West Nile virus has been found in birds in Haverhill.
The city has yet to have any mosquitoes test positive for West Nile virus, but continues to test twice a week to check for the disease. The results for the latest batch of tests will be known early in the week of Aug. 4.
"The mosquitoes we test go to Boston to be tested for the virus. If any were to come back positive, it would trigger a response and we would form a plan of attack. In the past, if a mosquito came back positive, we have used targeted spraying in the infected area," said Jack Card, operations manager of the Northeast Mosquito Control Program.
According to Card, a bird testing positive this year is not as significant as it once was. The general consensus is that even if the virus is found to be positive in birds, it may not be a good indicator that West Nile virus is in the immediate area. That is because birds travel so much, Card said.
"Mosquitoes stay local and don't travel, so if one were to show up positive it would be a better sign that it has indeed infected the immediate area," Card said.
In 2007, there were six human cases of West Nile virus in Massachusetts. While the illness can infect people of all ages, people over the age of 50 are at higher risk. It is usually spread to humans through the bite of an infected mosquito.
The virus can cause illness ranging from a mild fever to more serious diseases like encephalitis or meningitis. It was first identified in the United Sates in 1999.
The majority of people who are infected with the virus — approximately 80 percent — will have no symptoms.
A smaller number of people who become infected will have symptoms such as fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands. They may also develop a skin rash on the chest, stomach and back.
Less than one percent of people infected with West Nile virus will develop severe or life-threatening illness. The symptoms of severe illness can include a high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.
For more on this story, see the next edition of The Haverhill Gazette, on newsstands Aug. 7.