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State and local public health officials are reporting the season’s first human West Nile Virus (WNV) cases in Montana. The cases, reported in Custer and Lewis and Clark counties, both occurred in individuals over the age of 60, who are often at greater risk for severe disease.

Both required hospitalization and no further information is available at this time.

Most people who become infected with WNV experience no symptoms, but 1 in 5 develop a mild illness, with symptoms such as headache, body aches, joint pains, vomiting, diarrhea or a rash. Other individuals, fewer than 1 out of 150, may become severely ill with encephalitis or meningitis (inflammation of the brain or surrounding tissues). Most people recover completely, but fatigue and weakness can last for weeks or even months.

“This is typically when we see our first human cases in Montana following the hot drier weather of late July and early August,” said DPHHS Communicable Disease Epidemiologist Erika Baldry. “Our season can begin as early as July and because it can take some time to become ill, we can receive reports of ill individuals as late as October.”

Baldry stressed the importance of continuing to take steps to avoid exposure since our period of transmission is still occurring.

There is no available treatment for WNV infection other than supportive care. Individuals who develop any of these symptoms should see their healthcare provider. Detection of WNV in mosquito samples is a good indication that WNV is in Montana. WNV is a vector-borne disease meaning that for individuals to become infected, they must be bitten by an infected mosquito.

Positive mosquito samples were previously reported from Blaine, Cascade, Sheridan, Valley, and Yellowstone counties. In addition, one equine case of WNV was identified in Lake County this season. DPHHS continues to urge Montanans to take extra precautions to avoid being bitten by mosquitoes as summer winds to a close by following the 4 D’s of prevention.

The four Ds of West Nile Virus prevention:

DEET: Use insect repellent such as DEET or picaridin

Drain: Drain standing water around your house to prevent mosquito breeding

Dawn/Dusk: Mosquitoes are most active during dawn and dusk. Stay inside or take precautions to prevent mosquito bites during these times

Dress: When possible, wear long sleeved shirts and pants to protect yourself from bites

In 2018, there were a total of 51 human cases, including one death. In 2017, there were 13 cases identified.

Since arrival of WNV in Montana in 2002, case counts have varied widely each year. In 2002, there were two cases, while one year later, in 2003, there were 227 cases reported. The 17-year average, which includes two outbreak years consisting of 200 plus cases, is 37 cases.

For more information about WNV protection, contact your local health department or visit the state health department website at: https://dphhs.mt.gov/.

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