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Tuberculosis and Leprosy



I recently read that leprosy is caused by Micobacterium Leprae, which belong to the same family of bacteria causing tuberculosis. Both the diseases are transmitted by droplets coughed or sneezed out, but TB can be airborne, can Leprosy be airborne too? Can the leprosy bacteria survive in air after the droplets dry up or do they need to have mucus for survival? What about vector-transmission?

Although that they become non-contagious after given medication but with the long incubation time for symptoms of leprosy to show up, are infected person contagious during incubation period? Is it easy to catch Leprosy compared to TB? Can anyone catch leprosy by just walking past or sitting beside an untreated infected person? How common or rare is Leprosy in North America?

I have been recently diagnosed with having TB and was told that it is a very easy to catch infectious disease but what about leprosy since they are infectious as well. Ever since I came to know about this, I have been paranoid every time whenever someone sneezes or coughs. I have this immense fear that I might catch leprosy as well. Please do answer my questions and clear my doubt as they have been troubling me for the past few months and numerous searching for these answers have been in vain.

Thanking you in advance and waiting anxiously!


Tuberculosis, caused by the 4 bacteria in the mycobacterium tuberculosis complex typically causes infection in the lung. Tuberculosis is spread through the air when a person with tuberculosis coughs. Typically it requires hours of exposure to the patient with tuberculosis before transmission occurs. Most transmission therefore occurs within the household of the person who is sick. While tuberculosis is clearly infectious, we would consider it to be much less infectious than the respiratory viral infections like influenza.

Leprosy, caused by Mycobacterium leprae, is much much less infectious than tuberculosis. Transmission is not clearly understood, but it is believed to occur through respiratory secretions and perhaps skin to skin transfer.

Leprosy is very rare in North America. There are currently about 4200 registered cases and about 100 to 200 new cases are found annually.

There is no relationship between developing tuberculosis and developing leprosy. There is no reason to be fearful of coming in contact with leprosy. Transmission of leprosy in the US is extremely rare. Most cases are imported from other parts of the world.

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Response by:

Catherine A Curley, MD, MS Catherine A Curley, MD, MS
Assistant Professor of Medicine
School of Medicine
Case Western Reserve University