Laboratory Diagnosis of Viral Infections

Specific diagnoses of a viral infection are described in this chapter that are generally of five types: those that demonstrate the presence of infectious virus; those that detect viral antigens; those that detect viral nucleic acids; those that demonstrate the presence of an agent-specific antibody response; and those that directly visualize the virus. Most available routine tests are agent dependent—that is, they are designed to detect a specific virus and will give a negative test result even if other viruses are present in the sample. For this reason, agent-independent tests such as virus isolation and electron microscopy are still used to identify the unexpected or unknown agent in a clinical sample. Traditional methods such as virus isolation are still widely used; however, many are too slow to have any direct influence on the clinical management of an index case. For some economically important viruses, standardized diagnostic tests and reagents of good quality are available commercially; assays have been miniaturized to conserve reagents and decrease costs; instruments have been developed to automate tests, again often decreasing costs; and computerized analyses aid in making the interpretation of results as objective as possible in addition to facilitating reporting, record keeping, and billing. Respiratory diseases, diarrheal diseases of neonates, and some mucocutaneous diseases may be caused by a variety of different infectious agents, including viruses. Rapid and accurate identification of the causative agent can be the basis for establishing a management plan that prevents additional losses in the stable, kennel, flock, or herd.