Parasitic Development of Obeliscoides cuniculi in Rabbits

Abstract

Studies on the development of Obeliscoides cuniculi infections in New Zealand white rabbits showed that the second ecdysis was completed within 1 hr of infection and the parasitic third stage larvae penetrated into the gastric mucosa within 24 hr. The third ecdysis occurred in the mucosa and was completed by day 5 while the fourth ecdysis probably occurred as the worms migrated to the stomach surface. Migration from the mucosa started on day 5 and by the 14th day, 35% of the total infection was on the gastric surface. The prepatent periods of two infections were 19 and 25 days. The male to female worm ratio was 1.4:1 at 72 hr and 2.5:1 on day 5 but decreased subsequently to 1:1. Fewer worms were found embedded in the mucosa of the pyloric region of the stomach than in other gastric regions on and after the 14th day of infection. Similarities between the parasitic development of other trichostrongyles and 0. cuniculi are discussed. Alicata (1932) described the development of the preparasitic stages of Obeliscoides cunictli (Graybill), a trichostrongyle which occurs naturally in the stomach of domestic and feral rabbits. He also described the course of infection in the guinea pig which is an unnatural host for this nematode. In the guinea pig the larvae underwent two parasitic ecdyses before becoming adults and segmenting eggs were found in the uteri of most female worms by the 17th day. Alicata found that a smaller percentage of the infective dose reached sexual maturity in the guinea pig than in the rabbit. Worley (1963) concluded that guinea pigs were not particularly suitable hosts for 0. cuniculi since infectivity rates were low and infections were rapidly lost. Alicata (1932) reported adult worms embedded in the gastric mucosa of guinea pigs and Russell et al. (1966) found that as the size of the infective dose given to rabbits was increased, an increasing number of immature larvae appeared during patency. However, no histotropic phase of development has been reported in any host species. Obeliscoides cuniculi was first compared to Ostertagia circumcincta by Threlkeld (1934) on the basis of taxonomic similarities. Worley (1963) suggested the use of 0. cunictli infection as a model for the study of ruminant helminthiasis and Russell et al. (1966) extended this suggestion, noting similar gross pathological changes. Received for publication 23 August 1967. * This investigation was supported by U. S. Public Health Service Training Grant 1 T1 AI 302. t Present address: College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. This report concerns further investigation into the details of the parasitic phase of the life cycle of 0. cJuniculi. MATERIALS AND METHODS