Unit 4: Infectious Diseases

Infectious diseases are caused by pathogenic microorganisms, such as bacteria, viruses, fungi, or parasites. They can be spread, directly or indirectly, from one person to another.

1. Tuberculosis (TB)

• Cause: A bacterium called *Mycobacterium tuberculosis*.
• Transmission: Spreads through the air when a person with active TB disease (usually of the lungs) coughs, sneezes, or speaks.
• Types (States):
  • Latent TB Infection: The person has the TB germs in their body, but their immune system is keeping them from becoming sick. They have no symptoms and cannot spread the disease. However, they are at risk of developing active TB later.
  • Active TB Disease: The germs are active and multiplying, causing illness. This person is symptomatic and can spread the disease.
• Symptoms (Active TB):
  • A bad cough that lasts 3 weeks or longer.
  • Coughing up blood or sputum (phlegm from deep inside the lungs).
  • Chest pain.
  • General symptoms: Weakness, fatigue, weight loss, no appetite, fever, and night sweats.
• Diagnosis:
  • TB Skin Test (Mantoux test) / TB Blood Test: These tests show if a person has been *infected* with TB germs. They cannot tell if it is latent or active.
  • Chest X-ray: Used if the skin/blood test is positive. In active pulmonary TB, it may show infiltrates or cavities in the lungs.
  • Sputum Smear (AFB Smear): The definitive test for active pulmonary TB. Sputum is stained (using Ziehl-Neelsen stain) and examined for acid-fast bacilli.
• Prevention:
  • BCG Vaccine: Given to infants in many countries to protect against severe forms of TB.
  • Treating latent TB infection to prevent it from becoming active.
  • Good ventilation and isolation of patients with active TB.

2. Hepatitis

Hepatitis means "inflammation of the liver". It is most commonly caused by a group of viruses, specifically Hepatitis A, B, C, D, and E. It can also be caused by alcohol, toxins, and autoimmune diseases.

Types, Symptoms, and Diagnosis

• Common Symptoms: Many people have no symptoms. When they occur, they can include:
  • Fatigue, fever, nausea, loss of appetite.
  • Abdominal pain (upper right side).
  • Jaundice (yellowing of the skin and eyes).
  • Dark-colored urine and light-colored stool.
• Diagnosis:
  • Liver Function Tests (LFTs): Blood tests that measure liver enzymes (like ALT and AST). High levels indicate liver inflammation.
  • Hepatitis Serology: Specific blood tests that detect antigens (parts of the virus) or antibodies (the body's response) to determine which type of hepatitis virus is present (e.g., HBsAg for Hepatitis B).

Key Types of Viral Hepatitis