Comprehensive Study Guide: Viruses, Pathogenicity, Immunity, and Epidemiology (Chapters 13–17)

Chapter 13: Viruses, Viroids, and Prions

13-1: Viruses vs. Bacteria

• Viruses are acellular infectious agents, much smaller than bacteria, and require a host cell to replicate.

• Bacteria are unicellular prokaryotic organisms capable of independent metabolism and reproduction.

• Detection of Viruses: Their small size allowed researchers to infer their existence through filtration experiments before electron microscopy was available.

13-2: Structure of Viruses

• Enveloped viruses possess a lipid membrane derived from the host cell, often with glycoprotein spikes for attachment.

• Nonenveloped viruses lack this membrane and consist only of a protein capsid surrounding the nucleic acid.

• Polyhedral viruses (e.g., adenovirus) have many-sided capsids, sometimes with surface spikes for host interaction.

13-3: Viral Species

• A viral species is a group of viruses sharing the same genetic information and ecological niche.

• Unlike bacterial species, viral species are not defined by the ability to reproduce independently.

13-4: Virus Classification

• Viruses are classified into families (ending in -viridae) and genera (ending in -virus).

• Example: Papillomaviridae (family), Papillomavirus (genus), Human Papillomavirus (HPV) (common name).

13-5 & 13-6: Culturing Viruses

• Bacteriophages are cultured using the plaque method, where clear zones (plaques) indicate lysis of bacterial cells.

• Animal viruses are cultured in living animals, embryonated eggs, or cell cultures. Continuous cell lines are preferred for their longevity and reproducibility.

13-7: Virus Identification

• Techniques include serological tests (e.g., ELISA), nucleic acid analysis (PCR), and electron microscopy.

• To identify influenza virus: use rapid antigen tests, PCR, or viral culture.

13-8 & 13-9: Bacteriophage Life Cycles

• Lytic cycle: Virus attaches, injects DNA, replicates, assembles, and lyses the host cell.

• Lysogenic cycle: Viral DNA integrates into host genome (prophage), replicates with host, may later enter lytic cycle.

• Lysogenic conversion can confer new properties (e.g., toxin production in Vibrio cholerae).

13-10: Animal Virus Multiplication

• Key steps: Attachment, Entry, Uncoating, Biosynthesis, Maturation, Release.

• DNA viruses often replicate in the nucleus; RNA viruses in the cytoplasm.

13-11 & 13-12: Viruses and Cancer

• Oncogenes are genes that can transform normal cells into cancerous cells.

• Provirus: Viral DNA integrated into host genome (e.g., retroviruses).

• RNA viruses (retroviruses) use reverse transcriptase to integrate into host DNA, potentially causing cancer.

13-13 & 13-14: Latent and Persistent Infections

• Latent infections: Virus remains dormant (e.g., herpes simplex, shingles).

• Persistent infections: Virus is continuously present (e.g., HIV).

13-15 to 13-17: Viroids and Prions

• Virus: Nucleic acid + protein coat; infects many organisms.

• Viroid: Small, circular RNA molecules; infect plants (e.g., potato spindle tuber disease).

• Prion: Infectious protein; causes neurodegenerative diseases (e.g., Creutzfeldt-Jakob disease).

• Plant viruses often enter through wounds or via vectors.

• Prions are infectious due to abnormal protein folding.

Chapter 14: Principles of Disease and Epidemiology

14-1: Key Definitions

• Pathology: Study of disease.

• Etiology: Cause of disease.

• Infection: Invasion and growth of pathogens in the body.

• Disease: Abnormal state in which the body is not functioning normally.

14-2 to 14-4: Human Microbiome and Microbial Relationships

• Normal microbiota are permanent residents; transient microbiota are temporary.

• Relationships: Commensalism (one benefits, other unaffected), Mutualism (both benefit), Parasitism (one benefits at other's expense).

• Opportunistic pathogens cause disease when host defenses are compromised.

14-5: Koch’s Postulates

• Set of criteria to prove a specific microbe causes a disease.

• Exceptions: Some microbes cannot be cultured, or cause disease only in humans.

14-6 to 14-9: Disease Classification and Epidemiology

• Communicable diseases spread from host to host; noncommunicable do not.

• Incidence: Number of new cases; Prevalence: Total cases at a given time.

• Acute (rapid onset, short duration) vs. Chronic (slow onset, long duration) diseases.

• Herd immunity: Resistance of a population due to immunity of most members.

14-10 to 14-11: Disease Progression

• Predisposing factors: Age, genetics, climate, lifestyle.

