STRESZCZENIA REFERATÓW• ABSTRACTS OF PAPERS • PE3IOME ,Il;OKJIA,Il;OB
TRICHINOSIS IN THE UNITED STATES
BY
BENJAMIN SCHWARTZ
Agricultural Research Service, United States Department of Agriculture, Beltsville, Maryland, USA
Knowledge of the extent of occurrence in the musculature of pigs in the United States of Trichinella spiraliś originally stemmed from the data that were accumulated, between the years 1892 and 1906, in the course of routine microscopic inspection for trichinae of pork intended for export. At that time the incidence was between 1.5 and 2.5 percent. For nearly three decades after 1906 no further information on the prevalence of this nematode in swine was brought to light.
In the 1930's new information was accumulated on thousands of pigs, the diaph- ragms of which, taken at random in slaughtering plants, were digesteą, one by one, in an acidified solution of scale pepsin. The new data showed a comparative infection rate in farm-raised pigs of only about one-fifth or less of that reported in the earlier years, if the exceedingly light infections, usually discoverable by digestion and seidom by routine microscopic examination, are left out of considera- tion. A decade or more later, the decline was even more marked. The most recent rate of infection of pigs with Trichinella, based on random sampling of severa!
thousand of these animals from the most important swine-producing areas of the United States, was found to be only 0,6 percent, by diaphragm digestions. For comparative purposes, however, this incidence was probably only about 0.15 percent.
In garbage-fed pigs, on the other hand, the frequency of infection with Trichi- nella remained practically unchanged during a period of about 20 years, beginn- ing in 1933. The range in incidence, determined by the digestion method, was from 3.5 percent in some areas up to 11 percent in others. Moreover, the intensity of infection was significantly higher than in farm-raised pigs.
In 1944, when the cooking of garbage intended as a feed for swine first became mandatory in some of the States, primarily to check the spread of the swine dise- ase vesicular exanthema, a decline in the incidence of, and degree of infection with, Trichinella became apparent. This decline bacame more pronounced as more and more States began to enforce legislation requiring the cooking of garbage
304 MIĘDZYNARODOWA KONFERENCJA W SPRAWIE WŁOSNICY
intended as a swine feed. The current overall incidence of Trichine/la in garbage- fed pigs is somewhat over 2 percent in the areas where it was 11 percent five years ago. lt is only somewhat above 1 percent, if the exceedingly light infections that were discovered by the digestion of diaphragms are left out of consideration.
Although garbage-fed pigs represent on1y about 2 percent of the swine in the United States, they are, apparently, the main source of human trichinosis.
Along with the decrease in the extent and degree of infection of garbage-fed pigs with T. spiralis, there has been a decrease also in the prevalence of human clinical trichinosis, in the face of a steadily increasing population. The decline has been consistent during the past five years. The total number of reported cases of clinical trichinosis in man was 178 in 1957, approximately one case per million inhabitants, whereas the corresponding numbers were 395 in 1953 and 487 in 1948.
The fact that even a small percentage of pigs fed cooked garbage still acquire trichinae, even though the worms so acquired are fewer in number than in previo- us years, when the garbage was not processed by heat, points _to the probability that the cooking of garbage as carried out at present either is imperfect, or that trichinae from outside sources get into the garbage after it has been cooked. Natura- lly, the rat comes into first consideration as the most likely source of Trichinella in garbage, other than scraps of infected pork. But whatever the sources of infec- tion may be, it is cleąr that the current control measures must be steadily impro- ved, if the extent and degree of infection with Trichinel/a in pigs are to be further reduced. A rigid and sustained trichina prophylaxis would narrow, and perhaps ultimately błock altogether, the channels that now make possible the transfer of this parasite to pigs, and finally to man.
