Since 2003, mosquitoes carrying a disease known as the West Nile virus have appeared in the US thanks to the warming climate. According to the Centers for Disease Control (CDC), about 2,300 people in the US have died from the disease – and as the climate continues to warm, more cases will be found, experts have said.
As the name suggests, the virus, and the mosquitoes carrying it, originate from the Nile, in northern Africa, where conditions are much more warm and humid.
However, climate scientists believe that as the US, particularly in the south west such as California, gets warmer, more cases will be discovered which will inevitably lead to more deaths from the disease which currently has no vaccine.
A study from the University of California (UC) Berkeley analysed 2 million mosquitoes which had been captured across California between 2006 and 2016.
All of the mosquitoes had been tested for West Nile virus, and then machine learning software cross-referenced whether the virus was present, and where the mosquitoes had been found.
The team found that infection among captured mosquitoes was strongly associated with the average temperature in the neighbourhood, according to the research published in the journal Proceedings of the Royal Society B.
Nicholas Skaff, the lead author of the study and a former postdoctoral scholar in environmental health sciences at UC Berkeley’s School of Public Health, said: “Our data revealed a sharp transition, whereas temperatures shift between 70 to around 73 degrees Fahrenheit—the likelihood of capturing infected mosquitoes in LA neighbourhoods increases dramatically.
“Above this range, conditions become consistently favourable for transmission, and below this range, conditions are consistently unfavourable.”
The coast of California is expected to undergo noticeable warming in the coming decades, which could prove to be the perfect breeding ground for the disease-carrying mosquitoes, said Justin Remais, associate professor of environmental health sciences at UC Berkeley.
He said: “Coastal LA appears to be vulnerable to the expected warming of California’s climate by mid-century, which will push coastal climates more consistently into the favourable zone.
“Inland LA may not be as susceptible to these shifts, as the climate is already favourable.
“Yet, as climate warming progresses towards the century’s end, it is possible that temperatures become too hot in these areas.”
Mr Skaff continued: “Our research suggests that, rather than focusing on daily weather reports, it’s important to examine temperatures over the long haul.
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“If coastal Los Angeles experiences a month or two of warm temperatures during the summer or early fall, it’s probably a good time to be extra careful to avoid mosquito bites.
“Inland parts of LA are almost always sufficiently hot during the summer, so other factors end up determining whether intense transmission occurs there.
“You can think of the favourable temperature range we identified as a prerequisite—if other things don’t go right for the vector or the virus, transmission may still not occur, even when temperatures are favourable.
“For example, if most of the susceptible birds in the region were infected during the previous year or two because a large outbreak occurred, herd immunity will be high, and the risk to people will be limited.”
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