07- VIROLOGY (TCEPP Exam # 7) Flashcards
Describe the structural components of viruses
At a minimum, viruses contain a viral genome of ribonucleic acid (RNA) or deoxyribonucleic acid (DNA) and a protein coat— the capsid. The genome can be double stranded (ds) or single stranded( ss).
The genome and its protein coat together are referred to as what?
The nucleocapsid
The entire virus particle is called what?
Virion
How are viruses classified?
- Genome type (RNA or DNA)
- Number of strands in the genome (ds or ss),
- Morphology
- Presence or absence of an envelope
Viruses are obligate intracellular parasites. What does that mean?
They must be inside a living cell and use the host cell machinery to replicate.
Describe the basic steps of viral replication
- Absorption. In the first step for infection of a cell to occur, virions must absorb or attach to the cell surface.
- Penetration. Viruses can penetrate the cell by several different mechanisms and penetration is virus dependent.
- Uncoating.Once inside the cell, the virus loses its protein coat, releasing the genome. The viral genome then directs the host cell to make viral proteins and replicate the viral genome.
- Assembly or maturation of the virus particles.The new virions are formed and then released by lysis if they are naked viruses or by budding if they are enveloped viruses.
When should samples be collected for viral detection?
Viral shedding is highest in** early stages of infection** and decreases rapidly a few days after acute symptoms.
What is the optimal specimen for viral detection?
For optimal recovery, specimens for viral isolation should be **collected from the affected site. **
For example, secretions from the respiratory mucosa are most appropriate for viral diagnosis of respiratory infections. Aspirates, or surface swabs, are usually appropriate for lesions.
What types of swabs can and cannot be used for viral specimen collection?
- Swabs used must be made of Dacron or rayon.
- Do not use Calcium alginate or wood shafted swabs. They can inhibit the replication of some viruses and can interfere with nucleic acid amplification tests.
If a viral specimen must be frozen, what temperature should it be kept at?
–70 ° C
–70 ° C. Specimens should never be stored at − 20 ° C because this temperature facilitates the formation of ice crystals that will disrupt the host cells and result in loss of viral viability. Repeated freeze– thawing cycles are to be avoided because they can also result in loss of viral viability.
Define cytopathic effect (CPE) as it relates to viral identification
Many viruses produce distinctive and characteristic visual changes in infected cells referred to as a cytopathic effect (CPE).
Some viruses produce a very characteristic CPE that can provide a presumptive identification of a virus isolated from a clinical specimen. For example, HSV grows rapidly on many different cell lines and frequently produces a CPE within 24 hours. A predominantly cell-associated virus, HSV produces a focal CPE (in which adjacent cells become infected) and plaques, or clusters of infected cells. The combination of rapid growth, plaque formation, and growth on many different cell types is presumptive evidence for the identification of HSV.
Name 4 general types of cell cultures / lines used for viral isolation
- HDF, human diploid fibroblasts
- HEp2, human laryngeal carcinoma cell line
- PMK, primary monkey kidney
- RK, rabbit kidney
Describe the four major methods the clinical laboratory uses to diagnose viral infections.
- Direct detection of the virus in clinical specimens (microscopy, EIA)
- Nucleic acid– based detection (PCR)
- Isolation of viruses in cell cultures (gold standard but seldom used)
- Serologic assays to detect antibodies to virus
Name the phenomenon where slight antigenic change is seen in influenza viruses over time because of minor mutations in the ssRNA.
Antigenic drift
Name the phenomenon whereby an often-unexpected change occurs in influenza virus strains. This antigenic change is often so drastic that it triggers pandemics. Causes changes in H and N antigens.
Antigenic shift
Name that Virus
Most cases are asymptomatic. Those that are symptomatic usually involve the respiratory tract, eye, or gastrointestinal tract.
