17 Microbial Diseases

Types of Microbial Diseases

  1. Person-to-Person Microbial Diseases

    • Tuberculosis (TB)

    • AIDS (Acquired Immunodeficiency Syndrome)

  2. Vector-Borne and Soil Borne Diseases

    • Plague

    • Borreliosis (Lyme Disease)

    • Malaria

  3. Foodborne and Waterborne Diseases

    • Salmonellosis

    • EHEC (Enterohemorrhagic E. coli)

    • Campylobacteriosis

Tuberculosis (TB)

Definition

  • Infectious disease caused by the bacterium Mycobacterium tuberculosis

  • Characteristics:

    • Acid-fast, rod-shaped bacterium

    • Discovered by Robert Koch

    • Primarily affects the lungs but can also impact kidneys, bones, and adrenal glands.

Characteristics of Mycobacterium tuberculosis

  • Slow growth; cell division every 16-20 hours

  • Survives some disinfectants and dryness

  • Requires host cells to grow

  • Gram stain is weakly positive

  • Acid-fast (resistant to acid decolorization)

Pathology of TB

  1. Infection Process

    • Inhaled droplets contain M. tuberculosis which settle in the lungs.

    • Macrophages attack these bacteria, but many can survive within the macrophages, forming tubercles.

  2. Tubercles

    • Lesions can remain localized or become acute, leading to lung tissue destruction and spread to the body.

    • May result in scar tissue or continue as granulomas, which can reactivate, causing necrosis and cavitary lesions in the lungs.

  3. Inactive vs. Active TB

    • Inactive (Latent): No clinical symptoms, bacteria remain dormant, cannot spread.

    • Active: Shows symptoms, and is infectious - only about 10% of cases.

Transmission of TB

  • Spread through airborne droplets from coughs, sneezes, or talking.

  • Requires close, prolonged exposure for transmission.

At-Risk Groups

  • Individuals with a history of TB or non-compliance with treatment

  • Low socio-economic groups (homeless, overcrowding, malnutrition)

  • Immunosuppressed individuals (HIV, diabetes, etc.)

  • Infants and the elderly

  • Healthcare workers exposed to TB patients.

Diagnostic Investigations for TB

  • Chest X-Ray: Cannot diagnose TB solely based on X-ray findings.

  • Interferon-Gamma Release Assays: Blood tests for TB infection.

  • Tuberculin Sensitivity Test: Skin test.

  • Sputum or Urine Specimen: Tested via acid-fast staining.

  • Bronchoscopy and CT Scans: Advanced imaging tests.

  • Biopsy: For definitive diagnosis.

TB Therapy

  • Introduction of drug therapy in the late 1940s.

  • Use of the BCG vaccine for prevention.

  • Challenges: Emergence of multi-drug resistant M. tuberculosis and TB in HIV patients.

HIV/AIDS Overview

  • HIV/AIDS: A global pandemic with significant impact.

  • HIV (Human Immunodeficiency Virus) leads to progressive immune deficiency (AIDS).

  • Statistics: 40 million infected globally, with significant new infections and deaths annually.

HIV Transmission

  • Present in: Blood, semen, vaginal secretions, cerebrospinal fluid, and breast milk.

  • Main transmission routes include:

    1. Unprotected sexual contact

    2. Sharing contaminated needles

    3. Vertical transmission from mother to baby

    4. Blood transfusions (all now screened).

Pathogenesis of HIV

  • Attacks CD4 lymphocytes, crucial for immune response.

  • Leads to gradual depletion of these cells, impairing immune function.

  • Incubation varies from 1-3 months for antibody development and may progress to AIDS over years.

Diagnosing HIV

  • ELISA and Western Blot tests for antibodies.

  • HIV RNA Quantification via RT-PCR for viral load assessment.

HIV Treatment

  • Antiviral drugs (e.g., zidovudine/AZT) can effectively suppress the virus.

  • Patients adhering to treatment can expect a prolonged lifespan of up to 30 years.

AIDS-Related Illnesses

  • Common opportunistic infections include:

    • Mycobacterium avium: prevalent in patients with severe chronic lung conditions.

    • Toxoplasmosis: caused by Toxoplasma gondii.

Sources of Pathogens

  1. Reservoirs of Pathogenic Microorganisms

    • Animals, humans, and environment.

  2. Vector-Borne Diseases

    • Plague (Yersinia pestis)

    • Lyme Disease (Borrelia burgdorferi)

    • Malaria (Plasmodium spp.)

  3. Foodborne Diseases

    • Campylobacter

    • Salmonella

    • Pathogenic E. coli

  4. Waterborne Diseases

    • Vibrio cholera

Food Intoxication and Infection

Foodborne Pathogens

  • Campylobacter jejuni: Commonly associated with poultry, causes food poisoning.

  • Salmonellosis: Caused by Salmonella enterica, leading to severe gastrointestinal symptoms.

  • Pathogenic E. coli: Notably EHEC (Enterohemorrhagic E. coli), which can cause severe renal complications through contaminated meat.