Fever that follows viral infection is believed to be a defence mechanism of the body. High temperature is thought to harm virus more than the host. However, researchers at the University of Oxford, UK, have discovered that one virus has a chilling effect on the defences of the host.
Vaccinia virus, used to vaccinate people against smallpox, releases a protein that actually brings down the body temperature. When researchers infected mice with large doses of Vaccinia, expecting the animals to become feverish, their temperatures dropped instead, by 1C.
They assume that the virus releases protein receptors that mop up cytokine interleukin-1B from blood circulation. Cytokines are a group of signalling molecules which help organise the body's defences against infection, and are suspected to trigger fever in the infected person. According to immunopathologists, this discovery might imply that some viral infections go unrecognised because there is no fever associated with them (New Scientist, Vol 151, No 2051).