1 Viral infections
All viruses are small packages containing the genetic information needed to replicate themselves, but they can only do so by infecting cells of a host organism. However, beyond this basic description, viruses are enormously variable. Often they produce damage or disease in their host, including humans, and for this reason they are a very important group of pathogens.
It would be impossible in a short course to cover the great range of viruses that cause disease in humans. However, we can look at the life-cycle of a typical virus infection in Video 2.
Download this video clip.Video player: Video 2 Life-cycle of a typical virus infection
Transcript: Video 2 Life-cycle of a typical virus infection
DAVID MALE:
The diagram shows a generalised virus life-cycle. In step-1: A virus infects a cell by attaching to receptors on the cell surface and entering the cell. The virus is first taken into the cell in a vesicle called an endosome. The surface proteins of the virus fuses with the membrane of the endosome, releasing the virus’ genetic material into the cell. In step-2: The viral genome is replicated and viral proteins are synthesised by hijacking the cell’s machinery for replicating nucleic acids (DNA or RNA) and synthesising proteins. In step-3: New viruses are assembled within the infected cell, by packaging the viral genome inside new viral particles. Step-4 shows the new virus particles being released by budding from the surface of the infected cell, or in some cases directly killing the infected cell to allow escape. The virus can now spread to new cells within the host, or to a new host.
Video 2 Life-cycle of a typical virus infection
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