Review article

WATER-BORNE PROTOZOANPARASITIC INFECTIONS

' JS Edirisinghe

Abstract

Contamination of drinking water byhuman and animal excreta is a major publichealth problem the world over. A number ofserious protozoan parasitic infections aretransmitted to humans by way of contaminateddrinking water. Water used by humans forpurposes other than drinking such as washing,bathing, swimming, recreational and irrigationactivities could also transmit waterborneparasitic pathogenic agents resultingin disease.

Pathogenic protozoan parasitic agentsthat could be transmitted by drinking water are,Entamoeba histolytica, Giardia intestinalCryptosporidium parvum, Isospora belli,Blastocystis hominis, Cyclospora cayetanensisand Microsporidia. Naegleria fowleri andAcanthamoeba spp. are generally associated withwater related recreational activities.

Thereview includes a brief historicalaccount, clinical features and the mode ofexposure / association with water, under eachparasite listed.Key words - waterborne,outbreaks, protozoan,immunocompromized, diarrhoea, swimmingWater-borne protozoan parasiticinfectionsIntroduction

The mostprevalent health hazard associated withdrinking water is contamination. This couldoccur directly or indirectly by human or animalexereta, Water used by humans for purposesother than drinking such as washing, irrigationand recreation could also easily conveypathogenic agents to humans. These agentsinclude viruses, bacteria. protozoans andhelminths.

' Professor of Parasitology and Head,Department of Parasitology, Faculty ofMedicine, University of PeradeniyaSri Lanka

Journalofthe College of Community Physicians of Sri Lanka

Drinking water plays a major role in thetransmission of several important protozoanparasitic infections, namely, Entamoebahistolytica, Giardia intestinalis (syn.lamblia),Cryptosporidium parvum, Isospora belli,Blastocystis hominis, Cyclospora cayetanensis,and Microsporidia. Naegleria fowleri andAcanthamoeba spp. are generally associated withwater related recreational activities such asswimming. Parasitic agents suchasAcanthamoeba spp. gain access to the humanbody by wayof inhalation. The organismsareknown to be presentin droplets of water comingout of showers and air conditioning systems.

Thepositive effects of public health measuresinstituted several decades ago are now beingreflected in the improved life expectancy andfalling death rates worldwide. An increasingelderly population and an ever growingpopulation of immunocompromised persons as aresult of cancer chemotherapy, organtransplantation and HIVinfections have becomea global phenomenon. ‘These populationsconstitute the high risk groupsfor emerging andre-emerging infections. Opportunistic infectionssuch as cryptosporidiosis and cyclosporiasisillustrate this point.

Protozoan parasites are the most commonlyidentified pathogenic agents in waterbornedisease outbreaks. This review is confined toinformation on waterborne protozoan parasiticagents, some of which are well known whileothers are considered emerging.Detailed records of waterborne parasiticinfections in countries like Sri Lanka are non-existent, Published reports from elsewhereillustrate the seriousness and the magnitude ofwaterborne protozoan parasitic infections (3).Entamoebahistolytica and Entamoeba disparAmoebiasis refers to the infection of thegastrointestinal tract by Entamoeba histolytica, aprotozoan parasite that is capable of invading thelarge intestinal mucosa. It has the potential tospread to other organs, mainly the liver. Thetrophozoite (growing stage) of the parasite wasfirst described by Losch in 1873. Losch saw theparasite in the stools of a young Russian withchronic dysentery. Few years later Councilmanand LeFleur (1891) provided clinicalevidence toshow that there was an association betweenthepresence of the organism and dysentery (1).Quincke and Roos first described the cyst, stagethat is responsible for transmission, in 1893 (2).

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Schoudinn gave the name Entamoeba histolyticato theorganism in 1903. Brumpt first suggestedthe possibility that the parasite existed as amember of a complex of twospecies in 1925,following studies on the four-nucleated cyst (3).Hedifferentiated the two species into a non-pathogenic, non-invasive form and an invasivepathogenic form. The name Entamoebahistolytica was retained for the pathogenicinvasive form while the non-invasive, non-pathogenic species was named Entamoebadispar. This division did not receive supportfrom scientists and the species name disparwent into oblivion. The non-pathogenic form ofthe parasite was considered a differentstrain ofEntamoeba histolytica which had the capabilityof reverting back to the pathogenic state undercertain circumstances. It took more thanhalf acentury and a series of elegant laboratoryinvestigations by two persons, Sargeaunt andWilliams, to demonstrate the pathogenic and thenon-pathogenic strains of Entamoeba histolyticabased on the isoenzyme patterns of parasitesfrom different geographical locations (4).Brumpt’s original differentiation was re-examined by Clark and Diamond,this time usingbiochemical, immunological and genetic studies(S, 6, 7). They re-described the invasive formretaining the name Entamoeba histolytica andseparated the non-pathogenic form into a newspecies — Entamoeba dispar with no invasivepotential. However, the two species aremorphologically similar and are capable ofcolonising the humanlarge gut.

