Dental Optometry Parasitology

William H. Benjamin, PhDUAB Pathology

Important points for parasites• Life cycle• Definitive host• Intermediate host• Reservoir hosts• Vectors• How humans are infected• Migration pattern and where adults live in

humans• Diagnostic form in humans• Geographical distribution

Sedimentation concentration

Floatation concentration

Classification of Parasites• Protozoa - single celled eukaryotes

– mastigophora - Giardia lamblia– sarcodina - Entamoeba histolytica– sporozoa - Toxoplasma gondii, Cryptosporidium sp.

Plasmodium sp. (malaria)• Helminths - multi-cell eukaryotes (Worms)

– nematodes - round worms (Ascaris lumbricoides)– platyhelminths - flat worms

• trematodes - (flukes) Schistosoma sp.• Cestodes - (tapeworms) - Taenia sp. (pork tapeworm.)

Entamoeba histolytica

Entamoeba histolytica/dispar• Humans are the only host• world wide distribution• fecal oral or water borne - cysts are the infectious

form• diagnostic forms are cysts or trophozoites in

stool or serology• Causes amebic dysentery • invade and lyse tissue either in the colon or

extraintestinal sites usually liver or lung

Entamoeba histolytica/dispar

Non pathogenic ameba

• Entamoeba dispar - morphologically identical to E. histolytica

• Entamoeba hartmanni - small race E. histolytica• Entamoeba coli• Iodamoeba butschlii• Endolimax nana

Entamoeba coli

cysts

Giardia lamblia• The most commonly diagnosed and important

parasite of humans in the US• Transmission is fecal oral or water borne• Daycare centers• Fifty percent asymptomatic - 2 - 15% incidence• Symptoms - frothy fatty diarrhea - malabsorption,

osmotic diarrhea • Reservoir hosts - beaver and other animals• Diagnostic forms are cysts and trophozoites in stool

- noninvasive

Giardia lamblia

Giardia lamblia

Chilomastix mesnilinon-pathogenic flagellate

Toxoplasma gondii

• Cat litter organism• Congenital infections

Montoya, J. G., and O. Liesenfeld. 2004. Toxoplasmosis. Lancet 363:1965.

1st trimester

2nd trimester

3rd trimester

Transmission rate

Rate of Severe sequelae/stillbirth

Among infected infants

14%

8%

41%

0%59%

29%

Congenital Toxoplasmosis400 – 4000/ year750 deaths from toxoplasmosis/ year 50% food-borne

CNS lesions found in immunosuppressed patients

Toxoplasma gondii (cysts)

Cryptosporidium parvum• Zoonosis - first human cases in 1979-1982 Auburn• Worldwide distribution• Cysts are infective - resistant to chlorine

– Milwaukee - 1993 370,000 cases• Common in daycare centers• Intracellular in gut epithelium• Self limiting watery diarrhea in adults and children• Severe untreatable disease in AIDS patients

Cryptosporidium parvum

The little blue organisms lined up along the brush border of the small intestinal epithelium are Cryptosporidia. This infection causes diarrhea in immunocompromised hosts. medlib.med.utah.edu

Overview of Malaria Epidemiology

• 2.7 million deaths/year mostly children in Africa

• 300 to 500 million cases annually• 90 percent of them in sub-Saharan Africa• More than 40 percent of the world's

population lives in areas where malaria naturally occurs

• 1000 cases/year in the US

Plasmodium (malaria)

Malaria fever

Plasmodium vivax

Trophozoites: ameboid; deforms the erythrocyte

Gametocytes: round-oval Schizonts: 12-24 merozoites

Rings

Infected erythrocytes: enlarged up to 2X; deformed; (Schüffner’s dots)

Plasmodium falciparumMalignant malaria

Malaria prevention decreased contact with mosquito

• Night biting Anopheles mosquitos are the only intermediate host

• Insecticide-treated nets – cheap and, if used correctly, an effective means of

preventing malaria.• Indoor house-spraying with residual insecticides

(e.g. DDT) – Mosquito resistance– Ecological concerns

• wearing of protective clothing and insect repellents at dawn and dusk

US Cases of Cyclospora• Guatemalan spring raspberries

– 1995 retrospective cases in New York and Florida– 1996 1465 cases in 14 states and 2 provinces– 1997 90 cases before importation of raspberries stopped

