Nebraska is seeing an early increase in the number of mosquito pools, or batches of trapped mosquitoes, testing positive for West Nile virus, health officials said Friday.
Forty-two new pools tested positive for the virus across the state during the week that ended July 21, said Jeff Hamik, vector-borne disease epidemiologist with the Nebraska Department of Health and Human Services.
That means 60 pools total have tested positive so far this season. Usually, the number of West Nile-positive pools peaks later in the season, typically in August or September.
“We’re seeing an early increase, that’s for sure,” he said. Exactly why the early increase is occurring, however, is not clear.
Over the past five years, the state has recorded an average of 2.6 West Nile-positive pools by the same point in the season.
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Last year, 992 pools of Culex mosquitoes, the kind that can carry the virus, were tested. Of those, 88 were positive for West Nile. After this week’s samples are tested, Hamik said, health officials will have tested more Culex mosquitoes than in all of 2022.
So far, the high number of positive mosquito pools does not appear to be immediately translating into a larger number of human cases of West Nile. The virus is passed to humans through the bite of a mosquito that has acquired the virus by feeding on an infected bird.
However, Hamik said, human case reports can lag infections by three to six weeks. That’s why mosquito surveillance is considered a better indicator of risk from the virus.
Only one human case of West Nile has been documented so far this season. That case was reported in the jurisdiction of the Three Rivers Public Health Department, which serves Dodge, Washington and Washington counties. It also occurred earlier than usual.
Mosquitoes collected at both of the sample sites in the Three Rivers district tested positive last week, said Katie Schultis, the department’s environmental health coordinator.
The number of positive pools across the state, however, means it’s more important than ever for residents to take precautions to prevent mosquito bites, she said.
People can reduce their risk by using a repellent that contains DEET, picaridin, lemon eucalyptus oil or IR3535; wearing long-sleeved shirts, long pants, shoes and socks when outside; and taking extra precautions when going outdoors at dawn and dusk, the time when mosquitoes are most active.
To prevent mosquitoes from breeding near your home, drain standing water around homes and businesses, manage lawn and garden irrigation to avoid standing water and change water in bird baths, fountains and other outdoor receptacles at least once a week. Residents also can place mosquito-killing tablets, or dunks, in areas that are hard to drain.
Many people infected with West Nile have no symptoms or only mild flu-like symptoms. Less than 1% of people infected with West Nile become severely ill. However, people over 50 and those with weakened immune systems are especially vulnerable to the disease and are more likely to experience serious consequences.
Last year, 64 human cases of West Nile, including four deaths, were reported by early December in Nebraska. Twenty-four infections were reported among blood donors.