What were the first 2 viral diseases to be investigated, and by who?
rabies by Pasteur;
yellow fever by Walter Reed.
What are viruses and how can they be grown?
Viruses are non-living intracellular parasites that cannot be cultivated in cell-free media. Must be grown in tissue culture, frequently grown in embryonated bird eggs
What is the largest virus?
Poxviruses - 200 nm.
What is a single virus particle called?
Virion.
What is virus genome like?
Either RNA or DNA not both.
Where is the nucleic acid of a virus found at?
enclosed in protein coat called a capsid
nucleic acid + capsid = ?
nucleocapsid
Some viruses have Lipoprotein envelops acquired from where?
Host cell.
Virus envelopes have what for interaction with host cell?
Glycoprotein spikes.
What is a naked virus?
A virus with a capsid but no envelope.
What are the shapes of viruses?
including spherical, bullet shaped, or filamentous
What are the shapes of capsids?
Two primary types of symmetry of capsid 1. helical or 2. icosahedral
What is an agent with no detectable Nucleic acid?
Prion.
What is a prion?
A self replicating protein.
Prions are related to what?
Some scientists believe a relationship to viruses exists
What are prions responsible for?
Responsible for the neurodegenerative diseases classified as spongiform encephalopathies (SE).
Prion diseases cause what?
Diseases cause holes in tissue, brain appears as a sponge
Spongiform encephalopathies caused by prions include what 4 diseases?
SEs include mad-cow disease, Creutzfeldt-Jacob, Kuru, scrapie
How did we learn about virus replication?
Much of our understanding comes from studying bacteriophages (bacterial viruses)
What are the 5 stages of bacterial viral infection (reproduction)?
- Adsorption. 2. Penetration. 3. Prefabrication. 4. Maturation. 5. Viral release.
What is adsorption?
bacteriophage irreversibly adsorbs(stick to the side) to receptor site using tail fibers
What are the different receptor sites for adsorption?
Lipopolysaccharide of Gram neg. cells, pili, & flagella.
What period begins after adsorption and how long will it last?
Beginning of latent period- latent period continues until cell lyses
What is the 2nd step (penetration) like?
phage tail penetrates bacterial cell, nucleic acid enters leaving capsid on outside of host cell.
What period begins after penetration and how long will it last?
Beginning of Eclipse Period – defined as period during which no viral particles can be found either inside or outside cell, viral DNA is taking over machinery of host cell. Lasts UNTIL MATURATION
What is the first thing that happens once the nucleic acid enters the host cell during penetration?
First mRNA is transcribed to code for a repressor enzyme to prevent entry of other phages
What is the second thing that happens once the nucleic acid enters the host cell during penetration?
Second additional enzymes are produced to depolymerize host cell DNA
What does destruction of host cell DNA lead to?
Halt of host cell metabolism, Virus assuming control of host cell metabolism, Viral nucleic acid being assembled using host nucleotides, Use of host cell ribosomes for translation of viral mRNA
What happens during prefabrication?
Viral genome is replicated multiple times, • Necessary viral mRNA is synthesized, • All viral parts are “prefabricated”.
Maturation marks the end of what phase?
Eclipse period because viral particles are now found.
What happens in the maturation phase?
New viruses are assembled.
How do viruses grow?
Viruses DO NOT grow, cells grow, viruses are assembled
Viral release marks the end of what period?
end of latent period because the cell lyses.
After the new viruses are released they do what?
New viruses produce lysozyme
What will lysozyme do?
causes the bacterial cell wall to rupture and viruses are released.
For animal viruses what are the cell receptors like that are involved in adsorption?
Host cell receptors are normal surface molecules involved in routine cellular function
How is adsoprtion done by naked viruses?
capsid proteins bind to host cell receptorscapsid proteins bind to host cell receptorscapsid proteins bind to host cell receptorscapsid proteins bind to host cell receptors
How is adsoprtion done by an envelope viruse?
glycoprotein spikes bind to host cell receptorsglycoprotein spikes bind to host cell receptorsglycoprotein spikes bind to host cell receptorsglycoprotein spikes bind to host cell receptors
How will naked animal viruses do penetration?
