Human Health: Infectious Diseases and Body Defence Mechanisms

4.1 Infectious and Non-infectious Diseases

• A disease is an abnormal condition of body or mind causing discomfort, difficulty to function, or stress.
• Diseases are classified into infectious and non-infectious types.

Differences Between Infectious and Non-infectious Diseases

Infectious Diseases

• Caused by infection of pathogens directly through mediums and vectors.
• Examples: Tuberculosis, flu, ringworm, tinea, leptospirosis, dengue fever, malaria fever, and Zika fever.
• Transmissible from one individual to another.

Non-infectious Diseases

• Caused by genetic factors or lifestyle.
• Examples: Cancer, hypertension, diabetes, asthma, and cardiovascular diseases.
• Non-transmissible from one individual to another.

How are Infectious Diseases Spread?

• Infectious diseases are spread by pathogens (organisms that cause diseases).
• Pathogens include viruses, bacteria, protozoa, fungi, and worms.
• Pathogens are transmitted from an infected person (host) to another through vectors and mediums like water, air, and contact.
• The host is a weak victim easily infected and shows symptoms after infection.

Airborne Diseases

• Transmitted through droplet transmission and dust transmission.

Droplet Transmission

• Pathogen-containing droplets spray from the mouth and nose of an infected person through sneezing, coughing, talking, yawning, or breathing.

Dust Transmission

• Bacteria in the spit (saliva) of an infected person dry up and form spores which spread with dust in the air.

Prevention of Airborne Diseases

• Cover the mouth and nose when sneezing, coughing, or yawning.
• Do not spit everywhere.
• Avoid being in crowded places.
• Ensure living places get enough light as ultraviolet rays can kill certain microorganisms.
• Examples of airborne diseases: Tuberculosis, flu, Severe Acute Respiratory Syndrome (SARS), Influenza A (H1N1), and chicken pox.

Waterborne Diseases

• Infection through water usually happens in areas with inadequate water supply and poor sanitation.
• Faecal pathogens enter and pollute water sources.
• Infection occurs when drinking contaminated water.
• Floods can also spread infectious diseases.
• Examples of waterborne diseases: Cholera, typhoid, and amoebic dysentery.

Prevention of Waterborne Diseases

• Add chlorine to swimming pools and water supply systems.
• Build toilets with good sanitation.
• Boil drinking water properly.
• Wash hands with soap after using the toilet.

Infection of Diseases Through Contact

• Examples: Ringworm and tinea (caused by fungi).
• Occurs by touching infected skin or wearing clothes of an infected person.

Sexually Transmitted Diseases

• Examples: Syphilis and gonorrhoea spread through sexual intercourse; pathogens present in semen and vaginal fluid.
• HIV (causes AIDS) transmitted through sexual intercourse, blood, and sharing syringes.

Infection of Diseases Through Vectors

• Pathogens are transmitted from one host to another through animals (vectors).

Vectors and Pathogens:

• Cockroach: Salmonella typhi
• Fly: Salmonella typhi
• Aedes mosquito: Dengue virus
• Aedes mosquito: Zika virus
• Anopheles mosquito: Plasmodium malariae
• Rat: Leptospira sp. bacteria

Examples of Diseases, Symptoms, Pathogens, Vectors, and Ways of Infection

• Malaria:
  • Symptoms: Shivering, fever, and sweating
  • Pathogen: Plasmodium malariae
  • Vector: Female Anopheles mosquito
  • Infection: Mosquito bite
• Cholera:
  • Symptoms: Diarrhea and vomiting
  • Pathogen: Vibrio cholerae bacteria
  • Vector: Fly
  • Infection: Contaminated food and water
• Dengue:
  • Symptoms: Joint pain, fever, headache, and watery eyes
  • Pathogen: Dengue virus
  • Vector: Aedes mosquito
  • Infection: Mosquito bite
• Zika:
  • Symptoms: Fever, rashes, joint pain, and conjunctivitis
  • Pathogen: Zika virus
  • Vector: Aedes mosquito
  • Infection: Mosquito bite
• Typhoid:
  • Symptoms: Fever, intestinal bleeding, and red rashes
  • Pathogen: Salmonella typhi bacteria
  • Vector: Cockroach, fly
  • Infection: Contaminated food and water
• Leptospirosis:
  • Symptoms: Fever, headache, and muscle pain
  • Pathogen: Leptospira sp. bacteria
  • Vector: Rat
  • Infection: Contaminated soil, food, and water

How Vectors Spread Diseases

• Mosquito:
  • A mosquito with pathogens in its salivary glands sucks blood from an uninfected person.
  • Saliva secreted during blood-sucking transmits the infection.
• Fly:
  • A fly lands on dirt, collecting pathogens on its legs and body.
  • It transmits pathogens to food, infecting the person who eats the contaminated food.

The Mechanism to Prevent the Spread of Infectious Diseases

Three Stages of Prevention

• Primary stage:
  • Improving health:
    • Improving personal and family hygiene, cleanliness of living places, and sanitation systems.
    • Strengthening the body's defense system through vaccines and immunizations.
    • Frequent health check-ups.
  • Maintaining a healthy lifestyle:
    • Inhaling clean air.
    • Eating a balanced diet.
• Secondary stage:
  • Determining transmission of infections through active and passive case detection.
  • Giving early treatment to patients.
  • Separating patients from others.
• Tertiary stage:
  • Controlling vector populations:
    • Destroying vector breeding and hiding places.
    • Fogging to kill vectors.
  • Enforcing laws by issuing compounds to owners of dirty food premises.
  • Protecting hosts:
    • Using mosquito nets or mosquito coils.
    • Wearing thick clothes.

Body Defence Mechanism

The body defends itself against infections through three lines of defense.

First Line of Defence

• Prevents pathogens from entering the body.
• Includes:
  • Skin: A tough layer difficult for microorganisms to penetrate; sweat and sebum contain chemicals that kill microorganisms.
  • Mucous membrane: Lines the digestive and respiratory tracts; nasal hairs filter microorganisms, and mucous traps them.
  • Earwax, tears, and vaginal secretions: Function as antiseptics that kill microorganisms.

Second Line of Defence

• Fights pathogens that enter the bloodstream.
• Phagocytosis: White blood cells engulf and digest pathogens using enzymes.

Third Line of Defence

• Body immune system.
• Immunity: The ability of the body system to resist pathogens.
• Antibody: A protein produced by white blood cells in response to antigens.
• Antigen: A foreign substance that induces the production of antibodies.

Importance of Immunisation

• Immunisation stimulates the body's defense against infections through vaccines.
• Vaccines contain antigens from weakened or dead viruses or bacteria.
• Antigens stimulate the immune system to form immunity.

Passive Immunity and Active Immunity

Passive Immunity

• The body gains antibodies from external sources.
  • Natural: A baby receives antibodies from breast milk or the mother's blood via the placenta; immunity is temporary.
  • Artificial: An antiserum is injected into the patient's body to fight pathogens; immunity is fast and temporary.

Active Immunity

• The body produces its own antibodies when stimulated by antigens.
  • Natural: Occurs when a person recovers from an infection; immunity lasts long.
  • Artificial: A vaccine (containing dead or weakened pathogens) is injected, stimulating antibody production; immunity lasts long.

Strong Immune System

Causes That Weaken the Immune System

• Exposure to polluted air.
• Exposure to pesticides.
• Stress.
• Excessive intake of sugar.

Practices That Strengthen the Immune System

• Getting enough sleep and rest.
• Exercising and inhaling fresh air.
• Not smoking and avoiding exposure to cigarette smoke.
• Doing periodic health examinations.