On the Migration of Ascaris laevis Leidy, 1856 in Some Experimentally Infected Hosts

Abstract

Classification of ascarids is based primarily upon certain morphological characteristics of adult specimens. Since the reports of a migratory phase by larvae of Ascaris lumbricoides Linn., 1758 by Steward (1916), Ransom and Foster (1919), Ransom and Cram (1921), and Koino (1922), however, recent investigators have attempted to employ such migratory behaviors as factors in relating certain ascarids. Tiner (1953) stated, All ascarids from carnivores which have been tested will encapsulate in rodents. Raccoon, skunk, and marten ascarids can become established in final hosts when rodents containing encapsulated ascarids are eaten .. . Sprent (1951, 1952) observed two types of migratory behavior of larval ascarids in mice. The first, the tracheal type, consisted of a visceral migration and the eventual disappearance of the larvae from the tissues. The second, the somatic type, was a permanent encystment of living larvae within the tissues. This paper discusses the migration of A. laevis, a parasite of certain hibernating rodents (ground squirrels and woodchucks). A preliminary report of this investigation was published earlier (Babero, 1957). Larval morphology will be presented at a later date. The common migratory pathway of A. laevis in the definitive host is similar to that shown by A. lumbricoides, as described by Martin (1926) and Roberts (1934). A. laevis differs from A. lumbricoides and possibly all other Ascaris spp. in: 1) the time in which the organism completes its migratory cycle, 2) in its pathogenicity (Babero, 1959), and 3) in its growth and development. In experimentally infected hosts (ground squirrels, woodchucks, mice, guinea pigs, hamsters, and cats), A. laevis was not seen in organs other than the liver and lungs, and unlike human and carnivore ascarids the species did not encapsulate in these organs or in somatic tissues. In less than 24 hours after feeding to the experimental hosts single dosages of embryonated eggs of A. laevis ranging from 200-5000, secondstage larvae were observed in the liver. Larvae also were recovered from the portal vein. The number of larvae which entered the liver within the first week after infecting was relatively low compared with that which entered during the second week. Experimental data compiled indicated that the greatest number of larvae in the liver occurred during the second and third week after parasitizing. This suggested that some larvae spent part of their time within the intestinal wall, although none were found in the portal vein after the fourth day of infection. In the liver isolated unencapsulated larvae were seen within the hepatic parenchyma and blood vessels. Rarely was a larva observed in the bile duct.