Further Studies on Mammalian Susceptibility to Experimental Infection with Heterobilharzia americana

Abstract

The opossum, the coatimundi, the tree shrew, and 3 species of South American monkeys were tested for susceptibility to infection with Heterobilharzia americana. The worms developed to maturity in the opossum, but only degenerate eggs and shell fragments were deposited in the liver. The infection becomes patent in the coatimundi, and the animal's high susceptibility compares to that of the dog, and the raccoon, which is the main natural host. The tree shrew and the spider monkey were resistant, while the squirrel and the capuchin monkeys were moderately susceptible. Viable eggs with hatchable miracidia were deposited in the liver and intestinal wall of both monkey species, and they were passed in the feces of the squirrel monkey. Heterobilharzia americana was described by Price (1929), from a bobcat (Lynx rufus) from Florida, and was later found in the raccoon (Procyon lotor) in Texas (Price, 1943), North Carolina (Miller and Harkema, 1960), Louisiana (Malek et al., 1961), and Georgia (Byrd et al., 1967); from the opossum (Didelphis virginiana in Louisiana, Kaplan, 1964), and from the white-tailed deer (Odocoileus virginianus in South Carolina, Byrd et al., 1967). No observations were recorded for egg deposition and excretion in the case of the bobcat, the opossum, and the deer. Malek et al. (1961) and Malek (1961) found H. americana in Louisiana in the domestic dog, the marsh rabbit (Sylvilagus aquaticus), and in the nutria (Myocastor coypus). In several additional rabbits and nutrias examined since the latter two publications no eggs were observed in the feces, and only a few degenerate eggs and shell fragments were found in the liver. The raccoon and the dog, on the other hand, consistently contain many fully mature and viable eggs in the liver, intestinal walls, and feces. Susceptibility of laboratory animals to infection with this schistosome were carried out in this laboratory by Lee (1962). Malek and Armstrong (1967) found that infection with this schistosome did not produce a patent infection in rhesus monkeys or in man, and only schistosomula and preadult worms were reReceived for publication 15 April 1969. * This investigation was supported by Public Health Service Research Career Award K6-AI18,424 and by Research Grant AI-02898, from the NIAID. covered from the rhesus monkeys. Further susceptibility studies have since been carried out with special emphasis on other primate species not previously tested. The objectives were to investigate the schistosome adaptations to various hosts which occur within, and others which occur outside, its geographical range, and to study the biology of the infection in these animals. MATERIALS AND METHODS The opossums used in this study were supplied by a dealer in Virginia who obtained them in that state, which is outside the known geographical area of H. americana. The coatimundis and the monkeys were obtained from a New Orleans dealer who had imported them from South America. Fecal examination of the animals was carried out for 1 month, or longer, to determine their intestinal helminthic infections, and to ensure the absence of schistosome infection by any species. Cercariae were obtained from laboratory-infected lymnaeid snails, Pseudosuccinea columella and Fossaria cubensis. Exposure of the animal to the cercariae was performed as indicated by Malek and Armstrong (1967). White mice to serve as controls were exposed to cercariae from the same suspensions to ensure cercarial viability.