LEISHMANIASIS

Leishmaniasis is caused by protozoan parasites of the genus Leishmania that are spread by the bite of female phlebotomine sand flies of the genus Phlebotomus in the Old World and Lutzomyia in the New World.

Approximately 350 million people in eighty-eight countries are thought to be at risk for leishmania infection. The true number of infected individuals is unknown, as it is not considered a reportable disease in many of the affected countries. The World Health Organization (WHO) estimates that twelve million people are infected and that there are between 1.5 and 2 million new cases each year.

Leishmania infection occurs in a variety of mammalian hosts, including the domestic dog, rodents, and sloths. When a sand fly, a night-biting insect, takes a blood meal from an infected mammal, it will ingest leishmania parasites, called amastigotes, along with the blood. Over seven days leishmania multiply in the flight muscles and develop into infective, flagellated promastigote forms. When the sand fly next takes a blood meal, these promastigotes are injected into a new mammalian host, where they transform back into the amastigote form and begin to divide. Leishmania species are obligate intracellular parasites that infect and replicate in mononuclear phagocytic cells such as macrophages. Infection can also occur via blood transfusion, shared intravenous needles, or, rarely, direct contact with skin lesions. The incubation period in humans is usually from three to eight months, but can be as short as two weeks or as long as several decades.

The spectrum of clinical manifestations caused by leishmania is divided into three broad categories: cutaneous, mucocutaneous, and visceral leishmaniasis. Cutaneous leishmaniasis is found worldwide and results in skin lesions ranging from a single, discrete, self-healing ulcer to diffuse progressive induration. The spectrum of disease is determined by the species of the parasite and the ability of the host to mount a cell-mediated response. A hyper-immune response causes destructive changes such as those seen in mucocutaneous disease, and a hypo-immune response results in visceral and diffuse cutaneous leishmaniasis. In Old World cutaneous leishmaniasis, the usual causative species are L. major, L. tropica, or L. aethiopica. In the Americas, cutaneous lesions are usually the result of infection with L. braziliensis, L. mexicana, L. amazonensis, or L. panamensis.

In mucocutaneous leishmaniasis (also called espundia), the infection causes destruction of mucous membranes of the nose, mouth, and throat. This form of leishmania is found almost exclusively in the Americas and is seen predominantly in a subset of patients infected with L. braziliensis. Diffuse cutaneous leishmaniasisis, caused by L. aethiopica, is characterized by induration of skin without ulceration.

Visceral leishmaniasis, or kala-azar, is the most severe form of infection with parasites disseminated throughout the reticuloendothelial system. Patients experience fevers, night sweats, and weight loss. The spleen and liver become enlarged, sometimes massively. Blood work reveals anemia, leucopenia, thrombocytopenia, and a marked increase in gamma-globulin levels. If untreated, visceral leishmaniasis is virtually always fatal.

It used to be thought that each species of leishmania resulted in a particular clinical syndrome. However, it is now being recognized that there is considerable overlap in the clinical presentation of each species. Most people bitten by leishmania -infected sand flies will never manifest any evidence of the infection. After recovery from leishmaniasis, a person is immune for life from reinfection by that strain.

Conditions that impair cell-mediated immunity can result in more severe, disseminated leishmanial infections. This has been seen in organ transplant recipients and, most importantly, in persons infected with HIV (human immunodeficiency virus), in whom visceral leishmaniasis has become a frequent opportunistic infection in endemic regions.

Diagnosis is made by microscopic identification of the parasite in tissue samples, by growing the organisms in culture, or by polymerase chain reaction (PCR) of tissue. PCR is a test that will identify even trace amounts of leishmanial DNA in tissue. Samples are taken from the edge or base of a skin ulcer in cutaneous disease. Bone marrow or splenic aspirates are the best tissue samples in cases of visceral disease. Testing for serum antibodies against leishmania parasites may be helpful.

