Comparative study of different immunization protocols with thiol-binding proteins from Haemonchus contortus adult worms in goats.

Abstract

Haemonchus contortus is one of the most pathogenic gastrointestinal nematodes of small ruminants, that causes significant economic losses especially in warmer areas, where haemonchosis is a real threat. The increasing anthelmintic resistance reported in small ruminants, specially in goats, against this nematode and, the growing demand to reduce the presence of drug residues in food products, have generated a new interest to seek more sustainable methods of control. Because of that, different vaccination strategies have been developed. Therefore, based on previous publications that have showed the protective effect of cysteine protease-enriched fractions (CPFs) from adult H. contortus worms in small ruminants, in this study we evaluated the protective effect of CPFs in combination with DEAE-Dextran adjuvant, using more simple immunization protocols, in comparison to multiple immunizations with higher antigen doses in combination with Freund´s adjuvant. Faecal egg counts (FECs) were significantly lower in goats immunized with CPFs from H. contortus adult worms and Freund’s adjuvant (G1 and G2) and DEAE-Dextran adjuvant (G4) in comparison to non-immunized animals. These differences also translated into a reduction of cumulative faecal counts and a reduction in adult worm burden at the end of the experiment. We also showed a significant increase of specific IgG levels in serum from groups immunized with Freund’s adjuvant (G1 and G2), whereas groups immunized with DEAE-Dextran adjuvant (G3 and G4) showed moderate increases of this immunoglobulin. Interestedly, specific IgG levels were negatively correlated with parasitological parameters after the challenge, when specific IgG reached the peak and at the end of the experiment. Similarly, an increase of specific IgA level in serum were detected in the immunized groups that were negatively correlated with parasitological parameters after the challenge. Hence, levels of specific immunoglobulins of both isotypes from serum and mucus were statistically associated in all the immunized groups, during the challenge and specially at the end of the experiment. Because of that, the data presented here reveal the accuracy of all tests performed in the present study to analyse the humoral immune response.