NAME: Trichinella spp.
SYNONYM OR CROSS REFERENCE: Trichinellosis(1-3), trichinosis(2,4), trichiniasis. Human and animal pathogens include T. spiralis, T. nativa, T. britovi, T. murrelli, T. nelsoni, T. pseudospiralis, T. papuae, T. zimbabwensis, and Trichinella genotypes T6, T8, T9, and T12.
CHARACTERISTICS: Trichinella spp. are intestinal nematodes that belong to the family Trichinellidae . The larval stage is infective(1,3). Adult worms reproduce sexually in the intestinal mucosa. Males measure 1.4 mm to 1.6 mm in length, whereas females are about twice the size of males. Larvae migrate to and infect striated muscle cells. The species are divided into two clades: (i) species that encapsulate in host muscle tissue (T. spiralis, T. nativa, T. britovi, T. murrelli, T. nelsoni, and Trichinella genotypes T6, T8, T9, T12), and (ii) species that do not encapsulate following muscle cell invasion (T. pseudospiralis, T. papuae, and T. zimbabwensis )(1,3).
PATHOGENICITY/TOXICITY: Trichinella spp. are responsible for causing the parasitic disease trichinellosis(1-4). Infestation is almost always limited to striated musculature, caused by infective larvae. Larvae are released from ingested raw or undercooked meat by the process of digestion and they invade the mucosa of the upper small intestine. Larvae develop into adult worms that reproduce sexually to produce more larvae. These larvae migrate to striated muscle cells, transforming them into nurse cells, where they grow and may become encapsulated. Severity of infection, which may vary from mild disease to severe illness, generally depends on the number of larvae ingested and/or the worm burden(1,2,4). Gastrointestinal symptoms, which appear shortly after infection, include nausea, vomiting, epigastric pains, and diarrhoea and/or constipation. Cardinal symptoms, which appear with the onset of larval migration and penetration, include fever, oedema (particularly periorbital oedema), myalgia, and marked peripheral eosinophilia, which together is called trichinellotic syndrome or general trichinellosis syndrome. Neurologic and cardiac complications may develop and may be fatal if severe (particularly myocarditis).
EPIDEMIOLOGY: Trichinella spp. occur worldwide, most frequently in regions with temperate climates(2,4). The genus does not selectively infect a specific species and instead is capable of infecting all warm-blooded animals. Birds and reptiles are infected by specific species of the genus. Human infections are common in Eastern Europe, Kenya, the former Soviet Union, South America, Alaska, continental Asia, and other regions where eating practices involving raw or undercooked meat are employed(2). Approximately 27 million people are suspected to be infected worldwide. There have been several reported outbreaks with Trichinella among countries of the present European Union between 1975 and 1999, involving 6250 individuals. More specific distributions of the different species of the genus are presented below:
HOST RANGE: Natural hosts for encapsulated Trichinella spp. generally include domestic and sylvatic mammals (pigs, horses, bears, wild boars, and others), and sylvatic terrestrial and marine carnivores(1,3). Natural hosts for nonencapsulated Trichinella spp. include domestic and sylvatic mammals (mainly pigs), birds, and reptiles (crocodiles).
INFECTIOUS DOSE: Unknown(1).
INCUBATION PERIOD: Gastrointestinal symptoms due to intestinal worms develop as early as 2 days after infection, while systemic symptoms due to infective larvae develop about 1 to 3 weeks post infection(1).
COMMUNICABILITY: No evidence of human-to-human transmission.
RESERVOIR: Pigs, horses, bears, and game animals are most important reservoirs for Trichinella spp. leading to its transmission to humans(2,3). Synanthropic animals (e.g. rats) may also act as reservoirs for Trichinella spp.(1).
DRUG SUSCEPTIBILITY: Intestinal worms and larvae, not encapsulated, are susceptible to anthelmintics including mebendazole, pyrantel, and albendazole(1,2,4,5). Intestinal worms are also susceptible to thiabendazole, although it is not recommended due to side effects(2,4,6).
SUSCEPTIBILITY TO DISINFECTANTS: One-to-one mixtures of xylol and 95% ethanol and of phenol and xylol were found to be effective against the infective stages of nematodes(7).
PHYSICAL INACTIVATION: Trichinella larvae in meat can be inactivated by (i) cooking meat at (core) temperature of 71 °C or more for at least 1 min, (ii) freezing (at least -15 °C) cut pieces up to 15 cm in thickness for at least 3 weeks and cut pieces up to 50 cm in thickness for at least 4 weeks, and (iii) irradiation (0.3 kGy) for sealed packaged food only(1,8). Freeze-resistant species; however, cannot be inactivated by means of freezing.
SURVIVAL OUTSIDE HOST: Trichinella spp. can survive for extended periods of time in decaying carcasses(1). Encapsulated larvae species survive for longer durations compared to nonencapsulated larvae species. T. papuae (nonencapsulated) has been shown to survive for 9 days within decaying tissues of pig exposed at 35 °C. T. spiralis has been shown to survive up to 4 months in extremely rotten meat. These species can even survive low freezing temperature for extended durations.
SURVEILLANCE: Monitor for symptoms of disease. Common methods to diagnosis include trichinoscopy(1-4), serological tests, and artificial digestion methods(3). Trichinoscopy involves the direct microscopic examination of a muscle biopsy sample for Trichinella larvae(2-4). Serological tests (indirect hemagglutination, bentonite flocculation, indirect immunofluroscence, latex agglutination and enzyme-linked immunosorbent assay:ELISA) are commonly used to detect antibodies against the pathogen. ELISA is highly sensitive and produces reliable results followed by artificial digestion techniques and trichinoscopy(3).
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID/TREATMENT: Treatment of trichinellosis varies according to the stage and severity of disease(1,2,4). Treatment mainly involves administration of anthelmintics such as pyrantel (active during the intestinal phase, limits muscle invasion)(5), mebendazole, and albendazole(1,2,4). Anthelmintics are not recommended for pregnant women and children under 2 years of age(1), however, pyrantel may be administered to pregnant women. Corticosteroids, salicylates, and antihistamines may be administered to patients suffering from myositis and myocarditis, and with symptoms associated with inflammation(2,3).
LABORATORY-ACQUIRED INFECTIONS: It is possible that laboratory-acquired infections have occurred with Trichinella spp.; however, as is the case with other helminths, lab workers might become infected with low worm burdens resulting in few symptoms, if any, and are therefore less likely to be diagnosed(9).
PRIMARY HAZARDS: Ingestion and/or accidental parenteral inoculation of specimen containing infective larva(10).
SPECIAL HAZARDS: None
RISK GROUP CLASSIFICATION: Risk Group 2(11). The risk group associated with "Trichinella spp." reflects the genus as a whole, but does not n ecessarily reflect the risk group classification of every species within the genus.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infected or potentially infected 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 slashes(12).
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(12).
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, either by steam sterilization, incineration, or chemical disinfection, before disposal(12).
STORAGE: The infectious agent should be stored in sealed containers that are appropriately labelled(12).
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: July 2010
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.
Public Health Agency of Canada, 2010