Leishmaniasis lesions are sometimes referred to as "1-year sores."
Image credit: CDC/Dr. D.S. Martin
In many parts of the world, leishmaniasis is frighteningly commonplace. For the populations of poorer, hotter countries, the disease is a specter that haunts their daily lives. It has the ability to kill, maim and ostracize.
According to the World Health Organization (WHO), an estimated 12 million people are infected with leishmaniasis across 98 countries.
As many as 20,000-30,000 die at the hands of the disease yearly; millions more are permanently scarred.
Roughly 90% of leishmaniasis cases are to be found in just five countries: India, Bangladesh, Nepal, Sudan and Brazil.
Often referred to as a "flesh-eating" condition, leishmaniasis is a parasitic disease that can be fatal if sufficient health care is not received. Despite its prevalence, the West appears to be relatively ignorant of its horrors.
In this article, we will take a brief look at what leishmaniasis is, how it spreads and what might be done to limit its reach.
What is leishmaniasis and who is at risk?
Leishmaniasis is a disease spread by a protozoan parasite from the innocent-looking sandfly. At least 90 species of sandfly and upward of 20 species of Leishmania parasite work in conjunction to spread the life-threatening disease.
The cycle of infection begins when the sandfly feasts on the blood of an infected mammal. It then returns the parasite to the warmth of a new host with its next feed. Once within the body, the parasite sets up shop inside the host's immune cells, specifically the macrophages.
Macrophages are designed to kill intruders and break them into their constituent parts, but the leishmaniasis parasite is well-designed to avoid their onslaught. The protozoa uses proton pumps to protect itself from the acidic environment within the macrophages and acid phosphatases to disarm the host's enzymes; in this way, the Leishmania parasite is able to survive in the most hostile of environments.
It seems that this pairing of Phlebotomus sandfly and Leishmania parasite has been working against humanity since time immemorial. Some believe the so-called plague of boils in the Bible might refer to leishmaniasis:
Exodus 9:9: the "breaking out in sores on man and beast throughout the land of Egypt."
The people most at risk of the disease are those who live in areas frequented by the sandfly species that carry the parasite. These species are suited to a number of very different environments; they can thrive in forests or deserts or anywhere warm in between. This makes the disease's epidemiology multifaceted and incredibly difficult to control.
In general, it is the poorer nations of the world who are at greatest risk. This is partly because leishmaniasis relies on a host's immune system to be weakened by disease or malnutrition before it can take hold of the victim. Additionally, the conditions of poverty, as we shall see later, make the perfect breeding ground for sandflies.
In the US, according to the CDC, leishmaniasis is incredibly rare. Other than a small number of cases in Oklahoma and Texas, individuals with the disease have always recently returned from countries where leishmaniasis is resident.
Types of leishmaniasis
Because of the large variety of Leishmania parasites, the disease itself has a range of possible characteristics. In general, there are three major types of leishmaniasis, defined as follows:
- Leishmaniasis is caused by a parasite transmitted by a sandfly bite
- At least 98 countries are infected by leishmaniasis
- The conditions created by a war zone favor leishmaniasis transmission.
Cutaneous leishmaniasis (CL): CL is the most common form of the illness and is the origin of its "flesh-eating" moniker. Ulcers appear at the site of the sandfly's bite, they do not easily heal and leave permanent scars on the skin. The "diffuse" version of CL produces lesions across the entire body that resemble leprosy. Two thirds of new cases occur in Afghanistan, Algeria, Brazil, Colombia, Iran and Syria
Approximately 0.7 million-1.3 million new cases of CL are reported each year
Visceral leishmaniasis (VL): also known as kala-azar (black fever), the symptoms include fever, weight loss, anemia and enlarged organs, particularly the spleen and liver. This variant is fatal if left untreated. The majority of cases are to be found in Bangladesh, Brazil, Ethiopia, India, South Sudan and Sudan
There are around 200,000-400,000 new cases of VL reported worldwide each year
Mucocutaneous leishmaniasis (ML): ML is the rarest of the three types. If left unchecked, it can completely destroy the mucosal membranes of the nose, mouth and throat. Without treatment, ML is generally fatal. An estimated 90% of ML cases occur in Bolivia, Brazil and Peru
The number of ML cases that occur each year is unknown.
Worst affected by leishmaniasis are countries where the majority of the population live in poverty; along with Chagas disease, dengue and sleeping sickness, leishmaniasis is classed as a "neglected disease."
These neglected diseases receive little research funding. They are considered "diseases of poverty."
The social impact of cutaneous leishmaniasis
Alongside the obvious health implications of open sores in a poverty-stricken environment, the lesions caused by CL can have significant social ramifications.
A case of leishmaniasis in Jerusalem, 1917 - known in the region as "Jericho buttons."
Image credit: Library of Congress
Because the lesions of CL occur at the site of the sandfly bite, they are much more prevalent on exposed areas of skin, such as the hands and face. In other words, they are clearly visible.
In a survey conducted on the women of Kabul, a large majority believed the wounds caused by CL were transmissible by human-to-human contact or by "sharing meals and household goods."
People with the disease can be ostracized; women suffer particularly harsh consequences, being deemed unfit for marriage or raising children.
More than 1 in 5 of the questionnaire's respondents said that a mother with CL should not breastfeed her child; more than half admitted they would not let an afflicted individual touch or hug their child.
It is not difficult to imagine the negative psychological impacts of being ostracized, mistrusted and even feared.
Additionally, women are less likely to seek treatment for the disease because of the attached stigma.
