TB & Fungal Respiratory Infections Flashcards
mycobacterium tuberculosis - general overview
*M. tuberculosis complex (M. tuberculosis, M. africanum, M. bovis)
*acid-fast bacilli (aerobic, nonsporulating, rod)
*waxy cell envelope (mycolic acid + lipids):
-acid-fastness & impermeability to gram staining
-resistance to acid, alkali, drying, & germicides
-resistance to killing by antibody & complement
-slow growth
acid-fast bacilli
*acid-fast: retain color when stained, even after they have been washed in an acid solution
*sometimes referred to as a “red snapper”
mycobacterium tuberculosis virulence factor
*CORD FACTOR:
-aka TDM (trehalose-6,6’-dimycolate)
-most abundant cell wall lipid
-correlated with virulence
-causes organism to arrange into “serpentine cords”
TB epidemiology
*about 2 billion people worldwide have TB
*almost 1/3 of the world’s population
*in some countries, almost 80% have TB
*#1 cause of DEATH from INFECTIOUS DISESAE in the world
synergy between TB and HIV
*TB is the #1 cause of death due to infectious disease in people living with HIV (PLWH)
*risk of contracting TB DOUBLES within the first year of acquiring HIV and continues to increases as HIV progresses
*PLWH are at high risk of reactivating latent T and of becoming re-infected with TB after treatment
*TB often progresses at accelerated rate in PLWH
TB pathogenesis
*aerosolized respiratory droplets containing mycobacterium tuberculosis are inhaled (infectious dose = 10 bacilli)
*pulmonary macrophages phagocytose bacilli, but instead of being killed, the TB bacilli proliferate over next several weeks
*enough antigen has been produced to stimulate a cellular immune response (CD4 and CD8 T cells) attempt to contain the infection and/or kill infected cells
*macrophages and T cells wall off infection, forming GRANULOMAS
caseating granulomas and TB
*caseation:
-areas of necrosis, loss of tissue architecture
-caused by TNF, reactive oxygen species, cytotoxic agents (granzymes & perforin)
*granuloma:
-rim of healthy macrophages & T cells that are walling off infected macrophages, dead and dying infected cells, and free organisms
latent TB
*immune system successfully contains infection
*asymptomatic
*NOT contagious
*can advance to active TB
active TB
*TB is active and grows in body
*patients develop symptoms
*can spread from person to person
*progressive disease can result in death
symptoms of active TB
*fever
*night sweats
*weight loss
*cough
*hemoptysis (tissue destruction leads to erosion of a blood vessel)
*extrapulmonary TB: spine, joints, CNS, lymph nodes, pericardium, liver, intestines, other
diagnosis of latent TB
*no symptoms
*screening recommended for possible exposures and/or those with high risk of progression to active TB (HIV infection, etc)
*screening tests:
-tuberculin skin test
-interferon gamma release assay (IGRA)
diagnosis of active TB
*symptoms
*imaging (CXR, CT)
*sputum: AFB smear and culture; PCR
*biopsy:
-pathology
-AFB smear & culture
-PCR
tuberculin skin test (TST)
*TB antigens are injected into the skin
*if a person have memory cells from a prior TB exposure, those immune cells will react to the antigens by producing cytokines and inflammation
*48-72 hours later, the diameter of the induration (NOT the erythema) is measured:
-5mm is positive for: PLWH, organ transplant, other immunosuppressed people
-10mm is positive for: people have recently immigrated from areas with high TB incidence, experiencing homelessness, renal failure, diabetes, health care workers
-15mm is positive for: people with NO known risk factors
interferon gamma release assay
*a screening test used to assess for latent TB infection
*T cells in patient’s blood sample are stimulated with tuberculosis-specific peptides and the activity of the T cells is approximated by measuring interferon gamma
treatment for latent TB
*we treat to prevent progression of latent to active TB
*rifampin daily for 4 months OR INH or combination of both
active TB - isolation precautions
*place patients in special respiratory isolation (negative pressure room with use of N95 masks)
active TB treatment
- induction phase (4 drugs for 2 months): rifampin + INH + pyrazinamide + ethambutol
- continuation phase (2 drugs for 4 months): rifampin + INH
non-tuberculous mycobacteria (NTM) - overview
*>180 different species
*acid-fast bacilli
*saprophytic organisms that become pathogenic
*generally no person-to-person spread
*risk factors include: malignancy, organ transplantation, HIV infection, and structural lung disease
mycobacterium avium intracellulariae complex (MAI or MAC)
*non-tuberculous mycobacteria (NTM)
*2 presentations: 1) nodular bronchiectasis; and 2) fibrocavitary lung
*disseminated disease due to MAC: present with fever, weight loss, lymphadenopathy, diarrhea, particularly in persons with advanced HIV infection
important non-tuberculous mycobacteria (NTM) to be familiar with
*mycobacterium avium intracellulariae complex (MAI or MAC)
*mycobacterium marinum
*mycobacterium scrofulaceum
mycobacterium marinum - clinical presentation
*small, raised erythematous lesions, commonly involving the hand
*progressive spreading of nodular lesions up to elbow or farther
*no fever or other symptoms
*classic risk factor: water (ex. cleaning fish tanks without gloves)
*needle aspiration and AFB cultures reveal mycobacterium marinum
mycobacterium scrofulaceum
*mycobacteria causing cervical lymphadenitis
*requires biopsy and culture for diagnosis
nocardia spp. - overview
*aerobic, gram positive rod
*weakly acid-fast
*long, branching filaments
*found in the environment
nocardia spp - clinical syndromes
*pulmonary syndrome can mimic TB
*skin and soft tissue infection
*CNS infection (brain abscess)
