Evaluation of bovine coronavirus in Korean native calves challenged through different inoculation routes

Abstract

Bovine coronavirus (BCoV) is a pneumoenteric virus that can infect the digestive and respiratory tracts of cattle, resulting in economic losses. Despite its significance, information regarding BCoV pathogenesis is limited. Hence, we investigated clinical signs, patterns of viral shedding, changes in antibody abundance, and cytokine/chemokine production in calves inoculated with BCoV via intranasal and oral. Six clinically healthy Korean native calves (< 30 days old), initially negative for BCoV, were divided into intranasal and oral groups and monitored for 15 days post-infection (dpi). BCoV-infected calves exhibited clinical signs such as nasal discharge and diarrhea, starting at 3 dpi and recovering by 12 dpi, with nasal discharge being the most common symptoms. Viral RNA was detected in nasal and fecal samples from all infected calves. Nasal shedding occurred before fecal shedding regardless of the inoculation route; however, fecal shedding persisted longer. Although the number of partitions was very few, viral RNA was identified in the blood of two calves in the oral group at 7 dpi and 9 dpi using digital RT-PCR analysis. The effectiveness of maternal antibodies in preventing viral replication and shedding appeared limited. Our results showed interleukin (IL)-8 as the most common and highly induced chemokine. During BCoV infection, the levels of IL-8, monocyte chemoattractant protein-1, and macrophage inflammatory protein-1β were significantly affected, suggesting that these emerge as potential and reliable biomarkers for predicting BCoV infection. This study underscores the importance of BCoV as a major pathogen causing diarrhea and respiratory disease.

Keywords: Bovine coronavirus; inoculation route; interleukin-8; nasal discharge; virus shedding.

Figure 1

Comparison of bovine coronavirus (BCoV) shedding patterns from nasal (A) and rectal (B) swabs between the IN (intranasal; white circle) and oral (black square) groups. Real-time RT-PCR targeting the nucleocapsid gene was performed, and Ct values of ≤ 30 were considered positive.

Figure 2

Serum levels of anti-bovine coronavirus antibodies in calves infected through different inoculation routes. Data are presented as the mean ± SD of each time point. The IN (intranasal) and oral groups are indicated by white and black boxes, respectively.

Figure 3

Cytokine/chemokine concentrations of IL-8 (A), IFN-γ (B), IL-6 (C), IL-10 (D), IL-17A (E), IL-36RA (F), IP-10 (G), MCP-1 (H), MIP-1β (I), and VEGF-A (J) in the serum of calves after bovine coronavirus infection between the IN (intranasal; white box) and oral (black box) groups. Data are presented as the mean ± SD of each time point. Statistical analyses were performed using two-way ANOVA with repeated measures. Significance levels are indicated by *p < 0.05, **p < 0.01, and *** p < 0.001.