Influenza, Hepatitis and AIDS are known examples of prevalent infectious diseases in the Netherlands. Dengue, hantavirus and West-Nile are examples of viruses that infect people in Africa, Asia and South-America. The impact of a virus is almost unbelievable, given its incredibly small size.
But what is a virus exactly? The word ‘virus’ was introduced in 1899 by a Dutchman, the microbiologist Martinus Beijerinck, from Amsterdam. But it was not until 1933, when the first electron microscope was used, that we could make viruses visible.
Viruses are very small in size: their diameter differs from 20 to 400 nanometer (1 nanometer is a millimeter divided by a million). For example: the diameter of an influenza virus is 80 to 100 nanometer. A virus is not just very small, but it also depends on other micro-organisms to replicate. So officially a virus is not a living organism. But if it gets into the right host cell, the virus will become active. It takes over the metabolism of that cell to produce new virus particles. That can finally lead to destruction of the host cell. When that happens, the person gets ill and we speak about infection.