Scientists discover link between birds and West Nile virus
A West Nile virus outbreak in 2010 was responsible for the deaths of 35 people in Greece. Can wild or migratory birds influence the import and increase of West Nile virus? A Greek-British team of researchers led by the University of Thessaly in Greece investigated whether they can, finding evidence that wild birds could have permitted West Nile virus maintenance and amplification before and during the virus outbreak two years ago. The study, presented in the Virology Journal, was funded in part by the WILDTECH ('Novel technologies for surveillance of emerging and re-emerging infections of wildlife') project, which has received EUR 6 million under the 'Food, Agriculture and Fisheries, and Biotechnology' (KBBE) Theme of the EU's Seventh Framework Programme (FP7).
The bite of infected mosquitoes spreads West Nile virus, a flavivirus of major public health concern. Scientists discovered West Nile virus in Uganda 75 years ago; it was sporadically reported up until the 1990s, after which disease outbreaks were reported across the globe. This resulted in West Nile virus being given epidemic status.
Past research demonstrated that humans infected with West Nile virus do not have viremia levels high enough to infect new mosquitoes and thus pass on the virus. But birds do develop viremia levels with the capacity to infect mosquitoes, thus serving as amplifying hosts for West Nile virus.
Dr Charalambos Billinis of the University of Thessaly and colleagues examined serum and tissue samples from 295 resident and migratory wild birds harvested by hunters before and during the 2010 outbreak. The researchers used immunofluorescence assays and virus neutralisation tests to evaluate samples for the presence of West Nile virus-specific antibodies. They identified 53 avian samples with West Nile virus neutralising antibodies. They collected 14 positive serum samples from birds up to 8 months prior to the human outbreak. The team found genetic determinants of increased virulence in these samples.
According to the researchers, the findings showed that wild birds contributed to West Nile virus maintenance and amplification prior to and during the outbreak.
'The finding that migratory birds were previously exposed to West Nile virus prior to their arrival in Greece during autumn migration suggests that avian species with similar migration traits could have introduced the virus into Greece,' co-author Dr Billinis said.
Commenting on the results of the study, journal Editor-in-Chief Linfa Wang said: 'This study shows the importance of wild bird surveillance for zoonotic diseases such as West Nile virus. It also demonstrates that pre-emergence surveillance in wildlife can be a powerful tool as part of an effective pre-warning system to prevent and/or reduce the impact of emerging zoonotic diseases. It is a great example of the need for a One Health approach to combat emerging infectious diseases.'