Synonyms: EE, EEE, WEE
Note: This disease should not be confused with St. Louis Encephalits (SLE). Chickens are used as sentinels (test animals) in SLE suspect areas, such as southern Florida.
While SLE is also carried by mosquitos, that is where the similarities between the two encephalitis diseases end. Chickens do not get SLE. Refer to Factsheet VM71 (St. Louis Encephalitis—The Role of Chickens) for more information on SLE.
Species affected: Equine encephalitis is a contagious disease of birds (especially pheasants), mammals (especially horses), and people. Birds are the major source of the virus.
Clinical signs: Two forms affect birds: eastern equine encephalitis (EEE) and western equine encephalitis (WEE). The clinical signs are identical and include reduced feed consumption, staggering, and paralysis. Surviving birds may be blind, have muscle paralysis, and have difficulty holding their head up. Damage to the bird’s nervous system varies with species. In pheasants, there is pronounced leg paralysis, twisting of the neck, and tremors. Mortality is high. Chukar partridges and turkeys show drowsiness, paralysis, weakness, and death (see Table 2).
Transmission: Infected mosquitoes are the primary source of the virus. The Culiseta melanuria mosquito is the primary transmitter of the virus to poultry. Other mosquito species transmit the disease too, but feed mostly on other animals. Cannibalism of sick or dead birds by penmates is a major source of transmission within pens.
Prevention: Remove the source of infection by establishing mosquito control: keep weeds mowed in a 50-foot strip around bird pens. This removes cover and resting areas for mosquitos. Eliminate mosquito breeding areas. Fog areas with malathion. It is possible to immunize birds, especially pheasants, with the vaccine prepared for horses. The recommended dose is one-tenth of a horse dose per bird.
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