Comparative Development of Temperate Zone and Arctic Isolates of Trichinella spiralis in the White Mouse

Abstract

Experiments were conducted in white mice to compare infectivity, morphology, and developmental capacity of Trichinella spiralis isolated from laboratory animals in Michigan and North Carolina (temperate zone isolates) and those from a polar bear and an Alaskan dog (arctic isolates). Subsequent to a passage in guinea pigs and mice, each of 10 mice was inoculated with a single dose of 500 larvae of a particular isolate. Five mice infected with an isolate were killed 8 days after infection. Significantly greater numbers of adult worms were recovered from mice infected with the temperate zone isolates than from mice given the arctic isolates. Thirty days postinfection, significantly greater numbers of larvae were found in the skeletal muscles of the remaining mice infected with the temperate zone isolates than were found in mice infected with the arctic isolates. There were no differences between the temperate zone and the arctic isolates in morphology of adult worms or in the size of the cysts found in the diaphragms. Four consecutive passages of T. spiralis in white mice resulted in increased infectivity of all isolates. Variations in infectivity of Trichinella spiralis that are associated with different geographical regions have been reported by several workers. Nelson and Mukundi (1963) reported that a strain of T. spiralis from Kenya had little infectivity to rats and domestic pigs. Kozar and Kozar (1965) found that T. spiralis from Kenya had less infectivity and pathogenicity for mice and rats than did a strain from Poland. Nelson et al. (1966) found that T. spiralis from Kenya and from Alaska had little infectivity for rats. Recently, Read and Schiller (1969) reported that rats, hamsters, and mice were relatively refractory to T. spiralis from Alaska. Rappaport (1943a, b), on the other hand, found no morphological or biological differences among three strains of T. spiralis, two of human origin and one of suilline origin. The following study was made to determine if differences in infectivity and morphology exist between our temperate zone and arctic isolates of T. spiralis. MATERIALS AND METHODS The temperate zone isolates originated from 2 sources. One isolate from a human infection had Received for publication 30 December 1969. * Paper No. N.S. 710, published with the approval of the director, Wisconsin Agricultural Experiment Station. t Present address: Agricultural Research and Development Department, Pfizer Inc., Terre Haute, Indiana 47808. been maintained since 1938 in mice and rats at the Michigan laboratory of Dr. S. E. Could. The other isolate from a pig had been maintained since 1936 in rats and mice at the laboratory of Dr. J. E. Larsh, Jr., in North Carolina. Infected muscle tissue of a polar bear and an Alaskan dog, sent by Dr. R. L. Rausch, were the sources of the 2 arctic isolates of T. spiralis. After receipt of the original materials, infected muscle tissue of each isolate was fed separately to guinea pigs. Infective larvae were recovered from the skeletal musculature of guinea pigs following pepsin-HCl digestion. An additional passage in mice of each isolate was required, since the number of larvae recovered from guinea pigs was insufficient to carry out the planned experiments.