Leprosy epidemiology and demographics

Incidence
In 2002, the number of new cases detected worldwide was 763,917. In 2002, 96 cases occurring in the United States were reported to CDC. In 2002, WHO listed Brazil, Madagascar, Mozambique, Tanzania, and Nepal as having 90% of cases.

Epidemiology
Worldwide, two to three million people are estimated to be permanently disabled because of Hansen's disease. India has the greatest number of cases, with Brazil second and Myanmar third.

In 1999, the world incidence of Hansen's disease was estimated to be 640,000; in 2000, 738,284 cases were identified. In 1999, 108 cases occurred in the United States. In 2000, the World Health Organization (WHO) listed 91 countries in which Hansen's disease is endemic.

India, Myanmar and Nepal contained 70% of cases. In 2002, 763,917 new cases were detected worldwide, and in that year the WHO listed Brazil, Madagascar, Mozambique, Tanzania and Nepal as having 90% of Hansen's disease cases.

According to recent figures from the WHO, new cases detected worldwide have decreased by approximately 107,000 cases (or 21%) from 2003 to 2004. This decreasing trend has been consistent for the past three years.

In addition, the global registered prevalence of HD was 286,063 cases; 407,791 new cases were detected during 2004.

Hansen's disease is tracked by the Centers for Disease Control and Prevention (CDC). Its prevalence in the United States is believed to be rising and underreported. There are a rising number of cases worldwide, though pockets of high prevalence continue in certain areas such as Brazil, South Asia (India, Nepal), some parts of Africa (Tanzania, Madagascar, Mozambique) and the western Pacific.

Due to the rising numbers, several support groups exist, the headquarters of which is currently in Lynbrook, NY and headed by Brian Marasco, leprosy survivor.



Risk groups
At highest risk are those living in endemic areas with poor conditions such as inadequate bedding, contaminated water and insufficient diet, or other diseases (such as HIV) that compromise immune function. Recent research suggests that there is a defect in cell-mediated immunity that causes susceptibility to the disease. Less than ten percent of the world's population are actually capable of acquiring the disease. The region of DNA responsible for this variability is also involved in Parkinson's disease, giving rise to current speculation that the two disorders may be linked in some way at the biochemical level. In addition, men are twice as likely to contract leprosy as women.

Disease burden
Although annual incidence—the number of new leprosy cases occurring each year—is important as a measure of transmission, it is difficult to measure in leprosy due to its long incubation period, delays in diagnosis after onset of the disease and the lack of laboratory tools to detect leprosy in its very early stages.

Instead, the registered prevalence is used. Registered prevalence is a useful proxy indicator of the disease burden as it reflects the number of active leprosy cases diagnosed with the disease and retrieving treatment with MDT at a given point in time.

The prevalence rate is defined as the number of cases registered for MDT treatment among the population in which the cases have occurred, again at a given point in time.

New case detection is another indicator of the disease that is usually reported by countries on an annual basis. It includes cases diagnosed with onset of disease in the year in question (true incidence) and a large proportion of cases with onset in previous years (termed a backlog prevalence of undetected cases).

The new case detection rate (NCDR) is defined by the number of newly detected cases, previously untreated, during a year divided by the population in which the cases have occurred.

Endemic countries also report the number of new cases with established disabilities at the time of detection, as an indicator of the backlog prevalence. However, determination of the time of onset of the disease is generally unreliable, is very labour-intensive and is seldom done in recording these statistics.

Global situation
As reported to WHO by 115 countries and territories in 2006, and published in the Weekly Epidemiological Record the global registered prevalence of leprosy at the beginning of the year was 219,826 cases. New case detection during the previous year (2005 - the last year for which full country information is available) was 296,499. The reason for the annual detection being higher than the prevalence at the end of the year can be explained by the fact that a proportion of new cases complete their treatment within the year and therefore no longer remain on the registers. The global detection of new cases continues to show a sharp decline, falling by 110,000 cases (27%) during 2005 compared with the previous year.

Table 1 shows that global annual detection has been declining since 2001. The African region reported an 8.7% decline in the number of new cases compared with 2004. The comparable figure for the Americas was 20.1%, for South-East Asia 32% and for the Eastern Mediterranean it was 7.6%. The Western Pacific area, however, showed a 14.8% increase during the same period.

Table 2 shows the leprosy situation in the six major countries which have yet to achieve the goal of elimination at the national level. It should be noted that: a) Elimination is defined as a prevalence of less than 1 case per 10,000 population; b) Madagascar reached elimination at the national level in September 2006; and c) Nepal detection reported from mid-November 2004 to mid-November 2005.

Resources
CDC Leprosy Incidence