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EPI WATCH: Hansen’s Disease

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By Dana Elhassani, Epidemiology Program Intern

Hansen’s disease, also known as Leprosy, is a caused by an infection of Mycobacterium
leprae. This bacteria is a slow-growing, acid-fast, rod-shaped bacillus that can be transmitted
person to person via droplet transmission1. Once exposed, the incubation period can range
from 5-20 years2. A majority of people (95%) are naturally immune to developing an infection;
however, M. leprae can affect the peripheral nerves, skin, eyes, and nasal mucosa of infected
individuals. Characteristic dermal symptoms include symmetrically-distributed skin lesions,
nodules, plaques, and thickening of the dermis. Left untreated, Hansen’s disease can lead to
crippling nerve damage in the hands and feet, paralysis, and blindness1.

There are two predominant classification systems currently used to determine the severity of
illness, the Ridley-Jopling classification system and a method developed by the World Health
Organization (WHO)3,4. Both methods involve quantifying and assessing morphology of lesions.
The Ridley-Jopling system has six histological classification types for Leprosy: indeterminate
(I), tuberculoid (TT), borderline tuberculoid (BT), mid-borderline (BB), borderline lepromatous
(BL), lepromatous (LL). The WHO systems collapsed these categories into two categories,
either paucibacillary (I, TT, BT) or multibacillary (BB, BL, LL), for a field-friendlier
method that would reduce the dependence on a stable medical infrastructure4.

Treatment of Leprosy is accomplished through long-term multi-drug therapy (MDT). Antibiotics
used include dapsone with rifampicin, and for multibacillary infections, clofazimine. Typical
treatment time can last from 1-2 years; however due to the long adherence and difficulties
with patient compliance, treatment may last much longer2,6.

Historically, leprosy was identified in China, Egypt, and India as far back as 600 BC. The debilitating
symptoms of this disease often led to individuals being ostracized by their community
1. The advent of MDT has decreased the world wide prevalence from 5.4 million cases to a
few hundred thousand. The global incidence was 211,973 and prevalence 176,176 by the
end of 2015. Approximately 60% of new cases globally were identified in India, followed by
Brazil (13%), and Indonesia (8%). At this time, only thirty countries worldwide were able to
report zero new cases5.

In the United States, in the last 10 years, less than 300 cases have been reported. The states
with the highest transmission rates in the last ten years include California, Florida, Hawaii,
Louisiana and Texas. While there were only 101 cases in Florida between 2001 and 2010,
there were 27 cases reported in 2015 which is triple the state’s average annual incidence.
The counties with the highest incidence include Brevard, Volusia, Polk, Hillsborough, and

Leprosy is predominately contracted from another human. However, the nine-banded armadillos
have been found to carry strains of the bacteria that can affect humans. While the relationship
is not fully understood, persons should wear protective gloves while handling the
wildlife and wash hands before and after exposure1.

1. Moore SP, Wisely SM. Facts about Wildlife Diseases : Leprosy. Wildl Dis Risks to People Anim. 2015:1-4.
2. WHO. Leprosy. 2016. http://who.int/mediacentre/factsheets/fs101/en/.
3. U.S. Department of Health and Human. A summary of hansen ’ s disease in the United States-2014. 2015;(May):1-31.
4. Pardillo FEF, Tranquilino T. Fajardo RMA, Scollard D, Gelber and RH. Methods for the classification of leprosy for treatment purposes.
CID. 2007;44(15):1096-1099. doi:10.1086/512809.
5. Oh DH, Dabbagh A, Goodson JL, et al. Global leprosy update, 2015: time for action, accountability and inclusion. Wkly Epidemiol Rec.\
6.CDC. Hansen’s disease (leprosy). 2017. https://www.cdc.gov/leprosy/treatment/index.html.

Disclaimer: The information on this web site is general information, and not designed to be and should not be relied on as your sole source of information when analyzing.
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