IMMUNE-RESPONSES OF CALVES ANTIGENICALLY STIMULATED AND CHALLENGE EXPOSED WITH ANAPLASMA-MARGINALE DURING TICK INFESTATION OR TREATMENT WITH DEXAMETHASONE

  • 1 January 1984
    • journal article
    • research article
    • Vol. 45  (3) , 431-436
Abstract
Similar anamnestic antibody responses to a 2nd injection of an A. marginale vaccinal antigen were observed in calves infested with the tick Dermacentor albipictus and in tick-free calves. When challenge exposure of these calves to virulent A. marginale was done, infestation with the tick Boophilus microplus increased anemia (P < 0.01), but did not suppress antibody production to A. marginale or increase parasitemia. None of the vaccinated calves, regardless of infestation, experienced clinical anaplasmosis. Mitogenic responses of lymphocytes from infested animals were unaltered by either infestation. Tick infestations did not cause immune suppression in the calves; use of dexamethasone resulted in a significantly lower antibody response (P < 0.05) after a 2nd injection of vaccinal antigen. After challenge with virulent A. marginale, dexamethasone-treated calves showed more pronounced parasitemia (P < 0.01) and anemia (P < 0.01) than did control calves. Anaplasmosis did not prevent the calves from developing resistance to reinfestation, which was accompanied by immediate, but not delayed, hypersensitivity reactions against homologous tick extracts. D. albipictus did not seem to share common antigenic determinants with B. microplus; extracts from the latter did not elicit immediate hypersensitivity responses in calves sensitive to D. albipictus extracts. Calves were somewhat resistant to reinfestation as evidenced by reduced numbers of adult fed ticks, decreased weights of ticks after feeding and smaller egg masses.