Infectious Diseases

1. Infectious Diseases Dr. Meg-angela Christi Amores

2. Infectious Diseases • Tuberculosis • Leprosy • AIDS • Syphilis • Viral Infections • Pneumonia • Herpes

4. 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

5. 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

7. 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

8. 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

9. From exposure to infection • Patients whose sputum contains AFB are most likely to transmit infection • Most infectious patients have cavitary disease

10. 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

11. secondary (or postprimary) tuberculosis • Dormant bacilli persisting for years before reactivating • Mostly in adults • Pulmonary findings

12. 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

13. 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

14. 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

15. 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

16. Clinical Manifestations • PULMONARY • EXTRA-PULMONARY

17. 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

18. 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

20. 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

21. 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

22. 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 tuberculousspondylitis) • With advanced disease, collapse of vertebral bodies results in kyphosis (gibbus)

23. Extrapulmonary TB • Miliary TB • Disseminated TB • yellowish granulomas 1–2 mm in diameter that resemble millet seeds • chest radiography reveals a miliary reticulonodular pattern

24. Diagnosis • High index of suspision • XRAY consistent with TB • AFB microscopy: • Sputum exam • Tissue biopsy • Culture • Gold standard

25. Treatment • DOTS ( Direct Observed Treatment Strategy) • Treatment partner