Infectious Diseases and Immunity

• These study notes cover the topics:
  • Diseases and immunity
  • The difference between non-infectious and infectious diseases.

Unit 5: Diseases and Immunity

5-1: Infectious Diseases:

• Caused by pathogens and their transmission.
  • Similar to the common cold and athlete's foot, infectious diseases result from the transfer of a disease-causing agent from one organism to another, disrupting internal balance.
• Pathogens such as bacteria, viruses, protozoa, fungi, and parasites cause the disease.
• Preventative factors include bacteria and protozoa lining the genitourinary tract, certain bacteria on the skin and in hair follicle passages, which act as barriers against the growth and multiplication of harmful organisms.

Germ Theory and Koch's Experiments:

• Louis Pasteur discovered microorganisms in the air that can grow in nutrient solutions.
• Scientists and physicians began using this knowledge to develop the germ theory.
• The germ theory states that microorganisms cause diseases.
• Robert Koch developed and published Koch’s postulates - experimental steps to prove that an organism can cause a disease.

Koch’s Postulates state:

• Isolate the suspected pathogen from the diseased host at every disease stage.
• Culture the suspected pathogen in a pure culture in lab conditions.
• Introduce the suspected pathogen in a new, healthy host.
• Isolate the suspected pathogen from the new host.

Examples / Exceptions to Koch's Postulates

• Some pathogens, like those believed to cause syphilis, cannot be grown in pure culture and require nutrients.
• Viruses need host cells, therefore they cannot grow in industrial/lab environments.

Sources and Transmission of Pathogens:

• Sources of pathogens exist in the environment and include animals, humans, or non-living materials (e.g., soil).

Types of Sources:

• Human reservoirs are direct or indirect transmitters of illness, even before symptoms appear.
• Animal reservoirs involve vector animals transmitting diseases to humans, like rabies (bats, foxes, raccoons) and influenza (various birds).
• Other reservoirs such as soil with tetanus bacteria cause severe infections if a wound gets contaminated.

Transmission examples include:

• Direct contact with infected individuals.
• Indirect contact through contaminated objects.
• Vectors (living organisms) such as insects transmitting diseases (e.g., Lyme disease, malaria, West Nile fever).
• Air droplets (e.g., sneezing or coughing).

Manifestations and Patterns of Diseases:

• A pathogen invades cells, replicates, and exits through cell rupture or exocytosis.
• Bacteria release toxins or transmit them through the bloodstream, damaging tissues.
• This damage can stop certain organs from working
• The immune system's response triggers symptoms like coughing and sneezing.

Disease Patterns:

• Endemic diseases persist in small amounts: flu
• Epidemics represent large outbreaks in one area and affect many individuals.
• Pandemics are globally widespread epidemics.

Treatment and Management of Diseases:

• Antibiotics are medications that either kill or inhibit the growth of microorganisms, such as penicillin.
• Chemical treatments can target protozoa and fungi, while antiviral drugs treat infections, like the flu for the elderly.

Antibiotic Resistance:

• Bacteria can develop resistance to specific antibiotics through natural selection.
• Bacteria may possess traits for survival in the presence of a specific antibiotic and can transfer those traits to future generations.

Factors enabling resistance:

• Bacteria with resistance to antibiotics create difficulties for treating ailments.
• For example: penicillin is no longer effective for some diseases.
• Staphylococcus infections thriving in high-density living conditions can cause skin infections, pneumonia, or meningitis.
  • These infections are often caused by antibiotic resistant bacteria strains.

5-2: Immune System:

• The immune system has two categories of defence:
  • Nonspecific immune responses - act as the first line of defense which protect against any pathogens encountered.
  • Specific immune responses - respond to specific pathogens that enter.

Nonspecific Immunity:

• Uses physical and chemical barriers include the skin and mucous membranes.
• The skin is the first line of defense barrier made of multiple layers of cells that are covered in dead skin cells:
  • The dead skin cells help prevent microorganisms from entering by creating a barrier and digesting bacteria.

Chemical barriers such as -:

• Lysozyme, enzymes that break cell walls of bacteria and kill pathogens.
• Mucus, secreted by inner lining of the body, acts as a protective barrier that prevents bacteria from attaching to inner epithelial cells.
• Cilia, lining the respiratory tract, remove bacteria away from the lungs, which induces coughing, aiding expulsion.

Defensive cells such as neutrophils and macrophages ingest foreign microorganisms.

• These cells phagocytize pathogens and destroys them:
  • Complements facilitate phagocytosis and help bind pathogens.

