TRICHINOSIS — SCHWARTZ 419 



act that provided, among other things, for a microscopic inspection 

 of meat from all hogs for export in order that certificates could be 

 issued setting forth their freedom from trichinae. 



PREVALENCE OF TRICHINAE IN HOGS IN THE UNITED STATES 



As a result of systematic microscopic examinations of samples 

 of muscle tissue from millions of hogs, there accumulated in the 

 records of the Bureau of Animal Industry a vast array of data show- 

 ing the prevalence of trichinae in swine in this country. These data, 

 which were made public from time to time, showed that out of the 

 total of over 8,000,000 hogs, samples of which were examined micro- 

 scopically from 1898 to 1906, 1.41 percent contained live trichinae; 

 in addition, 1.16 percent contained bodies resembling trichinae or 

 disintegrating trichinae. The total percentage of infection with live 

 and dead or disintegrating trichinae was more or less uniform from 

 year to year during the 9-year period mentioned. 



Since it is well known that microscopic inspection is inherently im- 

 perfect, and that light and occasionally moderate infections are likely 

 to be overlooked, it is safe to conclude that during the period covered 

 by the data mentioned, approximately 1 out of 75 hogs contained 

 trichinae probably in sufficient numbers to cause clinical trichinosis in 

 human beings following the consumption of such pork in a raw or in- 

 sufficiently cooked state. Under the meat inspection act passed by 

 Congress in 1906, there was no specific provision for microscopic in- 

 spection for trichinae of pork intended for export, and the inspection 

 previously made was discontinued. 



Following the abandonment, in 1906, of microscopic inspection for 

 trichinae of pork intended for export, no up-to-date information was 

 available up to 1933 regarding the prevalence of these parasites in 

 swine. In 1933, there was inaugurated in the Bureau of Animal 

 Industry, under the direction of the writer, a research project involv- 

 ing a thorough examination of samples of pork muscle tissue for 

 trichinae by the laborious teclmique of digesting from each carcass 

 about 200 to 250 grams of muscle tissue taken from the pillars of the 

 diaphragm. While microscopic examination of pork for trichinae is a 

 hit-and-miss method, the digestion method as described by Ransom 

 (10), with certain modifications introduced by workers in the 

 Zoological Division, is the most accurate technique known at present 

 for determining the presence or absence of trichinae in pork and any 

 other meat. The information obtained by the writer and his associates 

 on the prevalence of trichinae in swine is applicable to research only. 

 This method gives a far more accurate insight into the incidence of 

 trichinae in hogs than was obtained by the routine microscopic inspec- 

 tion practiced by Bureau inspectors from 1892 to 1906. 



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