West Nile is transmitted to humans by mosquitoes that have fed on birds infected with the virus. In rare instances, the virus may spread in other ways. The disease affects the nervous system, and the majority of people infected will not exhibit any signs of illness. But those with health conditions could become seriously ill, officials point out.

Massachusetts sees an increased risk of West Nile virus and EEE in several communities, prompting health officials to encourage protective measures.

Record activity this summer involving two mosquito-borne diseases—chikungunya and West Nile virus (WNV)—suggests the European region is entering a new normal, driven by climate shifts, officials from the European Centre for Disease Prevention and Control (ECDC) said today.