Leishmaniasis

Leishmaniasis is caused by protozoan parasites of the genus Leishmania, with over 20 known species capable of producing disease in humans. The infection is transmitted to humans through the bite of an infected female phlebotomine sandfly, a small insect vector measuring 2–3 mm in length ^[2][3]. The disease typically operates as a zoonotic cycle, with wild or semi-domesticated animals—principally rodents and dogs—serving as reservoirs ^[4]. While some 20 different Leishmania species can cause disease, they produce three distinct clinical forms: cutaneous leishmaniasis, visceral leishmaniasis, and mucocutaneous leishmaniasis ^[2][3].

The clinical presentation of leishmaniasis varies substantially by form. Cutaneous leishmaniasis produces skin lesions, primarily nodules or painless ulcers, typically on exposed areas such as the face, arms, and legs; lesions may number up to 200 and invariably leave permanent scars that can cause stigmatization ^[2][3][4]. Visceral leishmaniasis (kala-azar) is a life-threatening condition characterized by irregular fever, substantial weight loss, hepatosplenomegaly, and severe anemia, with fatality rates reaching 100% within 2 years if untreated ^[2][3]. Mucocutaneous leishmaniasis destroys mucous membranes of the nose, mouth, and throat, causing severe disability and social exclusion ^[3]. A complication called post-kala-azar dermal leishmaniasis can develop months to years after VL treatment, appearing as macular, papular, or nodular rash predominantly on the face, upper arms, and trunk; it occurs in 5–10% of VL patients in East Africa and on the Indian subcontinent ^[5]. Most infected individuals remain asymptomatic and never develop clinical disease ^[2][3].

Leishmaniasis demonstrates a widespread but uneven global distribution, with cutaneous leishmaniasis accounting for approximately 80% of reported cases worldwide ^[5]. The Americas, particularly Brazil, represent major endemic regions, while East Africa shows endemicity for all forms with frequent visceral leishmaniasis outbreaks ^[5]. Cutaneous leishmaniasis is highly endemic in Algeria, visceral leishmaniasis is highly endemic in Iraq, Somalia, Sudan, and Yemen, and the disease is also endemic in parts of Europe ^[5]. The epidemiology is affected by environmental changes, deforestation, human incursion into forested areas, urbanization, migration, and climate factors that influence sandfly population size and geographic distribution ^[5]. Approximately 30,000 new visceral leishmaniasis cases and more than 1 million new cutaneous leishmaniasis cases occur annually ^[3]. Post-kala-azar dermal leishmaniasis occurs mainly in Sudan and on the Indian subcontinent ^[5].

Leishmaniasis is transmitted through the bite of infected female phlebotomine sandflies, which require blood meals to produce eggs ^[2][5][3]. Over 90 sandfly species are known to transmit Leishmania parasites ^[5]. The disease typically follows a zoonotic cycle, with approximately 70 animal species—including wild and semi-domesticated rodents and dogs—serving as reservoirs ^[5][4]. Humans can also act as reservoir hosts, particularly in anthroponotic transmission cycles ^[3][4]. Environmental factors affecting sandfly populations, including temperature, rainfall patterns, drought, and flood, influence transmission dynamics ^[5].

Prevention and control of cutaneous leishmaniasis (CL) remain inadequate, and the review explicitly identifies urgent priorities in this area. To further control and potentially eliminate CL, substantial improvements in vector control are required, along with better diagnostics and the development of efficient and safe vaccines ^[1]. The disease is transmitted by the female sandfly, which underscores why vector control is a central preventive strategy, yet the review emphasizes that current measures are insufficient given that CL affects 12 million people globally, causes around 2 million new cases annually, is endemic in almost 100 countries, and puts approximately 350 million people at risk ^[1]. The World Health Organization categorizes CL as an emerging and uncontrolled disease as well as a neglected tropical disease, reflecting the scale of the prevention challenge ^[1]. A major barrier to progress is that CL primarily affects poor populations, so biotechnical companies dedicate little investment to the research programs that could yield diagnostic, pharmaceutical, and vaccine innovations needed for effective prevention ^[1].

1. 1de Vries HJC et al. Cutaneous Leishmaniasis: A 2022 Updated Narrative Review into Diagnosis and Management Developments. Am J Clin Dermatol. 2022 Nov. PMID: 36103050. doi: 10.1007/s40257-022-00726-8.PubMed: https://pubmed.ncbi.nlm.nih.gov/36103050/
2. 2World Health Organization. Leishmaniasis [Internet]. cited 3 Sept 2026.Available from: https://www.who.int/news-room/questions-and-answers/item/leishmaniasis
3. 3World Health Organization. Leishmaniasis [Internet]. cited 3 Sept 2026.Available from: https://www.who.int/health-topics/leishmaniasis
4. 4Mokni M et al. [Cutaneous leishmaniasis]. Ann Dermatol Venereol. 2019 Mar. PMID: 30879803. doi: 10.1016/j.annder.2019.02.002.PubMed: https://pubmed.ncbi.nlm.nih.gov/30879803/
5. 5World Health Organization. Leishmaniasis [Internet]. cited 3 Sept 2026.Available from: https://www.who.int/news-room/fact-sheets/detail/leishmaniasis