Solid-phase enzyme immunoassay of bovine antibody responses following immunization against and natural infection with Pasteurella haemolytica.

A solid-phase enzyme immunoassay (EIA) was developed in order to monitor bovine antibody responses following immunization against and natural infection with Pasteurella haemolytica serotype A:1. Non-ionic surfactants, used in many antibody EIAs to reduce non-specific immunoglobulin binding, had to be avoided because they inhibited specific binding of bovine antibodies to P. haemolytica antigens. Calves were immunized with a KSCN extract of P. haemolytica. Subcutaneously immunized animals developed a significantly higher humoral antibody response than did intranasally vaccinated animals. Intranasally immunized calves developed a slightly, but not significantly higher nasal antibody response than did calves vaccinated subcutaneously. Field study results based on bacterial isolation and EIA detection of antibodies to P. haemolytica indicate that cattle can generate carrier states where bacteria are present in the upper respiratory tract, yet no humoral antibody response is induced. The converse was also found where cattle were free from P. haemolytica in the upper respiratory tract, yet possessed a good humoral antibody response to P. haemolytica.