Classification of Human Diseases: Etiology and Examples

Infectious and Parasitic Diseases

Prion Diseases

Caused by infectious agents called prions (proteins with a configuration different from the normal protein). Prions are transmitted to other proteins, affecting adjacent organs. Example: Bovine Spongiform Encephalopathy (BSE), commonly known as Mad Cow Disease.

Viral Diseases

Caused by acellular virus particles. Viruses consist of a nucleic acid (DNA or RNA) surrounded by a protein envelope. They self-replicate using the machinery of the infected cell. Treatment is often complicated.

Examples include: Yellow fever, Influenza A, Hepatitis, Mumps, AIDS, and Measles.

Bacterial Diseases

Caused by bacteria, which are unicellular living beings classified as prokaryotes (lacking a defined nucleus). While many bacteria are beneficial and necessary, pathogenic bacteria cause disease.

Examples include: Anthrax, Cholera, Plague, Tuberculosis, Brucellosis, Gonorrhea, and Leprosy.

Fungal Infections (Mycoses)

Caused by fungi, such as yeast, which are eukaryotic organisms (possessing a defined nucleus). Fungal infections can be difficult for complex organisms like humans to combat. Treatment is often topical.

Examples include: Ringworm, Athlete's foot, and Candidiasis.

Parasitic Protozoa

Caused by single-celled, heterotrophic eukaryotes that typically live in liquid media. Infection can occur by ingesting contaminated food or water (e.g., amebiasis) or via insect bites.

Examples include: Malaria, Chagas disease, and African sleeping sickness (Trypanosomiasis).

Parasitic Metazoans

Caused by multicellular parasites (metazoans), including both worms (helminths) and arthropods.

• Worms: Tapeworms (Cestodes) and other helminths.
• Arthropods: External parasites that cause itching and rashes. Examples include Lice and Scabies (mites).

Non-Infectious Diseases

Cancer

Cancer is caused by the abnormal proliferation of cells. During cell division, cells duplicate their DNA. Normally, if proliferation is uncontrolled, apoptosis (programmed cell death) occurs to prevent overgrowth. If cells evade apoptosis, they continue to live and produce a tumor.

Treatment typically involves radiotherapy, chemotherapy, and surgery.

Endocrine, Metabolic, and Nutritional Disorders

• Endocrine: E.g., Diabetes.
• Metabolic: E.g., High Cholesterol.
• Nutritional:

  Anorexia Nervosa

  A serious eating disorder characterized by an intense fear of gaining weight and body image distortion, often linked to depression or low self-esteem. Requires treatment by a psychiatrist.

  Bulimia Nervosa

  Often linked to anorexia, involving dietary imbalance, excessive intake of food followed by purging (e.g., vomiting) due to feelings of guilt.

Cardiovascular Diseases

These conditions affect the heart and blood vessels.

• Strokes (Cerebrovascular Accident): Occurs when the brain loses its blood supply, usually because a blood clot clogs a cerebral artery or due to the rupture of a blood vessel.
• Heart Attack (Myocardial Infarction): Caused by the obstruction of the coronary arteries. The affected heart tissue dies due to lack of oxygen.
• Arteriosclerosis: The thickening and hardening of artery walls.
• Hypertension (High Blood Pressure): Occurs when the pressure exerted by the blood on the arterial walls is excessively high.

Mental Health Disorders

These disorders alter the cognitive and affective processes of the individual.

• Psychoses: E.g., Schizophrenia.
• Organic Disorders: Related to substance consumption (e.g., alcohol, drug use).
• Affective Disorders: E.g., Depression.
• Anxiety Disorders or Neuroses.

Degenerative Diseases

• Parkinson's Disease

  Characterized by the destruction of neurons that produce dopamine, which are responsible for controlling and coordinating movement. Symptoms include tremors and slowness of movement.

• Alzheimer's Disease

  Typically affects persons aged 65 years and older. Patients experience memory loss and behavioral changes, eventually leading to dependency.