Case-control study of microbiological etiology associated with calf diarrhea

Abstract

Calf diarrhea is a major economic burden for the US cattle industry. A variety of infectious agents are implicated in calf diarrhea and co-infection of multiple pathogens is not uncommon in diarrheic calves. A case-control study was conducted to assess infectious etiologies associated with calf diarrhea in Midwest cattle farms. A total of 199 and 245 fecal samples were obtained from diarrheic and healthy calves, respectively, from 165 cattle farms. Samples were tested by a panel of multiplex PCR assays for 11 enteric pathogens: bovine rotavirus group A (BRV-A), bovine coronavirus (BCoV), bovine viral diarrhea virus (BVDV), bovine enterovirus (BEV), bovine norovirus (BNoV), Nebovirus, bovine torovirus (BToV) Salmonella spp. (Salmonella), Escherichia coli (E. coli) K99(+), Clostridium perfringens with β toxin gene and Cryptosporidium parvum (C. parvum). The association between diarrhea and detection of each pathogen was analyzed using a multivariate logistic regression model. More than a half of the fecal samples from the diarrheic calves had multiple pathogens. Statistically, BRV-A, BCoV, BNoV, Nebovirus, Salmonella, E. coli K99(+), and C. parvum were significantly associated with calf diarrhea (p<0.05). Among them, C. parvum and BRV-A were considered to be the most common enteric pathogens for calf diarrhea with high detection frequency (33.7% and 27.1%) and strong odds ratio (173 and 79.9). Unexpectedly BNoV (OR=2.0) and Nebovirus (OR=16.7) were identified with high frequency in diarrheic calves, suggesting these viruses may have a significant contribution to calf diarrhea.

Keywords: Calf diarrhea; Case–control study; Enteric pathogens; Multiplex PCR detection.

Fig. 1

Quantitative comparison of bovine norovirus (BNoV) and bovine coronavirus (BCoV) shedding in fecal samples from diarrheic (D) and healthy (H) calves. Mean (solid line) and median (dotted line) are shown on a boxplot with 50 percentile distribution. The lower and upper whiskers represent 10th and 90th percentile plot, resepctively, and dots represent outlayers. Virus shedding level between the 2 groups was compared based on Ct values by the non-parametric Wilcoxon rank-sum test.

Fig. 2

Age distribution of diarrheic calves whose feces were positive for one or more enteric pathogens. Animals are classified into 3 age groups: 0–4 weeks, 5–14 weeks and 15–34 weeks of age (A) based on the information provided by submitting veterinarians. Animals at 0–4 weeks of age are further broken down on the weekly basis after birth (B). BRV (bovine rotavirus), BCoV (bovine coronavirus), BVDV (bovine viral diarrhea virus), BEV (bovine enterovirus), BNoV (bovine norovirus), C. parvum (cryptosporidium parvum) and Cpt β (clostridium perfringens β toxin).

Fig. 3

Frequency (%) of concurrent infection in diarrheic (A) and healthy calves (B). Numbers (0–6) represent the number of pathogens concurrently detected within each fecal sample. Bovine enterovirus is not included in assessment.