Final answer:
EEE and WEE are severe diseases in horses caused by viruses and transmitted primarily through the bite of infected mosquitoes, with birds as reservoirs.
Step-by-step explanation:
Eastern equine encephalitis (EEE) is a severe disease in horses and humans caused by the Eastern equine encephalitis virus (EEEV).
The primary mode of transmission is accidental through the bite of infected mosquitoes, most commonly the Aedes, Coquillettidia, and Culex species. Birds serve as reservoirs of EEEV, and neither horses nor humans are reservoirs themselves, making them incidental hosts. While cases of EEE have been noted primarily along the US Gulf Coast and Atlantic states, it remains a very rare disease in the United States.
Similarly, Western equine encephalitis (WEE), caused by Western equine encephalitis virus (WEEV), predominantly spreads to horses and humans via Culex tarsalis mosquitoes. Once again, birds act as the natural reservoir for the WEEV. Although WEE is less severe than EEE, it still poses a risk to horses and humans.