Waterborne Pathogens: Parasites

February 23rd-25th, 2010

Parasitic pathogens in water

• Enteric and non-enteric diseases• Ingestion of contaminated water• Contact with contaminated water• Complicated life cycles taking place in water

and the human body with intermediate hosts

Categories of waterborne parasites

• Diseases contracted by ingestion of contaminated water

• Cryptosporidium• Entamoeba• Guinea worm disease

• Diseases contracted by contact with contaminated water

• Naegleria• Schistosomiasis

Cryptosporidiosis

• Cryptosporidium parvum• Protozoan parasite• Fecal-oral transmission• Humans and cattle are reservoirs• Contamination of water sources from cattle fields• Infectious stage is the extremely resistant

environmental stage (oocyst)• Resistant to chlorine disinfection• Diarrheal disease that can become chronic in

immunosuppressed people

Cryptosporidiosis

• Diagnosis through immunofluorescent staining and microscopy

Amoebiasis

• Entamoeba histolytica• Amoebic dysentery• Fecal-oral transmission• Infectious stage is the resistant environmental

stage (cyst)• Humans are reservoir• Disease is ubiquitous in areas of poor

sanitation

Amoebiasis

• Diagnosis via microscopy (fecal specimen)

Naegleria• Naegleria fowleri• Ubiquitous free-living amoeba• Reservoir: warm surface freshwaters• Primary amoebic meningoencephalitis• A common organism, but a rare disease• Infection by crawling up your nose into your

brain• Treatment with amphotericin B, but survival

rates are poor

Naegleria

• Diagnosis by microscopy of spinal fluid

Schistosomiasis

• Genus Schistosoma• Species mansoni, japonicum, and haematobiun• Blood flukes (parasitic worms)• Burden of disease is from chronic infection• Damage caused by eggs deposited in tissue

– Liver damage– Urinary tract damage

Schistosomiasis

• Humans are the main reservoir• Excrete eggs in feces• Important intermediate host: snails• Schistosomes live in the snail in freshwater• Infection from contact with water • Infectious stage is the cercariae• They leave the snail and penetrate skin • Migrate through the bloodstream to organs

Schistosomiasis

• Diagnosis by microscopy of eggs in stool or biopsy specimens

Schistosomiasis control

• Prevent contamination of water with adequate sanitation and disposal of feces

• Kill the cercariae by disinfection• Kill the intermediate host (molluscicides)• Drug treatment

– Praziquantel– Treatment of individuals who are infected– Mass drug treatment of communities as a

preventative measure

Guinea worm disease

• Dracunculus medinensis• Nematode (worm)• Humans are the reservoir• Intermediate host: small copepods that live

free in freshwater

Guinea Worm disease

• Worm larvae infect copepods• People ingest copepods, esp. when they drink

stagnant water• Larvae migrate from the stomach through the

body• Worms erupt though the skin• Putting affected areas of the body into water

releases the larvae to restart the cycle• Burden of disease from secondary bacterial

infections of skin lesions

Guinea Worm disease

• Diagnosis by microscopy of the larvae or seeing the worm crawl out of the skin

Guinea Worm control

• Target of a fairly successful eradication campaign

• Endemic only in Sudan, Ghana, Mali, Ethiopia• No effective drug treatment• Control by filtering water to remove the

copepods• Digging wells for safer water• Kill the copepods

Control of waterborne parasites

• Drinking water:• Prevention of water contamination

– ADEQUATE SANITATION• Barrier methods

– Treatment trains– Filtration– Most parasites are quite resistant to disinfection

Control of waterborne parasites

• Control of intermediate hosts (snails, copepods)

• Eliminating human infection to prevent further spread into the environment

• Preventing contact with high-risk sources