Leprosy, formally known as Hansen’s disease, dates back to ancient times, but millennia later, it remains a modern health threat. With an estimated 200,000+ new cases worldwide in 2016, Hansen’s disease is still a significant cause of global morbidity. While this disease typically concentrates in developing countries, even developed countries face cases and outbreaks—in fact, the US CDC reported between 78 and 89 cases annually from 2012 to 2016. Hansen’s disease is categorized among “neglected tropical diseases,” labeled as such because they do not typically receive the priority in public health programs necessary to adequately address them as health threats, even though they affect more than a billion people around the world. World Leprosy Day—recognized each year on the last Sunday in January (January 28 this year)—offers an important opportunity to highlight the ongoing health challenges posed by Hansen’s disease.

What is Leprosy?

As mentioned above, leprosy is alternatively known as Hansen’s disease—named after Gerhard Henrik Armauer Hansen, who discovered the causative bacterium, Mycobacterium leprae, in 1873. The disease primarily affects skin, peripheral nerves, and mucous membranes, typically presenting with patches of discolored skin accompanied by loss of feeling in the affected areas due to nerve cell damage. If left untreated, nerve damage from advanced Hansen’s disease can result in corneal ulcers, blindness, paralysis in affected muscles, reabsorption of affected fingers and toes, or other types of permanent deformities such as nose disfigurement or loss of eyebrows.

The myth that leprosy causes appendages to fall off likely stems from wounds in affected areas going unnoticed (due to loss of feeling as a result of nerve damage), which can lead to the spread of infections that could potentially result in permanent damage to fingers, toes, or other body parts. In extreme cases, the reabsorption of affected digits can give the appearance that the affected individual’s fingers and/or toes have fallen off. Another misconception includes the association with historical descriptions of leprosy. In the time before medical science could differentiate between various skin conditions, the term “leprosy” was applied to a vast array of diseases. Some of these were highly contagious, which is not necessarily consistent with Hansen’s disease as it is known today.

According to the US CDC, scientists have not yet identified a definitive route of person-to-person transmission; however, it is known that Hansen’s Disease requires “prolonged, close contact with someone with untreated leprosy over many months” to spread person to person, possibly via respiratory droplets. In fact, more than 95% of people are naturally immune to infection with M. leprae. The disease has an extremely long incubation period (on the order of years or even decades), which make it extremely difficult to link cases epidemiologically. Interestingly, some animals, including armadillos, may be naturally colonized with the M. leprae bacteria and could serve as sources of infection in humans, although this is difficult or impossible to determine for individual cases.

Hansen’s disease is largely treatable today through the use of combination antibiotic therapy.  Because the treatment course typically lasts for 1-2 years, several antibiotics are prescribed at once to mitigate the risk of the bacteria developing resistance to one of the drugs. Since 1995, the WHO has offered free treatment to all patients worldwide, funded through donations from The Nippon Foundation and Novartis. While the treatment can completely cure the bacterial infection and prevent the symptoms from worsening, it cannot repair the damage already incurred or restore nerve function. The US CDC estimates that 2-3 million individuals worldwide are living with permanent disability stemming from Hansen’s disease, including approximately 5,000 in the US.

Leprosy Today

The WHO reported 214,783 new cases of Hansen’s disease worldwide in 2016 (down from more than 5 million in the 1980s), and a year-end global prevalence of 171,948 cases. The WHO lists 22 high-priority countries, predominantly spread across Africa, South and Southeast Asia, and Oceana. In 2016, a total of 41 countries reported 100 or more cases (including the US with 168). Three of these countries—India, Brazil, and Indonesia—each reported more than 10,000 new cases. India alone accounts for 63% of new of cases globally, and 75% were in the WHO’s Southeast Asia Region.

In 2015, the US CDC reported 89 cases of Hansen’s disease across the US; however, this data may be misleading, as Hansen’s disease is not a reportable condition in every state. The National Hansen’s Disease Registry identified 178 new cases in 2015, with Florida (49), California (22), Texas (21), Louisiana (16), Hawai’i (11), and New York (10) accounting for more than 72% of domestic cases. More than half of the cases (96) were reported in states where M. leprae has been detected in indigenous armadillo populations. Additionally, climate change may be resulting in an expanded geographical range for armadillos, with recent reports of new armadillo sightings at least as far north as Champaign County, Illinois.

Hansen’s disease largely affects vulnerable populations in developing countries, who have limited access to effective medical care for diagnosis and treatment of the condition. Visible symptoms lead to social stigma and further discrimination for affected individuals and communities. This stigma is a substantial additional barrier to obtaining proper care. Historically, leprosy was believed to be highly contagious, and affected individuals were often cast into exile to live among other affected individuals. One article cites more than 1,000 of these so-called “leper colonies” in India alone as recently as 2015, with many more worldwide. In some places, these evolved into treatment communities, but patients were often still confined and vilified out of fear. Even today, it is legal in some countries to divorce one’s spouse solely because they suffer from Hansen’s disease, making it even more difficult for these individuals, often women, to seek medical care or provide for their children.

Future of Leprosy

In 1991, the World Health Assembly “adopted a resolution to eliminate leprosy as a public health problem by the year 2000.” The language of the WHA resolution defined elimination as “attaining a level of prevalence below one case per 10 000 population, at the global level.” While the WHO succeeded on the proposed timeline, some people claim that it sends mixed messages about the current threat posed by Hansen’s disease. Rather than truly eliminating the disease, the success of this effort effectively eliminated funding sources for many national leprosy control programs, significantly impairing treatment and surveillance efforts. The study cited in the article above claims that the actual annual incidence of leprosy may be as high as double the WHO estimate, resulting in potentially millions of undiagnosed cases worldwide—more than 4 million projected by 2020.

In 2016, the WHO followed up the success of the initial global leprosy control program by initiating the Global Leprosy Strategy 2016-2020, aimed at further mitigating the health impact of Hansen’s disease. The principal goals of this program are preventing pediatric disabilities due to the disease, cutting Grade-2 disabilities—defined by the WHO as visible deformity or damage to the hands or feet or severe visual impairment (worse than 6/60), lagophthalmos, iridocyclitis, or corneal opacities in the eyes—to fewer than 1 case per million people, and banning legislation worldwide that legalizes discrimination of affected individuals.

Like many preventable and treatable diseases that we have discussed over the past several months—including measles, pertussis, plague, and cholera—Hansen’s disease continues to cause global morbidity and mortality, particularly for some of the world’s most vulnerable populations. The temptation to divert critical resources and awareness away from these diseases threatens to squander the successes of global control efforts. And like many diseases that prey on the most vulnerable among us, elimination of effective education, surveillance, and treatment programs only serves to amplify the inequities faced by those who are affected, perhaps even more so for leprosy due to the lingering effects and disabilities caused by the disease and the associated social stigma and fear. Continued awareness and control efforts at the national and global levels are necessary to further reduce the burden of Hansen’s disease and prevent the associated lifelong debilitating and stigmatizing effects for its victims.


Photo: The leprosarium in Carville, Louisiana, USA operated from 1894 until 1999. When it was closed, many patients protested for their right to remain at the facility. The grounds are now home to the National Hansen's Disease Museum.

Photo courtesy of CDC/Elizabeth Schexnyder, National Hansen's Disease Museum, Curator

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