NAME: Schistosoma spp.
SYNONYM OR CROSS REFERENCE: Schistosoma mansoni, S. japonicum, S. haematobium, S. mekongi, S. intercalatum, schistosomiasis, bilharzasis, snail fever Katayama fever 1-3.
CHARACTERISTICS: Species of the genus Schistosoma are trematode blood flukes belonging to the Schistosomatidae family Footnote 4. They are dioecious, have a two host life cycle, and exhibit a high degree of sexual dimorphism Footnote 3Footnote 4. Adult worms are 7-28 mm in length and 0.3-0.6 mm in width Footnote 5. Fertilized adult female releases eggs which are deposited in the environment in feces or urine of the definitive host (humans and other mammals) Footnote 6. Size and shape of the eggs vary according to species. Schistosome eggs, housing the miracidia, are round or oval with one spiny appendage. Miracidia, viable only in fresh water, measure approximately 150 µm in length Footnote 7. Miracidia hatch from the eggs and penetrate their intermediate hosts (snails) Footnote 6. In the snail, each miracidium produces sporocysts that produce cercariae (the infective stage for humans) Footnote 6. Cercariae measure about 450 µm in length, and have forked tails which they shed upon infection Footnote 3Footnote 7.
PATHOGENICITY/TOXICITY: Symptoms are related to the amount and location of eggs in the human host Footnote 5. Any species of Schistosoma can cause acute schistosomiasis Footnote 3. Acute schistosomiasis is characterized by cercarial dermatitis and Katayama syndrome. Cercarial dermatitis is unusual among individuals exposed for the first time such as visitors and migrants, and is rare among endemic populations, travellers or migrantsFootnote 8Footnote 9. The clinical presentation of acute schistosomiasis includes fever, headache, generalized myalgia, abdominal pain, vertigo, vomiting, bloody diarrhea, and fatigue Footnote 3Footnote 5Footnote 10. When eggs become trapped in tissue, and they fail to clear, they can produce chronic schistosomiasis Footnote 3. The chronic disease, which is more prevalent in endemic areas, is due to a granulomatous response to parasitic eggs. Clinical presentation includes inflammation, hyperplasia, ulceration, and occult blood in feces. It is possible that there is an association between chronic schistosomiasis and colorectal cancer Footnote 3. When eggs are deposited in the liver, symptoms can include portal hypertension, hepatosplenomegaly, liver fibrosis, hepatic coma, ascites, and esophogeal varices Footnote 3Footnote 11. The latter are late stages of pipestem fibrosis with liver cell function relatively preserved early in the disease course. S. japonicum and S. mansoni are primarily associated with hepatic and intestinal pathology, including diarrhoea, abdominal pain, and hepatosplenomegaly24. Urinary schistosomiasis is caused by S. haematobium, and chronic S. hematobium infection is the major risk factor for for urinary tract carcinoma in Africa24. The clinical presentation includes dysuria, hematuria ,proteinuria, calcification in the bladder, obstruction of the ureter, renal colic, hydronephrosis, and renal failure Footnote 3. Secondary infection may occur with urinary schistosomiasis. It is associated with genital disease in 1 out of 3 infected women. S. haematobium is a leading cause of bladder cancer Footnote 12. Lung and CNS involvement can occur, producing lesions in the brain (S. japonicum and S. mekongi) and spinal cord (S. mansoni and S. haematobium) Footnote 11. Clinical manifestations of cerebral schistosomiasis include seizure, headache, acute encephalopathy, hemiparesis, and hemianopsia Footnote 11. Worms may survive for 30 years in the host Footnote 5.
EPIDEMIOLOGY: S. mansoni is endemic in Africa, the Middle East, Asia, South America, and the Caribbean Footnote 3. S. japonicum has been eradicated in Japan, and is endemic in China, Southeast Asia, Indonesia, and the Philippines. S. haematobium is endemic in Africa and the Middle East. S. mekongi is endemic in Cambodia, Laos, and Thailand. S. intercalatum is endemic in central and West Africa. 85% of schistosomiasis cases occur in sub-Saharan Africa. Schistosomes are currently estimated to infect 200 million people in 74 countries, and 500-600 million people are at risk Footnote 4. Infection with Schistosoma spp. is responsible for approximately 280,000 deaths per year in sub-Saharan Africa Footnote 13.
HOST RANGE: Humans for S. haematobium, S. mekongi, S. intercalatum Footnote 3. S. mansoni primarily infects humans, but can infect mammals occasionally. S. japonicum infects humans and bovine species. Other Schistosoma species primarily infecting mammals only rarely infect humans Footnote 3 Footnote 4.
INFECTIOUS DOSE: Not known.
MODE OF TRANSMISSION: Transmission occurs in water contaminated with feces or urine Footnote 3. Free swimming cercariae directly penetrate through the skin to infect humans.
INCUBATION PERIOD: Cercariae reach the portal venous system several days post-infection Footnote 3. 4-6 weeks usually pass before egg production begins Footnote 3. Toxemic schistosomiasis may develop 6-8 weeks post infection Footnote 5. Urinary schistosomiasis may develop 10-12 weeks post infection Footnote 5. Adult schistosomes may live 20 to 30 years.
COMMUNICABILITY: Not directly transmitted from person to person.
ZOONOSIS: Reservoir animals may be responsible for indirect zoonosis, especially with S. japonicum Footnote 5.
VECTORS: Snails. Biomphalaria spp. are associated with S. mansoni, Oncomelania spp. are associated with S. japonicum, Bulinus spp. are associated with S. haematobium and S. intercalatum, and Neotricula aperta are associated with S. mekongi Footnote 3.
SUSCEPTIBILITY TO DISINFECTANTS: 2% glutaraldehyde, sodium hypochlorite, 70% ethanol Footnote 16-18.
PHYSICAL INACTIVATION: Sensitive to low temperatures; S. japonicum does not develop at temperatures lower than 15.4°C Footnote 19.
SURVIVAL OUTSIDE HOST: Cercariae may survive in water for about 2 days Footnote 5.
SURVEILLANCE: Monitor for symptoms, confirm through direct observation of eggs in stool or urine (S. haematobium and rarely S. mansoni) Footnote 3. If a patient exhibits the clinical symptoms but lacks eggs in faeces or urine, a biopsy of the bladder or rectal mucosa can be performed. ELISA and PCR can be used, as well as a Kato-Katz thick smear Footnote 20. If too few eggs are excreted, the miracidium-hatching method can be employed Footnote 5.
FIRST AID/TREATMENT: Praziquantel is the primary drug used against schistosomiasis Footnote 3. Artemether is not used where malaria is present to prevent Plasmodium from developing resistance.
IMMUNIZATION: None Footnote 6.
LABORATORY-ACQUIRED INFECTIONS: One case reported as of 2010 Footnote 21.
SOURCE/SPECIMENS: Feces, urine, biopsy specimens Footnote 3.
PRIMARY HAZARDS: Cercariae in contact with skin or mucous membranes Footnote 21.
SPECIAL HAZARDS: None.
RISK GROUP CLASSIFICATION: Risk Group 2.
This risk group applies to the genus as a whole, and may not apply to every species within the genus.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures.
These containment requirements apply to the genus as a whole, and may not apply to each species within the genus.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk of exposure to splashes Footnote 23.
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities Footnote 23.
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply an appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up.
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism before disposing by autoclave, chemical disinfection, gamma irradiation, or incineration.
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled.
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: December 2011
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Copyright © Public Health Agency of Canada, 2011 Canada