Trichiniasis in Man and Animals in Cincinnati, Ohio

Abstract

Human diaphragms, swine diaphragms, pork products, and wild animals obtained in Cincinnati, Ohio, were examined for the presence of Trichinella spiralis. Larvae were found by means of standard methods of direct microscopic observation and artificial digestion. Of 332 human diaphragms obtained at necropsy 16 proved positive for the presence of T. spiralis, and five of 700 grainand garbage-fed hogs were infected. No evidence of T. spiralis infection was found in either the pork products or wild animals examined. Many studies on the incidence of Trichinella spiralis in man and swine have been conducted in the United States, but none have been done in the Cincinnati area. Most (1965) reviewed studies on human trichiniasis and reported an apparently significant reduction in incidence, mortality, and density of infection in man since 1944, and stated that the adult infection rate in the U. S. is probably 4% or less. Zimmermann and Brandly (1965) reviewed studies on the incidence of T. spiralis in swine, and noted a decline in incidence during the period of their study. Bachman and Rodriguez-Molina (1933) stated that T. spiralis is among the most euryxenous of nematodes. A great deal of controversy has arisen with respect to the importance of reservoir hosts in the epidemiology of the parasite. Among others, Most (1965), Gould (1943), and Wright (1940) discount the possibility of reservoir hosts as a source of infection for swine. On the other hand, Schwartz (1960) considered the role of reservoir hosts as uncertain, and several workers, including Spindler (1953), Olson and Robinson (1958), and Zimmermann et al. (1959), have demonstrated transmission of T. spiralis through the feces of infected animals to clean animals. In view of this experimental evidence of transmission through fecal contamination, and the availability of infected wild animal carcasses to swine, reservoir hosts remain an important possible factor in the epidemiology of T. spiralis. In an attempt to demonstrate a relationship between infected swine and wild animals, Martin et al. (1968) studied two Illinois swine farms. The swine from one farm were fed garbage, and had a history of T. spiralis infection, while the swine Received for publication 16 October 1968. of the other farm were fed grain. Since only two wild animals from each farm were found infected with T. spiralis, no conclusions were drawn regarding the effects of wild animals on the epidemiology of the parasite. MATERIALS AND METHODS Fresh human diaphragm samples were obtained from four Cincinnati hospitals and the Hamilton County Coroner's Office from October 1966 to August 1967. About one-half a diaphragm was collected from randomly selected cadavers at each hospital and data on age, sex, and race were obtained from hospital records whenever possible. All samples were examined by microscopic observation of pressed muscle, and by artificial digestion in 1% pepsin, 1% HC1 in 0.85% NaCl. The sediment from each digested sample was examined under a dissecting microscope. Swine diaphragm samples were obtained from a Cincinnati meat-packing company from January 1966 to September 1966. The swine used by this concern are a mixture of garbage-fed and grainfed animals, but it was not possible to divide the samples on the basis of feed. Swine diaphragm tissue was examined by artificial digestion only. Pork sausage was obtained from the company that provided the diaphragm samples, and from another Cincinnati meat-packing company. The pork products were examined by artificial digestion. A limited number of local animals were examined for T. spiralis larvae. More than 40 rats were trapped at the Cincinnati Zoo, and some commercially valuable fur-bearing animals were obtained from a Cincinnati furrier. The latter animals were taken from nearby areas, but exact collection data were not available. All animals collected were examined by artificial digestion of the diaphragm, tongue, and leg muscles.