Patent infections of Ascaris suum in pigs: effect of previous exposure to multiple, high doses of eggs and various treatment regimes

Ascaris suum infections in pigs born and raised on contaminated paddocks

The transmission of Ascaris suum was studied in outdoor reared pigs. From May to June 2001, 6 farrowing paddocks were naturally contaminated with A. suum using experimentally infected seeder pigs. Early July, 1 sow farrowed on each paddock. One piglet per litter was slaughtered every second week starting at week 3 post-partum (p.p.) for registration of liver white spots and recovery of A. suum from the lungs and the small intestine. The last pigs were slaughtered at week 19 p.p. Faeces was examined for parasite eggs and blood was analysed for A. suum-specific antibodies. Weaning took place at week 7 p.p. by removing the sow. Paddock infection levels were estimated by regular examination of soil samples and in late June and late November using parasite naïve tracer pigs. Paddock contamination was high but eggs developed slowly resulting in a low initial transmission to the experimental pigs. By week 5 p.p. transmission had increased and the numbers of infective eggs in the soil increased during the study. The results indicate a continuous uptake of infective eggs, but visceral larval migration was reduced with time, probably due to the development of a pre-hepatic barrier. Nevertheless, a rather large population of adult worms remained in the pigs throughout the study, and it may primarily have been eggs ingested in the early infection phase that gave rise to the patent infections. It is suggested that neonatal exposure may result in increased persistence and size of adult worm burden and that the higher 'life-time worm burden' may be of significant economic importance.

Specific systemic IgG1, IgG2 and IgM responses in pigs immunized with infective eggs or selected antigens of Ascaris suum

A total of 35 pigs aged 15 weeks old, and 21 pigs aged 8 weeks old were divided into 7 groups. Groups 1 and 2 were uninfected and challenge control groups, respectively. Groups 3 and 4 were infected weekly with 6 increasing doses of Ascaris suum eggs, and group 4 was additionally treated with pyrantel. Groups 5, 6, and 7 were immunized weekly with the 14, 42, or 97 kDa fractions from adult worms, respectively. Animals of groups 2-7 were challenged with 10000 A. suum eggs 7 days after the last infection/immunization. Serum was sampled weekly and specific IgG1, IgG2, and IgM responses were measured. Pigs of groups 5, 6, and 7 showed high IgG1 and IgG2 responses especially against adult worms antigens, while infected groups had high IgG1 and IgM responses, especially against larva. The IgG1 responses were negatively correlated to the numbers of larvae in the lungs, and positively associated with the liver white spot numbers. There was a positive correlation between IgG2 and the numbers of white spots and lung larvae, while IgM was negatively correlated with these parasitological measures. These findings are discussed and it is suggested that acquired resistance against A. suum larvae is correlated with the induction of IgG1 and IgM, and not with IgG2, and that future vaccination protocols may focus on inducing the Th2 activity.

Serological responses to Ascaris suum adult worm antigens in Iberian finisher pigs

Adult Ascaris suum were dissected to obtain different worm components (body wall, body fluid, ovaries, uterus and oesophagus) which were used as antigens when testing 95 sera of naturally A. suum-infected Iberian pigs by enzyme-linked immunosorbent assay (ELISA) and Western blot (WB). Pigs with patent Ascaris infections had significantly lower ELISA optical density values than pigs without adult worms when using the body fluid and the body wall as antigens. A poor negative correlation was found between adult intestinal worm burden or eggs in faeces and specific antibody responses, measured by ELISA and WB using all antigens. By WB, the recognition of specific bands was variable, but three groups of bands with molecular weights of 97 kDa, 54-58 kDa and 42-44 kDa were generally recognized by sera from naturally infected pigs as well as from hyperimmunized pigs when using the five antigen extracts. The ELISA and WB techniques may be used for immunodiagnosis, using somatic adult worm antigens, to declare young pigs to be Ascaris-free but cannot be used for individual Ascaris-diagnosis in adult Iberian pigs.

