VIRAL AGENTS

Viruses are the simplest type of microorganism and consist of a nucleocapsid protein coat containing genetic material, either RNA or DNA. In some cases the virus particle is also surrounded by an outer layer of lipids. Viruses are much smaller than bacteria and vary in size from 0.02 m m to 0.2 m m (1 m m = 1/1000 mm). Viruses lack a system for their own metabolism and are therefore dependent on the synthetic machinery of their host cells: viruses are thus intracellular parasites. This also means that the virus, unlike the bacterium, cannot be cultivated in synthetic nutritive solutions but requires living cells in order to multiply. The host cells can be from human beings, animals, plants, or bacteria. Every virus needs its own special type of host cell because a complicated interaction is required between the cell and virus if the virus is to be able to multiply. Many virus-specific host cells can be cultivated in synthetic nutrient solutions and afterwards can be infected with the virus in question. Another usual way of cultivating viruses is to let them grow on chorioallantoic membranes (from fertilized eggs). The cultivation of viruses is costly, demanding, and time-consuming. A virus normally brings about changes in the host cell such that the cell dies. This handbook will cover a virus considered by some to be the most likely viral agent that would be used in a BW attack, the alpha virus that causes Venezuelan equine encephalitis, known as VEE. We also discuss smallpox and hemorrhagic fever viruses which could potentially be employed as BW agents.