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

Cho, Yong-il; Yoon, Kyoung-Jin

Electron microscopy is commonly used for virus detection and identification based on morphological characteristics. There are two types of EM: direct EM and immuno-electron microscopy (IEM) [12] . Two different staining techniques (positive and negative staining) are performed to visualize the target. For direct EM, virus particles in a fluidal sample matrix are applied directly to a solid support and then visualized after a contrast stain is applied. This procedure is commonly referred to as "negative staining EM" whereas positive staining is generally used for thin-section EM of fixed tissues. Direct EM is not a specific test as this technique is performed to simply visualize viruses in samples and is not considered to be a sensitive procedure. In comparison, IEM has greater sensitivity than direct EM since the specimen is incubated with antibody specific for the target virus in order to agglutinate the virus before staining. The visualization of viruses, particularly ones not amenable to cultivation, is a major advantage for EM with rapid turnaround. Most bovine enteric viruses such as BNoV, Nebovirus, BRV, BToV, and BCoV are difficult to isolate or propagate in cell cultures, but these pathogens can be differentiated according to their unique morphology (both shape and size) under an electron microscope [29] . EM requires a large number of virus particles (approximately 10 4