Final > Infectious Agents: Viruses Flashcards by Allister Helton

What are the 5 main features of viruses that differentiate them from bacteria?

Obligatory intracellular parasites
Contain DNA or RNA
Contain a protein coat
No ribosomes
No ATP-generating mechanism

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What main replicative feature (used to differentiate bacteria) do viruses lack?

16S rRNA.

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Which bacteria share certain features with viruses but not other bacteria? What are these features?

Rickettsias and Chlamydias are both intracellular parasites and sometimes require a host for ATP generation.

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What is meant by the term “Host Range” with regards to viruses?

The spectrum of host cells a virus can infect.

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What 2 main factors determine the host range of a virus?

Specific host attachment sites

2. Protein-protein interaction

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What is the the size range of a bacteriophage?

20nm to 1000nm in length.

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Are bacteriophages specific to a certain type of bacteria?

Yes.

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What 4 components compose a virion (fully developed viral particle)?

Nucleic acid
Capsid
Envelope
Spikes

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Do all viruses have an envelope? Does influenza virus?

No, some don’t. Influenza does though (N protein).

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What is the name of the subunits which make up the viral capsid?

Capsomeres.

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What does a complex virus look like?

Its the one with the spider legs and polyhedral head. Iconic.

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Viral genus names end in ________.

-virus.

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Viral family names end in ________.

-viridae.

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Viral order names end in ________.

-ales.

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What is the definition of viral species?

A group of viruses sharing the same genetic information and ecological niche (host).

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Regarding a viral life cycle, what does the size of the virus indicate?

A more complex life cycle.

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How are bacteriophages grown in the laboratory? How can they be recognized?

In agar cultures of bacteria. Plaques (clear areas) form around bacteriophages on the agar surface.

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What unit can be used to quantify the presence of bacteriophages in an agar culture?

Plaque-forming units (PFU).

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Approximately what percentage of human infections are caused by viruses?

~20%.

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What must a virus also have it it carries its genetic material as RNA?

Reverse transcriptase.

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What must a virus also have if it carries its genetic material as DNA?

Regular ol’ transcriptase (polymerase).

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Where in a bacterial cell does viral infection occur? What about in eukaryotic cells?

Bacteria: cytosol
Eukaryotes: cytosol or nucleus

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Describe the eclipse period of a viral infection.

The period while the virus is replicating in the cell and before mature virions are released.

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Describe the acute period of viral infection.

When virion release from the cell ramps up and before the immune response takes over.

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What is the difference between the viral lytic cycle and a viral lysogenic cycle?

Lytic: phage causes lysis of cell upon replication Lysogenic: phage DNA incorporated into host DNA and replicates normally

What 5 main steps outline the viral lytic cycle?

1. Attachment 2. Penetration 3. Biosynthesis 4. Maturation 5. Release (lysis)

What term is used to describe the inserted phage DNA before it becomes a new virion?

A prophage. duh.

What is meant by "specialized transduction" with regards to bacterial/viral reproduction?

When a bacteria takes advantage of a phage to spread its genes to other bacteria for reproduction.

With 2 exceptions, RNA viruses reproduce in the cytosol and DNA viruses reproduce in the nucleus. What are these exception?

1. Influenza virus is RNA but reproduces in the nucleus | 2. Smallpox is DNA but reproduces in the cytosol

How are enveloped viruses released from the cell? What about non-enveloped viruses?

Enveloped: budding (endocytosis) | Non-enveloped: lysis

What kind of genome do class I viruses have? What are some examples of viruses in this category?

dsDNA. Ex: Smallpox, Herpes, HPV, Varicella, Epstein-Barr.

What kind of genome do class II viruses have? What are some examples of viruses in this category?

ssDNA. Ex: Parvovirus (non-pathogenic).

What kind of genome do class III viruses have? What are some examples of viruses in this category?

dsRNA. Ex: Rotavirus (non-notifiable) (but Rotavec is a vaccine on the schedule in BC!).

What kind of genome do class IV viruses have? What are some examples of viruses in this category?

ssRNA (+). Ex: Polio, WNV, Zika, Dengue, Hep A & C, Rubella, Yellow fever, Norovirus.

What kind of genome do class V viruses have? What are some examples of viruses in this category?

ssRNA (-). Ex: Measles, Mumps, Influenza, Rabies, Hantavirus, Ebola, Marburg.

What kind of genome do class VI viruses have? What are some examples of viruses in this category?

ssRNA with DNA stage. Ex: HIV, retroviruses in general.

What kind of genome do class VII viruses have? What are some examples of viruses in this category?

Partial dsDNA. Ex: Hep B (has an RNA stage, uses reverse transcriptase).

When was the first retrovirus discovered? By who?

David Baltimore and Howard Timmins discovered the first retrovirus in 1970.

Where in the host cell is the viral capsid synthesized?

In the cytoplasm.

What 2 notifiable diseases belong to class I (dsDNA viruses)?

1. Smallpox (poxviridae) | 2. Chickenpox (herpesviridae)

What does adenoviridae infection cause in humans? What about animals?

Adenoviridae causes respiratory infections in humans and tumours in animals.

What are some examples of poxviridae viruses? What does poxviridae infection cause in humans?

Smallpox, vaccinia, cowpox, monkeypox, camelpox. Causes skin lesions.

