Where is the NWS virus found?

The NWS virus, also known as the West Nile Virus, is primarily found in North America, where it has been extensively studied since its introduction. The virus is mainly transmitted by mosquitoes and can affect both humans and animals. While other regions have mosquito-borne viruses, the NWS virus specifically is most notorious for its presence in North America, particularly in the summer months when the risk of transmission is highest.

The other options represent regions where different mosquito-borne diseases may be prevalent, but they do not specifically pertain to the NWS virus. In Europe and Asia, for instance, there are other flaviviruses, but these are not the same as the NWS virus. Hence, the best context for the presence of the NWS virus is found primarily in North America.