Onchocerca spp: frequency in Thoroughbreds at necropsy in Kentucky

Area of Science:

• Veterinary Parasitology
• Equine Pathology

Background:

• Onchocerca spp. are filarial nematodes that can affect horses.
• The ligamentum nuchae is a common site for Onchocerca spp. in equids.

Purpose of the Study:

• To determine the prevalence of Onchocerca spp. in the ligamentum nuchae of Thoroughbred horses.
• To assess the relationship between age and Onchocerca spp. infection in Thoroughbreds.

Main Methods:

• Necropsy examination of the ligamentum nuchae from 523 Thoroughbred horses (1-29 years old) in Kentucky.
• Examination of suspensory ligaments and flexor tendons from fetlocks of 100 Thoroughbred horses (3-24 years old).

Main Results:

• Onchocerca spp. were identified in 306 (59%) of the 523 horses examined.
• Prevalence increased with age, from 3% in 1-year-olds to 42% in 5-year-olds, and 87% in horses aged 6-29 years.
• No Onchocerca spp. were found in the suspensory ligaments or flexor tendons of the fetlocks.

Conclusions:

• The ligamentum nuchae is a significant reservoir for Onchocerca spp. in older Thoroughbred horses.
• Age is a major risk factor for Onchocerca spp. infection in the nuchal ligament.
• The suspensory apparatus of the fetlock is not a typical site for this parasite.