Hansen's disease is an infectious illness caused by Mycobacterium leprae)1 which develops slowly and can have an incubation period of 2–7 years.2 This Gram-negative bacterium infects susceptible individuals, preferentially affecting the skin and peripheral nerves, causing loss of tactile sensitivity and motor disability.1

M. leprae is an intracellular acid alcohol-resistant bacillus that infects the cells present in the nervous system and epithelial tissue. M. leprae bacillus can be found in keratinocytes, macrophages, and neutrophils and affects Schwann cells within peripheral nerves.3 Keratinocytes may play an important role in the activation of the antimicrobial peptide beta-defensin, which acts in response to the bacillary antigen. When M. leprae enters the host cell, it triggers a metabolic lipid interaction in order to survive.4-6 Thus, after cell infection, an appropriate environment for bacterial multiplication is induced.7 This leads to dermatological manifestations and infectious nerve involvement which subsequently causes axonal alterations and demyelination, causing sensory damage, disability, and deformity.5,8,9

Leprosy can present itself in different ways, depending on the immune response of the infected individual. Therefore, it is necessary to use the Ridley-Jopling classification, which subdivided the syndrome into five types: polar tuberculoid leprosy (TT), borderline tuberculoid leprosy (BT), borderline–borderline leprosy (BB), borderline lepromatous leprosy (BL), and polar lepromatous leprosy (LL).10–13

There is also the less complex WHO classification system based on the number of associated skin lesions: up to five lesions are considered as paucibacillary form, and from six lesions as multibacillary leprosy.14

Clinically, the disease presents itself mainly through the skin lesions and sensory changes, although visceral involvement (such as eyes, testicles, and bones) may be present. Tuberculoid forms are generally characterized by the appearance of hypochromic macules with a hyposensitive component surrounding the lesion. On the other hand, the lepromatous form is generally more aggressive, with a large number of bilateral and asymmetric erythematous lesions (mainly on the face, auricular lobe, and fingers), in addition to bilateral, symmetrical, and diffuse peripheral neuronal involvement, which may be associated with hypertrophy of the affected nerve, as well as sensory and motor deficits.10–12

M. leprae can affect individuals of all ages and is less common in children. The infection is equally prevalent in both sexes. Transmission occurs through direct contact between an individual with an infection and household contacts.4

M. leprae transmission pathways are not fully understood, but several studies suggest that this bacillus is preferentially dispersed by the nose, instead of the skin.15–17 Genetically defined immunological mechanisms related to human leukocyte antigens (HLA) play an important role in the proliferation or destruction of bacilli and consequently in resistance to infection.18 The risk of developing leprosy is also associated with the endemic level, adverse socioeconomic conditions, and social and health precariousness, which explains a large number of cases in underdeveloped countries.19

Public health indicators can be an essential tool for predicting the behavior of this disease. Although there is currently a wide range of drug therapies that effectively cure Hansen's disease, the main challenges lie in monitoring new cases as well as the patient's adherence to the prescribed treatment.5

The increased effectiveness of therapeutic regimens that emerged in the 1980s enabled a significant reduction in the global prevalence of leprosy. In 1985, there were about 5.3 million cases and by the end of 2017 this number had dropped to 192,713 cases.20,21 However, in the last decade there was an increase of new cases: 210,758 in 2015, 214,783 in 2016, and 210,000 in 2017 in 150 countries, with a notification rate of 2.77 per 100,000 inhabitants.20,22 Prospective assessments of the disease are difficult to understand because of the ongoing changes proposed in its definition, its long incubation period, and changes in its control activities causing delay in case detection.23 Furthermore, as the surveillance systems of low-income countries are supposedly affected by significant inaccuracies, even in endemic areas, the available numbers are affected by a significant underreporting.21,24 In addition to these difficulties social stigma, untrained health professionals further compromise the appropriate patient assessment.25 In the Northeast region of Brazil, 7067 hospitalizations were reported with 147 deaths and a mortality rate of 2.08% between the period 2012 and 2017.26 Therefore, there is a need for extensive research to improve the understanding of leprosy in its various aspects including its epidemiology.

According to the United Nations, Brazil accounts for 11.6% of all leprosy cases worldwide. To modify these figures, the Brazilian Unified Health System operates through programs aimed at both treatment and prevention of this disease. The period between 1995-2000 marked a milestone in Hansen's disease in Brazil, with the implementation of measures outlined by the leprosy elimination plan (PEL). To increase resolution, this contingency plan prioritized its implementation at the municipal level so that in 2006 the plan was fully implemented at that level. Thus, there was better management and coordination in the fight against leprosy at the primary health level aiming to establish effective monitoring of this infection.27,28 Over the past decade, other initiatives at the municipal, state, and federal levels have been maintained or implemented. Understanding the outcome of these efforts is essential to outline combat strategies in the near future. Thus, this study aimed to evaluate the mortality rate due to the disease, as well as number of new cases, and the rates of physical disability and cure in the Federative Units of Brazil.

