Ovicidal efficacy of fenbendazole after treatment of horses naturally infected with cyathostomins.

This research investigates the effectiveness of fenbendazole, a type of anthelmintic (anti-parasitic drug), in treating horses infected with cyathostomins (a type of parasitic worm), even where these worms demonstrate resistance to a class of anthelmintics known as benzimidazoles (BZ). The study found that even in the face of BZ-resistance, fenbendazole has a persistent killing effect on the eggs of these parasites.

Objective and Background

• The researchers aimed to investigate an under-explored topic: the ovicidal (egg-killing) activity of benzimidazole (BZ) anthelmintics; specifically fenbendazole, in the context of BZ-resistant cyathostomins in horses.
• Despite product labels suggesting fenbendazole should be used against BZ-susceptible cyathostomins, susceptibility tests are rarely conducted, there is limited information regarding its efficacy against BZ-resistant cyathostomins.

Methodology

• The research was based on a field study involving horses (n=39) infected with BZ-resistant cyathostomins.
• Two different application methods for fenbendazole were tested: a single oral dose per os (given by mouth) (n=21 horses) and a dose given daily for five consecutive days via feed (n=18 horses). The dose was 7.5mg/kg body weight.

Results

• Both treatments showed suppression of egg hatch rate, indicating the ovicidal capabilities of fenbendazole, even against BZ-resistant cyathostomins.
• This efficacy was most noticeable for up to three days post-treatment, translating to a significant difference in hatch rate before and after the treatment, regardless of the application method used.
• After treatment, the numbers of eggs and larvae that were present remained significantly lower than the pre-treatment levels until the completion of the trial.

Conclusion

• The study concluded that fenbendazole maintains its ovicidal efficacy against cyathostomins that show resistance to BZ, up to three days after treatment. This is the case for both a single oral treatment and a longer treatment plan of five consecutive daily doses.