Studies on Host-Parasite Relationships: Syphacia obvelata in the Mouse

Abstract

Between the 4th and 9th weeks of life, mice develop a striking age resistance to Syphacia obvelata but no specific resistance, or immunity. This is attributed to lack of contact between the parasite and the tissues of the host, as demonstrated by the use of radioactive phosphorus. Antibodies could not be detected in the serum of infected mice by passive hemagglutination. The stimulus that induces female worms to migrate when gravid is innate, and not due to reactions of the host. It has been observed that, in a pinworminfected colony of white laboratory mice, only the young are likely to be heavily infected with Syphacia obvelata (Chan, 1952; also personal observations). The reduced worm burden of older mice could be due to a modification of the parasite's environment in the host, so that the parasite is unable to survive as well in older as in younger hosts. Such a change in the host's physiology might occur independently of previous infection with the parasite, and need not be directed specifically against the parasite. Alternatively, the generally heavy infections of the young mice might induce a specific resistance, or immunity, by the host to the parasite. The ability of mice to develop resistance, either specific or nonspecific, to S. obvelata was tested. On the basis of this result, experiments to determine the extent of tissue contact between parasite and host (using radioactive phosphorus and the passive hemagglutination test) were carried out. The possibility that host reactions might determine the life-span of the female worm was also tested. MATERIALS AND METHODS