“Leprosy” from the Greek, lepra, meaning “scab” or “peeling.”
What is Leprosy Disease?
A microbiological study of the infectious leprosy disease is fascinating. Leprosy is a chronic infection caused by the bacterium, Mycobacterium leprae also called Hansen’s bacillus. It is amongst the oldest recorded human diseases yet remains relatively poorly understood and somewhat misunderstood through centuries of stigmatisation. Most common in sub-tropical countries including India, Brazil and Indonesia, leprosy is being targeted by vaccination programmes in order to reduce the incidence of this unpleasant, debilitating disease. This blog article introduces the microbiology and pathology of leprosy, setting the scene for the second blog article on leprosy to describe the current approach to vaccination.
During invasion of the body M. leprae colonizes the Schwann cells of the peripheral nervous system leading to demyelination neuropathy, loss of sensation, often producing a disfiguring effect in the body’s extremities. The bacterium can survive within macrophages, the cells of the host that are responsible for killing invading pathogens, thus evading a major component of host immunity. Leprosy is classified clinically by the extent of the host’s immune response.
Tuberculoid leprosy results from an extensive cellular immune response to infection. Conversely, Lepromatous leprosy disease is characterised by no host response. In both forms, symptoms develop suddenly, diminish after several weeks only to re-occur for months. Lesions appear on the face, extremities and trunk. Patients go blind when eyes become inflamed. General muscle inflammation, joint inflammation and orchitis may occur.
Falling between the Tuberculoid and Lepromatous states are the three borderline categories characterised by red, hardened lesions, fluid accumulation in the periphery, sensory loss, and neuropathy. Symptoms develop gradually and typically persist for several weeks.
Leprosy is a socio-economic disease – disadvantaged life style circumstances promote the occurrence of the leprosy disease. Contrary to long-held misconceptions, leprosy is not easily transmitted between people. The bacterium takes two weeks to reproduce in the lab (the longest microbial generation seen) and in the patient infection takes on average 5 years before manifesting. Transmission is poorly understood. Prolonged exposure to sufferers appears important, casual interaction is not so the fact that 7,000,000,000 bacilli can be seen in a single gram of patient biopsy raises the question, what are the bacteria doing in situ?
Treating the patient
When M. leprae is sensitive to antibiotics, multi-drug treatment should be straightforward and effective. In the last three decades around 14 million patients have received antibiotics to treat leprosy. Irreversible disabilities are, of course, more challenging to treat; there are an estimated 2-4 million people in the world living with leprosy-induced disability.
What about a vaccine to prevent, rather than treat, leprosy? India and Brazil currently use the Bacillus Calmette Guerin (BCG) vaccine formulated against the disease tuberculosis to offer protection against Mycobacterium leprae. Experts differ in opinion regarding its efficacy. The second article to be posted on the BioLabTests website will describe the current strategies for a M. leprae vaccination. Did you know there is a World Leprosy Day? Organisation like Lepra are supporting the fight against leprosy, both prevention and cure.