War and leishmaniasis
Although leishmaniasis can only be contracted by a bite from a sandfly, people moving en masse in poverty stricken areas where these vectors are present can increase the rate of transmission.
For a number of reasons, war is a leading factor in leishmaniasis epidemics. The living conditions that go hand in hand with conflict benefit the sandfly and put people in harm's way:
- Poor housing and lack of sanitary conditions can increase sandfly breeding rates
- Sleeping in crowded areas encourages sandflies to visit for regular blood meals
- Low-quality diets that lack iron, protein, vitamin A and zinc increase the risk that an infection will take hold
- Movements of non-immune humans into new areas where different strains of leishmaniasis may thrive have no protection against the disease.
In 2004, in the midst of war and turmoil, the struggling city of Kabul faced another kick in its already troubled guts. Leishmaniasis took hold. An estimated 67,500 cases were reported in the city alone, making it the biggest center for leishmaniasis in the world.
The presence of uncollected sewage in the streets was (and is) a major factor in outbreaks and a prevalence of great gerbils (Rhombomys opimus) as a reservoir for the parasites compounds the problem. For the last decade, Kabul has been one of the worst-affected cities in the world.
Leishmaniasis has been present in Syria for many years, often referred to in the literature as "Aleppo boil" or the "1-year sore." In the past, the disease has been contained and well-managed, but Syria's present strife has worsened conditions beyond all measure.
The current conditions in Syria are perfect for the transmission of leishmaniasis.
The exact number of cases is not known, the country is divided and taking accurate stock of disease is not currently possible.
Conditions for the spread of leishmaniasis are perfect, and the mass exodus of medical professionals and rapid disintegration of infrastructure has only compounded the problem.
A direct and purposeful assault on medical institutions laid waste to their health care capabilities. According to the WHO, 40% of Syria's ambulances have been destroyed and 57% of public hospitals are significantly damaged, with 37% completely out of service.
An estimated 80,000 doctors have emigrated and hundreds more have been executed or imprisoned.
Some individuals in Europe and the US have raised concerns that an influx of Syrian refugees might spark an outbreak of leishmaniasis on home soil. But, because transmission is dependent upon the bite of a sandfly, this is not a concern of any substance.
Added to this, leishmaniasis generally does not create symptoms in humans. To take hold and manifest the disease, the individual must be significantly immunosuppressed and/or suffering from malnutrition.
Modern drugs are effective at controlling and halting leishmaniasis' progression; additionally, locally specific environmental projects are ongoing to minimize the number of sandflies, their ability to breed and their access to human flesh.
Effective medicines are available, but prevention is key.
As far as pharmaceuticals are concerned, VL can be treated by liposomal amphotericin B (an antifungal), a combination of pentavalent antimonials, paromomycin (antibiotic) and miltefosine (antimicrobial).
For CL, paromomycin, fluconazole (antifungal) or pentamidine (antimicrobial) have shown some level of success.
Environmental interventions vary significantly dependent on the type of environment being considered, but methods include insecticide spraying, distribution of insecticide-treated nets and environmental management of areas particularly suited to sandfly breeding.
As with many efforts in disease control, education and communication programs are as essential as distribution and access to drugs. Early detection and consequent treatment helps stem the flow of human vectors.
Could a large-scale dog cull save the day?
Although, in the countries most troubled by leishmaniasis, humans appear to be the major reservoir of the disease, some scientists believe that dog populations could also play a part.
There is no question that the leishmaniasis parasite can live in dogs, but how it impacts the level of disease in the human population is hotly debated.
Whether dog-culling might help in the fight against leishmaniasis is being hotly debated in the Americas.
In some areas of Brazil, a country with one of the worst leishmaniasis problems, up to 50% of dogs have been found to carry the parasite that transmits the most sinister variant of the disease - VL.
Veterinarians are required by law to check dogs for the parasite and, if found, the animal is euthanized. This sounds sensible, but it is causing a backlash. It is easy to imagine the trauma experienced by a dog owner who takes their pet for a routine visit to the vets only to have it put down and incinerated, despite the animal showing no outward signs of illness.
To make matters worse, the test for the leishmaniasis parasite throws out more than 20% false-positives, so there is a 1 in 5 chance that your beloved pet has been killed entirely without reason.
There is much discussion as to the effectiveness of dog culls. It is unclear how much difference it can make. In 1950s China, a leishmaniasis outbreak sparked an extensive dog cull. Animal control personnel aimed to kill at least 75% of all dogs in the worst affected areas.
The Chinese cull did seem to work initially, but 4 years later, the remaining dogs had an even higher prevalence of Leishmania infection than prior to the cull.
Another issue that accompanies a dog cull is the human response to a lost pet. One Brazilian study found that roughly 40% of dog owners whose pet had been culled swiftly went out and invested in another dog. Often this new dog was a puppy and consequently more prone to infection. Within months, slightly less than 40% of these replacement pets had also been euthanized.
Mathematical modeling is being wheeled out in an effort to estimate the benefits of culling. The jury is, and will be for some time, out.
The future of leishmaniasis
To end on a low note, the prevalence of sandflies and their proximity to humans is only set to increase the burden of leishmaniasis on the global population. Deforestation and the consequent movement into areas inhabited by sandflies increases the chances of infection.
Added to this, global warming is widening the sandfly's territory. Tiny changes in temperature can have a colossal impact on the potential range of these vectors.
Of course, the troubles in the Middle East are not looking likely to evaporate anytime soon, maintaining one of the major hotbeds of leishmaniasis infection. Without a pointed effort to control, educate and design better treatments, leishmaniasis is set to continue casting its shadow.