What is Visceral Leishmaniasis?

Visceral Leishmaniasis (VL) (also referred to as kala-azar) is a lethal infectious disease that is caused by small, single-celled organisms called Leishmania donovani. These parasites live in or on a host (can be humans or animals), and survive by feeding off the host’s nutrients, depriving hosts of essential nutrients, which can make the host extremely ill. VL is mainly spread through the bite of infected female sandflies. These parasites belong to a larger group that can be transmitted in other ways, such as consuming contaminated food or water, being bitten, or coming into direct contact with the parasite itself.¹

Common symptoms of VL:

• High temperature
• Severe weight loss
• Hepatosplenomegaly
• Constant fatigue and lack of energy
• Anaemia
• In some cases, abdominal pain caused by organ swelling

Endemic regions

VL is considered endemic in certain parts of Africa and Asia, which means it is consistently present in these regions. VL is often referred to as a neglected tropical disease, largely because it affects people in low-income, tropical areas that receive little global attention. Since VL is uncommon in more ‘developed countries’, pharmaceutical companies tend to overlook it, investing far less funding in research and treatment than they do for more widespread diseases such as HIV.

Another major challenge is the lack of awareness about VL in the regions where it is more prevalent. If left untreated, VL is almost always fatal (95% fatal). Unfortunately, in many of these endemic regions, access to healthcare is limited, and even when treatment is available, it is often unaffordable for the people who need it the most; this is one of the main reasons why the disease continues to have such a high mortality rate.^1,2

Epidemiology

Global overview

According to the World Health Organisation (WHO), most VL cases occur in Brazil, East Africa, and parts of Asia. Every year, it is estimated that 50,000-90,000 new cases are reported globally, however, only 25-45% of these cases actually get reported to WHO.²

VL affects the health of more than 400,000 people yearly and is responsible for around 40,000 deaths each year. In fatal cases, the mortality rate can be as high as 75-95% if left untreated.³ VL is endemic in over 70 countries, putting about 200 million people at risk. However, the vast majority of cases (over 90%) come from just a few countries: India, Brazil, Sudan, South Sudan, Ethiopia, Somalia, and Kenya.¹

In the past, VL rates were high between 1998-2005, then they dropped slightly for a couple of years, and then declined significantly between 2007-2009, especially in South East Asia.¹ However, VL tends to surge every 10-15 years, which is believed to be linked to declining herd immunity in affected populations.⁴ From 2015-2016, VL cases rose in Eastern Africa, while they declined in the Indian Subcontinent. In Brazil, the number of cases stayed relatively stable during that period.¹

Africa

Eastern Africa is one of the hardest-hit regions, where frequent outbreaks continue to occur. Roughly 66% of all global VL cases are reported from this region.^2,4 Among those:

• Over half (53%) of all cases are in children under 15 years old
• About one-third of cases are women

In 2011, there was a noticeable spike in cases due to major outbreaks in South Sudan, Kenya, and parts of India, however, numbers began dropping again after 2011.¹

India

India carries about 12% of the global VL burden. In 2005, an effective oral treatment called miltefosine was introduced, which improved VL-treatment outcomes.

Furthermore, health authorities in India, Nepal, and Bangladesh launched the kala-azar elimination programme (KAEP). Their goal was to reduce VL cases to less than 1 case per 10,000 people in high-risk areas by 2015. By 2021, this target was achieved in 98.8% of the targeted regions.⁴

Brazil

VL was not a major concern in Brazil until after the 1980s, when it began to spread in larger cities and the Amazon regions.⁵ Between 2001-2012, just 10 cities accounted for 12% of VL cases.⁵ Whereas now, Brazil accounts for 96% of all VL cases in the Americas, making it a prominent area for the disease in the Western Hemisphere.⁶

Social determinants of health

Social determinants of health refer to the broader factors that shape a person’s health including where someone is born, their income level, where they live, their work, and age. When it comes to VL, several of these social factors can impact how widespread and severe the disease becomes. Below are some of the main contributors to VL infection status.

Poverty

Poverty is one of the biggest driving factors behind VL transmission and mortality. Individuals living in poverty often cannot afford basic necessities such as food, safe housing, clean water, or access to healthcare, all of which are crucial for preventing and treating VL. The lack of financial resources makes it harder for them to seek early diagnosis and treatment, which increases the risk of complications and death.

Additionally, poor living conditions contribute to other risk factors including malnutrition, inadequate sanitation, and lack of protection against sandflies. According to WHO, poor sanitation, such as unmanaged waste and open sewage, creates ideal breeding grounds for sandflies. These insects thrive in crowded, unhygienic environments and are drawn to densely crowded homes, where it is easier to find humans to bite. People living in poverty might sleep outside or on the ground, further increasing their risk of being bitten and infected.^4,2 

Crowded living conditions

In places where VL is more common, like parts of India, Africa, and Brazil, overcrowded housing is a serious issue. These densely populated areas often have limited living spaces and poor ventilation, making it easier for sandflies to come into contact with people. The closer people live together, the easier it is for the disease to spread.

