254

opportunity for both direct and indirect transmission to occur in areas with poor 255

sanitation and higher contact rates with wildlife and domestic animal reservoirs of 256

infection.257

258

Poor hygiene has been shown to be a crucial factor in enhancing the transmission of 259

enteric protozoa (Ang, 2000; Alvarado and Vasquez, 2006; Diaz et al., 2006; 260

Balciogul et al., 2007; Azian et al., 2007). However, the term ‘poor hygiene’ is broad 261

and does not fully describe the range of risk factors involved. 262

263

Blastocystis, Cryptosporidium, Giardia, Entamoeba spp, and Balantidium can all be 264

transmitted in water, including drinking water sources, recreational water, as well as 265

lakes and streams. The impact of infection obtained from lakes and streams varies 266

greatly depending on geographic location as there exists significant variation in the 267

use of such water bodies throughout the world as well as within regions depending on 268

socioeconomic status. For example the predominant use of lakes and streams in 269

Europe is recreational whereas in Africa or Asia there is a much greater reliance on 270

these water sources for drinking and in the preparation of food and personal hygiene. 271

Waterborne transmission of parasites in the developed world is therefore more likely 272

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to be the result of contamination, or a process failure within water utilities, industry or273

in public places such as swimming pools (Welch, 2000; Stuart et al., 2003; Dawson, 274

2005; Shields et al., 2008). In the developing world in particular, areas which are 275

prone to flooding face an increased risk of waterborne infection particularly where 276

basic sewerage systems such as long-drop latrines are common. The risk is further 277

increased in those communities and societies where the keeping of animals (pets and 278

livestock) within or near the home is common and the risk of infection with specific 279

parasites including concurrent infections will vary culturally depending on the species 280

of zoonotic reservoir involved (Hunter and Thompson, 2005). 281

282

3.3. Foodborne transmission283

284

Cases of foodborne transmission have until recently been difficult to determine, and 285

linking infection to a contaminated food source remains so for the majority of 286

scenarios. Small scale outbreaks, where the point of initial contamination may be the 287

result of poor hygiene by an individual resulting in localised foodborne transmission 288

to family members or the immediate community, are extremely common particularly 289

in the developing world. Transmission resulting from contamination of food or drink 290

that leads on to larger scale infections, such as an outbreak of cryptosporidiosis in the 291

USA in 1993 arising from the consumption of infected fresh-pressed apple cider is a 292

relatively much rarer event (Millard et al.,1994). Again, according to reports 293

published in the primary scientific literature, the risk of becoming infected with 294

Blastocystis from contaminated food appears low, although infection arising through 295

poor hygiene practices of food handlers has a potentially much higher infection rate. 296

For example, a survey of 150 apparently healthy food handlers in Bolivar State, 297

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Venezuela, showed that 25.8% (n = 107) were in fact positive for Blastocystis298

(Requena et al., 2003), whereas a review of 103 published reports concerning 299

Blastocystis infection between 1990 and 2008 showed that none were able to 300

conclusively ascribe infection to conventional foodborne transmission (Smith and 301

Thompson, unpublished report, Food Safety, Zoonoses and Foodborne Diseases, 302

World Health Organization, Geneva). However, other enteric parasites are readily 303

transmitted on food and in some regions of the world farming and agricultural 304

practices such as the use of human waste for fertilisation and inefficient or absent 305

pasteurisation techniques positively enhance transmission. None the less, the majority 306

of indirect transmission from contaminated food arises from more proximate sources 307

of infection such as infected food handlers and poor hygiene, often resulting from 308

overcrowded living conditions where clean running water is scarce, and also from 309

children and adults with little or no health education.310

311

Foodborne transmission, whether arising as a result of agricultural practices or poor 312

hygiene within households, or by food handlers, is undoubtedly responsible for a 313

significant number of infections every year. Preliminary estimates derived from a 314

literature review of published reports and case notes for Cryptosporidium and Giardia315

occurrence, suggest that the number of cases of foodborne transmission resulting in 316

infection by Giardia range from 13 million in the WHO derived Eastern 317

Mediterranean region (EMR) to 76 million in the Western Pacific Rim (WPR) region 318

(Fig 1). Similarly, preliminary estimates for Cryptosporidium suggest there may be as 319

many as 6 million cases of foodborne transmission annually in the EMR region and 320

up to 27 million in the African region. However, these estimates must be interpreted 321

with extreme caution as the majority of publications upon which most estimates are 322

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based simply do not, or cannot, ascribe infection to a particular source or event such 323

as contact with contaminated food. Transmission between humans, either involving 324

intermediate vessels such as contaminated food or water, or via direct contact, is 325

ultimately responsible for most reported cases, with zoonotic parasites and parasite 326

strains as well as zoonotic sources of human strains also a major source of infection in 327

many parts of the world (Thompson 2000; Feltus et al., 2006; Ng et al., 2008; 328

Thompson et al., 2008). 329

330

4. Polyparasitism331

332

The clinical impact of zoonotic enteric protozoan infections is greatest in the 333

developing world where inadequate sanitation, poor hygiene and proximity to 334

zoonotic reservoirs, particularly companion animals and livestock are greatest. In such 335

circumstances, it is not surprising that infections with more than one species of enteric 336

protozoan is common, and in fact single infections are rare (see above). 337

Unfortunately, the impact on health of such concurrent/co-infections has not been 338

adequately taken into account. Awareness of the significance of polyparasitism 339

(concurrent/concomitant infections) in terms of malaria, schistosome infections and 340

more recently gastrointestinal (GI) helminths, is now well established (Cox, 2001; 341

Pullan and Brooker, 2008; Midzi et al., 2008; Koukounari et al., 2010; Supali et al 342

2010). However, the impact of polyparasitism in the context of enteric protozoan 343

infections has not been considered (Ouattara et al., 2008).344

345

Enteric protozoan infections are components of a complex ecological system, shared 346

with helminths and bacteria. As such, we should not study the components of such an347

