Mycobacterium leprae–helminth co-infections and vitamin D deficiency as potential risk factors for leprosy: A case–control study in south-eastern Brazil

•Schistosomiasis is more common in individuals with leprosy than their household contacts.•Vitamin D deficiency is more common in those with leprosy than community controls.•Children with leprosy have the highest burden of concomitant schistosomiasis.•Thus, comorbidities may contribute to ongoing reservoirs of infection. Evidence suggests that biological mechanisms involved in helminth infections and vitamin deficiencies increase susceptibility to other infections. The aim of this study was to investigate the associations of helminth co-infection and select micronutrient deficiencies with leprosy using a case–control design. From 2016 to 2018, individuals aged ≥3 years were recruited at clinics in and around Governador Valadares, Minas Gerais, Brazil in three groups: cases of leprosy, household contacts and community-matched (non-contact) controls. Helminths were diagnosed through stool Kato Katz examination and serum reactivity to anti-soluble adult worm antigen preparation IgG4. Serum ferritin, 25-OH vitamin D and retinol concentrations were measured. Multi-variate logistic regression was conducted to identify associations with active leprosy. Seventy-nine cases of leprosy, 96 household contacts and 81 non-contact controls were recruited; 48.1% of participants were male with a median age of 40 years. Helminths were found in 7.1% of participants on Kato Katz test, all but one of which were Schistosoma mansoni, and 32.3% of participants were positive for S. mansoni serology. On multi-variate analysis, cases were more likely to be infected with helminths (diagnosed by stool) than household contacts [adjusted odds ratio (aOR) 8.69, 95% confidence interval (CI) 1.50–50.51]. Vitamin D deficiency was common, and was more likely in cases compared with non-contact controls (aOR 4.66, 95% CI 1.42,–15.33). Iron deficiency was not associated with leprosy, and vitamin A deficiency was not detected. These associations suggest that the immune consequences of schistosomiasis and vitamin D deficiency may increase the risk of active leprosy. Comorbid conditions of poverty deserve further study as addressing co-infections and nutritional deficiencies could be incorporated into programmes to improve leprosy control.