Why West Nile virus is more dangerous in the elderly

West Nile virus (WNV) is particularly dangerous in older people, who account for a large number of severe cases and deaths caused by the virus, says a study.

Several critical components of the early immune response to the virus are impaired in elderly individuals, and that this can explain their vulnerability.

A mosquito-borne virus, the WNV infection turns serious when the virus crosses the blood-brain-barrier and wreaks havoc among nerve cells in the brain.

The study outlined in PlOS Pathogens suggests that several critical components of the early immune response to the virus are impaired in elderly individuals, and hence they are vulnerable.

"We have identified a series of key early defects associated with immune responses in old animals," said lead author Michael Diamond, from Washington University in Saint Louis.

The team analysed and compared the immune response to WNV infection in four-month-old (the equivalent of young adults) and 18-month-old (elderly) mice.

The older mice were more than three times as likely to die after WNV infection. In addition, to more virus in their blood and spleens, the older mice had 20-fold higher virus levels in their brains--which likely causes the excess deaths.

Older mice had less potent WNV-specific antibody responses during the early phase of infection. They also had weaker long-term antibody memory responses, the authors said.