Schein - + Strand RNA Viruses Flashcards
Which viruses are not enveloped of the positive strand variety?
Picornaviridae
Caliciviridae
Which viruses are enveloped of the positive strand variety?
Flaviviridae
Togaviridae
Coronaviridae
Within picornaviridae there is one subclass called enteroviruses and another called rhinoviruses. What is the difference between the two?
Entero - 37 degrees, acid stable, affects GI
Rhino - 333 degrees, acid labile, nose
Of the enveloped viruses, which two classes are arboviruses?
Togaviridae
Flaviviridae
Common features of positive strand RNA viruses?
Replicate in the cytoplasm
Genomic RNA serves as a message and is translated
Genomic RNA is infectious
Virions don’t contains any enzymes but rather viral proteins are translated as polyproteins from the mRNA transcript and then cleaved by proteases
General features of poliovirus
- small, naked, icosahedral virus
- positive sense
- virus contain 4 different proteins - VP1, VP2, VP3, VP4
- 3 serological types - because there are only three we can make vaccines against it.
Special features of viral RNA
- genetically encoded polyA sequence at the 3’ end
- there is no 5’ cap on the RNA
- instead of a 5’ cap there is a small virus-encoded peptide called VPg, which is covalently bound to the 5’ end of the viral RNA.
- After VPg there is a long 5’UTR. In it is what is called the IRES - internal ribosomal entry site.
IRES
Within the 5’UTR of viral RNA. The ribosomes see the IRES and attach to it rather than the AUG of normal cellular RNA. No 5’ cap necessary, just VPg.
How does the poliovirus get replicated/get into the the cell
Attaches to a specific receptor and then enters the cell via receptor-mediated endocytosis. Viral DNA then gains access to the cytosol where it binds to the ribosomes.
Translation and processing of viral proteins
The viral genome is just one long open reading frame. When it is done, there are two virus-encoded proteases that cleave the polyproteins giving rise to all the structural and nonstructural proteins.
How does poliovirus take over the cells ability to synthesize proteins?
One of the viral proteases cleaves a critical protein in the initiation complex, disabling its ability to synthesize cellular proteins.
Replication of poliovirus
One of the viral proteins that is made is RNA-dependent RNA polymerase (RDRP)
- the incoming + strand will serve as a template for the synthesis of the - strand. The - strand will then act as a template for many + strands.
- there will be many more + strands than - strands of course.
- viral structural proteins and RNA is packaged into particles, cells are killed, and viruses are released all in 5-6 hours.
Why is it that polio became more common once we were more developed?
It used to the that the kids would get the disease as infants and they still had their mothers antibodies so NBD. They would even begin to make their own memory cells against polio. Then, everything got cleaner so they wouldn’t get it as often so they wouldn’t get it as infants but rather as adults and they didn’t have any of moms antibodies so no protection.
Symptoms and spread of poliovirus
- enterovirus so usually GI related
- is spread via the fecal-oral route
- usually asymptomatic but can cause minor illness such s headache, sore throat, and nausea in some patients. In other patients it is more severe and can cause meningitis or muscle/respiratory paralysis.
Other than polio. What are the other viruses in the class of picornaviridae? What are the symptoms
Coxsackievirus - conjunctivitis, febrile rash, meningitis, hand, foot and mouth
Echovirus - conjunctivitis, febrile rash, meningitis rarely, diarrhea
Enterovirus - GI
What are the two types of viruses within the subclass of togaviridae?
Alphavirus and rubioviruses
Common features of both Flaviviridae and togaviridae
Non segmented + strand RNA genome
Viruses are enveloped
Most are arthropod-borne
Difference in replication strategies between flavi virus and toga virus?
Flavivirus - only one open reading frame, which makes one long polyprotein. The structural genes are on the 5’ end.
Togavirus - 2 messages are made. The - strand is made from the + strand and then from there either the whole positive RNA genome can be made or a sub-genome can be made that only has structural genes on it. The structural genes are on the 3’ end.
Alpha viruses and a little about each one
Eastern/western encephalitis virus - usually in Wild birds but mosquitoes accidentally transfer them to humans. Will cause inflammation of the meninges in humans.
Venezuelan equine encephalitis virus - similar to influenzae. Usually doesn’t cause encephalitis in humans.
Rubella
Member of Rubivirus (part of togaviridae)
- although genome structure is similar to the other togaviruses, it is a different clinical picture. Respiratory transmission (not arboviruses).
- causes fever, malaise, maculopapular rash
- can cause congenital malformations due to maternal Viremia. Especially during first trimester.
- have a live-attenuated vaccine.
WHat are some of the flavi viruses?
Japanese encephalitis virus Saint Louis encephalitis virus West Nile virus Dengue virus Yellow fever virus Zika virus
West Nile Virus
Mostly asymptomatic, mostly old people
- symptoms are fever, headaches, fatigue, myalgia, nausea, rash
- muscle weakness and confusion (Guillan Barre syndrome)
- used to be common in NY area but moved overs to the middle of. The country.
Dengue Fever
Otherwise known as break one fever
- symptoms include: fever, rash, sever bone and joint pain
- enlarged lymph nodes
- persists for many months
- very little mortality
- infects humans and monkeys via MOSQUITOES
Can cause Dengue Hemorrhagic Fever and Shock Syndrome
- starts off as same clinical symptoms but can progress into hemorrhage and shock in the GI and skin.
How are antibodies involved in the progression into hemorrhagic fever and shock syndrome?
Basically there are 4 serotypes. So, if a child is infected with one serotype and makes antibodies against it he is good. However, if he is then infected with a different serotype, because the antibodies are similar, the antibodies will be able to attach to the virus but not neutralize it. Therefore, the macrophage recognizes the Fc portion of the antibody and enfulfs it. Dengue spreads through the infection of macrophages so it spreads like wildfire.
Yellow Fever
Can occur in monkeys (Jungle yellow fever) or in humans (Urban yellow fever).
- symptoms include: jaundice, fever, headache, myalgia. Can spread to all organs leading to shock and upper GI bleeds.
- there is a vaccine against it
Zika virus
Classified as a flavivirus
- transmission via (Aedes) mosquito
- can have mild symptoms such as fever, rash, arthralgia, conjunctivitis
- biggest issue is that if a pregnant mother gets infected, the child will have microcephaly, sever fetal brain defects.
Corona Virus
Member of the flaviviridae subclass.
- it is called corona because of the glycoprotein spikes that resemble a crown.
- symptoms can be just the common cold or GI issues.
- could cause SARS or MERS-CoV though
SARS
Sever Acute Respiratory Syndrome
- caused by corona virus.
- causes pneumonia
- spread via respiratory aerosols
- common in chine
MERS-CoV
Middle Eastern Respiratory Virus
- Common in Saudi Arabia
- causes sever acute respiratory illness
- Spreads via close contact
Mnemonic to remember the families of positive strand RNA viruses
Please Cancel Filming The Corona
Mnemonic to remember the picornaviridae viruses
C(R)EEP
- The R is in parenthesis because it is a rhinovirus and the others are GI viruses.
What shape is poliovirus
Icosahedral
What are the viruses that are spread from mother to child?
TORCH TOxoplasma gondii Rubella CMV HSV2 and HIV
