Leishmaniasis

What is Leishmaniasis? Sounds a bit like a psychological disorder of some sort, but in fact it is a vector-borne disease caused by parasitic protozoa of the genus Leishmania (pictured above). Despite the fact that Leishmania is one of the most common disease-causing protozoa in the world, as well as one of the most deadly (second only to malaria), you have probably never heard of it. Leishmaniasis is predominately found in tropical and sub-tropical regions, but most especially those areas where poverty is rampant, including parts of Africa, the Middle East, India, and Brazil. Those of us fortunate enough to reside in more “developed” countries are unlikely to encounter this parasite without a bit of travel.

Skin lesions on a survivor of kala-azar.

A more serious case of kala-azar.

Depending upon the species of the infecting parasite, there are three common forms of the disease: cutaneous, mucocutaneous, and visceral leishmaniasis. Cutaneous leishmaniasis usually results in skin sores, while mucocutaneous leishmaniasis produces lesions in the mucosa of the nose, mouth, and throat. Visceral leishmaniasis (often called kala-azar) is the most deadly, as it affects internal organs such as the spleen and liver, as well as bone marrow, and is fatal without treatment. Even if treated, survivors may develop skin lesions that can eventually grow and spread, leaving a constant reminder of the battle with the disease.

Leishmaniasis is a vector-borne disease as it is transmitted by an insect known as the sandfly, belonging to the sub-family Phlebotominae (family Psychodidae). Sandflies are much like tiny mosquitoes, in that the female sucks blood from her unsuspecting prey, and in the process can spread the parasite from one host to another. The blood meal is required by most species to be able to reproduce. In general, there are about 30 species of sandflies that can spread approximately 20 species of Leishmania parasites. These guys are so small and stealthy that people often fail to notice them, or even realize that they have been bitten.

The sandfly Phlebotomus papatasi taking a blood meal.

According to the World Health Organization (WHO): “Leishmaniasis threatens about 350 million men, women and children in 88 countries around the world. As many as 12 million people are believed to be currently infected, with about 1–2 million estimated new cases occurring every year.” Hundreds of thousands of people die each year as a result of this parasite, and countless survivors bear the disfiguring marks for the rest of their lives. No vaccines or prophylactic drugs exist to prevent the spread of the parasite, though various drugs exist that can be used to treat an infection, depending on the species of the parasite and the condition of the patient. Unfortunately, such treatments are seldom available, or affordable, where they are most needed, and the amount of research being conducted to overcome this deficiency is insufficient. With good reason, leishmaniasis has been classified as a Neglected Tropical Disease.

Here is a recent overview of some of the global challenges being faced by those who seek to increase funding for leishmaniasis research:

http://www.nature.com/news/projects-set-to-tackle-neglected-diseases-1.14474

One of the interesting points that is raised in this article is the fact that funding for drug development disproportionately favors diseases such as cancer and heart disease, which are a problem among more affluent societies. In other words, “first world problems”. This certainly makes sense, economically speaking, given that much (if not most) drug development and research takes place in more developed and affluent nations. Since most drug companies are corporations that must look out for the interests of their shareholders, there is little financial motivation to develop drugs that are needed in countries and by people who do not have the resources to pay for them. It is far more rewarding to research prescription medications that combat cancer, heart disease, mental illness, and other diseases…especially if the patient will be taking the drug for the remainder of his or her life, and the drug can be patented.

This actually relates to one of the major problems that we face when it comes to antimicrobial resistance: too few companies are willing to conduct the research. Just 20 years ago, there were eighteen major companies working to develop antibiotics. Today there are only four. Why? Because it is not profitable. Ideally, a patient with an illness takes a course of antibiotics and then is done. Vaccines are even less appealing because the ideal vaccine only needs to be administered once. Compare the returns on that with something like cholesterol medication, which patients might stay on for months, years, or a lifetime. From the perspective of a drug company, the best antibiotic would be one that a person takes for the remainder of his or her life. Likewise, the best demographic is going to be the population of a developed nation with disposable income and health care, not a population with no health care, no income, and barely the means to take in enough calories each to just survive. As a result, most of the funding for research into diseases like leishmaniasis comes from governments and donations from private philanthropies.

As often happens when writing articles such as this, I find that I come away with far more questions than I have the time to answer. Sadly, many of those questions do not have answers that can be easily found with a Google search. Questions like: How do we increase research funding for neglected diseases? Should government funding (tax dollars) be spent on such research? How do we encourage companies to address needed research for neglected diseases? What obligation, if any, do private companies, governments, or even the members of an affluent, developed society have to care about diseases such as leishmaniasis? If there is no obligation to care, is there a economic or practical reason why we should care? I leave you to ponder such questions, as I am, and hopefully I will be able to address some of them in a future post.

Thanks for reading!

Leishmaniasis scars.

Category(s): Science Stuff

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