Massachusetts and Riverside County, California have become the latest areas to confirm human cases of the West Nile virus this year, the first for Massachusetts. Local health departments have warned citizens to prepare for the virus and take precautionary measures to decrease likelihood of infection.

Samples taken on August 11 and 12 from various areas in Riverside County came back positive for the West Nile Virus. The Riverside County Department of Environmental Health confirmed cases in Temecula, Hemet and Murrieta through reports from the Vector-borne Disease Section at the University of California (UC) Davis.

The first confirmed human case of the virus in Massachusetts was reported in Middlesex County, from a man who tested positive for the virus this past month.

The West Nile virus has been detected in 48 states in the US, with the exceptions of Hawaii and Alaska, with outbreaks occurring annually in the summer since 1999. There is currently no vaccine to prevent infection, and symptoms are vary among infected individuals, with lower immunity posing higher risks for more severe symptoms.

70 to 80 percent of infected individuals do not develop symptoms. Approximately one in five infected individuals develop febrile illness, including headaches, body aches, diarrhea and rash, but recover completely with some fatigue and weakness lasting up to a few weeks to months. A rare one percent of the infected population can develop severe neurological illnesses such as encephalitis or meningitis, resulting in coma, tremors, seizures or paralysis.

Governments are urging residents to actively fight the threat of the virus by controlling exposure to mosquitoes as much as possible. “We need to continue to take steps to protect ourselves against mosquito bites by using insect repellant, covering up, and reducing outdoor activities at dusk and after nightfall when mosquitoes are at their most active,” said DPH state public health veterinarian Dr. Catherine Brown.

Preventative measures have been highly recommended, including avoiding going outdoors during dawn and dusk (peak mosquito activity hours), using mosquito-repellant with deet, and consistently cleaning standing water to avoid providing a breeding ground for mosquito larvae. Local governments have also largely intensified mosquito surveillance in an effort to control adult and larval populations in highly sensitive areas.