Acquired resistance to Hypoderma lineatum: comparative immune response of resistant and susceptible cattle.

The humoral and cellular immune responses of previously infested and noninfested cattle were compared after a single experimental exposure to 1st-instar Hypoderma lineatum. No correlation was found between the development of humoral antibodies as measured by passive hemagglutination assay and resistance in cattle. However, the most resistant cattle had higher macrophage migration-inhibition activity before and 1 month after infestation than did low- or non-resistant animals, and resistant animals also had greater sensitivity to antigens from larvae as they penetrated the skin. These results suggest that acquired resistance to hypodermatosis involves a cellular component of the immune mechanism.

Migratory kinetics of Cuterebra fontinella (Diptera: cuterebridae) in the white-footed mouse, Peromyscus leucopus.

Larvae of the rodent botfly, Cuterebra fontinella, follow a consistent migration route thorough their natural host, the white-footed mouse, Peromyscus leucopus. Larvae that enter the eye or nares spend about 48 hr in the nasal cavity and then follow a caudally oriented path that leads through the nasal passage, trachea, thoracic and abdominal cavities, and ends in the subcutaneous tissues of the posteroventral abdominal region. Larvae that enter mice through the anus or by injection into the subcutaneous tissues of the back begin their migration from the trachea and from that point follow the usual path to the terminus.

Effects of some factors on the susceptibility of Peromyscus leucopus to infestation by larvae of cuterebra fontinella (Diptera: Cuterebridae).

Two levels of 3 factors, (1) host age, (2) host dietary state in regard to vitamin A, and (3) previous infestation history, were tested individually and in combinations for their effects on the susceptibility of Peromyscus leucopus to infestation by larvae of the rodent bot fly, Cuterebra fontinella. Previous infestation was the only significant single factor. Previously uninfested (Pu) mice usually were more susceptible to infestation than previously infested (Pi) mice. Interactions of age and state of vitamin A had the following effects: 1) Young Pu mice that had been denied vitamin A were much less susceptible to infestation than equivalent mice that had been fed diets containing the vitamin; and 2) when Pu mice were deficient in vitamin A, old mice were more susceptible than young mice but when Pu mice were not deficient in the vitamin, young mice were more susceptible. These findings may have significance for natural infestations of P. leucopus.