Infectious diseasesepidemiology and surveillance

Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures | Additional sources of information

Victorian statutory requirement

Leprosy (Group B disease) must be notified in writing within five days of diagnosis.

School exclusion: exclude until approval to return has been given by the Secretary. Contacts are not excluded.

Infectious agent

Mycobacterium leprae is the causative agent.

Identification

Clinical features
Leprosy is a slowly progressive bacterial infection involving the cooler body tissues, skin, superficial nerves, nose, pharynx, larynx, eyes and testicles. 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 non-immune 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 non-progressive with localised skin lesions, asymmetric nerve involvement, few bacilli present in the lesions and a positive lepromin skin test.

Method of diagnosis
Clinical suspicion is the crucial factor in making an early diagnosis of leprosy in non-endemic parts of Australia, like Victoria. Leprosy should always be considered in any undiagnosed patient with chronic skin lesions or a peripheral neuropathy. This is particularly important if they have spent more than brief periods in areas where the disease is endemic, or they have been a contact of a patient known to have leprosy.

Confirmation of diagnosis depends on the 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

The incubation period is difficult to determine. It probably ranges from nine months to 20 years with an average of four years for tuberculoid leprosy and eight years for lepromatous leprosy.

Public health significance & occurrence

Leprosy is occasionally detected on routine refugee screening. The world prevalence is estimated to be between ten to 12 million cases. The disease is endemic in tropical and subtropical Asia, Africa, Central and South America, Pacific regions and the USA (Hawaii, Texas, California, Louisiana, Puerto Rico).

Reservoir

Humans.

Mode of transmission

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

Period of communicability

Leprosy is not usually infectious after three months of continuous treatment with dapsone or clofazimine, or after two to three weeks of treatment with rifampicin.

Susceptibility & resistance

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 multi-bacillary case. Children aged between five and nine years are at greatest risk. The risk of progression to leprosy disease following infection is considered to be approximately the same as tuberculosis which is approximately a 10% lifetime risk.

Control measures

Preventive measures
BCG vaccination has some protective efficacy and is recommended for neonates born to a person diagnosed with leprosy.

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.

The minimal regimen recommended by WHO for lepromatous leprosy is triple therapy with rifampicin, dapsone and clofazimine for twelve months.

For tuberculoid leprosy, the recommended regimen is rifampicin and dapsone for a period of six 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

Not applicable.

Additional sources of information

• Fine, PE, Sterne, JA, Ponnighaus, JM et al. 1997, 'Household and dwelling contact as risk factors for leprosy in northern Malawi', Am J Epidemiol, vol. 146, no. 1, pp. 91?102.
• World Health Organization