History:
Leprosy is an ancient disease shrouded with suffering and misunderstanding. It has been known throughout the world since biblical times and many medical historians believe this disease has brought out both the best and worst of human nature. Current research suggests the disease has been infecting humans since as early as 4000 B.C, with some of the first written accounts on Egyptian papyrus at around 1550 B.C. In China and India leprosy is a very ancient disease, but many question marks remain as to when it reached the Middle East. If it arrived only recently, then is must have came even later to Western Europe, most likely carried North and West by the Romans and the Crusaders (Pain 2005). Later Europeans would bring the disease to the Americas. By the 12th century the disease had reached its peak. Though it has lower transmission rates and is rarely fatal, no other disease was more feared then leprosy. Due to the high degree of disfigurement, low understanding of the disease, and lack of a known treatment, many people believed the disease was a curse or punishment sent from the gods. In the 13th and 14th centuries, most countries possessed a strict policy of segregating those with the disease, often times placing them in "leper colonies". In even worse instances, many of those who possessed the disease were not just cast out, but killed. Of the many who were shunned from society, they were forced to rely on charity for survival. By the 13th century the disease was in decline, and by the 16th century it was virtually gone, remaining only within specific regions around the world. In 1873, Dr. Gerhard Henrik Armauer Hansen of Norway discovered the bacteria responsible for leprosy within samples taken from skin lesions. However, though he was able to determine this was an infectious disease, as opposed to the wrath of the gods, this still didn't limit the social stigma or ostracizing of those who possessed it. In the 1960's the prevalence rate of Mycrobacterium leprae was around 11 million people worldwide (Talha 2009), and currently is estimated to affect about 800,000 people worldwide (Moulten 2000).
Leprosy was once widely distributed in Europe and Asia, but now occurs mainly in resource-poor countries in tropical and temperate regions. Today the disease has all but died out within North America, with only a small number of cases diagnosed each year. India, Indonesia, and Myanmar possess about 70% of all cases of leprosy worldwide, with Africa being the 2nd most affected area.
Biology:
"Mycobacterium leprae is an acid-fast gram-positive bacillus, and an obligate intracellular parasite with tropism for macrophages and Schwann cells" (Britton 2004). It has parallel sides and rounded ends, measuring 1-8 microns in length and 0.2-0.5 micron in diameter, and closely resembles the tubercle bacillus. The complete genome of the bacteria possesses 3,268,203 base pairs. It possesses a unique ecological niche, with a very limited range of hosts, infecting only humans, chimpanzees, mangabey monkeys, and nine-banded armadillos. The disease mainly affects the skin, the peripheral nerves, mucosa of the upper respiratory tract, and the eyes. Once the bacteria is inside the host it begins to replicate, progressing slowly throughout the human body; searching out and destroying nerves. Damage to peripheral nerves results in sensory and motor impairment with characteristic deformities and disabilities (Britton 2004). The incubation period between infection and the onset of symptoms varies widely, from just months up to 30 years, with an average being around 4 years for tuberculoid and 10 years for lepromatous. Often, there can be a low rate of leprosy transmission which can continue for decades, however M. leprae is among the least contagious of human pathogens. It is estimated that the bacterium produces symptoms in less than 10 percent of the human population, and only then after prolonged exposure.
M. leprae has the longest doubling time of all known bacteria (13 days) which makes doing laboratory research (in vitro) on this organism quite difficult. It's been posited that the leprosy bacillus may be dependent on its host's metabolic products, which could explain its inability to grow in culture and even its long generation time. Its exact mode of transmission has yet to be proven, yet the likely means of transmission is aerosol spread of nasal secretions and uptake through nasal or respiratory mucosa. While human-to-human respiratory tramsmission is thought to be the likely cause of most infections, exposure to insect vectors, infected soil, and animal reservoirs may also be possible modes of transmission. M. leprae cannot be transmitted via intact skin, and the infection is not spread by touching.
There is currently no decent test for infection, and a vaccine treatment is highly unlikely. Those with an M. leprae infection can usually be treated with a multi-drug therapy (MDT), consisting of three antibiotics: rifampicin, loxacin, and minocycline. This regimen can render a patient noninfectious within 30 days, and noninfected within 6 to 9 months (Barret 2005) It has successfully cured more than 8.4 million people since 1981 (Moulten 2000). Yet, even those sufferers who have completed a MDT regime may still have sustained disability from the nerve damage already suffered. Thalidomide has also been used successfully to combat the disease, however, disease severity and treatment success are closely related to the individuals immune system. The widespread implementation of the MDT therapy has been associated with the decline in the prevalence of leprosy.
There is currently no decent test for infection, and a vaccine treatment is highly unlikely. Those with an M. leprae infection can usually be treated with a multi-drug therapy (MDT), consisting of three antibiotics: rifampicin, loxacin, and minocycline. This regimen can render a patient noninfectious within 30 days, and noninfected within 6 to 9 months (Barret 2005) It has successfully cured more than 8.4 million people since 1981 (Moulten 2000). Yet, even those sufferers who have completed a MDT regime may still have sustained disability from the nerve damage already suffered. Thalidomide has also been used successfully to combat the disease, however, disease severity and treatment success are closely related to the individuals immune system. The widespread implementation of the MDT therapy has been associated with the decline in the prevalence of leprosy.
