NAME: Echinococcus granulosus
CHARACTERISTICS: E. granulosus is a tapeworm of the class Cestoidea, order Cyclophyllidea, and family Taeniidae.
Adult Worm: Mature worms are only found in the small intestine of the definitive hosts, which are carnivores (dogs and other canine). Adult worms are 3 to 7 mm long with only 3 proglottids. The body consists of a typically Taeniid scolex, a short neck and the proglottids; the mature segment is in the middle and the gravid is the last segment Footnote 1Footnote 2Footnote 5Footnote 6.
Eggs: Eggs are found in the feces of the definitive infected hosts. Eggs are spherical with a diameter of 30-50 μm. The embryo, or oncosphere, is protected by the embryophore, which consists of keratin-like material. The embryophore is thick and impermeable, thus making the eggs extremely resistant.
Larvae form: When intermediary hosts (farm animals) or humans (accidental host) ingest the eggs, the oncospheres hatch and become activated and transported by the blood stream to the liver or other organs. Once the oncosphere reaches its final destination, it develops into a unilocular hydatid cyst which enlarges and produces protoscolices or daughter cysts within the hydatid cyst interior Footnote 2Footnote 7.
PATHOGENICITY/TOXICITY: Cystic echinococcosis is a chronic disease caused by cysts/metacestodes of E. granulosusFootnote 2Footnote 3. Many human infections remain asyptomatic. Hydatid cysts are usually observed as incidental findings by abdominal ultrasound screening or autopsy. The liver (>65%) is the most common site for the formation of cysts, followed by the lungs (25%), spleen (3-8%), kidneys, heart, bone, and central nervous system Footnote 2Footnote 3. However, cysts of the cervid form (northern sylvatic) localize predominantly in the lungs Footnote 8-10. Infections are generally acquired during childhood; clinical signs of disease may develop later in life (at a mean age of 50 years) due to the slowly growing nature of cysts Footnote 2Footnote 3. Clinical manifestations of the disease are variable and depend on the location, size, and condition of the cysts Footnote 2. Symptoms of hepatic echinococcosis include hepatic enlargement, right epigastric pain, nausea, and vomiting Footnote 2. Release of hydatid fluid, due to spontaneous rupture of the cysts can result in allergic reactions ranging from mild to fatal anaphylaxisFootnote 2Footnote 3. Multiple secondary infections can occur due to dissemination of E. granulosus protoscolices Footnote 2.
EPIDEMIOLOGY: Cystic echinococcosis is prevalent in temperate countries, including southern South America, the entire Mediterranean littoral, southern and central parts of the former Soviet Union, central Asia, China, Australia, and parts of Africa Footnote 2. Canada and parts of the United States are also considered endemic Footnote 3. Most infections in the United States occur in immigrants from countries where the disease is highly endemic Footnote 2. However, sporadic autochthonous cases are currently recognized in Northern Canada, Alaska, Arizona, and New Mexico Footnote 11. China is one of the most important endemic regions for E. granulosus. An estimated 0.6–1.3 million existing cases of human echinococcosis occur in China Footnote 12.
HOST RANGE: Dogs, foxes, wolves, coyotes, jackals other canids, and large cats such as lions and leopards are the definite hosts; sheep, goat, swine, cattle, horses, camel, deer, caribou, moose, and occasionally humans are the intermediate hosts Footnote 2Footnote 3Footnote 7.
INFECTIOUS DOSE: Unknown
MODE OF TRANSMISSION: Transmission to humans can occur through the fecal-oral route, ingestion of food or water contaminated with E. granulosus eggs released in the feces of final hosts such as dogs, or through hands contaminated with egg-containing soil, sand or hairs of infected dogs Footnote 2Footnote 3. Final hosts such as dogs acquire infection through ingestion of cysts, for e.g., slaughtered sheep carrying infectious cysts Footnote 3.
INCUBATION PERIOD: Less than 5 to 15 years Footnote 13. Ingestion of meat containing these cysts can cause infection in definitive hosts, where these cysts mature to form adult worms within 32-80 days Footnote 2.
COMMUNICABILITY: Person-to-person transmission has not been reported for E. granulosus.
VECTOR: Coprophagic flies, other arthropods and other animals may serve as mechanical vectors for transmission of Echinococcus eggs to humans Footnote 14.
DRUG SUSCEPTIBILITY/RESISTANCE: In most patients, cysts can be completely eliminated by benzimidazole compounds such as albendazole Footnote 2Footnote 14Footnote 15. Instrains resistant to benzimidazole compounds, praziquantel, and avermectins have been reported as having some activity Footnote 2Footnote 15.
SUSCEPTIBILITY/RESISTANCE TO DISINFECTANTS: Echinococcus eggs can be killed by exposure to 3.75 % of sodium hypochlorite for 10 minutes Footnote 3. Echinococcus eggs are resistant to phenol, aldehydes, and ethanol disinfectants Footnote 3.
PHYSICAL INACTIVATION: Echinococcus eggs can be killed by freezing at – 70 °C for 4 days or - 80 °C for 2 days; or by heating at >60°C for 3 min Footnote 3.
SURVIVIAL OUTSIDE HOST: Echinococcus eggs can survive for long periods in the environment if sufficient moisture is present Footnote 3. They are also resistant to cold temperatures (can survive at -18°C for at least 8 months) Footnote 3. They can, however, be killed by dryness and high environmental temperatures Footnote 3.
SURVEILLANCE: Monitor for symptoms. Imaging procedures, ultrasound, CT scan, and MRI can be used to detect cysts. Serological methods such as ELISA can be used for the detection of antibodies against lipoproteins antigen B and antigen 5. Polymerase chain reaction (PCR) or real-time-PCR can be used to detect Echinococcus specific nucleic acids in resected tissue specimens or biopsies Footnote 2Footnote 3Footnote 16Footnote 17.
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID TREATMENT: Cystic echinococcosiscan be treated in a number of different ways.
Surgery: Surgical removal of intact cysts, whenever possible, is considered an optimal treatment for complete cure Footnote 2Footnote 14. Chemotherapy is recommended 4 weeks before, and for 1 month after the surgery.
Chemotherapy: Cystic echinococcosis can be treated with albendazole Footnote 2Footnote 14. Praziquantel in combination with albendazole has been reported to be more effective in treating cystic echinococcosis than albendazole alone Footnote 2Footnote 14.
Percutaneous aspiration, injection, re-aspiration (PAIR): This is used in patients with inoperable intraparenchymatous cysts Footnote 3. Percutaneous puncture using ultrasound guidance, aspiration of cyst fluid, injection of a protoscolicidal agent (e.g., 95% ethanol or 20% hypertonic saline:NaCl) for at least 15 minutes, followed by re-aspiration Footnote 2Footnote 3Footnote 14.
SOURCES / SPECIMENS: Animal feces; human and animal tissues such as spleen, kidneys, heart, bone, and brain Footnote 2, sputum.
PRIMARY HAZARD: Ingestion of the infectious eggs Footnote 1-3.
RISK GROUP CLASSIFICATION: Risk Group 2.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures Footnote 21.
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 21.
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 21.
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 Footnote 21.
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism before disposing by autoclave, chemical disinfection, gamma irradiation, or incinerationFootnote 21.
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled Footnote 21.
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