A trichina is a tiny worm, a
parasite of
human beings and other mammals.
Pigs are a common host, perhaps because they are not very fussy about what they eat. Wild
bears,
boars and other game animals are often hosts as well.
Rats are an important host, and although human beings rarely eat rats, pigs will readily do so if they get the chance. The
disease produced by these worms is called
trichinosis.
Pigs and human beings become infected by eating the flesh of an infected animal in which the worms are encysted. Pigs commonly acquire the worms by eating rats, or fragments of uncooked pig; human beings, usually by eating pigs, sometimes by eating wild boar or other game animals. When the infected meat is digested, the juvenile worm is released, and takes up residence in the digestive tract. When the juvenile worms become sexually mature the female worms hatch the eggs inside their bodies, giving birth then to live young worms. From the intestine, the young worms enter the blood stream and the lymph vessels and are carried throughout the body. There they encyst in turn in the muscles, commonly around the eyes, tongue and chest. They can live for quite a long time, but they eventually die unless the muscle in which they are embedded is eaten by a suitable host.
Now all this is pretty disgusting, but not necessarily a cause for panic. The mature worms are only about 1 millimeter long. The adult worms in the intestine do no harm, and disappear from the body after a few months. It is probable that this parasite is more common than statistics would demonstrate, since many infected people have no symptoms, or only a slight digestive disturbance which is commonly misdiagnosed.
The damage to the victim, if any, occurs if the number of young worms produced in the intestine is very large. When all these worms mature they migrate through the body in great numbers. There may be muscle pains, muscular disturbance and weakness, fever, anemia, and swellings of various parts of the body. Death is rare, but may occur from heart or respiratory failure. Once the young worms are encysted in the muscles, the symptoms subside, though there may be permanent damage to the muscles. There are effective drug treatments, notably either thiabendazole or mebendazole.
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So, what to do? Inspecting all pork is very expensive, since examination under a microscope is usually required. Nevertheless, some countries in the European Union do inspect meat for the cysts, especially wild boar meat and horse meat imported from Eastern Europe. (Of course this is in addition to the prevention measures listed below.)
The United States has taken a different tack on this problem. Perhaps because of the quantities involved, or the astronomical cost of inspecting all American pork, by and large meat in the US is not inspected for trichina infestation. Instead the focus has been almost entirely on prevention. The following measures are required by the US Department of Agriculture (USDA):
- Uncooked waste products, table scraps and animal carcasses are not fed to pigs. This is particularly important in the case of carcasses from wildlife.
- Keep pigs separate from live wildlife. Create barriers which are effective in separating pigs from skunks, raccoons and other small mammals.
- Control rodents, especially rats. Good fencing, baiting, trapping and general cleanliness are all part of keeping rats out of barns (and homes, for that matter).
- Maintain good hygiene. Remove dead pigs as soon as they are found. Pigs will literally eat almost anything, including dead pigs (and human carcasses if they can get them).
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An important part of the US strategy is the urging, which one hears constantly, to cook pork thoroughly, since cooking destroys the encysted worms if any are present. (Freezing, however, does not.)
Both the strategy in the EU and the one in the US are working. Trichinosis is very rare to non-existent in Western Europe, though it continues to be a problem further east. Reported cases in the United States are on the order of 15 - 20 a year, with no deaths.
Kingdom: Animalia, Phylum: Nematoda, Class: Adenophorea, Order: Trichurida, Family: Trichinellidae, Genus: Trichinella, several species
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For further information see,
Pork Facts - Food Quality and Safety, H. Ray Gamble, USDA, Agricultural Research Service Parasite Biology and Epidemiology Laboratory, Beltsville, Maryland 20705
Trichinella, Richard Lawley - October 2008, Food Safety Watch