Tuberculosis: Etiology, Transmission, Pathogenesis, Diagnosis, and Treatment, Slides of Pediatrics

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Tuberculosis

Introduction

• Etiology: -Order:Actinomycetales.

-Family:Mycobcteriaceae.

• Mycobacterium tuberculosis.
• Mycobacterium bovis.
• Mycobacterium africanum.
• Characteristics:
• Hallmark: acid-fastness.
• Culture characteristics:

Epidemiology

• Adults: 2/3 are males.
• Childhood: females more than males.
• Favored age: 5-14 years.
• Where children get the infection?
• Drug resistant T.B.:

Transmission

• By airborne mucus droplet nuclei.
• Rarely by direct contact with infected

discharge or contaminated fomites.

• What factors that will increase the chance of

transmission?

• Young children with T.B. rarely infect other

children or adults.

Pathogenesis

• Partial obstruction
• Endo bronchial T.B. or fistula tract.
• Complete obstruction.
• Segmental lesion.
• Disseminated T.B.
• Remote foci become encapsulated and maybe

the origin of extra pulmonary or reactivation

T.B.

Pathogenesis

• Time between infection and disease is variable.
• Pulmonary T.B. occurs more than 1 year after primary infection due to endogenous re-growth of bacilli ( Reactivation ) while disseminated or meningeal T.B. occurs 2- 6 months after infection.
• 40% of infants with untreated infection develop the disease within 1-2 years and the risk declines throughout the childhood.
• 25-35% of children with T.B. develop extra pulmonary disease compared to 10% in adults.

Immunity

• Antibodies have little role in the defense.
• Role of Sulfatides.
• Cell-mediated immunity develops 4-8 weeks after infection at the same time of development of tissue hypersensitivity.
• It depends on :1- Mycobacterial antigen load.

2- Cell-mediated immunity.

3- Tissue hypersensitivity.

Tuberculin skin test

• It is due to delayed type hypersensitivity.
• Mantoux test vs. multi-puncture test.
• Induration is measured after 48-72 hours.
• The sensitivity & specificity are less than 100% but no better diagnostic test is available.
• Performing an initial test before the initiation of immunosuppressive therapy in any patient.
• It is interpreted on the basis of rule of 5,10,15 mm.

Tuberculin skin test

• Annual testing for :

 children who are infected with HIV or those

living in a household with persons infected

with HIV.

Incarcerated adolescents.

Tuberculin skin test

• Testing at 2-3 year intervals is indicated if the

child has been exposed to high-risk individuals

including those who are

homeless,institutionalized adults who are

infected with HIV, users of illicit

drugs,residents of nursing homes and

incarcerated adolescents or adults.

Tuberculin skin test

• Induration of 5mm or more is considered positive in:  Children having close contact with known or suspected contagious cases of the disease ,including those with household contacts with active T.B. whose treatment cannot be verified before exposure.  Children with immunosuppressive conditions or medications.  Children with abnormal CXR finding consistent with active T.B. ,previously active T.B., or clinical evidence of the disease.

Tuberculin skin test

• Induration of 10mm or more is positive in:

 Children who are at higher risk of dissemination of tuberculosis disease including those younger than 5 years or those who are immuno-suppressed because of conditions such as lymphoma,D.M., and malnutrition.  Children with increased risk of exposure to the disease including exposure to adults in high-risk categories ,those who were born in or whose parents were born in high-prevalence areas of the world, and those with travel histories to high- prevalence areas of the world.

Tuberculin skin test

• False negative:  Vaccination with live attenuated viruses Or infection by them.  Anergy.  Immuno-suppression & immune-deficiency.  Malnutrition.  Improper administration  Improper storage & contamination.  Overwhelming T.B..  Very young age.

Clinical picture and diagnosis

 Primary pulmonary disease : usually sub-pleural associated with pleurisy.

 All lobar segments are at equal risk of initial infection.

 Symptoms and physical findings are variable.

 Diagnosis : early morning gastric aspirate but negative cultures do not rule out the disease.

 Adequate proof : +ve P.P.D. + abnormal CXR consistent with T.B. + history of exposure to adult with infectious T.B.