MIDDLE TOWNSHIP — An assortment of colored lines stretched across Karen Hedstrom’s computer screen as she ran a test for diseases on a batch of pulverized mosquitoes.

One line represented Eastern equine encephalitis, a disease that kills a third of its human hosts. Another represented La Crosse encephalitis, a similar and rare virus that mainly affects children under 16 years old.

A third line stood for West Nile virus, which is currently in the midst of one of its worst outbreaks nationwide since being detected domestically in 1999. More than 3,100 people have been infected this year in the U.S., the most at this point of the year since 2003, and 134 have died.

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West Nile is the latest battlefront in a long-standing war between man and mosquito, and researchers are still trying to fully understand the threat and find better ways to fight back.

So far this year, 22 people have tested positive for West Nile statewide. A 77-year-old man from Burlington County died last week from the disease, and a 64-year-old Cape May County woman also remains hospitalized from it.

Another human case was found in Atlantic County and three more in Ocean County, plus one case in Monmouth County that was likely contracted in Ocean County. There were only seven cases of West Nile in all of New Jersey last year, and no deaths.

On this particular day, all the indicators on Hedstrom’s laptop remained relatively flat, which meant the sample examined Tuesday morning was negative for the virus.

However, this year’s threat of disease-transmitting mosquitoes will not end in New Jersey until the first frost, so there are many more tests left for Hedstrom, the chief microbiologist at the Cape May County Department of Mosquito Control.

“We’re probably at our peak now, and we should be on our way down,” said the scientist from Middle Township’s Del Haven section.

There is no definitive reason why West Nile virus has been more common this year in New Jersey.

“There are too many ingredients to go into the mix that we can’t really pinpoint,” said Peter Bosak, superintendent of mosquito control in Cape May County.

Fortunately, only a tiny percentage of people who get West Nile are ever truly in danger. About 20 percent of those infected will have a few days worth of mild effects, such as fever, headaches, body aches and nausea.

One out of 150 who get West Nile see serious symptoms that could develop into permanent neurological damage and even death, according to the Centers for Disease Control and Prevention.

People who are over the age of 50 or who have otherwise weakened immune systems are most at risk. There is no treatment for the virus. In severe cases, patients could go to a hospital for help with breathing, to receive intravenous fluids and get general nursing care.

Some questions about West Nile remain. In New Jersey, scientists are still trying to determine what species of mosquitoes serve as carriers, or vectors, for the disease. It gets to humans when mosquitoes bite infected birds and then bite people.

There are 45 different mosquitoes in Cape May County alone, which likely has the most varieties in one county because more than half of its area is wetlands — prime breeding grounds for the insects that typically lay eggs in water.

Only a few of those bite both birds and humans. Since West Nile is not native to the U.S., scientists are not sure how many of the native mosquitoes serve as effective vectors for the disease.

A major concern in recent years has also been the non-native Asian tiger mosquito. It carries West Nile, it bites aggressively during the day instead of night like most mosquitoes, and it spreads prodigiously.

“I’ve found Asian tiger larva in bottle caps,” Bosak said.

Bosak’s department is one of the pre-eminent mosquito control operations in the country. It is nearly a century old and Cape May County is the only county in the state with its own laboratory for examining and testing mosquitoes.

The department has more than 20 traps in the county it collects mosquitoes from daily and more than 100 that workers check periodically . They bring in thousands of mosquitoes a week, which help to monitor populations and track diseases.

On Tuesday morning, Diane McNelly, of Woodbine, picked through a pile of dead mosquitoes in one of the lab rooms at the department’s headquarters on Route 47. These insects came from a trap at the U.S. Coast Guard Training Center in Cape May over the weekend.

She would be separating the different species, and they would then go on to be ground up, put into vials and slid into a machine where they would be tested for viruses.

If a virus is found in a mosquito that does not bite humans it is not much of a concern. More than 11,000 different pools of mosquitoes have tested positive for West Nile or a type of encephalitis in New Jersey so far this year.

Finding a disease in a known bridge vector species, such as an Asian tiger, cattail or salt marsh mosquito, on the other hand, is something to be carefully monitored.

Despite recent deaths from mosquito-borne illness, humanity has been largely winning the war against mosquitoes, at least in the U.S. Malaria and yellow fever used to be major public health issues here, but they have since been wiped out in New Jersey.

Eastern equine encephalitis caused hysteria as recently as the 1950s, when it killed more than 20 people in one year in New Jersey. That led to a more concerted statewide effort to control mosquitoes, and cases of so-called “triple E” have been rare since.

Bosak said new fighting techniques are on the horizon, with more effective bacterial sprays being tested and a wider use of natural methods, such as deploying mosquito larva-eating crustaceans and fish.

In Cape May County, Bosak said they are also always looking for more specific pesticides to target particular mosquitoes. In an area with a growing eco-tourism industry, minimizing the impacts on other insects and wildlife is a priority.

Of course, eliminating harm to humans is still the ultimate goal.

“This area is all tourism-based, and mosquitoes don’t go well with tourists,” Bosak said. “Nor does disease that affects tourists.”

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