Cutaneous lesions often heal spontaneously. Treatment is undertaken when the lesions are in cosmetically disfiguring areas, when the infection is widespread, and for certain leishmania spp. that are less likely to heal (e.g., L. brasiliensis ). Pentavalent antimony (sodium stibogluconate, Pentostam), given either systemically or intralesionally, is the drug of choice for cutaneous lesions. Mucocutaneous and visceral leishmaniasis always require intravenous treatment with a pentavalent antimonial. Other effective medications for some species include amphotericin B (HIV-infected individuals) and pentamidine (for L. panamensis ).

As there are many animal reservoirs of infection, and as elimination of sand flies is unlikely, control of leishmaniasis depends on avoiding exposure to sand flies. This involves a combination of insect repellent, fine-meshed bed nets, and protective clothing, and avoiding areas known to harbor sand flies.

Martha Fulford

Jay Keystone

(see also: Communicable Disease Control; Tropical Infectious Diseases )

Bibliography

Arias, J. R.; Monteiro, P. S.; and Zicker, F. (1996). "The Reemergence of Visceral Leishmaniasis in Brazil." Emerging Infectious Diseases 2(2):145–146.

Berman, J. D. (1997). "Human Leishmaniasis: Clinical, Diagnostic, and Chemotherapeutic Developments in the Last 10 Years." Clinical Infectious Diseases 24:684–703.

Desowitz, R. S. (1991). "Kala Azar: The Long Anguish of the Black Sickness." In The Malaria Capers. New York: W. W. Norton & Company.

Evans, T. G. (1993). "Leishmaniasis." Infectious Disease Clinics of North America 7(3):527–546.

Hernandez-Perez, J. et al. (1999). "Visceral Leishmaniasis (Kala-azar) in Solid Organ Transplantation: Report of Five Cases and Review." Clinical Infectious Diseases 29:918–921.

Herwaldt, B. (1999). "Leishmaniasis." Lancet 354:1191–1199.

World Health Organization (2000). "The Leishmaniases and Leishmania /HIV Co-Infections—Fact Sheet No.116." WHO Information Fact Sheets. Geneva: Author.

leishmaniasis , any of a group of tropical diseases caused by parasitic protozoans of the genus Leishmania. The parasites live in dogs, foxes, rodents, and humans; they are transmitted by the bites of sand flies. There they infect the very white blood cells that normally would defend the body from such invaders. There are two forms of leishmaniasis. The more serious, called kala-azar or visceral leishmaniasis, affects the internal organs, causing fever, anemia, splenomegaly, and discoloration of the skin. Untreated, it can be fatal. The second, or cutaneous form, leaves deep, disfiguring sores at the site of the bite. Treatment is with amphotericin B and other drugs. Leishmaniasis is rarely seen in the United States, but is prevalent in South Asia, the Middle East, North Africa, and parts of the Mediterranean.

Leishmaniasis

What Is Leishmaniasis?

How Common Is the Disease?

Is It Contagious?

What Are the Signs and Symptoms of Leishmaniasis?

How Do Doctors Make the Diagnosis?

What Is the Treatment?

How Long Does the Disease Last?

What Are the Complications of Leishmaniasis?

Can the Disease Be Prevented?

Resources

Leishmaniasis (leesh-muh-NYE-uh-sis) is a parasitic infection spread by sand flies. It causes symptoms ranging from sores on the skin to damage to internal organs.

KEYWORDS

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Kala azar

Parasitic infections

Sand fly

Travel-related illnesses

What Is Leishmaniasis?

The disease occurs when a person becomes infected with any of several types of Leishmania parasites*. They spread to people through the bite of female sand flies and can cause different forms of illness, all of which are called leishmaniasis. Cutaneous (kyoo-TAY-nee-us) leishmaniasis affects the skin; mucocutaneous (myoo-ko-kyoo-TAY-nee-us) leishmaniasis attacks the mucous membranes* in the mouth, nose, and throat; and visceral (VIH-suh-rul) leishmaniasis (also known as systemic leishmaniasis or kala azar) damages internal organs, such as the liver* and spleen*.

