Understanding Pathogens: Fungi and Viruses

• The immune system protects the body from disease by destroying foreign substances like pathogens, thus maintaining overall health.

Pathogens

• Pathogens include fungi, parasites, viruses, and bacteria.
• Virulence refers to the severity of a disease's symptoms.
• R naught (R0) indicates the average number of people an infected individual will spread a disease to.

Fungi

• Fungi obtain nutrients from our cells or release toxins and can cause diseases like athlete’s foot.
• Athlete’s foot is transmitted through contact with infected surfaces and can be treated with antifungal medication.

Viruses

• Viruses attack specific cell types.
• Viruses are the smallest form of pathogen, consisting of genetic material wrapped in a protein coat (capsid).
• Viruses require a host cell to reproduce, attaching to the cell surface using proteins on their capsid or envelope and tricking the cell into endocytosis.
• Replication can damage, kill, or change the infected cell, with new viruses leaving to infect more cells.

Bacteria

• Bacteria are unicellular prokaryotes that obtain nutrients from our cells or release toxins.
• Bacteria reproduce asexually through binary fission, resulting in exponential growth.
• During binary fission, bacteria copy their DNA (plasmids and DNA strand), move the DNA to opposite sides of the cell, and grow a new cell wall down the middle to split apart.
• Plasmids are arranged randomly during binary fission, so one daughter cell might get more or less of them

Binary Fission Math

• To calculate the number of bacteria after a certain time: divide the total time by the division time to find the number of division cycles, then raise 2 to the power of the number of cycles.

Parasites

• Parasites steal nutrients or eat cells, as exemplified by hookworms and tapeworms.

Spread of Pathogens

• Infectious diseases spread through:
• Direct contact: Close contact between people (e.g., HIV/AIDS, Hepatitis B, Herpes).
• Contamination: Bacteria spread through contaminated water (e.g., Cholera).
• Airborne transmission: Tiny droplets released into the air through sneezing or coughing are inhaled (e.g., Measles, Tuberculosis, Chickenpox, common cold, flu).
• Indirect contact: Contact with contaminated substances or items like needles (e.g., ringworm).
• Vectors: Living organisms transmit pathogens to humans (e.g., Malaria, Lyme Disease).
• Disease spreads faster with increased global travel, poverty, limited access to safe food and water, high population density, population mixing, and poor hygiene.
• Prevention includes washing hands with soap for 20 seconds, sneezing or coughing into the elbow, and getting recommended vaccines.
• Zoonotic viruses mutate to bind to receptors in human cells, enabling the jump from animal to human.

Immune System Protection

• The first line of defense includes physical barriers like skin, mucus (membranes), and the cornea.

2nd Line of Defense

• The second line of defense involves non-specific WBCs called macrophages, which engulf pathogens through phagocytosis and break them down with enzymes stored in lysosomes.
• Macrophages are a part of the inflammatory response

3rd Line of Defense

• The third line of defense is the specific or adaptive immune response, targeting previously encountered pathogens.
• Leukocytes (WBCs) include lymphocytes (B and T cells) and phagocytes (macrophages).
• B cells have receptors that recognize specific antigens on pathogens, marking them with antibodies for T cell destruction; some B cells become memory cells.
• When the immune system responds, WBCs (B and T cells) work together to destroy pathogens, causing clumping and symptoms or death.
• Stem cells are unspecialized cells that produce specialized cells like WBCs in bone marrow.
• Foreign materials include allergens, pathogens, and organ transplants.
• Allergies occur when WBCs identify harmless substances as foreign and produce antibodies to attack them, leading to symptoms.

Immune system organs and tissues

• Lymph nodes filter bacteria and viruses, which are then destroyed by WBCs.
• The spleen filters blood and stores platelets and WBCs.
• The thymus is where T cells mature into disease-fighting cells.
• Bone marrow contains stem cells that mature into WBCs, RBCs, and platelets.
• The appendix's function is theorized to be as a storage site for good bacteria.

Vaccines

• Vaccines expose the body to dead or weakened pathogens.
• Vaccines provoke an immune response, leading to antibody production and immunity upon encountering the real pathogen.
• Immunocompromised individuals, newborns, and pregnant women may not be able to receive vaccines, relying on herd immunity.
• Herd immunity benefits even those not immunized when enough people are vaccinated, reducing outbreaks.
• Booster shots remind the immune system of pathogens, leading to a stronger and faster response if exposed again.
• Antibody numbers can decrease over time, reducing immunity, and viruses can mutate, changing their antigens.

Antibiotics/Antibiotic Resistance/Mutations

• Antibiotics target bacteria, interfering with cell wall formation and reproduction.
• During reproduction, the cell wall is destroyed and therefore the cell dies.
• Mutated bacterial cells can take over as other cells die due to antibiotics.
• Natural selection favors organisms with traits better suited to their environment, leading to the transmission of advantageous traits to offspring and population change over time.
• Probiotics like yogurt and kimchi are recommended during antibiotic use to replenish good bacteria.

Mutations

• During binary fission, bacteria make a copy of their DNA, leading to a higher chance of mutation.
• Bacteria compete for resources, and some mutations enable them to produce antibodies to kill other bacteria.
• Mutations are passed on during reproduction.
• Antibiotics give mutated bacteria an advantage by eliminating regular bacteria, allowing mutations to multiply, increasing chances for more mutations and antibiotic resistance.

Organ Transplants

• Organ transplants involve replacing damaged or missing organs from healthy donors with similar blood types.
• The body may recognize the transplanted organ as foreign, leading to an immune response and organ rejection.
• Immunosuppressants are administered to suppress the immune system and prevent organ rejection which can lead to a weakened immune system.

Learn about pathogens, including fungi and viruses, and how they affect the body. Explore fungal infections like athlete's foot, their transmission, and treatment. Discover how viruses attack specific cells and replicate within a host.