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ecological system in isolation (e.g., see Rohani et al., 2003) especially when 348

considering their impact on disease dynamics (Jolles et al., 2008). Polyparsitism will 349

lead to the stimulation of different components of the immune system that may act 350

synergistically, lead to competitive interactions and/or alter pathogenic behaviour of 351

one or more species (Thompson and Lymbery, 1996; Cox, 2001; Mideo, 2009; 352

Koukounari et al., 2010; Supali et al., 2010). These may have an additive and/or 353

multiplicative impact on nutrition and pathogenicity (Pullar and Brooker, 2008) 354

leading to an increase or decrease in clinical severity, and/or interfere with normal gut 355

microflora. 356

357

Current measures of determining the impact on health of parasitic disease (DALY) do 358

not take into consideration the “co-morbidities of polyparasitism” (Payne et al., 2009). 359

Payne and colleagues suggest a new approach where co-infections with more than one 360

infectious agent are defined as a specific disease, for example malaria, hookworm, 361

malaria + hookworm etc. This would appear a logical approach and should be readily 362

achievable with diseases such as malaria and hookworm where the pathogenic 363

mechanisms of the individual aetiological agents are reasonably well understood. This 364

would be much more of a challenge with most of the enteric protozoa since their 365

pathogenesis is still poorly understood, particularly in chronic infections. However, it 366

is an area of future epidemiological research that should be given priority.367

368

Available survey data, mostly from rural areas of developing countries, that provide 369

data on the prevalence of mixed infections with enteric protozoa show that they are 370

the rule rather than the exception and that children are at most risk with the majority 371

of the populations studied infected with at least two species of protozoan (Chunge et 372

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al., 1991; Ouattara et al., 2008; Nematian et al.,2008; Nguhiu et al., 2009; Aly and 373

Mostata, 2010). The most commonly represented protozoa in concurrent infections 374

are Giardia, Blastocystis, and Entamoeba coli, which are usually also found with the 375

cestode Hymenolepis nana (Chunge et al., 1991; Meloni et al., 1993; Ouattara et al., 376

2008; Nematian et al., 2008). Chronic helminth infections could have a significant 377

influence over the immune response and hence susceptibility to other pathogens 378

(Rodriguez et al., 1999). This was concluded in the context of GI nematode infections 379

but consideration should also be given to H. nana which is rarely found on its own in 380

developing areas of the world and usually co-infects with one or more enteric 381

protozoan species. Depending on the endemic area, E. histolytica and E. dispar may 382

also occur in mixed infections. In addition, other potentially zoonotic protozoa, such 383

as Chilomastix mesnili and Endolimax nana that may have been dismissed as having 384

no clinical consequence and not reported, are also probably common (e.g. Chunge et 385

al., 1991) and in the context of polyparasitism should be considered.386

387

5. Clinical significance388

389

The clinical impact of Entamoeba histolytica and Cryptosporidium in humans are 390

well understood. They have clearly defined individual effects on the host and the 391

resulting morbidity will be worsened in an additive way when other enteric protozoa 392

are present. The severity of Cryptosporidium infections is greatest in individuals with 393

an impaired or deficient immune system. Much less is known about the clinical 394

impact of other enteric prototozoa particularly in chronic and mixed infections.395

396

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The symptoms associated with Giardia infections vary greatly but have mostly been 397

documented on the basis of individual infections with the expression of short-lasting 398

diarrhoea the most common manifestation (Eckmann, 2003). However, there is 399

increasing realisation that the clinical impact of Giardia is greatest in children, 400

particularly in developing countries or disadvantaged communities where poor 401

hygiene and the proximity of animal reservoirs favour a high frequency of 402

transmission and the establishment of chronic infections (Thompson, 2009). In such 403

situations, nutrition may be suboptimal and Giardia infections contribute to poor 404

growth and development (‘failure to thrive’), zinc and iron deficiency, as well as 405

predispose to the development of allergic diseases (Muniz-Junqueira and Queiroz, 406

2002; Muniz et al., 2002; Nematian et al., 2008; Hesham et al., 2005; Savioli et al.,407

2006; Thompson, 2008; Boeke et al., 2010; Duran et al., 2010; Quihui et al., 2010). 408

Importantly, diarrheoa is not necessarily a symptom in such chronic infections (Nash 409

et al., 1987; Chunge et al., 1991; Flanagan 1992; Rodriguez-Hernandez et al., 1996; 410

Troeger et al., 2007), which are often shared with enteric parasites that contribute to 411

the syndome of failure to thrive, such as Entamoeba coli, Blastocystis and 412

Hymenolepis nana (see above). Reports from around the world suggest there are 413

differences in the clinical outcome in humans of infections with assemblage A (G. 414

duodenalis) and assemblage B (G. enterica) (Thompson and Monis, 2011). However, 415

it is difficult to directly compare between reported studies because of differences in 416

design and populations sampled. It has been suggested that infections with 417

assemblage A are usually short lasting, acute infections often associated with 418

diarrhoea whereas infections with assemblage B are more common in community 419

settings or localised endemic foci where the frequency of transmission is high 420

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resulting in chronic infections that may contribute to poor growth (Thompson and 421

Monis, 2011).422

423

There is now increasing recognition that Blastocystis is pathogenic, at least in 424

humans, although the circumstances and mechanisms associated with disease are not 425

understood (Boorom et al., 2008). Similarly, the spectrum of disease manifestations 426

associated with Blastocystis infections have yet to be clearly defined. Many of the 427

documented symptoms are non-specific and may be overlooked but the realisation 428

that Blastocystis is most often associated with chronic infections and that prevalence 429

increases with age, demonstrates that such symptoms may be indicative of a range of 430

disorders, often sporadic, not necessarily associated with an enteric pathogen, for 431

example inflammatory bowel disorders (Boorom et al., 2008). As with Giardia, it is 432

possible that some ‘strains’ of Blastocystis are more often associated with overt 433

disease than others (Boorom et al., 2008). The developmental cycle of Blastocystis is 434

not completely understood. It comprises a range of morphologically pleiomorphic 435

stages and it is not clear whether all are always represented and whether some are 436

more pathogenic than others.437

438

Most attention on the clinical effects of zoonotic enteric protozoa has focussed on 439

infections in humans. Comparatively little is known about the clinical consequences 440

of infections in domestic animals and livestock.441

442

Although infections with Giardia, and to a lesser extent Cryptosporidium, are 443

common in dogs and cats, infections are usually asymptomatic (Thompson et al., 444

