Arboviral (or arbovirus): [noun]
Any of several groups of viruses that are transmitted by bloodsucking arthropods (insects) such as ticks, fleas, or mosquitoes. The term comes from arthropd (AR) borne (BO) virus (VIRUS).

Enzootic: [adjective]
Native to a place or a specific fauna. West Nile Virus (WNV) and Eastern Equine Enchephalitis (EEE) are considered enzootic viruses in Massachusetts.

Epizootic: [adjective]
A disease that appears as new cases in a given animal population, during a given period, at a rate that substantially exceeds what is "expected" based on recent experience (i.e. a sharp elevation in the incidence rate). "Epidemic" is the analogous term applied to human populations.

Vector: [noun]
An insect or other organism that transmits a pathogenic fungus, virus, bacterium, etc. Mosquitoes are vectors of WNV and EEE to humans and horses in Massachusetts.