Objectives
We examined the role of
bovine coronavirus (BCV) in respiratory and enteric infections in feedlot
cattle, and determined the prevalence of Bovine Torovirus (BoTV) and other
enteric pathogens in diarrhea cases in cattle. In the first study, we
examined the respiratory and enteric shedding of BCV in cattle within 3
weeks after arrival in a feedlot, and studied the relationship between BCV
shedding, seroconversion, clinical signs (respiratory disease and diarrhea)
and weight gains. Fecal and nasal swab samples from 85 Ohio (OARDC) feedlot
cattle were collected at arrival (0) and at 4, 7, 14 and 21 days-post
arrival (DPA). An ELISA was used to detect concurrent shedding of BCV in
fecal and nasal samples. All samples ELISA positive for BCV were matched
with of BCV ELISA negative samples and analyzed by RT-PCR of the N gene.
Paired sera were collected at arrival and 21 DPA and tested for antibodies
to BCV using an indirect ELISA. Information on clinical signs, treatments
and weights were collected. The rate of BCV nasal and fecal shedding was 48%
(41/85) and 53% (45/85) by ELISA and 84% (71/85) and 96% (82/85) by RT-PCR, respectively, with
concurrent enteric and nasal shedding detected in 38% of cattle. The peak of
BCV nasal and fecal shedding occurred at 4 DPA. Only 11% of cattle had BCV
antibodies at 0 DPA, but 91% of cattle seroconverted by 21 DPA. The BCV
fecal and nasal shedding were statistically correlated with ELISA antibody
seroconversion (p<0.0001); however, BCV fecal and nasal shedding were not
significantly related to clinical signs. Seroconversion to BCV was inversely
related to average daily weight gains (P<0.06). Genetic characterization of
respiratory and enteric isolates of BCV in HRT-18 cells is in progress. Our
second objectives were to determine the prevalence of BoTV in bovine fecal
samples from diarrhea cases submitted to the Ohio Animal Disease Diagnostic
Laboratory (ADDL), and to establish the relationship between detection of
BoTV and other enteric pathogens. From Nov, 1999 to Feb, 2001, 252 specimens
from 52 calves (< 6 months-old), 37 young adults (< 2 years), 117 adults (>
2 years), and 46 animals of unknown ages were examined by ELISA and RT-PCR
assays developed in our lab to detect BoTV. Testing for other enteric
pathogens was performed by ADDL, and the results were analyzed with the BoTV
data. BoTV was detected by ELISA and/or RT-PCR in 6% (15/252) of the
clinical samples, 87% (13/15) of which were from calves (p<0.001)
representing 25% (13/52) of the calves tested. Of the BoTV-positive calves,
77% (10/15) were under 4 weeks of age. In 5/15 positive specimens, BoTV was
the only pathogen detected. Other enteric pathogens detected alone or in
combination with BoTV in calf samples were: rotavirus, BCV, Salmonella spp,
Cryptosporidium spp, and
Giardia spp, but no
consistent association was observed. Of the BoTV-positive specimens, 73%
were from winter. In summary, BoTV was detected in fecal samples from
diarrhea cases in cattle, but principally in young calves.
