West Nile Virus infections reported in Massachusetts for the first time in 2023


Two residents of Massachusetts have tested positive for West Nile Virus, a mosquito-borne disease that can cause serious illness or death. These are the first human cases of the virus in the state this year, according to the Massachusetts Department of Public Health (DPH).

What is West Nile Virus and how is it transmitted?

West Nile Virus is a viral infection that is spread by the bite of infected mosquitoes. Most people who are infected with the virus do not develop any symptoms, but about 20% of them may experience flu-like symptoms such as fever, headache, body aches, nausea, vomiting, and rash. In rare cases, about 1 in 150 people who are infected may develop severe neurological complications such as meningitis, encephalitis, or paralysis. These complications can be fatal in some cases.

The virus is mainly transmitted by the Culex species of mosquitoes, which are active from dusk to dawn. These mosquitoes breed in stagnant water sources such as bird baths, clogged gutters, flower pots, and old tires. The virus can also be transmitted through blood transfusions, organ transplants, or from mother to child during pregnancy or breastfeeding.

Who are the two cases and where were they exposed?

The DPH announced on Tuesday that the first case is a woman in her 70s who was exposed to the virus in a different part of the country. The second case is a man in his 40s who was exposed in Middlesex County, an area already known to be at moderate risk of infection.

West Nile Virus infections reported

The DPH did not disclose the names or locations of the two cases, citing privacy reasons. However, they said that both cases are recovering and that they are working with local health officials to monitor the situation and conduct mosquito surveillance and control activities.

What is the current risk level and how can it be reduced?

Right now, all of Suffolk County, the southeastern half of Middlesex County, and most of Plymouth County are at moderate risk for West Nile Virus infections, according to the DPH’s risk map. Parts of Norfolk, Bristol, Worcester, Hampden, Hampshire, and Berkshire Counties are also at moderate risk.

The risk level is determined by several factors, including the number of positive mosquito samples, human cases, weather conditions, and historical data. The risk level can change throughout the season depending on these factors.

The DPH said that humans are most at risk of being exposed to West Nile Virus in August and September, but some level of risk will continue for several more months. They advised people to take precautions to avoid mosquito bites and reduce mosquito breeding sites around their homes.

Some of the tips from the DPH include:

  • Use insect repellent when spending time outdoors
  • Avoid going outside from dusk to dawn, as these are peak hours when mosquitoes bite
  • Wear long sleeves, pants, and socks to prevent mosquitoes from reaching your skin
  • Drain any standing water around your home where mosquitoes can lay eggs
  • Repair any holes in your screens or doors to keep mosquitoes out
  • Report any dead birds to your local health department as they may indicate West Nile Virus activity

How common is West Nile Virus in Massachusetts and nationwide?

West Nile Virus was first detected in Massachusetts in 2000 and has been reported every year since then. Between 2011 and 2020, there were 148 human cases of West Nile Virus in Massachusetts, according to the DPH. Seven of those cases resulted in death.

Nationwide, there have been 1,050 human cases of West Nile Virus reported so far this year, according to the Centers for Disease Control and Prevention (CDC). Of those cases, 600 were classified as neuroinvasive disease and 450 were classified as non-neuroinvasive disease. There have been 41 deaths reported due to West Nile Virus this year.

The CDC said that West Nile Virus is the leading cause of mosquito-borne disease in the continental United States. The virus is found in all 48 contiguous states and the District of Columbia. The peak season for West Nile Virus activity is from July to October.


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