Effect of passive immunity on the development of a protective immune response against bovine viral diarrhea virus in calves.
OBJECTIVE
To determine whether passively acquired antibodies prevent development of a protective immune response to live virus in calves.


METHODS
18 calves.


METHODS
Calves were caught immediately after birth and tested free of bovine viral diarrhea virus (BVDV) and serum antibodies against BVDV. Within 48 hours, 12 calves were fed colostrum that contained antibodies against BVDV and 6 calves received BVDV antibody free milk replacer. Three milk replacer fed and 6 colostrum fed calves were exposed to virulent BVDV2-1373 at 2 to 5 weeks of life when passively acquired serum antibody titers were high. After serum antibody titers against BVDV had decayed to undetectable concentrations (at 7 to 9 months of age), the 3 remaining milk replacer fed calves, 6 colostrum fed calves previously exposed to BVDV2-1373, and 6 colostrum fed calves that had not been exposed to the virus were inoculated with BVDV2-1373.


RESULTS
Passively acquired antibodies prevented clinical disease in inoculated colostrum fed calves at 2 to 5 weeks of life. Serum antibody titers did not increase in these calves following virus inoculation, and serum antibody titers decayed at the same rate as in noninoculated colostrum fed calves. Inoculated colostrum fed calves were still protected from clinical disease after serum antibody titers had decayed to nondetectable concentrations. Same age colostrum fed calves that had not been previously exposed to the virus were not protected.


CONCLUSIONS
A protective immune response was mounted in calves with passive immunity, but was not reflected by serum antibodies titers. This finding has implications for evaluating vaccine efficacy and immune status.
Ridpath
Julia E
JE
Virus and Prion Diseases of Livestock Research Unit, National Animal Disease Center, USDA, Agricultural Research Service, Ames, IA 50010, USA.
Neill
John D
JD
Endsley
Janet
J
Roth
James A
JA
D000818:Animals; D000831:Animals, Newborn; D000914:Antibodies, Viral / Q000097:blood; D001831:Body Temperature; D001912:Bovine Virus Diarrhea-Mucosal Disease / Q000276:immunology* / Q000517:prevention & control / Q000821:virology; D002417:Cattle; D003126:Colostrum / Q000276:immunology / Q000821:virology; D001908:Diarrhea Viruses, Bovine Viral / Q000276:immunology*; D005260:Female; D007112:Immunity, Maternally-Acquired / Q000276:immunology*; D007958:Leukocyte Count / Q000662:veterinary; D008297:Male; D008892:Milk / Q000276:immunology / Q000821:virology; D009500:Neutralization Tests / Q000662:veterinary; D010976:Platelet Count / Q000662:veterinary; D011247:Pregnancy
D000914:Antibodies, Viral