Leishmaniasis

Synonyms

4

Overview

Leishmaniasis is a parasitic disease spread by the bite of infected sand flies. There are several different forms of leishmaniasis. The most common are cutaneous and visceral. The cutaneous type causes skin sores. The visceral type affects internal organs such as the spleen, liver and bone marrow. People with this form usually have fever, weight loss, and an enlarged spleen and liver. Visceral disease can be deadly without proper treatment. Leishmaniasis is found in parts of the Middle East, Central America, South American, Asia, Africa, and southern Europe. Most of these countries are in the tropics and subtropics. 

Leishmaniasis is considered one of the classic causes of a markedly enlarged (and therefore palpable) spleen; the organ, which is not normally felt during examination of the abdomen, may even become larger than the liver in severe cases.

Symptoms

Signs and symptoms can be divided by the type of leishmaniasis:

  • Cutaneous leishmaniasis is the most common form, which causes an open sore at the bite sites, which heals in a few months to a year and half, leaving an unpleasant-looking scar. Diffuse cutaneous leishmaniasis produces widespread skin lesions which resemble leprosy, and may not heal on its own.
  • Mucocutaneous leishmaniasis causes both skin and mucosal ulcers with damage primarily of the nose and mouth.
  • Visceral leishmaniasis or kala-azar ('black fever')  include fever, damage to the spleen and liver, and anemia.
  • Markedly enlarged (and therefore palpable) spleen; the organ, which is not normally felt during examination of the abdomen, may even become larger than the liver in severe cases.

Causes

Leishmaniasis is transmitted by the bite of infected female phlebotomine sandflies which can transmit the infection Leishmania. The sandflies inject the infective stage, metacyclic promastigotes, during blood meals. Metacyclic promastigotes that reach the puncture wound are phagocytized by macrophages and transform into amastigotes. Amastigotes multiply in infected cells and affect different tissues, depending in part on which Leishmania species is involved. These differing tissue specificities cause the differing clinical manifestations of the various forms of leishmaniasis. Sandflies become infected during blood meals on infected hosts when they ingest macrophages infected with amastigotes. In the sandfly's midgut, the parasites differentiate into promastigotes, which multiply, differentiate into metacyclic promastigotes, and migrate to the proboscis

Risk factors:
Risk factors include poverty, malnutrition, deforestation, lack of sanitation and urbanization 

Prevention

  • Leishmaniasis can be partly prevented by using nets treated with insecticide while sleeping.
  • Use of insecticide-impregnated dog collars and treatment/culling of infected dogs.
  • Spraying houses and animal shelters with insecticides.
  • Manage risk factors such as keeping good sanitation  

Diagnosis

Leishmaniasis is diagnosed in the hematology laboratory by direct visualization of the amastigotes (Leishman-Donovan bodies). Buffy-coat preparations of peripheral blood or aspirates from marrow, spleen, lymph nodes, or skin lesions should be spread on a slide to make a thin smear and stained with Leishman stain or Giemsa stain (pH 7.2) for 20 minutes. Amastigotes are seen within monocytes or, less commonly in neutrophils, of peripheral blood and in macrophages of aspirates. They are small, round bodies 2–4 μm in diameter with indistinct cytoplasm, a nucleus, and a small, rod-shaped kinetoplast. Occasionally, amastigotes may be seen lying free between cells. However, the retrieval of tissue samples is often painful for the patient and identification of the infected cells can be difficult. So, other indirect immunological methods of diagnosis are developed, including enzyme-linked immunosorbent assay, antigen-coated dipsticks, and direct agglutination test. Although these tests are readily available, they are not the standard diagnostic tests due to their insufficient sensitivity and specificity.

Several different polymerase chain reaction tests are available for the detection of Leishmania DNA. With this assay, a specific and sensitive diagnostic procedure is finally possible.

Most forms of the disease are transmitted only from nonhuman animals, but some can be spread between humans. Infections in humans are caused by about 21 of 30 species that infect mammals; the different species look the same, but they can be differentiated by isoenzyme analysis, DNA sequence analysis, or monoclonal antibodies.

Prognosis

Visceral leishmaniasis or kala-azar ('black fever') is the most serious form, and is potentially fatal if untreated.

Treatment

Approved therapies:

  • Amphotericin B Liposomal (AmBisome) - FDA-approved indication: Treatment of visceral leishmaniasis. 
  • miltefosine (Impavido) - FDA-approved indication: Treatment of visceral leishmaniasis due to Leishmania donovani; cutaneous leishmaniasis due to Leishmania braziliensis, Leishmania guyanensis, and Leishmania panamensis; and mucosal leishmaniasis due to Leishmania braziliensis.

Resources

Refer to Research Publications