ABSTRACT
274What is a virus and what is a viral infection? Whether or not viruses represent a life form may be a question of a philosophical nature, but viruses in general have a tremendous replication potential when the conditions are right. In contrast to bacteria, they are not cells and they do not generate energy, and thus they are dependent on being inside a host cell to replicate. Their ability to survive, or stay infective, in the environment outside host cells over time is thus, in general, limited, although some viruses are more robust than others. Every virus family has its specific strategy for replication. When they replicate, they basically take over the metabolic machinery of the host cell, and reprogram it to produce thousands of copies of the virus. Most viral infections are asymptomatic, meaning that in spite of the fact that the virus may replicate and produce many progeny (virus particles), the host copes with the infection and manages to balance and compensate, and can often clear the viral infection. However, depending on the type of virus, the infected host and cell type, immune response and many other factors, some viral infections results in disease: the virus impacts the host cells to such a degree that normal functions cannot be sustained. If many cells are infected, or the whole organ, such as the lungs, the liver or the kidneys, the infection may introduce a deficiency of the normal function of the organ, producing disease symptoms, such as difficult breathing, or liver or kidney deficiency. Viruses also have different strategies for transmission, and whereas some viruses establish chronic infections, latency and integration of their genome in the genome of their host, such as HIV and herpesviruses, other viruses have a “hit and run” strategy, with a quick spread to new hosts, even before the onset of clinical symptoms, as is the case for foot and mouth disease virus and others. Based on the nature of the virus and the host, different strategies are needed to be able to avoid, detect, monitor and control viral infections. Viruses are not susceptible to antibiotics used against bacterial diseases, and there are only a few anti-viral drugs against a very restricted repertoire of viruses on the market, such as HIV and herpesviruses. These drugs are mostly used in human medicine, although some anti-viral treatments also have been investigated for domestic animals.
