Viral Structure, Replication and Pathogensis Flashcards
What are the classifications of viruses?
Polio Rota Human papillo Adeno Semliki Influenza Paramyxo Smallpox
What is virology?
Scientific study of viruses and disease they cause
What is a virus?
Infective agent typically consisting of a of a nucleic acid in a a protein coat
Obligate intracellular parasite that depends on the host for reproduction
How are viruses similar to living organisms?
Proteins and glycoproteins
Nucleic acid
How are viruses different from living organism?
No polysaccharides, small molecules or ions
If they are lipid they are only enveloped
No ribosomes
Do antibiotics work against viruses?
No
Does a virus contain DNA and RNA?
No they can only have DNA or RNA, never both
What are possible structures for DNA viruses?
Single or double strand
Linear or circular
Open or closed
Continuous or nicked
What are some possible structure for RNA viruses?
Single or double strand
Linear
Possible segmentation
Single strand may be plus or minus sense
What are the steps to name a virus?
- Structure: size morphology and nucleic acid
- Biochemical characteristics: structure and mode of replication
- Disease
- Means of transmission:
- Cell, tissue or organ
- Host cell range
What a virion?
Structurally complete infective virus particle
What is a capsid and what are capsomeres?
A protein shell that encloses the nucleic acid
Capsomeres are units on the surface in clusters
What is a nucleocapsid?
Capsid along with the inside nucleic acid
What is the tegument of a virus?
Proteinaceous material between envelope and capsid
If a virus is said to have an icosahedral shape, what does it look like?
Rigid and uniform structure
ex. Multiside hexagon
If a virus is said to have a helical shape, what does it look like?
Swirly squiggly
A naked virus…
Protects viral genes from inactivation by adverse environments
Packaged, protect and deliver genome
Mediate attachment (VAP)
Release by cell lysis
An enveloped virus…
Has a lipid bilayer with embed proteins More susceptible to chemical agents Determines host cell specificity and penetration Facilitates attachment Released by budding
A virus is icosahedral naked. What types of genome does it have?
dsDNA, ssDNA, dsRNA, ssRNA
A virus with an icosahedral shape and is enveloped has what types of genome?
dsDNA, dsRNA, ssRNA
A virus has a helical shape and is naked. What are its genomes?
dsDNA, ssDNA, ssRNA
An enveloped helical virus is found. What genome will it have?
ssRNA
What are the 2 types of exceptions to viral symmetry?
Complex viruses: poxvirus and bacteriophages
What is tropism?
Factors that affect host range
What are some factors that allow viruses to enter cells?
Can use more than one receptor or many viruses use the same receptor
What are the most common routes of entry for a virus?
Blood and bodily fluids Insect bites Respiratory GI Direct contact
What are some viruses that enter through blood or fluid?
CMV, EBV, HBV, HCV, HIV
If an insect bites you, what viruses could it transmit?
Dengue, EEEV, WEEV, West Nile
Oh no! You touched a surface covered in viruses! What could viruses could you get?
HSV, smallpox, VZV
Viruses that can be inhaled are:
Small droplets: influenza, measles, smallpox, VZV
Large droplets: adenovirus, parainfluensa, parvovirus, smallpox
Direct to secretions: RSV, rhinovirus
What viruses can be transmitted through the GI tract (facal-oral)?
Enteric adenovirus, HAV, norwalk virus, polio, rotavirus
What the main routes for viral spread?
Hematogenous spread
Neural spread
Muliple pathways
In hematogenous spread, what does it mean when primary replication proceeds initial viremia?
There are asymptomatic for prodromal symptoms (Enteric or respiratory viruses)
Dissemination to other tissues leads to amped up secondary viremia
In hematogenous spread, what viruses travel freely or with other cells?
Enteroviruses, HBV, tagoviruses (free)
Rift valley fever, Colorado tick fever (RBCs)
CMV, EBV, HIV (lymph or monocytes)
In the neural spread of viruses, where can entry happen?
Near the CNS and then spreads
It can be near synaptic endings, motor neurons, sensory neuronsm infection of schwann cells and olfactory rods
(HSV, rabies, VZV)
What are the basic steps of entry of an enveloped virus?
Attachment to cell receptors
Penetration of host cell by fusion protein
Merging of viral envelope and cell membrane
What are the full steps to viral mutliplication?
Attachment/ absorption Penetration/ entry Uncoating/ release of nucleic acid Relication Assembly Release
When is the viral titer stable?
During the period of attachment
When is the viral titer unstable?
Eclipse phase: diassembly, transcription, translation, and genome replication
When does the titer increase?
As the viral progeny are assembled and are infectious
Which types of viruses make use of their own viral RNA polymerase for replication?
ssRNA+, ssRNA-, all dsRNA
Which types of viruses use viral host RNA polymerase?
Hepadnavirus
Retrovirus (also needs viral reverse transcriptase)
What viruses use viral RNA polymerase for protein synthesis?
ssRNA- and dsRNA
What viruses use host RNA polymerase for protein synth?
Hepadnavirus, ssDNA, dsDNA
Which viruses use host DNA polymerase for replication?
ssDNA
dsDNA (can also use viral DNA pol)
During early transcription of DNA viruses what is necessary?
Regulatory proteins
What is needed during late transcription of DNA viruses?
Structural proteins
What type of cycle is an acute viral infection and how does it cause infection?
Lytic cycle
Multiple rounds of replication resulting in cell death
Many progency viruses produced and released
(ex. polio or influenza)
What type of cycle is a chronic viral infection and how does it cause infection?
Non-lytic, productive
Undergoes replication and shedding that continues even after acute illness ends
+/- symptoms and cell injury
Continue infecting
Can be localized (warts) or systemic (HIV)
What is a latent viral infection?
No replication until signaled
Limited to macromolecules
Genetic material: incorporates into cell or host genome
DNA virus or retrovirus
How does a latent infection transform into an active one?
Malignancy of host cell
Invasive growth
Benign or cancerous growth
In the prodrome phase of an actue viral infection what cytokine is active?
IFNgamma
In the classical sign phase of an acute infection what immunoglobulin is active?
IgM (if primary infection)
In the recovery phase of an acute infection what immune cells and immunoglobulin are active?
CD4+, CD8+, IgG
What is a nonenveloped single stranded linear DNA virus?
Parvovirus
What is a nonenveloped double strand linear DNA virus?
Adenovirus
What are nonenveloped double strand circular DNA viruses?
Papillomavirus
Polymavirus
What are enveloped double stranded linear DNA viruses?
Herpesviruses
Poxvirus
What is an enveloped double stranded circular DNA virus?
Hepadnaviruses
What are nonenveloped single stranded positive sense RNA viruses?
Astroviruses
Caliciviruses
Picornaviruses
What are nonenveloped double strand RNA viruses?
Reoviruses
Rota viruses
What are enveloped single strand positive sense RNA viruses?
Togavirus
Flavivirus
Coronavirus
What are enveloped single strand negative sense linear RNA viruses?
Rhabdovirus
Paramyxovirus
What are enveloped single strand negative sense segmented RNA viruses?
Arenavirus
Bunyavirus
Orthomyxovirus
What are enveloped retroviruses (RNA)?
Lentivirus
Oncovirus
