Leprosy

Question 1

Mycobacterium leprae

Answer 1

Mycobacterium leprae infects:

Skin and mucus membranes ⇒ skin lesions

Peripheral nerves ⇒ anesthesia and neuritis

Question 2

Leprosy

Epidemiology

Answer 2

“Hansen’s disease”

• Most prevalent in tropical areas
  
  • Especially Africa, South and Southeast Asia, parts of Central and South America
• ~ 10 million cases worldwide
• Endemic in small areas of some southern states of USA

Question 3

Mycobacterium leprae

Morphology and General Characteristics

Answer 3

• Acid fast bacilli
• Usually straight or slightly curved
• Intracellular pathogen (obligate?)
• Often packed in cells and some may appear beaded
• Infectivity very low

Question 4

Mycobacterium leprae

Transmission

Answer 4

• Incompletely understood
• Ass. w/ prolonged (years) close contact w/ respiratory secretions of multibacillary pt (lepromatous)
• Children are more susceptible
• Genetics plays a role
• Incubation long but varied (3 to 20yrs)

Question 5

Mycobacterium leprae

Pathogenesis

Answer 5

Two clinical forms of leprosy ⇒ tuberculoid and lepromatous

Several intermediate stages

Question 6

Leprosy

Tuberculoid Form

Answer 6

Benign, non-progressive

Characterized by:

• Hypopigmented macular skin lesions containing few AFB
• Severe peripheral nerve damage and sensory loss
• ⊕ Lepromin (DTH) test
• Cell-mediated immunity is intact
  
  • Skin infiltrated w/ T-cells (Th1 cells) ⇒ ⊕ Mφ ⇒ ⊗ growth of the organisms
  • Rxn also cause severe skin and nerve damage

Question 7

Leprosy

Lepromatous Form

Answer 7

Malignant, progressive

Characterized by:

• Nodular skin lesions containing abundant AFB
• ⊖ Lepromin test
• Cell-mediated immunity is deficient, downregulated or the wrong type is activated (Th2)
• Results in extensive damage to skin and surrounding tissues

Question 8

Leprosy

Laboratory Diagnosis

Answer 8

• M. leprae cannot be cultured on artificial media
• Dx based on presence of acid-fast bacilli in smears of skin lesions, nasal scrapings, ear lobes and tissue secretions
• Can be cultivated in the armadillo and footpads of mice
• Organisms predominantly in modified mononuclear or epithelioid cells called lepra cells

Question 9

Leprosy

Treatment

Answer 9

• Tuberculoid pts
  
  • Dapsone combined w/ rifampin for 6 mo
• Lepromatous pts
  
  • Clofazimine & the other 2 drugs for at least 2 years and sometimes for life