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

Cho, Yong-il; Yoon, Kyoung-Jin

Calf diarrhea has been a major disease that negatively affects the cattle industry. The economic impact caused by this condition is significant although many new intervention strategies (e.g., vaccine, medications, and herd management) have been developed and implemented to minimize the economic loss. Persistence of this significant problem in the field may be attributed to the multifactorial nature of calf diarrhea including permutations of infectious diseases, a failure to clearly understand the disease ecology, poor environmental hygiene, and biased epidemiological data. Genetic diversity, continuous evolution, emerging pathogens, and/or environmental ubiquity of pathogens are factors that hinder effective control of the disease. Therefore, the genetic evolution of RNA viral pathogens such as BRV, BCoV, BVDV, BToV, BNoV, and Nebovirus should be kept in mind and monitored with regular genomic sequence updates. Non-group A BRV might be considered for future studies to increase the detection range of calf enteric pathogens. Emerging viruses should be regularly monitored for the evaluation of vaccines against calf enteric pathogens. Clinical significance of caliciviruses (BNoV and Nebovirus) must be carefully assessed to better control calf diarrhea in the future. The use of highly sensitive diagnostic tests has increased the detection frequency of pathogens that were previously neglected. Therefore, optimized and appropriate diagnostic methods or platforms should be employed for detecting target pathogens in an accurate and timely manner with a minimum testing outcome bias. Currently, real-time PCR-based techniques are widely implemented in many veterinary diagnostic laboratories. These methods are highly accurate and provide high throughput performance but sometimes might overestimate the significance of pathogens detected in cases of calf diarrhea. The pros and cons of diagnostic test results and their overall interpretation must therefore be cautiously evaluated by referring clinical history from practitioner when the causative etiology is being determined. Non-infectious risk factors have frequently been neglected by cattle producers, and also be considered equally important as infectious factors because the newborn animals are vulnerable to environmental stresses. The management and control of calf diarrhea before an outbreak is more cost-efficient than treating sick animals after the outbreak occurs. Although many enteric pathogens are involved in calf diarrhea, infection and transmission is accomplished via a fecal-oral route. Care must be thus taken to prevent pathogen transmission. Advice from professional consultants such as veterinarians and nutritionists is necessary to obtain an accurate diagnosis and control or manage risk factors associated with calf diarrhea in modernized large production systems. In summary, the effective control of calf diarrhea should be based on three major points. First, a clear understanding of pathogen characteristics (e.g., mechanism underlying pathogenicity, prevalence in the field, and genetic evolution) is required. Second, advantages and disadvantages of various diagnostic methods and their application to diagnostic investigation along with clinical history should be considered. Finally, proper cow-calf management is necessary for disease prevention and control.