NPR: ‘Flesh-Eating Parasites May Be Expanding Their Range As Climate Heats Up’ – According to models
Three years ago, Laura Gaither and her family spent their summer vacation in Panama City Beach, Fla. One afternoon, while rinsing sand off her feet, the 35-year-old Alabama resident felt something biting her legs and noticed tiny black bugs on her skin. Gaither brushed them away, and later, when she described the bites to local residents, they told her that she had likely been bitten by sand flies.
Three of Gaither’s five kids had been bitten, too, but she didn’t worry. The marks on their legs and arms looked like ant or mosquito bites, which can cause burning and itching, but usually subside within a week.
But about two weeks later, back at home, Gaither noticed that the bites had morphed into small open wounds. They worsened over the next couple of weeks, but when she took her children to their pediatrician, “he just chalked it up to eczema,” Gaither said.
Eventually Gaither took her young daughter, whose condition was the most concerning, to the emergency room at Children’s of Alabama, where she was tested for fungal and bacterial infections. The results came back negative, and the anti-fungal and steroid topical creams the doctors prescribed proved ineffective. Meanwhile, the ulcers kept growing larger and more painful.
Leishmaniasis, Gaither learned, is common in tropical and subtropical countries like Brazil, Mexico, and India. Looking through peer-reviewed papers, she saw pictures of leishmaniasis wounds that looked a lot like her own: crater-like ulcers coated with a thick, yellowish pus.
During the visits with her children’s pediatrician and in the ER, Gaither asked her doctors about the parasite. They dismissed the possibility that the family might have contracted a tropical disease without traveling abroad, she said. “Nobody would even entertain what I was saying.” That is, until the wound on Gaither’s knee worsened and, armed with research papers, she convinced her own physician to test a biopsy for leishmaniasis. The results were inconclusive.
Fortunately, by this time the children’s wounds had begun to heal. Three months after they appeared, the ulcers completely cleared up, leaving Gaither to wonder what really caused them. While her family’s ordeal has ended, scientists say the story of leishmaniasis in the U.S. is just beginning.
Now endemic in Texas and Oklahoma, the parasites may be moving north
Americans, it turns out, can be exposed to Leishmania parasites without leaving the country. The parasites are currently endemic in Texas and Oklahoma, and new studies suggest that they might be present in other states, including Florida. While reported cases of leishmaniasis contracted in the U.S. are currently negligible, they may soon be on the rise: As climate change pushes rodent and sand fly habitat northward, scientists caution that in the future, an increasing number of U.S. residents could be exposed to different varieties of the flesh-eating parasite.
Some strains of Leishmania parasites can be life-threatening. The one currently present in the U.S., Leishmania mexicana, induces milder symptoms and over time, can heal on its own. But if doctors fail to recognize it, or overreact to it, damages caused by wrong therapies and unnecessary toxic systemic medication can cause more harm than the disease itself.
Bridget McIlwee, an Illinois-based dermatologist, has treated patients who contracted leishmaniasis in Texas. She wants her colleagues to be more aware of the parasite’s expansion into the U.S. “It’s a pretty striking difference for a disease that we used to think of as limited to South America now extending as far north as Canada,” she said, “potentially within the next several decades.”
Every year, between 1.5 to 2 million people worldwide contract leishmaniasis, and around 70,000 die from it, mostly in poor rural areas. The most dangerous Leishmania strains, such as infantum and donovani, don’t just eat a person’s skin, they also infect the liver, spleen, and bone marrow, leading to death if not treated.
Drugs like miltefosine and amphotericin B, used to cure these strains of Leishmaniasis, are expensive or toxic, and not much funding goes into researching and developing better treatments. In 2007, the World Health Organization added leishmaniasis to the list of neglected tropical diseases, which mainly affect the word’s poor and do not receive much attention.
Different strains produce different symptoms
While Leishmania parasites are present in about 90 countries, the symptoms of an infection vary by strain. The mexicana strain, typically found in Mexico and Central America, causes skin sores that can sometimes take years to heal and leave ugly scars. Others, like panamensis, mostly found in Panama and Colombia, attack the mucous membranes that line the inside of the nose and mouth, disfiguring people permanently.
Most leishmaniasis cases treated in the U.S. are linked to international travel. But there is evidence that an increasing number of people are infected in the U.S., likely by Leishmania mexicana. Between 1903 and 1996, only 27 cases of locally-acquired leishmaniasis were reported in the U.S. Then, in just 10 years between 2007 and 2017, 41 new local cases were reported.
Scientists from the University of Texas at Austin and the National Autonomous University of Mexico spent hours doing fieldwork, catching sand flies and rodents in Texas and northern Mexico to pinpoint the species’ range. They then incorporated this data into computer models that map ecological niches — the highly specific environmental conditions in which these sand flies can sustain a population — and also took into account how temperatures across North America will be affected by climate change. This allowed the international team to predict the geographical expansion of sand flies and Leishmania-infected rodents.
According to the models, by 2020, the rodent-fly-parasite habitat was expected to extend to Oklahoma, Kansas, Arkansas and Missouri. By 2080, the results showed the habitat stretching as far north as southern Canada, exposing nearly 27 million North Americans to the disease.
“Climate change has a strong link with the emergence of zoonotic disease,” said Víctor Sánchez-Cordero, a study author and an ecology professor at the National Autonomous University of Mexico. “There is the possibility that there will soon be cases of human leishmaniasis in the U.S. where before [they] did not exist.” In fact, at least one case has already been reported as far north as North Dakota.