Virus Identification

Question 1

What are the types of virus identification?

Answer 1

Microscopy, Viral isolation, Antigen detection, Antibody detection, Molecular analysis

Question 2

How does microscopy work?

Answer 2

Light microscope- Stained/immunostained samples can
suggest/confirm virus infection
Electron microscope- Direct virus visualisation

Question 3

How does viral isolation work?

Answer 3

Predominantly cultured cells (tissue culture)
Presumptive diagnosis (cytopathic effect, CPE)
Diagnosis confirmed by immunostaining

Question 4

What is the difference between antigen and antibody detection?

Answer 4

Direct/indirect immunofluorescence (IF)
Enzyme immunoassays (EIA) (both)
Antibody- immunoblots

Question 5

How does molecular analysis work?

Answer 5

Nucleic acid amplification tests (NAATs)
Polymerase chain reaction (PCR)
Sequencing (genotype, drug resistance, epidemiology)

Question 6

What samples are needed for antigen/antibody detection and molecular analysis?

Answer 6

1. Antigen/Antibody detection
   Full size (≥4.5ml) brown-capped clotted blood sample
2. Molecular analysis
   Full size (≥ 4.5ml) red-capped anti-coagulated EDTA blood sample
   Direct swabs in virus transport medium (VTM)
   Other specimens: cerebrospinal fluid (CSF), vomit/stool, etc

Question 7

What is the process of host infection?

Answer 7

Attachment and entry into body (infection)
Local or general spread in body (spread)
Replication of organism (multiplication)
Evasion of host defences (evasion)
Production of progeny (shedding/egress) resulting in transmission
Damage to (and even death of) host may occur (pathology/disease)

Question 8

Describe the process of spread

Answer 8

Infection
Replication in lymph node/blood/body surface
Shedding in respiratory tract (influenza) or intestinal (rotavirus) or skin (warts)

Question 9

Describe the process of transmission

Answer 9

Horizontal- more common

Vertical- passed down generation by milk/ sperm/ egg/ placenta

Question 10

What are the outcomes of host infection?

Answer 10

-Acute lytic infection= Virus replication and release of virus progeny via cell lysis (Poliovirus, influenza A virus (flu))
-Persistent infection with shedding= Virus persists in cell and replicates at a slow rate (Hepatitis B virus (HBV))
-Latent infection with reactivation= Virus persists in cell but is quiescent (latency); disruption of latency triggers replication: reactivation/ Genetic material may persist in host cell nucleus (‘episome’) (herpesviruses)
-Persistent slow infection with/without acute stage= Genetic material may integrate into host cell genome (‘provirus’) (human immunodeficiency virus (HIV))
-Transformation= Disruption of normal growth processes
Epstein-Barr virus (EBV), human papillomaviruses (HPV)

Question 11

How may viruses effect transformation of host cells?

Answer 11

result of their direct or indirect dysregulation of the normal cellular growth machinery

Question 12

What do transformed cells show?

Answer 12

In vitro- greater saturation density/ higher growth rate/ loss of contact inhibition/ appearance of ‘new’ cell surface antigens (some viral, others foetal in origin)/ loss of anchorage dependence/ indefinite growth in vitro (‘immortalisation’)
In vivo- tumour induction in animal models

Question 13

What percentage of human cancers worldwide

are caused by infectious agents?

Answer 13

15-25%

Question 14

What viruses are associated with cancer?

Answer 14

• Epstein-Barr virus= Anaplastic nasopharyngeal carcinoma/ anaplastic gastric carcinoma/ Endemic Burkitt’s’ lymphoma/ Hodgkin’s lymphoma/ post-transplant/ lymphoproliferative disease
• HPV= Cervical carcinoma/ Oro-pharyngeal carcinoma/ anal carcinoma/ penile carcinoma
• Hepatitis C and B= Hepatocellular carcinoma
  Human T cell lymphotropic virus= T cell leukaemia

Question 15

Describe Poliovirus

Answer 15

Approx 30nm in size
Ss+ve RNA strand
Non-enveloped icosahedron made up of 4 capsid proteins
Replicates in cytoplasm
Cytopathic
Infects gut and replicates in Gut Associated Lymphoid Tissue
Can infect (and destroy) motor neurones

Question 16

Describe Poliovirus infection

Answer 16

Asymptomatic/mild infections in approx 99% of cases
Meningitis
Paralytic poliomyelitis (1:1,000 of poliovirus infections in children)
WHO polio eradication set for 2005; not yet reached
Small intestine invasion multiplication, lymph nodes, bloodstream, CNA, antibody in serum, paralysis, excretion in faeces

Question 17

Describe herpes simplex virus

Answer 17

Approx 150nm in size
ds DNA
Enveloped icosahedron (162 capsomeres)
Replicates in nucleus
Cytopathic
Infects epithelium, enters and ascends axons
Establishes latent infection (non-integrated) in neural ganglia
Reactivation results in descent along same axons and replication in epithelium (‘cold sore’)

Question 18

Describe herpes simplex virus infection

Answer 18

Primary infection: viral transit up peripheral nerve, latent virus in neuron in dorsal root ganglion
Reoccurrence: fever/ sunlight to face/ menstruation/ nerve section between spinal cord and dorsal root ganglion= activation of virus in neuron so viral transit down peripheral nerve
Varicella virus (chickenpox)- age/X-radiation- shingles

Question 19

Name antiviral targets and drug examples at each stage of replication

Answer 19

1. Entry- Maraviroc (HIV)
2. Penetration and uncoating- Amantadine (Influenza A)
3. Viral DNA/RNA synthesis- Aciclovir (Herpesviruses)/
   Reverse transcriptase inhibitors (HIV)
4. Viral protein synthesis- Interferons (HBV, HCV)
5. Assembly- Protease inhibitors (HIV)
6. Release- Neuraminidase inhibitors (Influenza A)

Question 20

Describe the mode of action of Aciclovir

Answer 20

Enters host cell
Viral thymidine kinase= Aciclovir monophosphate
Cellular kinases= Aciclovir triphosphate
Inhibition of viral DNA Polymerase incorporation into viral DNA
Chain termination due to inhibited DNA synthesis

Question 21

Where are the infection and shedding sites of viruses?

Answer 21

Infection- Respiratory tract, mouth, scratch injury (skin), conjunctiva, capillary, urinogenital tract
Shedding- respiratory, mouth, anus, capillary/arthropod, conjunctiva, urinogenital tract