Other components include:

• Interferon – a protein released by virus-infected cells and produces antiviral protections, and can increase permeability of blood vessels allowing leukocytes to pass.
• Hydrochloric acid - that can kill microorganisms present in digested nutrients.
• Inflammation - chemical response including vasodilation that attracts phagocytic cells to the injured area.

Lymphatic System:

Functions include:

• Filtering lymph and blood.
• Destroying foreign microorganisms.
• Absorbing fat.
• Lymph – the fluid in the body between tissues and cells that is collected by the lymphatic vessels and returned to veins near the heart.

Main components :

• Lymph nodes filter lymph and remove foreign material
• Tonsils contain protective tissue between the nasal and mouth cavities that protects mouth/nose from bacteria.
• Spleen stores blood, destroys damaged cells, and has lymphatic tissues that respond to foreign entities.
• Thymus gland activates T cells and is above the heart
• Bone marrow is where cells produce.

Key Points of Specific Immunity

• Antibodies (produced in B cells) are proteins that bind to foreign antigens.
• Antigens are foreign substances that trigger an immune response, such as viruses, bacterial components, or toxins.

Immune Response:

Process

• A phagocytic (scavenger) cell ingests an antigen and presents a fragment in the surface.
• A helper T cell binds to the presented fragment, activating the helper T cell.
• The activated helper T cell presents the antigen to a cytotoxic T cell to act together and destroy it.
• The activated helper T cell also presents the substance to a B cell and activates it.
• B cells continue dividing and producing antibodies. - Memory cells remain to act quickly if the body is reinfected

First v. Second Immune Response

• The first response to a pathogen’s invasion is slower with fewer antibodies.
• The secondary immune response occurs if they are invaded with the same infection in which the 2nd response is accelerated and with more antibodies.
• Memory cells ensure a faster response if the antigen is encountered again.

Active and Passive Immunity

Passive immunity

• Transferred antibodies from bodies or injected into a body.
• Examples: maternal antibodies transferred to offspring via placenta or breast milk.

Active immunity

• Developed because of the exposure of antigens to the immune system which then produces memory cells
• Examples: immunization (deliberate exposure to an antigen) and contracting a disease.

Immune System Failure:

• Can leads to infections or a cancer and can lead to AIDS
• AIDS = acquired immunodeficiency syndrome
• Caused by human immunodeficiency virus (HIV)

Details about HIV include:

• HIV is a retrovirus that infects helper T cells (CD4+ cells), converting them into virus factories and releasing new viruses, reducing the person's helper T cell population.
• Without treatment, HIV infection progresses to AIDS.

Treatment and Solutions:

• Treated with antiviral medications that control the number of viruses.
• Problems include resistant strains, expensive drugs, side effects.

5-3: Non-infectious Disorders:

• This will discuss the different types of non-infectious disorders such as genetic disorders, chronic diseases, metabolic diseases.
• Will also discuss diseases such as cancer and autoimmune disorders.

Genetic Disorders:

• Conditions like albinism, sickle cell anemia, Huntington's disease, hemophilia result from genetic mutations.

For example, heart disease can have a genetic cause to it, but it can have environmental risk factors such as diet.

• Affected family history increases risk two to seven times, but known genetic parts aren’t exactly known.

Chronic Diseases:

• Result from harm to a part of the body, possibly to some process.
• Arthritis is the most common by the age of 70 and includes arteriosclerosis or the disease with the stiffening of arteries.

Metabolic Diseases:

• Result from errors in biochemical pathways, leading to inability to digest certain amino acids or regulate bodily functions.

For example, diabetes occurs when body produces low amounts of insulin:

• But, as the glucose cannot properly enter and affects eyesight and kidneys.

Cancer:

• Is unregulated cell growth - normal cells are controlled by cell growth and maintenance.
• There is unregulated cell division and tumors:
  • Can destroy bodily functions and even lead to death.

Causes

• From the past, cancer can be caused by genes or a multitude of other reasons.
• Bone cancer and Egyptian mummies had this same disease, for comparison.

Inflammatory Disorders:

• Diseases where the body has extreme reactions against inflammation to a common substance.
• Examples are allergies and autoimmune disorders.

Allergies:

• Response to environmental antigens (allergens) like pollen, dust, and foods.
• Causes histamine release, leading to swollen eyes, runny nose, and skin rashes.

Autoimmune Disorders:

• Body develops antibodies against its own proteins, harming its cells.
• Examples include: rheumatoid arthritis, rheumatic fever, lupus.