Pathology: Viruses Flashcards
What defines a virus?
Acellular; no organelles (relies on host cell for replication)
What are the structural components of viruses?
Capsid (protein component); genome; envelope surrounding capsid (in some viruses that is a lipid bilayer)
What is the genome of a virus?
- ssDNA or dsDNA
- circular, ss, or ds
- ssRNA or dsRNA
What are the capsid shapes in viruses?
- Icosahedral
- Helical
- Complex
What are the general steps in the viral replication cycle?
Attachment -> Entry-> uncoating -> viral gene expression (via transcription and/or translation) -> genome replication -> assembly -> maturation and egress
Where in the replication cycle is the most infectious viruses? Least?
Most: assembly and maturation
Least: eclipse (while reproducing)
How are viruses classified?
- nucleic acid genome
- shape/structure
- replication strategy
- disease type
What are the consequences of viral infections in cells?
Lytic infection
Syncytium formation
Hyperplasia
Transformation
Rhinovirus does what to the nasopharyngeal cavities?
Causes lytic infections in the upper respiratory tract
Syncytia formation of viruses happens only with ______ type of virus.
Envelope viruses (HIV is an example)
What does syncytia formation do? How does the immune system react?
Ingrains glycoproteins in the host cell wall that binds them to surrounding cells (syncytia is the fused clump of cells)
-immune system atacc this
Epstein Barr virus and the Papilloma virus cause what type of cell change?
Hyperplasia (especially in cells that should not be replicating)
What is transformation caused by viral infection?
Transformation of regular cells causing true cancer (HTLV is the only known virus that directly causes cancer)
What is the initial clinical presentation of viral infections?
Asymptomatic
What causes acute diseases from viral infection?
Viral replication
What are latent or persistent infections?
Like herpes: has “down time” of replication, then gets activated again, replicates, then infection shows
What are the DNA containing virus families?
- parvoviridae (smallest)
- Polyomaviridae
- Papillomaviridae
- Adenoviridae
- Hepadnaviridae
- Herpesviridae
- Poxyviridae (largest)
What enzyme does a DNA Virus need? Where does it replicate if it does not have one? What do most DNA cells use?
DNA and RNA polymerase; nucleus
-MOST viruses use the host’s DNA/RNA polymerases
What is the target of many antivirals of DNA viruses?
Virus-endogenous DNA polymerase
What kind of DNA does parvoviridae have? Where does it replicate? Does it have its own enzyme? Where does p. B19 replicate?
- ssDNA
- In replicating host cell’s nucleus
- No it doesnt
- RBC to cause fifth disease and fetal death
What kind of DNA does polyomaviridae have? What is the speed of its replication cycle? Does it have its own enzymes?
Circular dsDNA
- slow replication
- uses cell’s enzymes to replicate
What family does JC Virus belong to? What does it cause?
Polyoma virus
Progressive multifocal leukoencephalopathy
What family does the BK virus belong to? What does it cause?
Polyoma virus family
Neuropathy in transplant patients
What family does the merkel cell virus belong to? What does it cause?
Polyoma virus family
Merkel cell skin carcinoma (assoc with the majority of these)(
What are the structural characteristics of the papillomaviridae family?
Genome: small dsDNA (circular)
Non-enveloped
What does papilloma viruses cause?
Wart-like lesions
While there are multiple types, the high-risk variation is assoc with genital cancer
What are the structural components of the adenoviridae family?
- med sized
- linear dsDNA
- fiber-spikes protruding from capsid to aid in attachment to cells
Where are adenoviruses found to cause most infections? What diseases are associated with them?
Mucous membranes and lymphoid tissue
-acute resp distress, conjunctivitis, gastroenteritis
What are the structural characteristics of the hepadnaviridae?
- small enveloped viruses
- circular, partially dsDNA
- lipid and viral surface antigen on envelope
What family is the hepatitis virus in? What does HepB cause?
Hepadnaviridae
Acute/chronic hepatitis and incr risk of liver cancer
What are the structural characteristics of the herpesviridae?
