Leprosy is among the oldest human-specific infections we currently know about. The common ancestor of the two modern bacterial species that cause leprosy, Mycobacterium leprae and M. lepromatosis, is thought to have become a parasite in early humans millions of years ago. This makes it far older than our own species, Homo sapiens. Nevertheless, leprosy continues to afflict hundreds of thousands of people every year.
World Leprosy Day raises awareness of the suffering caused by the disease. It remains endemic in India, where more than half of all worldwide cases occur, and in parts of South East Asia and Africa. World Leprosy Day is observed on the last Sunday of January to coincide with the anniversary of the assassination of Mahatma Gandhi, a vocal supporter of the fight against leprosy.
What is leprosy?
Leprosy is a chronic bacterial infection caused by two members of the genus Mycobacteria. It is usually thought to be transmitted between people via droplets when people breathe or cough, although armadillos may also play a role in transmitting the disease to humans.
Despite its continued prevalence, leprosy is actually one of the least infectious diseases we know. Globally, only about 5% of people are actually susceptible to leprosy due to a malfunction in the gene responsible for conferring immunity; the rest of the human population is immune. Furthermore, of the clinical cases that do occur, some 85% are non-infectious.
The number of new leprosy cases – roughly 200,000 a year – is all the more remarkable given the low risk of acquiring and transmitting the disease.
Since M. leprae and M. lepromatosis reproduce very slowly, the incubation time of leprosy can be up to five years. Symptoms may not appear for as long as 20 years, so the disease is rarely diagnosed in its early stages. When symptoms do appear, they include growths and discoloured lesions on the skin, and eye problems that can lead to blindness. The mucosal layers of the respiratory tract are also affected, leading to nosebleeds and breathing difficulties.
If it is not treated, leprosy can cause permanent damage to nerves and muscle paralysis in the extremities and face. Patients’ ability to sweat and feel pain is impaired, and injuries are common as a result. This can lead to the characteristic loss of fingers and whole limbs in many people who have leprosy.
In the 1940s, a drug called Dapsone was developed which stalled the disease and, if taken over many years, could cure it. However, the length of time required for treatment meant that patients could rarely take it consistently and for long enough. Furthermore, Dapsone-resistant strains of M. leprae began to appear soon after the introduction of the drug.
In the 1960s, two other drugs – rifampicin and clofazimine – were added to the drug combination used to treat leprosy, which became known as multi-drug treatment (MDT). MDT is effective in treating the disease and has been made available for free around the world since 1995.
Leprosy was technically eliminated on a global scale in 2000. This means that less than 1 case occurs per 10,000 people worldwide. However, the disease is still endemic in a number of countries, so the fight to completely eradicate it is not over.
With free MDT treatment available around the world, the most important measure to eliminate leprosy is to raise awareness of the disease and to remove the stigma associated with it. “Leper colonies” still exist in many areas where the disease is endemic, cutting infected people off from their families and support networks. Educating the population on leprosy, maintaining a regular supply of free MDT doses even in remote regions and monitoring the progress of elimination programmes are all crucial in ensuring that leprosy can soon become a thing of the past.
For further information, please see our article on Leprosy in the August 2014 edition of our quarterly magazine, Microbiology Today.