In Brazil’s Leprosy Heartland, a Hidden Web of Neglected Infections Comes to Light

In the municipalities surrounding Governador Valadares, a city of roughly 280,000 people in the Doce River valley of Minas Gerais, Brazil, a team of researchers has completed one of the most detailed snapshots yet of how several neglected tropical diseases overlap in the same communities. The study, published in PLOS Neglected Tropical Diseases, enrolled 1,311 residents aged three and older and tested their blood for immune signatures of three very different pathogens: the bacterium that causes Hansen’s disease, commonly known as leprosy, and two parasitic worms, the blood fluke Schistosoma mansoni and the intestinal roundworm Strongyloides stercoralis. The results paint a picture of a region where these infections are not isolated curiosities but simultaneous, everyday exposures, and where where a person lives may matter as much as any individual risk factor.

The scientific motivation behind the work goes beyond simple disease mapping. For decades, researchers have suspected that helminth infections, which chronically modulate the human immune system, might influence whether someone exposed to Mycobacterium leprae develops clinical disease or mounts an effective response. Prior studies have reported associations between helminths and both Hansen’s disease and tuberculosis, but the epidemiology of these interactions remains poorly characterized, particularly at the community level in areas where all of these pathogens circulate at once. Because neglected tropical diseases tend to cluster in the same impoverished settings, understanding whether they interact biologically or simply share the same social and environmental drivers is a question with real consequences for how control programs are designed.

To answer it, the research team, led by investigators including Audra Bass, Jessica K. Fairley of Emory University, and Lucia A. O. Fraga of the Universidade Federal de Ouro Preto, took a deliberately broad approach. Rather than testing for a single pathogen, they used a multiplexed bead assay, a laboratory platform that can measure antibodies against several antigens simultaneously in a small blood sample. Participants answered questionnaires covering demographics and infection history, and their serum was screened for reactivity against antigens from all three target organisms. This simultaneous measurement is technically important: it allows researchers to compare immune responses across pathogens within the same individuals, rather than piecing together associations from separate studies with different populations, laboratories, and methods.

The headline numbers are striking. Among the 1,311 participants, 72 people, or 5.5 percent, reported a prior history of Hansen’s disease. A further 94 individuals, 7.2 percent, tested positive for antibodies against LID-1, an antigen specific to M. leprae that indicates exposure to the bacterium even in people without diagnosed disease. Parasitic infections were even more widespread: 836 participants, a remarkable 63.8 percent, reported having at least one parasitic disease in the past. Serological testing confirmed substantial ongoing exposure to the two worms studied, with 153 participants, or 11.7 percent, carrying antibodies against schistosome egg antigen, known as SEA, and 69 participants, 5.3 percent, positive for the NIE antigen of Strongyloides stercoralis.

These figures confirm that the region deserves its reputation as a highly endemic area for Hansen’s disease. Minas Gerais has long been one of Brazil’s most affected states, and Brazil as a whole accounts for the overwhelming majority of new leprosy cases in the Americas. What the new study adds is a quantitative measure of subclinical exposure. Anti-LID-1 positivity at 7.2 percent suggests that for every person with a documented history of the disease, there are others in the community carrying immune evidence of contact with the bacterium. Serology of this kind is increasingly used as a surveillance tool because M. leprae cannot be cultured reliably in the laboratory and because many infections never produce symptoms, making case counts an incomplete measure of transmission.

When the researchers turned to the associations between these infections, the most robust finding was geographic rather than immunological. After adjusting for other variables, rural residence was positively associated with both anti-LID-1 positivity, with an adjusted odds ratio of 1.79 and a confidence interval of 1.07 to 3.38, and with a history of Hansen’s disease, with an adjusted odds ratio of 1.97 and a confidence interval of 1.14 to 3.38. In other words, people living in rural areas were roughly twice as likely to show either immune evidence of M. leprae exposure or a clinical history of the disease compared with their urban counterparts. This pattern held even though the study area is not remote; the communities sampled lie within and around a mid-sized city.

