VIRUSES AND DISEASES

Examples of common human diseases caused by viruses include the common cold, flu, chicken pox, polio, measles, mumps and rubella. Among the major diseases are caused by the Ebola virus, AIDS, avian flu and SARS. Other diseases are polio, mumps, rubella, hepatitis B, hepatitis C, yellow fever, dengue fever, smallpox (eradicated), and so on. Some diseases are under investigation to determine if they have a virus as the causative agent, for example, human herpesvirus-6 (HHV6) could be related to neurological diseases such as multiple sclerosis and chronic fatigue syndrome. It is also investigating whether the Borna virus, which causes neurological disease in horses, could be responsible for psychiatric illness in humans.

The relative ability of the virus to cause disease is described in terms of virulence. The viruses cause disease in the host through different mechanisms that rely heavily on the kind of virus. The mechanisms at the cellular level include mainly the analysis and subsequent cell death. In pluricellular agencies, if enough cells die, the whole body will start to be affected. The virus may also exist within a relatively ineffective body. This is called latent and is a feature of herpesvirus including the herpes simplex virus, which causes cold sores, the Epstein-Barr virus, which causes glandular fever, and varicella-zoster virus, which causes chickenpox. The chickenpox virus, after the disease returns in later life as shingles.

Some viruses can cause chronic infections, in which the virus is still replicating in the body, despite the host's defense mechanisms.This is a common infection of hepatitis B and hepatitis C. People chronically infected with hepatitis B virus serve as reservoirs of the virus (are carriers). When there is a high proportion of carriers in a population, it is said that the disease is endemic.