Leishmaniasis: causes, clinical forms, diagnosis, treatment and prevention

Clinical forms and typical features

• Cutaneous leishmaniasis: the most common form, producing one or more chronic skin lesions or ulcers that may scar. Patients typically present with painless or mildly painful sores; secondary bacterial infection is possible. See a discussion of skin ulcers.
• Mucocutaneous leishmaniasis: in some infections the parasite extends to mucous membranes of the nose, mouth or throat and causes destructive lesions that can lead to disfigurement and functional impairment.
• Visceral leishmaniasis (kala-azar): the most severe form, characterized by prolonged fever (fever), weight loss, anaemia (anemia), and enlargement of the spleen (splenomegaly) and liver (hepatomegaly). If untreated, visceral disease can be fatal.

More than twenty species of Leishmania infect humans and different species tend to produce particular clinical patterns and geographic distributions. Host factors such as malnutrition (malnutrition), immunosuppression and socioeconomic conditions (poverty) influence disease severity and outcome.

Transmission, life cycle and reservoirs

Leishmania parasites complete part of their life cycle in sandflies and another part within mammalian hosts. When an infected sandfly feeds it injects the parasite into the skin; the parasite is taken up by host immune cells and can multiply there or disseminate. In many regions the infection cycles between vectors and animal reservoirs rather than exclusively between humans. A variety of mammals may harbour infection (other mammals), with domestic dogs being important reservoirs in numerous endemic areas (dogs). Infection has also been recorded in cats, cattle and horses, as well as in wild rodents and other wildlife, complicating control efforts.

Diagnosis

Diagnosis combines clinical assessment with laboratory tests. Direct demonstration of the parasite by microscopy or culture of tissue aspirates or biopsies remains a key method (microscopic identification). For visceral disease, serologic tests and rapid diagnostic tests on blood and molecular assays (PCR) can aid diagnosis and provide non-invasive alternatives to bone marrow or splenic aspiration; rapid blood tests are commonly used in field settings (blood test). Differential diagnosis varies by presentation and may include other causes of chronic ulcers, mucosal lesions or febrile splenomegaly.

Treatment

Treatment depends on the clinical form, infecting species, geographic origin of infection and patient factors such as age and pregnancy. Several drugs are used, and national recommendations vary. For visceral leishmaniasis, recommended options include liposomal amphotericin B and combinations that may involve pentavalent antimonials and paromomycin or the oral agent miltefosine in appropriate settings. Cutaneous disease may be treated with local therapies (topical agents, intralesional injections) or systemic drugs where lesions are extensive or at high risk of complications. For up-to-date regimens and drug availability consult clinical guidance and lists of recommended medications and policy documents from public health authorities such as the World Health Organization.

Prevention and control

Preventive measures aim to reduce human–vector contact, limit reservoir exposure and ensure prompt case detection and treatment. Personal protection includes the use of insecticide-treated bed nets (insecticide-treated nets), topical repellents, protective clothing and measures to reduce sandfly entry into houses. Vector control through environmental management and targeted insecticidal measures can reduce sandfly populations. Community education, improved housing and rapid access to diagnosis and treatment reduce transmission. Because ecology and vectors differ by region, control strategies should be tailored to local conditions and informed by entomological and epidemiological data.

Epidemiology and public health significance

Leishmaniasis is endemic in parts of Asia, Africa, the Americas and southern Europe. Estimates cited by major agencies indicate millions of people live in areas at risk; historically, figures referenced include about 12 million people infected worldwide and roughly 2 million new cases annually, with annual deaths in the tens of thousands. Risk is amplified by poverty (poverty), malnutrition (malnutrition), environmental change such as deforestation and rapid urbanization, and by migration and conflict. Because multiple Leishmania species and animal reservoirs coexist in many settings, control requires integrated approaches combining surveillance, vector control, case management and public health measures. For regional guidance and current statistics consult national public health authorities and international sources (WHO and other disease information).

Understanding the local parasite species, vector biology and reservoir hosts is essential for selecting diagnosis, treatment and prevention strategies. Where relevant, collaboration between human and veterinary health sectors improves control of zoonotic transmission involving domestic animals such as dogs, cats, cattle and horses. Research continues to refine diagnostic methods, safer and more effective therapies and vaccines, while public health programs work to expand access to diagnosis and treatment and to reduce the burden of disease globally (further reading).