The immunological cross-associations, by contrast, were suggestive but not statistically significant. Participants with antibodies to the Strongyloides NIE antigen showed a positive, though non-significant, association with anti-LID-1 positivity, with an adjusted odds ratio of 1.57 and a confidence interval spanning 0.69 to 3.57. The direction of this result is intriguing because Strongyloides, like other helminths, is known to skew immune responses in ways that could theoretically affect how the body handles intracellular bacteria such as M. leprae. Meanwhile, the association between anti-LID-1 and schistosome SEA antibodies ran in the opposite direction, with an adjusted odds ratio of 0.79 and a confidence interval of 0.38 to 1.61, hinting at a possible inverse relationship that some immunological hypotheses would predict, since schistosome-induced immune polarization might, in principle, be protective against mycobacterial disease.

The authors are careful not to overinterpret these signals. Because neither the positive association with Strongyloides nor the negative association with Schistosoma reached statistical significance, the study cannot confirm that helminth infections modify M. leprae infection risk in this population. The confidence intervals are wide, reflecting the moderate number of seropositive individuals, and a cross-sectional design captures a single moment in time, which limits any claim about cause and effect. Someone’s current antibody status may reflect infections acquired years earlier, and the timing of helminth exposure relative to M. leprae exposure, which may itself be separated by years or decades, cannot be reconstructed from a single blood draw and questionnaire.

What the study does establish firmly is the sheer burden of neglected tropical diseases in this corner of Minas Gerais. Nearly two-thirds of participants reported a past parasitic illness, and measurable antibody responses to schistosomes and Strongyloides were present in more than one in ten and roughly one in twenty residents, respectively. The authors conclude that the high co-endemicity itself warrants attention, alongside the strong and statistically significant link between rural residence and M. leprae exposure. That geographic signal points toward spatial and environmental risk factors, such as contact patterns, housing conditions, water and sanitation infrastructure, or ecological features of the Doce River valley, that could be investigated with the kind of geospatial analysis the research team, which includes spatial epidemiologist Julie A. Clennon and Lance Waller, is well positioned to pursue.

The broader significance of the work lies in its method and its framing. By measuring seroreactivity to multiple pathogens simultaneously in a single community sample, the study demonstrates a practical template for integrated surveillance of neglected tropical diseases, an approach increasingly advocated by global health programs seeking to move beyond single-disease vertical campaigns. It also underscores a persistent truth about Hansen’s disease: transmission continues in endemic regions even where case detection and multidrug therapy have expanded, and the reservoir of exposure is larger than the case registry suggests. For the communities of Governador Valadares and its rural surroundings, the study’s message is twofold. These infections are common enough to be considered a shared background risk, and the places people live, particularly rural households, carry a measurably higher burden of exposure to the leprosy bacterium. Follow-up work on the environmental and spatial drivers of that exposure, the authors suggest, is the natural next step, and could ultimately sharpen both leprosy control and the integrated treatment of the parasitic diseases that so often travel alongside it.

Subject of Research: Coinfection epidemiology of Mycobacterium leprae exposure, Hansen's disease, and helminth infections in southeastern Brazil

Article Title: Mycobacterium leprae infection, Hansen’s disease, and helminth infections: A cross-sectional study in southeastern Brazil

Article References: Bass, A., Leite, H., Oliveira, L. B. P., Nedell, E., Marçal, P., Clennon, J. A., Collins, J. M., Ziegler, T. R., Silva, E. M., Vieira, M. P., Pinheiro, M. D. S., Branco, A. C., Ferreira, J. A., Waller, L., Fraga, L. A. O., & Fairley, J. K. (2026). Mycobacterium leprae infection, Hansen’s disease, and helminth infections: A cross-sectional study in southeastern Brazil. PLOS Neglected Tropical Diseases, 20(10), e0013285. https://doi.org/10.1371/journal.pntd.0013285

Image Credits: AI Generated

DOI: 10.1371/journal.pntd.0013285

Keywords: leprosy, Hansen's disease, Mycobacterium leprae, neglected tropical diseases, helminths, schistosomiasis, strongyloidiasis, serology, Brazil, Minas Gerais, rural health, coinfection