Leprosy (Hansen’s disease)

Notification requirement for leprosy

Leprosy is a ‘routine’ notifiable condition and must be notified by medical practitioners and pathology services in writing within 5 days of diagnosis.

This is a Victorian statutory requirement.

Primary school and children’s services centre exclusion for leprosy

Exclude until approval to return has been given by the Secretary. Contacts are not excluded.

Infectious agent of leprosy

Mycobacterium leprae, an acid-fast bacillus, is the causative agent.

Identification of leprosy

Clinical features

Leprosy is a slowly progressive bacterial infection involving the cooler body tissues: skin, superficial nerves, nose, pharynx, larynx, eyes and testes. Skin lesions may occur as pale, anaesthetic macules, papules or erythematous infiltrated nodules.

Neurological disturbances are manifested by nerve infiltration and thickening, with anaesthesia, neuritis, paraesthesia and trophic ulcers.

The disease is divided clinically and by laboratory tests into two overlapping types: lepromatous and tuberculoid. The lepromatous type (multibacillary or nonimmune form) is progressive, with nodular skin lesions, slow symmetric nerve involvement, numerous acid-fast bacilli in skin lesions and a negative lepromin skin test. The tuberculoid type (paucibacillary or immune form) is benign and nonprogressive, with localised skin lesions, asymmetric nerve involvement, few bacilli present in the lesions and a positive lepromin skin test.

Diagnosis

Clinical suspicion is the crucial factor in making an early diagnosis of leprosy in non-endemic parts of Australia, including Victoria. Leprosy should always be considered in any undiagnosed patient with chronic skin lesions, a peripheral neuropathy or anaesthetic skin patches. This is particularly important if they have spent more than brief periods in areas where the disease is endemic, or have been a contact of a patient known to have leprosy. Polymerase chain reaction (PCR) detection in specimens from the ear lobe or other relevant skin sites is increasingly being used for confirmation.

Confirmation of diagnosis also depends on the clinical form:

• Lepromatous disease requires demonstration of plentiful acid-fast bacilli in skin or nasal smears. Skin smears are made by scraping a small amount of tissue fluid from a superficial scalpel cut over a lesion and smearing it on a glass slide.
• Tuberculoid disease requires demonstration of typical granulomata with sparse acid-fast bacilli, in biopsies of either skin or nerve lesions.

Incubation period of Mycobacterium leprae

The incubation period is difficult to determine. It probably ranges from 9 months to 20 years, with an average of 4 years for tuberculoid leprosy and 8 years for lepromatous leprosy.

Public health significance and occurrence of leprosy

Leprosy is occasionally detected on routine refugee screening. The world prevalence is estimated to be 10–12 million cases, with 250,000 new diagnoses each year. The disease is endemic in tropical and subtropical Asia, Africa, Central and South America, Pacific regions and the United States (Hawaii, Texas, California, Louisiana and Puerto Rico).

Reservoir of Mycobacterium leprae

Humans are the reservoir.

Mode of transmission of Mycobacterium leprae

The mode of transmission is not clearly established. The organism is probably transmitted from person to person by aerosol, with a high subclinical rate of infection. Household and prolonged close contact seems important. There is anecdotal evidence that it may rarely be transmitted by inoculation, such as by contaminated tattoo needles.

Period of communicability of leprosy

Leprosy is not infectious soon after starting multidrug therapy.

Susceptibility and resistance to leprosy

Everyone is susceptible to infection; however, study results have suggested a strong age-related susceptibility to being infected or developing disease following close contact with a multibacillary case. Children aged between 5 and 9 years are at greatest risk. The risk of progression to leprosy disease following infection is considered to be approximately the same as for tuberculosis: approximately a 10 per cent lifetime risk.

Control measures for leprosy

Preventive measures

BCG vaccination has some protective efficacy and is recommended for neonates born to a person diagnosed with leprosy, Aboriginal neonates in some regions of Australia, and non-Aboriginal neonates who live in Aboriginal communities.

Control of case

Isolation of tuberculoid (paucibacillary) cases is unnecessary. Isolation of lepromatous (multibacillary) cases is indicated until treatment is initiated, particularly if nasal smears are positive. Nasal discharges of infectious patients should be disinfected or disposed of as infectious waste.

Rifampicin is the key to early control of disease, and rapid elimination of the risk of further transmission of infection to contacts. Minocycline can be used as an alternative.

For lepromatous leprosy, the minimal regimen recommended by the World Health Organization (WHO) is triple therapy with rifampicin, dapsone and clofazimine for 12 months.

For tuberculoid leprosy, the recommended regimen is rifampicin and dapsone for 6 months (for detailed treatment regimens and duration, see current WHO recommendations).

Control of contacts

Investigation of contacts and source of infection, and early detection and treatment of new cases is required. Prophylactic BCG has resulted in a considerable reduction in the incidence of tuberculoid leprosy among contacts in some trials. Other studies are currently in progress using a single dose of rifampicin as prophylaxis following leprosy exposure. Currently, treatment of contacts in Australia is not recommended.

Control of environment

Not applicable.

Outbreak measures for leprosy

Not applicable.