Poor housing conditions

Poor housing, especially in rural areas, is another key factor in VL transmission. Research shows that houses made from mud, with cracks in the walls, with damp conditions, and low light provide ideal habitats for sandflies. These homes are often built by local communities using natural, short-lasting materials, such as mud or leaves, in line with traditional building methods.

A number of studies highlight the risks:

• In rural and semi-urban Ethiopia, people living in houses with cracked walls were six times more likely to get infected with VL
• In urban Nepal, homes built from brick were found to be more protective compared to thatched houses with no windows
• In India, houses with mud-plastered walls were four times more likely to get VL compared to cement-plastered houses
• Another study in Nepal confirmed that mud-constructed homes were an independent risk factor for the disease⁷ 

In rural East Africa, people often live in small huts or barns, and during hot seasons, many sleep outside, exposing themselves even more to sandflies.⁴ Additionally, VL infection rates tend to be higher in places with poor sewage systems and no regular rubbish collection, which creates even more breeding grounds for the insects.⁸

Limited access to healthcare

Getting access to healthcare in many VL endemic areas is extremely difficult, and poverty plays a major role. In some regions, treatment is hard to access and unaffordable. For instance, in Nepal, studies found that the cost of VL treatment was higher than the average person’s yearly income. Many families resorted to using all their savings, taking out high-interest loans, or selling livestock just to cover treatment costs. Another study showed that 31-93% of households spent at least 5-15% of their income on VL treatment.⁹ 

Additionally, healthcare services could be physically inaccessible, especially in rural or remote areas. The nearest hospital could be hours away, and there may not be reliable transportation or the cost for transportation is too expensive. Even where treatment is technically free, people still face financial strain from travel, hospital stays, and other expenses.¹⁰ 

Furthermore, VL diagnosis and treatment are often only available at specific government hospitals or well-equipped health centers; this limited availability, along with understaffing and shortages of trained professionals, creates significant barriers to care. Additionally, there are challenges in maintaining a steady supply of diagnostic tools and drugs.¹⁰ Ultimately, poverty is the common denominator that ties together all these issues, whether it is limited access to healthcare, poor housing, or increased risk of infection due to environmental exposure.

Prevention and strategies 

Vector control

Indoor residual spraying (IRS) 

Indoor residual spraying involves spraying insecticides on the walls to kill sandflies that come into contact with these surfaces. IRS reduces the overall sandfly population by up to 95% for at least one month after application.¹¹ In India, IRS played a key role in reducing the spread of VL leading to a noticeable drop in both the number of cases and mortality.¹²

Insecticide-treated nets (ITNs) 

Insecticide-treated nets, including long lasting insecticidal nets (LLINs), are another important tool for controlling sandfly population and limiting the transmission of Leishmania donovani. Although research findings have somewhat mixed results, a number of studies support their effectiveness. For example, LLINs were found to reduce sandfly density by 43.7%, while households using ITNs had 60% lower sandfly population even 11 months after implementation. Additionally, female sandfly numbers dropped significantly within the first 3 months post-intervention, and in one case, sandfly density fell from 7.9 to 0.9 per house every night. Notably, when IRS and IRNs were used together, sandfly reduction reached 94-100%, with no reappearance of sandflies for over a year, highlighting the added benefit of combining interventions.¹³

Protection 

Wearing PPE (personal protective equipment) that covers exposed skin is a simple and effective way to prevent sandfly bites, especially in high-risk areas.

Surveillance

Keeping track of where VL cases and sandfly populations are appearing is important. Regular and effective surveillance helps healthcare teams monitor potential outbreaks and respond quickly with control measures to prevent further spread.

Early detection

Detecting VL early is crucial for treating the disease quickly and for controlling its transmission. Early diagnosis can lead to timely treatment, reduce mortality, and support more accurate surveillance efforts. Early diagnosis enables health professionals to identify hotspots and target them with early interventions. Since no vaccination for VL is available, early detection remains one of the most powerful tools in preventing its spread.

Summary

Visceral Leishmaniasis (VL) is a serious parasitic disease spread mainly by infected female sandflies. It causes high fever, weight loss, anaemia, and swollen organs, and can be fatal if untreated. The disease is most common in low-income regions of Africa, Asia, and Brazil, where poverty, poor housing, overcrowding, and limited access to healthcare increase the risk of infection.

VL continues to affect hundreds of thousands of people each year. Prevention focuses on reducing sandfly populations through spraying, using insecticide-treated nets, wearing protective clothing, and improving early diagnosis. These measures, along with better living conditions and access to treatment, are essential for reducing the spread and impact of the disease.