Washington DC is releasing 600,000 sterile male mosquitoes carrying Wolbachia bacteria to combat a surge in West Nile virus, as the US faces one of its worst seasons on record with at least 48 cases confirmed as of 30 June

22:17, 02 Jul 2026Updated 22:18, 02 Jul 2026

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A major city is releasing 600,000 mosquitos (file)(Image: Prasit photo via Getty Images)

Hundreds of thousands of mosquitoes are being unleashed across Washington DC as America grapples with one of its earliest and most severe West Nile virus outbreaks on record.

However, these 600,000 male mosquitoes aren't being deployed to target humans — quite the opposite, as they're designed to halt the virus's spread since they don't bite and carry sterilising gut bacteria called Wolbachia.

The mosquitoes will seek out biting females to mate with, but the females' eggs won't hatch, which helps control the overall population.

This comes as health officials across the US are urging people to use insect repellent and implement mosquito-control measures due to the particularly severe West Nile virus season.

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The mosquitos are to stop more virus outbreaks (file)(Image: Getty Images)

The US Centres for Disease Control and Prevention confirmed it had recorded at least 48 cases — 38 of them serious — as of 30 June. Since 2004, the average number of cases reported to the CDC by the end of June hovers around 10, reports the Mirror.

Federal health officials said 23 states have reported detecting West Nile virus, the highest figure in a decade.

Scientists believe many people — possibly tens of thousands annually — become infected without realising it because they experience no symptoms, or only mild ones including headaches, body aches, joint pain, vomiting, diarrhoea and rashes.

In serious cases, damage to the central nervous system triggers potentially fatal inflammation of the brain or spinal cord. Adults over 60 and people with underlying medical conditions or compromised immune systems face the greatest risk of such complications.

The Maryland-based firm Bee Safe Mosquito Control is releasing non-biting males in Washington.

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Federal health officials said 23 states have reported detecting West Nile virus (file)(Image: Nathan Posner/Shutterstock)

"When they mate with the female, they actually cause that female to then become infertile for the rest of her life," Todd Montgomery, owner of Bee Safe Mosquito Control, told WTOP. "She's going around laying eggs that will never hatch."

The mosquitoes from Bee Safe Mosquito Control, known as "ZAP males", are targeting the Asian Tiger mosquito, a common species in Washington that can also transmit other diseases such as encephalitis, dengue and yellow fever.

This method has been successfully implemented in various countries across South America, as well as in Singapore and Australia. "The tiger mosquito is a non-native invasive species, so removing it will not have a negative impact on the ecosystem," the company states on its website.

West Nile virus was first reported in the United States in 1999 in New York, and then gradually spread across the country. It reached its peak in 2003, when nearly 10,000 cases were reported.

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