Climate change is fuelling the spread of deadly tropical diseases

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Lomira Eisimgalale is a smiley and energetic kid. When a chicken fluttered across his path outside of his family’s hut, the seven-year-old wasted no time pursuing it, tailing the animal around the compound in his family’s village village near Korr in northern Kenya. Lomira gave a good chase, laughing as the animal squawked in annoyance, but in the end, the chicken won, slipping from Lomira’s grasp and vanishing into the tufts of grass that lay just beyond the hut. His small chest heaved with effort from beneath his green Ethiopia jersey, but he grinned despite his defeat.
His three-year-old sister was the same way, says his mother, Dubayo. “She was playful. She was joyous. She wasn’t shy at all.” Looking at Lomira now, with his full cheeks and bright eyes, it’s hard to picture the way he must have looked just months earlier, when he and his sister, Faridah, both fell sick with a mysterious illness that left them both with relentless high fevers and vanquished their appetites. Lomira was lucky: he recovered. Faridah did not.


When their children first became sick, Dubayo and her husband, Lolitay, didn’t know what to make of it. There was no evidence that the children had been bitten by anything – no rash, no red bumps, no itching. But pain relievers from the local dispensary failed to assuage their symptoms. After two weeks without improvement, they took them to the nearest hospital, more than 100 kilometres away in Marsabit. Doctors ran a battery of tests, drawing vial after vial of blood, a process that took an entire day. Each test came back negative. The doctors were puzzled, and Lolitay was growing desperate. “I asked the doctor, ‘What else have I not done for these children? Can we repeat anything? What is the problem?’” he says.
Finally, the doctors decided to test for kala-azar. It didn’t make sense, since it hadn’t been found in Korr before. Spread by the undetectable bite of female sandflies, kala-azar – Hindi for black fever – is one of the most deadly parasitic diseases in the world, second only to malaria. Early symptoms include fever and weight loss, but as it progresses, the internal organs enlarge, and the skin can take on a grayish hue – hence the name. Its victims are almost always those who are poor, and when left untreated, kala-azar has a mortality rate of 95 per cent. While it has existed in Kenya and several other countries for some time, lately, climate change is thought to be bringing it to places it never previously existed, like Korr.
Kala-azar, or visceral leishmaniasis, is just one of many vector-borne diseases proliferating in recent years. In July, the UN Environment Program released a report stating that warmer temperatures are fostering disease transmission both by increasing the population of vectors – including sandflies, mosquitos, and ticks – and by lengthening the season that the vectors are present.
“These insects are ectothermic, and more or less wholly at the mercy of the environment in which they live,” says Kris Murray, an associate professor of environment and health at Imperial College London’s MRC Centre for Global Infectious Disease Analysis. “So climate is going to affect pretty much all of the vector-borne diseases in some way, shape or form.”


While it’s impossible to know the full extent of the impacts that climate change are having on the spread of infectious disease, there are a few loose categories into which they can be organised: The first is the loss of biodiversity and changes in human land use – including deforestation, farming, and urbanisation—which disturbs the delicate buffer that has historically stood between humans and pathogens Then there are vector-borne diseases, like kala-azar, which are increasing as insects like mosquitoes, sandflies and ticks expand their geographic ranges and seasonal viability. Finally, warming temperatures are even bringing dead viruses back to life: an outbreak of anthrax in Siberia was thought to be caused by pathogens frozen inside a decades-dead reindeer, which were reanimated after a heatwave melted the permafrost.
Murray’s work focuses on modeling vector-borne diseases known to be climate sensitive already; namely, dengue, chikungunya and Zika, spread by the mosquito Aedes aegypti. “On a global level, the world’s becoming a more suitable place for this particular mosquito as a result of climate change,” he says.
This might be an understatement: last year, a study published in PLOS Neglected Tropical Diseases found that Aedis aegytpi, along with Aedes albopictus, will begin to creep into North America and Europe as those places become warmer. If no action is taken, they’ll pose a threat to 49 per cent of the world’s population by 2050. The range of malaria-carrying mosquitos is also growing, with increases in temperature, humidity and rainfall allowing them to proliferate in regions in the past they have not.
That said, human management has done a lot to decrease the burden of infectious diseases over the last several decades. In countries proactively tackling disease spread, infection rates have largely dropped. Malaria, for instance, has fallen dramatically in Asia: six countries along the Mekong River basin saw cases decrease by 76 per cent between 2010 and 2018.


