Leprosy

Also known as Hansen disease.

Obligate intracellular parasite.

Humans are the primary carriers of infection.

In the US, the 9-banded armadillo is a zoonotic reservoir.

Estimated that 6 million people worldwide have the disease.

Marked reduction in prevalence of the disease in recent decades.

The global prevalence is 1.4 per 10,000 population but 4.5 per 10,000 in 11 countries in which the disease is endemic.

Approximately 200,000 individuals worldwide and 200 to 300 people in the US are diagnosed with leprosy annually.

The most common route of transmission is through respiratory secretions, but skin contamination with tattooing and vertical transmission have been reported.

90% of cases are from endemic countries in Africa, Asia Latin America or the Pacific Islands.

200,000 new cases were detected worldwide between the years 2016 and 2019.

Approximately 7000 cases in the U.S., most of which are in immigrants.

Risk factors include poverty, genetic factors, rural living and exposure to armadillos in the U.S, immunosuppression and immuno deficiency.

The 9-banded armadillo is a zoonotic reservoir for M. leprae in the US.

Infects only humans.

M. leprae can not be cultured in vitro.

Clinical disease manifests in only a minority of infected patients.

Differential diagnosis includes: interstitial, granulomatous, dermatitis, granuloma annulare, granulomatous, dermatitis of immune deficiency, granulomatous drug irruption, psoriasis, and other mycbacterial or fungal infections.

Monkeys, armadillos and humans are the only known hosts for the organism Mycobacterium leprae.

The mechanism of transmission in unclear.

Because the organisms prefer cool temperatures the distal areas of the body are most commonly affected.

Leprosy is classified as multibacillary if there is six and more skin lesions, or is puucibacillary, if there are fewer than six lesions.

In the Ridley-Jopling classification there are five categories of leprosy: tuberculoid, borderline tuberculoid, borderline, borderline lepromatous, and lepromatous.

Incubation period averages 5-7 years but it ranges from 2-40 years.

Index cases are believed to be the main source of infection and prolonged contact with the patient is a known risk factor for its transmission.

Household contacts are at high risk for contracting the disease.

Household contacts also share a similar genetic background, which could contribute to a high susceptibility to leprosy than that in the general population.

The risk for leprosy among household contacts is 1300 times as high is that in the general population.

The most commonly involved areas include the skin, upper respiratory tract, testicles and peripheral nervous system.

Clinical manifestations include: thickened skin with symmetrical plaques or nodules, earlobe involvement, loss of hair including lateral eyelashes and eyebrows, upper respiratory symptoms of congestion, or epistaxis, nasal mucosal and cartilage damage leading to nasal collapse (saddle nose deformity), peripheral sensory neuropathy, destruction of distal digits.

Clinical manifestations and its spectrum related to interaction between the immune system and the bacterium.

Involvement of the facial skin can result in the classic “leonine” facies.

Sensory and motor nerve damage occur in the vicinity of skin lesions.