Trichinella larva in tongue muscle of a rat, stained with hematoxylin and eosin (H&E). Image was captured at 400x magnification.
Also called trichinosis, is caused by eating raw or undercooked meat of infected animals. Infection occurs commonly in certain wild carnivorous (meat-eating) animals such as bear or cougar, or omnivorous (meat and plant-eating) animals such as domestic pigs or wild boar.
Adult worms recovered from the small intestine. The female measures about 3 mm long while the male is only 1 mm long. The male has papillae on its tail (arrow), the female does not.
During 2008–2010, 20 cases were reported per year on average. The number of cases decreased beginning in the mid-20th century because of legislation prohibiting the feeding of raw-meat garbage to hogs, commercial and home freezing of pork.
If you eat raw or undercooked meats, particularly bear, pork, wild feline (such as a cougar), fox, dog, wolf, horse, seal, or walrus, you are at risk for trichinellosis
Trichinella spp./genotypes lack or differ in their level of infectivity to pigs
T. spiralis (from 12 current species) is better adapted to and more frequently detected in swine
- reaches high worm burden (up to 8000 larvae/g in the diaphragm pillar)
without clinical disease
- reaches high worm burden (up to 8000 larvae/g in the diaphragm pillar)
without clinical disease
Khumjui 2006- Outbreak in Thailand- T. papuae, most had eaten wild boar, only been detected in papua new guinea in previous reports
human outbreaks due to the consumption of meat from black bears in the United States (Roy et al., 2003).
human outbreaks attributed to the consumption of turtle and brown lizard meat in Thailand (Khamboonruang, 1991).
impact on export of meat could occur, as happened in France in 1998, when vacuum packed meat sold as wild boar imported from the United States
caused an outbreak of trichinellosis in humans in Normandy (Dupouy-Camet, 2000).
potential role of horses in the transmission to humans was largely ignored until 1975, when an outbreak of trichinellosis occurred among 89 persons in Italy, who had eaten horse meat (Mantovani et al., 1980).
1835 not realised worms in muscle were larval stage of a nematode (Owen, 1835)
Clinical significance recognised 1860
Trichinellosis is acquired by ingesting meat containing cysts (encysted larvae) of Trichinella.
After exposure to gastric acid and pepsin, the larvae are released from the cysts and invade the small bowel mucosa
where they develop into adult worms (4 weeks).
After 1 week, the females release larvae that migrate to the striated muscles where they encyst . Trichinella pseudospiralis, however, does not encyst. Encystment is completed in 4 to 5 weeks and the encysted larvae may remain viable for several years.
Ingestion of the encysted larvae perpetuates the cycle. Rats and rodents are primarily responsible for maintaining the endemicity of this infection. Carnivorous/omnivorous animals, such as pigs or bears, feed on infected rodents or meat from other animals. Different animal hosts are implicated in the life cycle of the different species of Trichinella. Humans are accidentally infected when eating improperly processed meat of these carnivorous animals (or eating food contaminated with such meat).
FIG. 4. Histological section (hematoxylin-eosin staining) of a muscle biopsy from a patient involved in a trichinellosis outbreak (100).
(A) Cellular infiltrates; (B) collagen capsule of a “nurse cell”; (C) intersected muscle larva. (Photograph courtesy of Dietrich-Bonhoeffer-Klinikum,
Neubrandenburg, Germany.)
100. Nockler, K., and C. M. O. Kapel. 2007. Detection and surveillance for
Trichinella: meat inspection and hygiene, and legislation, p. 69–97. In J.
Dupouy-Camet and K. D. Murrell (ed.), FAO/WHO/OIE guidelines for the
surveillance, management, prevention and control of trichinellosis. World
Organisation for Animal Health Press, Paris, France.
digested in stomach, (pepsin HCL acid) small intestine invades epithelial cells, lava moult 4 times (10-28 hrs post ingestion) adult worm (30-34hr post ingestion) 5 days newborn leavea shed, -no. larvea depends on immune status of host. Parasite epidemiology – wild carcesses are consumed by scavengers, infection widespread within biomes/ worldwide. Only humans clinically affected,
migrate allows transport to highly oxygen muscle which they penetrate, enzymes suspected not ruled out (21), inject directly to muscel penetration 10 mins (22)
22. Despommier, D. D., L. Aron, and R. Thorson. 1975. Trichinella spiralis: growth of the intracellular (muscle) larva. Exp. Parasitol. 37:108–116
Newborn larvae enter skeletal muscle, daiphram, tongue (stewart & charniga 1980 j. para. 66, 688-689), 20 days process of growth and development in differentiating muscle cell (myotube) (ritterson 1966-j. para. 52, 157-161; Humes and Aken, 1953-anat. Rec. 114, 103-113; Jasmer 1993-j. cell. Boil. 121, 785-793; Despommier 1975-am. J. pathol, 78, 477-496).
Sylvatic reserviour hosts important in presistance
T spiralis most adapted to domestic and wild swine, present on all continents except Antarctica (123)
Broad host spectrum, two clades in Tricinella first clade infects only mammals (eg. T. spiralis, t. native, T. britovi, 2nd clade infect birds and mammals (T. pseudospiralis. Or mamalas and reptiles (T. papuae). All species and genotypes are morphologically indistinguishable at all developmental stages, only molecular methods can realiabily id the genotype of the parasite.
