Epidemiology of Hansen's Disease
by Josafá Gonçalves Barreto
Epidemiological and operational indicators
Several epidemiological indicators are needed to assess transmission dynamics and the efficiency of Hansen’s disease control measures in a given territory and period. These indicators will not be covered exhaustively in this chapter, but to introduce their use we summarize in Table 1 the most important ones.
Table 1 - Epidemiological and operational indicators for Hansen’s disease in Brazil
Hansen’s disease worldwide
The number of new Hansen’s disease cases registered annually in the world has remained relatively stable at > 200,000 over the past 10 years, with an average of 220,367 cases. Of the 159 countries and territories that reported to WHO in 2018, 32 reported zero cases, 47 reported 1-10, 24 reported 11-100, 41 reported 101-1000, 12 reported ≥ 1,000 cases, and only three countries reported more than 10,000 cases. About 80% of all cases in the world are reported only in these three countries (India, Brazil and Indonesia). Among the 2018 notifications, 125,491 (60.2%) cases were male; 130,169 (62.4%) cases were classified as multibacillary (MB); 16,013 (7.7%) were under 14 years of age and 11,323 (5.4%) already had grade 2 physical disability at the time of diagnosis.2
Hansen’s disease in Brazil
Brazil has seen a decrease in the number of new case notifications in the past 15 years, however there has been an increase in the last two years as a result of increased active search efforts implemented by the Ministry of Health and some states and municipalities. In 2018, 28,660 new cases were detected in the country, resulting in an annual detection rate of 13.7/100,000 inhabitants, which is high according to the parameters of the Ministry of Health. As a result, Brazil reported 92.6% of all cases in the Americas in 2018. Other selected indicators show the following picture for Brazil in 2018: 1) Rate among children under 15 = 3.7 per 100,000 (high); 2) Proportion of grade 2 disability at diagnosis = 8.5% (medium); 3) Proportion of cases cured = 80.6% (acceptable) and 4) Proportion of contacts examined = 81.4% (acceptable).2,3
The spatial distribution of Hansen’s disease is highly heterogeneous in Brazil, with the annual detection rate ranging from 1.0 to 138.3 per 100,000 inhabitants in the states of Rio Grande do Sul and Mato Grosso in 2018, respectively. The average rate in the Brazilian Amazon states (47/100,000) is 4.2 times higher than the average in the non-Amazonian states (11/100,000).4 A video documentary entitled "Hanseníase: endemia oculta na floresta amazônica" [Hansen’s disease: Hidden endemic in the Amazon rainforest], showing the research work and active search for new cases among contacts of Hansen’s disease cases and among students under 15 years old in schools in the interior of Pará, helps to explain the role of social determinants in maintaining endemic disease and the challenges faced by health professionals in these areas.
These regional differences are also noticeable when we analyze other selected indicators: 1) Rate among children under 15 years of age (lowest = 0.1/100,000 in Rio Grande do Sul; highest = 30.1/100,000 in Tocantins); 2) Proportion of grade 2 disability at diagnosis (lowest = 4.8% in Espírito Santo; highest = 24.8% in Rio Grande do Sul); 3) Proportion cured (lowest = 59.9% in the Federal District; highest = 96.9% in Acre); 4) Proportion of contacts examined (lowest = 51.3% in Amapá; highest = 94.1% in Espírito Santo).3
Analysis of these selected indicators shows that Hansen’s disease remains a public health problem in Brazil, with large regional differences requiring different strategies according to the needs of different areas of the country. Hyper-endemicity among children under 15 years old in states such as Tocantins, Mato Grosso, Maranhão and Pará clearly indicate that the transmission of the disease is expanding in these states, whilst the high proportion of grade 2 physical disability at diagnosis in Rio Grande do Sul and in across the southern and southeastern regions of the country, with the exception of the state of Espírito Santo, reflects delay in the diagnosis of cases, contributing to the maintenance of the chain of transmission of the disease in regions of supposedly low prevalence.
Barriers to timely and early diagnosis of Hansen’s disease cases include patient-related issues such as fear of diagnosis, lack of information about the signs and symptoms of the disease, and even the search for traditional healers as the first or only treatment option. Barriers related to health services lead to errors and delays in diagnosis. It can take years for the patient to receive an accurate diagnosis and appropriate treatment,5-7 which is unacceptable in an endemic country like Brazil.
Hidden endemicity and the emergence of drug resistance
It is estimated that more than 4 million people in the world have Hansen’s disease without diagnosis and therefore without treatment. This large number of undiagnosed cases - hidden endemicity - is a constant threat to disease control, increasing the burden of infection in the community and the rate of transmission.8 Brazilian studies have demonstrated the magnitude of this problem in Brazil, including the high hidden prevalence in children under 15 years of age, which is up to 17 times higher than the registered prevalence.9-13
In addition to hidden endemicity, the emergence of strains of M. leprae that are resistant to components of the multidrug therapy (MDT) regimen recommended for the treatment of Hansen’s disease has created additional challenges to effective Hansen’s disease control. The first global prospective study, carried out by WHO in 19 countries, which included 1,932 people affected by Hansen’s disease, found 154 (8%) infected with M. leprae strains carrying drug-resistance gene variants.14 In the same study, Brazil reported double the proportion of cases resistant to rifampicin as India (9.1% versus 4.7%). Among new cases only, Brazil presented the highest proportion of resistant cases (15.6%), known as primary resistance.
A recent study in Vila do Prata, a former colony of persons affected by Hansen’s disease in Pará, detected 43.2% (16/37) resistant strains of M. leprae. Multiple resistance to rifampicin and dapsone was observed in 8 relapse and 4 new cases.15 Another study detected resistant strains in cities near the former Prata colony, and in several other areas of Brazil and the world.16 This alarming scenario of emerging primary resistance and transmission of resistant strains makes surveillance of drug resistance one of the priorities in the study of Hansen’s disease today.
Juliana Tancredo Carlini and
Lavínia Damacena Perin
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