Site Selection and Penetration Studies of Mesocestoides corti (Cestoda) Tetrathyridia in the Southern Pacific Rattlesnake, Crotalus viridis helleri

Abstract

Experimental infections with Mesocestoides corti tetrathyridia (larvae) have been reported in the southern Pacific rattlesnake, Crotalus viridis helleri (Mankau and Widmer, 1977, Jap. J. Parasitol. 26: 256-259). This study involved only two snakes and provided no data on site selection or the rapidity of penetration. Because such data are basic to any future host-parasite studies an experiment was performed to obtain this information. Southern Pacific rattlesnakes were collected from San Bernardino County, California, and maintained at ambient temperatures for a minimum of 12 wk prior to initiation of the experiment. This enabled each experimental snake to function as its own control. An infection of larvae in laboratory mice was established from an infected mouse received from Dr. Marietta Voge at UCLA. All infections of mice were made orally, 25 larvae per mouse. Twelve rattlesnakes were gavaged with an inoculum of 250 larvae each, and then transferred to an environmental chamber set at 30 C. Beginning at 3 days PI three snakes were examined every 24 hr through 6 days PI. General necropsy procedures were as outlined by Widmer (1967, J. Parasitol. 53: 362-363) except that the specific technique for examination of the gastrointestinal tract was modified slightly. This structure, excluding the cloaca, was removed, prior to separation and examination of the component segments and purged with physiological saline solution to remove unattached larvae. Removal of the cloaca and examination of the cloacal contents for larvae was a separate procedure. After 3 days of infection the majority of larvae were found in the small intestine with fewer larvae in the large intestine and stomach (Table I). No larvae were found in the coelomic cavity, systemic musculature, lungs, or liver. The recovery of the majority of larvae from the small intestine is consistent with the data presented by Mankau and Widmer (1977, loc. cit.). Gross anatomical examination of the intestinal tract at 3 days PI revealed larvae attached to the intestinal folds. Penetration into the mucosal layer was observed at 4 days PI and deeper penetration into the intestinal tissues was seen 5 and 6 days PI. Attachment and penetration times for Mesoestoides corti tetrathyridia in mice were reported by Specht and Voge (1965, J. Parasitol. 51: