

Leprosy: Causes, Symptoms, Diagnosis, Treatment & Prevention
Introduction
Leprosy, also known as Hansen’s disease, is an ancient infectious disease caused by Mycobacterium leprae and Mycobacterium lepromatosis, both of which are acid-fast bacilli. For centuries, people with leprosy were isolated and stigmatised due to a lack of understanding about the disease. However, leprosy does not spread through casual touch, and it is important to be cautious about misinformation
Historical Background of Leprosy
Leprosy is one of the oldest recorded diseases, with references dating back to ancient Egypt (1550 BCE) and Indian medical texts (600 BCE). It was widely misunderstood throughout history, leading to the
- Stigmatization
- Isolation of those affected
During the Middle Ages, leprosy was feared across Europe, and leper colonies were established to separate patients from society. The disease’s mention in religious texts further fueled misconceptions.
A major breakthrough came in 1873, when Dr. Gerhard Armauer Hansen identified Mycobacterium leprae as the cause of leprosy, debunking myths that it was a hereditary or divine punishment. This discovery paved the way for medical advancements, shifting the focus from isolation to effective treatment.
Today, leprosy is curable with multidrug therapy (MDT), and global efforts continue to eliminate stigma and ensure early diagnosis.
Transmission - How Does Leprosy Spread? Myths vs. Reality
Leprosy spreads primarily through prolonged exposure to respiratory droplets from an untreated infected person.
- It is not highly contagious and requires close, repeated contact over time.
- Additionally, leprosy can be contracted through direct contact with nine-banded armadillos (Dasypus novemcinctus), which serve as natural reservoirs of Mycobacterium leprae. However, this mode of transmission is rare.
Understanding Leprosy Incidence
Leprosy can affect individuals of all ages but is most commonly seen in:
- Children aged 5–15 years
- Adults over 30 years
However, 95% of people exposed to Mycobacterium leprae do not develop the disease due to natural immunity. Leprosy is more prevalent in poverty-stricken communities, where access to healthcare and early diagnosis may be limited.
Importantly, leprosy is not transmitted through pregnancy or sexual contact.
Who Is at Risk? Key Factors for Leprosy Development
Several factors can increase the risk of developing leprosy:
- Close contact with an untreated infected person
- Age – Higher risk in children (5–15 years) and adults over 30 years
- Genetic predisposition – Variants in the NOD2 gene may increase susceptibility
- Weakened immune system – Conditions like HIV, chemotherapy, or other immunosuppressive states
While these factors increase risk, most people exposed to Mycobacterium leprae do not develop the disease due to natural immunity.
How Leprosy Affects the Body: Pathogenesis Explained
Leprosy is caused by Mycobacterium leprae, an obligate intracellular parasite that primarily invades
- Epithelial tissue
- Peripheral nerves
It tends to affect the cooler regions of the body, including the
- Skin
- Eyes
- Nose
- Respiratory mucosa
Key characteristics:
- Slow-growing organism: Multiplies approximately every 12.5 days, making disease progression gradual.
- Chronic granulomatous disease: Persistent infection can lead to tissue damage, nerve impairment, and disability if left untreated.
Despite its ability to infect nerves, most individuals exposed to M. leprae do not develop symptoms due to natural immunity.
Recognizing Leprosy: Symptoms and Signs
Leprosy symptoms develop gradually over months or even years due to the slow-growing nature of Mycobacterium leprae. The disease primarily affects the skin, peripheral nerves, eyes, and mucous membranes, leading to symptoms based on the severity and type of leprosy.
