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Biodefense
Reference Library
Foreign
Animal and Zoonotic
Disease Center
Zoonotic
Disease Online Course
Presented
by
Stephen M.
Apatow, Director
of Research and Development
Humanitarian
Resource Institute
Biodefense Reference Library
Foreign
Animal and Zoonotic Disease Center
[Vitae][Email]
ZOONOTIC
DISEASES
TREMATODE
SCHISTOSOMIASIS
Centers for
Disease Control
and Prevention: National Center for Infectious Diseases
schistosomiasis
Disease
Overview:
Institutional
Animal Care and Use Committee, University of California, Santa
Barbara.
(Bilharzia,
Bilharziasis)
AGENT:
Schistosomiasis
infects more
than 200 million persons worldwide. The causative agents are
Schistosoma
mansoni, haematobium, and japonicum.
RESERVOIRS AND INCIDENCE:
Humans are the
reservoir for
S. mansoni and haematobium. S. japonicum infects cattle, water buffalo,
horses, dogs, cats, rodents and monkeys. Intermediate hosts are species
of snails (Biomphalaria and Bulinus). S. mansoni occurs in Africa,
South
America and some Caribbean islands (including Puerto Rico); S.
haematobium
in Africa and the Middle East; and S. japonicum in China, Japan, the
Philippines,
and South East Asia.
TRANSMISSION:
Cercariae in
contaminated water
penetrate human skin, especially in irrigated fields or rivers. In the
body the parasite migrates via the liver to the superior mesenteric
vein
where maturation takes place in about 6 weeks. Eggs are disseminated
throughout
the body via the blood, released into the intestinal lumen and
excreted.
In water miracidia develop and penetrate the snail, which in turn
excretes
cercariae into the water.
DISEASE IN ANIMALS:
Abdominal
pain, diarrhea, anemia,
and emaciation occur. Cattle have hematuria.
DISEASE IN HUMANS:
Penetration of
larvae through
the skin causes an itchy rash. With heavy infection, penetration of the
parasite through the skin gives rise to local dermatitis and pruritus
followed
by pneumonitis when the parasites reach the lung. The deposition of ova
provokes the growth of small multiple granulomata throughout the body.
Eventually intestinal and hepatic fibroses develop. With S. japonicum,
acute symptoms include fever, abdominal pain, cough, weight loss,
diarrhea
and dysentery. Chronic infection may result in symptoms months to years
later, with enlarged liver and spleen, cirrhosis, ascites, and fits due
to cerebral involvement.
DIAGNOSIS:
Definitive
diagnosis is made
by finding the characteristic eggs in excreta or by mucosal or liver
biopsy.
Screening for infection is possible by skin or serologic tests, but
neither
is sufficiently sensitive or specific to justify treatment.
TREATMENT:
Praziquantel,
metrifonate, or
oxamniquine.
PREVENTION/CONTROL:
Dispose of
feces and urine so
that viable eggs will not reach bodies of fresh water containing
intermediate
snail hosts. Reduce snail habitats by removing vegetation or by
draining
and filling. Treat snail-breeding sites with molluscicides. Prevent
exposure
to contaminated water (e.g., wear rubber boots and gloves). To minimize
cercarial penetration, towel dry, vigorously and completely, skin
surfaces
wet with suspected water. Apply 70% alcohol immediately to the skin to
kill surface cercariae. Provide water for drinking, bathing, and
washing
clothes from sources free of cercariae. Rapid treatment of patients to
prevent disease progression and to reduce transmission by reducing egg
passage.
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