But in Africa, where disease surveillance is lacking, cases have shot up, with an increase of one million cases between 2017 and 2018. This inconsistency in health protections, Murray says, makes it “very, very difficult to disentangle what we’re seeing with climate risk.”
It’s no secret, of course, that climate change is having outsized consequences for the world’s poor, in countries where management interventions are scarcest. In Kenya, kala-azar is thought to be spreading thanks to the changing distribution of sandflies, but also because of the way climate change is affecting human behaviours. Increasingly severe droughts have pushed the country’s pastoralist communities farther and farther afield to find water and graze their animals, exposing themselves to new diseases to which they have no immunity.
David Odhiambo Otieno, an epidemiologist who works in leishmaniasis control at the World Health Organization’s Kenya office, says one such drought is precisely what led to a major outbreak of kala-azar last year in Log-Logo, around 55 kilometres east of where the Eisimgalales live in Korr. In this case, the brutal dry spell forced herders to journey more than 250 kilometres from their native Samburu county, traversing northwest across a parched landscape rife with dangers ranging from armed raiders to wild animals.
While kala-azar is not endemic in Samburu, it does exist in arid Log-Logo. The herders, with immune systems weakened by malnutrition, paired with their lack of previous exposure to the sandflies, made ideal hosts for the disease to take hold. Within a few months, the number of cases had exploded. “It was a clear demonstration of the impact of migration, low-immunity, malnutrition, and population movements into a zone that is highly endemic,” Otieno says.
With better management, kala-azar could almost certainly be brought under control, regardless of the effects that climate change is having on its spread. But that lack of management is precisely what qualifies diseases like kala-azar as “neglected.” Even as cases of NTDs soar, funding for research is falling: In 2016, the United States spent $1.5 billion (£1.18bn) total for research on the three biggest three killers—HIV/AIDS, malaria, and tuberculosis. For the 20 NTDs identified by the WHO, it committed just $100 million (£78m) combined.
Evalyne Kanyina, a medical epidemiologist who authored a paper on the spread of kala-azar in Marsabit, says that she has seen sandflies spread to habitats where they were not before, flourishing in the new, drier conditions. Several studies from other parts of the world, like the Mediterranean and India, have shown that leishmaniasis-carrying sandflies are changing their range as temperature and precipitation shift. But lack of funding has prevented officials in Kenya from doing any sort of comprehensive surveillance.
“Kala-azar control and prevention has never had a budget line,” she says, adding that the Kenyan government – and international donors – have instead focused almost exclusively on the big three.
Disease prevention and control in Kenya falls to individual counties, which often lack the bandwidth to do anything more than respond to outbreaks as they happen. As a result, Kanyina says, efforts to control the disease are at best, sub-optimal. At worst, they’re nonexistent.
Lolitay Eisimgalale was in the hospital with his children for a month and a half. Treating kala-azar is expensive, painful, and comes with occasionally toxic side effects. Like many families in their menyatta, or homestead, money was an issue for the Eisimgalales. Lolitay had lost his job as a driver five years prior, and despite a desperate search, was never able to find another. To afford the hospital stay, food, treatment, and transportation, the Eisimgalales borrowed 20,000 Kenyan shillings, or around £150, from some shopkeepers in their community –an amount they were still working to repay eight months after the hospital visit.
Lomira began responding to treatments. But Faridah was only getting sicker. She was losing weight, and her abdomen was swelling. By now, her condition was becoming too serious for doctors in Marsabit to treat; Lolitay took her to another hospital in Meru, nearly 300 kilometers to the south. It’s a journey that takes at least half a day in good conditions, provided the dusty dirt roads haven’t been washed away by the fierce rains that punctuate the endless dry season. In Meru, doctors gave Faridah a CT scan, revealing dangerous enlargement of her spleen and liver. She needed to go to Nairobi.
It was decided that Lolitay would bring Faridah to the capital while Dubayo stayed behind with Lomira and their other four children. The ambulance to take them there would cost 10,000 Kenyan shillings, or around £75. Their village agreed to give the Eisimgalales the money. As Lolitay prepared himself to leave, Faridah died. “She was our only daughter,” he says. “We live every day remembering her.”
As the droughts worsen, it’s unclear how sandfly populations will react, and without adequate funding, researchers can only guess at where it will spread, and who will be affected. Scientists across all sectors have already observed massive repercussions from climate change, Murray says; what’s coming will be staggering.
The Eisimgalales are just one family, and kala-azar is just one disease. But NTDs kill more than 350,000 people each year. As climate change spirals out of control, it will always be the world’s poorest who bear the brunt of its effects. Not just from vector-borne diseases, Murray says, but “for every kind of effect that you can imagine for climate change.”
“It concentrates the impacts of these changes in the populations that are least able to cope with it in the first place,” he says.
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