The Massachusetts Department of Public Health on Thursday announced the state's sixth human case of Eastern Equine Encephalitis.
Officials said the patient is an Amesbury woman in her 60s. The woman remains hospitalized.
The EEE threat level was raised to Critical for Amesbury, Haverhill and Merrimac.
An additional human case of West Nile Virus was also announced. The patient was a Middlesex County resident in his 60s. He was treated and released from a hospital.
The West Nile Virus threat level was raised to High in Stoneham and Winchester.