ROLE OF THE BOVINE IMMUNE SYSTEM AND GENOME IN RESISTANCE TO GASTROINTESTINAL NEMATODES

Authors: GASBARRE, LOUIS; LEIGHTON, ELDIN - C-BAR GROUP, VA; SONSTEGARD, TAD - GEML, ARS, USDA

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2001
Publication Date: 7/12/2001
Citation: GASBARRE, L.C., LEIGHTON, E.A., SONSTEGARD, T. ROLE OF THE BOVINE IMMUNE SYSTEM AND GENOME IN RESISTANCE TO GASTROINTESTINAL NEMATODES. VETERINARY PARASITOLOGY. vol. 98(1-3), pp. 51-64, 2001.

Interpretive Summary: Worms in cattle interfere with the producers ability to efficiently raise cattle. Current control of the losses caused by these parasites are based on using de-wormers. There are a number of problems with this approach. After grazing most cattle become somewhat immune to the parasites, the exception is the brown stomach worm, Ostertagia. This prolonged susceptibility to this parasite is a major reason that this parasite remains the most economically important GI nematode. Although, individual animals remain susceptible to stomach worms, there does appear an increased herd immunity that reduces parasite transmission within the cattle herd by reducing the output of parasite eggs on the pasture. This reduction in the number of nematode eggs/gram (EPG) in feces of pastured cattle is strongly influenced by host genetics, and a small percentage of a herd is responsible for the majority of parasite transmission. Cattle can be separated into three types: 1) Type I which never demonstrates high EPG values, 2) Type II which shows rises in EPG values through the first 2 months on pasture which then fall and remain at levels associated with the Type I animals, and 3) Type III which maintain high EPG levels. Studies are in progress to identify the genes controlling resistance. Identification of these genes will offer the producer a number of alternatives for disease control.

Technical Abstract: Gastrointestinal nematode infections of cattle are a constraint on the efficient raising of cattle throughout the world. Most of the parasites found in cattle stimulate an effective level of protective immunity but cattle remain susceptible to infection by Ostertagia for many months. This prolonged susceptibility to reinfection is a major reason that this parasite remains the most economically important GI nematode in temperate regions of the world. Although, individual animals remain susceptible to reinfection for a prolonged period of time, there are a number of manifestations of the immune response that result in an enhanced level of herd immunity, and the overall result of these manifestations of immunity is a reduction in parasite transmission within the cattle herd. In cattle, the immune response seen in the abomasum shows high levels of expression of IL4 in the draining lymph nodes and in lymphocytes isolated from the mucosa. But effector cell populations in the tissues surrounding the parasites, are not typical, inferring that Ostertagia has evolved means to suppress or evade protective immune mechanisms. The number of nematode eggs/gram (EPG) in feces of pastured cattle is strongly influenced by host genetics, and a small percentage of a herd is responsible for the majority of parasite transmission. The best indicator of the number of Cooperia infecting a host is the EPG value, while Ostertagia is best measured by serum pepsinogen levels, weight gain, and measures of anemia. Calves can be separated into three types: 1) Type I which never demonstrates high EPG values, 2) Type II which shows rises in EPG values through the first 2 months on pasture which then fall and remain at levels associated with the Type I calves, and 3) Type III calves which maintain high EPG levels.