Pathogens and Diseases Overview

Pathogens

• Pathogens cause transmissible diseases.
• Pathogens are spread by direct contact, indirect contact, vectors, food/water contamination, and pollution.
• Examples of pathogens include viruses, bacteria, protozoa, fungi, and worms.

Diseases

• A disease is a state of being uncomfortable.
• Diseases are caused by pathogens and factors such as poor nourishment, genetics, and pollution.
• Poverty can contribute to disease due to lack of access to basic needs.

Classification of Diseases

• Infectious diseases are caused by pathogens.
• Non-infectious diseases are caused by internal factors and not by pathogens.
• Communicable diseases are spread from person to person or animal to animal.
• Non-communicable diseases are not contagious.

Types of Diseases

• Viral diseases: common cold, influenza, SARS, AIDS, dengue, COVID-19.
• Bacterial diseases: Tuberculosis, pneumonia, typhoid.
• Protozoal diseases: Cholera, typhoid, anthrax.
• Parasitic diseases: Malaria, sleeping sickness, worms (Ascariasis, Elephantiasis), fungi (ringworm, aspergillosis, athlete's foot).

Protozoal Diseases

• Amoebiasis, Malaria, Sleeping sickness, and Kala-azar are examples.

Worms

• Ascariasis and Elephantiasis are examples.

Fungi

• Ringworm, Aspergillosis, Athlete's Foot are examples.

Immunity

• The immune system helps protect the body from pathogens.
• Physical barriers include the skin, cilia, and mucous membranes.
• Chemical barriers include stomach acid, saliva, and tears.
• Cellular barriers include macrophages, neutrophils, dendritic cells, natural killer cells, and leukocytes.

Skin's Antibacterial Nature

• The skin contains a protein called dermicidin which is antibacterial.

Antigen vs. Immunogen

• Antigens are proteins or carbohydrates present on the surface of cells.
• Immunogens are non-self antigens that trigger an immune response.
• The immune system differentiates between self and non-self antigens.

Immune Response

• Macrophages and dendritic cells are essential in the immune response.
• Macrophages engulf pathogens, while dendritic cells present pieces of the pathogen (immunogen) to T-cells and B-cells.

Specific Immune Response

• T-cells recognize the presented immunogen.
• B-cells produce antibodies specific to the antigen.
• Antibodies attach to pathogens, making them immobile and easier for immune cells to destroy.

Adaptive Immune System

• The specific immune response is part of the adaptive immune system, which learns and remembers pathogens for future protection.
• Blood groups are determined by antigens on red blood cells.

Cholera

• The cholera bacteria creates a toxin that affects chloride ion secretion.
• This imbalance causes chloride ions to move from the blood to the small intestine.

Campylobacter

• Campylobacter causes food poisoning.
• It is a type of bacteria that is a pathogen.

Modes of Spread

• Airborne transmission: spread through the air by sneezing or coughing. (COVID-19, influenza)
• Water/Food transmission: spread through contaminated water or food. (cholera, typhoid)
• Indirect contact transmission: spread through contact with contaminated surfaces or objects. (conjunctivitis)
• Direct contact transmission: spread through direct contact with an infected person. (ringworm, AIDS, syphilis)

Vectors

• Vectors are organisms that transmit pathogens from sick individuals to healthy ones.
• Examples: Malaria, Dengue Fever, Plague.

Understanding the Body's Defenses

• The skin, mucous membranes, stomach acid, and saliva are physical and chemical barriers that prevent pathogens from entering the body. - The immune system, with its specialized cells, provides a further line of defense.
• The immune system remembers pathogens it has encountered to provide long-term protection.