Adenovirus
dsDNA
Family: Adenoviradae
Name that Virus
There are two species: HSV-1 and HSV-2. These viruses cause oral herpes, genital herpes, neonatal herpes, and ocular herpes. Also the leading cause of fatal sporadic encephalitis in the United States. Neonates are most at risk for HSV-2 encephalitis. HSV detection by culture is sensitive and is often positive in less than two days.
Herpes simplex viruses
(aka Human herpesvirus 1 and Human herpesvirus 2)
dsDNA
Family: Herpesviridae
Name that Virus
Congenital infection can be significant. If the mother acquires primary infection during pregnancy irreversible damage could result to the fetus. As a result, this virus is one of the leading causes of mental retardation, deafness, and intellectual impairment. Infants may develop a blueberry muffin rash.
Cytomegalovirus
(Human herpesvirus 5)
dsDNA
Family: Herpesviridae
Name that Virus
Virus infects B lymphocytes and stimulates the production of heterophile antibodies. Infection can present as infectious mononucleosis. Some cancers have been associated with this virus including Burkitt’s lymphoma. Atypical lymphocytes may been seen in hematological testing.
Epstein-Barr virus
(Human herpesvirus 4)
dsDNA
Family: Herpesviridae “kissing disease”
Name that Virus
Causative agent of chickenpox and shingles. Skin scrapings are the best specimens.
Varicella-Zoster virus
(human herpesvirus 3)
dsDNA
Family: Herpesviridae
Name that Virus
Associated with genital warts. Diagnosis is made from koilocytes on pap smears. Linked to cervical cancer.
Human papilloma virus (HPV)
dsDNA
Family: Papillomaviridae
Name that Virus
Infections are associated with Kaposi sarcoma.
Human herpesvirus 8 (HHV-8)
Name that Virus
Causative agent of smallpox.
Variola virus
dsDNA
Family: Poxviridae
Name that Virus
The most recognized symptom of an infection caused by this virus is erythema infectiosum (also called fifth disease) - a rash on the cheeks. Some referred to it as a slapped cheek appearance.
Parvovirus B19
ssDNA
Family: Parvoviridae
Name that Virus
Most common cause of viral gastroenteritis in infants and children.
Rotavirus
dsRNA
Family: Reoviridae
Name that Virus
A group of viruses transmitted by arthropods such as ticks and mosquitoes and can cause hemorrhagic fevers in humans.
Arboviruses
Name that Virus
A group of viruses carried by rodents and can cause hemorrhagic fevers in humans
Arenaviruses
Name that Virus
Causes gastroenteritis and is associated with outbreaks on cruise ships.
Norovirus
Name that Virus
Novel strains of this group of viruses has been associated with severe acute respiratory syndrome (SARS).
Coronaviruses
ssRNA
Family: Coronaviridae
Name that Virus
Infections with these two viruses are rare, but almost always fatal due to hemorrhagic fevers.
Ebola and Marburg virus
ssRNA
Family: Filoviridae
Name that Virus
These viruses have a segmented genome and are classified based on two major surface glycoproteins: hemagglutinin (H) and neuraminidase (N). They attack ciliated epithelial cells lining the respiratory tract and cause the flu.
Influenza virus A, B, and C
ssRNA
Family: Orthomyxoviridae
Name that Virus
These viruses are the primary cause of respiratory disease in young children. Type 1 is the primary cause of croup.
Parainfluenza viruses (1 through 4)
ssRNA
Family: Paramyxoviridae
Name that Virus
ssCauses bilateral swelling of the parotid glands.
Mumps virus
ssRNA
Family: Paramyxoviridae
Name that Virus
This virus causes a stuffy nose, cough, and Koplik spots.
Measles virus (also known as rubeola)
ssRNA Family:Paramyxoviridae
Koplik spots are white spots that appear on the mucous membranes of measles patients approximately 1 day before the appearance of the typical measles rash.
Name that Virus
Most common cause of severe lower respiratory tract disease among infants and young children.
Respiratory syncytial virus (RSV)
ssRNA
Family: Paramyxoviridae
