First human case of West Nile Virus confirmed in Mesa County

By Kathleen Goddeyne

The Colorado Department of Public Health and Environment (CDPHE) state lab has confirmed the first positive human case of West Nile virus (WNV), a virus transmitted through a bite from an infected mosquito, in an adult female resident in Mesa County.  So far this year, no mosquitoes trapped from the Grand Junction area have tested positive for the virus.

Human cases of WNV in Mesa County have varied over the last nine years with a high of 127 cases in 2004 and no cases reported in 2008 or 2011.

“It is often the case that we will confirm our first human case of WNV before we see mosquitoes text positive for the virus,” stated Jeff Kuhr, Director of Mesa County Health Department.  “This is the time of year for peak transmission and personal protective measures are prudent,” added Kuhr.

The Grand River Mosquito Control District, a Colorado special district facility that collects revenues through property taxes, traps the mosquitoes tested by the Colorado State Health Department.

The Grand River Mosquito Control District uses two trapping methods: the CDC light trap and gravid trap.

The CDC light trap uses carbon dioxide to draw in mosquitoes.  The mosquitoes are looking for a blood meal to produce eggs, so they go looking for the carbon dioxide.  A light is also installed in the trap to draw the mosquitoes further in, past the carbon dioxide.  Once the mosquitoes reach the light, a propeller located directly beneath the light pulls the mosquitoes into a net.

The gravid trap is used for mosquitoes that have already had their blood meal.  A basin is filled with bacteria rich water and a fan trap is set above the basin.  Mosquitoes who are ready to lay eggs land on the water and are sucked up into the fan where they are trapped again in netting.

Both tests are effective, but the CDC light test is favored because it can catch the presence of WNV before the mosquito has transmitted the virus.  The CDC light test is also easier to set up and manage.

“We set traps weekly throughout the district and come back in the morning to gather the nets full of mosquitoes, then we take them back to the lab to identify the species,” said Zane Mccallister, Manager of the Grand River Mosquito Control District. “We have identified 26 different species of mosquitoes in Mesa County, but only a dozen or so show any kind of regularity.”

The culex mosquito is known to be a prominent transmitter of the West Nile Virus, so that is the only species sent to the Colorado State Health Department for Polymerase Chain Reaction (PCR) testing.  PCR testing multiplies a small distinctive piece of the genetic material of the disease so that it can be measured.  It takes some time to generate the information, but once everything has processed, the tests come back with WNV results.

The Mesa County Health Department urges residents to use personal protective measures against West Nile virus.  The department recommends using insect repellent that contains DEET, Picairdin, or Oil of Lemon Eucalyptus, dressing in long sleeves and pants when in areas where mosquitoes are active, draining standing water on your property and to avoid being outdoors at dusk and dawn; this is when mosquitoes are most active.

Eighty percent of people who are infected with West Nile virus show no symptoms.  Those who show clinical illness are generally diagnosed with a milder form that includes headache, fever, body aches, nausea and occasionally a rash or swollen lymph nodes.  Some individuals will develop more severe illness and be diagnosed with meningitis (swelling of the lining of the brain) or encephalitis (swelling of the brain).  Symptoms include muscle weakness, high fever, neck stiffness and disorientation.  If you develop these symptoms, please contact your health care provider.