- Large, enveloped viruses
- linear, dsDNA
- latent infection capable
- has its own DNA polymerase***
- has glycoprotein spikes (peplomers)
Where does herpes replicate?
DNA in the nucleus, proteins in the cytoplasm
What is the result of the herpes virus infected cells?
Cytolytic (cells die after spread)
What does EpiBarr virus cause?
Mono (most acute mono infections)
What virus causes chickenpox and shingles? What family?
Varicella-zoster
-herpes family
What virus causes oral and genital lesions (herpes)?
Herpes simplex 1 and 2
What virus causes roseola? What family?
Human herpesvirus 6 and 7
What virus causes kaposi sarcoma?
Human herpesvirus 8
What are the structural characteristics of poxviridae?
- Large, brick shaped
- linear, covalently closed dsDNA
- 100 proteins, large genome
- encodes its own DNA/RNA polymerase
- Replicates in the cytoplasm
What diseases are associated with the pox virus?
Smallpox
Vaccinia
Molluscum contagiosum
Monkeypox
What RNA forms can RNA viruses have?
Double or single strand RNA
Can have multiple segments
How do RNA viruses get RNA polymerase? From host or endogenous?
They HAVE to produce their own (to transcribe mRNA from template and copy RNA genome into new genomes)
Do RNA polymerases have proofreading? If yes or no, whats the impact on RNA viruses?
No; RNA error rates= a lot of mutations and changes in the genome (they mutate a lot and adapt quickly)
What are some characteristics of picornaviruses?
- RNA virus
- Rhinovirus and enterovirus are the branches
- naked
- ssRNA genome
- viral RNa genome undergoes translation upon infection
What pH range does enteroviruses replicate at? Rhinoviruses?
Entero: -3-10 pH (WIDE range)
Rhino: 6-8pH (pretty much physiological pH)
Where do picornaviruses replicate?
In the cytoplasm
Where do enteroviruses primarily infect? Rhinoviruses? At what temps are they most optimized?
Entero: small intestine & 37*C
Rhino: Nasal mucosa & 33*C
What unique translation feature does picornaviruses use?
They can shut off host-cell transcription to take over machinery of cytoplasm of the host cell
What are some clinical syndromes of picornaviruses?
- aseptic meningitis
- encephalitis
- common cold
- Febrile rash illness
- Conjunctivitis
- Herpangina
- Myositis and Myocarditis
- Hepatitis
What are some characteristics of paramyxoviruses?
- negative ssRNA
- Enveloped
What family of viruses does measles and mumps belong to?
Paramyxoviruses
How are paramyxoviruses typically transmitted?
Respiratory route (they can cause respiratory tract infections)
Where does the viral RNA enzymes come from in paramyxoviruses?
They bring them with them into the host cell
What are the characteristics of orthomyxoviruses?
- negative, segmented ssRNA
- Enveloped (w/ surface glycoproteins)
- HAS antigenic variation
What are the two important glycoproteins in orthomyxoviruses? What do they do?
Hemagglutinin: attachment of virus to target cell
Neuraminidase: egress of virus from the infected cell
***change a lot in infections due to high variation
What family does the influenza virus belong to?
Orthomyxoviruses
Where do orthomyxoviruses enter the cell?
Endocytosis
Where does the RNA of orthomyxoviruses travel first? Why?
To the nucleus (unlike most RNA); steals the cap structures of post-cell transcripts to transcribe viral mRNAs
1) mRNAs are more recognizable by host ribosomes
2) disengages host transcription due to lack of capping
*****this is target of many new antivirals
What does antivirals target in orthomyxoviruses?
The RNA polymerase of the ortho
And maturation/release of the virus and genome
What are the characteristics of the reoviruses?
- dsRNA (8-11 segments)
- naked
What are rotaviruses? What family is this in? How does it cause its symptoms?
Most common cause of infantile diarrhea worldwide
- reovirus family
- infects enterocytes and destroys absorptive enterocytes
