Flashcards in Viruses Deck (125)
What does it mean for a virus to be “positive sense”?
Similar to an mRNA, it is ready for translation and does not need to bring along extra machinery (solely uses host machinery)
In general, all positive-sense RNA viruses replicate in the cytoplasm
CSF findings in aseptic (nonbacterial) meningitis
What are the TORCHeS infections?
Cross the placenta and cause infection in utero —> congenital disease
HIV and HSV
What does it mean for an RNA virus to be “negative-sense”?
It brings its own RNA polymerase
All negative-sense RNA viruses are single stranded except _____
Reovirus (includes rotavirus and colorado tick fever virus)
What are the segmented viruses?
What is the significance of segmented viruses?
Segmented viruses undergo antigenic variation
What are the 2 types of mutations associated with antigenic variation of viruses?
Antigenic shift: reassortment of different combos of HA and NA leading to new species; associated with PANDEMICS
Antigenic drift: point mutations in HA or NA, associated with epidemics (this is the reason for new flu shot each year)
Why is aspirin contraindicated in kids with suspected viral illnesses? What is the pathogenesis?
Can lead to Reyes syndrome — characterized by fever, rash, vomiting, liver failure, and encephalitis (can be fatal)
Result of OxPhos uncoupling in hepatocyte mitochondria
Where do viruses replicate in host cells?
In general, DNA viruses replicate in the nucleus and RNA viruses replicate in cytoplasm
T/F: all herpesviruses are enveloped
General characteristics of Picornaviridae family of viruses
Positive sense RNA virus
Naked (lack viral envelope)
Translated into polyprotein product and viral proteases cleave into infectious subunits
Transmission of Picornaviridae family of viruses
Fecal-oral (EXCEPT rhinovirus which is respiratory droplets)
3 clinical subgroups of Picornaviridae
Hepatitis A —> HSM
Enteroviruses (poliovirus, coxsackie A and B, echovirus)
Rhinovirus —> common cold
Is poliovirus acid-stable or acid-labile? What does this mean for pathogenesis?
Acid stable — survives in GI tract and infects Peyer’s patches (takes 2-3 weeks)
Then spreads to anterior horn of spinal cord causing asymmetric paralysis (often of LEs)
Also causes myalgias, decreased DTRs, aseptic meningitis, and respiratory insufficiency due to paralysis of diaphragm
Clinical manifestations of type A coxsackie virus
Hand, foot, and mouth disease
Red, vesicular rash
Infection more common in summer months
Clinical manifestations of type B coxsackie virus
“Devil’s grip” (Bornholm’s disease/pleurodynia) — unilateral, sharp, lower chest pain —> difficulty breathing
Is Rhinovirus acid labile or acid stable? What does this mean for its pathogenesis?
Acid labile — cannot survive GI tract. It is transmitted via inhalation - which may occur via fomites (on dirty hands)
Virus attaches to ICAM-1
The virus also grows best in cooler temps (33 C), so it colonizes upper respiratory tract which acts like an air conditioner
Besides being positive sense RNA, naked, fecal-orally transmitted virus, what are some other characteristics of Hepatitis A virus in terms of acid stable vs. labile, and how humans come into contact with it?
Shed in feces, so it can contaminate the water supply in developing countries. In developed countries, it can be found in uncooked shellfish that were caught in contaminated water from developing countries.
It is commonly seen in traveler’s to endemic areas
Clinical features of Hepatitis A
Often clinically silent, can even be anicteric (kids usually present this way)
Active infection = fever, hepatomegaly, jaundice; symptoms last roughly 1 month
There is no carrier or chronic state
Note that smokers with Hep A develop aversion to tobacco
Characteristics of Caliciviridae (norovirus)
Positive sense ssRNA virus
Produces long polyprotein - cleaved into infectious subunits by viral proteases
Where is norovirus commonly found and what is its clinical presentation?
Often occurs with many people in close quarters — 90% of cruise ship diarrheal illness! Also occurs in daycare, schools, or with consumption of shellfish at buffets.
Causes viral gastroenteritis —> explosive, watery diarrhea
Characteristics of Flaviviridae family of viruses
Positive sense RNA virus
What diseases are caused by the Flaviviridae family of viruses?
West Nile Virus
Characteristics of Dengue fever
Vector = aedes mosquito
Infects bone marrow; 4 types of Dengue, but type II is most important — known as “break-bone fever”
Causes thrombocytopenia and subsquent bleeding, so it is a hemorrhagic fever. Can eventually lead to renal failure and death
Vector and Clinical presentation of Yellow fever
Vector = aedes mosquito
Causes jaundice, backache, bloody diarrhea, hematemesis
Clinical features of West Nile virus including reservoir and vector, major complication, and diagnosis
Reservoir = birds
Vector = mosquitos
Major complication = encephalitis; also causes myelitis leading to flaccid paralysis, seizures, and coma
Dx by PCR and serology
Hepatitis C, belonging to the Flaviviridae family, is a positive sense RNA virus and is enveloped. What is its mechanism of transmission?
Most common method of transmission is via exposure to infected blood — can be through blood transfusion, IV drug use/needle-sharing, accidental needle-sticks, etc.
Can also be transmitted across placenta, sexual transmission (although Hep B is more common this way), or breastfeeding
What allows for antigenic variation of Hepatitis C virus if it is non-segmented?
It has no proofreading 3-5 exonuclease activity in viron-encoded RNA polymerase, so there are frequent mutations
Clinical findings in Hepatitis C infection
Acute: jaundice, RUQ pain, hepatomegaly, increased liver enzymes (ALT will rise and fall within 6 months)
Chronic (note that 60-80% of cases become chronic): cirrhosis, hepatocellular carcinoma
Associated with cryoglobulins = serum proteins containing IgM that precipitate in cool temps