A disease is a condition that affects the normal functioning of an organism, causing harm or discomfort. It can be caused by genetics, environment, lifestyle, or infection. A disease has a more objective, biological, or pathological basis. While often used interchangeably, "disease" and "illness" have distinct meanings. An illness is a person's subjective experience of feeling unwell. It may or may not be related to a specific disease. While disease focuses on the medical aspect, illness includes personal, social, and cultural factors. According to duration, diseases are of two types:
8.2 INFECTIOUS DISEASES
Infectious diseases can spread from person to person or from animals to people. An infection occurs when a pathogen enters and multiplies inside a person's body, causing disease. A pathogen is an agent that causes disease or infection. Types of pathogens include viruses, bacteria, fungi, protozoans and parasitic worms.