WNV can cause illness varying from a
mild fever to more serious disease like encephalitis or meningitis. WNV
grows in birds and is spread from bird to bird by infected mosquitoes.
If mosquitoes infected with the virus bite horses or humans, the animal
or person can become sick. In the United States, WNV was first
identified in New York during the summer of 1999. Since then, it has
spread throughout most of the continental U.S. It's not known how WNV
got to the U.S., but it has occurred naturally in Europe, Africa and
Asia for many years.
infections do not cause any symptoms. 80% percent of people that
contract WNV experience no symptoms. 20% of people experience mild
symptoms. Mild WNV infections can cause fever, headache and body aches,
often with a skin rash and swollen lymph glands. In less than 1% of
people infected by the virus, the disease can be serious, and at less
than 0.1%, even fatal. More severe infections can cause headache, high
fever, neck stiffness, stupor, disorientation, coma, tremors,
convulsions, paralysis and, sometimes at less than 0.1%, death. Persons
older than 50 years of age or a compromised immune system have a higher
risk of developing severe illness.
is no specific treatment for WNV infection. People with mild WNV
infections usually recover on their own. Doctors can provide supportive
therapy for people who have more serious complications, such as
encephalitis or meningitis.
usually is spread by adult mosquitoes that are infected by the virus.
Mosquitoes spread the virus by biting humans, horses, and other
animals. WNV can sometimes be spread in other ways. For example, WNV
can be spread to humans through blood transfusions and organ transplants
from infected donors. Also, it is possible the pregnant women or
breastfeeding mothers who become infected with WNV may pass the virus to
their baby. Because of the unknown risk at this time and the fact that
breastfeeding has well-established benefits, it is not recommended to
discontinue breastfeeding. Horses that have WNV infection cannot spread
the disease directly to humans. There is no evidence that a person can
get WNV from touching live or dead infected birds. Still, basic safety
precautions should be used when handling any dead animals, including a
dead bird. If you need to move or dispose of a dead bird, use gloves or
a shovel to handle it, and place it into two plastic bags (one inside
illness caused by WNV is uncommon and has been identified in a small
number of people in Massachusetts for the past several years.
Additionally, WNV has been found in horses, mosquitoes, and many species
of birds throughout the state. The mosquitoes that carry this virus
are common throughout the state, and these mosquitoes are found in the
city as well as in the woods and other less populated places.
developed a Surveillance and Response Plan that serves to coordinate
efforts of local officials and state agencies to reduce the risk of
WNV. The plan involves checking for the virus in mosquitoes and birds,
reducing the number of mosquitoes in the environment, and educating
people on ways to avoid mosquito bites. Every year from May until the
first hard frost, the Massachusetts Department of Public Health (MDPH)
and local mosquito control projects collect mosquitoes from various
locations around the state and send them to the State Laboratory for
testing. MDPH collects information on the number and locations of dead
birds reported in the state and tests selected birds for WNV. If WNV is
identified in birds or mosquitoes, MDPH will tell local boards of
health and mosquito control projects and ask them to increase their
education and mosquito control activities. MDPH provides educational
materials for physicians, veterinarians, local public health officials,
and the public along with updates on WNV activity in mosquitoes, horses
and humans online.