a1 Agriculture Canada, Health of Animals Laboratory Division, Halldon House, 2255 Carling Avenue, Ottawa, Ontario K1A 0Y9
a2 Environment Canada, Canadian Climate Centre, 4905 Dufferin Street, Downsview, Ontario M3H 5T4
Backward trajectories of winds were determined to identify possible sources of eastern equine encephalitis virus associated with isolation of virus from mosquitoes or birds or outbreaks in horses between 1980 and 1985 in Maryland, New Jersey, New York and Michigan, USA.
The results of the trajectory analyses suggested that eastern equine encephalitis virus could have been carried by infected mosquitoes on surface winds at temperatures 13 °C or higher from North Carolina north-eastwards along the Atlantic Coast to Maryland and New Jersey and thence to upstate New York and from western Kentucky to Michigan. Landing of mosquitoes was associated with the presence of a cold front and rain leading to variations in the location and timing of outbreaks from year to year. The mosquito responsible was most likely to have been Culiseta melanura, but Coquillettidia perturbans and Aedes sollicitans could also have been involved.
There may be a continual cycle of eastern equine encephalitis virus in mosquitoes and birds in south-eastern USA, from where the virus could be distributed by infected mosquitoes on the wind along the Gulf and Atlantic Coasts and up the Mississippi Valley.
(Accepted October 11 1989)