Strongyle infections in ponies. II. Reinfection of treated animals.

The research conducted a study on ponies to understand how repeared infections of strongyle worms impact their health and physiological pattern, discovering that reinfected ponies experienced clinical signs of illness and changes in their worm egg output.

Study Overview

• The study focused on ponies that had previously been treated for strongyle worm infections. A total of seven ponies had their worm burdens either completely removed or substantially reduced with repeated treatments of thiabendazole.
• Five out of seven of these ponies were deliberately reinfected with varying doses of small strongyle larvae. The larval doses ranged from 100,000 to 500,000.
• The purpose of this reinfection was to observe the changes in the ponies’ health and their body’s response to the worm infection.

Clinical Signs of Reinfection

• The reinfection resulted in the ponies exhibiting specific clinical signs. These included abnormal feces, a significant loss in weight, and a delay in shedding their winter coats.
• The researchers also observed a sudden increase in the levels of circulating eosinophils (white blood cells) in the ponies within the first three weeks following reinfection.

Change in Worm Egg Output

• As a result of the reinfection, the researchers noticed a change in the worm egg outputs in the ponies. Specifically, patent infections, where worm eggs become visible in the feces, developed in all the ponies from 12 to 15 weeks after they received the reinfecting larvae.
• The output of worm eggs in the feces followed a cyclical pattern, with four to five peaks occurring per year.
• However, in two of the untreated ponies, there was a significant drop in the high worm egg counts about two and a half years after they were reinfected. In these ponies, no worms were recovered in their feces after treatment, which led to the assumption that these ponies might have depleted their number of inhibited larvae.