S1: Principles of Infection II

Question 1

Describe the structure of herpes simplex virus

Answer 1

• This virus has an envelope, with the size varying from 120-300nm.
  
  • It cannot be seen under a light microscope.
  • There is a nucelocapsid inside the enveloped structure.
  • In between the nucleocapsid and the envelope there is the tegument.
• The virus has double stranded , linear DNA.

Question 2

What is the difference in transmission for HSV 11 and HSV 2?

Answer 2

Herpes simplex type 1 is transmitted by sex

Herpes simplex type 2 is transmitted by kissing

Question 3

Is HSV ‘curable’?

Answer 3

No

The virus will never be cleared after being infected. However, there will be periods of latency where virus replication stops and then reactivation where there is release of the latent virus.

Some infected people will never have recurrences, others may have frequent episodes.

Question 4

Give examples of herpesviridae viruses

Answer 4

Varicella zoster virus which causes chickenpox

Epstein Barr virus which causes glandular fever which is transmitted by kissing

Question 5

Describe Adenovirus

Answer 5

• No envelope
• DNA virus

It is transmitted by coughing or sneezing etc.

There are different serotypes (variations based on antigens) of adenovirus

Question 6

Describe Papillomavirus

Answer 6

• No envelope
• DNA virus

It can cause warts and cervical cancer

Question 7

Describe rotavirus

Answer 7

• Non enveloped small virus

can cause diarrhoea

Question 8

What is horizontal transmission?

Answer 8

Viruses transmitted by human to human

Question 9

Describe Ebola

Answer 9

• Enveloped
• RNA virus

Its natural reservoir has not yet been identified and its possible that the first patient was infected through contact with an infected animal, most likely bats or primates. Then this was/is spread by person to person transmission (horizontal), through direct contact with blood or body fluids. Or, through contaminated objects, such as needles/syringes.Its natural reservoir has not yet been identified and its possible that the first patient was infected through contact with an infected animal, most likely bats or primates. Then this was/is spread by person to person transmission (horizontal), through direct contact with blood or body fluids. Or, through contaminated objects, such as needles/syringes.

Question 10

Symptoms of Ebola

Answer 10

• Fever
  
  • Headache
  • Diarrhoea
  • Vomiting
  • Stomach pain
  • Muscle pain
• Unexplained bleeding or bruising

Question 11

How does ebola attack the body?

Answer 11

Ebola enters through the mucous membranes or breaks through the skin or possibly parenterally (taken in through body in a way other than digestive tract). It will then infect many cell types in the body. Then will migrate from the initial site of infection to the lymph nodes, then liver, spleen and adrenal gland.
Tissue necrosis occurs, inflammation and finally organ failure.

Question 12

Give an example of a virus that occurs by foetus vertical transmission

Answer 12

Rubella

Question 13

Give examples of viruses that enter via insect bites or animal bites

Answer 13

Virus may enter via insects bites, for example haemorrhagic fevers and yellow fever.

They may enter by animal bites e.g. rabie

Question 14

What are the 2 parts to diagnosing an infection?

Answer 14

1. Clinical

2. Lab based

Question 15

What factors are considered when you clinically (what you ‘see’) diagnose a patient?

Answer 15

▪ Patient symptoms
	▪ How long have the symptoms existed
	▪ Has there been contact with sources of infection
	▪ What is circulating in the population
	▪ Location
	▪ Lifestyle
	▪ Other risk factors

Question 16

What is immunoassay?

Answer 16

Looking for antibodies to virus in the blood

Question 17

What does the presence of IgM and IgG indicate?

Answer 17

▪ IgM which indicates recent infection (or current)

▪IgG which indicates a past infection that the patient has now recovered from

Question 18

Why is PCR important in diagnosing viruses?

Answer 18

t is difficult to detect the RNA/DNA as there is generally not enough in the sample to be detected directly. So viral DNA/RNA needs to be amplified, this is done by the polymerase chain reaction (PCR) which amplifies nucleic acids.

These can then be run on a gel (gel electrophoresis) and the amplified product can be seen as a band.

Question 19

What is immunofluorescence labelling method?

Answer 19

It looks for viral proteins in cell cultures

• An antibody directed against viral proteins is used and labelled with an immunofluorescence tag
• When they bind to viral proteins, the viral proteins can be seen