2008). Giardia infection in ruminants is also often asymptomatic, but may also be 445

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associated with the occurrence of diarrhoea and ill-thrift in calves (O’Handley et al.,446

1999; Geurden et al., 2006), as well as production losses (Olson et al., 1995). In this 447

respect, the effects of polyparasitism, with Giardia as one member of an often diverse 448

parasite community in livestock (O’Handley and Olson, 2006), requires further study. 449

Infections with Cryptosporidium in calves can be clinically significant with profuse 450

diarrhoea, depression and anorexia, and is often life threatening in housed animals 451

where stress associated with overcrowding may predispose to disease (Thompson et 452

al., 2008).453

454

The impact of enteric protozoa on wildlife is not known, but there is evidence of an 455

association with clinical disease of infections with Giardia and Balantidium in 456

primates (Graczyk et al., 2002). The stress associated with captivity may further 457

predispose to disease, particularly in the case of infections of Cryptosporidium in 458

wildlife. This incredible diversity of species and ‘strains’ of Cryptosporidium, 459

Giardia and Balantidium in wildlife clearly warrants further study in terms of their 460

potential impact on wildlife health. Habitat loss as a result of human encroachment 461

can lead to a variety of stressors (e.g. increased competition for food, mates and 462

refuge, as well as greater exposure to predators) that may exacerbate the clinical 463

consequences of infection with enteric protozoa in wildlife (Thompson et al., 2010a; 464

Johnston et al., 2010; Howells et al., 2011).465

466

6. Conclusions467

468

Although tremendous advances have been made in the development of 469

molecular epidemiological tools, their practical potential in terms of controlling 470

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enteric protozoan infections has yet to be realised. In both developed and 471

developing countries there has been little progress in identifying risk factors for 472

infection and understanding the outcomes of infection. This is particularly so for 473

the developing world where these infections are most common and the 474

frequency of infection very high. In such environments, the epidemiology of 475

diseases caused by enteric protozoa is poorly understood in terms of 476

transmission dynamics and sources of infection. Importantly, we must not 477

consider enteric protozoan parasites in isolation in terms of impact on their 478

hosts. A child or dog, on good planes of nutrition, harbouring a single infection 479

with Giardia in a developed country represents a very different host parasite 480

relationship to that in a developing country where Giardia rarely occurs as a 481

single infection but is accompanied by several other protozoa, nematodes and 482

cestodes in an environment usually deficient in some way, in terms of nutrients 483

available to the host. Unravelling the interactions and impact on their hosts in 484

such circumstances is an important challenge for the future.485

486

Acknowledgements and conflict of interest487

488

The Australian Research Council and Western Australian Department of Environment 489

and Conservation have supported some of the work reported here. The authors declare 490

that there is no conflict of interest.491

492

References493

494

Page 21 of 42

Accep

ted

Man

uscr

ipt

21

Alvarado, B.E., Vásquez, L.R., 2006. Social determinants, feeding practices and 495

nutritional consequences of intestinal parasitism in young children. Biomedica. 26, 496

82-94.497

498

Aly, N.SM., Mostata, M.M.M., 2010. Intestinal Parasitic Infection Among Children in 499

the Kingdom of Saudi Arabia. Aust. J. Basic Appl. Sci. 4, 4200-4204.500

501

Ang, L. H., 2000. Outbreak of giardiasis in a daycare nursery. Commun. Dis. Public 502

Health. 3, 212-213.503

504

Appelbee, A.J., Thompson, R.C.A. and Olson, M.E. 2005. Giardia and 505

Cryptosporidium in mammalian wildlife—current status and future needs. Trends 506

Parasitol 21, 370-6507

508

Appelbee, A.J., Thompson, R.C.A., Measures, L.M., Olson, M.E. 2010. Giardia and 509

Cryptopsoridium in harp and hooded seals from the Gulf of St. Lawrence, Canada. 510

Veterinary Parasitology 173, 19-23.511

512

Ash, A., Lymbery, A.J., Lemon, J., Vitali, S., Thompson, R.C.A. (2010). Molecular 513

epidemiology of Giardia duodenalis in an endangered carnivore – the African painted 514

dog. Vet. Parasitol. 174, 206-212.515

516

Azian, M. Y. N., San, Y. M., Gan, C. C., Yusri, M. Y., Nurulsyamzawaty, Y., 517

Zuhaizarn, A. H., Maslawaty, M. N., Norparina, I., Vythilingam, I., 2007. Prevalence 518

Page 22 of 42

Accep

ted

Man

uscr

ipt

22

of intestinal protozoa in an aborigine community in Pahang, Malaysia. Trop. Biomed. 519

24, 55-62.520

521

Balcioglu, I. C., Kurt, O., Limoncu, M. E., Dinc, G., Gumus, M., Kilimcioglu, A. A., 522

Kayran, E., Ozbilgin, A., 2007. Rural life, lower socioeconomic status and parasitic 523

infections. Parasitol. Int. 56, 129-133.524

525

Ballweber, L.R., Xiao, L., Bowman, D.D., Kahn, G., Cama, V.A. 2010. Giardiasis in 526

dogs and cats: update on epidemiology and public health significance. Trends 527

Parasitol. 26, 180-189.528

529

Barnish, G., Ashford, R.W., 1989. Occasional parasitic infection of man in Papua 530

New Guinea and Irian Jaya (New Guinea). Ann Trop Med Parasitol., 121-135.531

532

Barr S.C., 1998. Enteric protozoal infections. In: Greene C.E. (Ed). Infectious dieases 533

of the dog and cat. pp482-491. W.B. Saunders, Philadelphia. 534

535

Barta J.R,. Thompson R.C.A., 2006. What is Cryptosporidium? – Time to reappraise 536

its biology, taxonomy and phylogenetic affinities. Trends Parasitol. 22, 463-468.537

538

Bilal, C.Q., Khan, M.S., Avais, M., Khan, J.A., 2009. Prevalence and chemotherapy 539

of Balantidium coli in cattle in the River Ravi region, Lahore (Pakistan). Vet 540

