mictions appear usually at the end of tlie thiid week. Liuiita 

 tions of the use of these reactions for diagnosis of the disease 

 should l)e kept iu mind; after an attack of trichinosis, a posi- 

 tive skin test may he obtained for as long as 7 years and a 

 I)()sitive precipitin reaction for as long as 2 years. In addition, 

 persons with subclinical trichina infections may also give posi- 

 tive skin and precipitin reactions. 



For postmortem diagnosis, the compressor method and the 

 digestion-Bacrmann method are used. The former consists of 

 direct microscopic exauiination of a press preparation of mus- 

 cle. The l;itter method consists of the digestion of muscle in 

 jirtificial gastric .iuice, the digested nmterial being put through 

 the Baermann apparatus and examined microscopically for lar- 

 vae. Either of the two methods has special value and certain 

 limitations for certain types of infection, the two methods 

 being supplementary (Hall and Collins, 1!I37). Both methods 

 have therefore been used in recent surveys and on a quantita- 

 tive basis of trichinae per gram of diaphragm muscle examined. 

 The two methods have been described in detail by Nolan and 

 Bozicevich. 



Investigation (Sawitz, 1937; Schapiro et al, 1938) has shown 

 a correlation between the skin test for diagnosis of trichinosis 

 in living persons and postmortem findings. 



SYMPTOMATOLOGY 



Trichinosis is characterized by lack of regularity in its course 

 (Ransom, 191:1; Hall, 1937; Kaufman, 1940). A history of 

 eating raw or undercooked pork containing trichina may or may 

 not be followed by a gastrointestinal disturbance, including ab- 

 dominal pains, nausea, vomiting, diarrhea or constipation or one 

 succeeding the other, and intestinal henu>rrhages. Eosinophilia 

 of 10 to 45 percent and at times OS to 7S percent may be 

 present ; on the other hand it may not be present at all. There 

 may be edema (usually periorbital), high fever, myositis and 

 l>neumonia. The heart may be involved. There may be ner- 

 vous derangement, including encephalitis, meningitis and de- 

 lirium. The variegated clinical picture results from differences 

 in intensity of infection, organs invaded and resistance of the 

 patient. A clinical but nonfatal case may show at biopsy as 

 few as 8 larvae per gram of gastrocnemius (Ferenbaugh et al). 

 Hall (1937) tentatively designated as "heavy to critical" cases 

 showing 101 to 1,000 larvae per gram. Conclusions concern- 

 ing man can not be drawn from quantitative data from labora- 

 tory animals, as in man (Xevinny, cited by Roth, 1939) inflani- 

 matorj- and other injurious processes are more pronounced and 

 extensive, than in those animals. Schwartz (1938) found that 

 experimentally infected hogs showed no symptoms when there 

 were less than 800 to 900 larvae per gram of diajihragm muscle 

 tissue. 



EPIDEMIOLOGY 



In California outbreaks of trichinosis have resulted from the 

 eating of jerked bear meat (Walker, 1932; Geigcr and Hob- 

 maier, 1939) and in Europe from the meat of the polar bear 

 and the dog (cited by Kaufman, 1940) and the Coypu (Rubli, 

 1936;. These cases are rare, however; swine are the principal 

 source of infection to man and it is probable that most cases 

 of infection of other animals could be traced back ultimately 

 to swine. 



The incidence of trichinae in swine varies according to the 

 locality and manner of feeding, the principal source of the 

 infection being uncooked pork scraps fed to swine in garbage 

 or swill ; the eating by swine of infected rats or of carcasses of 

 infected pigs are very minor sources. Hall (1937a), Schwartz 

 (1938) and Wright (1939) have analyzed the data from dif- 

 ferent parts of the United States; trichinae were found in only 

 about 0.5 percent of swine fed on cooked garbage and southern 

 swine which range the fields and woods and get little garbage; 

 in 1 to 1.5 percent of swine iu the Central West, where feeding 

 of grain predominates over garbage feeding; in 4 to (5 percent 

 of swine fed on uncooked garbage; and in 10 to 20 percent of 

 swine fed on slaughter house offal, this last group now being 

 small. 



As regards the incidence in man, data have been inadequate; 

 due to the variability of symptoms, cases are frequently un- 

 recognized. To reports of outbreaks of acute trichinosis, which 

 have often involved large numbers of persons, and those of 

 sporadic cases must be added necropsy findings which detect 

 subclinical infections as well as previously undiagnosed clinical 

 cases. In the 94 year period, 1842-1936, according to Sawitz 

 (1938), there were between 5,000 and 6,000 clinical cases of 

 trichinosis diagnosed and recorded in the United States. Stiles 

 (1901) found that in Germany between 1860 and 1898 there 

 were reported 14,820 cases of trichinosis with 831 deaths, a 

 mortalitj' of 5.6 percent. Hall (1938a) points out that iu the 

 1880 's competent authorities maintained that the incidence of 



tricliinae was mucli greater in the United States than in 

 Europe and that these oi)iuions, long neglected, were borne out 

 by later findings which indicate that the United States has the 

 greatest trichinosis problem of any country in the world. The 

 incidence here is about 5 times greater than in middle Europe 

 (Magath, 1937), or even higher (Hall, 1938a). Comiiarative 

 data are Lacking from many parts of the world. A very low 

 iiu-idence has been found iu England (Van Someren, 1!I37). 

