After a particularly tough year for the West Nile virus in 2012, Massachusetts health officials are bracing for what could be another busy summer for the mosquito-borne illness.
Although, with so many factors playing into the problem, the track of West Nile is not an easy one to predict, said Kevin Cranston, director of the Bureau of Infectious Disease for the Massachusetts Department of Public Health.
“We can’t pin down all of the elements that go into why one season is bad and another season is not,” Cranston said.
But if this summer is similar to last summer—marked by extended periods of very hot weather—some parts of the state could see a high number of cases as occurred in 2012.
To give residents a sense of West Nile’s prevalence in the region, Patch has pulled together county-level 2012 data from the Centers for Disease Control and Prevention.
Different factors play into outbreaks
Long periods of warm weather can help accelerate the maturation of the type of mosquitoes known for spreading West Nile virus, Cranston said. Rainfall also might play a part in the problem, as these mosquitoes thrive in pools of stagnant water.
But there are other factors, too, related to mosquito abundance and activity and the amplification cycle of the virus.
The West Nile virus “season” lasts from around mid June until the first “killing frost”—when temperatures drop below 32 degrees for several hours in the local environment, effectively killing that area’s mosquito population, Cranston said.
Testing to begin soon
The Bureau of Infectious Disease begins collecting and reporting on mosquito samples the week of June 17 and continues testing throughout the season, Cranston said.
West Nile virus is reported through two main processes. First, the bureau works with the local mosquito control projects to trap and sort mosquitoes by species—different species are known for spreading different viruses. A pool of about 10 to 15 mosquitoes is then tested for the presence of viruses such as West Nile and Eastern Equine Encephalitis, or EEE.
“If even one mosquito in that pool has the virus it is considered to be a positive pool. We assemble that data over time to show how a given region of the state is more or less likely to have infected mosquitoes in the environment,” Cranston said.
Information also comes in from physicians when patients report symptoms that may be caused by West Nile virus. Samples are taken from the individual and tested at the state lab in Boston's Jamaica Plain. This not only helps the physician make a diagnosis and treat the patient but also assists the state in establishing risk levels.
“Clearly if one person got West Nile virus in a certain area, other people are likely to get it as well,” Cranston said.
The bureau compiles all this data and shares that information on a map on its Web page, identifying the risk level on a scale of one to four, from “low” to “critical.”
How to protect yourself from West Nile
“We consider West Nile virus essentially here to stay. It’s endemic in the environment, not just in Massachusetts but in many parts of the United States,” Cranston said. “West Nile virus has become a fairly consistent summertime reality.”
To help protect against the virus, the state works with local boards of health and mosquito control projects to conduct ground-level spraying of low-toxicity chemicals designed to kill adult mosquitoes.
But individuals can also do a lot to protect themselves against the insects that spread the West Nile virus.
Stagnant water supplies are perfect breeding grounds for these mosquitoes. Old tires, flower pots, bird baths that are not changed regularly and even storm gutters in need of a cleaning are possible places for the insects to breed.
“We urge folks to take a look around their environment and get rid of all the places mosquitoes might breed,” Cranston said.
The mosquitoes that spread West Nile virus tend to come out at night, so people should avoid spending extended periods of time outdoors without protection—wearing long sleeves and pants and applying insect repellent. More information about the type of products recommended by the Bureau of Infectious Disease can be viewed on the bureau website.
Who's at risk?
Most people who contract West Nile virus won’t even know they have it. About 80 percent of cases are “very mild” and may not even involve a trip to the doctor’s office, Cranston said.
About 20 percent of people affected will have the typical viral symptoms—headache, sore throat, muscle aches, a mild or even high fever. But even these symptoms can be hard to diagnose as being caused by West Nile virus, Cranston said.
However, a small group of people who contact the virus—less than 1 percent—will experience more serious neurological symptoms and can end up with meningitis or encephalitis, Cranston said.
These more serious issues tend to occur in people over the age of 50, he noted.
“Many people have had a West Nile virus infection and not known it,” he said. “If a person has signs of illness and is really feeling lousy, and certainly if there are signs or symptoms of brain involvement—headaches, high fever, difficulty looking directly at light—they should contact their physician.”
“We don’t expect widespread serious illness in this or any season, but the risk is always there,” Cranston said.
The Cases and Incidence Rates
You can see how counties across the state compare by using the interactive map above, which shows the number of West Nile cases in humans and the infection rate. West Nile – named after the district in Uganda where the virus was first discovered – spread to New York City in 1999, and has been migrating across the United States ever since. Last year was the deadliest year so far for West Nile in the United States, with more than 5,600 "confirmed and probable" cases, and at least 286 related deaths.
Local predictions for 2012 are very difficult to make. But nationally, "the number of humans with West Nile virus disease continues to rise in the United States," said Dr. Lyle Petersen, director of the CDC's Division of Vector-Borne Diseases.
No Vaccine, Little Reporting, But a High Cost
While there is a West Nile vaccine for horses, there isn't one for humans, according to Purdue University Professor Richard Kuhn. Furthering the problem is the fact that cases of West Nile often go unreported.
“It's always underreported because if someone has a mild case they might not report it; they might think it’s a cold,” said Judith M. Lavelle, Health Communications Specialist at the CDC.
There is currently no comprehensive treatment for someone infected by West Nile, which makes severe diagnoses all the more frightening. Patch spoke to one Texas man who survived a West Nile infection in 2006, and has dedicated himself to educating the public about the potentially debilitating disease.
“I was told point blank that I would never walk again - to forget it,” said Donnie Manry, of the Bryan County Police Department in Texas. “It was devastating.”
Manry, who was 43 at the time, said that within five days of being stung, encephalitis and meningitis left him paralyzed. Through rehabilitation, Manry was able to regain control of his body again, and now uses a cane to walk.
From Birds to Bugs to Humans
West Nile has also been detected in bird populations, notably in Central Michigan. “Certain types of birds serve as a reservoir for West Nile Virus,” Kuhn said. An infected bird can pass the virus along to an uninfected mosquito when bitten. That’s why Wisconsin has launched a hotline for people to report dead birds in the area.
Many states have begun testing mosquitoes for West Nile, withPennsylvania, Illinois and California all reporting positive detection in certain counties. After the virus was detected in California, LA County began overnight aerial spraying to stop the spread. Residents are cautioned to remain indoors during the spraying.
Prevention and Symptoms
- When weather permits, wear long-sleeved shirts and long pants outdoors.
- Place mosquito netting over infant carriers when you are outdoors.
- At least once or twice a week, empty water from flower pots, pet food and water dishes, birdbaths, swimming pool covers, buckets, barrels, and cans.
With the 2012 mosquito season was the highest on record, health officials are cautioning people to take immediate action if you believe you’ve been infected. The CDC website lists varying degrees of symptoms, including:
- Serious Symptoms in a Few People. About one in 150 people infected with WNV will develop severe illness, including high fever, headache, neck stiffness, stupor, disorientation, and paralysis.
- 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.
- No Symptoms in Most People. Approximately 80 percent of people infected with WNV will not show any symptoms at all.