Parasitol. 163, 1-2.541

542

Page 23 of 42

Accep

ted

Man

uscr

ipt

23

Boeke, C.E., Mora-Plazas, M., Forero, Y., Villamor, E. 2010. Intestinal Protozoan 543

Infections in Relation to Nutritional Status and Gastrointestinal Morbidity in 544

Colombian School Children. J. Trop. Pediatrics, Vol 56, No 5.545

546

Boorom, K.F., Smith, H.,Nimri, L., Viscogliosi, E., Spanakos, G., Parkar, U., Li, L-547

H., Zhou, X-N., Ok, U.Z., Leelayoova, S., Jones, M.S., 2008. Oh my aching gut: 548

irritable bowel syndrome, Blastocystis, and asymptomatic infection. Parasites & 549

Vectors, 1, 40.550

551

Borowski, H, Thompson, RCA, Armstrong, T and Clode ,PL 2010. Morphological 552

characterization of Cryptosporidium parvum life cycle stages in an in vitro model 553

system. Parasitology 137, 13-26.554

555

Campos Filho, P.C., Barros, L.M., Campos, J.O., Braga, V.B., Cazorla, I.M., 556

Albuquerque, G.R., Garvalho, S.M., Curso de Biomedicina, Universidade Estadual de 557

Santa Cruz (UESC) llheus, BA., 2008. Zoonotic parasites in dog feces at public 558

squares in the municipality of Itabuna, Bahia, Brazil. Rev. Bras. Parasitol. Vet. 17, 559

206-209.560

561

Chalmers R.M, Robinson G., Elwin K., Hadfield S.J., Xiao L., Ryan U., Modha D., 562

Mallaghan C., 2009. Cryptosporidium sp. rabbit genotype, a newly identified human 563

pathogen. Emerg Inf Dis 15, 829-830.564

565

Chunge, R.N., Karumba, P.N., Nagelkerke, N., Kaleli, N., Wamwea, M., Mutiso, N., 566

Andala, E.O., Kinoti, S.N., 1991. Intestinal Parasites in a Rural Community in Kenya: 567

Page 24 of 42

Accep

ted

Man

uscr

ipt

24

Cross-sectional Surveys with Emphasis on Prevalence, Incidence, Duration of 568

Infection, and Polyparasitism. East African Med. J. 68, 112-123.569

570

Conlan J.V., Sripa B., Attwood S., Newton P.N., 2011. A review of parasitic zoonoses 571

in a changing Southeast Asia. Vet. Parasitol. (in press).572

573

Covacin, C., Aucoin, DP., Elliot, A. and Thompson, RCA. (2011). Genotypic 574

characterisation of Giardia from domestic dogs in the USA. Vet. Parasitol. 177, 28-575

32.576

577

Cox F.E.G., 2001. Concomitant infections, parasites and immune responses. 578

Parasitology 122, S23-S38.579

580

Dawson, D., 2005. Foodborne protozoan parasites. Int. J. Food Microbiol. 103, 207-581

227.582

583

Diaz, I., Rivero, Z., Bracho, A., Castellanos, M., Acurero, E., Calchi, M., Atencio, R., 584

2006. Prevalence of intestinal parasites in children of Yukpa ethnia in Toromo, Zulia 585

State, Venezuela. Revista Medica De Chile, 134, 72-78.586

587

Dixon, B.R., Parrington, L.J., Parenteau, M., Leclair, D., Santín, M., Fayer, R., 2008. 588

Giardia duodenalis and Cryptosporidium spp. in the intestinal contents of ringed 589

seals (Phoca hispida) and bearded seals (Erignathus barbatus) in Nunavik, Quebec, 590

Canada. J. Parasitol. 94, 1161-1163.591

592

Page 25 of 42

Accep

ted

Man

uscr

ipt

25

Dixon, B., Parrington, L., Cook A, Pintar, K., Pollari, F., Kelton, D., Farber, J., 593

2011. The potential for zoonotic transmission of Giardia duodenalis and 594

Cryptosporidium spp. from beef and dairy cattle in Ontario, Canada. Vet. Parasitol.595

175, 20-26. 596

597

Duran, C., Hidalgo, G., Aguilera, W., Rodriguez-Morales, A.J., Albano, C., Cortez, J., 598

Jimenez, S., Diaz, M., Incani, R.N., 2010. Giardia Lamblia infection is associated 599

with lower body mass index values. J. Infect. Dev. Ctries. 4, 417-418.600

601

Eckmann, L., 2003. Mucosal defences against Giardia. Parasite Immunology, 25, 602

259-270.603

604

Eyles D.E., Jones F.E., Jumper J.R., Drinnon V.P., 1954. Amebic infection in dogs. J. 605

Parasitol. 40, 163-166.606

607

Farthing M.J.G., Cevallos A.M., Kelly P., 2003. Intestinal protozoa. In: Cook G.C., 608

Zumla A. (Eds). Manson’s Tropical Diseases, pp.1373-1410. W.B. Saunders, London.609

610

Feltus, D.C., Giddings, C.W., Schneck, B.L., Monson, T., Warshauer, D., McEvoy, 611

J.M., 2006. Evidence supporting zoonotic transmission of Cryptosporidium spp. in 612

Wisconsin. J. Clin. Microbiol. 44, 4303-438. 613

614

Flanagan, P.A. (1992). Giardia - diagnosis, clinical course and epidemiology. A 615

review. Epidemiol. Infn. 109, 1-22.616

617

Page 26 of 42

Accep

ted

Man

uscr

ipt

26

Geurden, T., Claerebout, E., Dursin, L., Deflandre, A., Bernay, F., Kaltsatos, V., 618

Vercruysse, J., 2006. The efficacy of an oral treatment with paromomycin against an 619

experimental infection with Giardia in calves. Vet. Parasitol. 135, 241–247.620

621

Gormley, F.J., Little, C.L., Chalmers, R.M., Rawal, N., Adak, G.K., 2011. Zoonotic 622

Cryptosporidiosis from Petting Farms, England and Wales, 1992-2009. Emerg. Inf. 623

Dis. 17, 151-152.624

625

Graczyk, T. K., Bosco-Nizey, J., Ssebide, B., Thompson, R. C. A., Read, C. & 626

Cranfield, M. R., 2002. Anthropozoonotic Giardia duodenalis genotype (Assemblage 627

