Infectious Diseases

Dr. Meg-angela Christi Amores

Infectious Diseases

• Tuberculosis• Leprosy• AIDS• Syphilis• Viral Infections• Pneumonia• Herpes

TUBERCULOSIS

• one of the oldest diseases to affect humans• caused by bacteria of the Mycobacterium

tuberculosis complex• Usually affects the lungs• untreated, the disease may be fatal within 5

years in 50–65% of cases• airborne spread of droplet nuclei

M. Tuberculosis• rod-shaped, non-spore-

forming, thin aerobic bacterium measuring 0.5 um by 3 um

• Neutral on gram staining• Acid-fast (once stained,

cannot be decolorized by acid alcohol)

• Acid fastness is due to the organisms high content of mycolic acid

Epidemiology

• More than 5 million new cases of tuberculosis were reported to the WHO in 2005

• > 90% are from developing countries• The WHO estimated that 8.8 M new cases of

tuberculosis occurred worldwide in 2005– Asia: 4.9 M– Africa 2.6 M– Middle East 0.6 M– Latin America 0.4 M

From exposure to infection

• M. tuberculosis is common transmitted through droplet nuclei, which are aerosolized by coughing, sneezing or speaking

• Determinants of the likelihood of transmission includes:– Intimacy and duration– Degree of infectiousness– Shared environment

From exposure to infection

• Patients whose sputum contains AFB are most likely to transmit infection

• Most infectious patients have cavitary disease

From infection to disease

• the risk of developing disease after being infected depends largely on endogenous factors, such as the individual's immunity and the level of function of cell mediated immunity

• primary tuberculosis – – Clinical illness directly following infection– common among children up to 4 years of age and

among immunocompromised persons– Not associated with high level transmissibility

• secondary (or postprimary) tuberculosis– Dormant bacilli persisting for years before

reactivating – Mostly in adults– Pulmonary findings

• secondary (or postprimary) tuberculosis– Age is an important determinant of the risk of

disease after infection• Risk is highest among late adolescent and early

childhood

– Women are more prone to acquire infection than men in early adolescence

– The most potent factor for M tuberculosis infection is HIV co-infection

Pathogenesis and Immunity

• Infection and Macrophage Invasion• Virulence of Tubercle Bacilli• Innate Resistance to Infection• The Host Response– phagosomes and lysosomes occurs– bacilli begin to multiply, ultimately

killing the macrophage

Pathogenesis and Immunity

• Granuloma Formation (Tubercles)– macrophages

• The Macrophage-Activating Response– Caseous necrosis

• The Delayed-Type Hypersensitivity Reaction• Role of Macrophages and T lymphocytes• Mycobacterial Lipids and Proteins

Immunity

• Skin Test Reactivity– PPD Skin test:– Due to delayed-type sensitivity– Coincident with immunity– Mainly due to previously sensitized CD4 T

lymphocytes– Positive Tuberculin Skin Test (TST): wheal• > 5mm on un-vaccinated persons• >10 mm on vaccinated persons• After 72 hours

Clinical Manifestations

• PULMONARY• EXTRA-PULMONARY

Pulmonary TB

• Primary– Mostly seen in children– most inspired air is distributed to the

middle and lower lung zones, these areas of the lungs are most commonly involved in primary tuberculosis

– In majority of cases, lesion heals spontaneously and may later be evident as a small calcified nodule (Ghon lesion)

– immunocompromised persons develop miliary TB

Pulmonary TB

• Secondary (Postprimary)– adult-type, reactivation– localized to the apical and posterior

segments of the upper lobes, where the substantially higher mean oxygen tension favors mycobacterial growth

– small infiltrates to extensive cavitary disease

Clinical Manifestations

• fever and night sweats, weight loss, anorexia, general malaise, and weakness

• cough eventually develops—often initially nonproductive and subsequently accompanied by the production of purulent sputum, sometimes with blood streaking

• Hemoptysis may also result from rupture of a dilated vessel in a cavity (Rasmussen’s aneuruysm)

• Often with no physical findings• The most common hematologic finding is mild anemia

and leukocytosis

Extrapulmonary TB

• Lymph-Node Tuberculosis – frequent among HIV-infected patients– historically referred to as scrofula

• Pleural TB• TB of upper airways• Genitourinary TB• TB Meningitis and Tuberculoma• Gastrointestinal TB

Extrapulmonary TB

• Skeletal TB– reactivation of hematogenous foci

or to spread from adjacent paravertebral lymph nodes

– spine in 40% of cases, the hips in 13%, and the knees in 10%

– Spinal tuberculosis (Pott's disease or tuberculous spondylitis)

– With advanced disease, collapse of vertebral bodies results in kyphosis (gibbus)

Extrapulmonary TB

• Miliary TB– Disseminated TB– yellowish granulomas 1–2 mm in diameter that

resemble millet seeds– chest radiography reveals a miliary

reticulonodular pattern

Diagnosis

• High index of suspision• XRAY consistent with TB• AFB microscopy:– Sputum exam– Tissue biopsy

• Culture – Gold standard

Treatment

• DOTS ( Direct Observed Treatment Strategy)– Treatment partner