5.1 - 5.4 - Health, disease and pathogens

5.1 · Health Is More Than No Disease

Health describes a person's overall state. The World Health Organization (WHO) includes three dimensions:

• physical well-being: the state and functioning of the body;
• mental well-being: psychological and emotional well-being;
• social well-being: relationships and participation in social life.

The words not merely are important. A person may have no diagnosed disease but still have poor mental or social well-being, so absence of disease alone does not meet the complete WHO definition. The three dimensions also interact: for example, a physical illness may restrict social activity and affect mental well-being.

5.2 · Communicable And Non-communicable Disease

The defining comparison is whether the disease can be transmitted between organisms.

In a communicable disease, it is most precise to say that the pathogen is transmitted; disease may then develop in the new host. Direct contact is not required for a disease to be communicable, because transmission can also be indirect.

Do not classify a disease by how serious, visible or long-lasting it is. A communicable disease is not necessarily severe, and a non-communicable disease is not necessarily mild. Transmission is the distinction required here.

5.4 · Pathogens Cause Disease

The words disease-causing do the classification work. A member of one of these groups counts as a pathogen when it causes disease; belonging to a group does not by itself make every member a pathogen. For example, not every bacterium is harmful.

Keep the cause and the outcome distinct:

• the pathogen is the disease-causing organism or infectious agent;
• the disease is the harmful condition that results in the affected host.

For 5.4, the required group list is exactly viruses, bacteria, fungi and protists. These are different biological groups, but disease causation is what gives a member pathogen status.