ACQUIRED-RESISTANCE AND ANTIBODY-RESPONSE OF RACCOONS (PROCYON-LOTOR)TO SEQUENTIAL FEEDINGS OF IXODES-SCAPULARIS (ACARI, IXODIDAE)

Captive-bred raccoons (Procyon lotor) developed immune resistance to i nfestation by the larval stage of the ixodid tick, Ixodes scapularis, the vector of Borrelia burgdorferi, following repeated applications of both nymphs and larvae, Resistance was expressed as a significant dec rease in the proportion of engorged larvae recovered from each cohort. Resistance to nymphs was not noted, but, only two such cohorts were a pplied. Utilizing an enzyme-linked immunosorbent assay (ELISA) develop ed to detect raccoon serum antibodies to tick salivary gland antigens, raccoons evidenced a two to ten-fold increase in anti-tick salivary e xtract antibody titer following the application of two cohorts of nymp hs and eights cohorts of larvae. The tick saliva antigens recognized b y both pre- and post-exposure raccoon sera were evaluated by Western b lotting. The production of antibodies correlated with the development of resistance to infestation, suggesting that the resistance was immun e-mediated and could be measured by anti-tick salivary extract antibod y titers, Resistance in exposed raccoons prevents nearly 90% of larvae from prolonged feeding. Prolonged feeding is required for engorgement and the transmission of various infectious agents, such as B. burgdor feri.