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For five days in the late summer of 2019, doctors fought to bring down John Hayden’s high fever.
The sudden onset of symptoms in Hayden, including a high fever, baffled everyone, her daughter Anne Hayden said, and her body appeared to be unresponsive to treatment. He succumbed to the inexplicable illness just after Labor Day with his family by his side.
Two days later, the only infectious disease doctor in Yolo County, California, where Hayden lived, told his family that a lumbar puncture showed Hayden had been infected with West Nile virus, a rare virus. spread by mosquitoes which can cause neurological disease and death. . Symptoms often include fever, headache, nausea, and vomiting, and severe cases can cause inflammation of the brain or its surrounding membranes. It is considered by public health officials to be the most serious vector-borne disease in the state of California.
“It changed my life,” said Anne, senior director of the environmental organization, the Environmental Defense Fund. It has added even more weight and urgency to the work she does.
West Nile virus was once associated with higher humidity and humidity, conditions that help mosquitoes thrive. But a growing body of research has found that drought conditions – such as those felt in the western United States – could amplify its effects. States are already on alert.
California reported its first death of the year in July. As of the end of this month, the state’s public health department (CDPH) had documented the virus in 4 people, 94 dead birds, 563 mosquito samples, 10 chickens and 1 horse.
“West Nile virus activity in the state is increasing, so I urge Californians to take all possible precautions to protect themselves against mosquito bites,” said Dr Tomás J Aragón, director of the CDPH, in a statement confirming the death of a man in San Luis Obispo County. .
Severe cases of West Nile virus remain rare and most people who contract the disease do not have any symptoms. But scientists point to its spread as an indicator that rising temperatures spurred by climate change are bringing new threats to human health.
A spokesperson for the CRPD told The Guardian that “warm temperatures are contributing to the increase in mosquito numbers and the increased risk of transmission of the virus to humans,” but this activity remains within expected levels. People 50 and older, or those with diabetes or high blood pressure, are most at risk.
West Nile virus is difficult to track because most people show no signs of infection and trends are not easy to spot from year to year. But Cameron Webb, medical entomologist and senior researcher at the Center for Infectious Diseases and Microbiology – Public Health, says research shows drought is accelerating its spread.
“During drought, water levels in pipes, pits and ponds drop, and the water is more likely to stagnate,” he said. “Fish die along with other animals that live in these systems, and mosquitoes have carte blanche.”
In stormwater systems, regular rainfall drives out young mosquitoes and puts strain on their populations. “When it’s dry, conditions in man-made structures are actually better for these types of mosquitoes,” Webb added.
It doesn’t take much – mosquitoes are able to reproduce in a few milliliters of water, hatching hundreds of eggs that will be ready to bite humans and animals in just over a week.
Water scarcity also brings bird clusters closer to human settlements, and they play an important role in the transmission of the virus. “Because there is little water in the environment and everything is dry, birds will seek water and refuge, which tend to be where people live,” said Webb. Birds that are generally dispersed in the environment become more concentrated in urban areas, which amplifies infection rates.
“You bring people, wildlife and mosquitoes together, and that seems to be one of the key factors that could increase the risk of West Nile virus during drought years,” Webb added.
By mid-century, the increasing severity of the drought could triple the number of West Nile cases in areas with low human immunity, according to a study published in 2017. Illustrating how the climate emergency can alter transmission dynamics , a team of scientists studied 15 years of human case data in the United States and found that outbreaks of the disease, which typically occur in summer and fall, were greatest during dry years.
“We thought epidemics would coincide with the most ideal temperatures for transmission,” said Marm Kilpatrick, associate professor of ecology and evolutionary biology at the University of California, Santa Cruz, in a statement upon the publication of study. “Instead, we found that the severity of the drought was much greater at the national level, and drought also seemed to be a key factor in the majority of individual states. “
But in addition to the increased risks during times of drought, the findings indicate that there are also tools to tackle increased transmissions – and these are the same strategies needed for conservation when water is scarce.
Water use restrictions dramatically reduce the number of dangerous mosquitoes, according to a separate study published earlier this year. Scientists at the University of California at Los Angeles and three other universities found that without the policies in place to adapt to the last major drought, which lasted from 2012 to 2016, mosquitoes in Los Angeles County , which is home to 13.3 million people, would have been 44% higher, and they would be 39% higher in Orange County.
“We’re going to have a warmer climate and the demand for water for outdoor irrigation in particular will increase,” Dennis Lettenmaier, UCLA professor of geography and lead author of the study, said in a statement. “Efforts to reduce urban water consumption have a secondary benefit: they reduce the abundance of West Nile virus mosquitoes. “
That’s why Hayden of the Environmental Defense Fund says she has hope.
“The link between West Nile virus and drought is another one of those unanticipated and truly unfortunate impacts that we’re going to see from climate change,” she said, noting that the loss of her father underscored how the devastating effects on individuals, families and communities can be. “But improvements can be made. We can create a positive impact if we can implement more resilient practices. “
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