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Biodefense Reference Library
Foreign Animal
and Zoonotic Disease Center
One Medicine: One Health (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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