Visceral leishmaniasis (VL), known as kala-azar, is a potentially fatal, neglected tropical disease caused by the protozoan parasite Leishmania. Transmitted through the bite of infected sandflies, VL primarily affects impoverished communities (1–4). VL is characterized by severe symptoms including fever, weight loss, fatigue, weakness, loss of appetite, enlarged liver and spleen, anemia, and swollen lymph nodes (2, 5). It is the most serious form of leishmaniasis, posing a life-threatening risk if left untreated (6). The parasite, Leishmania donovani, thrives in humans and sandflies, making human populations in Asia and Eastern Africa particularly vulnerable (1, 4, 7, 8). This neglected disease disproportionately impacts the poorest communities, highlighting the urgent need for improved prevention, diagnosis, and treatment strategies to combat its devastating effects (5).

VL is endemic in 80 countries with an estimated annual global incidence of 50,000–90,000 worldwide (9, 10). According to the 2022 World Health Organization (WHO) report, about 85% of global VL cases were reported from seven countries: Brazil, Ethiopia, India, Kenya, Somalia, South Sudan and Sudan (10). The 2017 World Health Organization (WHO) report revealed significant burden of VL in Eastern Africa, with South Sudan reporting the highest number of cases (3474) (11) followed by Sudan with 2902 (12), Ethiopia with 2,141 (13), and Somalia 1,166 cases (14). The disease has also been reported in Kenya, Uganda, and Eritrea (15–17). This trend continued in 2022, with Eastern Africa accounting for a staggering 73% of global VL cases. Alarmingly, half of these cases occurred in children under the age of 15, underscoring the devastating impact of this neglected disease on young lives (18).

A comprehensive global analysis of blood donor data revealed a pooled prevalence of visceral leishmaniasis at 7% (19). Different systematic reviews and meta-analysis conducted on human VL in Iran revealed that the pooled prevalence was 2–3% (2, 20). Moreover, systematic reviews and meta-analysis of studies conducted in Ethiopia, where VL is endemic, revealed a pooled prevalence of the disease ranging from 9.44 to 21%, 9.44% (21) to 21% (22), underscoring the high burden of VL within the country. VL imposes a significant economic burden on affected families in different countries. The costs associated with healthcare, including informal payments for accessing providers, diagnostics and medication, and transport costs for multiple visits can be substantial. These high direct expenses often force individuals to adopt coping strategies like selling or renting assets and taking out loans, which further exacerbating their financial hardship (23–25). Despite the goal of universal health coverage, remote areas with endemic visceral leishmaniasis (VL) face significant obstacles. Their weak and under-resourced health systems struggle to integrate complex VL diagnostic and treatment services into their limited basic healthcare packages. This challenge is further compounded by factors like economically driven migration or massive population displacements during conflicts, exacerbating the burden of the disease (26). Despite being a neglected tropical disease, visceral leishmaniasis (VL) has been prioritized for elimination by 2030 under the Sustainable Development Goals (SDGs), specifically Target 3.3 (27).

Preventing visceral leishmaniasis in Eastern Africa is a complex challenge due to the numerous interconnected risk factors associated with the disease. Factors such as age, sex, environmental conditions like the presence of certain trees or termite mounds, animal ownership such as cattle and dogs, living conditions, awareness levels, occupation, and education all contribute to the disease’s spread. To effectively address the impact and severity of VL, a multi-faceted approach is crucial, considering the interplay of these various risk factors (28–42). Behavioral factors, such as sleeping outdoors, neglecting bed nets, and inadequate insecticide spraying, along with housing conditions like wall type, have been identified as significant risk factors for VL in various studies (29, 31, 32, 34, 36–38, 43–45).

Although many primary studies have been carried out on human visceral leishmaniasis among the countries of Eastern Africa, the findings have not been consistent with the prevalence ranging from 1.8 to 84.8%. Moreover, the findings were not conclusive, and these could hamper the assessments of ongoing intervention efforts and activities (46, 47). Moreover, no study provides evidence of the pooled prevalence of human visceral leishmaniasis in Eastern Africa. Therefore, this systematic review and meta-analysis aimed to estimate the pooled prevalence of human visceral leishmaniasis and identify its risk factors in Eastern Africa. This systematic review and meta-analysis underscore the critical need for prioritizing primary prevention of human visceral leishmaniasis in Eastern Africa. This evidence-based information will be invaluable for policymakers, healthcare planners, and other stakeholders in developing and implementing comprehensive strategies to prevent, control, and mitigate the impact of VL. These insights can contribute to a future where the burden of this neglected tropical disease is significantly reduced in Eastern Africa.

