Abstract

It is well known that a very large proportion of Ascaris suum are expelled shortly after infection of pigs - both under natural conditions and after experimental infections. Until now the question whether there are differences between the small residual population of Ascaris that remain in the pig compare to the majority of parasites that are expelled has not been explored in a systematic manner. In order to investigate the effect of parasite genetics on establishment, pigs were infected with eggs of known genotypes and then killed at different time points: before, under and after expulsion. A PCR-RFLP method applied on the mitochondrial DNA was developed and used to discriminate between the offspring originating from four different Ascaris females (Type A, B, C and D). Each of 26 pigs was then inoculated with 2000 infective eggs (500 eggs of each type) and 6, 6 and 14 pigs were slaughtered at day 14 (before expulsion), 17 (during expulsion) and 28 pi. (after expulsion), respectively. At slaughter the small intestine was divided into 8 sections of similar length. Larvae from each section were isolated using an agar method. At day 17 pi. larvae were also isolated from 10% of the colon content. The length of the larvae was measured using photo equipment (day 14 and 17 pi.) and a regular scale (day 28 pi.) and the larvae were genotyped in order to identify the female from which they were originating from (A, B, C or D). At the three slaughtering days 6 (100%), 5 (80%) and 5 (37%) pigs, respectively were positive for Ascaris and a total 1908, 1616 and 675 larvae were analysed for each day, respectively. Random effect models with pig included as a random variable were used to analyse the response variable length on each day. Section (1-8) and type (A, B, C and D) were included as explanatory variables. The random effect (covariance) caused by pig was non-significant (P = 0.12; P=0.16; P=0.33). Both at day 14 pi. and 17 pi. the length of the larvae was significant affected by the interaction between type and section (P < 0.0001) as well with the total number of larvae in the sections (P < 0.001). At day 28 pi. the interaction between section and type was significant at P=0.03. In conclusion we have found preliminary evidence for a parental effect on the outcome of the size of the offspring in addition to a location-size effect, both possibly with a consequence on larvae fitness and therefore survival in the host.