An intradermal test to detect latent warble (Hypoderma spp.) infection in cattle.

An intradermal test was developed to screen cattle for infection with the first-instar larvae of the warble flies Hypoderma lineatum and H. bovis. The diagnostic antigen, prepared from the first-instar larvae of H. lineatum, produced a distinct dermal reaction in cattle infected with the first-instar larvae of either species, but not in cattle in which the infection could not be confirmed later either on necropsy or by the appearance of warbles in the back. The reaction to the antigen was unpredictable in cattle with warbles in their backs. The diagnostic property of the antigen was also demonstrated in rabbits and guinea pigs artificially sensitized to the antigen.