Climate change is causing diseases like dengue, as well as flesh-eating bacteria to flourish
An outbreak of a deadly and rare brain disease has killed at least 11 people in the United States so far this year. Scientists say the mosquito-borne illness, Eastern equine encephalitis, may be worse because of unseasonably warm temperatures. It’s one of just several diseases scientists worry are being affected by climate change.
The nation’s changing climate patterns are bringing heatwaves, flooding, warming waters and droughts. These in turn alter the environment, and the microbes, viruses and insects that inhabit it in ways that can cause them to increase or appear in new areas and at different times than before.
While it’s difficult to attribute any particular disease event to global warming, it’s safe to say that climate change will change disease dynamics, said Erin Mordecai, a professor of biology at Stanford University in California, who studies the ecology of infectious disease.
“We’re poised for a lot of surprises,” Mordecai said.
Eastern equine encephalitis virus
One is Eastern equine encephalitis virus, or EEE, which kills a third of all people who get it. A mosquito-borne virus, it tends to come in cyclical waves with large outbreaks occurring many years apart. This is the biggest outbreak since the 1950s or 1960s, said Mordecai.
There are no definitive ties to global warming in this outbreak but “this is such an emerging story there hasn’t been time to research it yet,” Mordecai said.
What is known is that the mosquitoes which transmit the virus thrive in warmer temperatures and die off at the first hard frost.
That’s where climate change comes in. The Earth just had its warmest September on record. The past five years have been the warmest since modern record-keeping began in the 1880s, according to NASA.
Earlier springs, later falls and hotter months in between contribute to higher mosquito populations and a greater chance of infection.
“The longer the breeding season, the more baby mosquitoes that are going to hatch and the more your chance of getting bitten,” says George Rutherford, a professor infectious disease and epidemiology at the University of California, San Francisco.
EEE isn’t the only disease doctors are concerned about. Other illnesses that might be getting worse because of climate change include:
Transmitted by mosquitoes, some cases of dengue fever can result in a rare haemorrhagic form that can kill. Dengue was once known as “breakbone fever” for the severe muscle and joint pain it can cause. There have been outbreaks in Hawaii, Florida and Texas. And there is some concern it might spread because of longer mosquito breeding seasons caused by warmer weather.
“There’s been dengue in southern Texas, Hawaii and Florida and there will be dengue in other places,” said UCSF’s Rutherford.
West Nile Virus
West Nile virus is transmitted by infected mosquitoes and ticks. it was first discovered in 1937 in Uganda, but in recent years has spread; Germany reported its first case earlier this year. In a tiny percentage of cases it causes brain inflammation that can take weeks or months to recover from and sometimes causes permanent effects, according to the Centres for Disease Control and Prevention.
It is spread through the bites of infected mosquitoes and ticks. Last year, 167 people died from it in the US, according to the CDC, while around 90 died across Europe.
Chronic kidney disease
The “kidney stone risk belt” is an area across the warmer parts of the southeastern United States were the incidence of kidney stones is higher, which researchers believe is linked to hotter temperatures. When people sweat more they produce less urine, which raises their risk for kidney stones.
Research at the University of Texas Southwestern Medical Centre in Dallas predicts that the proportion of the US population living in high-risk zones for kidney stones will increase from 40 per cent in 2000 to 56 per cent by 2050 and to 70 per cent by 2095.
“The assumption is that the ‘stone belt’ will eventually expand as areas that were not as hot get hotter. We predicted that will lead to an increasing kidney stone rate across the United States,” said Yair Lotan, one of the authors of the research paper.
Such an infection is called primary amoebic meningoencephalitis, or PAM for short, and is almost always fatal.
For decades this very rare disease was mostly reported in the southern part of the United States. Infections in northern states, however, have begun to increase as water temperatures rise, according to the National Institutes of Health.
Vibrio vulnificus is a bacteria that lives in warm brackish water. It’s actually erroneously described as “flesh-eating” because it releases enzymes that can rot flesh and shut down internal organs. Infection can occur after handling or consuming seafood or coming into contact with seawater.
Warmer coastal water and flood conditions, which are increasing with climate change, can create a more hospitable environment for the bacteria, according to the CDC. The number of cases in areas where it was once rare also has been increasing.
Ticks that can carry Lyme disease, Rocky Mountain Spotted Fever and Babesiosis are all expanding into higher latitudes as temperatures rise. This is creating a larger area across which they can be transmitted.
The ticks are also emerging from their winter hibernation earlier and remaining active later into the autumn, increasing the possibility they will bite and infect humans.