Visceral leishmaniasis is a devastating parasitic disease that has continued to be a global burden to have a substantial impact on health that primarily affects the poorest and most marginalized communities in the world (25, 73). The burden of VL is particularly high in South Asia, East Africa, and the Mediterranean basin. The economic and social consequences of VL are severe, as the disease disproportionately affects individuals who are already vulnerable (10, 25). VL is a major public health problem, particularly in Eastern Africa, where it is considered a neglected tropical disease. The disease is endemic in countries of Eastern Africa like Ethiopia, Kenya, Sudan, and South Sudan, with high transmission rates in rural communities (25, 74, 75). The impact of VL in East Africa is compounded by factors like poverty, poor sanitation, conflict, and displacement (26).

The pooled prevalence of human visceral leishmaniasis in Eastern Africa was 26.16% [95%; CI: 19.96, 32.36%]. However, the report is higher than the pooled prevalence of VL obtained from a global systematic review and meta-analysis done among blood donors (7%) (19) and peoples with human immunodeficiency virus (HIV) (6%) (76). Moreover, the figure is higher than the findings of systematic reviews and meta-analysis pooled prevalence report of human VL in Iran conducted by Rahmanian et al. (3%) (20) and Rostamian et al. (2%) (2). The finding is also higher than the reported pooled prevalence of visceral leishmaniasis in Ethiopia by Haftom et al. (9.44%) (21) and Ayalew Assefa (16%) (22). The high prevalence and the pattern might reflect the lack of and inefficient access to affordable and active drugs, incorrect prescribing, and poor compliance undermine case management and perpetuate anthroponotic infection, and inadequate and unsustainable vector control (77). Other evidence suggests that this trend is continued due to the continuing widespread conflict in Eastern Africa, which destroyed housing and health care infrastructure. This in turn resulted in forced migrations to endemic areas that promote the emergence of VL (78). Moreover, the lack of advancement in diagnostics in field and facility settings, proficient vaccination of the disease, and unaffordability of the new advanced technologies contribute to the pattern to continue (79, 80).

Regarding subgroup analysis, the pooled prevalence of visceral leishmaniasis across the study setting is significantly heterogeneous after a univariate meta-regression. This might be because community-based studies often include a broader and more diverse population, including asymptomatic individuals or those with mild symptoms who might not seek medical care. In contrast, healthcare facility studies typically involve patients already symptomatic and seeking treatment, leading to higher observed prevalence rates. Moreover, community-based studies might use random sampling, while healthcare facility studies often use convenience sampling, which can introduce bias.

The univariate meta-regression analysis also found that the sample size category was a significant factor for the heterogeneity of the pooled prevalence of visceral leishmaniasis in Eastern Africa. This might be due to the statistical power in which the studies with smaller sample sizes often have less statistical power which leads to greater variability in prevalence estimates. This variability can contribute to heterogeneity when these studies are pooled with larger studies. Moreover, the sampling errors might be the reason for the significant heterogeneity of the pooled prevalence as smaller studies are more susceptible to sampling error, where the sample may not accurately represent the broader population. This can result in prevalence estimates that differ significantly from those of larger, more representative studies.

The odds of VL infection were higher among males compared to females. This finding is supported by a systematic review and meta-analysis report in Ethiopia in which males were 67% at higher risk of VL infection as compared to females (21), and a study conducted in India and Nepal which revealed that males were at greater risk of VL infection by a factor of 2.4 as compared to females (81). This might be because, socio-culturally, men are often more exposed to environments where sandflies, the vectors of the disease, are prevalent. This is because men are more likely to engage in outdoor activities such as farming, herding, or sleeping outside, which increases their risk of being bitten by infected sandflies which results in VL infection (82, 83).

The odds of VL infection were higher among people aged below 15 years compared to people aged 15 years and above. This finding is supported by the fact that Eastern Africa accounted for 73% of global VL cases, half of which occurred in children aged under 15 years in 2022 according to the WHO (84). This might be due to people aged less than 15 years being more likely to engage in activities that increase their exposure to sandfly bites, such as playing outdoors, which further elevates their risk. However, contrary to this finding, a cross-sectional study conducted in Southeastern Nepal revealed that the risk of VL infection among people aged ≥15 years was 5.5 times greater as compared to people aged <15 years (4). This inconsistency might be due to the difference in outdoor movement practiced by people under fifteen years and their counterparts. The odds of VL infection were 2.83 times higher among people who had a family of more than five as compared to their counterparts. This finding is supported by a study conducted in Nepal which elucidated that the risk of VL infection among families ≥6 in number was greater by a factor of 4.4 compared to their counterparts (4). Similarly, another study conducted in Nepal evidenced that large size households (>5 persons) were 3.6 times at greater risk of VL infection (85).

