Leishmaniasis

Picture of a sand fly; photo courtesy of the CDC.

• Leishmaniasis is a disease caused by a parasite. The parasite spreads to mammals (humans or dogs, for example) from the bite of an infected sand fly getting its blood meal.
• Leishmania species of protozoa parasites cause the disease as they produce the symptoms during part of their life cycle in humans or other mammals.
• Receiving a sand fly bite is the major risk factor for leishmaniasis.
• Leishmaniasis is not contagious person to person.
• The incubation period varies from two weeks to years with an average of about two to six months.
• Symptoms and signs vary somewhat with the protozoal species (over 20 different species) from only skin lesions (ulcerations) to diffuse lesions on mucosal surfaces and for some patients, organ enlargement, fever, anemia, thrombocytopenia, and death.
• Medical professionals diagnose leishmaniasis by using microscopic exams of biopsy samples, PCR, and other immunologic tests.
• There are several drugs that treat the disease under certain conditions; however, miltefosine is the FDA-approved drug that treats all types of leishmaniasis.
• The prognosis for the disease ranges from fair to poor, as scarring often develops and most patients with untreated visceral disease will die.
• There is no vaccine or drug to prevent leishmaniasis. However, avoiding sand fly bites by wearing protective clothing and using insect repellent (for example, a DEET-containing spray) may reduce the risk of infection.

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).

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.