A) infections in habitats of free-ranging human-habituated gorillas, Uganda. J. 628

Parasitol. 88, 905-909.629

630

Hesham, M.S., Azlin, M., Nor Aini, U.N., Shaik, A., Sa’iah, A., Fatmah, M.S., Ismail, 631

M.G., Firdaus, M.S.A., Aisah, M.Y., Rozlida, A.R., Norhayati, M., 2005. Giardiasis 632

as a predictor of childhood malnutrition in Orang Asli children in Malaysia. Trans. 633

Roy. Soc. Med. Hyg. 99, 686-691.634

635

Hopkins, R.M., Meloni, B.P., Groth, D.M., Wetherall, J.D., Reynoldson, J.D., 636

Thompson, R.C.A., 1997. Ribosomal RNA sequencing reveals differences between 637

the genotypes of Giardia isolates recovered from humans and dogs living in the same 638

locality. J. Parasitol. 83, 44-51.639

640

Page 27 of 42

Accep

ted

Man

uscr

ipt

27

Hopkins, R.M., Constantine, C.C., Groth, D.A., Wetherall, J.D., Reynoldson, J.A., 641

Thompson, R.C.A., 1999. PCR-based DNA fingerprinting of Giardia duodenalis 642

using the intergenic rDNA spacer. Parasitology, 118, 531-539.643

644

Howells, M.E., Pruetz, J., Gillespie, T.R., 2011. Patterns of Gastro-Intestinal Parasites 645

and Commensals as an Index of Population and Ecosystem Health: The Case of 646

Sympatric Western Chimpanzees (Pan troglodytes verus) and Guinea Baboons (Papio 647

hamadryas papio) at Fongoli, Senegal. Am. J. Primatol. 73, 173-179.648

649

Hunter, PR, Thompson, RC. 2005. The zoonotic transmission of Giardia and 650

Cryptosporidium. Int J Parasitol. 35, 1181-1190.651

652

Hussein, A.I.A., Yamaguchi, T., Nakamoto, K., Iseki, M., Tokoro, M., 2009. 653

Multiple-subgenotype infections of Giardia intestinalis detected in Palestinian clinical 654

cases using a subcloning approach. Parasit. Intl. 58, 258-262.655

656

Inpankaew, T., Traub, R., Thompson, R.C., Sukthana, Y., 2007. Canine parasitic 657

zoonoses in Bangkok temples. S. E. Asian J. Trop. Med. Public Health, 38, 247-255.658

659

Johnston, A.R., Gillespie, T.R., Rwego, I.B., McLachlan, T.L., Kent, A.D., Goldberg, 660

T.L., 2010. Molecular epidemiology of cross-species Giardia duodenalis transmission 661

in Western Uganda. PLoS. Nefl. Trop. Dis., 11, 4.662

663

Page 28 of 42

Accep

ted

Man

uscr

ipt

28

Jolles, A.E., Ezenwa, V.O., Etienne, R.S., Turner, W.C., Olff, H., 2008. Interactions 664

between Macroparasites and Microparasites drive infection patterns in free-ranging 665

African Buffalo. Ecology, 89, 2239-2250.666

667

Karanis, P., Kourenti, C., Smith, H., 2007. Waterborne transmission of protozoan 668

parasites: a worldwide review of outbreaks and lessons learnt. J. Water Health 5, 1-669

38.670

671

King, C. H., 2010. Health Metrics for Helminthic Infections. Adv. Parasitol. 73, 51-672

69. 673

674

Kirkoyun Uysal, H., Boral, O., Metiner, K., Ilgaz, A., 2009. Investigation of Intestinal 675

Parasites in Pig Feces that are also Human Pathogens. Turkiye Parazitol Derg. 33, 676

218-221.677

678

Koukounari, A., Donnelly, C.A., Sacko, M., Keita, A.D., Landoure, A., Dembele, R., 679

Bosque-Oliva, E., Gabrielli, A.F., Gouvras, A., Traore, M., Fenwick, A., Webster, 680

J.P., 2010. The impact of single versus mixed schistosome species infections on liver, 681

spleen and bladder morbidity within Malian children pre- and post-praziquantel 682

treatment. BMC Infectious Diseases, 10, 227.683

684

Kutz S.J., Thompson R.C.A., Polley L., Kandola K., Nagy J., Wielinga C.M., Elkin 685

B.T., 2008. Giardia assemblage A: human genotype in muskoxen in the Canadian 686

Arctic. Parasites and Vectors 1, 32.687

688

Page 29 of 42

Accep

ted

Man

uscr

ipt

29

Lasek-Nesselquist, E., Welch, D.M., Thompson, R.C.A, Steuart, R.F., Sogin, M.L., 689

2009. Genetic exchange within and between assemblages of Giardia duodenalis. J. 690

Eukaryot. Microbiol. 56, 504-518.691

692

Leonhard, S., Pfister, K., Beelitz, P, Thompson, R. C. A. 2007. The molecular 693

characterisation of Giardia from dogs in southern Germany. Vet. Parasitol. 150, 33-694

38.695

696

Meloni, B.P., Thompson, R.C., Hopkins, R.M., Reynoldson, J.A., Gracey, M., 1993. 697

The prevalence of Giardia and other intestinal parasites in children, dogs and cats 698

from Aboriginal communities in the Kimberley. Med. J. Aust., 158, 157-159.699

700

Mideo, N., 2009. Parasite adaptations to within-host competition. Trends Parasitol. 701

25, 261-268.702

703

Midzi, N., Sangweme, D., Zinyowera, S., Mapingure, M.P., Brouwer, K.C., Munatsi, 704

A., Mutapi, F., Kumar, N., Woelk, G., Mduluza, T., 2008. The burden of 705

polyparasitism among primary schoolchildren in rural and farming areas in 706

Zimbabwe. Trans R Soc Med Hyg., 102, 1039-1045.707

708

Millard, P. S., Gensheimer, K. F., Addiss, D.G., Sosin, D.M., Beckett, G.A., Houck-709

