Observations on development of Strongyloides westeri in foals nursing dams treated with cambendazole or thiabendazole.

This research studied the development of the parasite, Strongyloides westeri, in young horses or foals, particularly looking at the effects of cambendazole and thiabendazole treatment in mares on the development of the parasite in their offspring. The findings suggest that cambendazole may be more effective than thiabendazole in preventing the emergence of S. westeri in foals.

Strongyloides westeri Development

• The experiment recorded a prepatent period, which is the time from infection to when the parasites can be detected, of 8 or 9 days in four pony foals infected with the parasitic 3rd stage larvae through the postpartum milk of a mare.
• This is notably quicker than the commonly observed time it takes for eggs of S westeri to appear in naturally infected suckling foals’ feces in central Kentucky, which is usually 2 to 6 days longer.

Treatment with Cambendazole or Thiabendazole

• The scientists conducted additional studies where mares were treated with either cambendazole or thiabendazole within 2 days of giving birth and continued this treatment for a period of between 7 to 16 days.
• The objective was to observe if the appearance of S westeri eggs in the foals’ feces would be influenced by whether their mothers were treated with cambendazole or thiabendazole.

Results of the Treatment

• Cambendazole, but not thiabendazole, was found to prevent the appearance of S westeri in the foals’ feces during the treatment period and for at least a week after treatment ended.
• However, the effectiveness of cambendazole varied depending on the method of administration and dosage, with better results observed in mares administered with larger doses.
• The administration of thiabendazole did not show any evident benefits in the prevention of S westeri development in the foals.

Possible Explanation of the Results

• Based on their observations, the researchers proposed that cambendazole was likely effective against the parasitic 3rd stage larvae located in the mares’ mammary tissue or milk.
• However, they also suggested that cambendazole may just as well have an inhibitory effect on the developmental stages of S westeri in the foals, thus accounting for the decreased incidence of the parasite in treated foals.