zoonoses and communicable diseases common to ... - PAHO/WHO

DISEASES CAUSED BY NONTUBERCULOUS MYCOBACTERIA 107DISEASES CAUSED BY NONTUBERCULOUSMYCOBACTERIAICD-10 A31.0 pulmonary mycobacterial infection;A31.1 cutaneous mycobacterial infection;A31.8 other mycobacterial infectionsSynonyms: Mycobacteriosis, nontuberculous mycobacteriosis, nontuberculousmycobacterial infection.Etiology: The etiologic agents of nontuberculous mycobacteriosis (NTM) form agroup separate from those that cause tuberculosis in mammals, Mycobacteriumtuberculosis, M. bovis, M. africanum, and M. microti (the agent of tuberculosis inrodents). Previously called anonymous, atypical, or unclassified mycobacteria, theyhave since been characterized and given specific names.Mycobacteria potentially pathogenic for man and animals currently include some15 species. The most important group among these species is Mycobacterium aviumcomplex (MAC), replacing what was formerly called MAI (M. avium-intracellulare)or MAIS (M. avium-intracellulare-scrofulaceum). These mycobacteriaare important pathogens for birds (avian tuberculosis) and some mammals (swinetuberculosis). MAC has become important as a human pathogen due to theAIDS epidemic.There are both genetic and antigenic indications that M. paratuberculosis, theagent of chronic hypertrophic enteritis in cattle and sheep, should be included in thesame complex as M. avium (Grange et al., 1990). There are also data suggesting thatthe mycobacterial strains isolated from patients with Crohn’s disease are geneticallyrelated to M. paratuberculosis (Sanderson et al., 1992).M. paratuberculosis is characterized by its requirement of mycobactin (a lipid thatbinds iron) for growth in culture media. There are also strains similar to MAC thatare mycobactin-dependent to a greater or lesser degree, among them the strains isolatedfrom the wild pigeon (Palumba palumbus), which through experimental inoculationin cattle produces a disease similar to paratuberculosis.DNA:DNA hybridization studies demonstrated that M. avium, M. paratuberculosis,and the mycobacteria of the European wild pigeon (Palumba palumbus) belongto a single genomic species. Based on numerical taxonomy studies of mycobactindependentmycobacteria, DNA sequences, and genotype and other studies, Thorel etal. (1990) suggest dividing the species into M. avium subsp. avium, M. avium subsp.paratuberculosis, and M. avium subsp. silvaticum. The latter would correspond tothe mycobacteria isolated from the wild pigeon.MAC is composed of 28 serotypes (1–28); the first three belong to M. avium, andthe rest to M. intracellulare. Serotyping has been valuable in research but is notapplicable in routine laboratories and has been discontinued. Runyon’s classification,developed in 1959, is still in use. It subdivides the mycobacteria into four largegroups: photochromogens (Group 1), scotochromogens (Group 2), nonchromogens(Group 3), and rapid growers (Group 4). The different species of mycobacteria aredistinguished by their phenotypic characteristics, such as optimum growth temperature,rapid or slow growth, utilization of niacin, nitrate reduction, and other biochemicalproperties (Wayne and Kubica, 1986).