What causes viruses to be infectious?

Viruses are parasites -- they constantly need host cells to function. That’s why it is hard to categorize them as either living or non-living things. So how do these pesky parasites perform the dynamic activity of causing dangerous infections?

Viruses are basically just a set of genetic material, surrounded by a cover of protein. They do not perform any other biochemical functions except reproduction, so they can live for years without a host cell. But to reproduce, they must have a host cell.

When viruses are expelled from other host cells, say for instance, due to a sneeze, they immediately look for other hosts to carry on with their reproduction. They enter through our nose, mouth or open wounds and start looking for the right host cell to infect. Once they find their way to the right host cells, they either dissolve into them or attach themselves to the hosts and start releasing their genetic material into them. They start taking over the cell’s enzymes and begin to replicate their own genetic material. Once the new viruses are formed, they break free from the host cell and start attacking other cells. This way, they infect the whole body.

Some viruses such as the HIV do not reproduce immediately but wait for the host cell to reproduce and then they begin reproduction, so that the viral genetic material gets copied into the offspring of the host. That is why a person infected with HIV can live without showing symptoms of AIDS for years, but they can still spread the virus to others.

Resources:

Learn more about why viruses cause infection.

Further details about viruses and infection, with diagrams.

Learn how to prevent viruses and infection.

June 7, 2003