Understanding Health, Disease, and Infectious Agents

Health and Disease

Until recently, health was defined as "the absence of disease." However, the World Health Organization (WHO) has developed a more comprehensive definition. Health is a state of complete physical, mental, and social well-being.

Disease, on the other hand, is the state in which a person's health is altered, whether due to physical or social causes. We can distinguish three types of diseases:

• Physical diseases: Produced by injury, infection, or a degenerative process in the body. They are classified into:
  • Infectious diseases: Caused by a pathogen that reproduces within our body.
  • Non-infectious diseases: Due to other causes.
• Mental illness: Caused by a malfunction of the brain, resulting in a decline in mental capacity or some alteration of behavior.
• Social diseases: Caused by the existence of a social environment with serious violent, economic, or educational deficiencies, making it hostile to humans.

Infectious Diseases

Infectious diseases are caused by microorganisms that alter the normal functioning of our body. These microorganisms can be:

• Bacteria: Unicellular prokaryotic organisms (no nucleus) that can cause many different diseases, such as pneumonia and salmonellosis.
• Viruses: They do not show cell structure and are obligate parasites, meaning they need a cell to multiply. Viruses are responsible for common diseases such as influenza or AIDS.
• Protozoa: Unicellular eukaryotic organisms, such as the parasite that causes malaria or the trypanosome that causes sleeping sickness.
• Fungi: Eukaryotic organisms that often cause infections on the surface of the skin, mouth, or vagina, usually not serious. A fungal infection is called histoplasmosis. Ringworm, for example, affects the scalp, and athlete's foot are diseases caused by fungi that grow on the surface of our skin.

Transmission of Infectious Diseases

Organisms found in soil, air, water, or other individuals are transmitted to humans through two mechanisms:

• Direct transmission or direct contagion: A person carrying the organism spreads the disease to another by contact through the surface of the skin, sex, etc., or through droplets that emerge when talking, coughing, or sneezing.
• Indirect transmission: Using objects such as towels, cups, brushes, or any type of instrument; through water, air, or food contaminated with microorganisms; or carrier animals, in which case we talk of a vector (rats, insects, ticks, etc.).

An epidemic is the sudden onset of a disease, infectious or otherwise, that spreads rapidly through a population and affects many people at once in a given region. An epidemic is also seen as the emergence of a few cases of a disease in a population that was free of it. If the epidemic affects a single country, it is called endemic, and if it extends throughout the world, it is called a pandemic.

Development of Infectious Diseases

The microorganism in our body destroys cells and tissues by producing substances and dividing or multiplying. Infectious diseases develop in three stages or phases:

• Incubation period: Time elapsed since the entry of the pathogen to the appearance of the first signs and symptoms.
• Prodromal phase: Nonspecific signs and symptoms appear, which may correspond to many diseases, such as fever, headache, etc.
• Phase of overt disease or acute phase: The specific signs and symptoms of the disease appear.
• Convalescent phase: The infectious agent is removed, and the body recovers.