Unit 5: Infectious Diseases

February 21, 2026

Semester 2
BP204T

Introduction to Infectious Diseases

Unit 5 covers pathophysiology of major infectious diseases that pharmacists encounter worldwide. This unit bridges microbiology with pharmacology, explaining how pathogens cause disease and which organ systems they target. Understanding pathogenesis helps pharmacists comprehend why specific antibiotics or antivirals are chosen for treatment.

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Syllabus & Topics

  • 1Meningitis: Definition, causative organisms (bacterial, viral, fungal), pathogenesis, CSF findings.
  • 2Typhoid Fever: Causative organism (Salmonella typhi), pathogenesis, ‘Rose spots’, Widal test.
  • 3Leprosy (Hansen’s Disease): Causative organism (M. leprae), types (tuberculoid vs lepromatous), treatment.
  • 4Tuberculosis (TB): M. tuberculosis, Pathogenesis, Primary vs Secondary TB, Ghon complex.
  • 5Drug-Resistant TB: MDR-TB and XDR-TB.
  • 6Urinary Tract Infections (UTIs): Causative organisms, ascending vs descending infection.
  • 7HIV/AIDS: HIV structure, CD4 T-cell destruction, stages (Window period, AIDS), opportunistic infections.
  • 8AIDS: Immunological basis of AIDS (CD4 count <200 cells/µL).
  • 9Syphilis: Causative organism (Treponema pallidum), Stages (Primary, Secondary, Tertiary).
  • 10Gonorrhea: Causative organism (Neisseria gonorrhoeae), complications.

Learning Objectives

Diagnose by CSF: Describe the CSF findings in Bacterial vs Viral Meningitis.
TB Pathogenesis: Describe the formation of the Ghon complex in primary TB.
HIV Life Cycle: Explain how HIV infects CD4 cells and uses Reverse Transcriptase.
STD Stages: Describe the three stages of Syphilis.
TB Treatment: Explain the RHEZ regimen used for Drug-Sensitive TB.

Frequently Asked Questions (FAQs)

Q1. What is the pathogenesis of Tuberculosis?

Mycobacterium tuberculosis is inhaled and engulfed by alveolar macrophages. It resists intracellular killing, leading to a granuloma formation (Ghon focus). In Primary TB, the infection is usually contained. In Secondary (Reactivation) TB, the granuloma breaks down, causing caseation and cavitation.

Q2. How does HIV cause Immunodeficiency?

HIV selectively infects and destroys CD4⁺ T-helper cells. Over time, as the CD4 count falls below 200 cells/µL, cell-mediated immunity collapses, predisposing the patient to opportunistic infections (e.g., PCP pneumonia, CMV infection, Cryptococcal meningitis).

Q3. What is the difference between Bacterial and Viral Meningitis on CSF analysis?

Bacterial Meningitis: Turbid/purulent CSF, ↑ WBCs (mainly PMNs), ↓ glucose, ↑ protein.
Viral Meningitis: Clear CSF, ↑ lymphocytes, normal/slightly ↓ glucose, normal protein.

Q4. What are the Stages of Syphilis?

  • Primary: Painless chancre at the site of infection.
  • Secondary: Skin rash (palms/soles), fever (bacteremia stage).
  • Latent: Asymptomatic carrier stage.
  • Tertiary: Gummas, cardiovascular syphilis (aortitis), neurosyphilis.

Q5. What is MDR-TB?

Multi-Drug Resistant Tuberculosis (MDR-TB) is caused by Mycobacterium tuberculosis resistant to at least Isoniazid and Rifampicin, the two most potent first-line anti-TB drugs. It is a major global public health problem.