No Australian indicator for West Nile virus

Scientists at CSIRO’s Australian Animal Health Laboratory (AAHL) in Geelong, Victoria, have found that birds are unlikely to be used as part of an ‘early warning’ system for the deadly West Nile virus in Australia.

The AAHL research was part of an Australian Biosecurity Cooperative Research Centre (AB-CRC) for Emerging Infectious Disease program, focusing on finding effective methods for detecting West Nile virus in Australia.

While the zoonotic disease, West Nile virus, is not present in Australia, it has been reported for many years in eastern Mediterranean and southern European countries.

It was first detected in North America in 1999 — emerging in New York City and rapidly spreading to all 48 US states, Canada and Mexico. It’s estimated more than 200,000 people in the US have been infected with the virus.

The virus is transmitted to humans by infected mosquitoes and the reservoir host is a wide range of birds. The majority of infected humans display only mild flu-like symptoms or no symptoms at all. However, some individuals may suffer severe illness due to encephalitis, which may result in death.

Research leader, CSIRO’s Dr John Bingham, said in the US dead-bird surveillance is considered the most sensitive early detection system for the virus, with dead birds (mainly crows) appearing weeks before human cases.

The study aimed to determine if the early detection methods of dead-bird pick-ups was valid for the New York strain of West Nile virus in an Australian context.

“We couldn’t assume that West Nile virus would be highly lethal to Australian corvid species — ravens and crows — as has been observed in the US. Our bird species are different and we have a virus similar to West Nile — Kunjin virus — here already.

“Although it has not been reported to cause disease, Kunjin virus may confer immunity in birds to the highly pathogenic West Nile virus,” Bingham says.

The project investigated what happens when the common Australian little raven (Corvus mellori) was exposed to West Nile or Kunjin virus.

Dr Bingham says the study found Little Ravens were relatively resistant to the New York strain of West Nile virus and Kunjin virus.

“Unlike American corvids, who suffer high mortality rates when exposed to West Nile virus, the Australian ravens exposed to the virus showed only mild clinical signs and all infected birds recovered,” he said.

“This means Australia’s Little Raven could not be used as an early warning sentinel, indicating the presence of West Nile virus in Australia.”

The study also provided information which can be used to further validate AAHL’s diagnostic tests for the virus.

Researchers at Queensland Health are undertaking further work to help find an alternative early warning system for West Nile virus in Australia, based on examination of mosquitoes.