Comparative Infectivity of Heligmosomoides polygyrus (= Nematospiroides dubius) in Three Species of Peromyscus

Abstract

Attempts to establish patent infections of a strain of Heligmosomoides polygyrus bakeri (Strain 50) in laboratory-reared Peromyscus maniculatus gambeli failed. This nematode was originally isolated in 1950 from a wild P. m. gambeli and subsequently has been passaged in laboratory mice (Mus musculus) for 21 years. Mice varying from 5 to 82 days of age were given from 25 to 1,200 infective larvae. Other mice were given 350 rads of whole-body gamma radiation (1/2 LD 50/30) and 2 to 8 days later received 200 infective larvae. Six per cent of the orally inoculated infective larvae invaded the mucosa of the fundic region of the stomach during the first 36 hr after inoculation and provoked a local inflammatory response. A further 2% passed through the digestive tract of the host. The remainder of the larvae could not be accounted for. Adult worms transferred surgically to the small intestines of P. m. gambeli did not survive; however, adult worms similarly transferred to P. leucopus noveboracensis and P. e. eremicus survived for at least 5 days. While infections were not established in P. leucopus and P. m. nubiterrae following oral inoculation of infective larvae, they were established in 80% of P. eremicus similarly infected. Of the species of Peromyscus tested, P. eremicus proved to be the best host, whereas P. maniculatus gambeli, the original host of this nematode, was the poorest. In 1950 a strain of Heligmosomoides polygyrus (= Nematospiroides dubius) was isolated from a deer mouse (Peromyscus maniculatus gambeli) trapped near Woodland, California (Ehrenford, 1954). Since that time this strain, referred to as Strain 50 of H. polygyrus by Forrester (1971) and subsequently described as H. p. bakeri by DuretteDesset, Kinsella, and Forrester (1972), has been maintained in various inbred strains of laboratory mice (Mus musculus). Forrester (1971) reported that this nematode would not infect laboratory-reared P. maniculatus after 16 years of passage in laboratory mice. This report presents further information on attempts to infect P. maniculatus with H. p. bakeri and also provides data on comparative infectivity studies with this nematode in two other species of Peromyscus. MATERIALS AND METHODS All wild rodents used in this study were laboratory-reared from wild stock trapped in the following areas: Peromyscus maniculatus gambeli near Mt. Shasta, California (Forrester, 1971), P. m. Received for publication 8 August 1972. * Supported in part during the initial stages by Graduate Training Grant 5T1-762 from the U. S. Public Health Service while the senior author was in the Department of Veterinary Microbiology, University of California, Davis, 95616. Florida Agricultural Experiment Stations Journal Series No. 4537. nubiterrae near Highlands, North Carolina, P. leucopus noveboracensis near Ann Arbor, Michigan, and P. e. eremicus near Phoenix, Arizona. Two strains of commercially obtained laboratory mice (Mus musculus) were used: (1) Webster (CFW) and (2) ICR. Since both of these strains of mice serve as suitable hosts for this nematode, they were used as controls in each of the experiments to check the viability of orally inoculated larvae or surgically transplanted adult worms. Experimental animals were maintained at 70 to 74 F with an 18-hr photoperiod. Water and Purina Mouse Breeder Chow were provided ad lib. Mice were exposed to whole-body radiation in a cobalt-60 gamma-ray irradiator described by Romani et al. (1962). Dose rates were determined by the Fricke ferrous sulfate dosimeter method (Chase and Rabinowitz, 19162). Irradiated mice were maintained in the usual fashion except that water bottles and drinking tubes were autoclaved and drinking water was adjusted to a pH of 2.1 to reduce the pathogenic effects of Pseudomonas aeruginosa and coliform bacteria (McPherson, 1963). One strain of H. polygyrus (Strain 50 from wild P. maniculatus gambeli of Forrester, 1971) was used in all experiments. Stock cultures were maintained either in Webster or ICR mice. The techniques of culturing, collecting, and administering infective larvae and obtaining and counting adult worms have been described by Forrester (1971). The presence of H. polygyrus eggs in feces was determined by using the flotation technique with sodium dichromate (specific gravity = 1.35) as the diluting fluid. Surgical transfer of adult worms from mouse to mouse was conducted following the technique outlined by Mulligan et al. (1965). Stomachs and small intestines were digest