‘The acceptance of Entamoeba dispar as aseparate non-pathogenic species has had aprofound impact on the current knowledgeof theepidemiology of amoebiasis. This is mainlybecause the large number of asymptomaticinfections worldwide is now attiibuted to thenon-pathogenic Entamoeba dispar* Together,E.histolytica and E.dispar infect about 10% ofthe world’s population (8). However, infectionswith E.dispar is much more common so that thetrue prevalence of invasive amoebiasis,worldwide would be around 1%. As parasiticcauses of death, only malaria. andschistosomiasis surpass amoebiasis (9).E.histolytica is capable ofinfecting any part ofthe human body but the most commonform ofextraintestinal amoebiasis is amoebic liverabscess. This clinical entity which results frommigration of amoebic trophozoites from thecolon to thé liver via the portal circulation, is 10

Journalofthe College of Community Physicians of Sri Lanka

times more common in adults thanin childrenand 3 times commonerin males(10).

Clinicalfeatures of amoebiasis

The incubation period varies from a fewdays tomonths depending on the endemicity of theinfection in the locality. In highly endemic areasfor pathogenic Entamoeba species, the onset isusually rapid. This is the usual picture inwaterborne infections. Generally, the onset isgradual with prodromal episodes of diarrhoeaand abdominal cramps, The hallmark of amoebiccolitis is diarrhoea with blood and mucus. Thesesymptoms may continue for weeks and areaccompanied by nausea, anorexia and weightloss. In extraintestinal amoebiasis the signs andsymptoms are related to the organ or tissueaffected...Modeofexposure/ Association with water

Humans are the primary reservoirs of theinfection with histolytica. Hencecontamination of water supplies (both drinkingand recreational) with domestic sewagehelps inthe transmission of the infection, Severaloutbreaks of infection have been traced tosewage contamination of drinking water (11).Contaminated swimming pool water has alsobeen incriminated as a source ofinfection (11).The chances of water supplies gettingcontaminated with amoebic cysts are greater inthe tropics where carrier rates are high andenvironmental sanitation poor. The cysts remainviable for months in water at 0°C, 3 days at30°C, 30 minutes at 45°C and 5 minutes at 50°C(11). The cysts are highly resistant tochlorination (12).Acanthamoeba spp.Acanthamoeba is a free-living amoeba capableof causing severe disease in humans, Themembers of the genus Acanthamoeba wereformally referred to as Hartmannella (Alexicieff1912), In 1975, Sawyer and Griffin proposed thenew family Acanthamoebidae for the amoebaethat possess acanthopodia (spines) (13). Untilrecent times members of Hartmannella(Acanthamoebidae) were known to bepathogenic to mammals although they had beenisolated from the throat (14) and the nasalpassage (15) of children. In 1982, Cleland et alreported the first case of chronic amoebicmeningoencephalitis in a Nigerian patient whosecerebrospinal fluid harbouredthe organism (16).Acanthamoeba species can cause severe eyelesions in humans. Keratitis and uveitis are

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common manifestations due to this organism(17). Serumantibodies against AcanthamoebaSp. are quite common in keeping with theubiquitous nature of the parasite (18). Theorganism has been isolated and cultured fromnormal flora of the upper respiratory tract ofhumans (19, 20). This implies that the infectionis common and non-pathogenic inimmunocompetent persons.

Clinical features ofAcanthamoeba infections

The incubation period varies with a number ofhost factors. Mild injuries to the eye predisposetoinfections rapidly. Swimming while wearingcontact lenses is also considered a predisposinghostfactor. Contact lens wearers may developkerat Acanthamoeba also—_causesgranulomatous amoebic encephalitis, a chroniccentral nervous system disease, inimmunocompromisedpersons.

