Download Vaccination, Environmental Health, and Polio Control

Waterborne Pathogens: Parasites
February 23rd-25th, 2010
Parasitic pathogens in water
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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
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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
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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
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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
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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
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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
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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