What Is Leishmaniasis?
Leishmaniasis is a disease caused by an intracellular parasite (genus Leishmania) transmitted to humans by the bite of a female phlebotomine sand fly. Each year, about 900,000 to 1.3 million people develop leishmaniasis. Currently, about 12 million people worldwide suffer from leishmaniasis. There are about 20 or more pathogenic species of the genus Leishmania and about 30 to 500 different sand fly species, all of which can participate in transmitting the disease to humans and other mammals (for example, dogs).
What Are the Types of Leishmaniasis?
The types of this disease depend on which categorization system is chosen. There are two major systems to categorize leishmaniasis; one is based on clinical disease and are categorized as cutaneous, mucocutaneous, and visceral disease. Cutaneous can be further subdivided into localized, diffuse, and recidivans, while post-kala-azar dermal leishmaniasis occurs after recovery from visceral leishmaniasis. The second categorization system is based on geographic occurrence and has two major divisions -- Old World leishmaniasis (found in Africa, Asia, the Middle East, the Mediterranean, and India) and produces cutaneous or visceral disease, while the second division is termed New World leishmaniasis (found in Central America and South America) and produces cutaneous, mucocutaneous, and visceral disease.
What Causes Leishmaniasis?
The infectious intracellular protozoa, Leishmania, spread to mammals and humans when a very small (2-3mm or about half or one-third the size of a mosquito) female sand fly bites, and while getting a blood meal, transfers the parasite.
What Are Risk Factors for Leishmaniasis?
Exposure to sand fly bites are the highest risk factor. Sand flies are most active from dusk to dawn. People living in rural areas are at greater risk.
Is Leishmaniasis Contagious?
Picture of the leishmaniasis life cycle; image courtesy of the CDC.
Leishmaniasis is not contagious person to person. Sand fly bites are necessary to transfer the parasite from the sand fly to the human. The sand fly is the vector for the disease. The protozoan parasite has a life cycle that requires development in both the sand fly and a mammal (human, dogs and others).
What Is the Incubation Period of Leishmaniasis?
The incubation period for leishmaniasis is quite variable and may range from approximately two weeks to several years. However, most individuals develop symptoms after about two to six months.
What Are Leishmaniasis Symptoms and Signs?
Picture of a leishmaniasis skin lesion; photo courtesy of the CDC.
The symptoms of leishmaniasis depend on the area of the body affected:
- Cutaneous -- skin lesions (wet or dry ulcers) are usually painless (unless secondarily infected) and localized, but may become diffuse in people with a poor immune system. In some patients, even years after a lesion has healed, new ulcers may form from parasite reactivation or from a new sand fly bite containing another species of the parasite -- this is termed leishmaniasis recidivans.
- Mucocutaneous -- some types of cutaneous infections that spread (diffuse) to mucosal surfaces, especially the nose, mouth and/or throat; may be termed tegumentary
- Visceral -- an infrequent parasite type (viscerotropic) that spreads from the skin lesions to internal organs (for example, spleen, liver, lymph nodes, and/or the bone marrow) that result in organ enlargement, fever, anemia, and thrombocytopenia and can be life threatening. Kala-azar is a type of visceral leishmaniasis.
How Do Medical Professionals Diagnose Leishmaniasis?
Medical professionals use biopsy specimens to examine the tissues for parasites. Blood tests (for example, PCR and antibody detection) are methods that CDC infectious disease specialists use to detect and diagnose this disease.
What Is the Treatment for Leishmaniasis?
Some patients need no treatment and resolve the infection on their own. Treatment protocols should be individualized to the patient and the area of the body affected and, in the U.S., set up with consultation with the CDC as some treatment restrictions apply. Pentostam is available under an IND (investigational new drug) protocol from the CDC. Liposomal amphotericin B (AmBisome) is FDA approved for only visceral leishmaniasis. In 2014, the FDA approved miltefosine to treat all types of leishmaniasis. Other drugs used selectively are amphotericin B deoxycholate, pentamidine, and paromomycin, as well as some "azoles" like ketoconazole.
What Is the Prognosis for Leishmaniasis?
Cutaneous leishmaniasis may have a prognosis ranging from fair to poor as many patients may have scars where the skin and/or mucosal lesions first appeared. Untreated visceral disease usually is fatal.
Is It Possible to Prevent Leishmaniasis?
No vaccine or drug is available to prevent the disease. Avoiding sand fly bites by using protective clothing, remaining in screened areas and using insect repellants like DEET may prevent or reduce the chance of infection. Research centers on vector control (sand fly population reduction) and others are trying to determine if new drugs have effects on the parasites ability to survive in treated hosts.
C. "Leishmaniasis Clinical Presentation." Medscape.com. July 30, 2018. <https://emedicine.medscape.com/article/220298-clinical>.
United States. Centers for Disease Control and Prevention. "Parasites -- Leishmaniasis." July 26, 2018.