leishmaniasis
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What is leishmaniasis?
Leishmaniasis is a human protozoal infection transmitted through the bite of sand flies and is prevalent in tropical regions. It is caused by various species of the flagellate protozoan Leishmania, which infects vertebrates like rodents and canines. The parasites have two stages: the flagellated promastigote in the sand fly and the nonmotile amastigote in vertebrate cells. Depending on the Leishmania species and the host's immune response, three main types can occur.
Cutaneous leishmaniasis, the most common form, features skin lesions that can become ulcers and open sores. Visceral leishmaniasis affects the liver, spleen, and bone marrow. Mucocutaneous leishmaniasis can spread to mucous membranes. Treatments include antimicrobial drugs, antifungal drugs, and antimony compounds. Preventing the spread involves controlling sand fly populations.
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What causes leishmaniasis in the human body?
Leishmaniasis in humans is caused by various species of flagellate protozoans of the genus Leishmania. These parasites are transmitted through the bite of infected sand flies (specifically, Lutzomyia in the Americas and Phlebotomus in the Old World).
The parasites exist in two forms:
* Promastigote: The motile, flagellated form found in the sand fly's digestive tract.
* Amastigote: The nonmotile form found in vertebrate cells. Sandflies ingest amastigotes from infected vertebrates, which then transform into promastigotes in the sandfly's gut. These promastigotes migrate to the fly's saliva and are transmitted to humans during a blood meal, initiating a new infection.Depending on the Leishmania species and the host's immune response, leishmaniasis can manifest in three main forms: visceral, cutaneous, and mucocutaneous.
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How does leishmaniasis affect the skin and other organs?
Leishmaniasis, transmitted by sand fly bites, manifests in three main forms: visceral, cutaneous, and mucocutaneous. Cutaneous leishmaniasis results in skin lesions and ulcers, potentially leading to scars and disability. Mucocutaneous leishmaniasis can spread to the mucous membranes of the face, causing destruction of the nose, mouth, and throat. Visceral leishmaniasis affects the liver, spleen, bone marrow, and other viscera, leading to fever, weight loss, and enlargement of the spleen and liver. If untreated, visceral leishmaniasis is usually fatal.
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What are the main types of leishmaniasis and how do they differ?
Leishmaniasis, prevalent in tropical areas, is a human protozoal infection transmitted by sand fly bites. The three main types are visceral, cutaneous, and mucocutaneous.
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Visceral leishmaniasis (also called kala-azar), caused by L. donovani subspecies, affects the liver, spleen, bone marrow, and other viscera. Symptoms include fever, weight loss, and spleen and liver enlargement. If untreated, it is usually fatal.
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Cutaneous leishmaniasis, caused by several Leishmania species, results in skin lesions, ranging from pimples to large ulcers, mainly on the legs, feet, hands, and face. Old World cutaneous leishmaniasis is caused primarily by L. major, L. tropica, and L. aethiopica, while New World is mainly caused by L. mexicana and L. viannia braziliensis.
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Mucocutaneous leishmaniasis is a complication of New World cutaneous leishmaniasis that spreads to the oral and nasal mucous membranes, potentially destroying the lips, throat, palate, and larynx. It may appear years after the initial cutaneous lesion has healed.
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How does the immune system react to leishmaniasis?
When a sand fly transmits Leishmania parasites into a host, the host's immunologic response determines the type of leishmaniasis that may arise.
Leishmania are intracellular parasites that infect macrophage cells. In cutaneous leishmaniasis, infected macrophages stay at the infection site, causing lesions. In visceral leishmaniasis, infected macrophages travel through the blood to visceral organs.
The parasites fool the immune system by shedding their glycoprotein coat and replacing it with one containing different amino acid sequences. The host produces new antibodies against each variant, giving the parasite time to replenish its numbers.
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What are the main complications that can happen from the disease's effects on the body?
Leishmaniasis, transmitted by sand fly bites, presents in three major forms: visceral, cutaneous, and mucocutaneous. Cutaneous leishmaniasis leads to skin lesions that can develop into ulcers, which are susceptible to secondary bacterial infections, potentially resulting in lifelong scars and disability. Mucocutaneous leishmaniasis can spread to the mucous membranes of the nose and mouth, causing destruction of the throat, lips, and larynx. Visceral leishmaniasis affects the liver, spleen, and bone marrow, causing fever, weight loss, and a reduction in white blood cells. If untreated, visceral leishmaniasis is usually fatal.
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leishmaniasis, human protozoal infection spread by the bite of a sand fly (subfamily Phlebotominae). Leishmaniasis occurs worldwide but is especially prevalent in tropical areas. Three major forms of the disease are recognized: visceral, cutaneous, and mucocutaneous.
Leishmaniasis is caused by various species of the flagellate protozoan Leishmania, of the order Kinetoplastida. These parasites infect a variety of vertebrate animals, such as rodents and canines. They are transmitted to humans by the bite of a bloodsucking sand fly, which belongs to the genus Lutzomyia in the Americas and to Phlebotomus in the Old World. Leishmanial parasites have two morphologic stages in their life cycle. One form, which inhabits the digestive tract of the sand fly, is an elongated, motile, flagellated form called a promastigote or leptimonad. The other, a round or oval, nonmotile form, called an amastigote, is found in certain cells (i.e., macrophages) of vertebrates. If a sand fly dines on an infected vertebrate, it will ingest cells containing amastigotes, which develop into promastigotes in its gut. There the promastigotes multiply, eventually entering the fly’s saliva. From here they can enter another vertebrate through the wound made during the sand fly’s next blood meal, thus initiating a new infection.
Depending on the species of Leishmania that invades a host and on the host’s immunologic response to the infection, one of three principal types of leishmaniasis can arise. Visceral leishmaniasis, also called kala-azar, is produced by several subspecies of L. donovani. It occurs throughout the world but is especially prevalent in the Mediterranean area, Africa, Asia, and Latin America. This form of the disease is systemic, primarily affecting the liver, spleen, bone marrow, and other viscera. Symptoms, which include fever, weight loss, reduction in the number of white blood cells, and enlargement of the spleen and liver, usually appear two months or more after infection. The disease is usually fatal if not treated.
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Cutaneous leishmaniasis is caused by several Leishmania species. It is characterized by lesions that range from pimples to large ulcers located on the skin of the legs, feet, hands, and face, most of which heal spontaneously after many months. A distinction is made between cutaneous leishmaniasis of the Old World and of the New World. That of the Old World, also called Oriental sore, is endemic in areas around the Mediterranean, in central and northeast Africa, and in south and west Asia. It is caused primarily by L. major, L. tropica, and L. aethiopica. Cutaneous leishmaniasis of the New World, which is found in Central and South America and parts of the southern United States, is caused mainly by L. mexicana and L. viannia braziliensis. This infection may spread to the oral and nasal mucous membranes, a complication referred to as mucocutaneous leishmaniasis, or espundia. Destruction of the lips, throat, palate, and larynx can ensue. Mucocutaneous leishmaniasis may not appear until years after an initial cutaneous lesion has healed.
Leishmaniasis is treated with various agents, including antimicrobial drugs, such as miltefosine; antifungal drugs, such as amphotericin B, fluconazole, ketoconazole, or itraconazole; and compounds of antimony, such as sodium stibogluconate. Spread of the disease is prevented by controlling sand fly populations.