• Stages: Incubation, Prodromal, Illness, Decline, Convalescence.

14-12 to 14-14: Reservoirs and Transmission

• Reservoirs: Human (carriers), animal (zoonoses), nonliving (soil, water).

• Transmission: Contact (direct/indirect), vehicle (food, water, air), vector (mechanical, biological).

14-15 to 14-18: Healthcare-Associated Infections (HAIs)

• HAIs (nosocomial infections) are acquired in healthcare settings.

• Factors: Microbes in hospital, compromised host, chain of transmission.

• Prevention: Hand hygiene, aseptic technique, infection control programs.

14-19 to 14-22: Emerging Diseases and Epidemiology

• Emerging diseases: New or increasing in incidence (e.g., COVID-19, Ebola).

• Epidemiology: Study of disease occurrence and spread.

• Types: Descriptive (patterns), Analytical (cause/effect), Experimental (hypothesis testing).

• CDC: Centers for Disease Control and Prevention; monitors and controls disease spread.

• Morbidity: Illness rate; Mortality: Death rate; Notifiable diseases: Must be reported to authorities.

Chapter 15: Microbial Mechanisms of Pathogenicity

15-1 to 15-3: Portals of Entry and Adherence

• Portals: Mucous membranes (respiratory, GI, urogenital), skin, parenteral route (injury).

• ID50: Infectious dose for 50% of population; LD50: Lethal dose for 50%.

• Adherence: Microbes use adhesins (e.g., fimbriae, spikes) to attach to host cells.

15-4 to 15-8: Evasion of Host Defenses

• Capsules and cell wall components (e.g., M protein) inhibit phagocytosis.

• Enzymes: Coagulases (clot fibrin), kinases (digest clots), hyaluronidase (digests connective tissue), collagenase (breaks down collagen).

• Antigenic variation: Pathogens alter surface antigens to evade immunity (e.g., influenza virus).

• Some bacteria manipulate host cytoskeleton for entry (e.g., E. coli causes membrane ruffling).

• Mechanisms to avoid phagocytosis: Capsules, survival inside phagocytes, inhibition of phagolysosome fusion, escape into cytoplasm, resistance to oxidative burst, etc.

15-9 to 15-14: Pathogenicity Factors

• Siderophores: Bind iron, making it available to bacteria.

• Direct damage: Pathogen physically destroys host cells.

• Toxigenicity: Ability to produce toxins (exotoxins, endotoxins).

• Exotoxins: Proteins, secreted, specific effects, high toxicity (e.g., diphtheria toxin).

• Endotoxins: Lipid A of LPS in Gram-negative bacteria, cause fever and shock.

• Mechanisms: A-B toxins (active and binding components), membrane-disrupting toxins, superantigens, genotoxins.

• LAL assay: Detects endotoxins using horseshoe crab blood extract.

• Plasmids and lysogeny can confer virulence factors (e.g., toxin genes).

15-15 to 15-17: Cytopathic Effects and Nonbacterial Pathogenicity

• Cytopathic effects (CPE): Visible effects of viral infection (e.g., cell lysis, syncytia, inclusion bodies).

• Fungi, protozoa, helminths, and algae cause disease via toxins, tissue damage, or immune modulation.

• Portal of exit: Route by which pathogens leave the host (e.g., respiratory tract, GI tract).

Chapter 16: Innate Immunity: Nonspecific Defenses of the Host

16-1 to 16-2: Innate vs. Adaptive Immunity

• Innate immunity: Nonspecific, present at birth, rapid response (e.g., skin, phagocytes).

• Adaptive immunity: Specific, develops after exposure, memory (e.g., antibodies, T cells).

• Toll-like receptors (TLRs): Recognize pathogen-associated molecular patterns (PAMPs) and activate immune responses.

16-3 to 16-5: First Line of Defense

• Physical barriers: Skin, mucous membranes, cilia, tears.

• Chemical barriers: Lysozyme, low pH, sebum, antimicrobial peptides.

• Normal microbiota: Compete with pathogens (microbial antagonism).

16-6 to 16-7: Leukocytes

• Granulocytes: Neutrophils (phagocytosis), eosinophils (parasites), basophils (histamine release).

• Agranulocytes: Monocytes (become macrophages), lymphocytes (B, T, NK cells).

• Differential WBC count: Proportion of each type of white blood cell.

16-8 to 16-10: Lymphatic System and Phagocytosis

• Lymphatic system: Returns interstitial fluid to blood, filters pathogens.

