Microbiology-Viral URIs Flashcards
You go to school and see someone sneeze on a door handle. You touch it hours later, forgetting that it happened. 2 days later you have a runny nose for the 3rd time that winter. What does this story tell you about the general characteristics of rhinovirus?
They are non-enveloped (exist as foamites). They are infectious because they are +ssRNA (mRNA). There are 100+ serotypes (recurrence of cold). They bind to ICAM-1 receptors and replicate most efficiently at 88-90F (primarily affects nasopharyngeal mucosal cells).
What is the pathogenesis behind all of the congestion, soreness and erythema in the nasal mucosa when you have a cold?
Rhinoviruses infect cells, bind directly to ribosomes and are translated into V1-V4 proteins. They then lyse the cell and release more viruses. Lysing the cell releases pro-inflammatory mediators (type I interferons).
What is the normal incubation period after someone has been infected with rhinovirus?
2-4 days
What antibodies are protective against rhinovirus infection?
IgA in nasal secretions
A 1 month old baby born with heart problems has been receiving care in the NICU. What virus is this child particularly susceptible to and why are you extra careful about preventing exposure to this child?
Respiratory Syncytial Virus (RSV, part of the paramyxovirus family). Premature infants
What are the viral characteristics of RSV?
Enveloped, -ssRNA (not infectious by itself), attachment protein G and fusion protein F (allow for fusion with host cell membrane) and it encodes its own RNA-dependent RNA polymerase.
Where and how does RSV replication take place?
Nasopharyngeal epithelium. 1st it must make an mRNA template from its -ssRNA. Then viral replication occurs, expression of G and F proteins on the cell membrane occurs and causes “giant-cell” formation (syncytium).
What two histological features of RSV infection are used to diagnose RSV?
Syncytium formation and presence of inclusion bodies.
What are the symptoms of an RSV infection and why do they vary?
Symptoms vary depending on protein expression. The typical symptoms include runny nose, tachypnea, wheezing, lip cyanosis and bronchiolitis in immunocompromised individuals.
How do you diagnose and treat an RSV infection?
Diagnose with nasal swab and ELISA or PCR. Treatment is with Ribavirin (RNA replication inhibitor) and oxygen supplementation.
What passive immunity measures are available for treatment of RSV in patients who are young or very immunocompromised and at high risk for lower respiratory tract disease?
Polyclonal antibody (RespiGam) and anti-F monoclonal antibody (Synagis).
What are the viral characteristics of adenovirus?
Very typical icosahedral capsid. DS linear DNA that replicates in the nucleus. Largest non-enveloped virus (foamite). 51+ serotypes (recurrent infections). Encodes its own DNA polymerase.
What are the cells commonly infected by adenovirus and how does the virus normally gain entry
Mucoepithelial cells in respiratory tract, GI tract and eye (conjunctive/cornea). They get in by CAR (Coxsackie/Adenovirus receptor) or by binding to integrins.
If you were developing a drug that targeted replication of adenovirus, what would be a good target that would inhibit its replication?
Replication of the viral proteins happens temporally. If you can inhibit the 1st gene, you can inhibit all of replication.
Where are adenoviruses latent and where are they lytic?
Latent - adenoid cells. Lytic - mucoepithelial cells
What are the serotypes of adenovirus that are endemic currently?
Ad3.7 (swimming pools). Ad4.7 (acute respiratory disease)
What disease processes manifest in the respiratory tract as a result of adenovirus infection?
Pharyngoconjunctival fever, ARD, pertussis-like syndrome and pneumonia.
How does our body attempt to get rid of adenoviruses? How does adenovirus evade these attempts?
Serotype specific antibodies are made by B cells with T cell help. CD8 cells also help get rid of infection. Adenoviruses avoid these measures by expressing E3 protein which will down regulate MHC I and inhibit TNF-mediated lysis.
How do you treat adenovirus?
The disease usually resolves within 7-10 days.
What is a gamma-herpesvirus that can infect epithelial cells find latency in lymphoid cells?
Epstein-Barr Virus
What are the viral characteristics of Epstein-Barr virus?
Enveloped, linear dsDNA, replicates in the nucleus, encodes its own DNA-dependent DNA polymerase and encodes numerous host proteins to evade the immune response.
A 14 year old male comes to see you in the primary care clinic complaining of general malaise and weakness lasting over a month. A cold has also persisted during this time. If you took a tissue biopsy where would you take it and what would you expect to see?
This is EBV induced mononucleosis. It replicates in epithelial and B cells, so you would take the biopsy in epithelium or lymph nodes (tonsils are ideal). You would expect to see increased numbers of monocytes, hence the term mononucleosis.
A patient comes to see you with a sore throat. Physical exam reveals swollen lymph nodes and red, swollen tonsils. He says he has felt this way for about three weeks and has missed many days of school. You do a peripheral blood smear and see the results below. What is your diagnosis and what is the normal incubation period of this pathogen?
EBV, note the “atypical lymphocytes” that happen as a result of mass T-cell activation by infected B cells. Typical incubation period is 6-8 weeks.
How does EBV virus go from initial exposure to latency in B cells?
The virus enters the B cells via the CD21 or CR2 receptor. They then cause mass replication of B cells. The B cells activate CD8 (non-specific) and CD4 T cells (virus specific) and you get mass production of T cells. The virus then causes the B cells to express proteins that allow it to escape the immune system. It becomes latent as it decreases its protein expression.
You got mono when kissing your girlfriend in the 7th grade and it took about a month to go away. What is the greatest complication associated with mono?
Cancer. It promotes all sorts of lymphoid cancer in immunocompromised people due to B cell infection.
What tests exist if you want to diagnose someone with EBV?
Histology for atypical lymphocytes, agglutination test for IgM antibodies (early infection) that react with RBCs (heterophile), ELISA (capsid-specific IgG for later infections) or PCR (during active infection).
What immune cells play a key role in limiting the spread of EBV?
CTLs. The kill the infected B cells.
Rhinovirus, RSV, Adenovirus and EBV URI summary of the follow categories:
*
