A virus that commonly infects young children has been found to love warm summers, and so could become more widespread as the planet heats up.
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Large outbreaks of hand-foot-mouth disease could increase by up to 40 per cent if global warming is left unchecked, according to a study published Wednesday in the Nature science journal.
The findings add to a growing pool of evidence that climate change worsens the spread of infectious diseases and creates greater headaches for already stretched health systems in developing countries.
Millions get the hand-foot-mouth disease every year, as the virus spreads easily between people. Outbreaks are common in the warmer months, and typically cause fever, rashes and oral sores in children. Japan faced a particularly strong episode in July with over 35,000 cases in each of the first three weeks, health officials reported.
The disease is rarely fatal, but there have been records of severe bouts. In 2012, over 50 children in Cambodia died from an especially strong variant of the virus, out of 78 cases uncovered in an investigation involving the World Health Organisation.
In the latest study, United States scientists dug into how strains of enteroviruses that cause the ailment in China and Japan had spread under various weather conditions in recent years. The transmission patterns were extrapolated to a worst-case future scenario United Nations scientists use, that roughly corresponds to over 5 degrees Celsius of planetary heating by year 2100. The world is currently about 1.3°C warmer than pre-industrial times.
The researchers found a clear connection between warm weather and early onset of outbreaks in a year. Humidity and rain, which are expected to increase in many parts of the world with climate change, did not appear to matter much. The link to temperature remains even when school semester dates – when children are packed into classrooms and can easily spread bugs – are accounted for.
Where climate change causes more seasonal extremes, there could also be fewer infections in a colder winter, creating less herd immunity and greater vulnerability to a big outbreak in the subsequent warm summer.
Such patterns are complex, but researchers believe they could matter even more than long-term temperature rise.
“Climate change implies more severe outbreaks in the future, but…changes to the seasonal range of temperature may matter more than changes to mean temperature for these types of diseases,” they wrote in the paper. A better understanding of these patterns could help build an early warning system for epidemics, they added.
The data for hand-foot-mouth disease was also cross-checked against transmission patterns for a sibling virus that causes polio – an infection that can lead to paralysis and death. Records from the United States many decades ago, before vaccination was common, were used. The polio numbers exhibited the same patterns against warm weather, but future projections were not made.
Globally, mass immunisation programmes have mostly defeated polio, though it still spreads in Pakistan and Afghanistan. Health authorities now worry of polio cases in Gaza, with its medical facilities wrecked by Israel’s invasion.
Climate change is already known to worsen many other forms of diseases. A 2022 study found that over half of known infectious illnesses will be aggravated by higher temperatures. For instance, a warmer and wetter world helps bring pathogen-laden mosquitoes to new places, widening the spread of dengue and malaria. The few major ailments bucking the trend include winter influenza.
Medical journal The Lancet reported at the end of last year that there have been “few, if any, signs of the urgently needed progress” to quit fossil fuels and halt climate change.
“The multiple and simultaneously rising risks of climate change are amplifying global health inequities and threatening the very foundations of human health,” wrote a group of over 100 doctors for the journal’s annual climate review.
