US and Brazilian researchers say they’ve taken a big step toward a vaccine that could stop a flesh-eating parasite that’s moving northward due to climate change.
Leishmaniasis is a disfiguring condition that causes skin ulcers and boils and sometimes launches potentially life-threatening attacks on the digestive system. It’s caused by a single-celled pest that’s passed to humans by the bite of the sand fly, sickening as many as 1 million people a year and killing up to 30,000, according to the World Health Organization.
But scientists may have found a way to disrupt the Leishmania parasite using a bioengineered, virus-like particle and a compound that unmasks the parasite and opens it up to attack from the body’s own defenses.
“It can help the whole immune system to target this parasite,” said Alexandre Marques, a microbiologist who studies parasites at Brazil’s Federal University of Minas Gerais. “It won’t allow this parasite to reproduce inside your cells or reach different organs to cause different symptoms.”
In study results published Tuesday, Marques and Georgia Tech chemist MG Finn found their potential vaccine effectively eliminated the parasite in mice whose immune systems had been genetically modified to mimic human defenses. It targets a carbohydrate found on the parasite that helps the organism evade detection and hole up inside the body.
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The process uses an artificially generated, virus-like particle developed at Georgia Tech to boost the body’s production of antibodies. Once activated, the antibodies seek out and destroy the parasite. All of the mice who received the vaccine had extremely low or non-detectable levels of Leishmania afterward, Marques said.
Using a virus-like particle allows scientists to trick the immune system into reacting, Finn said. It’s safer than other vaccines that use a weakened or inert form of a disease, but are not always as effective, he said.
Of 15 mice that received vaccinations, none showed any signs of the parasite. Autopsies on six of those mice confirmed they were Leishmania-free, Marques said.
Most of the time, leishmaniasis causes skin lesions that leave permanent scars — but it can spread to the liver and spleen, causing fever and anemia. The more serious form is called visceral leishmaniasis, often known as kala azar. There is no vaccine, and treatments can involve side effects ranging from nausea to pancreatic and heart conditions.
Leishmaniasis is already in about 90 countries Southern Europe, Central America, and Mexico. A few cases of cutaneous leishmaniasis — the kind that causes skin sores — have turned up in Texas and Oklahoma, according to the US Centers for Disease Control and Prevention.
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But the sand flies that carry the parasite can thrive in rainy environments with temperatures above 30 degrees Celsius (86 degrees Fahrenheit), Marques said — conditions that are expected to become more common in North America in an era of warming temperatures.
“This facilitates the conditions for the sand fly to survive because they have the rain, temperature, and humidity that are perfect for them to survive, reproduce, and pass the parasite to new hosts,” he said.
The findings appeared in ACS Central Science, a research journal of the American Chemical Society.
Marques said the same process might help in the search for a vaccine for Chagas disease, another tropical parasite similar to Leishmaniasis. But studies will have to be done on more complex animals like primates before the vaccine will be ready for human trials.
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