Las Vegas sees surge in mosquitoes carrying West Nile virus

Record numbers of mosquitoes are carrying the West Nile virus in and around Las Vegas, prompting local health officials to issue a public warning. Take precautions To avoid getting bitten.

West Nile virus causes fever, headache, vomiting and diarrhea and is fatal in about 1 in 150 cases. There is no vaccine or medicine to treat or prevent the mosquito-borne disease.

In recent weeks, 169 of more than 24,000 mosquito swarms tested for West Nile virus in 25 Southern Nevada ZIP codes tested positive, meaning at least one mosquito in the swarm was carrying the virus. The number of mosquitoes and positive swarms recorded this early in the season broke the regional records for both indicators set in 2019.

“The mosquito population is huge and we've already seen significant numbers of mosquitoes carrying the West Nile virus,” said Vivek Raman, environmental health inspector for the Southern Nevada Health Department.

Health officials also identified six swimming pools in the Las Vegas area where people had tested positive for the St. Louis encephalitis virus, a mosquito-borne disease that causes potentially fatal inflammation of the brain.

For decades, climate scientists and public health officials have warned that climate change could increase the range of various infectious diseases, particularly those transmitted by mosquitoes. The Las Vegas mosquito surge and regional increase in West Nile virus outbreaks provide an important case study in how climate affects human health.

Climate change will increase the global average temperature and precipitation, creating ideal conditions for mosquitoes, who breed in still, warm water. It will also lengthen the warm season, lengthening the mosquito season. These changes will Human exposure risk Even in places where no cases have been recorded before, there is an increased risk of contracting diseases such as West Nile virus.

The first case of West Nile virus was recorded in Las Vegas in 2004, five years after the first case in the United States was recorded in New York City in 1999. The most recent West Nile virus outbreak in Las Vegas was five years ago, when 43 people were infected, and area health officials fear the situation could get even worse this summer.

Spring weather is coming to Nevada and much of the Southwest. It gets warmer Summer heat waves have become more intense in recent decades. In Las Vegas, the average spring temperature is 6.2 degree increase since 1970This month, the city has already A week of record-breaking heatwave.

Rising temperatures in Southern Nevada are creating favorable conditions for mosquitoes, said Nishay Mishra, an assistant professor of epidemiology at Columbia University. Additionally, the state's ongoing drought has lowered groundwater levels throughout the Colorado River basin, including Lake Mead, which could unexpectedly benefit the insects.

“Mosquitoes typically breed in places that are moist and hot,” Mishra says, “but in Nevada, when small bodies of water dry up, they create shallow water that's perfect for mosquito breeding.”

Las Vegas' mosquito surge has been enormous: Last year, local health officials counted 6,000 mosquitoes in traps set across Clark County between April and June. This year, the number is already over 24,000.

Most of these mosquitoes are Culex mosquitoes, which are the primary vectors of the West Nile virus. But another mosquito species that doesn't carry the virus, Aedes aegypti, has also become common in Las Vegas. It was first spotted in the area in 2017, and Raman attributes its spread in part to climate change.

Along with climate, human behavior also plays an important role in the spread of vector-borne diseases. Culex mosquitoes and Culex pipiens mosquitoes breed in many Las Vegas backyards, the former breeding in small pools of water such as those left by sprinklers, and the latter often breeding along the surface of untended swimming pools.

Raman said the best ways to prevent infection are to empty water containers outside, take care of swimming pools, wear protective clothing and use bug repellent to prevent insect bites.

Louise Ivers, professor of global health and social medicine at Harvard Medical School and director of the university's Global Health Institute, said situations like the one in Las Vegas will become more common as infectious diseases continue to rise around the world due to climate change.

“We expect to see new infections, the resurgence of old ones, and changes in the transmission patterns of existing ones like West Nile virus,” Ivers said. “We may no longer be able to do things that we were previously free to do without worrying as much about protection from vectors like mosquitoes and ticks.”