Mosquitoes Test Positive for WNV in Eight Montana Counties

The Montana Department of Public Health and Human Services (DPHHS), in collaboration with Carroll College and Montana State University, has confirmed this season’s first signs of West Nile virus (WNV) in eight of the state’s counties.

In addition, an American White Pelican near the Medicine Lake National Wildlife Refuge in Sheridan County tested positive.

Although no case of human infection has been reported in Montana, 174 cases of WNV have been reported to the Centers for Disease Control and Prevention from other states. The highest rates reported this year have been in North and South Dakota.

"Montana has been fortunate in recent years with relatively few cases of WNV reported," said DPHHS Director Richard Opper. "However, recent activity in neighboring states is a concern. We want to remind everyone that WNV is preventable and taking simple precautions can make a big difference."

In 2012, six human cases of WNV were reported in Montana, including one death. Nationwide, there were 5,674 cases of WNV in 2012, and of those 286 were fatal. 

Said Joel Merriman of the DPHHS Communicable Disease Control Bureau, a seemingly late summer has stalled the increase in numbers of C. tarsalis, Montana’s common mosquito WNV vector.

"This may explain the absence of reported human disease, to date, this season," Merriman said.

Mosquito trapping, sampling, and testing began in mid-June, and will continue until approximately the end of September.

To keep the mosquito population at bay around your home and stable, drain standing water in old tires, barrels, buckets, cans, clogged rain gutters, and other items that collect water. Change water in pet bowls, flowerpots, and birdbaths at least twice a week.

For more information about WNV protection and detection efforts, contact your local county health department, or visit the DPHHS website at

For more information, see's WNV Fact Sheet.

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