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

Cho, Yong-il; Yoon, Kyoung-Jin

The virus isolation test is still considered the 'gold standard' for detecting viral pathogens in specimens [114] although new methods such as an ELISA and PCR-based tests have been developed. Cell culture techniques are commonly used to isolate virus for diagnostic purposes as well as virus propagation for vaccine production or further virus characterization procedures such as antigenic variation determination or gene sequencing [117] . Several cell lines (e.g., Madin Darby Bovine Kidney [MDBK], human rectal tumor HRT-18, and African green monkey kidney MA104 cells) are used for certain viruses due to variations in viral susceptibility of the different cells [1, 140] . Embryonating eggs and laboratory animals are also used for isolating and propagating viruses which do not grow in cells in vitro (this is the case for many enteric pathogens) or increasing viral production. The viability of target viruses in a specimen is critical for successful virus isolation [121] . Specimens should be kept at a low temperature and in transport medium during shipping to a diagnostic laboratory and delivered to the lab as soon as possible after collection. The virus isolation test is a confirmatory method; however, it takes a time to prepare the cells and propagate the virus (i.e., slow turnaround of the results). This technique is therefore laborious and expensive compared to an ELISA or PCR.