Dupouy-Camet 2008
The main reservoir was located in the wildlife with a parasitic prevalence ranging from 2,08% (wild-boar) to 22,55% (red-fox). Prevalence in dogs and cats ranged from 5,49% to 52,15% depending on the region of Romania
Horsemest 1975 france/Italy (mantovani et al., 1980) , 12 other outbreaks in europe, tongue most likely sample to contain detectable numbers, eu regulation- 5g tongue, 10g in origin from high prevenlannce area, epidemiology studies id high risk areas, test horse meat European legislation directive 94/59/eec, publice education- culinary preferances not changed.
slaughter crocodiles (135), ‘serology tests the presence of anti-trichinella ab in blood or meat juices- suitable for surveillance and epidemiology investigations not for examining individual carcasses,
135. Pozio, E., I. L. Owen, G. Marucci, and G. La Rosa. 2005. Inappropriate feeding practice favors the transmission of Trichinella papuae from wild pigs to saltwater crocodiles in Papua New Guinea. Vet. Parasitol. 127:245–251.
Walrus – prevention programme pre-consumtion testing of meat samples from harvested walrus at a regional lab (Canada) 1987 - fox and polar bear too (13,14)
13. Nunavik Department of Public Health. Summary of reportable dis-eases: Kuujjuaq. Kuujjuaq, Quebec, Canada: Nunavik Department of Public Health, 1998.
Pozio 2007
Worldwide not beenreported in antarcitca (pozio&murell, 2006), global distribution varing on human eating habits- main factor, ethnic minorities and tourists, political and economical changes – revolution/war- increase prevalence amoung human po. (murell&pozio, 2000; Bolpe&Boffi, 2001; Marinculic et al., 2001; Djordjevic et al., 2003), muslim do not consum pork (main resouviour), countries with no report may be from lack of investigation/recognition or lack of parasite presence in domestic and human populartions, could be in wild fauna.
A food thermometer should be used to measure the internal temperature of cooked meat. Do not
sample meat until it is cooked. USDA recommends the following for meat preparation
Whole cuts-as measured with a food thermometer placed in the thickest part of the meat, then allow the meat to rest* for three minutes before carving or consuming.
According to USDA, "A 'rest time' is the amount of time the product remains at the final temperature, after it has been removed from a grill, oven, or other heat source. During the three minutes after meat is removed from the heat source, its temperature remains constant or continues to rise, which destroys pathogens.“
Homemade jerky and sausage were the cause of many cases of trichinellosis reported to CDC in recent years.
Meat inspection an example of veterinary public health measures- prevention of human trichinellosis, food safety, producer guarantee, meet regulations.
Freezing bear meat does not kill trichinella
Gamble 1999
Prevelance and infection intentity decreased in usa, pigs raised in conditions which do not include risk factors for exposure to trichinae limit or eliminate risk factors- possible to produce pigs which do not pose tricinella risk.
To help prevent Trichinella infection in animal populations do not eat meat, including rats, which may be infected with Trichinella.
Trichinella sp. life cycle. (A) Main sources of Trichinella sp. infections for humans (including pigs, horses, wild boars, dogs, walruses,
foxes, and bears).
(B) Trichinella sp. cycle in the host body. In the enteral phase, muscle tissues are digested in the stomach, and larvae are released
(1); larvae penetrate the intestinal mucosa of the small intestine and reach the adult stage within 48 h p.i., and male and female mate
(2); female worm releases newborn larvae in the lymphatic vessels (from the fifth day p.i. onwards; the length of newborn production, from 1 week to several weeks, is under the influence of host immunity)
(3). In the parenteral phase, the newborn larvae reach the striated muscle and actively penetrate in the muscle cell
(4); the larva grow to the infective stage in the nurse cell (the former muscle cell)
(5); and, after a period of time (weeks, months, or years), a calcification process occurs
(6). (Modified from www.iss.it/site/Trichinella/index.asp with permission of the publisher.)
Cost effective survallience health hazards from animals, target high infection group not whole population,
surveillance data collected and used to access further infection risks, model- “discounting historical evidence” output data is absence of infection, Denmark / danish pigs no pigs tested positive for 70 years, prevalence <1 per million pigs- target outdoor raised pigs (contact with wildlife, Nockler et al., 2004- j. vet. Med. b51, 297-301), all sows and boars, also incorporate wildlife surveys.
meat-borne. EU 6 countries reported cases of trichinelosis 2005. Import private slaughtering cases trich higher. EU regulations 854/2004, 2075/2005- tric free holdings- reduced survalience, pooled carcass + digestion method 0.15 euro per pig, 3.5mill annal (kapel, 2005- vet. Parasitol. 132, 189-194)
Backyard businesses
Veterinary services should fully test all pigs using networks of field laboratories
Move funds & efforts to control Trichinella in pigs from controlled to non-controlled management conditions (backyard and free-ranging).
- Testing for infection has dual role of providing consumer protection and collection of epidemiological data
Veterinary services should introduce a risk-based surveillance system for Trichinella spp.
monitor housing / feed conditions on pig farms, public health services should promote consumer education
animals should escape testing only if confirmed reared under controlled management conditions
need change cultural factors ; traditional dishes based on raw or undercooked meat or meat-derived
Funds needed to educate consumers, farmers, and hunters
OR Trichinella will continue to circulate in disadvantaged regions of the world causing human outbreaks.
Pozio, 2014