Resistance against migrating ascaris suum larvae in pigs immunized with infective eggs or adult worm antigens

Resistance to Ascaris suum infections was investigated in 8- and 15-week-old Iberian pigs. Groups of 3 or 5 pigs were immunized weekly for 6 weeks with antigens of adult A. suum: a 97 kDa body wall (BW) fraction, a 42 kDa fraction of pseudocoelomic fluid (PF) or a 14 kDa PF-fraction; or were inoculated with increasing doses of infective eggs (500-20,000), with or without abbreviation by pyrantel pamoate. All immunized pigs and unimmunized control pigs, were challenged with 10,000 infective eggs 7 days after the last immunization. The number of liver lesions and lung larvae was substantially lower in the older pigs than in the younger ones 7 days after challenge, but the resistance in immunized pigs of both age groups was similar in comparison to the challenge controls of the same age. The highest degree of resistance against lung larvae was observed in pigs immunized with A. suum eggs (97-99%). The pigs immunized with the 14 kDa and 42 kDa PF-fractions were also well protected (67-93%), while no protection was produced by the 97 kDa BW fraction (0-49%). The reduction of white spots following immunization was less evident, with a maximum of 82% reduction in egg-inoculated young pigs.

Experimental Ascaris suum infection in the pig: protective memory response after three immunizations and effect of intestinal adult worm population

The protective immune response to larval migration in pigs, with or without adult intestinal worm populations, 10 weeks after 3 weekly Ascaris suum inoculations, was studied in 45 pigs. Controlled adult worm populations were achieved by oral transfer of 10 adult worms to previously immunized pigs after anthelmintic drenching. A significant reduction in larval recovery from lungs on day 7, and small intestine on day 14, was observed in immunized pigs compared with previously uninfected control pigs after challenge inoculation. The strong anamnestic response to larval migration was characterized by blood eosinophilia and specific immune responses measured by peripheral blood enzyme-linked immunospot and immunosorbent assays using larval excretory-secretory products and adult body fluid as well as Western blotting with a panel of stage-specific A. suum antigens. Immune detection of a previously unreported 10 kDa band, specific to the L2 larval stage and egg hatch fluid, emerged in all pigs after challenge, while the major adult body fluid constituent, ABA-1, remained unrecognized. No significant effect of an intestinal adult worm burden on the larval recovery after a challenge inoculation or on the immune response before or after challenge inoculation could be detected. These results indicate that a significant protective memory immune response to A. suum challenge inoculation can be induced in pigs, and that this protective immunity is not significantly modulated by the presence of adult parasites in the gut.

Drug-abbreviated infections and development of immunity against Trichostrongylus colubriformis in sheep

A protective immune response without liveweight loss can be induced in sheep against T. colubriformis but results depend on the anthelmintic used and duration of immunizing infections. More than 90% protection was achieved in sheep immunized by three 15- or 7-day oxfendazole abbreviated infections or three 21-day nonabbreviated infections. Only 41% protection was induced by 3-day oxfendazole abbreviated infections. Significantly higher worm burden and faecal egg counts were present after challenge in sheep immunized by 7-day levamizole abbreviated infections compared to 7-day oxfendazole abbreviated infection. Liveweight gains of sheep immunized by 15- and 7-day abbreviated infections were not significantly different than non infected controls. Liveweight loss seemed to be associated with high activity of mucus peroxidase and high numbers of eosinophils in the intestinal lumen. High parasite numbers seemed to be associated with low activity of alkaline phosphatase in mucus. Mucus peroxidase, arylsulphatase, larval migration inhibition of mucus, mucus or serum antibody against L3 excretory/secretory antigen or somatic L3, L4 and adult antigen were not associated with protection.

Fenbendazole and its effect on the immune system of the sheep

Ten parasite-free 6-month-old lambs were drenched on days 0 and 28 with fenbendazole and 1 day after each drench were injected with human erythrocytes and ovalbumin. Ten other lambs injected with the antigens were not drenched with anthelmintic and served as controls. Lymphocytes from the fenbendazole-drenched lambs collected 3 days after the first antigen injections and cultured in vitro in RPM1 1640 plus 5% foetal calf serum, and lymphocytes collected at 3 and 7 days and cultured in RPM1 plus 50% autologous serum, had decreased blastogenic activity compared with lymphocytes from control lambs. Similarly, decreased blastogenesis was observed with lymphocytes collected 7 days after the second antigen injections from drenched lambs and cultured in 50% autologous serum containing concanavalin A. In contrast, increased blastogenesis was seen with lymphocytes collected 14 days after the second antigen injections from the drenched lambs and cultured in 50% autologous serum containing phytohaemagglutinin. Similar antibody responses were seen for the drenched and control lambs in response to the injections of both antigens except that, after the second injection, there was a significant reduction in antibody response to human erythrocytes in the fenbendazole-treated lambs. Decreased serum complement levels were seen particularly 3 and 7 days after the second antigen injections in drenched lambs. These serum samples had increased conglutinin activity. At the end of the experiment, the fenbendazole-drenched lambs were significantly heavier than the control lambs. However, this did not appear to be related to any effects of fenbendazole on levels of growth promoting hormones.