:The Laurel Outlook:Big Story

Mosquitoes trapped July 16, east of Laurel, have tested positive for West Nile Virus, according to Laurel Public Works Director Steve Klotz. He was notified of the positive test results last Friday.

The City of Laurel participates in the Montana Mosquito and West Nile Virus Survey Program to identify the presence of the West Nile Virus through the use of portable mosquito traps at 156 sample sites located across the state. After the mosquitoes are collected, they are sent to a lab at Montana State University-Bozeman, sorted by species and tested for West Nile Virus.

Two species of mosquito are identified as carriers of West Nile Virus - tarsalis and pipiens. Half of the 107 mosquitoes caught in the trap were from those two species. Tests conducted on the tarsalis and pipiens mosquitoes were positive for the presence of West Nile Virus.

The mosquitoes are trapped in a collection device made of a small nylon net, attached below a small electric fan, powered by a 6-volt battery. The electric fan sucks the mosquitoes into the net. Mosquitoes are attracted to the trap by carbon dioxide gas. The CO2 is created by a gas generator filled with dry ice that gives off the CO2. The generator is hung in a tree next to the collection device. When the collection is completed the net is closed and the mosquitoes collected are trapped.

According to Klotz, the program has made positive identification of the presence of WNV in mosquitoes in Laurel (Yellowstone County), Harlem (Blaine County), Miles City (Custer County), Glasgow (Valley County) and Medicine Lake (Sheridan County).

The City began participating in the mosquito trapping last summer and this is the first time results have come back positive for WNV, Klotz said. Results from an earlier mosquito collection at the end of June were negative for WNV.

City Maintenance Superintendent Kurt Markegard set a mosquito collection trap again late Monday afternoon. He collected it Tuesday morning and sent it to the MSU lab in Bozeman. Results of this latest collection should be available in 10 days to two weeks.

Klotz was told by program officials that it usually takes a couple weeks for WNV to show up in people and horses after it has been identified in mosquitoes.

Krayton Kerns, owner of Beartooth Veterinary Clinic, said he is not aware of any reported WNV cases that have been reported in horses in Montana. He advised that horse owners who haven't had their animals vaccinated for WNV should do so now. He said he believed many horse owners now routinely have their horses vaccinated for WNV and he did not expect a flurry of new activity from this announcement.

The recent appearance of West Nile virus-type symptoms in pelicans at the Medicine Lake National Wildlife Refuge and the discovery of infected mosquitoes elsewhere in the state indicates that the virus could soon emerge in other parts of Montana.

In the past, that meant the virus would appear two to three weeks later in other parts of the state. The Medicine Lake National Wildlife Refuge is located in northeast Montana between Plentywood and Culbertson.

“Mosquito collection sites along the Milk River and Yellowstone River are usually first to produce West Nile Virus-infected mosquitoes following virus activity at Medicine Lake,” according to Montana State University entomologist Greg Johnson.

He suggested that people avoid areas with high densities of mosquitoes, such as wind breaks made up of trees, grass and shrubs. He also suggested that people wear long-sleeve clothing and use mosquito repellents.

“Two mosquito repellents that I would recommend (and we use) are products containing DEET or picaridin. We use repellents containing around 30 percent DEET. Picaridin, found in Cutters Advanced, doesn't have the oily feel or smell of DEET and appears to be as effective as DEET. Repellents need to be re-applied depending on the level of outdoor activity.”

Johnson, his students and volunteers have been trapping mosquitoes since 2003 when West Nile virus was discovered in Montana.