Neglected Tropical Disease Leishmaniasis Is Spreading Again

The Parasite Nobody Talks About Is Back

The female sandfly is not a dramatic insect. She is small enough to slip through standard mosquito nets. She does not buzz. Her bite is painless. By the time you notice anything is wrong, weeks have passed. Then a small red bump appears on your skin. It looks like a mosquito bite that never healed. Then it grows. Then it opens into a ulcer. Then it stays that way for months.

This is cutaneous leishmaniasis. It is caused by a protozoan parasite called Leishmania, transmitted by the bite of an infected female sandfly. The World Health Organization calls it an emerging and uncontrolled disease. It is also a neglected tropical disease, which is a polite way of saying that the people who get it are poor, and the people who could cure it have better things to do.

According to de Vries and Schallig (2022), there are currently 12 million cases of cutaneous leishmaniasis worldwide. Every year, 2 million new infections occur. The disease is endemic in nearly 100 countries. Around 350 million people are at risk. And despite all of this, most doctors in wealthy countries have never seen a case. Most medical textbooks give it a paragraph. Most pharmaceutical companies have never bothered to develop a proper treatment.

That is starting to become a problem.

Why This Disease Is So Hard to Diagnose

Cutaneous leishmaniasis presents a diagnostic puzzle that would frustrate any clinician. The initial bump looks like dozens of other skin conditions. It can be mistaken for a bacterial infection, a fungal infection, a spider bite, or even skin cancer. By the time the ulcer appears, the patient has often been treated with antibiotics and antifungals that do nothing.

The real trick is that the Leishmania parasite is not one single organism. It is a complex of multiple species, each with different behaviors and different responses to treatment. De Vries and Schallig (2022) emphasize that species determination is critical for optimal clinical management. Treat a patient for the wrong species and you might as well be giving them sugar pills.

The gold standard for diagnosis has traditionally been microscopic examination of tissue samples. A clinician scrapes the edge of the ulcer, smears the material on a glass slide, stains it, and looks for the characteristic amastigote forms of the parasite. This works. But it requires skill, experience, and a decent microscope. In the remote rural areas where leishmaniasis is most common, these are not guaranteed.

New DNA techniques have changed the picture. Polymerase chain reaction tests can identify the specific Leishmania species with high accuracy. But de Vries and Schallig (2022) note that these methods are not easily implemented in resource limited settings. The equipment is expensive. The reagents need cold storage. The technicians need training. And the patients are often hours away from the nearest laboratory.

So the situation is this: we have the technology to diagnose the disease properly, but we cannot deploy it where it is needed most. The authors call this a desperate need. That word is not an exaggeration.

The Treatment Problem Nobody Solved

If you have cutaneous leishmaniasis in a developed country, you will likely receive a course of intralesional therapy. This means a doctor injects an antimonial drug directly into the edge of each lesion. It is painful. It requires multiple visits. But it works, at least for the most common species.

De Vries and Schallig (2022) state that intralesional therapeutic options are the first treatment option for most cutaneous leishmaniasis patients. But there is a catch. For patients with mucocutaneous involvement, where the parasite has spread to the mucous membranes of the nose and mouth, or for those with disseminated disease, where lesions appear all over the body, local treatment is not enough. These patients need systemic therapy, which means taking drugs orally or intravenously that circulate throughout the body.

The problem is that the systemic drugs available for leishmaniasis are toxic. Pentavalent antimonials can cause pancreatitis, cardiac arrhythmias, and liver damage. Amphotericin B is effective but has a reputation among clinicians as a drug that makes patients feel terrible. Miltefosine is the only oral agent, but it causes gastrointestinal side effects and is teratogenic, meaning it cannot be used in pregnant women.

The authors point out that different Leishmania species vary in their treatment outcomes. What works for one species may fail for another. This is why species identification matters so much. But it also means that even if you get the diagnosis right, you might not have the right drug available.

There is a special tragedy here for children. De Vries and Schallig (2022) specifically highlight the desperate need for novel, less toxic, and less painful treatment options for children with cutaneous leishmaniasis. Children get the same painful injections. They get the same toxic drugs. But their bodies are smaller and more vulnerable. The authors note that large, well conducted studies required to provide the necessary evidence for pediatric treatments are lacking. Nobody has done the trials.

Why Drug Companies Are Not Interested

This is the part that makes the whole situation feel avoidable.

Cutaneous leishmaniasis primarily affects poor people. De Vries and Schallig (2022) state this directly: biotechnical companies dedicate little investment into the research programs that could lead to diagnostic, pharmaceutical, and vaccine innovations because the disease primarily affects poor people.

