What is visceral leishmaniasis and can it be eliminated?

There are three main forms of leishmaniasis: visceral, cutaneous and mucocutaneous. Visceral leishmaniasis, or kala-azar, is the most severe. 

Leishmaniasis is a vector-borne disease caused by Leishmania parasites and transmitted to humans through the bites of infected female sandflies. The same sandflies also bite animals such as dogs, rodents and cattle, which can then act as reservoirs of Leishmania parasites. 

Visceral leishmaniasis symptoms include fever, weight loss, enlargement of the spleen and liver, and anaemia. An estimated 50,000–90,000 new cases occur worldwide each year, but gaps in reporting and disease surveillance mean the true number is likely far higher. Without treatment, visceral leishmaniasis is almost always fatal.

Some people who recover from visceral leishmaniasis later develop post kala‑azar dermal leishmaniasis (PKDL) after completing treatment. This often starts as a rash on the face before spreading to other areas including the arms, trunk and legs, with lesions containing Leishmania parasites. PKDL can be chronic and stigmatising, and because the lesions harbour parasites, it allows continued transmission of the disease within the community.

Eastern Africa bears the heaviest visceral leishmaniasis burden, reporting almost 80 percent of cases, with additional hotspots in Brazil and the Indian subcontinent. Children are disproportionately affected, and mortality is highest among those under five. 

Whilst Bangladesh eliminated visceral leishmaniasis as a public health problem in 2023, the situation in eastern Africa is more complex. Progress is challenging for many reasons, including increased genetic diversity of Leishmania parasites, wider endemic spread, and frequent population movement sustaining transmission. 

The disease is closely linked to poverty. Cracked walls and damp interiors in poorly built housing create favourable conditions for sandfly resting, increasing the risk of bites and transmission. Not everyone exposed to infected sandflies develops the disease – populations living in affected areas can develop natural immunity, so outbreaks are more likely when non-immune people move to endemic areas. Separately, having a weakened immune system, for example due to malnutrition or HIV co-infection, also increases the risk of severe illness. 

Visceral leishmaniasis is also spreading to new locations. Climate change is expanding the range of sandflies by creating new breeding habitats, and population movements, land-use changes and conflict are bringing people into closer contact with transmission zones.

There is no licensed vaccine for visceral leishmaniasis. Prevention rests on finding and treating people quickly to reduce onward transmission. 

Diagnosis involves a combination of clinical symptoms and rapid diagnostic tests, but access to these tests is limited and results are not always reliable, particularly in African settings. Often, diagnosis must be confirmed by finding parasites in tissue samples or with more sensitive lab tests. 

Once diagnosed, visceral leishmaniasis is curable – but treatment is challenging. The most widely used treatments in endemic settings still rely on drugs first developed in the 1940s. These can be painful, require injections or prolonged hospital stays, and carry toxic side effects. They also come with high indirect costs: travel, food and lost income during treatment. Newer drugs, including liposomal amphotericin B and miltefosine, offer improvements in some regions, but no single treatment works well everywhere because efficacy varies by parasite species and geography.

Access to care is a further barrier. The communities most affected by visceral leishmaniasis are often in areas with the weakest health systems, making it difficult for patients to reach diagnosis and treatment in time.

Other prevention measures exist but are not widespread or consistently applied. These rely mainly on controlling sandfly populations through insecticide-treated bed nets or indoor spraying. Both approaches have limits: they only target sandflies indoors and their effectiveness depends on housing quality. Reliance on chemicals also creates a risk of resistance in sandflies, underlining the need for new approaches.

With the right resources, visceral leishmaniasis is both preventable and treatable. The World Health Organization has set a global target of eliminating it as a public health problem by 2030, meaning that fewer than 1 in 100 cases are fatal. This will only be possible with bold, transformative action. 

At Wellcome, we’re investing in research and innovation to tackle the biggest barriers to progress. This includes:

• Working with partners in Kenya and Ethiopia to build a clearer picture of how visceral leishmaniasis spreads. By modelling infection patterns and sandfly behaviour, researchers can generate evidence to help local decision-makers identify the most effective interventions for their communities.
• Supporting the development of new oral treatments, including candidates being trialled in India and Ethiopia. These could reduce the need for painful injections and long hospital stays, offer safer alternatives to current drugs, and make care easier to access.
• Backing innovative vector-control research, including research into Delftia bacteria, which can disrupt the development of Leishmania parasites inside sandflies and may offer an alternative to insecticides.
• Strengthening the wider research ecosystem by convening experts to identify the most urgent research gaps and galvanise support for action.

Together, this work links to a single purpose: to reduce the impact of visceral leishmaniasis by achieving optimised use of the right interventions, where they’re needed most.