West Nile

08.08.2012 - New Haven, CT - Theodore G. Andreadis, the Chief Medical Entomologist with the Connecticut Agriculture Experiment Station says the locations where West Nile apears is consistent from year to year. Photograph by MARK MIRKO | mmirko@courant.com (Mark Mirko / August 10, 2012)

Standing in a swampy, wooded section of Beaver Pond Park, Michael Misencik assembled two mosquito traps. One, "a gravid trap," lures mosquitoes with water infused with decomposed hay.

"I should warn you," Misencik said, "it smells terrible, but the mosquitoes like it."

The site was chosen for the traps because all the standing water makes it a mosquito-friendly area. Being late morning, though, they weren't biting too much.

A research technician at the Connecticut Agricultural Experiment Station, Misencik had already been to Beaver Pond earlier in the morning, collecting the previous day's take. Once he was done setting the new traps at Beaver Pond, Misencik took off to do the same in four other towns.

It was part of a procedure for monitoring and quantifying the risk of mosquito-borne disease in the state — a process that involves super-cold freezers, African green monkey cells and cutting-edge biochemical technology.

Because of the dry summer, this year's mosquito count isn't nearly what it was last year, but state entomologist Dr. Ted Andreadis said there's more West Nile virus activity than he has ever seen at this point in the season. As of last week, mosquitoes carrying West Nile virus had been found in 32 municipalities in the state.

Researchers at the agricultural station set and collect traps Monday through Friday from June to October. Each of the 91 locations in Connecticut gets a new trap set each week. Once West Nile activity has been found at a certain location, workers set traps two or three times a week. The Agricultural Experiment Station has six seasonal workers who set and collect the traps. Misencik works year-round in another lab at the experiment station and was filling in last week for one of the seasonal workers.

To Catch A Skeeter

There are two kinds of traps. Besides the gravid trap, there's the "light trap," which looks like a typical thermos filled with dry ice and fitted with a small light bulb. A small hole in the bottom emits carbon dioxide slowly — as long as it's less than 100 degrees out, the ice can last until the next day. Attracted to both the light and the CO2, mosquitoes fly to the trap.

Both traps use a small fan to blow the insects into a net. The fan's breeze also prevents the skeeters from flying out. It's important that the mosquitoes be kept alive so that the virus also stays alive for testing.

After he collected the mosquitoes from all five towns, Misencik put them in a cooler in the trunk of his car and took them to the agricultural station.

At the New Haven lab, research technicians pour the contents of the traps onto a chilled tray and use tweezers to sort out the junk, such as horseflies and bits of debris.

The mosquitoes then are viewed under a microscope to be categorized by species. Stripes on the abdomen, size of the proboscis and hairs on the thorax all help researchers distinguish one species from another. Up to 40 species of mosquitoes live in Connecticut.

Once identified, the mosquitoes are sorted into different vials according to species. Each vial can hold up to 50 specimens. The vials are then taken to the experiment station's biosafety level 3 lab, built in 2003. Every person who enters needs clearance from the FBI, although visitors can look into the labs' many windows. The vials are placed in a mixer mill, a machine that shakes them powerfully. A BB placed in each vial knocks the mosquitoes apart.

The vials are then placed in what is essentially a high-tech salad spinner that uses centrifugal force to separate the mosquitoes' body parts from any viruses that might be present. A 100-microliter sample from the vial is then stored in a solution of African green monkey cells.

"Viruses grow really well in it," Andreadis said. If a virus is present, it will begin to show in about four days.

Once isolated, the lab uses polymerase chain reaction amplification (PCR), to determine which mosquito-borne virus it is. Any new virus identified is stored permanently at the lab at minus-80 degrees Celsius. If a virus is found for the first time in another region, Andreadis said, the lab's bank of viruses can be used to identify it.

Looking For Trouble

For most of the summer so far, Andreadis and his team have focused on Culex pipiens mosquitoes, the predominant species that carries West Nile. Now that it's mid-August, the researchers are also on the lookout for the Culiseta melanura mosquito, which carries eastern equine encephalitis. EEE is much rarer than West Nile and a lot deadlier.

Since West Nile was first identified in the U.S. in 1999, Connecticut has had 79 diagnosed human cases and three fatalities. So far this year, no human cases of West Nile have been reported in the state, but nationwide, according to the Centers for Disease Control and Prevention, there have been 390 human cases reported, and eight people have died. New York and New Jersey are the states nearby that have reported human cases of West Nile this year.

There has never been a confirmed human case of EEE in Connecticut, Andreadis said, but there have been cases elsewhere in New England. It can be fatal in about a third of those infected; survivors are often left with brain damage

"If this mosquito were a more aggressive human-biter," Andreadis said, "we'd be in a lot more trouble."