Naked viruses undergo a major change in capsid structure on adsorption to plasma membrane, so that their nucleic acids are released into the cytoplasm
How will animal viruses with envelopes do penetration?
two different ways; 1.viral envelope may fuse with the host cell cytoplasmic membrane and the nucleocapsid is released into the cytoplasm. 2. o animal viruses enter by endocytosis whereby the host cell cytoplasmic membrane invaginates and pinches off, placing the virus in an endocytic vesicle. Lysosomes fuse with vesicle and uncoat releasing nucleic acid.
Synthesis of DNA virsuse early synthesis equals what?
host cell is overtaken- viral DNA is synthesized and transcribed to RNA, inhibit host cell DNA, RNA and protein synthesis
Viral DNA replication occurs where?
Viral DNA replication usually occurs in host nucleus (exception = poxviruses are replicated in the cytoplasm)
DNA viruses often do what?
DNA viruses often remain latent in the infected cell
Late and early animal viral genes transcribe DNA into what?
Early viral genes transcribe DNA binding proteins and enzymes, Late viral genes transcribe structural proteins
What are the 4 groups of animal RNA viruses?
Positive strand RNA, Double strand RNA, Negative strand, retroviruses.
With positive strand RNA what is the positive strand used for?
As giant mRNA.
What will the gian mRNA be translated into?
Host ribosome translates giant mRNA into various viral enzymes
With positive strand RNA the RNA polymerase produces what?
RNA polymerase produces a (-) strand RNA
What is the (-) strand used for?
The (-) strand is then used to synthesize more (+) strands to be used as mRNA or to be inserted into new viruses
What do double strand RNA viruses do?
These viruses (reoviruses) have a transcriptase that copies the (-) strand of their genome to generate mRNA
What is the mRNA from double strand RNA be translated into?
mRNA is translated into various enzymes to synthesize new viruses
Negative strand RNA will do what?
A viral transcriptase converts (-) strand RNA to (+) strand RNA
What will the (+) strand RNA made from negative strand RNA do?
The (+) strand acts as mRNA
How will new viruses be made from negative strand RNA viruses?
A viral replicase produces double stranded RNA (+/-) that assembles new viruses
What is the genome of a retrovirus like?
Possess single stranded (+) RNA genome
How will the retrovirus replicate the RNA genome?
Synthesize mRNA and replicate RNA genome by converting RNA to DNA
How will the retroviruse convert RNA into DNA?
Reverse transcriptase converts (+) RNA to (-) DNA
The (-) DNA made from reverse transcriptase will do what?
The (-) DNA is copied to create a double stranded DNA called proviral DNA
Proviral DNA synthesizes what?
Proviral DNA synthesizes (+) RNA genome for new viruses
How are capsids formed in maturation of animal viruses?
Capsid protein synthesis is directed by late genes (structural), Spontaneously self-assemble- capsid around nucleic acid, Location of maturation is virus specific.
How are envelops formed in maturation of animal viruses?
Late viral mRNA transcribes glycoproteins, Glycoproteins are inserted into the host cell membrane, Virus particle acquires the glycoprotein envelope during exocytosis.
How will naked viruses be released from animal cells?
infected cell usually lyses and the virions are released
How will enveloped viruses be released from animal cells?
The cells may or maynot lyse.
How will animal viruses obtain their envelopes?
Virus obtains its envelope by budding from membrane bound organelles within the cell
If the animal cell will not lyse how will the viruses be released?