Jankoski, A., Hudson, A., 1994. An outbreak of cryptosporidiosis from fresh-pressed 710

apple cider. JAMA. 272, 1592-1596.711

712

Page 30 of 42

Accep

ted

Man

uscr

ipt

30

Monis, PT, Caccio, SM, Thompson, RCA. 2009. Variation in Giardia: towards a 713

taxonomic revision of the genus. Trends in Parasitology, 25, 93-100.714

715

Moro, D., Lawson, M.A., Hobbs, R.P. and Thompson, R.C.A., 2003. Pathogens of 716

house mice on arid Boullanger Island and subantarctic Macquarie Island, Australia. J. 717

Wild. Dis. , 762-771718

719

Muniz P.T., Ferreira M.U., Ferreira C.S., Conde W.L., Monteiro C.A., 2002. 720

Intestinal parasitic infections in young children in Sao Paulo, Brazil: prevalences, 721

temporal trends and associations with physical growth. Ann. Trop. Med. Parasitol. 96, 722

503-512.723

724

Muniz-Junqueira M.I., Queiroz E.F., 2002. Relationship between protein-energy 725

malnutrition, vitamin A, and parasitoses in children living in Brasilia. Rev. Soc. Bras. 726

Med. Trop. 35, 133-141.727

728

Nash, T. E., Herrington, D. A., Losonsky, G. A. and Levine, M. M., 1987. 729

Experimental human infections with Giardia lamblia. Journal of Infectious Diseases 730

156, 974-84.731

732

Nematian, J., Gholamrezanezhad, A., Nematian, E., 2008. Giardiasis and other 733

intestinal parasitic infections in relation to anthropometric indicators of malnutrition: 734

a large, population-based survey of schoolchildren in Tehran. Trop Med Parasitol. 735

102, 209-214.736

737

Page 31 of 42

Accep

ted

Man

uscr

ipt

31

Ng J., Eastwood K., Durrheim D., Massey P., Walker B., Armson A., Ryan U. 2008. 738

Evidence supporting zoonotic transmission of Cryptosporidium in rural New South 739

Wales. Exp. Parasitol. 119, 192-195. 740

741

Nguhiu, P.N., Kariuki, H.C., Magambo, J.K., Kimani, G., Mwatha, J.K., Muchiri, E., 742

Dunne, D.W., Vennervald, B.J., Mkoji, G.M., 2009. Intestinal polyparasitism in a 743

rural community. East Afr Med J., 86, 272-278.744

745

Nolan, M.J., Jex, A.R., Haydon, S.R., Stevens, M.A., Gasser, R.B., 2010. Molecular 746

detection of Cryptosporidium cuniculus in rabbits in Australia. Inf. Gen. Evol. 10, 747

1179-1187.748

749

Nyarango, R.M., Aloo, P.A., Kabiru, E.W., Nyanchongi, B.O., 2008. The risk of 750

pathogenic intestinal parasite infections in Kisii Municipality, Kenya. BMC Public 751

Health, 8, 237.752

753

O’Donoghue, P.J., 1995. Cryptosporidium and Cryptosporidiosis in Man and 754

Animals. Int. J. Parasitol. 25, 139-195.755

756

O’Handley, R.M., Olson, M.E., 2006. Giardiasis and cryptosporidiosis in757

ruminants. Vet. Clinics of North America, Food Animal Practice 22, 623–643.758

759

O’Handley, R.M., Cockwill, C.L., McAllister, T.A., Jelinski, M., Morck, D.W., 760

Olson, M.E., 1999. Duration of naturally acquired giardiasis and cryptosporidiosis in 761

dairy calves and their association with diarrhea. J. Am. Vet. Med. Assn. 214, 391–396.762

Page 32 of 42

Accep

ted

Man

uscr

ipt

32

763

Olson, M.E., McAllister, T.A., Deselliers, L., Morck, D.W., Cheng, K.J., Buret, A.G., 764

Ceri, H., 1995. Effects of giardiasis on production in a domestic ruminant (lamb) 765

model. Am. J. Vet. Res. 56, 1470–1474.766

767

Ouattara, M., Silue, K.D., N’Guessan, A.N., Yapi, A., Barbara, M., Raso, G., 768

Utzinger, J., N’Goran, E., 2008. Prevalence and Polyparasitism of intestinal protozoa 769

and spatial distribution of Entamoeba histolytica, E. dispar and Giardia intestinalis 770

from pupils in the rural zone in Cote d’Ivoire. Sante, 18, 215-222.771

772

Owen, I.L., 2005. Parasitic zoonoses in Papua New Guinea. J. Helminthol. 79, 1-14.773

774

Parkar U., Traub R.J., Kumar S., Mungthin M., Vitali S., Leelayoova S., Morris K., 775

Thompson, R.C.A., 2007. Direct characterisation of Blastocystis from faeces by PCR 776

and evidence of zoonotic potential. Parasitology 134, 1-9.777

778

Parkar U., Traub R.J., Vitali S., Elliot A., Levecke B., Robertson I.D., Geurden T., 779

Steele J., Drake B. and Thompson R.C.A., 2010. Molecular characterization of 780

Blastocystis isolates from zoo animals and their animal-keepers. Vet. Parasitol.781

169, 8-17.782

783

Payne, R.J., Turner, L., Morgan, E.R., 2009. Inappropriate measures of population 784

health for parasitic disease? Trends Parasitol., 25, 393-395.785

786

Page 33 of 42

Accep

ted

Man

uscr

ipt

33

Pruss, A., Kay, D., Fewtrell, L., Bartram, J., 2002. Estimating the burden of disease 787

from water, sanitation, and hygiene at a global level. Env. Health Perspectives 110,788

537-542. 789

790

Pullan, R., Brooker, S., 2008. The health impact of Polyparasitism in humans: are we 791

under-estimating the burden of parasitic diseases? Parasitology, 135, 783-794.792

793

Quihui, L., Morales, G.G., Mendez, R.O., Leyva, J.G., Esparza, J., Valencia, M.E., 794

2010. Could giardiasis be a risk factor for low zinc status in schoolchildren from 795

northwestern Mexico? A cross-sectional study with longitudinal follow-up. BMC 796

Public Health, 10, 85.797

798

Requena, I., Hernández, Y., Ramsay, M., Salazar, C., Devera, R., 2003. Prevalence of 799

