Global leprosy (Hansen disease) update, 2021: moving towards interruption of transmission

Overview

Leprosy is a neglected tropical disease (NTD) caused by Mycobacterium leprae. Since the introduction of multidrug therapy (MDT), the registered prevalence has decreased substantially, from more than 5 million cases in the 1980s to 133 802 cases in 2021. New cases continued to occur, however, indicating continuing transmission of infection. Screening of contacts and chemoprophylaxis with single-dose rifampicin were recommended as a crucial step to break the chain of transmission. The Global Leprosy Strategy 2021–20302 was developed as constituent of the NTD road map 2021–2030,3 with the goal of eliminating leprosy (i.e., interruption of transmission).

Global leprosy situation

WHO collects statistics on leprosy annually from countries to assess the situation and to publish an annual global leprosy update. Paper-based data collection was gradually replaced with a web-based data management system based on the District Health Information System 2 between 2014 and 2017. An abridged Excel® sheet was used in low-endemicity settings where very few or even no new autochthonous cases are detected.

In 2021, 143 countries provided statistics, as compared with 127 in 2020: 37 in the African Region (AFR), 27 in the Americas Region (AMR), 21 in the Eastern Mediterranean Region (EMR), 16 in the European Region (EUR), 11 in the South-East Asia Region (SEAR) and 31 in the Western Pacific Region (WPR). Reports were received from all 23 global priority countries. Most countries reported for the calendar year January–December 2021, while a few reported for a different 12-month period (April 2021–March 2022). Rates were calculated per million population according to estimates (medium variant) provided by the United Nations Department of Economic and Social Affairs, World Population Prospects 2022 revision. The population of children (≤15 years) was used as the denominator for calculating child case detection rates.

Globally, the registered prevalence of leprosy (number of cases on treatment at the end of 2021) was 133 802, and the prevalence rate was 16.9 per million population. The number of registered cases at the end of the year was 20 960 (prevalence rate 18.0) in AFR, 25 053 (24.3), in AMR, 4206 (5.5) in EMR, 81 222 (39.4) in SEAR and 2360 (1.2) in WPR