Human viruses: discovery and emergence

Woolhouse, Mark; Scott, Fiona; Hudson, Zoe; Howey, Richard; Chase-Topping, Margo

The result is shown in figure 4 . The most striking feature of the plot is that there are no examples of human viruses with broad host ranges that do not use highly conserved cell receptors (i.e. more than 90% amino acid sequence homology). Statistical analyses requires correction for phylogenetic correlation: viruses in the same family are both more likely to use the same cell receptor and more likely to have a narrow or broad host range. This can be crudely (but conservatively) allowed for by testing for an association between host range and receptor homology at the family, not species, level. This gives a statistically significant result (x 2 1 ¼ 5:86, p ¼ 0.015). We conclude that the use of a conserved receptor is a necessary but not sufficient condition for a virus to have a broad host range encompassing different mammalian orders. It follows that a useful piece of knowledge about a novel mammalian virus, helping to predict whether or not it poses a risk to humans, would be to identify the cell receptor it uses. However, this may not always be practicable: at present, we do not know the cell receptor used by over half the viruses that infect humans, and this fraction is considerably smaller for those that infect other mammals.