Leishmaniasis

Leishmaniasis is a group of diseases caused by tiny parasites called Leishmania. These parasites are spread by the bite of small flying insects called sandflies. The disease is most common in warm parts of the world, including Africa, Asia, the Americas, and southern Europe.

There are three main types of leishmaniasis. The skin form causes sores on the body. The form that affects the nose and mouth causes sores there as well. The form that affects internal organs starts with skin sores and later causes fever, tiredness, and swelling of the liver and spleen.

People can help prevent leishmaniasis by using special nets to keep sandflies away and by treating the disease early. Doctors can diagnose the disease by looking at samples under a microscope or by doing blood tests. Treatment depends on the type of infection and where it was caught. Many millions of people live in areas where leishmaniasis is common, and the World Health Organization works to help provide treatment.

Signs and symptoms

Leishmaniasis causes skin sores that appear weeks to months after being bitten by infected sandflies.

There are three main types: cutaneous leishmaniasis, which causes open sores that heal over time but may leave scars; mucocutaneous leishmaniasis, which affects both the skin and the inside of the nose and mouth; and visceral leishmaniasis, the most serious form, which can be very dangerous without treatment. This form may lead to fever, problems with the spleen and liver, and anemia.

Cause

Leishmaniasis is spread by the bite of infected female phlebotomine sandflies. These sandflies can carry a tiny organism called protozoa Leishmania. When a sandfly bites, it can pass these organisms into the skin. The organisms then change and grow inside special cells in the body, causing different health problems depending on the type of Leishmania involved.

Sandflies can get infected when they bite animals or people who already have the disease. Inside the sandfly, the organisms change again and get ready to spread to new hosts. Scientists have studied the genes of some Leishmania types, which helps them understand how the disease works and look for new ways to treat or prevent it.

Vector

In most places, the genus Phlebotomus is the main carrier of leishmaniasis, though in some areas, Lutzomyia also plays a role.

Possible non-human reservoirs

Some animals, like certain monkeys, can carry types of Leishmania that can infect people, though the amount of organisms they pass on is usually small.

Organisms

The severe form of the disease is often caused by Leishmania donovani, L. infantum, or L. chagasi. The skin form can be caused by more than fifteen different Leishmania species.

Risk factors

Factors that increase the chance of getting leishmaniasis include poor nutrition, living in areas without good sanitation, having a weaker immune system, and changes in the environment that help sandflies thrive. Living in crowded or dirty conditions, not having enough healthy food, moving to new areas where the disease is common, and changes in climate or land use can all make people more likely to get sick from leishmaniasis.

Diagnosis

Leishmaniasis is diagnosed in special laboratory tests where scientists look for tiny parts of the parasite called amastigotes. These can be found in blood or tissue samples taken from the body. The samples are spread on a slide and stained to make the amastigotes easier to see. They look like small, round bodies with a nucleus inside them.

Other tests, like enzyme-linked immunosorbent assay and polymerase chain reaction (PCR), can also help find the parasite’s DNA. These tests are very sensitive and can detect even very small amounts of the parasite. Different species of the parasite can be identified using special tests that look at the parasite’s DNA.

Prevention

Leishmaniasis can be prevented by using insect repellent on exposed skin and under the ends of sleeves and pant legs, following the instructions on the label. Repellents that contain DEET are usually the most effective.

To reduce the number of sandfly bites, you can use nets treated with insecticide or insect repellent while sleeping. Fine mesh sizes of 0.6 mm or less are best, but a mosquito net with 1.2 mm mesh can also help a little. Many Phlebotomine sandfly attacks happen around sunset, so putting nets over doors and windows or using insect repellents can be useful.

Spraying houses and animal shelters with insecticides, using insecticide-impregnated dog collars, and treating or managing infected dogs are also important steps in prevention.

Controlling leishmaniasis needs many different actions. Insecticide spraying, treated nets, and caring for sick people are common ways to help, and scientists are looking for new methods to control the disease in the long term.

