Spillover: Animal Infections and the Next Human Pandemic

by David Quammen

But viruses aren’t all roundish. Some are cylindrical, some are stringy, some look like bad futuristic buildings or lunar landing modules. Whatever the shape, the interior volume is minuscule. The genomes packed within such small containers are correspondingly limited, ranging from 2,000 nucleotides up to about 1.2 million. The genome of a mouse, by contrast, is about 3 billion nucleotides. It takes three nucleotide bases to specify an amino acid and on average about 250 amino acids to make a protein (though some proteins are much larger). Making proteins is what genes do; everything else in a cell or a virus results from secondary reactions. So a genome of just two thousand code letters, or even thirteen thousand (as for the influenzas) or thirty thousand (the SARS virus), is a very sketchy set of engineering specs. Even with such a small genome, though, coding for just eight or ten proteins, a virus can be wily and effective.