Tuberculosis (TB)-Notes.pdf microbiology notes

Microbiology

1. Tuberculosis (TB)

2. •Tuberculosis (TB) is a dangerous and highly contagious bacterial disease
caused by Mycobacterium tuberculosis. It primarily affects the lungs, but
if left untreated, it might spread to different parts of the body.
•There are two different types of tuberculosis:
Pulmonary Tuberculosis-infection affecting the lungs.
Extra pulmonary Tuberculosis-It is usually seen in immunocompromised
patients. There are several types:
•Tuberculosis Meningitis
•OstealTuberculosis
•Lymph Node Disease
•Renal Tuberculosis
•Adrenal Tuberculosis

3. Causes of TB
•Tuberculosisisacontagiousairbornedisease,whichcanbeacquired
fromclosecontactwithaninfectedperson.
•Mycobacteriumtuberculosisisoneoftheleadingcausesofthis
dreadfulinfectiousdisease.Itisapathogenicbacterialspeciesand
mainlycomprisesfourothertypesofTB-causingbacteria,namely:
–Mycobacteriumbovis,
–Mycobacteriumcanettii,
–Mycobacteriummicroti,
–Mycobacteriumafricanum.

4. Pathogenesis
•TBinfectionbeginswhenthemycobacteriareachthealveolarair
sacsofthelungs,wheretheyinvadeandreplicatewithin
endosomesofalveolarmacrophages.
•Macrophagesidentifythebacteriumasforeignandattemptto
eliminateitbyphagocytosis.
•Duringthisprocess,thebacteriumisenvelopedbythemacrophage
andstoredtemporarilyinamembrane-boundvesiclecalleda
phagosome.
•Thephagosomethencombineswithalysosometocreatea
phagolysosome.

5. •Inthephagolysosome,thecellattemptstousereactiveoxygen
speciesandacidtokillthebacterium.However,M.tuberculosishas
athick,waxymycolicacidcapsulethatprotectsitfromthesetoxic
substances.
•M.tuberculosisisabletoreproduceinsidethemacrophageandwill
eventuallykilltheimmunecell.
•Tuberculosisisclassifiedasoneofthegranulomatousinflammatory
diseases.Macrophages,epithelioidcells,Tlymphocytes,B
lymphocytes,andfibroblastsaggregatetoformgranulomas,with
lymphocytessurroundingtheinfectedmacrophages.

6. •Whenothermacrophagesattacktheinfectedmacrophage,theyfuse
togethertoformagiantmultinucleatedcellinthealveolarlumen.The
granulomamaypreventdisseminationofthemycobacteriaandprovide
alocalenvironmentforinteractionofcellsoftheimmunesystem.
•Thebacteriausethegranulomastoavoiddestructionbythehost's
immunesystem.Macrophagesanddendriticcellsinthegranulomasare
unabletopresentantigentolymphocytes;thustheimmuneresponseis
suppressed.
•Bacteriainsidethegranulomacanbecomedormant,resultinginlatent
infection.Anotherfeatureofthegranulomasisthedevelopmentof
abnormalcelldeath(necrosis)inthecenteroftubercles.Tothenaked
eye,thishasthetextureofsoft,whitecheeseandistermedcaseous
necrosis.

8. Symptoms of Tuberculosis
TB bacteria or Mycobacterium tuberculosis multiply once it gets into the
lungs cause severe symptoms such as:
•Coughing up blood and mucus from deep inside the lungs
•A bad cough that lasts three weeks or longer
•Weakness or fatigue
•Sweating at night
•Pain in the chest
•Weight loss
•No appetite
•Chills and Fever

9. Diagnosis
•BloodTest:Inthisprocedure,Bloodsamplesarecollectedand
testedinthelaboratoriesforthepresenceorabsenceofTBgerms
inthebloodcells.Thetuberculosis(TB)bloodtest,alsocalledan
InterferonGammaReleaseAssayorIGRA,isawaytofindoutif
youhaveTBgermsinyourbody.
•SkinTest:Itisthemostcommontypeoftest.Inthisprocedure,a
smallsampleofTuberculin–apurifiedproteinisinjectedunder
thepatient’sskin.Iftheskinaroundthesiteoftheinjectiongets
swollenmorethanfivemillimetres,thenitisaclearindicationof
TBinfection.

10. Imagingtests
•Ifyou'vehadapositiveskintest,yourdoctorislikelytoordera
chestX-rayoraCTscan.Thismightshowwhitespotsinyourlungs
whereyourimmunesystemhaswalledoffTBbacteria,oritmight
revealchangesinyourlungscausedbyactivetuberculosis.
Sputumtests:
•IfthechestX-rayshowssignsoftuberculosis,samplesofthe
sputum(themucusthatcomesupwhenyoucough)arecollected.
ThesamplesaretestedforTBbacteria.
•Sputumsamplescanalsobeusedtotestfordrug-resistantstrains
ofTB.Thishelpsyourdoctorchoosethemedicationsthataremost
likelytowork.Gettingresultsofthesetestscantakefourtoeight
weeks.
•TBbacteriaculturedinEgg-enrichedmediawithglyceroland
asparagineLowenstein-Jensenmediumormediasupplemented
withbovinealbuminMiddlebrookmedium

12. Prevention and Control
BCGvaccination
•TheBCG(BacilleCalmette-Guérin)isalivevaccineagainst
tuberculosis.Thevaccineispreparedfromastrainoftheweakened
bovinetuberculosisbacillus,Mycobacteriumbovis.
•TheBCGiscurrentlytheonlylicensedvaccineagainstTB,andhas
beeninusesince1921.Itisoneofthemostwidelyusedvaccines
worldwide.
•80%effectiveinpreventingTBfor15yearsandmoreeffective
againstcomplexformsofTBinchildren.
Ahealthyimmunesystem
•Havingahealthyimmunesystemisthebestformofdefence
againstTB:60%ofadultswithahealthyimmunesystemcan
completelykillTBbacteria.

13. Early diagnosis
•Early diagnosis and treatment is the most effective way to prevent
the spread of tuberculosis.
•A person with infectious tuberculosis can infect up to 10–15 other
people per year. But once diagnosed with TB, and started on
treatment, the majority of patients are no longer infectious after
just two weeks of taking the medication.
Managing your environment
As TB is an airborne infection, TB bacteria are released into the air
when someone with infectious TB coughs or sneezes. The risk of
infection can be reduced by using a few simple precautions:
•good ventilation:as TB can remain suspended in the air for several
hours with no ventilation
•natural light:UV light kills off TB bacteria
•good hygiene:covering the mouth and nose when coughing or
sneezing reduces the spread of TB bacteria.

14. Treatment of Tuberculosis
•Drugtreatmentisoneofthemostefficientwaystotreatthis
infectiousdisease.ForpatientswithLatentTBinfections,doctors
generallyprescribeanantibioticcalledisoniazid,Rifampinfor
preventingthelatentinfectionfrombecomingactive.
•ActiveTBDiseaseswillbedeadlyifleftuntreated.Theprocedure
involvedistakingacombinationofethambutol,INH,Priftinand
Pyrazinamideforatermofthreemonths,followedbyamixofINH
andpyrazinamidefor12months.
•Isoniazid,alsoknownasisonicotinicacidhydrazide(INH)