Diseases Due to Mycobacteria
By tradition, the term tuberculosis refers to infection and disease associated with M. tuberculosis (var. hominis and var. bovis). It has long been known that other Mycobacteria species exist in nature, some of which cause disease in animals_ For years, by arbitrary and, in retrospect, amusing definition, a mycobacterium was considered an alumni pathogen only if it produced disease in the guinea pig.
This notion prevailed until modem culture methods demonstrated some of these guinea pig nonpathogens present in diseased human tissue. Several species of mycobacteria, some not previously known, have recently been identified as potential human pathogens. A few of these have received the formal taxonomic designation, P8legger firelffain. ge.de mosiiinportant, have not Much of the most important bacteriologic work on 1124 se “45rfir; v2, ” ‘arratryttious,' or itrickissififed5′ mycobacteria has been carried out by Runyon, who classified them into four groups primarily on the basis of the presence and type of pigment product Cian and growth rate.
This tentative arrangement has been useful and widely accepted. (See Bacteriology in the article on Tuberculosis). More recently most of the known human pathogens have received tentative but widely accepted species designations, which will be employed herein. The relationship of these to the Runyon classification is as follows: M. kansasii and M. marinurn Runyon Group I (photochromogens); M. scrofula-acetum Runyon Group II (scotochromogens); M.intracellulare* (Battey bacillus), M. avium, and. xenopei. Runyon Group III (non-pigmented species); and M.fortuitum Runyon Group IV (rapid growers).
The diseases produced by these organisms have roentgenology, pathologic, and to a large extent clinical similarities to tuberculosis, but there are distinct differences in virulence, treatment, and prognosis. The term mycobacteriosis has been suggested for diseases produced by this group of infections to differentiate them from tuberculosis. However, species orientation is preferable, because there are differences in organ susceptibility, treatment, and prognosis within the group. It is convenient from a clinical standpoint to group these infections according to organ involvement.
Pulmonary disease is the most common clinical manifestation. Lymphadenitis and granulomatous skin lesions are less frequent. The widespread tissue involvement that may be produced by the more virulent M.'tuberculosis is not seen in mycobacteriosis save for rare instances of disseminated opportunistic infection in abnormal hosts, unusual skeletal involvement, and, occasionally, abscesses at injection sites.