A rare virus spread by mosquitoes has killed one person in the US. The death, announced on 27 August, occurred in New Hampshire and is the state鈥檚 first known case of the virus since 2014. Massachusetts, New Jersey, Vermont and Wisconsin have each reported a case as well. The situation has become so concerning that some towns have closed parks after dusk 鈥� peak mosquito-biting hours 鈥� and restricted outdoor activities and public events.
Eastern equine encephalitis, which has a 30 per cent mortality rate, is endemic to the US. Yet outbreaks have become more frequent in recent years largely due to climate change, says at the Massachusetts Department of Public Health. While Massachusetts usually sees outbreaks every ten to 20 years, only four years have passed since the last one ended.
Warmer weather in spring and fall and wetter conditions have allowed mosquitoes to emerge earlier and survive later into the year, giving them a longer period in which to transmit disease, says at the University of Florida. Between 1979 and 2022, annual 鈥� when weather conditions are suitable for the pests 鈥� have increased by more than two weeks across much of the US. A warming climate also expands the insects鈥� geographic range. As a result, mosquito-borne illnesses are spiking across the world.
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For instance, Brazil has seen an increase of more than 800 per cent from last year in cases of Oropouche virus, which causes symptoms similar to dengue or Zika virus. Across five South American countries there have been more than 8000 cases 鈥� these include two deaths, the first ever known to be caused by the virus.
This year is already the worst on record for dengue, as well. As of July, more than 11 million cases of the virus, including more than 7000 deaths, have been reported worldwide. That is almost double the historically high number of cases seen in 2023. Dengue cases have been trending upwards for years now. For instance, there were about 170 cases of locally acquired dengue in the continental US in 2023, roughly equivalent to the . Europe has seen a similar trend, with only 73 locally acquired cases occurring on the continent between 2010 and 2021. But 2022 and 2023 saw a decade鈥檚 worth or more of cases in a single year.
This is partly due to the expanding range of mosquito species that can transmit dengue, such as Aedes albopictus. European regions with established populations of this species than doubled between 2013 and 2023. 鈥淚f we think about the sweet spot for transmission in terms of things like temperature and sufficient rainfall, as those shift poleward, you have more opportunities for [mosquito] introduction into new places,鈥� says Ryan.
To combat mosquito-borne illnesses, we can use lessons from the past. For example, the US was able to eradicate malaria in 1951 after spraying the now infamous pesticide DDT across affected communities. While effective, this had unintended consequences, decimating wildlife and raising people鈥檚 risk of cancers and neurological disorders.
But that doesn鈥檛 mean we should forego pesticides. We just have to be smarter about using them. For instance, Massachusetts began aerial spraying a pesticide called Anvil 10+10 this week to control the eastern equine encephalitis outbreak. Not only is this pesticide safer than DDT, but officials now warn residents to stay indoors during applications.
However, the simplest measures can sometimes be the most effective, says Ryan. This includes installing screens on windows and doors, emptying outdoor containers with stagnant water and wearing protective clothing. 鈥淭hose basic, household level protective measures can be a genuine game changer,鈥� she says.
Article amended on 30 August 2024
We clarified which states have recorded a death due to eastern equine encephalitis