Blastocystis hominis among food handlers from Caroni municipality, Bolivar State, 800

Venezuela. Cad. Saúde Pública 19, 6.801

802

Robertson, L.J., Gjerde, B.K., Furuseth Hansen, E., 2010. The zoonotic potential of 803

Giardia and Cryptosporidium in Norwegian sheep: A longitudinal investigation of 6 804

flocks of lambs. Veterinary Parasitology, 171, 140-145.805

806

Robinson, G., Wright, S., Elwin, K., Hadfield, S.J., Katzer, F., Bartley, P.M., Hunter, 807

P.R., Nath, M., Innes E.A., Chalmers, R.M., 2010. Re-description of Cryptosporidium 808

cuniculus Inman and Takeuchi, 1979 (Apicomplexa: Cryptosporidiidae): 809

Morphology, biology and phylogeny. Int. J. Parasitology, 40, 1539-1548.810

811

Page 34 of 42

Accep

ted

Man

uscr

ipt

34

Rodriguez-Hernandez, J., Canut-Blasco, A. and Martin-Sanchez, A.M. (1996) 812

Seasonal prevalence's of Cryptosporidium and Giardia infections in children 813

attending day care centres in Salamanca (Spain) studied for a period of 15 months. 814

Eur. J. Epidemiol. 12, 291-295.815

816

Rodriguez, M., Terrazas, L.I., Marquez, R., Bojalil, R., 1999. Susceptibility to 817

Trypanosoma cruzi modified by a previous non-related infection. Parasite Immunol. 818

21, 177-185.819

820

Rohani, P., Green, C.J., Mantilla-Beniers, N.B. , Grenfell, B.T., 2003. Ecological 821

interference between fatal diseases. Nature, 422, 885-888.822

823

Salb A.L., Barkeman W.B., Elkin B.T., Thompson R.C.A., Whiteside R.C.A., Black 824

S.R., Dubey J.P., Kutz S.J., 2008. Parasites in dogs in two northern Canadian 825

communities: implications for human, dog, and wildlife health. Emerg. Inf. Dis. 14, 826

60-63.827

828

Savioli L., Smith H., Thompson R.C.A., 2006. Giardia and Cryptosporidium829

join the 'Neglected Diseases Initiative'. Trends Parasitol. 22, 203-8830

831

Schuster F.L., Visvesvara G.S., 2004. Amebae and ciliated protozoa as causal agents 832

of waterborne zoonotic disease. Vet. Parasitol. 126, 91-120.833

834

Schuster, F.L., Ramirez-Avila, L., 2008. Current World Status of Balantidium coli. 835

Clin. Microbiol. Rev. 21, 626-638.836

Page 35 of 42

Accep

ted

Man

uscr

ipt

35

837

Shields, J. M., Gleim, E. R., Beach, M. J., 2008. Prevalence of Cryptosporidium spp. 838

and Giardia intestinalis in swimming pools, Atlanta, Georgia. Emerg. Inf. Dis. 14, 839

948-950.840

841

Slapeta J., 2011. Naming of Cryptosporidium pestis is in accordance with the ICZN 842

Code and the name is available for this taxon previously recognised as C. parvum 843

‘bovine genotype’. Vet. Parasitol. (in press).844

845

Smith, H.V., Cacciò, S.M., Cook, N., Nichols, R.A., Tait, A., 2007. Cryptosporidium846

and Giardia as foodborne zoonoses. Vet. Parasitol. 149, 29-40. 847

848

Sprong H., Caccio S.M., van der Giessen J.W.B., 2009. Identification of zoonotic 849

genotypes of Giardia duodenalis. Plos Negl. Trop. Dis. 3, e558.850

851

Stensvold C.R., Lebbad M., Victory E.L., Verweij J.L., Tannich E., Alfellani M., 852

Legarraga P., Clark C.G., 2011. Increased sampling reveals novel lineages of 853

Entamoeba: consequences of genetic diversity and host specificity for taxonomy and 854

molecular detection. Protist (in press).855

856

Stuart J.M., Orr H.J., Warburton F.G., Jeyakanth S., Pugh C., Morris I., Sarangi J., 857

Nichols G., 2003. Risk factors for sporadic giardiasis: a case-control study in 858

southwestern England. Emerg. Infect. Dis. 9, 229-233.859

860

Page 36 of 42

Accep

ted

Man

uscr

ipt

36

Sulaiman I.M., Fayer R., Bern C., Gilman R.H., Trout J.M., Schantz P.M., Das P., Lal 861

A.A., Xiao L., 2003. Triosephosphate isomerase gene characterization and potential 862

zoonotic transmission of Giardia duodenalis. Emerg. Infect. Dis. 9, 1444-1452.863

864

Supali T., Verweij J.J., Wiria A.E., Djuardi Y., Hamid F., Kaisar M.M.M., Wammes 865

L.J., van Lieshout L., Luty A.J.F., Sartono E., Yasdanbakhsh M., 2010. 866

Polyparasitism and its impact on the immune system. Int. J. Parasitology, 40, 1171-867

1176.868

869

Szostakowska B., Kruminis-Lozowska W., Racewicz M., Knight R., Tamang L., 870

Myjak P., Graczyk T.K., 2004. Cryptosporidium parvum and Giardia lamblia871

recovered from flies on a cattle farm and in a landfill. Appl. Environ. Microbiol. 70, 872

3742-3744.873

874

Teichroeb J.A., Kutz S.J., Parkar U., Thompson R.C.A., Sicotte P., 2009. Ecology 875

of the gastrointestinal parasites of Colobus vellerosus at Boabeng-Fiema, Ghana: 876

possible anthropozoonotic transmission. Am. J.Phys. Anthropol. 140, 498-507.877

878

Thompson, R.C.A., 2000. Giardiasis as a re-emerging infectious disease and its 879

zoonotic potential. Int. J. Parasitol. 30, 1259-1267.880

881

Thompson, R.C.A. 2008. Giardiasis: modern concepts in control and management. 882

