Principles of infection 2

Question 1

What are the general key structural features of viruses?

Answer 1

• Small size
• Can only be seen under electron microscope
• Can be enveloped or non enveloped
• Nucleic acid - DNA or RNA

Question 2

Describe the herpes simplex virus

Answer 2

• Enveloped
• Size varies between 120 to 300nm
• Can not be seen under light microscope
• Nucleocapsid inside enveloped structure
• In between the nucleocapsid and envelope there is the tegument
• Virus has DNA

Question 3

What is herpesviridae?

Answer 3

Name of the family of herpes viruses

Question 4

List members of the herepsviridae

Answer 4

• Varicella zoster virus (chickenpox)
• Epstein Barr virus
• Herpes simplex I
• Herpes simplex II

Question 5

Describe the Epstein Barr virus

Answer 5

• Causes glandular fever
• DNA
• Enveloped

Question 6

Describe adenovirus

Answer 6

• No envelope
• DNA virus
• Different ‘serotypes’ of adenoviruses
• Eye infection, respiratory infection, GI infection

Question 7

Describe papillomavirus

Answer 7

• No envelope
• DNA genome
• Warts
• Cervical cancer

Question 8

Describe HIV

Answer 8

• RNA virus
• Enveloped

Question 9

Describe rotavirus

Answer 9

• Non-enveloped
• Small
• Causes diarrhoea

Question 10

Describe Ebola

Answer 10

• RNA virus
• Enveloped
• Natural reservoir not yet identified
• Infects many cell types
• Migrates from initial site of infection to lymph nodes then liver, spleen, adrenal gland
• Tissue necrosis
• Inflammation
• Organ failure

Question 11

What are the symptoms of ebola?

Answer 11

Symptoms appear from 2 to 21 days after exposure and ebola is only transmitted once symptoms begin

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

Question 12

What is horizontal transmission?

Answer 12

Human to human transmission

• measles
• mumps
• adenoviruses
• influenza
• ebola

Question 13

What is vertical transmission?

Answer 13

Mother to foetus

E.g. Rubella virus

Question 14

How is herpes simplex I transmitted?

Answer 14

Oral contact

Question 15

How is herpes simplex II transmitted?

Answer 15

Sexual contact

Question 16

How is EBV transmitted?

Answer 16

• Most common is through saliva
• Using saliva contaminated objects can also result in transmission
• Can also be transmitted through blood and semen

Question 17

How is adenovirus transmitted?

Answer 17

Depends on virus serotype

Respiratory - Droplets

GI - Ingestion of contaminated food or water

Eye - Contact with contaminated objects

Question 18

How is papillomavirus transmitted?

Answer 18

Skin contact

Sexual contact

Question 19

How is measles transmitted?

Answer 19

• Contact with infectious droplets
• Airborne transmission

Question 20

How is mumps transmitted?

Answer 20

Direct contact with saliva or respiratory droplets

Question 21

How is rabies transmitted?

Answer 21

Animal bites

Question 22

How is rotavirus transmitted?

Answer 22

Mainly faecal oral

Question 23

How is ebola transmitted?

Answer 23

• Person to person transmission
• Direct contact with blood or body fluids
• Contaminated objects- needles, syringes
• Can enter through mucous membranes or breaks in skin
• Contact with infected bodily fluids, blood, faeces and vomit
• Also detected in breast milk, urine and semen

Question 24

How can a viral infection be diagnosed clinically?

Answer 24

• Patient symptoms
• How long have the symptoms existed
• Have there been contacts with sources of infection
• What is circulating in the population
• Location
• Lifestyle
• Other risk factors

Question 25

How can a viral infection diagnosed in a lab?

Answer 25

• Immunoassay - Looking for antibodies for the virus
• 2 types of antibodies:
  
  • IgM - Indicates recent infection
  • IgG - Indicates past infection
• Look for virus by electron microscopy - not used anymore, this is historical data
• Culture virus in cells - light microscopy looking for cytopathic effect - not in common use in diagnostic labs, this is historical
• Culture virus in cells and look for viral proteins in cell cultures
• Use immunofluorescence labelled antibody directed against viral proteins. You can see the viral proteins - Not used in diagnostic labs

Question 26

What are the current methods used to diagnose viral infections?

Answer 26

• Look for viral RNA/DNA in tissue or blood
• To detect these, the viral DNA or RNA must be amplified
• To amplify the nucleic acid, PCR is used
• Most recent methods use Real Time PCR equipment. Monitors amplification of a targeted DNA molecule during PCR.