Health, Disease, and Infectious Diseases: A Comprehensive Overview

1. Health and Disease

1.1. Definitions

Health: A state of complete physical, mental, and social well-being, not merely the absence of disease.

Disease: A change in health status, i.e., a temporary or permanent loss of physical, mental, and social well-being.

Quality of Life: The comfort level, happiness, and satisfaction in a person that allows them to act and feel positively about their lives. This depends on their physical and mental health, their level of independence, and social relationships. One of the main indicators is life expectancy at birth.

1.3. Genes, Lifestyle, and Health

There are genetic diseases due to alterations in the genome (e.g., Down syndrome, hemophilia, or certain types of diabetes).

In other cases, the genotype determines susceptibility to a disease. A person may be predisposed to a disease, but the environment in which they live also influences its development. Being predisposed to a disease does not mean it will manifest.

Congenital diseases are manifested at birth due to some disturbance that occurred during embryonic development or during birth.

2. Environmental Factors and Health

2.1. Physical Environmental Insults

Ionizing Radiation: A form of energy that can cause changes in our cells and alter our health status.

Noise: May cause sleep disturbances, behavioral problems, and hearing loss.

Temperature Variations: High temperatures and excess moisture prevent the evaporation of sweat and the cooling that it entails, which can be lethal. Extreme cold can also cause injury.

2.2. Chemical Environmental Insults

Air Pollution: Human activities change the composition of the air, adding compounds that affect health.

Carbon Monoxide: Toxic to humans because it affects the transport of oxygen in the blood.

Nitrogen Oxides: Affect the lungs and are toxic.

Water Pollution:

• Organic: Sewage and livestock waste, pesticides, grease, and plastics. These cause the growth of microorganisms and are toxic.
• Inorganic: Nitrates and phosphates from fertilizers, acids, salts, and toxic metals. These favor the proliferation of algae and microorganisms and are toxic.
• Biological: Microorganisms.

Food Contamination:

3. Infectious Diseases

Infectious diseases are caused by microorganisms: bacteria, viruses, protozoa, and fungi. The organisms that cause disease are called pathogens.

3.2. Transmission of Infectious Diseases

Direct Contact

Some organisms that cause skin diseases are transmitted when the healthy skin of a person comes into contact with the skin of a sick person.

Many respiratory diseases are transmitted through droplets produced by sneezing or coughing.

For the transmission of other microorganisms, close contact is required, such as sexual intercourse. These are sexually transmitted diseases (STDs).

Waterborne Transmission

This occurs when water is contaminated by feces from humans or animals.

Foodborne Transmission

Vector-borne Transmission

Animals that can transmit diseases are called vectors. For example, mosquitoes.

3.3. The Development of Infectious Diseases

1. Infection: The organism reaches the body, penetrates inside, and starts to multiply.
2. Incubation Period: The time from infection until symptoms begin to appear.
3. Acute Period: The disease is fully manifested.
4. Decline: The disease symptoms are subsiding.
5. Convalescence: The patient is regaining their strength until they return to being healthy.