Several mosquito species throughout the United States are major nuisance pests that transmit diseases to humans in urban and suburban areas. The most commonly contracted mosquito-borne diseases in the country include the West Nile virus (WNV), Eastern Equine Encephalitis (EEE), Western Equine Encephalitis (WEE), St. Louis Encephalitis (SLE), La Crosse (LAC) encephalitis, dengue fever, powassan, and chikungunya. In Massachusetts, the West Nile virus and EEE are the two primary mosquito-borne disease threats to humans. While residents in all northeastern states have been contracting diseases from mosquito bites each year for decades, recent years have seen an increase in the rate of annual arbovirus cases throughout the entire country.

Last year alone, 12 new EEE cases and six EEE-related deaths were reported in Massachusetts. The 1950s was the last time a comparable number of EEE infection cases were reported during a one year period in Massachusetts. Unfortunately, EEE occurs in waves that last for two or three consecutive years every 10 to 20 years, and last year was the first year that saw infection cases skyrocket in Massachusetts. This pattern indicates that a relatively high number of people in the state will contract EEE from mosquito bites again this year, but public health officials insist that this is not a certainty.

According to Dr. Asim Ahmed, an infectious disease doctor at Boston Children’s Hospital, there is a good chance that EEE will once again pose a significant public health threat in Massachusetts this year, but it is obviously not uncommon for EEE infection rates to remain low despite the cyclical nature of the disease. Climate is the most significant factor influencing EEE infection rates, as the number of mosquitoes that emerge in human-populated areas during the summer depends on the degree of precipitation that occurred during the previous winter and spring seasons. Since mosquitoes depend entirely on water in order to breed, a relatively dry winter and spring season will deprive eggs and developing larvae of the moisture they need to reach maturity, and it will also reduce the amount of breeding sources available to adults.

Do you believe that EEE infection cases will skyrocket this year and again next year?