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the etiology of non-tuberculous mycobacteriosis and what are the causes of non-tuberculous mycobacteriosis

the etiology of non-tuberculous mycobacteriosis and what are the causes of non-tuberculous mycobacteriosis

Etiology of non-tuberculous mycobacteriosis

(a) the cause of the disease

Non-tuberculous mycobacteria are widely found in soil, dust, water, fish and poultry in nature. The transmission route is mainly from the environment, such as sewage, but human-to-human transmission is rare. Usually, the pathogenicity of these mycobacteria to human beings is lower than that of Mycobacterium tuberculosis, but if there are susceptible factors, which make the local or systemic immune function of the host dysfunction, it can lead to pathological changes.

The more common pathogens include M.avum complex, M.kansasii, M.xenopi, M.scrofulaceum, M.szulgai, M.simine, M.fortuifum compuex, M.malmoense, M.asiaticum, M.shimodii, M.celatum, M.marinum, and occasionally M.terus rac complex, M. gordonae and M. gastri.

(B) Pathogenesis

1. Route of infection

(1) Environmental infection: It is the main recognized route of infection. NTM exists widely in water, soil and dust, Aerosol particles generated by water, Soil and dust particles may form bacteria-carrying particles, which are inhaled by healthy people. The gateway to human body is upper respiratory tract, which is confirmed by the isolation and discovery of NTM in pharyngeal lymphoid tissue, and the existence of intracellular, Gordon, toad and Kansas mycobacteria has also been isolated in pools, oceans and tap water, so NTM was once named environmental mycobacteria (EM).

(2) Animals infect people: Mycobacterium kansas, avian intracellular, Gordon and lymph node were isolated from pasteurized milk, and Mycobacterium avium was isolated from eggs laid by hens infected with Mycobacterium avium. Mycobacterium avium can be cultivated from animal meat or body such as cattle, pigs, chickens, horses, rats and apes, and poultry breeders suffer from mycobacterium avium more. But some people hold different opinions.

(3) Human-to-human infection: In patients who have reported infection with Mycobacterium kansasiae, the positive rate of their contacts to Kansasiantin (PPD-Y) is increased. It has also been pointed out that there are cases of mutual infection among the same family members. Some believe that there is no more definite evidence of human-to-human infection.

In addition, drinking water contaminated with NTM can also invade tonsils, pharyngeal lymph nodes and cervical lymph nodes, causing non-tuberculous mycobacterium tonsillitis, pharyngeal lymphadenitis and cervical lymphadenitis. Mycobacterium marine invades small wounds of skin, and can also cause non-tuberculous mycobacteriosis of skin.

2. There are two types of pathogenic NTM: pathogenic and non-pathogenic, of which 2/3 are non-pathogenic and only 1/3 are pathogenic. The pathogenicity of pathogenic NTM has the following characteristics:

(1) The pathogenicity to human is lower than that of Mycobacterium tuberculosis.

(2) Non-tuberculous mycobacteriosis caused by human beings is a small part of independent primary disease, and most of it is secondary. It is a secondary or accompanying disease of other diseases.

(3) The strong chance of pathogenesis is a remarkable feature, so NTM is also called conditional or opportunistic mycobacterium. There are many opportunities or conditions for NTM to cause diseases in human body, such as old age, chronic bronchitis, chronic obstructive pulmonary disease, bronchiectasis, malignant tumor, hemodialysis, organ transplantation, use of corticosteroids, immunosuppressants and other opportunities to reduce immune function, all of which can be secondary to non-tuberculous mycobacterium lung diseases.

(4) AIDS patients with Pneumocystis carinii pneumonia accounted for the first place, The second is cytomegalovirus pneumonia, and the third is non-tuberculous mycobacterium lung disease. Besides these opportunistic pneumonia, AIDS patients are significantly more infected with tuberculosis or complicated with tuberculosis than healthy people. For example, 50% of AIDS patients in Europe and America are infected with NTM, of which 10% ~ 15% are disseminated by bird intracellular complex, and 90% of new tuberculosis patients in Africa are HIV antibody positive.

(5) NTM is mostly resistant to common anti-tuberculosis drugs, which prolongs the course of disease for many years and becomes a chronic bacterial excretion or refractory case.

In a word, NTM causes more than 90% of non-tuberculous mycobacterial lung diseases, and causes less extrapulmonary diseases, such as cervical lymphadenitis, osteomyelitis, skin ulcer and abscess, meningitis, endocarditis, corneal ulcer, dacryocystitis, intestine, myocardium, oral mucosa and facial nerve diseases. Among 1224 cases of non-tuberculous mycobacteriosis reported in Japan, 1188 cases of non-tuberculous mycobacteriosis accounted for 97%. In addition, Mycobacterium avium complex (MAC) can cause hematogenous dissemination (DMAC) when human immune function is deficient. For example, CDC reported that 5.5% of AIDS patients were complicated with disseminated non-tuberculous mycobacterium infection (DNTM), of which DMAC infection accounted for 96.1%, and the incidence of DMAC in autopsy of AIDS patients was as high as 50%. Patients with hypoimmune function should pay attention to the occurrence of opportunistic septicemia.

The pathological changes of non-tuberculous mycobacteriosis are similar to those of tuberculosis, but the pathological changes of non-tuberculous mycobacteriosis are mild, epithelial nodules are more common, cheese necrosis is less, collagen fibers proliferate and show hyaline changes, which are the main characteristics different from tuberculosis. Acid-fast bacilli can be found in pathological changes, pathological tissues can be cultured and identified, or pathological changes can be diagnosed by TBPCR.


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