doctor discussing leprosy risk factors

Leprosy Risk Factors

Leprosy is a bacterial infection also called Hansen’s disease, in reference to the doctor who first saw the microbe that causes it. Called Mycobacterium leprae, it results in damage to the nerves and soft tissues, particularly skin and mucous membranes. Although it is treatable, if antibiotics are not taken early in the onset of the disease, irreversible and debilitating damage can result. Leprosy is a frightening prospect, and although the World Health Organization (WHO) launched a campaign several decades ago to eradicate it, it does still exist. Here’s a look at the prospective risk factors of Hansen’s disease. 


Despite the images Hansen’s disease conjures of leper colonies filled with people suffering from skin lesions and muscle damage, there is good news regarding leprosy. Approximately 95% of the world’s population has a natural immunity to it. This does, however, leave millions of people at risk for developing it -- and millions of people were developing it every year, until WHO discovered and drew up a multi-drug therapy treatment protocol. 

Once antibiotics are given, infected persons stop being contagious within a couple of weeks. However, if you don’t realize you have leprosy, you aren’t likely to seek treatment. Hansen’s disease has an incubation period of many years, even decades, before the first signs appear. This means 10 years could pass with an infected person coming into close contact with people on a daily basis, unwittingly passing the bacteria. 

Experts believe transmission occurs through the moisture that spreads during a cough or sneeze by someone infected by Mycobacterium leprae, although further research is needed on the subject. Thus, one of the biggest risk factors is for someone who is not innately immune to spend a lot of time with someone who has not been diagnosed or treated for the disease. 


The latest figures show less than 200,000 new cases globally. Leprosy in the United States accounts for only 200 of these infections, and of those, 72% occurred in only seven states. Leprosy is most common in tropical, subtropical, and temperate regions. The Health Resources and Services Administration reports that these states included Arkansas, California, Florida, Hawaii, Louisiana, New York and Texas. Likewise, the National Institute of Health’s U.S. National Library of Medicine (NIH) states that most of the United States’ cases occur in California, Hawaii, the Southern region, Guam, and a few islands. 

For those 5% without a natural immunity, living in a location where leprosy is still relatively widespread can be a potentially serious risk. The Center for Disease Control (CDC) names “Angola
Brazil, Central African Republic, Democratic Republic of Congo, Federated States of Micronesia, India, Kiribati, Madagascar, Mozambique, Nepal, Republic of Marshall Islands, [and] United Republic of Tanzania“ as areas where leprosy is still “widespread.” Living in these regions -- or even traveling to them -- can be risky in regards to leprosy. 

Further Risks

Beyond location and interaction, there seems to be little that impacts the likelihood of someone without immunity contracting leprosy. The HRSA’s 2015 statistics regarding leprosy show that 66% of patients were male, but this may simply be a result of increased travel or ability to move to the United States from key countries rather than an increased likelihood of males to contract leprosy. 

Age ranges ran from childhood to late adulthood. It is important to note that anyone with a less effective immune system, from the elderly, to small children, to those with autoimmune diseases (such as HIV/AIDS) are more likely to develop any infection, including leprosy, although, again, this is without the natural immunity. If you are concerned about developing leprosy and meet these risk factors, talk to your doctor as soon as possible to minimize transmission and maximize treatment efficiency. 

Last Updated: December 09, 2016