 Eleven clinical cases arc known from the Hawaiian Islands 

 (Alicata, 1938); trichinae have been found in the rat, mon- 

 goose and wild .-md domestic pigs there. Apparently only 

 one hunmn case has been reported from Chiim although the dog, 

 cat and swine have been found infected there (Ch'n, 1937). 



Early examinations of necropsy material were confined to 

 direct microscopic examination of muscle by the compressor 

 method and for the most part did not represent real surveys. 

 In more recent years a digestion method has also been used; 

 there is evidence that either technique alone fails to detect one- 

 third of the infections, so that a correction figure of 33% per- 

 cent should be applied if only one method is used. Local sur- 

 veys have been nmde in various parts of the United States 

 (Table 9) and a nationwide surveys of unselected cases from 

 various population groups (Table 10) is in progress. To date 

 the findings from necropsy examinations of over 9,000 persons 

 show that 15 percent were infected with trichinae, and the ac- 

 tual incidence figure would be higher if corrections could be 

 made to eliminate all variables. As regards severity of infec- 

 tion, the majority of 488 positive cases (Wright, 1939) showed 

 less than 11 larvae per gram of diaphragm but 2.5 iierceiit of 

 the cases had between 101 and 1,000 larvae per gram. 



An analysis of the findings according to sex, age, lace, oc- 

 cupation and social-economic status of 2,000 individuals 

 (Wright, 1939) failed to show any special correlation in most 

 of the groups represented. However, a geographical correlation 

 is indicated, especially as regards reported cases of cliiiical 

 trichinosis; the heaviest incidence is found along the North 

 Atlantic coast and along the Pacific coast, correlated with gar- 

 bage feeding. In New York, Massachusetts and California from 

 501 to over 1,000 clinical cases per state were reported up to 

 1938 (Hall, 1938) ; these are areas where there is extensive 

 feeding of uncooked garbage to swine. 



CONTROL 



With regard to trichinosis, the significance of chemotherapy 

 is decidedly different than in the case of most other helminth 

 infections, "as in oxyuriasis (p. 324). In trichinosis it is en- 

 tirely therapeutic, administered only for the patient's sake; in 

 oxyuriasis it is both proi)hylactic and therapeutic, preventing 

 reinfection of the patient and infection of others. 



Since human trichinosis results from the operation of two 

 factors (Hall, 1938), its prevention lies in control of those 

 faetors— namely, (1) food habits of the individual, including 

 infection from accidents and failures of cookery, and (2) the 

 frequency of occurrence of live trichinae in swine supplying 

 the pork. It is evident from necropsy findings as well as from 

 numerous sporadic cases and occasional outbreaks of trichino 

 sis, that a very large number of persons have eaten unprocessed, 

 uncooked or undercooked infected pork. The great majority of 

 swine are free from trichinae; pork from a small minority of 

 swine serves as the principal source of both human and porcine 

 trichinosis. This source may be combatted (Hall, 1936; 1937a; 

 1938a; Schwartz, 1938; Wright, 193S) by (1) meat inspection; 

 (2) avoidance of the use of raw or inadequately cooked pork or 

 pork products; (3) the swine sanitation system; (4) cooking 

 of garbage; and (5) rat destruction. 



In Germany microscopical inspection of pork for trichinae 

 was instituted iu 1875. Exclusion of American pork from Ger- 

 many caused a loss of millions of dollars to farmers and ex- 

 porters in the United States and led to diplomatic complica- 

 tions. Stiles' (1901) study of the German system indicated 

 that inspection can not detect all infected meat, that there was 

 a false sense of security from inspected meat and that the 

 system was very elaborate and expensive. In the United States 

 tiiere has never been federal meat inspection for trichinae in 

 pork intended for domestic consumption. The principal mea- 

 sures relied upon have been education as to cooking pork thor- 

 oughly, and the preparation under meat inspection of pork 

 products customarily eaten raw. Freedom from infective 

 trichinae is assured "by cooking at 137° F. (that this tempera- 

 ture requirement, originally set by Ransom and Schwartz 

 (1919), is adequate has been verified by Otto and Abrams, 

 (1939), by refrigeration at 5° F. for not less than 20 days 

 (Ransom, 1916), or by special processing of the pork (Ransom, 

 Schwartz and Raffensperger, 1920). That the intradermal test 

 be applied to all hogs killed in all slaughter houses, for the 

 detection of trichina infections, has been advocated (Nelson, 

 1939) but the evidence (Spindler and Cross, 1939; Lichterman 



317 



