Leishmaniasis

Leishmaniasis is a disease caused by protozoal parasites of the Trypanosomatida genus Leishmania. It is predominantly transmitted through the bite of infected female phlebotomine sandflies, primarily Phlebotomus and Lutzomyia. This disease is most prevalent in the tropical and sub-tropical regions of Africa, Asia, the Americas, and southern Europe.

Signs and Symptoms

Leishmaniasis presents in three main forms: cutaneous, mucocutaneous, and visceral.

• Cutaneous leishmaniasis is the most common and manifests as open sores at the bite sites, which may take months to a year and a half to heal, often leaving scars. Diffuse cutaneous leishmaniasis resembles leprosy and might not heal spontaneously.
• Mucocutaneous leishmaniasis affects the skin and mucosal areas, leading to ulcers in the nose and mouth.
• Visceral leishmaniasis, or kala-azar, is the most severe form, potentially fatal if untreated. It starts with skin ulcers and progresses to fever, anaemia, and enlargement of the liver and spleen.

Cause and Transmission

The disease is caused by over 20 species of Leishmania, with transmission occurring through the bite of infected sandflies. The lifecycle of Leishmania involves the transformation and multiplication of promastigotes and amastigotes within the host and vector.

Sandflies inject metacyclic promastigotes during blood meals, which are then phagocytized by macrophages and transform into amastigotes. The parasites multiply within infected cells and affect different tissues based on the Leishmania species involved. The sandflies become infected by ingesting these amastigotes during blood meals.

Diagnosis

Diagnosis typically involves the direct visualisation of amastigotes in tissue samples. These samples are stained and examined under a microscope, though the procedure can be painful and challenging. Other diagnostic methods include enzyme-linked immunosorbent assay, antigen-coated dipsticks, and direct agglutination tests. PCR tests offer a sensitive and specific means to detect Leishmania DNA, especially useful for low parasite loads.

Prevention

Preventative measures include using insect repellent, sleeping under insecticide-treated nets, and spraying insecticides in homes and animal shelters. Finer mesh sizes in bed nets provide better protection but can reduce air circulation. In areas where dogs are reservoirs, insecticide-impregnated collars and treatment or culling of infected dogs are recommended.

Treatment

The treatment of leishmaniasis depends on the form of the disease, the Leishmania species, and the geographic region of acquisition. For visceral leishmaniasis, liposomal amphotericin B is often recommended, especially in India, South America, and the Mediterranean. In Africa, a combination of pentavalent antimonials and paromomycin is used. Miltefosine is effective for both visceral and certain forms of cutaneous leishmaniasis but has limitations based on the Leishmania species.

For cutaneous leishmaniasis, topical treatments, including paromomycin, fluconazole, or itraconazole, may be effective depending on the Leishmania species. Heat therapy has also been looked at as a treatment option.

Epidemiology

Leishmaniasis affects up to 12 million people worldwide, with 1.5–2.0 million new cases annually. The disease is endemic in 97 countries, predominantly in tropical and sub-tropical regions. The visceral form has a high incidence in countries like India, Bangladesh, Brazil, Ethiopia, and Sudan. The cutaneous form is prevalent in Afghanistan, Algeria, Brazil, and Iran, while mucocutaneous leishmaniasis is common in Bolivia, Brazil, and Peru.

History

Leishmaniasis has been documented since ancient times, with descriptions dating back to 1500 to 2500 BCE. Various terms have been used to describe the disease across different cultures and regions. The causative parasite was identified in the late 19th and early 20th centuries by researchers such as William Boog Leishman, Charles Donovan, and Ronald Ross.

Society and Culture

Efforts to address leishmaniasis include the reintroduction of paromomycin, facilitated by organisations like the Institute for OneWorld Health and the Drugs for Neglected Diseases Initiative. The World Health Organisation has also negotiated reduced costs for essential medications.

Research

While no human vaccines are available as of 2017, research is ongoing. Effective vaccines for dogs exist, and public health measures could control the disease without a vaccine. Pyrimidine-based drugs are being looked at as potential treatments.

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Self-assessment MCQs (single best answer)

What is the primary vector for the transmission of Leishmaniasis?

Which form of Leishmaniasis is also known as kala-azar?

Which diagnostic method involves the direct visualisation of amastigotes in tissue samples?

What is the most common form of Leishmaniasis?

In which regions is Leishmaniasis most prevalent?

Which species of sandflies primarily transmit Leishmaniasis?

What is the recommended treatment for visceral leishmaniasis in India?

Which form of Leishmaniasis can lead to ulcers in the nose and mouth?

What is a common preventative measure against Leishmaniasis?

Which organisation has negotiated reduced costs for essential medications to treat Leishmaniasis?