Introduction to Communicable Diseases

Communicable diseases, also known as infectious diseases, pose a significant public health challenge in Africa, particularly among infants and children. Communicable diseases are illnesses that can be spread from one person to another. These diseases spread from person to person and, alongside malnutrition, are major contributors to illness and mortality on the continent. However, many of these diseases are preventable with proper interventions.

Health and Disease

• Health: Health refers to a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity.
• Disease: A disease is a specific abnormal condition that affects the body or mind and impairs normal functioning. It is often characterised by specific symptoms and signs.

Factors Influencing the Spread of Communicable Diseases

The spread of communicable diseases is influenced by a complex interplay of factors, commonly referred to as the “epidemiological triangle/Epidemiological Triad”:

1. Agent: The infectious organism itself, characterised by its ability to survive, multiply, and transmit.
2. Host: The individual who can be infected by the agent, influenced by factors like age, immune status, and underlying health conditions.
3. Environment: The surrounding conditions that facilitate the survival and transmission of the agent, such as climate, sanitation, and access to healthcare.

Aetiology of Diseases

Introduction

There are three elements that determine the etiology of health problems in a population: Agent, Host, and Environment. These are referred to as the epidemiological triad.

• Epidemiology is the study of the distribution and determinants of diseases and health-related events in human populations.
• A disease occurs when the agent is more powerful than the host, causing the host to weaken and the environment to become favorable for the growth, multiplication, and survival of the agent.
• This is possible when the host becomes stronger, the agent is removed, and the environment becomes unfavorable to the agent.
• The epidemiology framework used to study and analyze the epidemiology of a disaster is the Sendai Framework.

Agent

• It is a factor whose presence or absence causes a disease.
• It is a specific factor without which a disease cannot occur.
• A disease agent is defined as a substance, living or nonliving, or a force, tangible or intangible, the excessive presence or relative lack of which is the immediate cause of a particular disease.

The disease agent is classified as follows:

1. Physical Agents: Various mechanical forces or frictions that may produce injury, as well as atmospheric abnormalities such as extremes of heat, cold, humidity, pressure, radiation, electricity, sound, etc.
2. Biological Agents: Include all living organisms such as viruses, bacteria, rickettsia, chlamydia, protozoa, fungi, helminths, among others.
3. Chemical Agents: a) Endogenous: Some chemicals may be produced in the body as a result of decayed function, e.g., urea (uraemia), ketones, ketosis, sodium, bilirubin (jaundice), uric acid (gout), CaCO3 (kidney stones), among others. b) Exogenous Agents: These arise from outside the human host, such as allergens, metals, fumes, insecticides, etc. They may be acquired by inhalation, ingestion, or inoculation.
4. Genetic Agents: Transmitted from parent to child through genes.
5. Mechanical Agents: Chronic friction and other mechanical forces resulting in injuries, trauma, fractures, sprains, dislocations, and even death.
6. Nutrient Agents: Dietary components needed for survival, e.g., proteins, fats, carbohydrates, vitamins, minerals, and water. The excessive or deficient intake of nutrients can lead to malnutrition, which in turn leads to susceptibility to disease.