Viruses have been described as “organisms at the edge of life”, unable to reproduce outside the cells of those they infect. But this status has not impeded their evolutionary success. Children, in particular, experience a multitude of viral illnesses during their early years, which gradually reduce over time as their natural immunity develops.
Viral infections may be fleeting (think influenza) or chronic (HIV, for instance), affecting various parts of the body to cause a diverse array of symptoms. These differences have important implications for the spread of that particular viral disease.
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