Modeofexposure/ Association with water

Acanthamoebae are ubiquitous in nature, Theyhave been foundin tap, fresh, coastal and bottledmineral water, contact lens solutions, eyewashstatins, soil, dust, air, sewage, heating,ventilation and air conditioning units, dialysismachines and dental units, hot tubs andgastrointestinal washings (20, 21, 22). The

fection can easily be transmitted via drinkingwater, water in swimming pools and naturalwater bodies. Infections leading to keratitis occurduring warm weather swimming in lakes andponds while wearing contact lenses (17, 18).Home made contact lens cleaning solutions andwashingof eyes with household water followingminor injuries are also common modes oftransmission. Cysts of Acanthemoebae arehighly resistant to chlorination (12),

NaegleriafowleriNaegleria fowleri is a free-living amoeba. It isthe aetiological agent of primary amoebicmeningoencephalitis. The organism has beenknown for quite sometime but was confused withother genera. A case reported by Derrick wherethe amoeba described resembled Jodamoebabuetschlii was probably N. fowleri (23, 24, 25).This is now considered to be thefirst pubiicationdescribing N,fowleri infection in man. To datenearly 200 cases have beenreported worldwide.The numbers scem insignificant but the exposureto infection is much more commonas seen bythe widespread presence of antibodies toNaegleria species (18, 26).

Journalofthe College ofCommunity Physicians ofSri Lanka

Clinical features of Naegleriafowleri infectionThe incubation period is about 2 to 7 days, Theonset of meningoencephalitis is sudden withheadache, fever, nausea, vomiting and signs ofpharyngitis,

Modeofexposure/ Association with water

N,fowleri is a thermophilic amoeba and has acosmopolitan distribution in surface watersnaturally heated by the sun. They toleratetemperatures ranging between 40 - 45°C. Theorganism can also thrive in industrial coolingwater towers and geothermal springs (27).Nfowleri may be found in poorly chlorinatedswimming pool water, artificial lakes and inwarm water near discharge outlets of powerplants (20). Large numbers of organisms havebeen found in water with high content of ironand manganese (3). Some species of Naegleriainteract with Legionella species and have beenincriminated for the dissemination of Legionellain water (3).Giardia lamblia

Leeuwenhoek first saw this flagellate protozoanparasite in 1681 in his own stools. The credit forthefirst description goes to Lamble (1859) whocalled it Cercomonas intestinalis. Stiles in 1915created the binomial Giardia lamblia in honourof Giard of Paris and Lamble of Prague.Giardiasis is the most commonly diagnosedprotozoan flagellate infection of the intestinaltract (29). Using stool microscopy, detectionrates vary between 2 and 5% in industrialisedcountries and between 20 and 30% in developingcountries (3).Clinical features of giardiasisThe incubation period is about 2 weeks but maybeprolonged to several months. Watery or fattydiarrhoea is the main symptom which is worse inthe morning. Diarthoea is often described asexplosive with offensive stools. There is noblood or pus in the stools. Some experiencedyspepsia with dull upper epigastric pain.Modeofexposure / Association with water

Epidemic giardiasis associated with drinkingwater has been reported from the USA, Canada,England and Sweden (30, 31, 32, 33). Drinkingwater has been incriminated for giardiasis intravelers, particularly in the former Soviet Union(34), Animal reservoirs of the infection areknown (11). Giardia cysts are highly resistant toordinary disinfection (11). In the USA,

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backpackers and picnickers who drink streamwater are al risk. Giardia has also been

incriminated for swimming pool associatedoutbreaks of gastroenteritis (35).Cryptosporidium parvum‘The genus name Cryptosporidium was proposedby Tyzzer in 1910 for the organisms hefrequently encountered in the gastric glands oflaboratory mice. Tyzzer established the new

species Cryptosporidium parvum in 1912 fororganisms which exclusively infected theintestinal epithelial cells of mice. The organismis a coccidian like Toxoplasma gondii. It wasonly in 1976 that the first cases ofcryptosporidiosis were reported in humans (36).In persons with normal immune functions, theinfectionis either asymptomatic or self-limiting,In immunocompromised persons, the infectiontakes a serious course with intractable diarrhoea.People with a CD4 cell counts over 180 cells /mm’ have been shown to clear the infectionspontaneously while those with lower counts hadpersistent disease (37). The parasite is capable ofinfecting a wide range of animal species as wellas humans. The lack of host specificity has beendemonstrated in cross transmission studies (38).A study carried out in a paediatric unit in SriLanka has shown that about 6% of acutediarrhoea in children is associated withCparvum (39).Clinical features of eryptosporidiosisTheincubation period varies between 5 to 28days. Symptoms vary from self limiting acutediarrhoea to severe prolonged diarrhoea withdehydration, In immunocompromised patients,the parasite causes intractable watery diarrhoearesulting in malabsorption and wasting.Modeofexposure / Association with water