1. Skin Symptoms
- Hypopigmented or reddish skin lesions – Patches with reduced sensation (numbness)
- Loss of sensation – Affected areas may not feel pain, temperature, or touch
- Thickened, dry skin – Often due to nerve damage affecting sweat glands
- Nodules or lumps – More common in lepromatous leprosy, often on the face (leonine facies)
- Ulcers or non-healing wounds – Due to repeated injuries in numb areas
2. Nerve Symptoms
- Peripheral nerve thickening – Swollen, enlarged nerves (e.g., ulnar, common peroneal)
- Nerve pain and tingling – Burning or electric-shock-like pain
- Muscle weakness or paralysis – Especially in the hands, feet, and face (e.g., claw hand, foot drop)
- Loss of reflexes – Affected nerves impair normal movement response
3. Eye Symptoms
- Reduced blinking and dry eyes – Due to nerve damage affecting eyelid muscles
- Corneal ulcers and blindness – If left untreated, severe nerve damage may lead to vision loss
4. Nasal and Respiratory Symptoms
- Nasal congestion and nosebleeds – Due to infiltration of the nasal mucosa
- Nasal collapse (saddle nose deformity) – In severe cases due to cartilage destruction
5. Systemic and Immunologic Reactions
Leprosy can trigger immune system reactions, leading to inflammation and worsening symptoms:
- Type 1 Reaction (Reversal Reaction) – Sudden swelling, pain, and redness in skin lesions (common in borderline leprosy)
- Type 2 Reaction (Erythema Nodosum Leprosum, ENL) – Painful nodules, fever, joint pain, and neuritis, common in lepromatous leprosy

Subtypes of Leprosy
Leprosy is classified into different subtypes based on the number of skin lesions, bacterial load, and nerve involvement.
1. Paucibacillary (PB) Leprosy – “Tuberculoid Leprosy”
- Fewer than five well-defined, dry, hypoesthetic (reduced sensation) skin lesions
- Early nerve involvement – Enlarged peripheral nerves, neuropathic pain, and loss of sensation
- Stronger immune response – Fewer bacteria present in the body
- Single-lesion paucibacillary – A variant with only one lesion
2. Multibacillary (MB) Leprosy – “Lepromatous Leprosy”
- Six or more symmetrical skin lesions, often appearing as diffuse, nodular plaques
- Leonine facies – Thickened facial skin, loss of eyebrows, nodules, and enlarged pinna
- Delayed nerve involvement, progressing gradually
- Weaker immune response – Higher bacterial load, making it the most common subtype
3. Borderline Leprosy
- Mixed characteristics of both paucibacillary and multibacillary leprosy
- Unstable form that can shift towards either PB or MB leprosy depending on immune response
These classifications help guide diagnosis and treatment, ensuring patients receive the most effective care.
Complications and Other Manifestations of Leprosy
Leprosy can lead to several serious complications if left untreated or poorly managed. Here are some of the most common and impactful complications:
1. Neuropathy
- Sensory loss – Affected areas may lose the ability to feel pain, touch, or temperature
- Muscle weakness – Nerve damage can impair motor function, leading to weakness, paralysis, or deformities like claw hand or foot drop
- Amputations – Prolonged nerve damage, ulcers, and untreated injuries increase the risk of amputation
2. Ophthalmic Injury
- Weakening of eye muscles – Affects the ability to blink properly, leading to dryness and potential corneal damage
- Dry eyes – Lack of normal tear production can result in eye dryness, making the eyes more prone to abrasions and infections
- Corneal abrasions – Due to loss of sensation in the eye, minor injuries may go unnoticed and worsen
3. Immunologic Reactions
Leprosy can trigger immune responses that may worsen the disease or cause new symptoms:
Type 1 (Reversal Reaction) –
- Occurs primarily in borderline leprosy patients
- Sudden onset of swelling, redness, and pain in skin lesions
- Inflammation in nerves, leading to worsening pain and nerve damage
Type 2 (Erythema Nodosum Leprosum, ENL) –
- Seen in lepromatous leprosy
- Sudden appearance of painful, red nodules on the skin, along with fever, joint pain, and neuritis
- May involve systemic complications such as kidney involvement or nerve damage
These complications underscore the importance of early diagnosis and treatment, as well as the need for regular follow-ups to prevent severe disability.
Diagnosing Leprosy: Key Methods
The diagnosis of leprosy relies on a combination of clinical presentation and laboratory tests to confirm the presence of Mycobacterium leprae.
1. Skin Biopsy
- Acid-fast bacilli (AFB) staining – Detects the characteristic acid-fast bacilli in skin lesions. This is a primary method for identifying the bacteria responsible for the infection.
