Science Series #6: Leishmaniasis
What is leishmaniasis?
Leishmaniasis is a parasitic disease that is found in parts of the tropics, subtropics, and southern Europe. It is caused by infection with Leishmania parasites, which are spread by the bite of infected sand flies. Leishmaniasis is a neglected tropical disease and is associated with poor living conditions, malnutrition and lack of resources. More than 1 billion people live in areas that are endemic for the disease, thereby placing them at risk of infection. It is estimated that about 1 million cases occur annually.
Over 90 sand fly species are known to transmit Leishmania parasites. There are 3 main forms of the disease:
- Visceral leishmaniasis (VL), also known as kala-azar, is fatal if left untreated in over 95% of cases. It is characterized by irregular bouts of fever, weight loss, enlargement of the spleen and liver, and anemia. Most cases occur in Brazil, East Africa and in India.
- Cutaneous leishmaniasis (CL) is the most common form of leishmaniasis and causes skin lesions, mainly ulcers, on exposed parts of the body, leaving life-long scars and serious disability or stigma. About 95% of CL cases occur in the Americas, the Mediterranean basin, the Middle East and Central Asia.
- Mucocutaneous leishmaniasis leads to partial or total destruction of mucous membranes of the nose, mouth and throat. Over 90% of mucocutaneous leishmaniasis cases occur in Bolivia (the Plurinational State of), Brazil, Ethiopia and Peru.
(Source: World Health Organization)
How is leishmaniasis transmitted?
Leishmaniasis is transmitted by the bite of infected female phlebotomine sand flies. The sand flies inject the infective stage (the promastigotes) from their proboscis during blood meals. Promastigotes that reach the puncture wound are phagocytized by macrophages and other types of mononuclear phagocytic cells. The curious thing about this disease is that the infected body tries to defend itself with macrophages but the parasite manages to replicate inside of the human cells.
Parasite, host, and other factors affect whether the infection becomes symptomatic and whether cutaneous or visceral leishmaniasis results. Sand flies become infected by ingesting infected cells during blood meals. In sand flies, amastigotes transform into promastigotes, develop in the gut, and migrate to the proboscis.
(Source: Centers for Disease Control and Prevention)
- Breathing difficulty
- Skin sores, which may become a skin ulcer that heals very slowly
- Stuffy nose, runny nose, and nosebleeds
- Swallowing difficulty
- Ulcers and wearing away (erosion) in the mouth, tongue, gums, lips, nose, and inner nose
Adults usually have a fever for 2 weeks to 2 months, along with symptoms such as fatigue, weakness, and appetite loss. Weakness increases as the disease gets worse.
- Abdominal discomfort
- Fever that lasts for weeks; may come and go in cycles
- Night sweats
- Scaly, gray, dark, ashen skin
- Thinning hair
- Weight loss
(Source: National Organization for Rare Disorders)
How is leishmaniasis diagnosed?
It’s important to tell your doctor if you lived in or visited a place where leishmaniasis is common. That way your doctor will know to test you for the parasite. If you have leishmaniasis, your doctor will use other tests to determine which species of Leishmania is the cause.
Your doctor may take a small amount of skin for a biopsy by scraping one of the ulcers. They’ll often look for the DNA, or genetic material, of the parasite. They can use a variety of methods to identify the species of parasite causing the infection.
Many times, people don’t remember a bite from a sand fly. This can make the condition hard to diagnose.
A history of living or traveling to an area of leishmaniasis is helpful. Your doctor may first perform a physical exam to look for an enlarged spleen or liver. They may then perform a bone marrow biopsy or take a blood sample for examination.
A variety of specialized tests aid with diagnosis. Special chemical stains of bone marrow can help identify immune cells infected with the parasite.
How can I prevent leishmaniasis?
There is currently no vaccine or prophylactic medication available. The only way to prevent leishmaniasis is to avoid getting bitten by a sand fly.
Follow these steps to help prevent being bitten by a sand fly:
- Wear clothing that covers as much skin as possible. Long pants, long-sleeved shirts tucked into pants, and high socks are recommended.
- Use insect repellent on any exposed skin and on the ends of your pants and sleeves. The most effective insect repellants contain DEET.
- Spray indoor sleeping areas with insecticide.
- Sleep on the higher floors of a building. The insects are poor fliers.
- Avoid the outdoors between dusk and dawn. This is when sand flies are most active.
- Use screens and air conditioning indoors when possible. Using fans might make it more difficult for the insects to fly.
- Use a bed net tucked into your mattress. Sand flies are much smaller than mosquitos, so you need a tightly woven net. Spray the net with insecticide containing pyrethroid if possible.
- Buy bed nets, insecticides, and repellents before traveling to high-risk areas.
The most commonly used drugs in the treatment of cutaneous and mucosal leishmaniasis are pentavalent antimonials, in two different formulations: antimonate N-methylglucamine and sodium stibogluconate. Drugs such as pentamidine isethionate, miltefosine, amphotericin B and liposomal amphotericin B are other therapeutic options.
However, no single drug completely eliminates the parasite. Treatment includes disease management of the patient, the reduction of the parasite’s burden on the body and the resolution of skin or mucosal lesions by the monitored use of the appropriate medicines. The severity of adverse effects associated with systemic drugs treatment has led to the acceptance of local treatment (intralesional administration of meglumine anitmoniate or thermotherapy) for localized cutaneous leishmaniasis.
(Source: Pan American Health Organization)
Our background in Leishmaniasis
In 1948 Dr. Jacinto Convit began studies on leishmaniasis, another dermatological disease of great relevance in endemic regions. With the initial experience in leprosy, Dr. Convit and his team described the similarities between these two diseases according to the clinical, immunological and pathological aspects.
Years later, after the success of the leprosy therapeutic vaccine, in 1986 Dr. Convit used the same model to develop a vaccine to treat leishmaniasis. He mixed dead Leishmania promastigotes, harvested from in vitro cultured parasites, plus BCG vaccine. The effectiveness of the vaccine was mainly evaluated in the Localized Cutaneous Leishmaniasis form (LCL). The results showed that the therapeutic vaccine is very effective, managing to cure the disease in an adequate time without secondary phenomena, as well as being an accessible treatment.
In 2010, the World Health Organization recognized Dr. Convit’s treatment for leishmaniasis, as part of the first generation of vaccines against this condition. This vaccine has been used widely in Venezuela, and in certain countries of Latin America, to treat patients with LCL. Currently, it is not being produced, therefore new efforts need to be made to retake its production and application in poor endemic areas, where the chemotherapy treatment is less accessible or scarce.