Exam 1: Intro to Virology Flashcards

Question

Most **RNA viruses** replicate in the ___ except for ___ and \_\_\_\_.

Answer 1

**cytoplasm** Exceptions: * **Influenza** ⇒ replicates in the nucleus * **Retroviruses** ⇒ integrates DNA copy into host chromosome

Answer 2

* Not present in eukaryotic cells * Viral encoded * Can be _produced within host cells_ for **SS ⊕-sense** RNA viruses * Must be _brought along within capsid_ for **SS ⊖-sense** RNA viruses * **Other viral proteins** may be required as accessory factors for RNA synthesis

Answer 3

Addition of **5' cap** and **3' poly-A tail** required. Neccessary for recognition by host translation machinery.

Answer 4

Poliovirus & West Nile Virus

Answer 5

* **Functions directly as mRNA** * Translated by cellular ribosomes into viral proteins * Can be translated as one large **polyprotein** * Cleaved by viral proteases to make individual proteins

Answer 6

* Parental **⊕ ssRNA** replicated by **viral RNA-dependent RNA-polymerase (RdRp)** * Makes **⊖ ssRNA** * Used by RdRp to make more **⊕ ssRNA** * Serves as additional mRNA for protein synthesis by cellular ribosomes * Packaged into new virions

Answer 7

Influenza & Measles virus

Answer 8

* ⊖ ssRNA ⇒ ⊕ mRNA by viral RdRp * Translated into proteins by cellular machinery

Answer 9

* **⊖ ssRNA acts as a template to make ⊕ ssRNA** * **Virus must carry RdRp within capsid** * Eukaryotes cannot recognize ⊖ ssRNA * **⊕ ssRNA used as template by RdRp** * Makes more ⊖ ssRNA for new virions

Answer 10

Reoviruses & Rotaviruses

Answer 11

* Cannot function directly as mRNA * **Viral RdRp** transcribes a **⊕ mRNA** using **⊖ strand of RNA** as template * **Genome always segmented** * Each segments transcribed to produce a unique mRNA * ⊕ mRNA used by host machinery for protein synthesis

Answer 12

* **Viral RdRp** transcribes a **⊕ ssRNA** using **⊖ strand of parental dsRNA** as template * **⊕ ssRNA** used by RdRp to produce complementary **⊖ strand** * Makes new copies of parental dsRNA

Answer 13

* **Cellular + viral proteins** needed for _viral DNA replication_ * Except poxviruses ⇒ do not use cellular components * **Some use celluar DNA polymerase** * Parvoviruses & Papovaviruses * **Some encode their own viral DNA polymerase** * Adenovirus & Herpes viruses * **Some induce cells to enter into S phase** * Papovacirus & Adenovirus * **Some inhibit cellular DNA synthesis** * Herpes viruses

Answer 14

Parvoviruses

Answer 15

* **Replication occurs in host cell nucleus** * Uses host enzymes * **Viral DNA serves as template for:** * **mRNA** * Translated into proteins by host machinery * **Intermediate dsDNA** * Used as template to make more ssDNA for new virions

Answer 16

* Adenoviruses * Herpes viruses * Papillomavirus * Poxviruses

Answer 17

circular or linear

Answer 18

* dsDNA used by **host RNA polymerase** to make mRNA * mRNA produced **contains exons and introns** * mRNA synthesized using **multiple overlapping reading frames** * Reduces amount of DNA needed to encode viral proteins

Answer 19

* Typically occurs in host nucleus * **Uses either host or viral DNA polymerase** * Smaller viruses use host machinery * Not enough room in the capsid * Ex. Parvociruses & Papovaviruses * Larger viruses code for their own DNA pol * Ex. Adenovirus & Herpes viruses * **Cellular + viral proteins** needed for viral DNA replication

Answer 20

Poxviruses

Answer 21

Ex. retroviruses: * **SS ⊕-sense RNA** acts as template to make **viral DNA** * By viral **RNA-dependent DNA polymerase** (reverse transcriptase) * **DNA integrated into host genome** * Transcribed to mRNA by host machinery * Translated into viral proteins * Used as ssRNA for new virions