Ann. Nestle 66, 29-35.883

884

Thompson R.C.A., 2009. The impact of Giardia on science and society. In: G.885

Page 37 of 42

Accep

ted

Man

uscr

ipt

37

Ortega Pierres, S.M. Caccio, R. Fayer, T.G. Monk, H.V. Smith and R.C.A.886

Thompson (Eds). Giardia and Cryptopsoridium: from molecules to disease, pp.1-11,887

CAB International, Wallingford.888

889

Thompson R.C.A., 2011. Giardia Infections. In: Palmer S.R., Soulsby E.J.L., 890

Torgerson P., Brown D. Zoonoses. Oxford University Press, Oxford (in press).891

892

Thompson R.C.A., Lymbery A.J., 1996. Genetic variability in parasites and host-893

parasite interactions. Parasitology 112, S7-S22.894

895

Thompson, R.C.A., Monis, P.T., 2004. Variation in Giardia: implications for 896

taxonomy and epidemiology. Adv. Parasitol. 58, 69–137.897

898

Thompson R.C.A., Monis P.T., 2011. Taxonomy of Giardia species. In: Giardia: a 899

model organism (Lujan, HD and Svärd, S). Springer (in press).900

901

Thompson, R.C.A., Palmer, C.S., O'Handley, R., 2008. The public health and clinical 902

significance of Giardia and Cryptosporidium in domestic animals. Vet. J., 177, 18-25.903

904

Thompson R. C. A., Colwell D. D., Shury T., Appelbee A. J., Read C., Njiru Z., 905

Olson, M. E., 2009. The molecular epidemiology of Cryptosporidium and Giardia906

infections in coyotes from Alberta, Canada, and observations on some cohabiting 907

parasites. Vet. Parasitol., 159, 167-170.908

909

Page 38 of 42

Accep

ted

Man

uscr

ipt

38

Thompson R.C.A., Lymbery A.J., Smith A., 2010a. Emerging parasite diseases and 910

wildlife. Int. J. Parasitol. 40, 1163-1170.911

912

Thompson R.C.A., Smith A., Lymbery A.J., Averis S., Morris K.D., Wayne A.F., 913

2010b. Giardia in Western Australian wildlife. Vet. Parasitol. 170, 207-211.914

915

Traub R. J., Monis P. T., Robertson, I. D., Irwin P. J., Mencke N., Thompson R. C. 916

A., 2004. Epidemiological and molecular evidence supports the zoonotic transmission 917

of Giardia among humans and dogs living in the same community. Parasitology 128, 918

253-262.919

920

Troeger H., Epple H.J., Schneider T., Wahnschaffe U., Ullrich R., Burchard G.D., 921

Jelinek T., Zeitz M., Fromm M., Schulzke J.D., 2007. Effect of chronic Giardia922

lamblia infection on epithelial transport and barrier function in human duodenum. Gut923

56, 316-317924

925

Vassalos C.M., Papadopoulou C., Vakalis N.C., 2008. Blastocystosis: an emerging or 926

re-emerging potential zoonosis? Veterinaria Italiana 44, 679-684.927

928

Walzer P.D., Judson F.N., Murphy K.B., Healy G.R., English D.K., Schultz M.G., 929

1973. Balantidiasis outbreak in Truk. Am. J. Trop. Med. Hyg. 22, 33-41.930

931

Welch T, P., 2000. Risk of giardiasis from consumption of wilderness water in North 932

America: a systematic review of epidemiologic data. Int. J. Infect. Dis. 4, 100-103.933

934

Page 39 of 42

Accep

ted

Man

uscr

ipt

39

Wielinga, C., Ryan, U., Thompson, R.C.A., Monis, P., 2011. Multi-locus analysis of 935

Giardia duodenalis intra-Assemblage B substitution patterns in cloned culture isolates 936

suggests sub-Assemblage B analyses will require multi-locus genotyping with 937

conserved and variable genes. Int. J. Parasitol. 41, 495-503. 938

939

Yoshikawa H., Wu Z., Pandey K., Pandey B.D., Sherchand J.B., Yanagi T., Kanbara 940

H., 2008. Molecular characterization of Blastocystis isolates from children and rhesus 941

monkeys in Kathmandu, Nepal. Vet Parasitol. 160, 295-300.942

943

Youn, H., 2009. Review of Zoonotic Parasites in Medical and Veterinary Fields in the 944

Republic of Korea. Korean J. Parasitol., 47, S133-S141.945

946

Zaman V., 1998. Balantidium coli. In: Cox, F.E.G., Kreier, J.P., Wakelin D. (Eds). 947

Topley and Wilson’s Microbiology and microbial infections, pp.445-450. London, 948

Arnold.949

950

951

952

953

954

955

956

957

958

959

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40

960

961

962

963

964

Table 1. 965

Proposed and existing species in the genus Giardia966

Species Hosts

G. duodenalis

(=Assemblage A)

Wide range of domestic and wild mammals

including humans

G. enterica

(=Assemblage B)

Humans and other primates, dogs, some

species of wild mammals

G. agilis Amphibians

G. muris Rodents

G. ardeae Birds

G. psittaci Birds

G. microti Rodents

G. canis

(=Assemblage C/D)

Dogs, other canids

G. cati

(=Assemblage F)

Cats

G. bovis

(=Assemblage E)

Cattle and other hoofed livestock

G. simondi

(=Assemblage G)

Rats

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967

968

969

970

971

972

973

Fig. 1. Estimated prevalence of Blastocystis, Cryptosporidium, Giardia and 974

Entamoeba within children from rural and urban regions for each or the World Health 975

Organisation (WHO) defined regions of the world: European Region (EUR), South-976

East Asian Region (SEAR), Western Pacific Region (WPR), African Region (AFR), 977

Region of the Americas (AMR) and Eastern Mediterranean Region (EMR). 978

979

980

981

982

983

984

985

986

987

988

989

990

991

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42

992

993

994

995

996

997

998

999

1000

1001

1002

0

50

100

Pre

val

en

ce

WPRRural

0

50

100

Pre

val

ence

SEARRural

Urban

0

50

100

Pre

val

en

ce

EURRural

Urban

0

50

100

Pre

vale

nc

e

EMRRural

0

50

100

Pre

val

ence

AFRRural

0

50

100

Pre

val

ence

AMRRural

1003