An Important Step Toward Stopping a Parasitic Disease

/ 23 Oct 2017

An Important Step Toward Stopping a Parasitic Disease

BYBLOS, Lebanon—Researchers in Lebanon are racing to decode the genetics of a harmful and little-studied parasite that causes a disease that can spring up in the crowded confines of refugee camps. Understanding the parasite’s genetics could lead to a vaccine for the disease.

“Children are the most affected. We need to do work like this to help them,” says Tamara Salloum, who is collaborating on the research as part of her Ph.D. work at the Lebanese American University here.

Two years ago, the parasitic disease known as Leishmaniasis broke out among displaced Syrians in Lebanon. Doctors rushed to informal settlements where Syrians live to take tissue samples from patients for their diagnoses. They preserved the samples in formaldehyde. But formaldehyde degrades the parasite’s DNA, frustrating Salloum, who wanted to learn the specific characteristics of the strain causing the outbreak. Eventually she managed to get hold of an intact sample, which has now formed the basis of research that is the first step in a long journey toward a Leishmaniasis vaccine and improved treatment.

Some versions of the disease affect internal organs, but Salloum is focusing on the type of Leishmaniasis that occurs on the skin.

“This was the first time we’ve had this disease in Lebanon. It’s more common in Syria where they had around 50,000 cases a year before the war. It’s known as the Aleppo boil,” says Sima Tokajian, Salloum’s supervisor and an associate professor of molecular microbiology at the Lebanese American University.

Although an estimated one million new cases of the disease occur each year globally, it gets little attention from researchers. Financial support for the research is scarce, and the disease is officially classified as neglected by the United Nations. The researchers who are interested in the parasite say the shortage of funds is particularly frustrating because the parasite’s biology is not that complex. A way to defeat the disease could be found if researchers got better support, says Alvaro Acosta-Serrano, a senior lecturer in the department of parasitology at the Liverpool School of Tropical Medicine.

“Rich countries don’t pay attention because it only affects poor countries,” he says. “We would have found solutions by now if there was a market for the pharma companies.”

A resident of the Bekaa Valley camp points to raw sewage running between tents. Such conditions give sand flies, which carry the parasite, a place to breed. (Photo: DFID, Russell Watkins)

Leishmaniasis is often called a flesh-eating disease. That isn’t technically true, but the parasite does create disfiguring ulcers on the skin, which can become infected. A lot of stigma surrounds the disease, says Salloum, which means patients are often embarrassed and wait for a long time before seeking a doctor. That just provides the parasite and the ulcers it causes more time to spread.

The disease mostly affects refugees because of the conditions in camps. “You need to have sand flies and that’s linked to hygiene,” says Tokajian. Garbage and waste left in the open give sand flies a place to breed, and the flies, which are a third the size of mosquitos, bite humans and pass on the parasite. Cases have been seen in Jordan’s refugee camps too.

“This is just one of the many infectious diseases refugees are suffering from,” adds Salloum.

Before the war, Syrian government workers regularly sprayed pesticides to kill the sand flies, but that practice has ceased. The insect’s resistance to the pesticides has also increased, and sand flies can often slip through mosquito nets.

“The development of a vaccine is important because we’re never going to get rid of the disease by controlling the vector,” says Acosta-Serrano.

That’s why Salloum and Tokajian are working to decode the parasite’s genetic material. “When you sequence its genome, it will be like getting an instruction manual for how the parasite works, but you’ll still have to figure out how to read the manual,” says Acosta-Serrano.

“When you understand a parasite’s genes, you understand more about its biology and its origins,” says Tokajian.

The researchers hope the information they extract from the DNA will be the crucial first step toward a preventive vaccine.

“Different strains of the parasite have different susceptibility to the same drug and no one knows why,” says Salloum. “By looking at the genome we hope to find out why and then exploit this for drug or vaccine development.”

The current remedies for Leishmaniasis work, but they aren’t without considerable drawbacks.

One therapy consists of a series of painful, daily injections directly into the lesions. “For children to go through this, sometimes with ulcers on their face, is very traumatic,” says Acosta-Serrano.

Additionally, the treatment can harm the kidneys and liver.

Acosta-Serrano stresses that Salloum’s work is meaningful, but says it’s only the very first step toward improving disease treatment and prevention. Realistically, a vaccine is at least a decade away, he says.

“This is a long-term research aim,” he says. “Not to sound negative, but a vaccine is a dream and just sequencing a genome won’t do it. You need vaccination candidates, then you have to go through animal trials followed by human trials, and that needs millions of dollars.”

Tokajian agrees that it won’t happen in the short term, but ultimately takes a more optimistic outlook. “It might not be too late for the next outbreak,” she says.




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