Outbreak of "Winter Dysentery" (Bovine Coronavirus, BCoV) infection in dairy cows housed in a farm in Sicily

Introduction - Bovine Coronavirus (BCoV) is an important pathogen of livestock that causes an enteric and respiratory disease in cattle (Winter Dysentery) and calves (Neonatal Calf Diarrhea). The BCoV infection rarely causes death but shows high morbidity (up to 100%) that induces economic losses in farms. Aim - This paper describes a case of BCoV infection occurred on December 2016 in a high milk production farm, placed in Ragusa (Sicily, Italy). Materials and methods - All bovines farmed (nr. 150 subjects) showed hyperthermia (41 degrees C), watery dysentery mixed to blood and fibrin, buccal and gengival erosions, high reduction of milk production. Four days before the appearance of these symptoms, the involved animals had been vaccinated with a delete vaccine against Bovine Viral Diarrhea Virus (BVDV). Whole blood, sera, feces and nasal swabs were collected from 15 animals that showed more severe symptoms. Serological (ELISA) and Virological tests (RT-PCR, Real Time RT-PCR, ELISA) were carried out to detect BCoV, Rotavirus, BVDV, Bluetongue Virus (BTV), Infectious Bovine Rhinotracheitis/Infectious Pustular Vulvovaginitis Virus (IBR/IPV), Herpes Bovine Virus type 4 (BHV4), Bovine Respiratory Syncytial Virus (BRSV) and Schmallenberg Virus (SBV). Feces were also analyzed for BCoV detection through Immunoelectron Microscopy (IEM). Results and discussion - Blood and swabs samples gave negative results for all virological tests. All feces samples resulted positives for BCoV by Semi Nested RT-PCR but they resulted negative by ELISA. Viral particles, referable to BCoV, were also observed at IEM. Serological tests gave positive results for Rotavirus, BVDV, IBR/IPV, VRSB, BHV4. In this study, BCoV was the only etiological agent detected in feces collected from cows affected by severe clinical signs. RT-PCR and IEM were found to be two reliable methods for the diagnosis of BCoV, showing a greater sensitivity than ELISA. Serological positivity detected for IBR/IPV, BTV, BVDV, BHV4 and VRSB were connected to previous vaccinations, while, the presence of antibodies against Rotavirus showed previous circulation of this virus in farm. Conclusions - BCoV infection, usually referred as "Winter Dysentery" (WD) is also reported as "Conditioned Disease" because it is induced by various stressors. Vaccination against BVDV could have been one of the putative stressor, responsible for the disease. Although BCoV infection has had a benign evolution, without mortality in affected animals, it has caused significant economic losses. Therefore, a control of stressors and a correct management of animal welfare represent the only valid prevention tool.