Answer 22

* Final steps in viral replication cycle * **Assembly often occurs spontaneously** * Release * **Naked viruses** usually released with **cell lysis** * Can be released through exocytosis * **Enveloped viruses** usually released by **budding** * Some require **further virion maturation** before they acquire infectious potential * Ex. HIV-1 needs proteolytic processing of virion proteins in released particles

Answer 23

**Eclipse period** ⇒ intracellular growth period **Exponential growth period** ⇒ detectable # of viruses significantly increase through cell lysis, exocytosis, or budding **Yield per cel**l ⇒ difference between infectious load and viral count after one round of division

Answer 24

1. **Acquisition** ⇒ entry of the virus into the body of the host 2. **Initiation of Infection** ⇒ binding and entry of the virus into primary host cell 3. **Activation of innate protections** 4. **Incubation period** ⇒ period when the virus is amplified and may spread to a secondary site * **Asymptomatic** * **Prodrome** ⇒ non-specific early symptoms * **Symptoms** ⇒ caused by tissue damage and systemic effects 5. **Replication** ⇒ causes characteristic disease symptoms 6. **Immune response** * Limits infection and clears the virus * May contribute to disease ⇒ **immunopathogenesis** 7. **Contagion ⇒** virus production in tissues that facilitates spread of the virus to other people 8. **Resolution** * Clearance of infecting virus * Or persistent infection/chronic disease ⇒ **viral latency**

Answer 25

1. **Inhalation** 2. **Skin breaks** 3. **Mucous membranes** * Eyes, respiratory tract, mouth, etc * Tears, mucus, ciliated epithelium, stomach acid, bile, sIgA protects

Answer 26

* Enter via **inhalation** * **Most important entry site for viruses** * Some remain localized * Influenza, rhinovirus, coronaviruses * Some spread systemically * Mumps, measles, rubella

Answer 27

* Enter via **ingestion** * **Infections only caused by non-enveloped viruses** * Resistant to degradation by low pH of stomach * Ex. rotaviruses * Some can disseminate beyond the GI tract * Neurovirulent poliovirus * Some other enteroviruses * Coxsackie * ECHO

Answer 28

* **Enter via skin abrasions, animal bite, arthropod vector, injection** * _Only localized viral skin infection_ are warts caused by **papillomavirus** * _Disseminated infections_ caused by: * Herpesvirus * Rabies virus * Hepatitis B, C, D * HIV-1 and 2

Answer 29

* **Causes local lesions on genitalia and perineum** * Herpes simplex * Papillomaviruses * **No local lesions but disseminate to target organs** * Hepatitis B * HIV

Answer 30

* **Plasma membrane receptors** * The more ubiquitous the receptor, the wider the host range * Examples: * Epstein-Barr virus ⇒ CR2 on B cells * HIV ⇒ CD4 on T cells * Rabies ⇒ ACh receptors * **Intracellular proteins** * Use cellular transactivator proteins and enzymes for replication

Answer 31

* **Age** * Most are more virulent in young or old * **Nutrition** * Malnourishment increases susceptibility * **Pregnancy** * Many infections more severe during pregnancy * Likely due to mild immunosuppression * **Genetics** * ∆ host-virus interactions * Certain MHC molecules do not present some viral Ag

Answer 32

**Time difference between infection and first manifestation of disease.** * Short if viral infection localized * Much longer if systemic spread required to reach target organ * Varies enormously due to: * Viral characteristics * Size of inoculum * Types: * Asymptomatic * Prodrome ⇒ nonspecific early sx * Symptomatic ⇒ caused by tissue damage and systemic effects

Answer 33

* Local spread on epithelial surfaces * Subepithelial invasion / Lymphatic spread * Blood transport ⇒ viremia

