Human Diseases > Communicable / Infectious Diseases

A disease caused by a specific pathogenic organism and capable of being transmitted to another individual by direct or indirect contact is known as communicable (infectious) disease.

A communicable or infectious disease is a disease caused by a specific pathogenic organism and capable of being transmitted to another individual by direct or indirect contact.

• Disease is the interruption of the normal structure and function of any part of the body, shown by characteristic signs and symptoms.
• Infection occurs when harmful organisms called pathogens invade the body and begin to reproduce.
• These diseases spread from an infected person to a healthy person.
• Spread may occur through air, contaminated water, contaminated food, vectors, direct contact, or indirect contact.
• When germs of a particular disease enter the body and begin to grow, the person develops the disease.

• An infectious disease may not appear immediately after infection.
• The incubation period may vary from a few hours to a few days, and in some diseases, from a few hours to several months.

Given examples include:

• Pneumonia 1–3 days
• Diphtheria 2–5 days
• Cholera 2–6 days
• Typhoid 7–14 days
• Measles 10–12 days
• Chicken pox 14–21 days
• Rabies about 1 month
• Leprosy up to several years
• HIV/AIDS up to 12 or more years

• Communicable / Infectious diseases are caused by pathogens and spread from an infected to a healthy person via air, water, food, vectors, or contact.
• Common pathogens: bacteria (cholera, typhoid, TB), viruses (AIDS, hepatitis), protozoa (malaria), and helminths (ascariasis, filariasis).
• Incubation period: time between infection and symptoms — varies from hours (cholera) to years (HIV/AIDS, leprosy).
• TB (Mycobacterium tuberculosis) spreads through air; prevented by BCG vaccine, isolation, and DOTS.
• Hepatitis spreads through contaminated water, needles, or blood; prevented by boiled water and hygiene.
• Cholera, typhoid, and dysentery spread through contaminated food and water; prevented by hygiene, boiled water, ORS, and vaccination.