VIROLOGY- INTRO Flashcards
A submicroscopic, obligate intracellular parasite, among the smallest of all infectious agents, capable of infecting any animal, plant, or bacterial cell.
virus
What is essential for the survival of viral infectious agents?
Their ability to infect and reside in a living organism.
Where are viruses found?
In every ecosystem.
Can viruses replicate without a living host cell?
No, they are strict obligate intracellular parasites and cannot replicate without a living host cell.
Major changes in viral genomes that result in novel viral antigens.
antigenic shift
The specificity of virus types, where each virus has a limited number of hosts it can infect.
viral tropism
The emergence of a new viral disease across a very large geographic region (worldwide) with prolonged human-to-human transmission.
Pandemic
Minor changes in viral genomes that occur infrequently.
antigenic drift
What is the term for a virus that emerges as a completely new entity?
A completely new or “novel” virus.
What are the two or three parts that make up a virus particle (virion)?
-Inner nucleic acid core (RNA or DNA)
-Protein coat (capsid)
-Lipid-containing envelope (in some larger viruses)
It surrounds and protects the nucleic acid.
protein coat (capsid)
How are enveloped viruses typically transmitted?
By direct contact: respiratory, sexual, or parenteral contact.
Why are “naked” viruses resistant to environmental factors?
Because they do not have an envelope, making them very stable.
are extensions from the surface of the virus.
glycoprotein spikes
The nucleic acid genome surrounded by a symmetric protein coat.
nucleocapsid
It encodes the proteins required for viral penetration, transmission, and replication.
Nucleic acid genome
What determines the mechanism for viral replication?
The structure of the viral genome (e.g., (+) sense-strand RNA, (–) sense-strand RNA, and DNA genomes).
protects the viral genome and is responsible for the tropism to specific cell types in naked viruses.
Viral capsid
It is responsible for viral entry into the host cell.
lipid envelope
It lies between the envelope and the nucleocapsid and may have enzymatic activities or biological functions related to infection, such as inhibition of host-cell transcription
Matrix protein
very susceptible to drying and destruction in the environment
Enveloped viruses
Typically are composed of repeating structural subunits referred to as?
Capsomeres
Because of their stability, they are typically transmitted by the fecal-oral route
“Naked” viruses
What factors influence specimen selection for viral detection?
The specific disease syndrome, viral agents suspected, and time of year.
When should specimens for viral detection be collected?
As early as possible after the onset of symptomatic disease.
How can the recovery and detection of viral agents be enhanced?
By using validated devices or containers.
Which type of specimen is superior for recovering viruses: nasopharyngeal aspirates, throat swabs, or nasopharyngeal swabs?
Nasopharyngeal aspirates.
For which viruses are throat swabs acceptable for recovery?
Enteroviruses, adenoviruses, and HSV.
Which specimens are preferred for the detection of RSV, influenza, and parainfluenza viruses?
Nasopharyngeal swab or aspirate specimens.
Are all respiratory specimens acceptable for culture of most viruses?
Yes,all respiratory specimens are acceptable for culture of most viruses.
What specimens are excellent for detecting viruses that infect the lower respiratory tract?
Washings and lavage fluid collected during bronchoscopy.
Which viruses are especially detected using bronchial and bronchoalveolar washes?
Influenza viruses and adenoviruses
What specimens are used to detect rotavirus, enteric adenoviruses (serotypes 40 and 41), and enteroviruses?
Stool and rectal swabs of fecal specimens.
Which is preferable for rotavirus and enteric adenovirus testing: stool specimens or rectal swabs?
Stool specimens.
When are rectal swabs acceptable for detecting enteroviruses?
In patients suspected of having an enteroviral disease, such as aseptic meningitis.
What should be done with a rectal swab after collection?
It should be placed in appropriate transport media.
Which viruses can be detected in urine?
Mumps, rubella, measles viruses, polyomaviruses, and adenovirus can be detected in urine
How much stool is sufficient and preferred for rotavirus and enteric adenovirus detection?
Five to ten mL of freshly passed diarrheal stool or stool collected in a diaper from young infants
What is the recommended urine specimen volume for improved virus recovery?
A minimum specimen volume of 10mL from a clean-catch first morning urine
How can viral recovery be increased in urine specimens?
Viral recovery may be increased by processing multiple (two or three) specimens in parallel
What techniques improve virus recovery from urine specimens?
-improved by centrifugation or filtering to remove contaminants
-neutralizing the pH with a 7.5% solution of sodium bicarbonate
Which viruses can be detected in vesicular lesions of the skin and mucous membranes?
