Preferential Susceptibility of Male Jirds (Meriones unguiculatus) to Infection with Brugia pahangi

In two trials, 17 litter-mate pairs of jirds (Meriones unguiculatus) were inoculated subcutaneously in the groin with infective-stage larvae of Brugia pahangi to determine if sex of the host was a factor in establishing infection. The mean prepatent period for 14 male jirds ranged from 67 to 76 days. Only 2 female jirds developed peripheral microfilaremia, one at 87 and the other at 94 days postinoculation. In 3 other females, microfilariae were found only in cardiac blood. More adult worms were recovered from male animals than from females; for males the percentage of inoculum recovered was 1 to 32%, in females it was 0 to 18%. In males, adult worms were found primarily in the testes and the heart and pulmonary arteries, whereas adult worms occurred almost exclusively in the heart and pulmonary arteries of female jirds. It appears that male animals, for unexplained reasons, are more susceptible to infection with lymphatic-dwelling filarial worms than are females. Earlier studies on the development of Brugia pahangi and subperiodic B. malayi in jirds indicated that male hosts appeared to be more readily infected than females (Ash and Riley, 1970a, b). This report summarizes observations made on two series of litter-mate pairs of jirds inoculated with B. pahangi to determine if one sex was more susceptible to infection than the other. MATERIALS AND METHODS The origin of the strain of B. pahangi used here was as reported earlier (Ash and Riley, 1970a). Armigeres subalbatus and Aedes aegypti (Liverpool strain) served as vector mosquitoes and were fed on an anesthetized cat that had a microfilarial density of 100 to 200 per 20 mm3 of blood. Maintenance of mosquitoes and the recovery of infective-stage larvae from them were as previously described (Ash and Riley, 1970a). Litter-mate pairs of Meriones unguiculatus, 4 to 6 weeks old, from a colony maintained in the UCLA Vivarium, were used. Male and female animals were inoculated alternately by pipetting a known number of larvae into a subcutaneous pocket close to the left testis in males and into the left groin in females. Animals were bled at weekly intervals beginning 56 days after inoculation; the prepatent period was computed as the mean day between the last bleeding in which no microfilariae were found and the day on which microfilariae were first found. The techniques of bleeding and Received for publication 12 January 1971. * This investigation was supported by the United States-Japan Cooperative Medical Science Program administered by the NIAID of the NIH, Department of Health, Education and Welfare, U. S. Public Health Service Research Grant AI-07770. necropsy of infected animals were as previously described (Ash and Riley, 1970a).