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Trichinellosis |
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Causative Agent |
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Click on the image to enlarge. |
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Life cycle of
Trichinella sp. |
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Distribution |
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Geographic:
Seasonality:
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Hosts, Transmission and Life Cycle |
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Hosts:
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Primarily a disease of carnivores with scavenging or cannibalistic tendencies.
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Several wildlife species in North America are known to be affected, including bears, wild dogs and cats, pigs, seals and walruses, rodents and
mustelids.
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Humans can become infected by T. spiralis by consuming undercooked, infected meat.
Generalized Life Cycle:
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Refer to the above generalized life cycle diagram of Trichinella sp.
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Transmission between hosts occurs when infected meat is consumed.
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Cysts
containing larva are digested; larvae form
cysts in the inner surface of the small intestine where they mature into adults and mate.
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New larvae move via the bloodstream to muscle where they remain as the infective stage until eaten by a susceptible carnivore or scavenger.
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Cysts
may remain in muscle for 6-12 months and can survive after the death of the host, and so infect scavengers.
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Signs and Symptoms |
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Like other adult
roundworms, T. spiralis are unsegmented, cylindrical and tapered at both ends, and can measure between 1.2 – 2.2 cm in length.
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In wildlife, disease can occur at two stages of infection: in the muscle and in the intestines
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muscle: muscle pain,
edema, fever; large burdens of
cysts may lead to death.
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intestines: adult worms may cause
hemorrhage.
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In humans, symptoms such as
edema around the eyes, muscle pain, fever, diarrhea, itchiness in the skin, and
lesions of the skin have been described.
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More serious cases in humans have caused breathing difficulties as a result of an infected diaphragm,
inflammation of the brain, and heart failure.
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Meat Edible? |
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Humans may contract T. spiralis from eating improperly cooked meat of an infected animal.
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Meat from an infected animal should not be fed to dogs or cats.
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Human Health Concerns and Risk Reduction |
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Trichinella
is a potential
zoonosis.
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Infection can be spread to humans through consumption of improperly cooked meat, especially from bears and seals.
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To minimize the chances of infection, meat must be cooked at 77°C throughout to kill all larvae that may be present. Microwave ovens do not uniformly cook meat and as a result may not kill the parasite.
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Freezing meat is NOT a reliable way of killing Trichinella
roundworms.
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Several safe and effective prescription drugs are available to treat trichinellosis. Treatment should begin as soon as possible and the decision to treat is based upon symptoms, exposure to raw or undercooked meat, and laboratory test
results.
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Samples for Diagnosis |
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Muscle tissue containing larval
cysts should be submitted for diagnosis.
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Cysts may be difficult to see with the naked eye; however, active muscles such as the tongue, diaphragm and muscles of the jaw usually contain the highest concentrations of infective larvae.
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Further Reading |
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Canadian Cooperative Wildlife Heath Centre. 1995. Trichinosis. Pp. 41-42. Health risks to wildlife personnel: hazards from disease-causing agents. Canadian Cooperative Wildlife Heath Centre, Western College of Veterinary Medicine, University
of Saskatchewan. Saskatoon, SK.
Dick, T. A., and E. Pozio. 2001. Trichinella spp. and Trichinellosis. Pp. 380-396 in W. M. Samuel, M. J. Pybus, and A. A. Kocan (eds.), Parasitic Diseases of Wild Mammals. 3rd Ed. Iowa State University Press, Ames, IA.
Elkin, B, and R. L. Zamke. 2001. Common wildlife diseases and parasites in Alaska. Alaska Department of Fish and Game. Anchorage, AK.
US Centers for Disease Control and Prevention - trichinellosis information (human implications)
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