West Nile virus in the United States (1999-2005).

This research focuses on the spread and impact of West Nile Virus in the United States between 1999 and 2005, detailing its origins, transmission patterns, effects on different species, and the preventative measures available.

Introduction and History

• The study begins by outlining the accidental introduction of the West Nile Virus (WNV) in New York City in 1999. This disease originally came from the Old World, which typically refers to Africa, Asia, and Europe.
• The arrival of the virus triggered an epidemic among humans, horses, and birds that quickly spread from the east coast to the west coast within 3 years.

Transmission

• The research explains that WNV is primarily transmitted through the bite of infective mosquitoes to native birds susceptible to the virus in the US.
• These infected birds serve as “amplifying hosts”, allowing for the rapid spread of the virus due to the high concentration of the virus in their bloodstream, sufficient for passing the virus back to uninfected mosquitoes that feed on them.

Hosts and Disease Impact

• Although humans and horses can contract the disease and fall severely ill, the paper notes that they are regarded as “dead-end hosts” since considerably less virus is produced in their blood compared to birds, making them inefficient at transmitting the virus back to mosquitoes.
• Therefore, while the disease can lead to significant health problems in humans and horses, they do not contribute much to the wider transmission and spreading of the virus.

Prevention and Protection

• The study advises that the best way humans can protect themselves from the West Nile Virus exposure is by staying indoors during periods of high mosquito activity, and/or by using recommended repellents to prevent mosquito bites.
• For horses, effective vaccines against the West Nile Virus are available, which can help in preventing the disease in this species.