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Trichina

muscle, cyst, disease, host and intestinal

TRICHINA, a small nematode parasitic in the rat, pig, and man which is the cause of a much dreaded disease termed trichinosis or trichiniasis. The scientific name of the parasite is properly Trichinella spiralis and it is believed to have been originally a rat parasite from which host it went over into the hog and from that to man. Two stages are distinguished: (a) Muscle trichina, the immature form, en cysted and inactive, and (b) intestinal trichina, the adult form, free and ultimately sexually mature. The species is highly specialized for the parasitic existence and the entire life his tory is passed within some host. The encysted trichina in muscle tissue if brought living into i the stomach of some flesh-eater is set free by the digestion of the cyst. It passes into the intestine and within two and one-half days reaches sexual maturity. After pairing the male dies and the female grows greatly in size. The species is ovo-viviparous, and the first young are produced in about one week from the date of infection. Before giving birth to any, however, the female bores her way into an intestinal villus and lying with the genital pore in a lacteal vessel, pours out all the young into the lymph fluid. They are carried into the musculature and permeate muscle fibres which undergo granular degeneration, while a cyst is formed about each by an in filtration of round cells. Eighteen days are demanded to complete the process, and the young trichina coiled within the cyst is ready for transfer to another host; but it may wait even years before this transfer is effected. Meanwhile there is laid down in and around the cyst calcareous material which gradually encroaches upon and ultimately involves the entire capsule, transforming it to a granule of lime in the muscle. The original discovery of

the trichina was made in a dissecting room in London by Dr. Paget who noticed that minute granules in the muscle dulled the edge of the scalpel, and on investigation found the para site. The cyst may undergo fatty degeneration rather than calcareous. While very resistant against smoking, pickling and even decom position of the meat, the trichina is readily killed by cooking, so that no danger attaches to the consumption of well-done pork. Pro longed cooking is necessary to bring the centre of large pieces of meat to the proper tem perature. Epidemics of trichinosis were very frequent in the last century, especially in Ger many where the consumption of smoked but uncooked ham is general. By a system of rigid meat inspection, carried out at large ex pense, the cases of the disease have been very greatly reduced in Germany. Epidemics have been rare in other countries, though, as will appear later, errors in diagnosis are easy if the disease is not suspected.

The disease manifests three stages: (a) Intestinal irritation during the growth of the adult trichina; (b) myositis with rheumatic pains and fever due to the invasion of the muscles by the larva, and (c) period of subsidence corresponding to the encystment of the worms. The severity of the symptoms de pends evidently on the individual but primarily on the number of encysted trichina that were ingested. Violent symptoms in the first stage have been mistaken for dysentery or cholera, and in the second for rheumatism, while con fusion with typhoid is very common. The ex amination of a fragment of excised muscle will afford positive evidence of trichina if present.