The infection reservoir for arthropod-borne viral encephalitis is generally accepted to be:

The correct answer is that the infection reservoir for arthropod-borne viral encephalitis is generally accepted to be birds.

Birds play a critical role in the transmission cycle of many arthropod-borne viruses, such as those causing West Nile virus and Eastern equine encephalitis. They serve as primary amplifying hosts for these viruses, allowing them to replicate to high enough levels that when mosquitos feed on them, the virus is able to be transmitted to other hosts, including humans and horses. This ecological dynamic is crucial for the cycle of infection, as it enables the continuation of the virus's presence in the environment.

In contrast, while horses and humans can be hosts for certain types of arboviruses, they are not considered reservoirs because they do not sustain the virus populations; their infections lead to disease and don't effectively contribute to further transmission. Fish, on the other hand, do not have any known role in the transmission of arthropod-borne viruses. Thus, birds are recognized as the primary reservoirs due to their ability to harbor and propagate the virus, making them essential for the ecology of arthropod-borne viral encephalitis.