Infection and Host Resistance Notes

There is a close connection between microbes and humans.
- Roughly 50% of human DNA is derived from viruses embedded in ancestors' reproductive cells.
Microbes occupy all body surfaces: skin, gut, and mucous membranes.
- Humans possess approximately 10 times more bacterial cells than human cells.
- The gut microbiome has at least 10 trillion organisms representing over 1,000 species that help prevent colonization by pathogens, synthesize vitamins, break down food, and stimulate the immune system.
Most microbes are non-harmful, establishing as persistent colonists, often providing mutual benefits with their hosts.

Changes in human ecosystems (e.g., population growth, deforestation) increase encounters with potential pathogens.
The global population has grown from 1.6 billion in 1900 to nearly 7 billion today.
Expansion into new environments facilitates contact with unseen pathogens.

Pathogens typically enter the body through:
- Mouth, eyes, nose, urogenital tract, or through breaches in the skin.
Transmission can occur via:
- Direct contact (skin, body fluids).
- Indirect contact (surfaces).
- Airborne droplets (sneezing/talking).

Direct: Includes viruses like herpes simplex and STIs such as AIDS.
Indirect: Could involve touching contaminated surfaces and later touching mucous membranes (e.g., eyes, mouth).

Diseases can spread via evaporation/airborne particles, exemplifying pathogens like measles and hantavirus.

Contaminated food, water, blood can transmit organisms like E. coli and Salmonella.

Infection occurs when microbes enter and multiply in the body.
Illness results when body cells are damaged, presenting symptoms.
Many symptoms (fever, malaise) arise from the immune response targeting the invader.
- Pathogenic strategy includes cellular damage or toxin release that exacerbate immune reactions.

Immunology studies immune system aspects including response to non-self entities (antigens).
Immune response involves the production of antibodies and cellular interactions.

Nonspecific (Innate) Response:
- First line: skin, mucosal membranes (acidity, lysozyme in tears).
- Second line: inflammation, fever, complement activation.
Specific (Adaptive) Response:
- Third line: B and T cell mediated responses.

Inflammation localizes infection, preventing spread and aiding repair.
- Major events involve vasodilation, increased capillary permeability, and white blood cell accumulation.

Body temperature over 37.8°C can slow pathogen growth, stimulate WBC proliferation, and reduce iron availability.

There are two leukocyte types:
- Granulocytes (neutrophils, eosinophils, basophils): contain granules aiding in pathogen destruction.
- Agranulocytes (lymphocytes, monocytes): involved in adaptive immunity.

Active Immunity: Acquired through exposure to antigens.
Passive Immunity: Acquired through antibodies from another individual or mother.

Enhances immune response, lysis of cells, inflammation mediator production, opsonization, and supports antibody-mediated response.

Two branches of immunity: antibody-mediated (humoral) and cell-mediated immunity.
- Humoral Response: Involves B cells and antibody production.
- Cell-Mediated Response: Involves T cells targeting affected cells and tumor cells.

Immunization can either activate an immune response through vaccination or through passive means.
Safety screenings during administration, appropriate dosages, and timing are crucial in vaccination efforts.

Unvaccinated individuals face disease risks leading to long-term health issues or death.

Driven by laws and policies aimed at providing equitable access to vaccinations, influencing public health positively.