1911 Encyclopædia Britannica/Trichinosis

TRICHINOSIS, or Trichiniasis, a disease, in man and other animals, caused by infection by the parasite trichina or trichinella spiralis. The presence of encysted trichinae in the muscles was discovered by Sir James Paget (q.v.) in 1835, and they were named by Sir R. Owen; but it was not until some years after that the clinical characters of the acute disease caused by the invasion of the parasite were discovered. This discovery was made in 1860 by Friedrich von Zenker (1825-1898) on examining the abdominal muscles of a patient who died at Dresden with symptoms taken to be those of typhoid fever, the cases being afterwards accounted one of trichinosis on the post mortem evidence. Epidemics of this disease occur from time to time, especially in north Germany, from the eating of uncooked swine's flesh, in which trichinae are not uncommon. Out of 6329 cases in Germany during the years 1891 to 1898, 5456 occurred in states where raw pork is a common article of food. And, from the point of view of public health, the hog is the animal which is the main source of infection, others—except rats—being only rarely infested with the parasite. The greatest care is now taken to examine the carcases of swine for trichinae, a piece of the diaphragm of every animal being searched with the microscope by an inspector specially appointed, and the trichinous hogs being condemned. But it has not been found that this microscopic examination serves as an effective check; indeed it is apt to create a false feeling of security. Over 32% of the German cases of trichinosis between 1881 and 1898 were traced to meat so inspected and passed as free from trichinae. In America accordingly microscopic examination is not considered to give any guarantee of soundness from trichinae, in spite of a government mark “inspected and passed” (see B. H. Ransom, Circular 108 of U.S. Dep. of Agriculture, 1907). The symptoms in man are occasioned by the presence of the free parasites in the intestine, by the development of young trichinae from the eggs, and most of all by the migration of the parasites from the intestinal canal to the muscles, where they become quiescent. This cycle occupies from four to six weeks. Lime-salts become deposited in the capsule, the calcification rendering the cyst visible, and this change usually takes five or six months. When consumed in small quantity, the parasites may give rise to no marked symptoms, and they are sometimes found accidentally in muscular fibre in the bodies of those who had probably experienced no definite symptoms from their invasion. In the more acute and serious cases, sometimes ending fatally, the early symptoms are nausea, failure of appetite, diarrhoea and fever; later, when the migration to the muscles begins, there is more fever, stiffness, pain and swelling in the limbs, swelling of the eyelids, continued exhausting diarrhoea, perspirations and sometimes delirium. During convalescence there is desquamation of the cuticle. The discovery by T. R. Brown of a marked leucocytosis with an extraordinary increase of eosinophiles now enables a diagnosis to be made in cases where the symptoms are obscure. If the diagnosis be made early in the case, brisk purgatives, particularly calomel, are the best treatment; if the parasites are already on their way to the muscles, the only thing left to do is to support the patient's strength. There need, however, be no fear of infection at all if the meat be thoroughly cooked and cured before eaten. This is the only effective precaution.