Leprosy Cases Rising in Rural Tanzania After 25 Years of Declining Global Numbers

Leprosy, one of humanity’s oldest recorded diseases, is quietly changing shape in rural Tanzania. A new retrospective analysis spanning a quarter of a century has documented a steady and statistically significant increase in new leprosy diagnoses at a single specialist center in the country’s southeast, even as the world celebrates historic declines in the disease overall. The findings, drawn from more than 800 patient records collected between 2000 and 2024, suggest that the battle against Hansen’s disease is far from over and that its epidemiological character may be shifting in ways that demand renewed attention from public health authorities.

The study, published in PLOS Neglected Tropical Diseases, was conducted by a team of Tanzanian and international researchers led by Robert Machang’u of the Nazareti Leprosy Center in Ifakara. The center, located in the Kilombero Valley, has long served as a referral hub for leprosy patients across a largely rural region where the disease remains endemic. Because the facility has maintained routinely collected clinical records for decades, it offered the researchers an unusually long window into how the disease’s presentation has evolved across two and a half decades of treatment programs, demographic change, and shifting health policy.

The researchers took a retrospective cross-sectional approach, extracting data from the records of every patient newly diagnosed with leprosy and registered at the center between 2000 and 2024. For each case, they recorded demographic characteristics such as age and sex, the clinical classification of the disease, the operational category used to guide treatment, and the degree of disability present at the time of diagnosis. Leprosy is conventionally divided into paucibacillary disease, which involves few skin lesions and low bacterial burden, and multibacillary disease, in which bacteria are abundant and the patient is far more infectious. Disability is graded on a scale from zero to two, with grade 1 indicating loss of protective sensation in the hands or feet without visible deformity, and grade 2 indicating visible damage such as clawed fingers, foot ulcers, or facial impairment.

To analyze the trends hidden in these records, the team applied statistical methods suited to count data over time. Poisson regression was used to estimate how case notifications changed year by year, expressed as incidence rate ratios with 95 percent confidence intervals. Logistic regression was used to test whether the characteristics of patients, such as their sex, age group, disease classification, or disability grade, shifted significantly across the study period, with results reported as odds ratios. This dual approach allowed the researchers to distinguish genuine temporal trends from random year-to-year fluctuation in a dataset of modest but meaningful size.

What emerged was a portrait of a disease that is not simply persisting but intensifying in specific ways. In total, 801 new cases of leprosy were registered at the center over the 25-year span. Men bore the clear majority of the burden, accounting for 67.4 percent of all cases, a pattern consistent with the well-documented male predominance in leprosy notification seen across many endemic countries. The age distribution skewed older, with the largest single share of cases, 33.2 percent, occurring among people aged 50 and above. Multibacillary disease dominated the clinical picture, making up 62.7 percent of diagnoses, and more than half of all patients, 52.7 percent, already had grade 1 disability by the time they were diagnosed.

The temporal trends were the most striking element of the analysis. Case notifications rose by an average of 4.0 percent per year across the study period, an increase the researchers reported as highly significant, with an incidence rate ratio of 1.04 and a confidence interval running from 1.03 to 1.07. When the team disaggregated the trend by demographic group, the rise was concentrated among men and among people aged 50 or older, both of whom showed significant increases over time. Multibacillary cases and grade 1 disability at diagnosis also climbed significantly, indicating that patients were arriving at the clinic not only more frequently but also with more transmissible and more damaging forms of the disease.

Against these worrying trajectories stood one genuinely encouraging finding: childhood cases declined significantly over the study period. In leprosy epidemiology, the proportion of cases occurring in children under 15 is treated as a sensitive barometer of ongoing transmission in the community, because children with the disease have typically been infected recently. A falling share of pediatric cases suggests that transmission intensity around Ifakara may be easing, even as older adults continue to be diagnosed in growing numbers. The researchers interpret this divergence as evidence of an evolving epidemiological profile rather than a simple story of resurgence or retreat.

Why are more cases being detected, and why are they more severe? The study’s retrospective design cannot fully answer that question, but several explanations are consistent with the data. Rising notifications could reflect genuine increases in transmission, but they could also indicate improved case-finding efforts, greater community awareness, or expanded outreach that brings long-untreated patients into contact with health services. The high proportion of multibacillary disease and disability at diagnosis, however, points toward delayed detection as a persistent problem. Patients who harbor the infection for years before diagnosis accumulate bacterial loads and nerve damage that multidrug therapy cannot reverse, and they remain infectious for longer, sustaining chains of transmission. The concentration of cases among older men, a group that may be less engaged with routine health services, fits this pattern of late presentation.

The findings carry weight beyond the Kilombero Valley because they arrive at a moment when global leprosy strategy is at a crossroads. The World Health Organization’s multidrug therapy programs, which combine rifampicin, dapsone, and clofazimine, have driven a dramatic reduction in the global disease burden since the 1980s, and leprosy was once widely expected to approach elimination as a public health problem, defined as fewer than one case per 10,000 population. Yet transmission has proven stubbornly persistent in pockets of South Asia, Africa, and South America, and the new Tanzanian data illustrate how national-level statistics can conceal local trends running in the opposite direction. A single rural district where notifications climb 4 percent annually for 25 years represents thousands of preventable infections and disabilities.

The authors conclude that intensifying early case detection, community awareness, treatment, and surveillance is essential if leprosy is to be eliminated as a public health concern in the region. In practical terms, that means strengthening contact tracing around known cases, since household contacts carry an elevated risk of infection; training frontline health workers to recognize early skin lesions and nerve involvement before disability sets in; and sustaining the free multidrug therapy that remains the backbone of control. The declining childhood burden shows that progress is possible, but the rising tide of severe, multibacillary disease among older adults is a reminder that the final mile of leprosy elimination will be the hardest, demanding sustained investment in the rural clinics and specialized centers where the disease’s last strongholds are being fought.

Subject of Research: Epidemiological trends of leprosy cases diagnosed at a rural Tanzanian treatment center over 25 years

Article Title: Epidemiological profile of leprosy cases at Nazareti Leprosy Center, Tanzania: A retrospective analysis (2000–2024)

Article References: Machang’u, R., Kagesyeko, J. N., Edward, M., Ameh, W. O., Chuwa, L., Upunda, G., & Tibenderana, J. R. (2026). Epidemiological profile of leprosy cases at Nazareti Leprosy Center, Tanzania: A retrospective analysis (2000–2024). PLOS Neglected Tropical Diseases, 20(9), e0014761. https://doi.org/10.1371/journal.pntd.0014761

Image Credits: AI Generated

DOI: 10.1371/journal.pntd.0014761

Keywords: leprosy, Hansen's disease, Tanzania, neglected tropical diseases, epidemiology, multibacillary leprosy, disability grades, multidrug therapy, case detection, public health surveillance, retrospective study, rural health