EFFECTS OF TRICHINELLA SPIRALIS ON SURVIVAL, TOTAL MASS, AND ORGAN MASS OF OLDFIELD MICE (PEROMYSCUS POLIONOTUS)

Trichinella spiralis is a parasitic nematode that infects many mammals, including humans. Hosts may experience significant physiological changes or may die because of acute inflammatory immune responses toward the parasite. In this study, oldfield mice ( polionotus) were used as a new experimental host for T. spiralis. Males of P. polionotus were infected with increasing doses of T. spiralis to determine the effect infection had on survival, mass change, total mass, and relative organ masses. Total juvenile worm burden increased in an asymptotic fashion with infective dose. Large doses ( $600 juveniles) significantly reduced survival. There were significant negative correlations between infection intensity (log 10(juveniles)/g) and both mass gain and final total mass. Infection had no effect on liver or spleen size. But there were significant negative correlations between T. spiralis intensity and both testis and seminal vesicle masses. These effects on male size and reproductive organs may help explain behavioral changes, such as the elimination of male dominance, seen in previous studies on mice infected with T. spiralis. Parasites can affect the ecology and evolution of their hosts if infection has harmful (i.e., fitness reducing) consequences (Anderson and May, 1991). The physiological effects of most parasites have not been measured; however, for parasites that infect many species, their effects have usually been examined in only a small number of potential hosts. In this project, the effects of a well-studied parasite ( Trichinella spiralis) were studied in a new experimental host, the oldfield mouse Pero- myscus polionotus. Trichinella spiralis causes trichinosis or trichinellosis in a wide variety of vertebrates, and it serves as a model organism for studying many aspects of the biology of gastrointestinal nematodes (Campbell, 1983; Despommier, 1983). Its life cycle is unusual in that it is an intracellular macroparasite, and the same host serves as both the definitive and the intermediate host. When hosts ingest muscle containing infective juveniles, the worms escape from the muscle tissue and burrow into the intestinal cells to mature and reproduce. Live-born juveniles leave the intestinal lumen, are carried to the heart by lymphatic and venous systems, and then circulate throughout the body. Once they reach skeletal muscle of the thighs, jaws, tongue, or diaphragm they penetrate and reside in individual cells. They alter the muscle cell's gene expression to form a capsule, known as the nurse cell, where they live and receive nutrients. Pathol- ogy to hosts can occur during the acute phase of infection ( #45