• Phagocytes: Ingest and destroy microbes (fixed vs. wandering macrophages).

• Phagocytosis stages: Chemotaxis, adherence, ingestion, digestion.

16-11 to 16-14: Inflammation and Fever

• Inflammation: Redness, heat, swelling, pain; functions to contain infection and initiate repair.

• Mediators: Vasodilation (histamine, kinins, prostaglandins, leukotrienes).

• Phagocyte migration: Margination (adhesion to endothelium), diapedesis (movement through vessel wall).

• Fever: Systemic response, inhibits pathogens, enhances immune function.

16-15 to 16-17: Complement System

• Complement: Group of serum proteins that enhance immune responses.

• Activation pathways: Classical (antibody-mediated), Alternative (pathogen surface), Lectin (mannose-binding lectin).

• Outcomes: Opsonization, inflammation, cytolysis.

16-18 to 16-21: Interferons and Antimicrobial Substances

• Interferons (IFNs): Cytokines that inhibit viral replication (IFN-α, IFN-β, IFN-γ).

• Iron-binding proteins: Sequester iron to inhibit microbial growth; pathogens may produce siderophores to compete.

• Antimicrobial peptides (AMPs): Small proteins with broad-spectrum antimicrobial activity.

Chapter 17: Adaptive Immunity: Specific Defenses of the Host

17-1 to 17-2: Adaptive Immunity Overview

• Adaptive immunity: Specific, memory-based; includes humoral (B cells, antibodies) and cellular (T cells) immunity.

• Vaccination is an example of adaptive immunity.

17-3 to 17-4: Antigens and Antibodies

• Cytokines: Signaling proteins (e.g., interleukins, chemokines, interferons, TNF).

• Antigen: Substance that elicits an immune response; epitope: specific region recognized by antibody; hapten: small molecule that becomes antigenic when attached to a carrier.

17-5 to 17-6: Antibody Structure and Classes

• Antibodies are Y-shaped proteins with variable regions for antigen binding.

• Five classes: IgG, IgM, IgA, IgD, IgE; each has distinct functions (e.g., IgG crosses placenta, IgA in secretions).

17-7 to 17-10: B Cells and Clonal Selection

• T-dependent antigens: Require T helper cells for B cell activation.

• T-independent antigens: Activate B cells without T cell help.

• Plasma cells: Produce antibodies; memory cells: Provide long-term immunity.

• Clonal selection: Activation and proliferation of specific B cells upon antigen exposure.

17-11 to 17-14: Antigen-Antibody Reactions and T Cells

• Outcomes: Agglutination, opsonization, neutralization, complement activation.

• M cells: Facilitate antigen uptake in mucosal tissues.

• T helper (TH) cells: Activate B cells and other immune cells.

• T cytotoxic (CTL) cells: Kill infected cells.

• T regulatory (Treg) cells: Suppress immune responses.

• TH1, TH2, TH17 cells have specialized roles (e.g., TH2 in allergies).

17-15 to 17-20: Immune Regulation and Memory

• Apoptosis: Programmed cell death.

• Antigen-presenting cells (APCs): Present antigens to T cells (e.g., dendritic cells).

• Natural killer (NK) cells: Destroy cells lacking MHC I molecules.

• Antibody-dependent cell-mediated cytotoxicity (ADCC): Antibodies direct NK cells to target cells.

• Primary vs. secondary immune response: Secondary (anamnestic) is faster and stronger due to memory cells.

• Types of adaptive immunity: Active natural (infection), active artificial (vaccination), passive natural (maternal antibodies), passive artificial (injection of antibodies).

Table: Comparison of Exotoxins and Endotoxins

Feature	Exotoxins	Endotoxins
Chemical Nature	Protein	Lipid A (LPS)
Source	Mostly Gram-positive bacteria	Gram-negative bacteria
Heat Stability	Unstable (destroyed by heat)	Stable
Toxicity	High	Low
Effect	Specific (e.g., neurotoxin)	General (fever, shock)
Immunity	Stimulate antitoxin production	Do not stimulate immunity well

Table: Types of Adaptive Immunity

Type	Source of Immunity	Example
Active Natural	Infection	Recovery from measles
Active Artificial	Vaccination	MMR vaccine
Passive Natural	Maternal antibodies	IgG crossing placenta
Passive Artificial	Injection of antibodies	Gamma globulin injection

Additional info: Where the original content was brief or in question form, academic context and definitions were added for clarity and completeness. Tables were constructed to summarize key comparisons and classifications relevant to the chapters.