Enteroviruses, HSV, VZV, and in rare cases CMV or pox viruses can be detected in these lesions
What is the purpose of a Tzanck smear in viral detection?
used for the detection of HSV or VZV in cutaneous vesicles when PCR testing is not available.
What are some examples of sterile body fluids other than blood?
Cerebrospinal fluid (CSF), pericardial fluid, and pleural fluid.
Which viruses can be found in cerebrospinal fluid (CSF)?
Enteroviruses, herpes simplex virus (HSV), varicella-zoster virus (VZV), influenza viruses, and cytomegalovirus (CMV).
Can pericardial and pleural fluids contain viruses?
Yes, they can contain enteroviruses, HSV, VZV, influenza viruses, or CMV.
is used primarily to detect CMV; HSV, VZV, enteroviruses, and adenovirus occasionally may be encountered
Viral culture of blood
What is CMV viremia associated with?
Peripheral blood leukocytes.
How much anticoagulated blood is needed for viral culture?
Five to ten mL
What types of anticoagulated blood are acceptable for CMV detection?
Heparinized, citrated, or ethylenediaminetetraacetic acid (EDTA) anticoagulated blood.
Which type of anticoagulated blood should be used when considering other viruses?
Citrated blood.
What can serum be used for in blood tests?
Serologic tests and nucleic acid assays.
How should bone marrow for virus detection be handled?
It should be added to a sterile tube with anticoagulant.
What types of anticoagulants are acceptable for bone marrow virus detection?
Heparin, citrate, or EDTA anticoagulants.
How are bone marrow specimens collected?
By aspiration
Which virus is an exception to the rule that most viruses are detected more readily from sites other than bone marrow?
Parvovirus B19.
Which viruses commonly infect the lungs and can be detected in tissue specimens?
CMV, influenza virus, adenovirus, and sin nombre virus.
What type of tissue is preferred for nucleic acid assays?
Fresh tissue.
Which virus commonly infects the gastrointestinal tract and brain that can be detected in tissue specimens?
Herpes simplex virus (HSV) and Cytomegalovirus (CMV).
How are tissue specimens typically collected?
During surgical procedures.
Can formalin-fixed and paraffin-embedded tissues be used for virus detection?
Yes, but they must undergo deparaffinization and extraction first.
Which viruses are often detected using genital specimens?
Herpes simplex virus (HSV) and human papillomavirus (HPV).
should be used for ulcerations and placed in appropriate viral transport media
Genital swabs
How cervical specimens should be collected?
Using a swab or brush and placing them in viral transport media.
What types of devices are appropriate for nucleic acid testing of cervical specimens?
Most manufactured endocervical or liquid-based cytology devices.
When should the convalescent serum specimen be collected?
A minimum of 2 to 3 weeks after the acute specimen
How much serum is typically collected for antibody testing?
3 to 5 mL of serum collected by venipuncture.
What should be done with specimens for viral isolation to prevent degradation?
They should not be allowed to sit at room or higher temperature and should be kept cool (4°C).
What should be done if there is a delay in transporting specimens for viral isolation?
The specimen should be refrigerated, not frozen, until processed.
Within what time frame should specimens ideally be processed?
Within 12 to 24 hours of collection.
How should specimens be stored if they need to be held for several days before processing?
Up to 5 days at 4°C; for 6 days or longer, at –20°C, preferably –70°C.
Flashcard 6:
What should be done to specimens before freezing them?
They should first be diluted or emulsified in viral transport medium.
Which types of swabs are acceptable for specimen collection?
Most types of synthetic swabs, such as rayon and Dacron.
Which types of swabs are not recommended for specimen collection?
Swabs with cotton tips and wooden shafts.
What should be done with swab specimens before transport to the laboratory?
They should be emulsified in viral transport medium, especially if transport will occur at room temperature and requires longer than 1 hour.
is not acceptable for the culture-based detection of HSV
Calcium alginate.
What are some examples of viral transport media?
-Stuart’s medium,
-Amie’s medium,
-Leibovitz-Emory medium,
-Hanks’ balanced salt solution (HBSS),
-Eagle’s tissue culture medium,
-and the commercially available M4, M5, and universal transport media.
How should respiratory, rectal, and stool specimens be maintained?
In modified Stuart’s medium, modified HBSS, or Leibovitz-Emory medium containing antimicrobials.
How should blood for viral culture be transported?
In a sterile tube containing anticoagulant, refrigerated at 4°C until processed.
Serum can be stored for hours or days at ____
or for weeks or months at ____ or lower
before testing
4°C
–20°C
Where should viral specimens be processed whenever possible?
In a Biological Safety Cabinet (BSC).
What is required if there is a delay in processing fluid specimens?
They should be diluted in a transport medium (1:2-1:5) before storage.
