6Vaccines:A vaccine against tuberculosis has been available since early in the twentieth century.It is produced from bacilli Calmette-Guerin (BCG), an attenuated strain of M.bovis. when injected intradermally,it can confer tuberculin hypersensitivity & an enhanced ability to activate macrophages that kill pathogen
7Mycobacterium lepraeHumans are the natural hosts, + armadilloThe optimal temp. for growth (30ْC) is lower than body temperature; It therefore grows preferentially in the skin & superficial nerves. It grows very slowly with a doubling time of 14 days.This makes it the slowest growing human bacterial pathogen. One consequence of this is that antibiotic therapy must be continued for a long time, usually several years.
8Transmission:Infection is acquired by prolonged contact with patients with lepromatous leprosy, who discharge M.leprae in large numbers in nasal secretions & from skin lesions. The disease occurs world wide, with most cases in the tropical areas of Asia & Africa.
9Pathogenesis:The organism replicates intracellularly, typically within skin histiocytes, endothelial cells, & Schwann cells of nerve.There are two distinct forms of leprosy – tuberculoid & lepromatous-
10In tuberculoid leprosy, the cell-mediated immune response to the organism limits its growth, very few acid-fast bacilli are seen, granulomas containing gaint cells form, & the lepromin skin test result is positive. The lepromin skin test is similar to the tuberculin test. An extract of M.leprae is injected intradermally, & induration is observed 48hrs later in those in whom a cell-mediated immune response against the organism exists
11In lepromatous leprosy, the cell mediated response to the organism is poor, the skin & mucous membrane lesions contain large numbers of organisms, foamy histocytes rather than granulomas are found, & the lepromin skin test result is negative.
12Tuberculoid leprosy1-The lesions occur as large maculae in coolar body tissues ,eg,skin (nose, outer ears), testicles, superfecial nerve endings.Cell mediated IRLow infectivitythe lepromin skin test(+)very few acid-fast bacilli-----progression of disease
132-lepromatous leprosy Extensive dustruction of skin Immunity is severely depressedHigh infectivity
14Likelihood of transmitting leprosy Lepromatous leprosyTubercloid leprosyfeaturemanyfewType of lesionNo.of bacillihighlowLikelihood of transmitting leprosyReduced or absentpresentCell med. response to M.lnegativepositiveLepromin skin test
17Lab identification: M. leprae is an acid fast bacillus Lab identification: M.leprae is an acid fast bacillus. It has not been successfully maintained in artificial culture, but can be grown in the footpads of mice & in the armadillo,Laboratory diagnosis of lepromatous leprosy, where organisms are numerous, involves acid fast stains of specimens from nasal mucosa or other infected area. In tuberculoid leprosy, organisms are extremely rare, & dignosis depends on clinical findings & the histology of biopsy material.
18Treatment:Several drugs are effective in the treatment of leprosy, including sulfones such as dapsone, refampin, & clofazamine.. Treatment is given for at least 2 years or until the lesions are free of organisms.