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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

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Sedimentation concentration

Floatation concentration

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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.)

Entamoebahistolytica

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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

Entamoebahistolytica/dispar

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Non pathogenic ameba

• Entamoeba dispar - morphologically identical toE. histolytica

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

Nonpathogenic amoeba

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Entamoeba colicysts

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

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Giardia lamblia

Giardia lamblia

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Giardia lamblia

Chilomastix mesnilinon-pathogenic flagellate

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Toxoplasmagondii

• Cat litter organism• Congenital infections

Toxoplasma gondii

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CNS lesions found inimmunosuppressed patients

Toxoplasma gondii (cysts)

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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

Cryptosporidiumparvum

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Cryptosporidium parvum

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

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Plasmodium (malaria)

Malaria fever

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Plasmodium falciparumMalignant malaria

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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 CountyHospital 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

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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

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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 723

Cryptosporidium sp. 81

Dientamoeba fragilis 77

Ascaris lumbricoides 59

Entamoeba histolytica 52

Trichuris trichiura 44

Hookworm 45

Enterobius vermicularis 49

Strongyloides stercoralis 36

Hymenolepis nana 17

Isospora sp. 7

Microsporidia 6

Clonorchis sp. 4

Others 24

1224 positive patients 58,000 specimens

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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

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Ascaris lumbricoidesRoundworm

“Vomit worm”Ascaris lumbricoides

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Strongyloidesstercoralis

• 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

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Strongyloidesstercoralis

Strongyloides stercoralis

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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

Schistosomaspecies

Blood flukes

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Schistosoma mansonieggs

Schistosoma mansoni

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Taenia soliumpork tape worm

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

• Humans can be both definitive host andintermediate 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)

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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

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Dracunculus medinensisGuinea worm

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Dirofilaria immitisDog heartworm in situ