Mosquito-borne DiseasesFriday, Oct. 24, 2025 State Health Officials Announce Ninth Human Case of West Nile Virus in Massachusetts. Some risk for WNV will continue until there is a hard frost. September 26, 2025 State Health Officials Announce two additional human cases of West Nile virus (WNV) in Massachusetts this year. One is a woman in her 60s with exposure in Middlesex County, and the other is a man in his 50s with exposure in Suffolk County. “We are almost out of the peak season for the spread of West Nile virus to people in Massachusetts,” said Public Health Commissioner Robbie Goldstein, MD, PhD. “Over the last 10 years, 80 percent of people became sick in August or September, with 12 percent developing illness after October 1. But because some risk will continue until the first hard frost, we are encouraging everyone to continue to take the necessary steps to protect themselves from mosquito bites by using mosquito repellent and wearing long sleeves and pants to reduce exposed skin.” West Nile Virus (WNV) risk levels are moderate in Hampshire County.
September 19, 2025 The Massachusetts Department of Public Health (DPH) announced on September 19th two additional human cases of West Nile virus (WNV) in Massachusetts this year. Both are men in their 60s with likely exposure in Worcester County. These cases bring the total number of confirmed human cases of WNV this season to six. West Nile Virus (WNV) risk levels in Hampshire County remain in the low to moderate range.
September 5, 2025 The Massachusetts Department of Public Health (DPH) today announced two additional human cases of West Nile virus (WNV) in Massachusetts this year. One is in a man in his 40s who was likely exposed to the virus in Hampden County and the other is in a man in his 80s with exposure in Middlesex County. “Given how many mosquitoes have been found carrying West Nile virus this summer, we expected that there would be human infections this year,” said Public Health Commissioner Robbie Goldstein, MD, PhD. “Infections can continue to occur until the first hard frost of the season, which is likely still many weeks away. We are encouraging everyone to continue to take the necessary steps to protect themselves from mosquito bites, including by using mosquito repellent, wearing long sleeves and pants to reduce exposed skin, and to drain anything that may be collecting water outside your home.” West Nile Virus (WNV) risk levels in Hampshire County remain in the low to moderate range.
September 3, 2025 State public health officials have announced a second human case of West Nile Virus (WNV), just one day after confirming the state’s first case. The first individual is a woman in her 70s who was exposed in Middlesex County, while the second case involves a woman in her 60s who was exposed in Essex County. “West Nile virus can be a very serious disease and its presence in mosquitoes remains high right now in Massachusetts,” said Public Health Commissioner Robbie Goldstein, MD, PhD. “While September brings cooler air and the return to school for many in the state, the risk from WNV is going to be elevated for some time. Residents should continue to take precautions to avoid mosquito bites.” West Nile Virus (WNV) risk levels in Hampshire County remain in the low to moderate range.
July 23, 2025: State Public Health Officials Announce Season’s First EEE-Positive Mosquito Sample
The Massachusetts Department of Public Health (DPH) today announced that Eastern equine encephalitis (EEE) virus has been detected in mosquitoes in Massachusetts for the first time this year. The presence of EEE was confirmed in a mosquito sample collected on July 21 in the town of Belchertown in Hampshire County.
“This is around the time we would expect to find EEE in mosquitoes in Massachusetts, especially after an active EEE season last year with four recorded human cases,” said Public Health Commissioner Robbie Goldstein, MD, PhD. “This is only a first finding and mosquito surveillance will be key to tracking any developing areas of increasing risk. Today’s finding is an important reminder for residents to take measures to protect themselves from mosquito bites.”
EEE is a rare but serious and potentially fatal disease that can affect people of all ages. EEE is generally spread to humans through the bite of an infected mosquito. There were four human cases of EEE in Massachusetts in 2024 with one death. There were also four EEE-infected horse cases last year. No human or animal cases of EEE have been detected so far this year.
“EEE activity in Massachusetts tends to occur in outbreak cycles,” said State Epidemiologist Dr. Catherine M. Brown. “When EEE is found in mosquitoes at this point in the season, the risk may increase throughout the rest of the summer. We rely on our mosquito surveillance program to monitor for the presence of virus to let people know when and where the risk is occurring.”
June 17, 2025: The Massachusetts Department of Public Health (DPH) announced today that West Nile virus (WNV) has been detected in mosquitoes in Massachusetts for the first time this year. The presence of WNV was confirmed by the Massachusetts State Public Health Laboratory in a mosquito sample collected on June 13 in the town of Shrewsbury in Worcester County.
While no human cases have been reported yet in 2025, officials are urging residents to take precautions against mosquito bites, as WNV and EEE can lead to serious illness, particularly in older adults.
Please see this week’s MDPH Arbovirus Report and visit our site for information on recent arbovirus detections and risk level changes in your area. https://www.mass.gov/info-details/massachusetts-arbovirus-update Please note: A table of Travel Associated Dengue and Chikungunya cases has been included in the 2025 report to highlight the ongoing Dengue outbreak in the Americas. To date, local transmission has not been identified. https://worldhealthorg.shinyapps.io/dengue_global/Sept |
