Lecture 3 Transmission/ID of Viruses

Question 0

Describe AIRBORNE transmission.

Answer 0

Transmission of upper respiratory tract infections through aerosol droplets (from coughing and sneezing, eg rhinovirus)
Pustules or vesicle lesions may shed virions into the air (eg herpesvirus)

Question 1

What are the 5 principle means of viral transmission?

Answer 1

1. Airborne transmission
2. Body fluid/tissue transmission
3. Faeco-oral transmission
4. Vector transmission
5. foetal and neonatal transmission

Question 2

Describe BODY FLUID/TISSUE transmission.

Answer 2

Transmission of virus via blood products, organ and tissue transplantation and saliva.
Rigorous infection control procedures are implemented with relation to body fluids and tissues in hospitals

Question 3

Describe FAECO-ORAL transmission.

Answer 3

GIT viruses are often shed in faeces. Faecal contamination of food and water is a major problem in areas with poor sanitation, such as third world countries.
Faeco-orally transmitted viruses include hep A, rotavirus and enteroviruses.

Question 4

Describe VECTOR transmission.

Answer 4

The transmission of viruses via a animal, arthropod or insect vector.
Includes arboviruses.

Question 5

Describe FOETAL and NEONATAL transmission. What are the consequences of maternal viral infections?

Answer 5

Transmission from mother to unborn or newborn baby.
Consequences of maternal viral infections are:
Vertical transmission: hep B, HIV
Congenital defects: rubella, EMV, varicella zoster
acquired viral diseases during birth: herpes simplex –> herpes encephalopathy

Question 6

What is latrogenic transmission?

Answer 6

Infection of a patient as a result of the actions of a healthcare worker.

Question 7

What is nosocomial transmission?

Answer 7

Infection of a patient while in a hospital or other healthcare facility.

Question 8

What is vertical transmission?

Answer 8

Transmission of a virus between a parent and offspring.

Question 9

What is germ line transmission?

Answer 9

Pro viral DNA is transmitted as part of the genome.

Question 10

What are 6 methods of viral identification?

Answer 10

1. Electron microscopy
2. Serology
3. Electrophoresis
4. Molecular techniques
5. Immunofluorescence
6. Viral culture

Question 11

Describe electron microscopy.

Answer 11

Uses an electron beam to illuminate a specimen and produce a magnified image.
Need to prepare an extremely thin section of specimen.
This technique was used to identify Zaire Ebola virus.

Question 12

Describe serology techniques.

Answer 12

Analysis of blood sample for IgM and IgG.
IgM indicates recent infection, IgG indicates earlier infection.
Most useful in determining patients immune status, and for epidemiological studies.
Viral diseases diagnosed by serology include HIV, hep ABC, Ross river virus.

Question 13

Describe electrophoresis for viral identification.

Answer 13

Separates viral proteins by size and charge using polyacrylamide gel and charge.
Pattern of separation used to distinguish and identify viruses.
Used to identify HSV-1 and 2

Question 14

Describe molecular techniques used in viral identification.

Answer 14

PCR and DNA/RNA typing: test for presence of live virus in fluids or tissues.
Commercial kits are available for the detection of HPV in cervical cells.
Can test for HIV, influenza A and B, and hep B and C

Question 15

Describe immunofluorescence techniques used in viral identification.

Answer 15

Detects virus using specific fluorescently labelled antibodies for virus.
Gives a rapid result, usually in 2-4 hours.
Only applicable if viral particles are present in high numbers.

Question 16

Describe culture techniques used in viral identification.

Answer 16

Living cells in culture are inoculated with the virus.
Often used to confirm other identification tests, and used in research and in the absence of other identification methods.
Expensive and time consuming. Most viral cultures use cell cultures.

Question 17

Describe cell culture technique.

Answer 17

Uses cell lines such as primary monkey kidney cells, human foetal diploid cells
Grow mono layer of cells in tissue culture flasks
Inoculate virus into culture
Used to identify influenza, enteroviruses, HSV, adenoviruses etc

Observe:
Cytopathic effects of virus
Analyse heterologous interference
Analyse haemagglutination
Analyse plaque forming units

Question 18

What are cytoplasmic effects?

Answer 18

The effect a virus has on host cells. Includes:
Appearance of inclusion bodies
Generation of syncytia
Morphological changes, eg occurrence of spindle shaped cells
Cell death (formation of plaques)

Question 19

Give an example of heterologous interference.

Answer 19

Rubella virus interferes with the replication of picornaviruses

Question 20

What is haemagglutination? How is it analysed in cell culture?

Answer 20

Haemagglutination is the congregation of RBCs.
Haemagglutination inhibition test: strain of virus in haemagglutination assay may be identified by specific antibody that blocks haemagglutination.

Question 21

Name 2 methods of quantitating viruses.

Answer 21

Plaque assay and detection of viral genome (PCR).

Question 22

Describe plaque assay.

Answer 22

10 fold dilution series made form viral stock.
3 most dilute samples are cultured on cell mono layer.
Each plaque formed represents one virus.
Can calculate the concentration of the initial viral suspension (PFU/mL) by dividing number of plaques present by (dilution factor x mL innoculum per plate).

Question 23

What is the viral titre?

Answer 23

The greatest dilution in a plaque assay that retains the following properties:

1. TCD50: titre causing cytopathic effects in 50% of culture cells
2. LD50: titre that kills 50% of inoculated cells
3. ID50: titre that innitiates detectable response (infection) in 50% of cells

Question 24

Describe the detection of viral genomes (PCR).

Answer 24

Viral DNA and/or RNA is extracted from sample. For RNA, a reverse transcription reaction is needed to create complimentary DNA. DNA template is used for quantitative (real time) PCR. Absorbance of sample at the end of each PCR cycle can be measured. This is then compared to a standard curve in order to determine concentration of original sample.