Effect of Preliminary Deworming with "Ivergel" on the Formation of Humoral Immunity During Vaccination of Horses Against Streptococcus equi

Abstract

This study evaluated the effect of preliminary deworming with "Ivergel" (0.4% ivermectin oral gel) on the efficacy of vaccination against equine strangles (Streptococcus equi). The experiment was conducted in 2025 at "Duniye-Agro" LLP (Almaty region, Kazakhstan) using 30 clinically healthy horses aged 1–5 years, randomly assigned into two equal groups ( n = 15 ). The experimental group received a single dose of "Ivergel" (200 µg/kg) 14 days prior to vaccination, whereas the control group was vaccinated without prior anthelmintic treatment. Coprological analysis revealed that "Ivergel" reduced fecal egg counts (EPG) from  540 ± 120  to  20 ± 18 , achieving an antiparasitic efficacy of  89.8 ± 3.7%  ( p < 0.01 ). Enzyme-linked immunosorbent assay (ELISA) demonstrated that specific antibody titers against S. equi in pretreated horses reached  1:640 ± 80  on Day 14 and  1:920 ± 90  on Day 28 post-vaccination, which was significantly higher than in the control group ( 1:390 ± 70  and  1:580 ± 60 , respectively;  p < 0.05 ). No adverse reactions were observed in the experimental group, while mild post-vaccination side effects were recorded in individual control animals. These results confirm that preliminary deworming reduces parasitic burden and optimizes the formation of post-vaccination humoral immunity against strangles.