Leishmaniasis overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Leishmaniasis is a disease caused by protozoan parasites that belong to the genus Leishmania and is transmitted by the bite of certain species of sand fly (subfamily Phlebotominae). Although the majority of the literature mentions only one genus transmitting Leishmania to humans (Lutzomyia) in America, a 2003 study by Galati suggested a new classification for American sand flies, elevating several subgenera to the genus level. Elsewhere in the world, the genus Phlebotomus is considered the vector of leishmaniasis.[1]
Most forms of the disease are transmissible only from animals (zoonosis), but some can be spread between humans. Human infection is caused by about 21 of 30 species that infect mammals. These include the L. donovani complex with three species (L. donovani, L. infantum, and L. chagasi); the L. mexicana complex with 3 main species (L. mexicana, L. amazonensis, and L. venezuelensis); L. tropica; L. major; L. aethiopica; and the subgenus Viannia with four main species (L. (V.) braziliensis, L. (V.) guyanensis, L. (V.) panamensis, and L. (V.) peruviana). The different species are morphologically indistinguishable, but they can be differentiated by isoenzyme analysis, DNA sequence analysis, or monoclonal antibodies.
Cutaneous leishmaniasis is the most common form of leishmaniasis. Visceral leishmaniasis is a severe form in which the parasites migrate to the vital organs.
Classification
In the medical field, leishmaniasis is one of the famous causes of a markedly enlarged spleen, which may become larger even than the liver. The four main forms of leishmaniasis include visceral leishmaniasis, cutaneous leishmaniasis, diffuse cutaneous leishmaniasis and mucocutaneous leishmaniasis.
Pathophysiology
Leishmaniasis is spread by the bite of some types of phlebotomine sand flies. Sand flies become infected by biting an infected animal (for example, a rodent or dog) or person. Since sand flies do not make noise when they fly, people may not realize they are present. Sand flies are very small and may be hard to see; they are only about one-third the size of typical mosquitoes. Sand flies usually are most active in twilight, evening, and night-time hours (from dusk to dawn). Sand flies are less active during the hottest time of the day. However, they will bite if they are disturbed, such as when a person brushes up against the trunk of a tree where sand flies are resting. Rarely, leishmaniasis is spread from a pregnant woman to her baby. Leishmaniasis also can be spread by blood transfusions or contaminated needles.
Epidemiology and Demographics
The number of new cases of cutaneous leishmaniasis each year in the world is thought to be about 1.5 million. The number of new cases of visceral leishmaniasis is thought to be about 500,000.
Risk Factors
People of all ages are at risk for leishmaniasis if they live or travel where leishmaniasis is found. Leishmaniasis usually is more common in rural than urban areas; but it is found in the outskirts of some cities. The risk for leishmaniasis is highest from dusk to dawn because this is when sand flies are the most active. All it takes to get infected is to be bitten by one infected sand fly. This is more likely to happen the more people are bitten, that is, the more time they spend outside in rural areas from dusk to dawn. Adventure travelers, Peace Corps volunteers, missionaries, ornithologists (people who study birds), other people who do research outdoors at night, and soldiers are examples of people who may have an increased risk for leishmaniasis (especially cutaneous leishmaniasis).
Diagnosis
Symptoms
Human leishmanial infections can result in 2 main forms of disease, cutaneous leishmaniasis and visceral leishmaniasis (kala-azar). The factors determining the form of disease include leishmanial species, geographic location, and immune response of the host.
Physical Examination
A physical exam may show signs of an enlarged spleen, liver, and lymph nodes. The patient may have been bitten by sandflies, or was in an area known for leishmaniasis.
Laboratory Findings
Diagnosis of visceral leishmaniasis may require taking a blood sample and/or taking a biopsy from the bone marrow to show the parasite. Diagnosis of cutaneous leishmaniasis will require a small biopsy or scraping of the ulcer. Diagnosis of mucocutaneous leishmaniasis requires a biopsy of the affected tissues.
Biopsy samples are examined by microscopy, culture and other methods to look for the parasite and identify the specific kind of Leishmania causing the ulcer. Some of these methods will give results within a few days, but culture may take 2-4 weeks to demonstrate the parasite.
Examination of Giemsa stained slides of the relevant tissue is still the technique most commonly used to detect the parasite.
Treatment
Medical Therapy
Medicines called antimony-containing compounds are the main drugs used to treat leishmaniasis. These include meglumine antimoniate and sodium stibogluconate. Other drugs that may be used include amphotericin B, fluconazole and pentamidine.
Surgery
Plastic surgery may be needed to correct the disfigurement caused by sores on the face (cutaneous leishmaniasis). Patients with drug-resistant viral leishmaniasis may need to have their spleen removed.
Prevention
The best way for travelers to prevent leishmaniasis is by protecting themselves from sand fly bites. Vaccines and drugs for preventing infection are not yet available.
References
- ↑ Myler P; Fasel Nhirf;f). (2008). Leishmania: After The Genome. Caister Academic Press. p. [page needed]. isbn = 978-1-904455-28-8.