This is not a conspiracy. This is basic market economics. Pharmaceutical companies spend billions developing new drugs because they expect to make billions in return. A drug for leishmaniasis, sold mainly in rural Africa, the Middle East, and South America, will not generate that return. A drug for erectile dysfunction or baldness will.

So the research that does exist comes from academic institutions, government agencies, and nonprofit organizations. It is underfunded, understaffed, and slow. The authors describe the situation as one where we urgently need to improve vector control, diagnostics, and vaccines. But urgency is not the same as action.

The Vector Problem

The female sandfly is not easy to control. She breeds in cracks in walls, in animal burrows, in piles of rubble. She is active at dusk and during the night. She feeds on blood to develop her eggs, and she picks up the Leishmania parasite when she feeds on an infected human or animal.

Standard mosquito control measures do not work well against sandflies. Insecticide treated bed nets help, but the sandfly is small enough to pass through the mesh if it is not fine enough. Indoor residual spraying works, but it requires consistent application and maintenance. And in areas of conflict or displacement, which are often the same areas where leishmaniasis is spreading, these measures fall apart.

The authors call for improved vector control, but they do not pretend there is an easy solution. The sandfly is adaptable. The parasite is adaptable. And the human populations at risk are often mobile, displaced, and lacking access to basic healthcare.

What the Research Does Not Tell Us

De Vries and Schallig (2022) provide a comprehensive review of the current state of cutaneous leishmaniasis management. But the paper is a narrative review, not a randomized controlled trial. It synthesizes existing knowledge rather than generating new data. This means there are important questions the paper cannot answer.

We do not know exactly how many cases go undiagnosed. The 2 million annual new cases is an estimate, but the true number is likely higher. Many patients in endemic areas never seek medical care. They treat their ulcers with traditional remedies or simply wait for them to heal on their own, which can take months or years.

We do not know why some people develop severe disease while others have mild symptoms that resolve spontaneously. The immune response to Leishmania is complex and poorly understood. Some people clear the infection without treatment. Others develop disfiguring lesions that persist for years.

We do not know the full extent of drug resistance. The authors note that treatment outcomes vary by species, but systematic surveillance for drug resistance is lacking in most endemic areas.

And we do not know how climate change will affect the distribution of the disease. Sandflies are temperature sensitive. As the planet warms, their range is expanding into areas that were previously too cold. Cutaneous leishmaniasis has been reported in southern Europe, in Texas, and in parts of Central Asia where it was previously rare. The paper does not address this directly, but the implications are clear.

A Disease of Neglect

The word "neglected" in neglected tropical disease is not a clinical term. It is a political one. It describes diseases that affect the world's poorest populations and receive a fraction of the research funding that goes to conditions affecting wealthier people.

Cutaneous leishmaniasis is not a disease that kills quickly. It does not cause the dramatic hemorrhagic fevers that make headlines. It does not spread through the air like influenza. It does not cause global pandemics. It just causes ulcers that last for months, scars that last for life, and social stigma that lasts forever.

In many endemic areas, people with visible facial lesions are ostracized. Women with scars are considered less marriageable. Children are kept out of school. The psychological burden is enormous, but it is not measured in the same way as mortality rates.

De Vries and Schallig (2022) list the disease as an emerging and uncontrolled disease. That word "emerging" is carefully chosen. It means the situation is getting worse, not better. It means the old approaches are not working. It means the disease is spreading into new areas and new populations.

What This Actually Means

The paper by de Vries and Schallig (2022) is a call to action, but it is a measured one. The authors are clinicians and researchers who have spent years working on this disease. They are not alarmists. They are realists.

• ▸If you are a clinician in a non endemic area, learn to recognize cutaneous leishmaniasis. Travelers and migrants are bringing it with them. A non healing ulcer in someone who has been to Central America, the Middle East, or East Africa should raise suspicion. Species identification is critical. Send tissue for PCR if you can.

• ▸If you work in public health, push for better diagnostics in endemic areas. The DNA techniques exist. The barrier is not scientific, it is logistical and financial. Mobile PCR platforms and point of care tests could change the picture, but they need investment.

• ▸If you are involved in drug development, consider that the market for leishmaniasis treatments is not zero. There are 12 million existing cases and 2 million new ones every year. The patients are poor, but the global burden is large. Pediatric formulations are especially needed.

• ▸If you are a funder, look at the vaccines. There is no licensed vaccine for cutaneous leishmaniasis in humans. The authors state that we urgently require efficient and safe vaccines. The science is there. The investment is not.

• ▸If you are a patient or a caregiver, do not accept a diagnosis of "mystery ulcer" without a proper workup. Push for species identification. Ask about intralesional therapy. And understand that the treatment may be painful and prolonged, but it is better than letting the disease run its course.

The female sandfly will keep biting. The parasite will keep multiplying. The ulcers will keep forming. The only question is whether we will keep ignoring them.