Schad G A, Duffy C H, Leiby D A, Murrell K D, Zirkle E W
J Parasitol. 1987 Feb;73(1):95-102.
A hog found infected with Trichinella spiralis at slaughter was traced to its farm of origin, where an epidemiological investigation found the infection prevalent in swine and rats. Garbage-feeding was not responsible for maintaining the high prevalence of infection on this farm, although it may have been responsible historically for the introduction of the infection. Poor husbandry, malnutrition, and intercurrent disease resulted in frequent death and the availability of porcine carcasses for cannibalism. Tissue samples from partly devoured carcasses contained T. spiralis larvae, implicating cannibalism as a major vehicle for the spread of T. spiralis in the herd. Rats also fed on these carcasses, and their rate of infection increased markedly during the first 5 mo of observation. Experimental investigation indicated that rats could also be important in maintaining a high prevalence of infection in swine. For the purpose of our investigation, the farm was depopulated of swine and restocked with parasite-free, sentinel pigs confined in 3 groups exposed to increasing degrees of contact with rats. Pigs exposed to large numbers of rats acquired infections rapidly, whereas pigs with strongly limited rat exposure failed to acquire infection during a 12-mo period. These results indicate that, when rats are available to swine and the prevalence of T. spiralis infection in the former is high, predation (or scavenging) on rats may be as effective as cannibalism in maintaining a high prevalence of porcine T. spiralis infection.
