2019 Marks 2 Decades Since the Arrival of West Nile Virus in the US

It’s been nearly 20 years since West Nile virus was first detected in the Western Hemisphere and, now with the arrival of summer, health officials around the United States are reporting the first West Nile activity of the 2019 season.

In 2018 there were 2544 reported cases of West Nile virus in the United States, a slight uptick from the case counts reported in the previous 5 summer seasons. The last time the US saw more cases was in 2012 when there were 5674 cases reported. According to the US Centers for Disease Control and Prevention (CDC), West Nile virus is now the leading cause of mosquito-borne disease in the continental United States. As of June 11, 2019, there have been 8 human cases documented in 2019.

In wake of the recent cases, health officials are reminding the public to be aware of the risk of West Nile and its symptoms. Although 8 out of 10 cases of the virus occur without any symptoms, those who do experience symptoms may have a fever, headache, body aches, joint pains, vomiting, diarrhea, or a rash. In about 1 in 150 people with West Nile, the infection can progress to encephalitis or meningitis and severe illness with symptoms including high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, and paralysis. As such, the CDC reports both neuroinvasive and non-neuroinvasive cases, although the majority of non-neuroinvasive cases go unreported.

In Texas, Dallas County Health and Human Services (DCHHS) confirmed on June 12 that mosquitos in the county had tested positive for West Nile virus and that mosquito abatement teams would be treating impacted areas in the overnight hours. “DCHHS encourages residents in affected areas to be a part of the solution by eliminating insect breeding areas and larvae before mosquitoes reach the adult stage. Standing water can be treated with EPA-registered larvicides that are available for retail purchase. Larvicides are products used to kill immature mosquitoes before they become adults. Larvicides are applied directly to water sources that hold mosquito eggs, larvae, or pupae.”

On June 20 Michigan’s Department of Health and Human Services (MDHHS) reported its first West Nile virus activity of the year, including mosquitos in Saginaw and Oakland counties and a Canada goose in Kalamazoo County. Birds carrying the virus can transmit it to mosquitos and become infected from their bites as well, and play a key role in the West Nile virus transmission cycle.

Joneigh Khaldun, MD, MPH, MDHHS chief medical executive and chief deputy director for health, noted that in 2018 Michigan saw 104 serious illnesses and 9 deaths related to West Nile virus. “It only takes 1 bite from an infected mosquito to cause a severe illness, so take extra care during peak mosquito-biting hours, which are dusk and dawn,” she said. “We urge Michiganders to take precautions such as using insect repellant wearing long-sleeved shirts and long pants when outdoors during those time periods.”

To prevent mosquito bites, the CDC recommends the use of Environmental Protection Agency-registered insect repellents with active ingredients including DEET, picaridin, IR3535, lemon eucalyptus oil, para-methane-diol, or 2-undecanone. For babies younger than 2 months of age, insect repellent is not recommended, and infants should instead be dressed in clothing that covers their arms and legs. Strollers and baby carriers should be covered with mosquito netting, particularly during the hours of dusk and dawn when mosquitos are most active.