Causative agent
Hansen's disease (Leprosy) is a chronic infectious disease caused by Mycobacterium leprae (a slow growing bacteria).
Globally, according to the WHO, Hansen’s disease occurs in more than 120 countries, with more than 200 000 new cases reported every year. Although there has been a gradual reduction in the number of cases globally, Brazil, India and Indonesia still reported more than 10 000 new cases each year from 2018 to 2022, while some countries like the Philippines, Nepal, Myanmar, etc reported 1 000 to 10 000 new cases each year during the same period. Hong Kong has officially declared the successful elimination of Hansen’s disease when the prevalence rate fell well below 1 per 10,000 population in mid 1980's.
Hansen’s Disease (Leprosy) is a notifiable disease in Hong Kong. The number of cases reported has declined significantly from around 100 in the early 1970s (1970-1974) to between 20 and 30 in the early 1990s (1990-1994) to under 10 (varying from one to nine cases per annum) during 2014 to 2023. This is due to improvements in health of the general population and better health and sanitation facilities.
Mode of transmission
Hansen’s disease can be transmitted by nasal droplets or by close skin contact. However, the disease does not spread easily between people and not spread through casual contact with a person who has leprosy like shaking hands or hugging, sharing meals or sitting next to each other. Prolonged, close contact (e.g. household) over months with someone with untreated leprosy is needed to catch the disease.
The disease is not spread through sex, and it is not passed to the fetus during pregnancy.
The patient stops transmitting the disease when they begin treatment.
Incubation period
Symptoms may occur within 1-5 year but occasionally can take as long as 10-20 years to occur.
Clinical features
The disease affects the skin, the peripheral nerves, mucosa of the upper respiratory tract, and occasionally the eyes and joints. Without treatment, loss of sensation leading to disabling deformities can occur in old days.
Management
Hansen’s disease is curable and early treatment can prevent disability. Drugs for effective treatment of leprosy is available in Hong Kong. Early diagnosis especially to people with prolonged stay in leprosy prevalent countries is crucial.
Prevention
Apart from early treatment, there is strong evidence that BCG vaccination for tuberculosis is also effective to prevent Hansen’s disease and that it has contributed to the decline in the incidence of the disease globally according to the World Health Organization.
In Hong Kong, BCG vaccine, first introduced in 1952, is given at birth and very high coverage rates above 98% have been maintained over the past years. With high coverage of BCG vaccine in the local population and being a disease that does not spread easily between people, the risk of Hansen’s disease in Hong Kong is perceived to be extremely low.