Portal de Periódicos da CAPES

Studies on Trichostrongylus axei (Cobbold, 1879). VIII. Some Quantitative Aspects of Experimental Infection of the Mongolian Gerbil (Meriones unguiculatus)

1963; American Society of Parasitologists; Volume: 49; Issue: 4 Linguagem: Inglês

10.2307/3275769

1937-2345

S. E. Leland,

Rabbits: Nutrition, Reproduction, Health

The Mongolian gerbil was found to be an excellent host for the domestic animal pathogen Trichostrongylus axei. Single doses of 250 to 6,000 larvae from rabbits resulted in worm recoveries ranging from 16 to 102% in gerbils. An average prepatent period of 21.8 days, an average male/female worm ratio of 0.75, and an average of 27.9 eggs/female/24 hr were observed. Two methods of LD5o analysis resulted in values of 1,000 and 1,070 larvae with a standard error of 0.1394. T. axei cultivated from gerbil infections developed to patency when inoculated into susceptible gerbils. Worms from the lamb or calf were larger than worms of the same or other isolates cultivated in gerbils. Gross gastroduodenal lesions in severe and fatal cases in gerbils closely resembled the lesions seen in the rabbit, ruminant, and horse. The lesion begins with a hyperemia and progresses to catarrhal inflammation, necrosis, and chronic proliferative inflammation. Worm eggs per gram of feces and eggs per 24 hr were easily followed. Some of the technical and economic disadvantages associated with studying or maintaining T. axei in large domestic animals are overcome with the use of this small host. Drudge et al. (1955) and Leland and Drudge (1957) have shown that the domestic rabbit, hamster, and guinea pig are susceptible to experimental infection with various isolates' of Trichostrongylus axei. The rabbit was found to be the most satisfactory host. Records of the present author indicate patency Received for publication 12 February 1963. * project of the Kentucky Agricultural Experiment Station published by permission of the Director of the Station and supported by National Science Foundation Research Grant G14215; and the Animal Disease and Parasite Research Division, ARS, U. S. Department of Agriculture; and contributing to Regional Project S-21, Gastro-intestinal Parasites of Ruminants. t Present address: Department of Veterinary Science, University of Florida, Gainesville. The term is now preferred over by the author since there is no conclusive evidence which would indicate the various isolations of T. axei recorded in the literature differ sufficiently to give strain status. Isolate here is defined as the population of a single worm species resulting from infective larvae originally cultivated from a single host of a particular host species though not necessarily maintained in the laboratory in the original host species. 617 in the rabbit can exist in excess of 4 years following a single inoculation of larvae. The technical and economic advantages in maintaining and studying a pathogen of a large domestic animal in small laboratory animals has prompted further study. The purpose of the present paper is to report in detail the observations published in abstract (Leland, 1961), along with subsequent findings relative to the susceptibility of the Mongolian gerbil to various isolates of T. axei. MATERIALS AND METHODS Infectivity was established from qualitative trials where worm eggs and adult worms were recovered but not counted from inoculated gerbils. The procedure for quantification of the infection consisted of inoculating groups of gerbils with increments of T. axei larvae from the various isolates. The ages of the gerbils varied from approximately 8 weeks to adults 2 to 3 years old. Gerbils listed in Table I were in excess of 1 year of age. Gerbils number 1, 2, and 3 had been used in susceptibility trials with Haemonchus placei prior to inoculation with T. axei. Patency for H. placei had not been established in these or four other gerbils. This content downloaded from 207.46.13.111 on Tue, 09 Aug 2016 05:40:07 UTC All use subject to http://about.jstor.org/terms THE JOURNAL OF PARASITOLOGY Two equine (S and A) and one bovine (0) isolates of T. axei in pure culture were used in the present study. These isolates have been maintained in rabbits since 1954. During this 6-year period, isolate has experienced an occasional ruminant passage. Gerbils 25 and 26 were inoculated with S-isolate larvae, which were cultured from gerbils 11 and 15. Gerbils 28, 29, and 30 were inoculated with A-isolate larvae cultured from gerbils 20 and 24. In one case (gerbil 27), mixed species of larvae of bovine origin were used. Third-stage larvae were baermannized from sphagnum moss cultures. In the case of gerbil 31, the larvae were cultured axenically from the egg to the infective third stage. Water and a commercial laboratory ration (Purina Laboratory Chow, Ralston Purina Co., St. Louis 2, Missouri) were available ad lib. Infection technique was as described in the rabbit study (Leland and Drudge, 1957) except that the inoculum of larvae was suspended in a smaller quantity of water (0.5 ml) and the tube and syringe wash was reduced to 0.5 ml. This reduction was necessitated by the smaller size of the gerbil's stomach. Daily salt flotations were used to establish the presence of eggs in determining patency. After patency was established, feces for a 24-hr period were placed in a previously weighed 125-ml Erlenmeyer flask. Reweighing after the addition of feces gave the weight of feces for the 24-hr period. Water was added to the flask in a quantity sufficient just to submerge the feces. The flask was stored overnight in the refrigerator. The flask was shaken and the contents with washings poured into a graduated cylinder and made up to a volume in ml equal to 10 times the 24-hr fecal weight in grams. One ml of the well-mixed fecal suspension was transferred by pipette to a 12-ml centrifuge tube, the top of which had been ground flat. The tube was then filled with saturated NaCl to the extent that when a cover slip was placed on the ground glass the solution came in contact with the cover slip. The tube with cover slip in place was centrifuged 5 min at 100 g. After removal of the first cover slip, a second was placed on the tube to insure a more complete recovery of eggs. The eggs counted on the two cover slips per tube were totaled. By multiplying the number of eggs counted in 1 ml of the suspension by the factor 10, eggs/g were obtained; while multiplying the eggs in 1 ml of the suspension by the total ml of suspension gave eggs/24 hr. Twenty-four hr fecal collections were made 5 to 7 times a week for 42 days after infection and 3 times a week thereafter. The number of eggs/24 hr/female worm was calculated from the average 24-hr egg count of the 3 days prior to necropsy and the total number of female worms recovered at necropsy. Thus, in animals that died and for which a 3-day average of the 24-hr egg count was not available, the value of eggs/24 hr/female worm was not calculated. The entire gastrointestinal tract was removed, digested in 100 ml of 0.5% pepsin, 0.5% HC1 solution, then fixed in formalin, and the worms counted in a manner described earlier (Leland and Drudge, 1957). In calculating the LD5o, the methods of Reed and Muench (1938) and Karber (1931) as outlined by Boyd (1947) were used. The standard error of the LD5o (Karber) was determined by the method of Irwin and Cheeseman (1939) as outlined by Boyd (1947). Animals that died 60 days or more after inoculation of larvae were considered as survivors. To compare size, the total length of 25 male and 25 female worms from gerbils representing each of the T. axei isolates was measured. In addition, an equal number of worms of isolates A were measured from a lamb (Lamb 41A of Leland et al., 1960) and a calf (Calf 43 of Leland et al., 1959). The duration of infection (61 to 80 days) was approximately comparable in the various hosts selected for worm measurements. The means of the various groups of 25 measurements were statistically analyzed to determine any level of significant difference between the groups.