Outbreaks of cryptosporidiosis have beenassociated with untreated drinking water, watertreated by chlorination only and water subjectedto conventional treatment —_(coagualation,sedimentation, sand filtration and chlorination)(12). This is mainly due to the extremely small

of the oocyst (4 — 6 um), which isresponsible for transmission of the infection,Among. the protozoans under consideration,Cparvum has the smallest and most chlorineresistant infective stage(oocyst), and hence, theeasiest to be transmitted via drinking water.Historically, the massive outbreak in Milwaukee,USA,is the largest even reported where drinkingwater was found to be the source of infection

Journalofthe College ofCommunity Physicians ofSri Lanka

(35). Swimming pool and recreational waterhave been incriminated for outbreaks of

cryptosporidiosis (40, 41, 42).Isospora belliThetwospecies Isospora hominis and Isosporabelli, both coccidian parasites, were thoughttobesimilar until it was discovered that they havemarkedly different life cycles. The formeris nowclassified under Sarcocystidae. Wenyon namedIsospora belli in 1923. Virchowis credited withthefirst description of the parasite in 1860 in theintestine of a manat autopsy. Wenyon and othersencountered the parasite frequentlyin soldiersduring war times. It is now thought to be theonly Isospora species that infects humans, theparasite’s only known hosts (43). The infectionhas been reported from both developed anddeveloping countries (3). Intestinal signs andsymptoms are unusual in immunocompetentpersons. Outbreaks of diarrhoea due to theparasite have been reported in mental wards, daycare centres , World War 11 veterans from thePacific and HIV infected persons (3, 44).

Clinical features ofIsosporabelli infection

Mostinfections are asymptomatic, The mainfeature of [belli infection is diarrhoea and, inthose who have mild symptoms, theinfection isusually self-limiting. In immunocompromisedpersons, diarrhoea takes a prolonged courseleading to malabsorption and wasting.Modeofexposure/ Association with water

Poor environmental and personal sanitationleading to contamination of drinking water andother food with oocysts is the currently acceptedexplanation for the spread ofthe infection (3).Blastocystis hominisB.hominis was classified a yeast by Brumpt(1912). In 1967, Zierdt suggested that theorganism was a protozoan andlaterconsideredita potential pathogen (45, 46). Although itspathogenic role is not accepted universally, somestudies suggest that it could lead to intestinaldisturbances (47, 48). The infection is alsoKnown to take an aggravated course inimmunocompromised persons (49).Clinical features ofblastocystosis

Diarrhoea is the main symptom. It is usuallyself-limiting but in some, particularly in theimmunocompromised, the infection takes aprolonged course with anorexia, flatulence,colicky abdominal pain and low gradefever.

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Modeofexposure / Association with waterTheinfective stage ofthe parasite is the cyst.Drinking water is the major mode oftransmission(50). Drinking water sources couldget contaminated with cysts of B.hominis indomestic sewage. In a recent study in Thailand,blastocystosis. was shown to be significantlyassociated with unboiled, unfiltered drinkingwater (51).

Cyclospora cayetanensisEimer first noticed Cyclospora in 1870 in theintestines of moles. The organism hassubsequently been recorded from moles, otherrodents and snakes. The first human cases were

from Papua New Guinea. Cyclospora-likeorganisms were isolated fromthree patients butwere thought to be organisms belonging todifferent Isospora species (52). From 1985onwards, organisms, 8 — 10 um in size, stainingred with modified acid fast stains have beenisolated frequently from humans. At one timethey were described as cyanobacteria-like bodies(blue green algae) or coccidian like bodies (3).These were implicated for frequent diarrhoealepisodes. The coccidian like bodies resembledclosely the unsporulated coccidian organismsindiarrhoeal stools of Peruvian children andattempts were madeto ‘sporulate’ them, Basedon the morphology ofthe sporulated bodies, theorganisms were then placed in the genusCyclospora (3). Severe Cyclospora infectionshave been described in patients with AIDS (53,34),

