West Nile Virus – what you need to know

A recent report indicates that a 46-year-old Boston woman has been diagnosed with West Nile Virus, the first human case of the mosquito-borne virus in Massachusetts this past summer. Although the chances of acquiring West Nile Virus are very low, here are some things you should know about the illness:

What Is West Nile Virus?
West Nile virus (WNV) is a potentially serious illness. Experts believe WNV is established as a seasonal epidemic in North America that flares up in the summer and continues into the fall.

What types of mosquitoes are known to transmit the West Nile Virus?

The northern house mosquito, Culex pipiens, found in urban and suburban areas. The female mosquito lays its eggs in any receptacle containing stagnant water such as tires, birdbaths, children’s toys, buckets, flower pots, clogged rain gutters, and plastic wading pools. A single container can produce tens of thousands of mosquitoes over a season. Female mosquitoes prefer to lay eggs on water that may be described as aged, stagnant and putrid. A well maintained swimming pool filled with clear, clean water is unlikely to breed mosquitoes.

West Nile Virus has also been found in several species of floodwater mosquitoes, common in floodwaters like the meadowlands, woodland pools, flood plains and marshes. It has also been isolated in mosquito species which breed in discarded tires.

How does the mosquito transmit the West Nile Virus?

Scientific evidence suggests that a mosquito bites an infected bird and may become infected with the West Nile Virus. If the infected mosquito then takes a blood meal from a human, the West Nile Virus may be transmitted to the human.

What are the symptoms of WNV?

  • Serious symptoms in a few people. About one in 150 people infected with WNV will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent.
  • Milder symptoms in some people. Up to 20 percent of the people who become infected have symptoms such as fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for as short as a few days, though even healthy people have become sick for several weeks.
  • No symptoms in most people. Approximately 80 percent of people (about 4 out of 5) who are infected with WNV will not show any symptoms at all.

How soon do infected people get sick?
People typically develop symptoms between 3 and 14 days after they are bitten by the infected mosquito.


Centers for Disease Control and Prevention: https://www.cdc.gov/ncidod/dvbid/westnile/wnv_factsheet.htm

NJ Department of Environmental Protection: https://www.nj.gov/dep/mosquito/depfs.htm