Leprosy diagnosis can be delayed by multiple factors. There is still a lot of prejudice surrounding the disease. Thus, infected people tend to hide their diagnosis from household contacts, who should also be monitored and receive adequate attention. Furthermore, it is difficult to diagnose the disease, and this leads to postponement of treatment, which implies in higher grades of disease complications and even death.

In the present study, it was possible to find new cases and deaths in various parts of the country and identify a significant reduction in the number of leprosy cases in Brazil in the last decade. Furthermore, there were discrepancies in the distributions of notifications and mortality in the different macro-regions of Brazil. The North and Midwest regions had higher mortality rates. The largest number of cases was found in Tocantins and Mato Grosso, states in inner Brazil. Finally, we report that the cure rate in the southeast and south regions were negatively correlated with the mortality rate in these regions.

To overcome these problems, many efforts have been made over the years, and understanding the effectiveness of these efforts is vital. Epidemiological studies contribute significantly to understanding the disease and its implications and serve indirectly to verify whether public health policies minimize the damage caused by the disease as well as the costs for the state.

The reductions in new cases and mortality, observed in the study, are presumably due to proper implementation of the Leprosy Control Program in primary care nationwide. From an epidemiological perspective, such a result points to a tendency of low prevalence or even stabilization of the endemic.18 In addition, the leprosy prevalence rate per year in the analyzed period showed a decreasing trend, as well as stability. On the other hand, Brazil is still one of the countries with the highest prevalence of leprosy cases worldwide and has not managed to reach the WHO goal of one case per 10,000 inhabitants.28

Herein, we show the variation in death rates among the Brazilian Federative Units, corroborating other studies, which have indicated regions with the highest incidences.29–31 In other words, when comparing the different macroregions in terms of the number of deaths per 100,000 inhabitants (Fig. 2), there was a more significant decrease in deaths rates in the Southeast and South regions than in other regions (North, Northeast, and Midwest). This decrease in the deaths rates in the two regions mentioned above is certainly influenced by the presence of a better network of medical services as well as by the greater availability of healthcare facilities, enabling earlier diagnosis and more effective treatment.30

In addition, data from the Southeast and South regions of Brazil can be explained by better implementation of prevention and control measures, such as active search for cases and health education of the population. The data showed no significant correlation in the Northeast, North, and Midwest regions. There have been no significant reductions in death rates in these regions. Therefore, these data are positive since there has been a significant increase in the population in these regions in recent years. In the case of the Southeast and South regions, the data are very promising because, with a significant reduction in the number of deaths, it is possible to predict that in the coming years, there may be acceptable levels of death rates for this disease in the population.

Correlations were found between the rates of new cases of leprosy per 100,000 inhabitants and rates of disability, cure and mortality in different Brazilian states. A higher rate new cases of leprosy in two states of the Federation, the states of Mato Grosso and the state of Tocantins, located in the Midwest and north region, respectively (Fig. 3) throughout the study period. The distribution of cases is quite heterogeneous among the Brazilian macro-regions.32,33 In this study, there was a predominance of cases of Hansen's disease in the Midwest and North regions corroborating the data found in the two states, Mato Grosso and Tocantins. The higher rates of new cases in the states of Mato Grosso and Tocantins indicate the need to assess the associated factors, such as economic factors, health structure, and fewer preventive measures. In fact, in the regions where the two states are located, there are fewer control actions and other peculiarities that promote a higher incidence and mortality.34

Another important point analyzed in this study was the possible correlations between the number of new cases of Hansen's disease and the rates of physical disability and cure. The data showed a significant loss of physical capacity in patients with leprosy. These findings are related to the difficulty in making an early diagnosis. In other words, it appears that primary health policies are not sufficient to reach the entire population affected by Hansen's disease. The greater the degree of physical disability, the longer the patient has not received adequate treatment. Thus, a worrying scenario is observed, since the presence of physical disability leads to high treatment costs and the need to implement policies in order to improve the skills of health workers for early diagnosis and treatment of the disease. Consequently, avoiding sequelae and ensuring a better recovery for those who already have physical disability.28

Concerning cure rates among the Brazilian macro-regions, it was observed that the Southeast and South regions had higher rates among the new cases of leprosy in the evaluated period. Furthermore, the higher the cure rate, the lower the death rate per 100,000 inhabitants. These results suggest that these two regions have health services that meet the parameters established by the PEL in Brazil, which includes not only expanding the network of diagnosis and care for people affected by Hansen's disease but also an effective treatment network, thus providing greater success in curing the disease.34

The discrepancy in the period available and validated for notifications of new cases and death due to leprosy through the information system was a limitation of the study. In addition, there is underreporting of the disease in some regions of the country.35,36 which may limit the strengthen and consistency of our findings. The consolidation and dissemination of properly qualified health professionals trained in prevention, early detection of the disease and in its treatment can guarantee better results in the control of leprosy.