Studies on Onchocerca cervicalis Railliet and Henry 1910. I. Onchocerca cervicalis in British horses.

Abstract

1. 903 horses were examined at 3 abattoirs in South East England. 10(22–7%) of the horses at the London Colney abattoir, 23(13–9%) of those at the Braintree abattoir, Essex, and 90(12–9%) of those at the Islington abattoir, London, were infected with O.cervicalis. All 105 horses examined in Southern Ireland were found to be negative.2. The adult worms of O.cervicaliswere found without exception, in the ligamentum nuchae of infected horses. The suspensory ligaments of the fetlock and flexor tendons were always negative.3. The microfilariae of O.cervicalisconcentrate along the abdominal mid-line of the host. In 5 complete horse hides, 95% of the microfilariae were found within 6 inches of the linea alba. The examination of 31 other horses infected with O.cervicalisconfirmed this pattern of microfilarial distribution.4. The microfilariae were concentrated along the ventral mid-line, of the host; presumably an adaption to accommodate the habits of the vector C.nubeculosus, which bites preferentially in this area.5. Seasonal variations in the number of microfilariae in horse skin, as reported by Japanese workers, was not observed. Evidence was found, however, to suggest that the microfilariae migrate into the deeper levels of the dermis during the Winter. Histological examination of infected horse skin showed that the microfilariae have a very uneven distribution in the dermis. They congregate together in isolated “clumps” or “nests” and are frequently found in close proximity to the sweat glands or hair follicles.