• Sweet Basil– Washington DC and Virginia 61 events with at least 1700

cases• Lettuce - specialty baby leaves

– 2 events, 1 cruise ship

Cyclospora cayetanensis

• First found in Nepal, Peru and Cook County Hospital 1989 - 1990

• Found to be a coccidian and named 1993• Reservoir unknown• Infects small intestine epithelial cells• Profuse watery diarrhea for 4 - 7 days. Multiple

relapses over 3 - 4 months• Treatment trimethoprim - sulfamethoxazole usually

more than one course required

Cyclospora cayetanensis

Helminth species* x 106

Ascaris lumbricoides 1472Ancylostoma Duodenale and Necator americanus 1298Trichuris trichiura 1049Schistosoma haematobium 114Wuchereria bancrofti 107Schistosoma mansoni 83Taenia saginata 77Hymenolepis nana 75Strongyloides stercoralis 70Paragonimus westermani and related species 21Onchocerca volvulus 18Brugia malayi and Brugia timori 13Loa loa 13Opisthorchis viverrini and Opisthorchis felineus 10Taenia solium 10Diphyllobothrium latum 9Clonorchis sinensis 7

Helminth species* x 106

Echinococcus granulosus and E. multilocularis 2.70Fasciola gigantica and Fasciola hepatica 2.40Schistosoma intercalatum 1.73Schistosoma japonicum 1.55Schistosoma mekongi 0.91Metagonimus yokogawai and related species 0.66Heterophyes heterophyes and related species 0.24Fasciolopsis buski 0.21Echinostoma ilocanum and related species 0.15Dracunculus medinensis 0.08

58,000 specimens from 601 US laboratories

Parasite PatientsGiardia lamblia 723Cryptosporidium sp. 81Dientamoeba fragilis 77Ascaris lumbricoides 59Entamoeba histolytica 52Trichuris trichiura 44Hookworm 45Enterobius vermicularis 49Strongyloides stercoralis 36Hymenolepis nana 17Isospora sp. 7Microsporidia 6Clonorchis sp. 4Others 241224 positive patients 58,000 specimens

Ascaris lumbricoideslarge roundworm

• World wide distribution• Humans are the only definitive host• Embryonated eggs are infective (not food handler)• Eggs hatch in duodenum, larvae penetrate the

intestine and migrate through the lungs, swallowed• Large round worm - 20 - 35 cm long• Adults live in small intestine• life span is 6 months to 1 year• Diagnostic form is eggs in stool or passed adult• Erratic adult worms

Ascaris lumbricoides

Ascaris lumbricoidesRoundworm

“Vomit worm”Ascaris lumbricoides

Strongyloides stercoralis

• Free living• “life time

infection”

Strongyloides stercoralis• Mainly tropical distribution• Can have free living adult forms• Infection is by larvae boring through intact skin• Adult females are small (2 mm long) and live in

the mucosa of the small intestine• Autoinfection can lead to hyperinfection syndrome • Infections can be subclinical for decades• Eosinophilia is common• Diagnostic forms are larvae in stool or sputum

Strongyloides stercoralis

Schistosoma sp. (blood flukes)• S. mansoni, S. haematobium and S. japonicum• Geographic distribution - tropics• Adults (1 - 2.5 cm long) reside in conjugal bliss in

venules• Infection is by cercaria penetrating intact skin• Snails are the intermediate host - humans acquire

infection in snail infested water • Zoonotic - except S. haematobium• Diagnostic form is ova in stool or urine or serology

Schistosoma species

Blood flukes

Schistosoma mansoni eggs

Schistosoma mansoni

Taenia soliumpork tape worm

• Found where ever people eat uncooked pork and allow pigs to scavenge human waste

• Humans can be both definitive host and intermediate host

• Infective forms for humans– cysticerci in pork - adult tape worm (10 years)– ova from human stool - cysticerci in humans

• Adult tapeworms are 2 - 7 meters long• Diagnostic forms are ova in stool or passed worm

segments. CAT/MRI scans for cysticerci

Adult Taenia (tapeworm)

Measly porkSource of Taenia solium

(Pork tapeworm)

Other cestodes - tapeworms

• Taenia saginata - beef tapeworm• Diphyllobothrium latum - broad fish tapeworm• Hymenolepis nana - dwarf tapeworm• Hymenolepis diminuta - rat tapeworm

Dracunculus medinensisGuinea worm

Number of dracunculiasis cases by country 19993.5 million 1985

Cuterebra sp.• Adult flies do not bite or feed• Deposit eggs where hosts will be exposed • Eggs hatch in response to body heat gain

entrance through nose or mouth migrate to the subcutaneous area and complete development in 30 days

UAB Botfly in eye Cuterebra sp. ??

Hypoderma spp ??

Acanthamoeba sp.

• No flagella• Cyst form often in tissue• Can cause amoebic

meningoencephalitis can be more chronic because of cysts

• Contact lens wearers are at risk of corneal infections

• Resistant to chlorine • More susceptible to NaCl• Somewhat more treatable

than Nagleria.

River blindnessOncocerca volvulus

• Tropical Africa and South America

• Transmitted by the black fly

• Diagnosis is by skin snips

• Endotoxin from bacteria in the worm causes the inflammation in the eye