Immune responses of pony foals during repeated infections of Strongylus vulgaris and regular ivermectin treatments.

The research study examines the immune responses in pony foals during repeated infections with a particular parasite, Strongylus vulgaris, and treatment with the drug ivermectin. The study finds no significant difference in immune responses between horses treated with ivermectin and those left untreated.

Study Methodology

• The study involved ten helminth-free pony foals divided into three groups. Eight of these foals were experimentally infected with 50 Strongylus vulgaris infective larvae in the mouth, for four weeks.
• One foal died due to acute verminous arteritis, leaving seven foals who continued to receive 50 S. vulgaris infective larvae every 2 weeks for another 20 weeks.
• The infected foals were split into two groups: four foals remained untreated (Group 1), while three of the infected foals were given doses of ivermectin at 8, 16 and 24 weeks post initial infection (Group 2).
• Group 3 with two foals served as the control group.

Study Findings

• The untreated foals from Group 1 developed eosinophilia, a condition characterized by a high level of eosinophils in the blood, throughout the course of the infection.
• Group 2 foals also developed mild eosinophilia, but their eosinophil numbers significantly decreased for 3 weeks following each ivermectin treatment.
• Only foals in Group 1 developed other significant conditions, such as hyperproteinemia (high protein levels in the blood), hyperbetaglobulinemia (excess beta globulins in the blood), and a reversal of the albumin/globulin (A/G) ratio, 4 weeks after the initial infection.
• Significant immunoglobulin G (IgG) anti-S. vulgaris ELISA titers were observed in foals in both Groups 1 and 2, three weeks after infection, and lasted for the timeline of the experiment.
• When it came to the blastogenic reactivity (a measure of the immune system’s response) of the foals’ peripheral blood mononuclear cells (PBMC) to specific antigens, no significant differences were observed between the groups.
• However, PBMCs from foals in Groups 1 and 2 displayed significant blastogenic reactivity to the S. vulgaris antigen at 25 weeks post-infection.
• The mesenteric lymph node cells from Group 2 showed a higher reactivity to the antigen than those from Group 1, though the difference was not statistically significant.

Conclusion

• Despite the high parasite infections and the alterations seen in traditional clinical parameters related to the immune system (e.g., eosinophilia, hyperproteinemia, and immune globulins), the study found no significant changes in the immune response of ponies to S. vulgaris after treatment with ivermectin.
• The results suggest that the immune response alterations observed are not due to the killing of larvae by ivermectin treatment, but potentially due to natural immune response to S. vulgaris infection.