Efficacy of ivermectin against experimental and natural infections of Gasterophilus spp in ponies.

This study evaluates the effectiveness of ivermectin, an antiparasitic drug, against infections caused by the Gasterophilus species in ponies. The study reveals that ivermectin is 100% effective against these infections and no adverse reactions were observed when administered orally or by intramuscular injection, though potential issues arose with intravenous use.

Experimental Design

• The study involved a total of 60 ponies divided into two groups: 36 treated with ivermectin and 24 untreated. This created a control group for comparison.
• The ponies were intentionally infected with G intestinalis larvae in two doses given 14 and 7 days prior to the treatment. This ensured that the infection was present at the time of the commencement of the experiment.
• On the day of treatment, ivermectin was administered either by intravenous (IV) injection, intramuscular (IM) injection or orally as a paste, providing a variety of administration methods to assess potential differences in effectiveness.
• The ponies were subsequently euthanized and necropsied 21 days after the treatment to study the extent of the parasites.

Results and Observations

• The untreated group of ponies showed persistent invasion of G intestinalis and G nasalis in the mouth and stomach. These included varied growth stages of the parasite.
• On the other hand, no bots (empty larval skins of Gasterophilus species) were found in any of the ivermectin-treated ponies. This indicates that ivermectin was completely effective in eliminating the parasites at both oral and gastric stages.
• None of the ponies administered ivermectin by IM injection or orally showed any adverse reactions, indicating the treatment was safe.
• However, there were cases of anaphylactic reaction in one pony who received the vehicle (the substance in which the drug is dissolved) IV and in one pony who received ivermectin (in the vehicle) IV. This resulted in the death of the latter pony.

Conclusions

• Based on these results, the study concluded that ivermectin is highly effective and safe when administered orally or by IM injection in treating Gasterophilus infections in ponies.
• The adverse reaction after administration through IV is speculated to be caused by histamines released as a reaction to the vehicle components. This may suggest that this mode of administration needs further investigation for safety.