Infection and Infectious Diseases

Definition: Infectious diseases are illnesses caused by specific infectious agents (e.g., bacteria, viruses) or their toxic products. They arise from the transmission of these agents from an infected individual, animal, or environment to a susceptible host, either directly or through intermediaries.

Viruses: Non-cellular entities that infect host cells to replicate and spread.
Bacteria: Single-celled microorganisms that can be pathogenic.
Fungi: Eukaryotic organisms that can cause infections in humans.
Parasites: Include protozoa, helminths, and arthropods, all of which can establish infections.
Prions: Infectious proteins that cause neurodegenerative diseases.

Describes the interaction between host, agent, and environment:
- Human Adaptation: Humans evolve and adapt to infectious agents.
- Pathogen Adaptation: Infectious agents evolve and mutate.

Most infections in humans stem from animal sources, highlighting the importance of understanding zoonotic (animal to human) transmission.
Spillover: Refers to the transmission of a pathogen from an animal to a human population that has not been previously exposed.

Comprised of three lines of defense:
1. First Line: Physical and chemical barriers to prevent entry (e.g., skin, mucous membranes).
2. Second Line: Innate immunity, which is non-specific and includes inflammation and phagocytosis. This provides an immediate response but lacks memory.
3. Third Line: Adaptive immunity, which is specific and includes T-cells and B-cells that provide long-term protection and memory against pathogens.

Cellular Response: Mediated by T-cells; involves direct attack on infected cells.
Humoral Response: Mediated by B-cells; produces antibodies that neutralize pathogens and support immune response.

As individuals age, their immune response may weaken, leading to increased susceptibility to infections.
Factors contributing to immunosenescence include stress, sleep deprivation, and chronic inflammation.

The rates of STIs such as chlamydia, gonorrhea, and syphilis have been rising in Canada.
Chlamydia: Most prevalent STI, transmitted by sexual contact, can be treated effectively.
Gonorrhea: Known for developing antimicrobial resistance, presents significant public health challenges.
Syphilis: Increasing rates among reproductive-age females pose risks for congenital syphilis.
- 2022 reported cases for infectious syphilis reached 13,953 (36.1 cases per 100,000 population).

Defined as the resistance of infectious agents to standard antimicrobial treatments, making infections harder to treat.
Globally Significant: AMR is projected to contribute to millions of deaths annually and is seen as a major public health threat.
Consequences: Extended hospital stays, increased healthcare costs, and severe health complications.

Employing Antimicrobial Stewardship is crucial in controlling the misuse of antibiotics, including:
- Using the Shortest Effective Duration of Therapy: Limiting the length of antibiotic courses can help reduce resistance development.

Understanding infectious diseases, their transmission, and how to strengthen immune responses is vital in public health efforts to combat outbreaks, especially in the context of rising STIs and AMR challenges.