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

It is unknown how West Nile virus entered the U.S. in 1999. What would be the most likely source(s) for its introduction?

1. Infected humans

2. Infected horses

3. Any infected mammal

4. Infected mosquitoes and birds

The correct answer is: Infected mosquitoes and birds

The introduction of West Nile virus into the U.S. in 1999 is most likely attributed to infected mosquitoes and birds. West Nile virus is primarily transmitted through a vector-borne transmission cycle involving mosquitoes acting as the primary vector, which can then infect avian hosts, commonly birds. Birds are considered the amplifying hosts of the virus, and specific species, such as crows and jays, have been found to be particularly susceptible to severe illness from the virus. Infected mosquitoes, particularly those from the genus Culex, are capable of transmitting the virus while feeding on infected birds. When the mosquito bites an infected bird, it acquires the virus and can later transmit it to other birds or even to mammals, including humans and horses, during subsequent feedings. This dual role of mosquitoes and birds in the disease cycle is crucial, as it allows for the maintenance and spread of the virus in new areas. While infected humans and horses can contract the virus, they do not play a significant role in its introduction or as reservoirs for further transmission. Therefore, the most plausible sources of introduction for West Nile virus into the United States are the interactions between infected mosquitoes and birds, which facilitate the cycle of transmission and spread of the virus in