Leprosy

Overview

Leprosy, also known as Hansen’s disease, is a chronic infectious disease caused by Mycobacterium leprae. The disease mainly affects the skin and the peripheral nerves.

Disease epidemiology

Worldwide incidence of leprosy appears to be declining. This is due to improvements in socioeconomic conditions and access to effective treatment. Humans and armadillos are the only known reservoirs. Susceptibility is genetically determined with more than 90% of the population naturally immune. Leprosy incidence rates in Singapore have declined significantly.

Pathogen(s)

Mycobacterium leprae.

Transmission

The exact mode of transmission is not clearly established; household and prolonged close contact appears to be important for transmission to take place. Transmission is believed to be from respiratory secretions, and less effectively, direct skin-to-skin contact.

Incubation period: Typically 3 to 10 years; ranging from a few weeks to 30 years.

Infectious period: Patients can be considered non-infectious shortly after starting therapy.

Clinical features

The disease mainly affects the skin and the peripheral nerves. Most patients present with asymptomatic skin lesions while some (<5%) present with nerve deficits without skin signs. The affected skin may be pale or red, and it may be a plaque, nodule, or tumour. Loss of pin-prick sensation within skin lesions is pathognomonic of leprosy. Peripheral nerve involvement may cause muscle weakness and paralysis of limbs. Examination may reveal enlarged nerves with or without functional deficit.

For treatment purposes, leprosy is classified into 2 groups according to clinical manifestations and skin smear results. More commonly however, patients exhibit features of both types (i.e. borderline leprosy).

1. Paucibacillary (tuberculoid) leprosy: Characterised by 1 to 5 hypopigmented or hyperpigmented anaesthetic macules or patches in an asymmetric distribution

2. Multibacillary (lepromatous) leprosy: Multiple symmetrically distributed skin lesions (papules, nodules or plaques) that may not exhibit sensory loss

Risk factors

Risk factors include:

• Persons living in endemic areas in close contact with multibacillary cases.

Diagnosis

Demonstration of acid-fast bacilli in a slit skin smear or dermal nerve, or identification of non-caseating granulomas with peripheral nerve involvement characteristic of leprosy on histology.

Treatment and management

Multidrug therapy is recommended for the treatment of leprosy. The type and duration of treatment depends on the number of skin lesions (which is an indication of bacillary load).

Leprosy is a treatable cause of permanent physical disability. Early treatment can prevent or even reverse nerve damage. Management of leprosy patients include measures that avoid injury to anaesthetic limbs and rehabilitation of disabled limbs.

Precaution, prevention, and control

Isolation measures

Standard precautions apply in healthcare settings.

Contact management

Examination and follow up of close contacts are recommended. No quarantine of contacts is required.

Vaccination

There is currently no available vaccine for leprosy (although the BCG vaccine is partially protective).

Notification

Leprosy is a legally notifiable disease in Singapore.

Who should notify:

• Laboratories

When to notify:

• On upon laboratory confirmation

How to notify:

• Please refer to the Infectious Disease Notification for more information.

Notification timeline:

• As soon as possible. No later than 72 hours.

Resources

For more information on leprosy, please refer to the World Health Organization website.

For general travel advisory, please refer to Health Advice for Travellers.