How Do Outbreaks Start? Pathogens and Immunology: Crash Course Outbreak Science #2

Summary

This Crash Course Outbreak Science episode explores the human body's defenses against pathogens, including physical barriers like skin and mucus, and the immune system's two lines of defense: the innate response involving cells like macrophages and the adaptive response with B-cells and T-cells. It also touches on how vaccines leverage the adaptive immune system and the challenges pathogens pose, including disease transmission and immune system overreactions.

Takeaways

• 🛡️ The human body has evolved numerous defenses like skin, tear ducts, and hair in nostrils to protect against pathogens.
• 🦠 Pathogens are microscopic organisms like bacteria, viruses, protozoa, fungi, and prions that can cause diseases.
• 🦠 Viruses are unique pathogens that require host cells to reproduce and can cause a wide range of diseases.
• 🌐 Bacteria are single-celled organisms with circular genetic material; some are beneficial while others are pathogenic.
• 🐛 Protozoa are single-celled eukaryotes that can cause diseases like malaria when they enter the human body.
• 🍄 Fungi, including molds and yeasts, can be both beneficial and pathogenic, causing diseases like athlete's foot.
• 🐛 Parasitic worms are pathogenic animals that live inside humans, feeding off what they consume.
• 🧬 Prions are misfolded proteins that can cause other proteins to misfold, leading to diseases like Creutzfeldt-Jakob Disease.
• 🚪 The body has various entry points for pathogens, including obvious holes like mouth and nostrils, and less apparent ones like tear ducts.
• 🛡️ The immune system provides multiple layers of defense, including physical barriers like skin and mucus, and the innate immune system with cells like macrophages.
• 💉 Vaccines leverage the adaptive immune system's ability to remember pathogens, preparing the body to fight future infections more effectively.

Q & A

What is the primary function of the skin in defending against pathogens?

The skin acts as a physical barrier to prevent pathogens from entering the body. It is slightly acidic, which inhibits bacterial growth, and sweat contains enzymes that break down bacterial cell walls.

How do viruses reproduce if they are not considered fully 'living' organisms?

Viruses reproduce by infecting host cells and injecting their genetic material into the cell. They hijack the host cell’s resources to replicate themselves, which can disrupt the body's organs and cause sickness.

What are the main differences between bacteria and viruses?

Bacteria are single-celled organisms with genetic material free-floating inside them, while viruses lack cells and must infect host cells to reproduce. Some bacteria can be beneficial (like those in our gut), while viruses primarily cause illness.

What is the role of the immune system's innate defenses?

The innate immune system acts as a nonspecific barrier to detect and destroy invaders. It includes cells like monocytes, macrophages, and natural killer cells that patrol the body and eliminate pathogens.

What are prions, and why are they dangerous?

Prions are misfolded proteins that can cause other proteins to misfold as well. This leads to severe damage in the organ they affect, such as in Creutzfeldt-Jakob Disease (mad cow disease).

How does the adaptive immune system differ from the innate immune system?

The adaptive immune system targets specific pathogens and has the ability to 'remember' them for quicker responses in future infections. B-cells and T-cells are key components of this system, producing antibodies and destroying infected cells.

What are the most common modes of pathogen transmission?

Pathogens can be transmitted through direct contact with bodily fluids, contaminated surfaces, airborne droplets, contaminated food and water, or by vectors like mosquitoes that inject pathogens into the bloodstream.

Why are memory B-cells and T-cells important in the immune response?

Memory B-cells and T-cells store information about pathogens they have encountered before, allowing for a faster and stronger immune response if the same pathogen invades again. This process is key in preventing reinfection.

What are some examples of pathogens that can be transmitted by vectors?

Malaria, caused by protozoa, is transmitted by mosquitoes, while other vectors like ticks and fleas can transmit diseases such as Lyme disease or plague.

How do vaccines support the immune system?

Vaccines help the immune system by exposing it to a harmless form or part of a pathogen, prompting the body to produce antibodies and memory cells. This prepares the immune system to defend against the actual pathogen in the future.