Horse resistance to natural infestations of Anocentor nitens and Amblyomma cajennense (Acari: Ixodidae).

This research explores the resistance of horses to two common tick species, Anocentor nitens and Amblyomma cajennense, over a two-year period. The study revealed that horse resistance varies depending on the season and found evidence of horses developing cross-resistance to these ticks.

Methodology

• Over two years, the researchers investigated various aspects of horse resistance to A. nitens and A. cajennense tick infestations.
• To examine the impact of seasons, the researchers used free-living stages of A. nitens ticks.
• They removed ten engorged female ticks, each weighing 150-329 mg, from naturally infested horses every two weeks and placed them individually in glass tubes which were then kept in an incubator.

Measurements and Findings

• The researchers measured several biological parameters, including reproductive efficiency, maximum larval survival (MLS) and egg-hatching rates, and observed that these parameters were significantly lower in the spring/summer season than in the fall/winter season.
• Every 14 days, they counted female ticks of both species on each side of five mares.
• The researchers found greater variance in infestation levels between horses with the highest and lowest infestation when it came to A. nitens compared to A. cajennense.
• Ten animals were found to carry a major proportion, i.e., 64.9% and 88.6%, of the total parasite burden of A. cajennense and A. nitens respectively.

Interpretation of Results

• The study found noticeable seasonal variation in horse resistance to A. nitens but not to A. cajennense.
• The researchers also found evidence of cross-resistance in horses, with animals exhibiting the highest total number of A. cajennense and the highest number of A. nitens adults showing significant correlations.

Conclusion

• The researchers concluded that there are seasonal changes in horse resistance to A. nitens, but not to A. cajennense.
• Furthermore, they suggested that horses develop cross-resistance to these tick species, specifically when considering the female stage of A. nitens and the total population of A. cajennense.