The odds of VL infection were higher among people who had termite hills/mounds near their homes compared to their counterparts. This finding is supported by a systematic review that explored the burrows of mammals, caves, crevices, termite hills, and walls with cracks that may serve as breeding sites for sand flies which later increase the transmission and infection of VL (86). The finding is also supported by a study conducted in Ethiopia in which the presence of termite hills was a risk factor for visceral leishmaniasis (87). Moreover, the presence of termite hills is one of the major landscape factors associated with increasing the risk of leishmaniasis infection. The presence of termite hill increases the risk of infection by a factor of 2.4 (88). This might be due to the roles as breeding and resting sites for sandflies, the primary vectors of the disease. This is evidenced by a study conducted in Colombia (89) in which termite hills provide an ideal microhabitat with stable temperature and humidity, which are conducive to the lifecycle of sandflies. These insects thrive in such environments, increasing the likelihood of human-sandfly interactions, especially in rural areas where people live or work near termite mounds. Consequently, individuals in these areas are at a higher risk of being bitten by infected sandflies, leading to a greater incidence of visceral leishmania.

The odds of VL infection were higher among people who had cattle/domestic animals compared to their counterparts. This aligns with findings from a systematic review of South Asian VL (90) and a study in India (91), which indicated that livestock ownership increases the risk of VL infection. In this meta-analysis, it was revealed that the odds for the occurrence of VL infection among people who practiced outdoor sleeping were 3.76 times higher when compared to people who did not practice outdoor sleeping. This finding is supported by a systematic review on VL (86) and a study conducted in India (92) which evidenced that sleeping outside was associated with increased risk of VL. This might be due to the increased exposure to sandflies which are most active during the night and sleeping outdoors increases the likelihood of being bitten by these insects, which can carry the Leishmania parasite. Moreover, lack of protective measures such as insecticide-treated bed nets or screens, and environmental factors of the outdoor environments (like vegetation, humidity, and temperature) especially in endemic areas, often provide ideal breeding grounds for and attract sandflies to outdoor sleeping areas which increase the chance of sandfly biting and risk of VL infection in the end.

The odds of VL infection higher among people who had VL- infected family member/s compared to those who did not have VL- infected family member/s. This finding is supported by a systematic review and meta-analysis of factors associated with visceral leishmaniasis in the Americas (93), and a systematic review of environmental and socioeconomic risk factors associated with visceral leishmaniasis (86). Another study conducted in Nepal supported this finding and evidenced that the proximity to previous VL cases was a strong risk factor for VL by 3.79-fold (85). Moreover, this is also congruent with another study conducted in India (92) in which living in the same household with a VL case was associated with a markedly elevated risk of VL. The reason for this might be the shared environmental and behavioral factors within households, such as living conditions and exposure to sandflies (the vector for VL), contribute to the increased risk of the disease.

The odds of VL infection were higher among people whose homes are near water source/pathway compared to their counterparts. This finding is supported by a study in Nepal, which demonstrated that living near water sources, such as ponds, significantly increased the risk of VL infection by a factor of 3.7 (4). Similarly, a study in India also found that proximity to water bodies increased the risk of VL infection (91).

In this study, the recorded pooled prevalence of human visceral leishmaniasis in Eastern Africa was higher (26.16%). Gender, age, family size, presence of termite hill/mound, presence of cattle/domestic animals, outdoor sleeping, presence of VL infected family member/s, and presence of water source/pathway near home were the risk factors significantly associated with human visceral leishmaniasis. While further research is needed to determine the most effective and timely intervention methods for visceral leishmaniasis, this study highlights the urgent need for comprehensive intervention strategies in Eastern Africa. This includes rigorous health education for residents, covering the disease’s cause, transmission, vector, and breeding sites, with strong collaboration between the WHO, government officials, non-governmental organizations (NGOs), and healthcare providers. Additionally, promoting health-seeking behavior for prompt treatment and implementing prevention strategies like avoiding outdoor sleep between dusk and dawn, wearing protective clothing, and using insect repellents are crucial steps toward controlling VL in the region.