Hybridization Studies of Angiostrongylus siamensis Ohbayashi, Kamiya and Bhaibulaya, 1979 and A. costaricensis Morera and Cespedes, 1971

Abstract

Hybridization has been studied in Angiostrongylus spp. parasitic in the pulmonary arteries. Bhaibulaya (1974, Int. J. Parasit. 4: 567-573) crossed A. cantonensis with A. mackerrasae, and Cross and Bhaibulaya (1974, Southeast Asian J. trop. Med. Pub. Hlth 5: 374-378) crossed A. cantonensis with A. malaysiensis, confirming the validity of A. cantonensis, A. mackerrasae and A. malaysiensis. We have reported that A. siamensis are present in the mesenteric arteries of rodents from Thailand (Ohbayashi et al., 1979, Jap. J. Vet. Res. 27: 5-10). The life cycle of A. siamensis is presumed to have a wide host range in murid rodents (Kamiya et al., 1980, Jap. J. Vet. Res. 28: 114-121). Furthermore, a suspected accidental case of A. siamensis in a crab-eating monkey has been reported (Oku et al., 1983, Jap. J. Vet. Res. 31: 71-75). A. siamensis is very similar to A. costaricensis in its development and migration route within mice as a final host (Kudo et al., 1983, Jap. J. Vet. Res. 31: 151-163). An aquatic snail, Biomphalaria glabrata, can serve as an experimental intermediate host of this parasite (Katakura et al., 1981, Jap. J. Parasit. 30: 23-30). A. costaricensis is also parasitic in the mesenteric arteries of rodents in the Americas (Ubelaker and Hall, 1979, J. Parasit. 65: 307), and causes human abdominal angiostrongylosis. A. siamensis and A. costaricensis are suspected to be closely related taxonomically. Their validity as species have been determined by experimental hybridization. The A. siamensis used in this study were originally obtained from Rattus sabanus in Thailand, and has been maintained in our laboratory since 1978 by using B. glabrata as an intermediate host, and the following laboratory animals as definitive hosts: mice, rats, cotton rats (Sigmodon hispidus) and jirds (Meriones unguiculatus). The A. costaricensis used in this study were provided by Professor Pedro Morera, The University of Costa Rica, San Jose, Costa Rica, and have been maintained in snails and laboratory mammals similar to A. siamensis. The C3H/He mice used in these studies were obtained from the CLEA Breeding Laboratory, Kawasaki, Japan. The jirds and snails, B. glabrata, were supplied by the animal laboratory of the Department of Parasitology, Faculty of Veterinary Medicine, Hokkaido University, Japan. Third-stage larvae of A. siamensis and A. costaricensis were obtained from B. glabrata, which had been infected with first-stage larvae for 35 days, after conventional digestion with HCI and pepsin for about 1 hr. One third-stage larva of each species was inoculated via stomach tube into each of 35 mice. Thirty-six days PI, the mice were killed and the heart, aorta and mesenteric and iliac arteries were examined for adult worms, and the intestines were examined for evidence of eggs and first-stage larvae. The first-stage F1 hybrid larvae obtained from the intestines of some of the mice were used to infect B. glabrata. Twenty third-stage larvae recovered from the snails 7 wk PI were presented orally to each of 6 jirds and 13 mice. The infected jirds and mice were killed and examined for adult worms, eggs and first-stage larvae. Adult worms were fixed in 10% formalin and cleared in lactophenol until examined, and the firstand third-stage larvae were killed by heat and measured. The results of inoculation with a single thirdstage larva of each species are given in Table I. Among the 35 inoculated mice, 15 mice were found to be infected with 1 parasite, and 4 mice with 2 parasites of the same sex. Thirteen mice were uninfected. Two mice harbored A. siamensis 6 and A. costaricensis 2 and 1 mouse harbored A. siamensis 2 and A. costaricensis 6. As the mouse was dead when examined live firststage larvae could not be obtained. The F1 hybrids reported here are hybrids between A. siamensis 6 and A. costaricensis Y. Eggs were found in the intestinal wall of the mice which harbored