Transport vesicles carry the virus to the cell surface where it is released by exocytosis
What are persistant viral infections?
persistent infections are those in which the virus is not cleared from the host following primary infection, but remains associated with specific cells
What is transformation of a viral infection?
some DNA viruses and retroviruses establish persistent infections that stimulate uncontrolled cell growth causing transformation or immortalization of the cell (cancer cells)
What is immunological escape of viruses?
many viruses have evolved systems of immunological escape to evade detection ie herpes viruses escape detection by integration into host cell DNA
What is the leading cause of Human viral diseases?
Influenze and cold viruses.
What is the second (second to influenze and cold viruses) leading cause of human viral diseases?
Herpes viruses.
What is the most common cause of viral congenital disease?
Cytomegalovirus (CMV).
What is unique about papulae found with the chicken pox?
They are found on the scalp.
Why should you not scratch chicken pox papulae?
can cause bacterial superinfection
When can chicken pox infections be serious?
Major problems may be caused by infection in utero during the first trimesterMajor problems may be caused by infection in utero during the first trimester
What is a treatment for chicken pox?
Chemotherapy includes: various nucleotide analogs
Why will HSV 1 and HSV 2 infect different areas of the body (HSV1 above waiste and HSV2 below waiste)?
this reflects the mode of transmission not ability of virus to cause disease
When will people with genital herpes be infectious?
Whether there is an apparent active disease or not, an infected patient remains infectious without overt symptoms
What are the 2 types of treatment mentioned for herpes simplex viruses?
- Patient counseling. 2. Drugs.
What are the drugs used to treat herpes simplex virus?
Acyclovir (valacyclovir, famciclovir …) both oral and topical.
How will the drugs used to treat herpes simplex virus work?
Acts as nucleotide analog, inhibits DNA polymerase. No action against latent infection. Does reduce symptoms.
What type of viruses are amoung the most resistant known?
Paroviruses.
What is Sub-acute sclerosing pan encephalitis ?
progressive neurological disorder characterized by inflammation of the brain
Congenital infections of Togaviridae (rubella aka german measles) infants can infect others for how long?
Congenital infections can infect others after birth for a year
What causes smallpox?
Variola virus
What causes cow pox?
Vaccinia virus
What is Orf?
Orf is a viral pox infection of the skin contracted from sheep and goats
Diagnosis- chickenpox and shingles, what is the main thing to look for?
“giant cells” with inclusions
What is Herpetic Whitlow?
Herpes infection of fingers and hands
Diagnosis of EBV main dx?
Atypical white blood cells - Downey cells
Are Adenoviruses enveloped?
NO!
What are Koplik’s spots?
Koplik’s spots on mucosal membranes small (1 - 3mm), irregular, white spots, with bluish halo
What disease causes Koplik’s spots?
Measels (Rubeola)
Paramyxoviruses – Rubeola (measles) and mumps, parainfluenza (DESCRIBE SHAPE & NUCLEIC ACID)
- Enveloped, negative strand (-) RNA viruses
* “Helical” symmetry
Togaviridae- rubella (German measles). (DESCRIBE SHAPE & NUCLEIC ACID)
- Positive strand (+) RNA virus
- Enveloped
- Icosahedral symmetry
- Only member of the Rubrivirus genus of the Togavirus family
“Slapped cheek”= erythema infectiosum is a rash caused by what virus?
Human Parvovirus
Human Papillomavirus, describe shape.
- Wart-causing viruses
- Naked dsDNA virus
- Icosahedron capsid symmetry
Human herpes virus 6 causes what?
Causes roseola infantum (sudden rash, 3 day fever, rose rash, 6th disease)
Human herpes virus 7 causes what?
o HHV 7 causes NO known disease
What is HHV 8?
Formerly known as Kaposi’s sarcoma associated herpes virus and is found in the saliva of many AIDS patients
Adenoviruses describe shape and nucleotide.
- Non-enveloped viruses
- Genome is made of double-stranded DNA
- Capsid is icosahedral with 12 penton fibers
What is the shape of HPV?
Naked ds Isocohedral
What is the shape of the polyoma virus?
Naked ds Isocohedral
Polyoma & HPV are what kind of viruses?
Papovaviridae