*parasites

(PAIR-uh-sites) are organisms such as protozoa (one-celled animals), worms, or insects that must live on or inside a human or other organism to survive. An animal or plant harboring a parasite is called its host. Parasites live at the expense of the host and may cause illness.

*mucous membranes

are the moist linings of the mouth, nose, eyes, and throat.

*liver

is a large organ located beneath the ribs on the right side of the body. The liver performs numerous digestive and chemical functions essential for health.

*spleen

is an organ in the upper left part of the abdomen that stores and filters blood. As part of the immune system, the spleen also plays a role in fighting infection.

Cutaneous and mucocutaneous infections can lead to severe scarring and permanent disfigurement. In patients with a mucocutaneous infection, the disease can destroy soft tissue in the mouth and nose, drastically deforming the face. The visceral form of the disease is considered the most dangerous. It can grow worse over time and is usually fatal if not treated. Leishmaniasis damages the immune system so that it cannot fight off infections; these infections are generally the cause of death, not leishmaniasis itself. In some countries, visceral disease has been found with increasing frequency in people who also have human immunodeficiency virus* infection.

*human immunodeficiency

(HYOO-mun ih-myoo-no-dih-FIHshen-see) virus , or HIV, is the virus that causes AIDS (acquired immunodeficiency syndrome).

How Common Is the Disease?

The infection is most common in tropical and subtropical regions, such as countries in South America, Africa, and Asia, and the number of areas where it occurs continues to grow. The U.S. Centers for Disease Control and Prevention (CDC) estimates that one and a half million people around the world contract cutaneous leishmaniasis each year and half a million people experience the more serious visceral form of the disease. Ninety percent of the visceral cases are found in just five countries: India, Nepal, Bangladesh, Sudan, and Brazil. Leishmaniasis is exceptionally rare in the United States, although a few cutaneous cases have been diagnosed in rural southern Texas.

Is It Contagious?

People cannot get leishmaniasis directly from other people. Instead, the disease spreads through the bite of blood-sucking sand flies. A fly bites an infected animal or person and takes in the parasite with its meal of blood. The Leishmania parasites reproduce in the fly, which can spread them when it bites another person. Sand flies are quite small—about a third of the size of a mosquito—and fly silently, so people often do not even know the flies are nearby. Less often, the disease can be transmitted through contaminated blood in a transfusion*, by sharing or reusing needles for injecting drugs, or from a mother to her baby during pregnancy or birth.

*transfusion

(trans-FYOO-zhun) is a procedure in which blood or certain parts of blood, such as specific cells, are given to a person who needs them because of illness or blood loss.

What Are the Signs and Symptoms of Leishmaniasis?

Cutaneous leishmaniasis is marked by sores that often look like volcanoes: they have a central pit and a raised rim. They can be painful or painless and may be covered by scabs. The sores tend to appear on the face, arms, and legs, and some people have as many as 200 of them. Patients with cutaneous leishmaniasis also may have swollen lymph nodes* near the sores. In mucocutaneous cases, the lesions appear in the mouth, nose, and throat and gradually destroy the soft tissues in those areas.

*lymph

(LIMF) nodes are small, bean-shaped masses of tissue that contain immune system cells that fight harmful microorganisms. Lymph nodes may swell during infections.

The visceral form of the disease can cause lack of appetite, serious weight loss, fever (which can last from 2 weeks to 2 months), and increasing weakness. It also can lead to an enlarged spleen and liver and sometimes swollen lymph nodes. Blood tests may show that the patient has low levels of white blood cells, red blood cells, or platelets*. As the disease progresses, the skin can become dark and dry—a symptom that gave the disease the name kala azar (meaning “black fever”). In children, visceral leishmaniasis often begins suddenly, with fever, diarrhea, and cough.

*platelets

(PLATE-lets) are tiny, disk-shaped particles within the blood that play an important role in clotting.

Cutaneous leishmaniasis affects the skin, causing sores that may look like volcanoes: they have a central pit and a raised rim. The disease can destroy tissue and lead to permanent scarring. AP/Wide World Photos

How Do Doctors Make the Diagnosis?