- Polymerase Chain Reaction (PCR) – Highly sensitive test that detects M. leprae DNA. PCR is particularly useful in confirming early-stage leprosy or cases where skin lesions are not yet well-formed.
2. Histopathology
- Granulomatous inflammation – Histological examination of skin tissue reveals the presence of granulomas, which are a hallmark of chronic inflammatory conditions like leprosy.
- Presence of AFB in macrophages – Infected macrophages contain acid-fast bacilli, which can be observed under a microscope, confirming the diagnosis of leprosy.
These diagnostic tools are combined with clinical features such as skin lesions, nerve involvement, and sensory loss to establish a definitive diagnosis.
Leprosy Treatment: Multidrug Therapy (MDT)
The cornerstone of leprosy treatment is Multidrug Therapy (MDT), which combines several antibiotics to effectively combat the infection, prevent resistance, and promote recovery. The regimen varies based on the subtype of leprosy:
1. Single-lesion Paucibacillary Leprosy
- Single-dose regimen of:
- Rifampin
- Ofloxacin
- Minocycline (ROM)
This treatment is for limited cases with only one skin lesion, offering a quick and effective cure for uncomplicated cases.
2. Paucibacillary Leprosy
- Daily dose of Dapsone
- Monthly dose of Rifampin for 6 months
This regimen is used for cases with multiple lesions but low bacterial load. Dapsone and Rifampin work together to eradicate the bacteria and control the disease.
3. Multibacillary Leprosy
- Daily dose of Dapsone
- Monthly dose of Rifampin
- Monthly dose of Clofazimine for 12 months
- Low-dose Clofazimine daily for 12 months
For more severe cases with extensive skin lesions and high bacterial load, this comprehensive treatment plan ensures effective elimination of the bacteria while preventing complications and resistance.
Note: MDT is highly effective when followed correctly. Adherence to the full course of treatment is essential to avoid relapse and complications.
Preventing Leprosy: Key Measures to Reduce Risk
While the chances of contracting leprosy are relatively low, certain preventive measures can further reduce the risk of infection:
1. Avoid Prolonged Close Contact
- Limiting extended close contact with untreated, infected individuals is essential to reducing transmission. Since leprosy is transmitted primarily through respiratory droplets, prolonged exposure to these droplets should be avoided.
2. BCG Vaccination
- BCG (Bacillus Calmette-Guérin) vaccine – This vaccine, commonly used against tuberculosis (TB), has been shown to offer partial protection against leprosy, particularly in children. Though not a guaranteed prevention, it can reduce the risk of developing the disease in individuals exposed to M. leprae.
Other Preventive Considerations
- Early diagnosis and treatment: Ensuring that individuals diagnosed with leprosy receive timely treatment with MDT can help prevent transmission to others.
- Improved living conditions: Reducing factors like poor hygiene and crowded living conditions, which are often seen in communities with higher leprosy prevalence, can help lower transmission rates.
Preventive measures focus on reducing exposure and increasing immunity, ensuring the fight against leprosy continues effectively.
Take Away
When should I see my healthcare provider?
If you experience persistent skin sores, numbness, or muscle weakness, consult a healthcare provider promptly. Early diagnosis and treatment can prevent complications.
World Leprosy Eradication Day
Observed on January 30th, World Leprosy Day aims to raise awareness about the disease, its impact on individuals and communities, and the importance of early diagnosis, treatment, and prevention. It also focuses on combating the stigma that leprosy patients often face, promoting a more compassionate and informed perspective.
The theme for World Leprosy Day 2025 is:
“Beat Leprosy, End Stigma, and Advocate for Mental Wellbeing.”
This theme highlights the need to:
- Combat stigma and discrimination that still surrounds leprosy, ensuring that individuals affected by the disease are treated with respect and dignity.
- Advocate for the mental well-being of those affected, as leprosy can lead to social isolation, depression, and other psychological challenges.
- Promote education and awareness to reduce misconceptions about the disease and encourage early diagnosis and treatment.
By coming together on this day, communities, healthcare workers, and organizations can
- Raise awareness
- Dispel myths
- Support efforts toward the elimination of leprosy globally

TAC Desk
Reviewed by Dr Aarti Nehra (MBBS, MMST)