An overview of calf diarrhea - infectious etiology, diagnosis, and intervention

Cho, Yong-il; Yoon, Kyoung-Jin

The clinical symptoms of BVDV infection vary from subclinical to fatal disease depending upon host immune status, pregnancy and gestation period, and the presence or absence of co-infection with other pathogens. Most infected animals develop mild clinical signs such as low-grade fever, leukopenia, anorexia, and decreased milk production. Acute BVD infection is characterized by diarrhea, pyrexia, depression, anorexia, decreased milk production, oral ulcerations, hemorrhagic syndrome, and lymphopenia/leucopenia leading to immunosuppression [2] . Immunosuppressed cattle become susceptible to other diseases due to the concurrent infection with other pathogens (e.g., bovine respiratory disease complex). Although most immunocompetent animals eventually clear the virus and recover from the disease, some infected cattle occasionally harbor the virus for a long time with periodical appearance of transiently detectable viremia from time to time (i.e., transiently infected animals). Pregnant cows and heifers deliver persistently infected (PI) calves if they are exposed to a noncytopathic BVDV during 45∼125 days of gestation since the fetus is not immunocompetent. Most PI calves are born weak and susceptible to other pathogens, and experience poor growth. The PI animals also develop fatal "mucosal disease" when exposed to either exogenous or endogenous cytopathic BVDV [11] . Mucosal disease is clinically characterized by mucosal ulceration, vesicle formation, erosions, diarrhea, and death. BVDV can cause calf diarrhea in two major ways: 1) persistent infection resulting in primary damage to enterocytes and susceptibility to co-infection, or 2) transient infection with replication in crypt enterocytes and lesion formation contributing to diarrhea.