Understanding Diseases: Types, Causes, and Transmission

Posted on Feb 2, 2025 in Microbiology

Diseases: An Overview

A disease is a disturbance of health, caused by physical or mental impairment, characterized by symptoms observed by the patient and doctor.

Infectious Diseases

Infectious diseases originate from the colonization of the body by pathogenic agents or vermin infestation.

Routes of Transmission

Infection spreads from sick to healthy individuals through direct or indirect transmission. Common routes include:

  • Air: Talking, coughing, or sneezing (e.g., tuberculosis).
  • Water: Contaminated water (e.g., cholera).
  • Food: Contaminated by microorganisms or parasites (e.g., Salmonella, BSE).
  • Animals: Insect vectors (e.g., malaria) or pets (e.g., tapeworms).

Infectious Agents

These include bacteria, protozoa, fungi, animal parasites (worms), and cell structures like viruses and prions. Infection results from the establishment and multiplication of microorganisms, causing damage and symptoms. Microbial diseases progress through phases: colonization, penetration, multiplication, invasion, and tissue alteration.

Bacterial Diseases

  • Tuberculosis: Caused by Koch’s bacillus, transmitted through the air, affecting lungs and bones, especially in immunocompromised individuals.
  • Cholera: Caused by Vibrio cholerae, producing a toxin that affects the intestinal epithelium, leading to vomiting, diarrhea, and dehydration. Lack of clean water and contaminated food cause epidemics.
  • Meningococcal Meningitis: Inflammation of the meninges, affecting children and young people, with symptoms like high fever, neck and head pain, and skin spots.
  • Pneumonia: Often follows flu or cold, causing fever, pain, and shortness of breath.
  • Tetanus: Caused by Clostridium tetani, entering through wounds, leading to violent muscle contractions.

Fungal Diseases

Also known as fungal or yeast infections, often caused by a weakened immune system. Examples include athlete’s foot, ringworm, and candidiasis.

Protozoal Diseases

  • Malaria: Caused by protozoa that infect red blood cells, transmitted by the Anopheles mosquito, with symptoms like high fever and chills.
  • Sleeping Sickness: Another disease caused by protozoa.

Viral and Prion Diseases

  • Viruses: Examples include AIDS, rabies, and smallpox.
  • Prions: Particles causing diseases in animals that can infect humans, such as mad cow disease.
  • AIDS: Caused by HIV, attacking T cells, leading to immune system suppression, tumors, and transmitted sexually, through contaminated blood, and from mother to child.

Diseases Caused by Animal Parasites

These include:

  • Ectoparasites: Living on the body’s surface (e.g., lice, fleas, ticks).
  • Endoparasites: Living in the body’s inner cavities, sometimes using intermediate hosts (e.g., worms). Examples include trichinosis.