Migration And Distribution Of Ascaris Representing Different Genotypes In C57BL/6 Mice

Ascaris lumbricoides (Linnaeus, 1758), the largest and most common of the intestinal helminthes of humans, has a world wide distribution. More than 1 billion of world population was reported to be infected. Ascaris suum (Goeze, 1782) is one of the most ordinary parasites which infects pigs and causes huge economic losses. There has been a controversy as to whether Ascaris lumbricoides from humans represents a different species to Ascaris suum from pigs. Recently DNA technique has provided useful complementary tools to study the genetics of Ascaris and added new knowledge helpful to understand the taxomomic status of the two parasites. The investigations on genotypic variability within Ascaris from humans and pigs in China (Peng et al 2003), and the extending research on the variation of host affiliation in pigs and mice showed by Ascaris with particular genotypes (peng et al 2006) have led a question that if the variation in host affiliation would be related to a possible difference in migration and distribution of the Ascaris larvae representing different genotypes.In the present study, we experimentally infected mice with Ascaris infectious eggs representing particular genotypes of G1 and G3, which have been used in previous studieds by Peng et al (2006), to compare if there would be differences in migration and distribution of the larvae in the mice. Mice (C57BL/6, male, SPF, n=160) were individually inoculated orally with～1000 eggs representing Ascaris genotypes G1 or G3 respectively. Five mice from each group were euthanized at the intervals of 2 hours during the period of early infection (until 12 hours of post-inoculation), or at the intervals of 2-10 days during the late infection period (1-34 days after inoculation) to recover eggs/larvae from the small and large intestines, thoracic and abdominal cavities, peripheral blood, livers and lungs.Results from this study showed that there is hatching difference in numbers and locations between the two genotyped eggs. The number of hatched eggs of G1 genotype was much higher than G3 eggs, suggesting the intestinal environment of C57BL/6 would no be suitable for hatch of G3 type eggs.The G1 eggs were hatched either in small and large intestines and no obvious difference in the number of hatched larvae between the two locations. But the G3 eggs mainly hatched in large intestine. The pattern of migration for the larvae of two genotyped Ascaris was found to be similar except for the difference in the time of first appearing or last disappearing of larvae in the organs. The distribution of the two genotyped Ascaris in the organs or locations was different which was characterized by obvious difference in the number of larvae recovered. Finally, the mean spleen weight of mice infected with G1 genotyped eggs was obviously changed in comparison with mice infected with G3 eggs suggesting a different way of host immune defense.