Mosquitoes in the Durango area have tested positive for the West Nile virus, but Pine River Valley residents aren’t sure if the mosquitoes in eastern La Plata County are carrying the virus.
San Juan Basin Public Health reported La Plata County’s first human case of the virus last week. The Durango area has an official district that monitors for the virus, but Bayfield, Ignacio and the Southern Ute Indian Tribe reservation do not. A contractor manages the disease-vector mosquito population and doesn’t test for the presence of the virus. Without tests, residents do not know when the virus might be active in mosquitoes in their communities.
“We did (test) in the past; we haven’t the last few years,” said Rhiannon Tanner, Vector Disease Control International program manager for the valley. “I can’t let anybody know if any of our (mosquito) pools test positive. That’s something that’s going to be changing for next year.”
Not all mosquito species are vectors, or carriers, for the virus. The Western Encephalitis mosquito, or culex tarsalis, is the vector that VDCI tracks in its population samples. However, Tanner can’t test for whether a vector species sample is positive for West Nile in her office. Without the equipment or permits, she would have to send samples to Denver.
“I do not understand why we quit testing,” she said, adding that the decision was made prior to her time as program manager.
Tanner plans to send samples to Denver next summer, based on a request from Mark Garcia, interim town manager of Ignacio.
“Most areas of Colorado don’t test for West Nile virus because it’s so expensive. That’s a political decision. It depends on whether different communities have money,” said Michael “Doc” Weissmann, chief entomologist at VDCI.
In Bayfield, Tanner sprayed pesticide once this summer after finding 25 to 30 Western Encephalitis specimen at a trap near the Tamarack Drive neighborhood.
Anytime Tanner counts more than 25 Western Encephalitis mosquitoes in a trap, she sprays in the area. The count threshold is below her required 60-mosquito threshold and low compared with 100-mosquito thresholds in northern Colorado, she said.
She did not find enough of the vector species to trigger sprays in Ignacio or on the reservation this summer; however, she did conduct sprays if there were 60 adult mosquitoes of any species in a trap.
“West Nile is not going anywhere. It’s here to stay, unfortunately,” Tanner said.
VDCI posts spray notifications on its website and notifies its clients. VDCI did not notify the public of the Bayfield spray triggered by the vector mosquito count.
As of Sept. 4, Colorado had 14 human cases of West Nile virus, according to data from the Colorado Department of Public Health and Environment.
Most people infected with mosquito-borne viruses don’t get sick. Those who do start experiencing symptoms two to 14 days after getting a mosquito bite, according to a news release from San Juan Basin Public Health.
During the 2018 season, there were 96 cases of human West Nile virus. Fifty-two of those cases had neuro-invasive involvement, leading to five deaths, according to a July CDPHE report. In addition to the 96 people who experienced illness, there were two blood donors with infection who did not develop symptoms of the disease, the report said.
Symptoms of West Nile virus include fever, nausea, headache and muscle aches. In rare instances, the virus can also cause encephalitis and meningitis and can be fatal. Anyone with West Nile virus symptoms should see a health care provider.
Tanner said that while West Nile is consistently present in the state, mosquitoes in the area do not always test positive for the virus – which would mean people do need to be notified more frequently.
“It is important, I think, (for the public) to know that there are mosquitoes in my district that do test positive,” she said. “There’s nothing we can do to stop it not from being around. We just have to do our best to educate the public not to be having any kind of standing water, stuff like that.”
For more prevention information, visit cdc.gov/westnile/prevention/index.