Florida is the epicentre of a re-emerging, viral brain disease that has spread as far north as Canada, according to chickens in the area.

The birds, known as sentinel chickens, were tested for antibodies to eastern equine encephalitis virus (EEEV), an insect-borne disease that can become neuroinvasive.

Only 70 human cases have been reported since 2008, but EEEV has a 30% mortality rate, and often leaves survivors with lifelong neurological impairment.

Writing in The American Journal of Tropical Medicine and Hygiene, Researchers led by Suman Das of Vanderbilt University, Tennessee, US, conclude that the panhandle of Florida has a sustained, year-round presence of the virus and is the likely source of outbreaks, although other areas of Florida show seasonal activity.

According to the US Centres for Disease Control (CDC), the disease has re-emerged in the past two decades, although it is not immediately clear why. From 2004 to 2007, the northern states of Massachusetts and New Hampshire experienced “overlapping epidemics.” In 2012, Massachusetts had its greatest number of deaths from the disease since the 1950s, while Vermont, another northern state, recorded its first-ever death from the disease.{%recommended 8372%}

With its hot, humid climate and prolific mosquito populations, Florida can claim a number of vector-borne diseases, including EEEV and West Nile Virus. For this reason, in 1978, the state started a “sentinel chicken” program.

Under the scheme, captive chickens are regularly tested for antibodies to a range of viruses. The birds do not show symptoms, but develop antibodies within two weeks, providing the state with a kind of early alert system before human or equine cases break out.

“If the [chicken] lab results are positive the health department generates action notices to the public on the cited mosquito activity and recommends implementation of precautionary measures to diminish the exposure,” says Florida’s Brevard County website.

Das and colleagues found that the peaks of positive results in the chickens coincided “with many peaks in human and equine cases in Florida and the United States, but the correspondence was not perfect”.

The researchers suggest that in years with high rates of the disease in chickens, but no outbreaks, preventative measures may have succeeded. Years with low incidence in chickens but peaks in human and equine cases “may indicate program shortcomings,” they write.

Narrowing the geographic locus of activity to the Panhandle gives health officials a clear target for preventative action.