Epidemiologic factors and isotype-specific antibody responses in serum and mucosal secretions of dairy calves with bovine coronavirus respiratory tract and enteric tract infections

Abstract

SUMMARY Blood, feces, and nasal swabs specimens were collected 12 to 24 hours after birth and then 3 times/week (blood only once per week) from one group of 10 calves until they were 10 weeks old and from a second group of 10 calves until they were 10 to 20 weeks old. Colostrum was collected from all calves’ dams and tears from 5 randomly selected calves in the first group. All fecal and nasal specimens were assayed for bovine coronavirus (bcv) antigens by elisa. Nasal epithelial cells were examined for bcv antigens by direct immunofluorescence. Isotype antibody titers to bcv in all samples from 5 calves in group 1 were evaluated by elisa. Zinc sulfate turbidity (zst) values were determined on the first serum samples taken from all calves in group 1. To determine whether any correlation existed between zst values, isotype antibody titers to bcv (12 to 24 hours after birth), number of respiratory sick days, number of enteric sick days, or days to first shedding of virus, a Spearman rank order correlation coefficient was done. Bovine coronavirus respiratory tract and enteric tract infections were common on this farm. Most initial infections developed when calves were 1 to 3 weeks old; however, there were also multiple incidences of shedding of viral antigens or seroconversions at later times during the study. Persistence of infection or reinfection of the upper respiratory tract with bcv was common. Colostral antibody titers to bcv (IgG1) were in all cows at moderate amounts; however, calf serum antibody titers and zst values (12 to 24 hours after birth) were highly variable. Significant correlations were found between zst values and bcv IgG1, IgG2, and IgA serum antibody titers (12 to 24 hours after birth); and number of respiratory sick days and zst values, IgG1, IgG2, and IgA serum antibody titers (12 to 24 hours after birth). All calves in group 1 had serum antibody IgM titer increases to bcv when they were 1 to 2 weeks old and many had subsequent IgA, IgG2, and IgG1 serum antibody titer increases in the first 4 weeks. Six calves had a second serum antibody titer increase with IgM or IgA isotypes when they were 5 to 9 weeks old. In the second group, IgM, IgA, and IgG serum antibody titers were increased > fourfold in 6 of 9, 8 of 9, and 5 of 9 calves, respectively. Most calves had passive IgG1 bcv antibodies in their nasal secretions or tears when they were 1 week old and all calves had at least one transient increase in active IgM antibody titers followed by a sharp and persistent increase in IgA titers. All calves had bcv antibodies (IgG1, IgA, or IgM) in their feces when they were 1 week old and at least one transient increase in fecal IgM (4 of 5 calves) or IgA (3 of 5 calves) antibody titers in the 9-week period.