Life cycle of Brugia pahangi (Nematoda) in nude mice, C3H/HeN (nu/nu).

The development of Brugia pahangi (Nematoda: Filarioidea) was studied in nude (congenitally athymic) mice C3H/HeN (nu/nu) and in their phenotypically normal littermates (nu/+). Nude mice were highly susceptible to this parasite. As in the natural host (the cat), the nematodes' third molt in nude mice occurred at 7 to 10 days. The final molt occurred at about 24 days for male worms and 33 days for female worms. Adult worms were smaller than those from other hosts, such as the cat. After inoculation of various numbers of infective larvae, recoveries of adult worms averaged about 15% of the inoculum. In long-term infections initiated with 100 larvae, about 75% of the worms localized in the heart or lungs. Patent infections were seen as early as day 50 PI. Microfilaremia developed in most nude mice given 100, 50, or 25 infective larvae, but was less frequent in those given only 10. Mean filaremias generally rose during the first 6 mo, but in individuals usually did not exceed 500-600/20 mm3 of blood. As in the Mongolian jird, intraperitoneal inoculations yielded large quantities of worms and microfilariae. Few worms could be recovered from normal mice after day 40, even when large (1,000 larvae) inocula were used. Microfilaremia was not detected in normal mice. Although recoveries of adult worms from some nude females were not as high as those from nude males, neither nude nor normal mice showed consistent evidence of a differential susceptibility based on sex. Given the strong, consistent dichotomy of response to B. pahangi between nude and normal mice, this system may be useful in studies of protective immune responses in filariasis.