One important method is Vector Control using an Integrated Vector Management (IVM) approach to reduce sand fly numbers. New ideas being studied include changing sand flies genetically so they can’t spread the parasites, using special baits that attract and kill sand flies, and creating barriers with spatial repellents and insecticidal paint.

For Reservoir Control, managing domestic dogs is important because they can carry the parasites. Instead of removing many dogs, which hasn’t worked well and causes concern, special dog collars treated with deltamethrin are now used as a safer and better choice. Controlling wild animals that can carry the parasites, like rodents and marsupials, is harder because of worries about protecting nature.

Vaccination: Vaccines for dogs have been made and are used in some places to help stop the spread. Vaccines for humans are being tested and could provide long-term protection in the future.

Treatment

The way to treat leishmaniasis depends on where the disease was caught, the type of Leishmania, and what kind of infection it is. For a serious form of the disease found in India, South America, and the Mediterranean, a medicine called liposomal amphotericin B is usually used and works very well. In India, another medicine doesn’t work as well, but in Africa, a mix of two medicines is used. There is also a pill called miltefosine that can help with different kinds of leishmaniasis and usually has fewer side effects.

Researchers are looking into new ways to treat leishmaniasis, like mixing medicines or using very small particles to deliver drugs better. For a skin form of the disease, different treatments work depending on the strain, and doctors may use creams or pills to help. Scientists are still studying whether adding special foods or supplements can make treatment better. Some groups are working hard to find new medicines and make existing ones more affordable.

Epidemiology

Leishmaniasis affects about 12 million people around the world, with around 700,000 to 1 million new cases each year. It is found in 97 countries, mainly in warm parts of Africa, Asia, the Americas, and southern Europe. The disease is spread by sandflies and can appear in three main ways: on the skin, inside the mouth and nose, or deep inside the body.

The skin form is the most common, with about 600,000 to 1 million new cases each year. The deep form can be serious and happens in places like Bangladesh, Brazil, Ethiopia, India, and Sudan. Most cases are reported in just a few countries, such as Brazil, Ethiopia, India, Somalia, South Sudan, and Sudan. The disease is also found in parts of the Americas, from northern Argentina to South Texas, and may spread further north because of changes in climate.

History

Early writings and drawings show signs of a skin disease that might be leishmaniasis. Ancient tablets from King Ashurbanipal around the seventh century BCE and even older texts mention skin sores. Persian doctors, like Avicenna in the 10th century, described a condition called "balkh" sore. In 1756, a doctor named Alexander Russell gave a very detailed description of the disease after studying a patient from Turkey.

In India, the disease was known as "kala-azar", meaning "black fever". Evidence of the skin form of the disease has also been found in very old pottery from Ecuador and Peru. Some old writings from the time of the Incan people and Spanish explorers also mention sicknesses that sound like leishmaniasis.

The person who first discovered the tiny creature that causes the disease is not known for sure. In 1898, a doctor named Peter Borovsky described the parasite correctly but his work was not well known. In 1901, William Leishman found the organism in a patient who had died from an illness called "dum-dum fever". Soon after, Charles Donovan confirmed these findings in patients in Madras, India. Later, Ronald Ross named the parasite Leishmania donovani. During the Second World War, leishmaniasis became a problem for soldiers fighting in Sicily, and a treatment called pentostam was found to work well.

Society and culture

Leishmaniasis can cause visible scars and changes to the face, which may lead to social challenges. People with these signs might face difficulties in jobs, school, and social life because others may treat them differently. As more people learn about the disease, support for mental health and education in communities becomes important.

The disease can also bring financial hardship, especially in places where treatment is not free. People may lose income due to being sick, and animals used for work or farming can become sick too, making life harder for families. In some areas, beliefs about the disease being caused by spiritual reasons can affect when people seek medical help.

Research

As of 2017, there was no vaccine for humans to prevent leishmaniasis. Scientists are working hard to create one. Right now, there are effective vaccines for dogs. Another way to stop leishmaniasis is through good public health practices. Researchers are also looking into special drugs made from pyrimidine to help treat the disease.