Answer 34

* Local spread on epithelial surfaces * Replicate in epithelial cells @ site of entry * Spread to neighboring cells * Fluids transport virus along epithelial surface * Shed into the environment

Answer 35

* Gains access through: * Tissue damage * Phagocytosis * Transport past mucoepithelial layers of MM * Picked up by macrophages * Brought to the local lymphatics

Answer 36

**Viremia** ⇒ the first time the virus enters the blood. _Often procedes delivery of virus to target tissues._ * Gains access through: * Tissue damage * Phagocytosis * Transport past mucoepithelial layers of MM * **Transported free in plasma or in WBCs** * Phagocytosed viruses inactivated, replicate, or delivered to other tissues

Answer 37

**Amplification of infection by viral replication in macrophages, endothelium, or liver.** The _second time_ the virus enters the blood after already reaching target tissues.

Answer 38

_Viruses cause disease by:_ * Breaching the body's natural defensive barriers * Evading the host's immune response * Directly killing infected cells * Triggering destructive immune and inflammatory processes

Answer 39

1. ∆ cellular macromolecular synthesis 2. Disruption of lysosomes 3. ∆ cell membrane permeability 4. Toxic effects of viral products 5. Chromosomal aberrations 6. Enhanced necrosis 7. Apoptosis 8. Cell fusion ⇒ syncytia

Answer 40

1. Interaction of the virus with target tissue 2. Cytopathic activity of the virus 3. Host protective responses 4. Immunopathogenesis

Answer 41

1. **Access of virus in the body** 2. **Viral stability** * Temp & pH 3. **Ability to cross skin or mucous epithelial cells** 4. **Ability to establish viremia** 5. **Target tissue type** * Specificity of viral attachment proteins * Tissue-specific expression of viral receptors

Answer 42

1. **Efficiency of viral replication & gene expression** * Optimum temp for replication * Permissiveness of cell for replication 2. **Cytotoxic viral factors** 3. **Inhibition of cellular processes** 4. **Accumulation of vial proteins and structures** (inclusion bodies) 5. **Transformation**

Answer 43

1. **Innate immunity** * IFN, NK cells, Mφ 2. **Adaptive immunity** * T-cells, Ab 3. **Viral evasion of host immune response**

Answer 44

* Interferon ⇒ flu-like systemic symptoms * T-cell responses * Antibodies * Inflammatory responses

Answer 45

* **Necessary to maintain viral infection in populations** * **Occurs at different stages depending on viral infection** * _Localized infections_ ⇒ same body openings for entry and exit * _Generalized infections_ ⇒ greater variety of shedding mechanisms * Nasopharyngeal secretions * Blood * Fecal matter * SKin * _Persistent infections_ ⇒ more common with latent infections, virus continuously made * Urine * Blood * Saliva * Genital secretions * Does not occur when humans are **dead-end hosts** * Rabies * Eastern and western equine encephalitis

Answer 46

The study of the spread of disease through a population

Answer 47

1. **Aerosols** 2. **Food/water** 3. **Fomites** ⇒ contaminated objects 4. **Direct contact with secretions** ⇒ saliva, semen 5. **Sexual contact / birth** 6. **Blood transfusions / organ transplant** 7. **Zoonoses** ⇒ viral disease shared by animals and insects

Answer 48

* Stability of virus in the environment * Replication and secretion of virus into transmissible aerosols * Asymptomatic transmission * Transient or ineffective immune response to control reinfection or recurrence

Answer 49

* Age * Health * Immune status * Occupation * Travel history * Lifestyle * Children in daycare * Sexual activity

Answer 50

The **minimum size** of a closed population within which a **human-to-human, non-zoonotic pathogen** can **persist indefinitely**. Depends on the # of seronegative, susceptible people.

Answer 51

* **Presence of cofactors / vectors** * **Habitat and season for arthropod vectors** * **School session** * Close proximity and crowding * **Home-heating season** * Limited fresh air circulation

Answer 52

* Quarantine * Elimination of the vector * Immunization * Natural infection * Vaccination * Treatment