A record-high number of mosquitoes in and around Las Vegas carry the West Nile virus. This has led to advice from local health officials that people should be careful not to get bitten.
The West Nile virus can cause fevers, headaches, vomiting, and diarrhea. In about one out of every 150 cases, it ends in death. There are no vaccines or medicines that can help or stop the illness that mosquitoes spread.
In the past few weeks, tests on more than 24,000 groups of mosquitoes in 25 southern Nevada ZIP codes found that at least one of the mosquitoes in the group had the West Nile virus. Both the number of bugs seen and the number of positive pools this early in the season are higher than the previous highs set in the area in 2019.
A supervisor for environmental health for the Southern Nevada Health District, Vivek Raman, said, “These are a lot of mosquitoes, and we’ve already found a worrying number of them carrying the West Nile virus.”
Health officials have also found six pools in the Las Vegas area that tested positive for the St. Louis encephalitis virus. This is a disease that is spread by mosquitoes and can kill by inflaming the brain.
For many years, climate experts and public health officials have been warning that climate change could make it easier for some diseases to spread, especially those that are spread by mosquitoes. The rising number of West Nile Virus-carrying mosquitoes in Las Vegas is a good example of how climate change can affect people’s health.
Climate change raises the average temperature and amount of rain around the world. This makes conditions perfect for mosquitoes, which lay their eggs in still, warm water. It also makes the warm times last longer, which makes the mosquito season last longer. People are more likely to get diseases like West Nile virus because of these changes, even in places where cases have never been reported before.
In 2004, the first case of West Nile virus was found in Las Vegas. This was five years after the first case was found in New York City, USA, in 1999. The last West Nile outbreak in Las Vegas was five years ago, and 43 people got sick. People in charge of health in the district are worried that this summer could be even worse.
Over the last few decades, springtime weather in Nevada and much of the Southwest has gotten warmer, and summer heat waves have gotten worse. Since 1970, the average spring temperature in Las Vegas has gone up by 6.2 F. The city has already been through a record-breaking heat wave that lasted for a week this month.
An assistant professor of epidemiology at Columbia University named Nischay Mishra said that the higher temperatures in southern Nevada are making it a good place for mosquitoes to live. On top of that, the state’s ongoing drought has caused the water table to drop across the Colorado River Basin, including in Lake Mead. This may actually be good for the bugs, which seems illogical.
“Mosquitoes like it when it’s hot and wet,” Mishra said. “But in Nevada, when smaller bodies of water dry up, they leave behind shallow water that is perfect for mosquitoes to lay their eggs in.”
There have been a lot of mosquitoes in Las Vegas: The district health office counted 6,000 mosquitoes in traps across Clark County from April to June of last year. There have already been more than 24,000 this year.
Most of them have been Culex mosquitoes, which are the main carriers of the West Nile virus. But Aedes aegypti mosquitoes, which don’t carry the virus, have also become more common in Las Vegas. Aedes was first seen in the area in 2017, and Raman says that its growth there is also due to climate change.
Along with environment, how people act is a big part of how vector-borne diseases spread. Both Aedes and Culex mosquitoes like living in the backyards of many homes in Las Vegas. Aedes mosquitoes lay their eggs in small pools of water, like those left behind by sprinklers, while Culex mosquitoes often lay their eggs on the surface of swimming pools that aren’t being kept.
Raman said the best way to stay healthy and avoid getting sick is to keep swimming pools clean, protect yourself with clothes, and use bug spray to keep from getting bitten.
Professor of global health and social medicine at Harvard Medical School and head of the school’s Global Health Institute, Louise Ivers, said that situations like the one in Las Vegas will happen more often because climate change is making infectious diseases spread around the world.
“We should expect to see new infectious diseases, old infectious diseases come back, and changes in how people get West Nile virus and other existing infectious diseases,” Ivers said. “We might not be able to do the things we used to be able to do without worrying as much about being safe from mosquitoes and ticks anymore.”