Final Exam SG Pt .2

BIO 220

Basic characteristics of all viruses:

1. Extremely small

2. Acellular

3. Cannot metabolize, grow, or reproduce without the aid of a host

Nucleic acid

DNA or RNA, most are single-stranded RNA; codes for replication, assembly, timing, host defense modulation, spread

Capsid

protein shell (made of capsomers) enclosing nucleic acid;

shapes: helical, polyhedral, complex

protects nucleic acid, allows attachment to host cells, allows entry/injection into host cell

Nucleocapsid

nucleic acid + capsid together

Envelope

only apart of some viruses; lipid bilayer surrounding nucleocapsid; obtained from host cell membrane during budding, but with virus's own proteins

Enzymes

only apart of some viruses; polymerases (make DNA/RNA) or replicases (copy RNA)

Spikes (ligands)

glycoproteins on envelope that attach to host cell receptors

Virion

the entire intact virus particle

6 steps of viral reproduction in animal cells:

1. Absorption

2. Penetration (entry)

3. Uncoating

4. Replication & Protein production (synthesis)

5. Assembly

6. Release: Budding and Lysis

Antigenic Drift

H and N spikes gradually change structure over time; immune system less able to recognize them; reason we need a new flu vaccine each year

Antigenic Shift

a MAJOR change in RNA sequence/spikes due to genetic reassortment between 2+ species; responsible for global pandemics

Hemagglutinin (H)

helps virus attach to target cells (ciliated respiratory epithelial cells)

Neuraminidase (N)

breaks down protective mucous coating, helps virus fuse with and enter host cell

Antiviral drugs

must target processes/structures uniquely viral (not shared with host cells), because viruses share many metabolic mechanisms with the host cell — if the drug hit host processes too, it would be toxic to the patient

5 possible modes of action for antiviral drugs:

• Inactivate extracellular virus particles

• Prevent viral attachment and/or entry

• Prevent replication of the viral genome

• Prevent synthesis of specific viral protein(s)

• Prevent assembly or release of new infectious virions

What are the 2 types of immunity?

Innate and Acquired

Innate immunity:

1st line (Physical barriers): skin, mucous membranes, cilia, hair, defecation/vomiting

1st line (Chemical barriers): lysozyme, gastric juices, saliva, skin acidity, sebum

2nd line (Bloodborne): Inflammation, Complement, Phagocytosis & Degranulation, NK Cells & Interferon

Acquired immunity:

• 2 parts: Cell-Mediated Immunity (CMI) — Helper T cells, Cytotoxic T cells (CTLs), Regulatory T cells

• Humoral Immunity — B cells, Antibodies

Primary immune response (1st exposure):

antigen binds a B cell receptor; takes several days to produce enough IgM → slow response

Secondary immune repsonse (2nd exposure, same antigen)

memory B cells rapidly recognize antigen, multiply, become plasma cells, produce IgG → fast and effective response

Cell-Mediated Immunity (CMI):

• APC presents antigen with MHC Class I → activates CD8+ T cells → become Cytotoxic T cells (CTLs) → kill virus-infected cells, cancer cells

• APC presents antigen with MHC Class II → activates CD4+ T cells → become TH1, TH2, or Treg cells

Humoral Immunity:

TH cells release interleukins → activate B cells → B cells become Memory B cells (long-lived, fast 2° response) or Plasma B cells (produce antibodies)

IgM

largest; 1st antibody produced in a new response; slow; activates complement

IgG

produced during 2nd exposure; fast response; only antibody that crosses the placenta; most abundant in blood

IgA

primary antibody in mucosal secretions

IgE

produced in allergies, anaphylactic shock, asthma

IgD

function unknown; acts as B cell receptor

T cells:

Helper T cells, Cytotoxic T cells, Regulatory T cells

Helper T cells (TH)

secrete interleukins to activate B cells (antibody production) and instruct Cytotoxic T cells

• TH1 — CMI, intracellular pathogens, inflammation, activates B cells for antibody production

• TH2 — parasitic infections, allergies, asthma

Cytotoxic T cells (CTLs, CD8+)

kill virus-infected cells and cancer cells

Regulatory T cells (Treg)

regulate immune system, maintain tolerance to self-antigens, suppress/downregulate other T cells, prevent autoimmune disease

B cells

• produce antibodies (humoral immunity)

• Can also present antigen to T cells

• Split into Memory B cells (long-lived, fast 2° response) and Plasma B cells (produce 1 of the 5 antibody classes)

Pathology

study of the cause (etiology) and development (pathogenesis) of disease

Infection

invasion/colonization of pathogenic microorganisms into the body

Disease

abnormal state where all/part of body isn't functioning properly (can be acute or chronic); infection can exist without detectable disease

Symptoms

subjective changes (pain, malaise, discomfort)

Signs

objective, measurable changes (fever, inflammation)

Syndrome

specific group of symptoms/signs associated with a particular disease

Communicable disease

spreads from host to host (ex. cold, TB, STDs)

Contagious disease

easily spread person to person (ex. flu, chicken pox, AIDS, hepatitis)

Noncommunicable disease

not spread host to host; caused by normal flora or bugs that only cause disease upon entry (ex. Clostridium tetani)

Endemic disease

constantly present in a population (ex. malaria, cold)

Epidemic disease

present for a short time in a given area (ex. flu, chicken pox outbreak)

Pandemic disease

epidemic present worldwide (ex. AIDS, flu at times)

Septicemia

bacteria multiplying in blood

Toxemia

toxins present in blood (ex. tetanus, toxic shock, E. coli food poisoning)

Viremia

viruses in blood

Normal microbiota/flora

permanently colonize body, don't normally cause disease; opportunistic pathogens = normal flora that cause disease in an abnormal body location

Transient microbiota/flora

present temporarily (hours-months), then disappear

Whats NOT used to identify the bug?

Koch’s postulates

Steps of Koch’s postulates in order:

1. Same pathogen must be present in all cases of the disease

2. Pathogen must be isolated from the diseased host and grown in pure culture

3. Pathogen from pure culture must cause the disease when introduced into a healthy, susceptible animal

4. Pathogen must be re-isolated from the inoculated animal and shown to be the same original bug

Nosocomial infection (HAI)

hospital-acquired infection; primarily caused by E. coli, Pseudomonas, and S. aureus

Most common type of HAI:

urinary tract infections; 2nd most common: surgical incision infections

Best prevention for HAI:

hand washing — the #1 method for controlling nosocomial infections

Reservoir of infection

continuous source that allows an infection to be perpetuated; can be human, animal, or nonliving

Zoonosis

transmission of an infection from an animal host to a human

Ways people are infected (transmission types):

• Direct — transfer of bodily fluids (blood, semen, saliva)

• Indirect — via a fomite (inanimate object like a cup, tissue, bedding)

• Droplet — sneezing, coughing, laughing, talking; droplets travel <1 meter

• Vehicle — spread through a medium (food, water, air); airborne transmission lets the bug stay in the air a long time

• Vector — spread through insect bites/contact