Development of Brugia malayi in Mongolian gerbils previously exposed to Wuchereria bancrofti.

Twelve Mongolian gerbils, Meriones unguiculatus, were infected with 100 third-stage larvae of Wuchereria bancrofti. One month later these animals, along with 4 control animals, were given 100 third-stage larvae of Brugia malayi. Eleven of the 12 experimental animals and the 4 controls survived, and 8 of the experimental animals and all of the controls demonstrated microfilaremia after 3 months. The animals were killed at 6-months post-infection and examined for parasites. One W. bancrofti larva was found in one of the experimental animals, and 15% of the B. malayi given were recovered as adults from the testes, viscera, and carcass. Thirty-eight percent of the worms given to the controls were recovered from the testes, viscera, and pelt. The worms from the experimental animals also appeared to be smaller. This study suggests that gerbils are able to develop partial resistance to Brugia malayi following a previous infection with Wuchereria bancrofti.

Hybridization between Brugia malayi and Brugia pahangi from south Kalimantan, Indonesia.

Hybridization experiments were carried out between sub-periodic Brugia malayi and B. pahangi recovered from cats originating from the same area in South Kalimantan (Borneo), Indonesia. Five to six week-old immature males and females of both species from Mongolian gerbil (Meriones unguiculatus) intraperitoneal infections were inoculated into the peritoneal cavity of other gerbils. Mating occurred between the species and microfilariae developed into infective third-stage larvae in mosquitoes. Larvae from the mosquitoes developed into adults in the peritoneal cavity of gerbils but microfilariae were not produced since the males were sterile. Back-crossing between hybrids and males and females of the parental species were also done and female hybrids produced microfilariae when crossed with parental males but females from the parental species did not produce microfilariae when mated with the hybrid males. This confirmed that the males were sterile but the females were not. If these species are hybridized in nature and humans are exposed to hybrid third-stage larvae, could this lead to occult filarial infection? These results confirmed previous hybridization experiments of these species orginating from other geographic areas.

Studies on trypanosomes in the Taiwan monkey.

Fifty-three or 9% of 594 Taiwan monkeys, Macaca cyclopis, were found infected with a Trypanosome species. The parasites were recovered from monkey blood in diaphasic blood-agar culture medium with a Locke's solution overlay. Trypanosomes were found on only a few thick blood smears and no dividing or multiplying forms were found. Some of the organisms had a free-flagellum (4.7 microns), an undulating membrane and both ends of the body were pointed. The total length averaged 41.7 microns; nucleus was slightly anteriorly located. Blood from culture positive monkey would not infect monkeys or other animals, but cultured parasites readily infected monkeys and one mouse, and one rat treated with cortisone. Triatoma rubrofasciata and Triatoma protracta fed upon culture-positive monkeys did not become infected but one of the former became infected after membrane feeding upon cultured parasites mixed with monkey blood. Studies were also done on the development of Trypanosome conorhini in monkeys and other animals. The parasite was recovered from the hind-and mid-gut of naturally infected Taiwan Triatoma rubrofasciata (109 of 117). Some bugs also had salivary gland infections. Most laboratory animals (rats, mice, Mongolian gerbils, guinea pigs, rabbits) developed infections detected by blood-smear and culture. The parasite was serially passaged through monkeys and bugs monthly for one year but there was no change in the development pattern. Only trypmastigotes were present in blood smears; no dividing forms were found. Triatoma rubrofasciata and Triatoma protracta readily developed gut infections when fed upon monkeys, but only a few Rhodnius prolixus became infected.(ABSTRACT TRUNCATED AT 250 WORDS)

Further studies on the development of Wuchereria bancrofti in laboratory animals.

In an attempt to obtain a small animal laboratory model for Wuchereria bancrofti Mongolian gerbils and hamsters were infected with third-stage larvae of strains of the parasite from Indonesia and China. Gerbils were necropsied at 7 to 591 days and larvae recovered up to 219 days. The third molt occurred on or before 10 days and worms found after 14 days were in the fourth stage. More worms were recovered early in the infection (7 to 30 days) than in older infections. The worms were usually recovered from the testes, pelt and carcass and heart and lungs. An adult male worm was recovered on one occasion from the lung of a gerbil at 92 days. The parasite was also found to develop in hamsters with results similar to those in gerbils. Gerbils and hamsters were given antithymocyte sera before and after infection and more worms were recovered and the worms larger in size in some treated animals. Continued studies with geographic strains of W. bancrofti in various animals should be encouraged in order to find a small laboratory animal model for the parasite.