Clinical features of Cyclospora cayetanensisinfectionThe symptoms are similar to those produced bycryptosporidiosis. In patients with AIDS, theinfection may last for several months.Modeof exposure / Association with waterAlthough proven cases. of waterborneCyclospora infections are few, itis thought to bethe major modeof transmission ofthe parasite.The prolonged sporulation time (1 - 2 weeks)also supports this view. Cyclospora infectionacquired via chlorinated drinking water has beenreported (55). Reports of drinking untreatedwater or reconstituted milk have been obtainedfrom patients with infection (56, 57, 58). InChicago, in an outbreak in a hospital where 20resident doctors contracted the infection, thesource was traced to the rooftop water reservoir

Journalofthe College of Community Physicians of Sri Lanka

(59). A. child who acquired the infectionfollowing a swim in lake Michigan has beenreported (3). The infection has also been reportedin Nepal and the organism has beendemonstrated in sewage water (60). Anotherindication of the association of Cyclospora withwater is found in a report from Indonesia wherethe incidence ofdiarrhoea due to this organismwas highest in expatriates during the rainyseason(61).

Microsporidia‘Microsporidia’ is a non-taxonomic term usedtodesignate members of the order Microsporidia ofthe phylum Microspora. The organisms are

jous and are known to infect a wide rangeof vertebrates, Thefirst documented human casewas in 1985 (3). Five genera have been reportedto be pathogenic to humans. These are,Encephalitozoon, Enterocytozoon , Septata,Pleistophora and Vittaforma. Based on DNAanalysis, Septata intestinalis may now be placedin the genus Encephalitozoon and, based on theultra structure, Nosema corneae is now calledVittaforma corneae (62).

Clinicalfeatures of Microspora infection

The incubation period is not known. This isbecause the exact route of infection has not yetbeen characterised. The infection leads tochronic diarhoea, dehydration and weight loss.The clinical course is severe in theimmunocompromised. The parasites may alsocause keratitis, hepatitis, myositis and nervoussystem disease.

Modeof exposure / Association with water

Microsporidia are commonly found in ditch andother surface waters. Most of them have zoonoticorigins but E. bieneusi is thought to be a naturalhuman parasite (3). Under normal environmentalconditions, these organisms are able to survivefor long periodsof time. At 4°C Microsporidiacan remain viable in water for about a year (3).Food and water contaminated with spores arethought to be the most probable modes oftransmission (40).Quality assurance of drinking andrecreational water

Drinking water supplies should be sufficient inquantity, wholesome and non-injuriousto health,Microbiological testing provides a sensitiveindicator of the effectiveness of the sourceprotection, treatment and distribution, Withregards to detection of parasites and their stages

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in water, the currently available laboratorytechniques are grossly inadequate, For detectionof cysts of Giardia and oocysts ofCryptosporidium, methods are being developedin industrialised countries. Research on theselines has not even been attempted in developingcountries. Even the bacteriological qualitytesting for which the techniques are available arenot being carried out properly in poor countries.Many are still without treated pipe bornedrinking water. With regards to recreational‘waters, almost nothing has been done in the wayofparasitological testing, with chlorination beingthe only treatment. Protozoan cysts andcoccidian ooccysts are highly resistant tochlorination and this procedure therefore will nothelp in preventing transmission (11, 12).Giardiasis and cryptosporidiosis are the mostcommonly recognised parasitic protozoaninfections associated with ‘recreational water(40).For poor developing countries, the only avenueopen currently is to improve the diagnosticlaboratory techniques sothat emerging infectionsand their patterns could be methodicallymonitored. These records will point to outbreaksof possible waterborne parasitic infections in aprecise locality or in a high-risk group. Untilsuch time these countries acquire the technologyand the resources to monitor parasitologicalquality of water, the early detection andtreatment of those whoare infected remain theonly solution, When monitoring waterborneparasitic infections the fact that many havezoonotic origins should not be forgotten.Acknowledgements

This review was prepared while onsabbatical leave in Florida, USA. I thank theUniversityof Peradeniya, Sri Lanka, for grantingmeleave of absence, It is a grest pleasure tothank the librarian and the administration of the‘Archbold Biological Station, Lake Placid,Florida, USA, for allowing me to use theirfacilities. My thanks are also due to Dr.DJWeilgainafor his comments on the manuscript.

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