Transboundary Emerging and Exotic Animal Disease/ Exotic Animal Disease Practice Exam

In endemic areas, West Nile virus primarily cycles between which two groups?

1. Birds and mosquitoes

2. Horses and humans

3. Mosquitoes and reptiles

4. Humans and birds

The correct answer is: Birds and mosquitoes

In endemic areas, the primary transmission cycle of the West Nile virus involves birds and mosquitoes. This relationship is crucial because birds serve as the key amplifying hosts for the virus. When mosquitoes bite infected birds, they acquire the virus and can subsequently transmit it to other birds and, occasionally, to mammals, including horses and humans. Birds are particularly effective at hosting the virus due to their ability to spread it rapidly through their populations, while mosquitoes are the vectors that facilitate the transmission. This cycle is why birds and mosquitoes form the basis of West Nile virus ecology in endemic regions. While the other choices involve different species interacting with the virus, they do not represent the primary cyclical relationship that drives the transmission in endemic areas. For example, while horses can become infected with West Nile virus, they do not play a significant role in its transmission cycle; instead, they are considered dead-end hosts. Humans likewise do not significantly contribute to the virus's lifecycle in terms of transmission because they don’t spread the virus to mosquitoes effectively. Thus, the association between birds and mosquitoes is central to understanding how West Nile virus persists and spreads in affected regions.