EEE Spreading In US
Eastern equine encephalitis (EEE) season is now in full swing in the US. Cases are being reported in horses in several US states, including Florida, Georgia and Louisiana. Infected mosquitoes have been found over a wider range, including as far north as Massachusetts. That’s not particularly surprising because this seasonal mosquito-borne viral infection typically occurs at this time of year in eastern/southeastern coastal regions.
The risk of EEE varies greatly across North America. For EEE to be a problem:
- EEE virus must be present in birds in the area. Birds are the reservoir hosts and are not typically affected by the virus.
- Mosquito populations must be large enough to facilitate transmission of EEE virus between birds and from birds to horses (or humans).
- The types of mosquitoes that are present must be those that like to feed off both birds and horses/humans. These "bridging vector" mosquitoes are critical since they are the ones that allow the infection to spread beyond birds.
Not all mosquitoes are the same in terms of their feeding patterns and likelihood of carrying EEE virus and transmitting it from birds to horses and people. Not all bird species have the same likelihood of carrying EEE virus. These factors play an important role in explaining why EEE can be a major problem in some areas but not in others.
Photo: Aedes vexans, one of the mosquito species capable of transmitting EEE from birds to mammals (click image for source).
