Eastern and Western Equine Encephalitis

Equine Encephalitis Equine encephalitis is a virus us humans in south texas are exposed to through the abundance of a common vector, mosquitos. Mosquitos are known to be the most obligatory biological vector for transmitting these viruses. Of the three different types of “Group A” arboviruses, the eastern equine encephalitis and western equine encephalitis are the ones native to our area and can also cause febrile disease in humans and horses. EEV also utilizes hosts in two different way. One being a reservoir host (wild birds, rodents) and the other is a “dead end” host(horses, humans). The clinical disease occurs when the virus begins to replicate on site of the bite and the proceeds to enter the blood stream and begins attacking the central nervous system. While cases in humans and horses are rare, it is important especially in our region where the vectors are active, to know the method of transmission, common vectors and hosts, as well as the maintenance and spread of the EEEV and WEEEV. Eastern equine encephalitis is known to be a disease of wild birds and can be found near wetland habitats. Typically very rare because in the united states there have only been five to ten cases reported per year with the first case being recognized in1938. In the U.S EEEV is most common east of the Mississippi where the environment is woody and adjacent to swamps and marshes. In the regions relevant to south texas and the gulf coastal areas, the EEE virus is an antigenic variant of the strains in the Northern regions. The mortality rate for EEEV in horses is up to almost 90% but for humans who contract the disease mortality can be as high as 65% and survivors experience serious brain damage. It is contracted through the mosquito as it bites other animals hosting the virus and then bites the human. However, for EEEV, the particular mosquito vector (Culiseta spp) are specifically involved in the cycle amoung birds whereas humans are more likely to contract the virus from