Leishmaniasis

Leishmaniasis refers to several different illnesses caused by infection withan organism called a protozoan.

Protozoa are considered to be the most simple organisms in the animal kingdom. They are all single-celled. The types of protozoa which cause leishmaniasisare carried by the blood-sucking sandfly. The sandfly is referred to as thedisease vector, simply meaning that the infectious agent (the protozoan) is carried by the sandfly and passed on to other animals or humans in whom the protozoan will set up residence and cause disease. The animal or human in whichthe protozoan then resides is referred to as the host.

Once the protozoan is within the human host, the human's immune systemis activated to try to combat the invader. Specialized immune cells called macrophages work to swallow up the protozoa. Usually, this technique kills a foreign invader, but these protozoa can survive and flourish within macrophages. The protozoa multiply within the macrophages, ultimately causing the macrophage to burst open. The protozoa are released, and take up residence withinother neighboring cells.

At this point, the course of the disease caused by the protozoa is dependenton the specific type of protozoa, and on the type of reaction the protozoa elicits from the immune system. There are several types of protozoa which causeleishmaniasis, and they cause different patterns of disease progression.

At any one time, about 20 million people throughout the world are infected with leishmaniasis. While leishmaniasis exists as a disease in 88 countries around the globe, some countries are hit harder than others. These include Bangladesh, India, Nepal, Sudan, Afghanistan, Brazil, Iran, Peru, Saudi Arabia, and Syria. Other areas which harbor the causative protozoa include China, manycountries throughout Africa, Mexico, Central and South America, Turkey, and Greece. Although less frequent, cases have occurred in the United States, in Texas.

In some areas of southern Europe, leishmaniasis is becoming an important disease which infects people with weakened immune systems. In particular, individuals with acquired immunodeficiency syndrome (AIDS) are at great risk of thisinfection.

There are a number of types of protozoa which can cause leishmaniasis. Each type exists in specific locations, and there are different patterns to the kind of disease each causes. The overall species name is Leishmania (commonly abbreviated L.). The specific types include: L. Donovani, L. Infantum, L. Chagasi, L. Mexicana, L. Amazonensis, L. Tropica, L. Major, L. Aethiopica, L. Brasiliensis, L. Guyaensis, L. Panamensis, L. Peruviana. Some of the namesare reflective of the locale in which the specific protozoa is most commonlyfound, or in which it was first discovered.

Localized cutaneous leishmaniasis occurs most commonly in China, India, AsiaMinor, Africa, the Mediterranean Basin, and Central America. It has occurredin an area ranging from northern Argentina all the way up to southern Texas.It is called different names in different locations, including chiclero ulcer, bush yaws, uta, oriental sore, Aleppo boil, and Baghdad sore.

This is perhaps the least drastic type of disease caused by any of the Leishmania. Several weeks or months after being bitten by an infected sandfly, thehost may notice an itchy bump (lesion) on an arm, leg, or face. Lymph nodes in the area of this bump may be swollen. Within several months, the bump develops a crater (ulceration) in the center, with a raised, reddened ridge aroundit. There may be several of these lesions near each other, and they may spread into each other to form one large lesion. Although localized cutaneous leishmaniasis usually heals on its own, it may take as long as a year. A depressed, light-colored scar usually remains behind. Some lesions never heal, and may invade and destroy the tissue below. For example, lesions on the ears mayslowly, but surely, invade and destroy the cartilage which supports the outerear.

Diffuse cutaneous leichmaniasis occurs most often in Ethiopia, Brazil, Dominican Republic, and Venezuela.

The lesions of diffuse cutaneous leishmaniasis are very similar to those of localized cutaneous leishmaniasis, except they are spread all over the body. The body's immune system apparently fails to battle the protozoa, which are free to spread throughout. The characteristic lesions resemble those of the dread biblical disease, leprosy.

Mucocutaneous leishmaniasis occurs primarily in the tropics of South America.The disease begins with the same sores noted in localized cutaneous leishmaniasis. Sometimes these primary lesions heal, other times they spread and become larger. Some years after the first lesion is noted (and sometimes severalyears after that lesion has totally healed), new lesions appear in the mouthand nose, and occasionally in the area between the genitalia and the anus (the perineum). These new lesions are particularly destructive and painful. Theyerode underlying tissue and cartilage, frequently eating through the septum(the cartilage which separates the two nostrils). If the lesions spread to the roof of the mouth and the larynx (the part of the wind pipe which containsthe vocal cords), they may prevent speech. Other symptoms include fever, weight loss, anemia (low red blood cell count). There is always a large danger of bacteria infecting the already open sores.

Visceral leishmaniasis occurs in India, China, the southern region of Russia,and throughout Africa, the Mediterranean, and South and Central America. Itis frequently called Kala-Azar or Dumdum fever.

In this disease, the protozoa uses the bloodstream to travel to the liver, spleen, lymph nodes, and bone marrow. Fever may last for as long as eight weeks, disappear, and then reappear again. The lymph nodes, spleen, and liver areoften quite enlarged. Weakness, fatigue, loss of appetite, diarrhea, and weight loss are common. Kala-azar translates to mean "black fever." The name kala-azar comes from a characteristic of this form of leishmaniasis. Individualswith light-colored skin take on a darker, grayish skin tone, particularly oftheir face and hands. A variety of lesions appear on the skin.

Diagnosis for each of these types of leishmaniasis involves taking a scrapingfrom a lesion, preparing it in a laboratory, and examining it under a microscope to demonstrate the causative protozoan. Other methods that have been used include culturing a sample piece of tissue in a laboratory to allow the protozoa to multiply for easier microscopic identification; injecting a mouse orhamster with a solution made of scrapings from a patient's lesion to see ifthe animal develops a leishmaniasis-like disease; and demonstrating the presence in macrophages of the characteristic-appearing protozoan, called Leishman-Donovan bodies.

In some forms of leishmaniasis, a skin test (similar to that given for TB) may be used. In this test, a solution containing a small bit of the protozoan antigen (cell markers which cause the human immune system to react) is injected or scratched into a patient's skin. In a positive reaction, cells from theimmune system will race to this spot, causing a characteristic skin lesion. Not all forms of leishmaniasis cause a positive skin test, however.

The treatment of choice for all forms of leishmaniasis is a type of drug containing the element antimony. These include sodium sitogluconate, and megluminantimonate. When these types of drugs do not work, other medications with anti-protozoal activity are utilized, including amphotericin B, pentamidine, flagyl, and allopurinol.

The prognosis for leishmaniasis is quite variable, and depends on the specific strain of infecting protozoan, as well as the individual patient's immune system response to infection. Localized cutaneous leishmaniasis may require notreatment. Although it may take many months, these lesions usually heal themselves completely. Only rarely do these lesions fail to heal and become moredestructive.

Disseminated cutaneous leishmaniasis may smolder on for years without treatment, ultimately causing death when the large, open lesions become infected with bacteria.

Mucocutaneous leishmaniasis is often relatively resistant to treatment. Untreated visceral leishmaniasis has a 90% death rate, but only a 10% death rate with treatment.

Prevention involves protecting against sandfly bites. Insect repellents usedaround homes, on clothing, on skin, and on bednets (to protect people while sleeping) are effective measures.

Reducing the population of sandflies is also an important preventive measure.In areas where leishmaniasis is very common, recommendations include clearing the land of trees and brush for at least 984 ft (300 m) around all villages, and regularly spraying the area with insecticides. Because rodents often carry the protozoan which causes leishmaniasis, careful rodent control should be practiced. Dogs, which also carry the protozoan, can be given a simple blood test and then either treated or put to sleep.

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