Abstract
The first methods for detection of bacterial infections were available around 1880. After staining, bacterial pathogens were recognized in the light microscope because of their size and could be cultivated in culture media. Viruses evaded this approach, as they are significantly smaller, and as obligate parasites are not able to multiply in cell culture media. Although some viral infections could be associated with specific cellular changes and certain depositions in the infected tissue around the turn of the century, e.g. Negri inclusion bodies in nerve cells during rabies, a specific diagnosis was only possible through the development of cell culture methods and modern molecular biology. Today, viral infections can be detected directly by determining the agents, individual viral proteins, or their genetic information, or other materials in the blood of infected people or animals by using appropriate methods. Direct detection of viruses is possible, with the exception of latent or persistent infection forms, only during the acute phase of the disease. In some cases, the pathogens are present in the infected organism only before the symptomatic phase, so the direct detection of the virus is frequently not successful. Therefore, infections or contact with pathogens is usually demonstrated in virus diagnostics indirectly by characterization of the developing specific immune response.