State reports additional cases of West Nile virus

The Nevada Department of Agriculture is reporting additional cases of West Nile virus are turning up in Nevada including Churchill County.

On Friday, the animal disease laboratory in Reno reported 42 mosquito samples tested positive for the virus. In addition to Churchill County, positive sampless were taken from Carson City and Clark, Douglas, Elko, Lyon and Washoe counties.

The laboratory also conducted surveillance for two additional arthropod borne viruses, Saint Louis Encephalitis virus (SLE) and Western Equine Encephalitis virus (WEE). The laboratory confirmed the presence of WEE in a mosquito sample from Clark County and the presence of SLE in mosquito specimens from Douglas County and Elko County, respectively.

Churchill County Mosquito, Vector and Weed Control District has been active in dealing with the West Nile virus.

“The district’s annual response to West Nile virus and other potential arboviruses in the Lahontan Valley involves an integrated program of surveillance, testing, prioritization, and treatment of mosquitoes,” said General Manager Nancy Upham. “The surveillance involves staff continually assessing water sources and/or adult mosquito service requests made through the district office. We encourage property owners to call if their adult mosquito populations in their areas have increased or if they have standing water around their property possibly contributing to the presence of adult mosquitoes in the area.”

Upham said only one of the 10 species collected this year by the district so far has tested positive for West Nile virus. The species testing positive was Culex tarsalis.

“Areas of dense populations of Culex mosquitoes are prioritized for fogging by either truck or airplane dependent on accessibility, size of the area, weather factors and a number of other variables,” she said. “The district has been trapping adult mosquitoes weekly since July. As of mid-August, 1,442 of the 1,750 mosquitoes tested at the state laboratory were from Churchill County. Three of the submissions known as “pools” (of up to 50 mosquitoes) were confirmed positive for West Nile virus.”

According to Upham, the district also maintains 10 chicken flocks throughout the Lahotnan Valley. Every two to three weeks, she said blood samples are drawn and tested for West Nile virus, St. Louis Encephalitis and Western Equine Encephalitis. She said one flock of chickens tested positive at the beginning of September for West Nile virus.

“The mosquito ‘pools’ and the sentinel chicken flocks serve as indicators of areas with virus activity,” she added. “This testing of both mosquitoes and chickens works into the prioritization of adult mosquito treatment and control. When an area has been treated for adult mosquitoes, the effect interrupts the transmission cycle of virus in the area. These areas are then reassessed and retested for virus activity. Areas of confirmed activity have been reassessed and retested for reduced populations and viral activity.”

Upham said district personnel are working on both immature and adult mosquito areas as well as service requests, which are handled and appreciated by the staff.

According to the Nevada Department of Agriculture, West Nile virus established itself in this area in 2003, and detection of viral transmission either in positive mosquito pools, birds or horses usually starts in mid to late July in Northern Nevada. Mosquito season usually ends with the first killing frosts in October.

“All horse owners should update their animal’s West Nile Virus vaccination,” said Dr. Annette Rink, acting state veterinarian and supervisor of the Animal Disease and Food Safety Laboratory.

She said four effective vaccines exist for horses, but vaccine development for humans is still under way with currently no available product in sight.

The Centers for Disease Control reports people bitten by infected mosquitoes can suffer flu-like symptoms with extreme cases leading to death.

About 1,200 have died since 1999. The state reports seven human cases have been reported in Nevada in 2013 — six in Clark County and one in Douglas.

There is no vaccine for humans.

“Nevada has had cases of West Nile Virus since 2003,” Rink said. “This should serve as a reminder, especially to people 50 years and older, to use repellent containing DEET and to wear long sleeves, pants and socks when outside, especially during dawn and dusk. Also, people remove any standing water from around their house and check to make sure their window screens fit properly.”