What is the origin of vaccinia (a type of poxviridae)?

No one knows for sure!

Why is it important for the variola virus genome to have inverted tandem repeats at both ends? How are these sometimes activated?

To enable circularization/insertion. Sometimes triggered by UV light exposure.

List as many examples of Herpesviridae viruses as you can (HHV-1 to HHV-8).

``` HHV-1 Simplexvirus HHV-2 Simplexvirus HHV-3 Varicellovirus HHV-4 Epstein-Barr virus HHV-5 Cytomegalovirus HHV-6 Roseolovirus HHV-7 Roseolovirus HHV-8 Rhadinovirus ```

What is Kaposi's sarcoma?

A cancer of the connective tissue which presents as reddish purple colour under the skin.

What is an example of a papovaviridae? What does this cause in humans?

Papillomavirus. Can cause warts and transform cells to cause cancer (esp. in women).

How can HPV be implicated in cancer development?

Because one of its early genes binds to p53, a well known oncogene.

What virus covered in class was the only example of a ssDNA virus

Parvovirus B19 (non-pathogenic).

What virus covered in class was the only example of a partial dsDNA virus? What can infection by this virus cause?

Hepatitis B virus. Can cause jaundice.

What differentiates ssRNA (+) from ssRNA (-)?

(+): sense, RNA acts as mRNa and is translated directly. | (-): antisense, transcribed to + strand before translation.

What virus covered in class was the only example of a dsRNA virus? What can infection by this virus cause?

Rotavirus. Non-notifiable but can cause infant diarrhea and mild respiratory infection.

What is a picornavirus?

A large family of small, non-enveloped, cytoplasmic, ssRNA (+) viruses with a capsid. No lipid membrane.

What is the most well known example of an enterovirus (in the family picornaviridae)?

Poliovirus.

What is the most well known example of a rhinovirus (in the family picornaviridae)?

Rhinovirus (common cold).

Besides the rhinoviruses and the enteroviruses, what other prominent virus belongs to the picornaviridae family?

Hepatitis A virus.

What are togaviridae?

A family of enveloped ssRNA (+) viruses with a capsid. (pretty much identical to flaviviridae, but a little bigger)

What differentiates picornaviridae from togaviridae?

Picornaviridae: non-enveloped Togaviridae: enveloped

Into what 2 genera is the togaviridae family divided?

1. Alphavirus | 2. Rubivirus

What 3 viruses are countered by the MMR vaccine given to children? What genotype does it target?

1. Measles 2. Mumps 3. Rubella Target A genotype, though effective against some others.

What are flaviviridae?

A family of enveloped ssRNA (+) viruses with a capsid. (pretty much identical to togaviridae, but a little smaller)

What are 3 examples of viruses belonging to the flaviviridae family (ssRNA (+))?

1. Hepatitis C 2. West Nile virus 3. Yellow fever virus * Both WNV and YFV are transmitted by arthropods. Neat!

How is hepatitis C transmitted?

By blood, sex, pregnant mother to infant, needles, etc.

What virus in the norovirus genus is notifiable, can cause gastroenteritis, and is most common in winter?

Norwalk virus.

What are rhabdoviridae?

A family of bullet-shaped, enveloped ssRNA (-) viruses with a capsid. Must first transcribe mRNA before replication.

What is the only example of a virus in the rhabdoviridae family that was shown in class?

Rabies.

What are the 2 examples of paramyxoviridae that were presented in lecture? What class do they belong to?

1. Measles (morbillivirus) 2. Mumps (rubulavirus) Both are class V ssRNA (-).

What class does hantavirus (family: hantaviridae) belong to? How would this best be treated?

Class V ssRNA (-). Treat with drugs which target polymerase and inhibit synthesis.

What makes the structure of the filoviridae virus family so unique? What is an example of a virus in this family?

A long, enveloped helical virus that's more like a spaghetti than a d20. Ex: Marburg virus, Ebola virus.

In Canada, what is the only notifiable disease from the retroviridae virus family? What class does this belong to?

HIV/AIDS. Class VI ssRNA with a DNA stage.

What do class VI viruses require for replication that class IV viruses do not? Why?

Reverse transcriptase to produce DNA from the viral ssRNA genome for integration into the host chromosome.

What is another way to say "reverse transcriptase"?

RNA-dependent DNA polymerase.

What is HAART? How does it work?

Highly Active AntiRetroviral Therapy (for HIV). Prevents replication and limits viral load.

What is a sarcoma?

A cancer of the connective tissue.

What is an adenocarcinoma?

A cancer of glandular epithelial tissue.

What is an oncogenic virus?

A virus which integrates with the host cell's DNA and induces tumours.

What are some examples of DNA oncogenic viruses?

- Hepatitis B - Hepatitis C - Human Papillomavirus (HPV) - Smallpox (+other pox) - Epstein-Barr - Any retroviruses!

What is a latent virus? What are some examples?

A virus which remains asymptomatic in host cells for long periods. Ex: Herpes, Leukemia, Shingles

What is a persistent viral infection? What are some examples of viruses which can cause these?

Infection over a long period, usually fatal. Ex: Measles, Rubella, HIV, HPV, Hepatitis B

What is Epstein-Barr virus also known as? What condition is it the leading cause of?

Also known as human herpes virus 4. Known to be a primary cause of infectious mononucleosis (mono).