Western equine encephalitis virus

A virus causing encephalitis in humans and horses

Western equine encephalitis virus (WEEV) is a mosquito-borne virus that causes encephalitis in humans and horses. It is a member of the genus Alphavirus and the family Togaviridae. The virus is primarily found in North America, particularly in the western United States and Canada.

Virology

WEEV is an enveloped virus with a single-stranded, positive-sense RNA genome. It is classified within the Alphavirus genus, which includes other encephalitic viruses such as Eastern equine encephalitis virus and Venezuelan equine encephalitis virus. The virus is transmitted to humans and horses through the bite of infected mosquitoes, primarily of the Culex species.

Transmission

The primary vector for WEEV is the Culex tarsalis mosquito, which breeds in irrigated fields and other areas with standing water. The virus is maintained in nature through a mosquito-bird-mosquito cycle, with birds serving as the primary reservoir hosts. Humans and horses are considered dead-end hosts because they do not develop high enough levels of viremia to infect mosquitoes.

Clinical Features

In humans, WEEV infection can range from mild febrile illness to severe encephalitis. Symptoms typically appear 5 to 10 days after exposure and may include fever, headache, nausea, vomiting, and neurological symptoms such as confusion, seizures, and coma. The disease is more severe in infants and the elderly.

In horses, WEEV infection can cause fever, depression, ataxia, and neurological signs such as circling, head pressing, and paralysis. Mortality rates in horses can be as high as 20-50%.

Diagnosis

Diagnosis of WEEV infection is based on clinical presentation and confirmed by laboratory testing. Serological tests such as ELISA and neutralization tests can detect specific antibodies against the virus. Polymerase chain reaction (PCR) can also be used to detect viral RNA in clinical samples.

Prevention and Control

Prevention of WEEV infection focuses on reducing exposure to mosquito bites. This includes using insect repellent, wearing protective clothing, and eliminating mosquito breeding sites. Vaccines are available for horses, but there is currently no vaccine for humans.

Epidemiology

WEEV is endemic in the western United States and Canada, with sporadic outbreaks occurring in humans and horses. The incidence of WEEV infection has decreased significantly in recent years, likely due to improved mosquito control measures and changes in agricultural practices.

Related pages

• Eastern equine encephalitis virus
• Venezuelan equine encephalitis virus
• Alphavirus
• Togaviridae
• Mosquito-borne diseases