Flashcards in Microbiology - Virology-2 Deck (46):
What must a positive (+) stranded RNA virus do/have to replicate?
Nothing. The positive (+) stranded RNA can immediately be translated by the host’s ribosomes into protein.
What must a negative (-) stranded RNA virus do/have to replicate?
Negative (-) stranded RNA viruses must carry, in their capsid, an enzyme called RNA-dependent RNA polymerase.
What does the retrovirus carry in order to replicate? How does the retrovirus replicate?
With reverse transcriptase, RNA is transcribed to DNA. DNA undergoes transcription to mRNA, which is then translated to proteins.
In a DNA virus, which strand is read?
The positive (+) strand is read, and the negative (-) strand is ignored.
What are the two types of capsids?
Icosahedral and helical
What are the DNA viruses?
Mnemonic: HHAPPPy viruses
Which DNA virus is single stranded?
Which DNA virus does not have icosahedral symmetry?
Which DNA viruses are naked? Which are enveloped?
Which RNA virus is double stranded?
Which RNA viruses are noneveloped?
Picorna, Calici, and Reoviridae
Which RNA viruses undergo replication in the nucleus?
Retro and Orthomyxo
In DNA virus replication, what are the three stages and what is produced during each?
Immediate early and Early: initially transcribed mRNA here encodes enzymes and proteins needed for DNA replication and for further transcription of late mRNA.
Late: The capsid structural proteins are synthesized from the late mRNA genome.
What are the orthomyxoviridae viruses?
What is the structure of the orthomyxoviridae viruses?
The orthomyxoviridae are spherical virions. At the virion cent er lie 8 segments of negative (-) stranded RNA put together with a protein (nucleocapsid protein – NP) into a helical symmetry capsid.
What are two glycoproteins that stud the outer membrane of the orthomyxoviridae?
Hemagglutinin Activity (HA)
Neuraminidase Activity (NA)
What is the function of HA and NA?
Hemagglutinin (HA) can attach to host sialic acid receptors, present on the surface of RBCs and on upper respiratory tract cell membranes.
HA is needed for adsorption.
Neuraminidase (NA) cleaves neuraminic acid and disrupts the mucin barrier covering mucosal epithelial cells. This exposes the sialic acid sites.
What is antigenic drift? Antigenic shift?
Antigenic drift: mutations to the HA or NA, leading to changes in their antigenic nature.
Antigenic shift: a complete change of HA, NA, or both.
What are some differences between Paramyxoviridae and Orthomyxoviridae?
a) the negative (-) stranded RNA is in a single strand, not segmented
b) HA and NA are part of the same glycoprotein spike, not 2 different ones
c) Fusion (F) protein causes host cells to fuse together into multinucleated giant cells
What are the four paramyxoviridae? Where do they all infect?
Respiratory syncytial virus
All adsorb to and replicate in the upper respiratory tract.
What is croup?
Croup is a parainfluenza infection of the larynx and other upper respiratory sructures (laryngotracheobronchitis) that occurs in children. Swelling of these structures produces airway narrowing. Stridor (wheezing sound) and a barking cough occur as air moves through the narrowed upper airways.
What is the number one cause of pneumonia in young children?
Respiratory Syncytial Virus (especially in infants less than 6 months of age)
How does RSV differ from the other paramyxoviridae?
RSV lacks both HA and NA glycoproteins
What structures are involved in mumps virus infection?
Parotid gland (Parotitis)
What is another name for Measles? How does it spread?
Spreads through nasopharyngeal secretions by air or by direct contact.
What is the path of infection for measles?
Two week incubation
Prodrome: conjunctivitis, swelling of the eyelids, photophobia, high fevers, hacking cough, rhinitis, and malaise
What are Koplik’s spots?
A day or two before the rash, patients infected with measles develop small red-based lesions with blue-white centers in the mouth
What is the measles rash? How does it spread?
The measles rash is red, flat to slightly bumpy (maculopapular).
It spreads out from the forehead to the face, neck, and torso, and hits the feet by the third day. As the measles rash spreads downward, the initial rash on the head and shoulders coalesces.
What is a severe complication of measles?
Encephalitis: rare, but 10% of patients die
Subacute sclerosing panencephalitis (SSPE): slow form of encephalitis caused by measles virus. Slowly progressing CNS disease, with mental deterioration and incoordination.
Match the virus with its family:
How are the hepatitis viruses transmitted?
Hepatitis A and E are transmitted via the fecal-oral route.
Hepatitis B, C, D, and G are transmitted via blood-to-blood (parenteral) contact.
What lab values are found in acute viral hepatitis? Why?
AST and ALT are very high
GGT, alkaline phosphatase, and bilirubin are slightly elevated
In viral hepatitis, necrosis of hepatocytes causes the release of AST and ALT. GGT and alkaline phosphate are enzymes found in the bile pericanalicular cells, which are destroyed later on and to a lesser extent. As the infection worsens, the liver swells and the canaliculi narrow, resulting in bilirubin backup.
What are the symptoms of hepatitis A infection?
Acute hepatitis (never chronic)
Fulminant hepatitis (1-4%) and death (1%)
What indicates an old HAV infection and no active disease?
Anti-HAV IgG. This antibody lasts indefinitely and is protective against future infection with HAV.
What is the intact Hepatitis B virus called?
When a patient has anti-HBsAg, what does it mean? What about HBeAg?
Anti-HBsAg: The patient is immune against HBV.
HBeAg: this is a marker for active disease and a highly infectious state.
When can pregnant mothers transmit HBV to their offspring?
When HBeAg is in the mother’s blood (90% transmission rate).
What are the disease states caused by HBV?
1) Acute hepatitis
2) Fulminant hepatitis: severe acute hepatitis with rapid destruction of the liver.
3) Chronic hepatitis:
a) Asymptomatic carrier: never develops antibodies against HBsAg, harbors virus without liver injury
b) Chronic-persistent hepatitis: low-grade “smoldering” hepatitis
c) Chronic active hepatitis: acute hepatitis state that continues without normal recovery (lasts > 6-12 months)
d) Co-infection with HDV
What causes liver injury during infection with HBV?
Liver injury appears to occur from a cell-mediated immune system attack on HBV. Viral antigens on the surface of infected hepatocytes are targets for cytotoxic T cells. Immune complexes can deposit in tissues and activate the immnune system, resulting in arthritis, and skin and kidney damage.
What patients are more likely to be asymptomatic carriers of HBV?
Patients who have immunosupressed states, such as malnutrition, AIDS, and chronic illness, are more likely to be asymptomatic carriers because their immune system does not attack.
What does the presence of HBsAg mean?
The presence of HBsAg always means there is a LIVE virus and infection, either acute, chronic, or carrier.
What allows infection of Hepatitis D virus? What are the disease states of HDV and which one is more severe?
HDV is an RNA virus that can only replicate in the presence of HBV envelope, HBsAg.
Co-infection: HBV and HDV are transmitted together parenterally.
Superinfection: HDV infects a person who has chronic HBV infection. More severe, as lack of Anti-HBsAg allows both viruses to infect chronically.
What are complications of HCV infection?
50% of patients get chronic hepatitis
20% develop cirrhosis
Increased risk of hepatocellular carcinoma
What two hepatitis viruses can predispose patients to chronic active hepatitis, cirrhosis, and hepatocellular carcinoma?
HBV and HCV.