A key to making the diagnosis is learning whether the patient has traveled to a country where leishmaniasis occurs. During the physical examination, the doctor also checks the patient’s body for the types of sores seen with the infection. The doctor may take blood samples and tissue samples from any sores that are found. These samples will be cultured*, examined for signs of the parasite, or tested for antibodies* to the parasite. For suspected cases of visceral infection, biopsies* of the abnormal tissue may be done.

*cultured

(KUL-churd) means subjected to a test in which a sample of fluid or tissue from the body is placed in a dish containing material that supports the growth of certain organisms. Over time, ranging from hours to weeks, the organisms will grow and can be identified.

*antibodies

(AN-tih-bah-deez) are protein molecules produced by the body’s immune system to help fight specific infections caused by microorganisms, such as bacteria and viruses.

*biopsies

(BI-op-seez) are tests in which a small sample of skin or other body tissue is removed and examined for signs of disease.

What Is the Treatment?

Doctors treat the infection with prescription medications; many of these medicines contain antimony*. Cutaneous cases usually can be treated at home, but visceral disease may require hospitalization and supportive care, such as intravenous* fluids. Patients who have severe disfigurement from cutaneous, and especially mucocutaneous, leishmaniasis often need reconstructive surgery to regain a normal appearance. However, such extensive (and expensive) treatment is not available to vast numbers of people in developing countries who contract this disease.

*antimony

(AN-tih-mo-nee) is an element that has properties of both metals and nonmetals and can kill or inhibit the growth of certain bacteria.

*intravenous

(in-tra-VEE-nus) means within or through a vein. For example, medications, fluid, or other substances can be given through a needle or soft tube inserted through the skin’s surface directly into a vein.

How Long Does the Disease Last?

Although some cases of cutaneous leishmaniasis clear up on their own, most cases of mucocutaneous and visceral infection will not get better without treatment. Left untreated, visceral disease typically leads to death within 2 years. Cutaneous cases may take several months to heal, even with treatment, and may return after the treatment has been completed.

What Are the Complications of Leishmaniasis?

The cutaneous and mucocutaneous forms of leishmaniasis often cause widespread scarring. In mucocutaneous cases, destruction of tissue in the mouth and nose can lead to facial deformity. Visceral disease can damage the immune system to the point that it is unable to fight off other infections. Some patients may need to have the spleen removed if it is trapping and destroying too many of the person’s blood cells, and advanced cases of disease often result in death.

Can the Disease Be Prevented?

Avoiding sand fly bites is the best way to limit the spread of leishmaniasis. In areas where the flies live, people are advised to stay inside from dusk until dawn, when the insects are most active. Wearing long-sleeved shirts, long pants, and socks and tucking pants into socks can reduce the amount of bare skin that is vulnerable to fly bites. Using insect repellent, staying in screened-in or air-conditioned areas, sleeping under mosquito netting, and spraying living areas with an insecticide to kill flies also can help lessen the risk of being bitten.

See also

Travel-related Infections

Trypanosomiasis

West Nile Fever

Resources

Organizations

U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA 30333. The CDC provides a fact sheet and other information on leishmaniasis at its website.

Telephone 800-311-3435 http://www.cdc.gov

World Health Organization (WHO), Avenue Appia 20, 1211 Geneva 27, Switzerland. WHO tracks disease outbreaks around the world and offers information about leishmaniasis at its website.

Telephone 011-41-22-791-2111 http://www.who.int

leishmaniasis (leesh-mă-ny-ă-sis) n. a disease, common in the tropics and subtropics, caused by parasitic protozoans of the genus Leishmania, which are transmitted by the bite of sandflies. cutaneous l. leishmaniasis that affects the tissues of the skin. See espundia, oriental sore. visceral l. leishmaniasis in which the cells of various internal organs are affected. See kala-azar.

leish·man·i·a·sis / ˌlēshməˈnīəsəs/ • n. a tropical and subtropical disease caused by leishmania and transmitted by the bite of sandflies. It affects either the skin or the internal organs.