Principles of infection 2

Question 1

Herpes simplex virus

envelope?
size?
light microscope? 
other structures?
dna?

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 nucelocapsid and the envelope there is the tegument, the virus has DNA

Question 2

Herpesviridae (class of viruses)

how is the two types transmitted?

Answer 2

Herpes simplex type 1 is transmitted by sex

Herpes simplex type 2 is transmitted by kissing

Question 3

Transmission

how?
how can transmission be increased?

Answer 3

herpes virus type I - mainly oral contact

Transmission may be increased if an individual has multiple sexual partners, although more sexual partners are more likely to have antibodies to HSV2. If you have a single sexual partner you may still be infected, if your partner has multiple sexual partners

Question 4

Latency + re-activation

what happens after infection?
what does this mean?

Answer 4

The virus will never be cleared after being infected, 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. The most common is between one and five per annum

Question 5

Examples of herpesviridae virus

2 examples and what they cause

Answer 5

Varicella zoster virus which causes chickenpox

Epstein Barr virus which causes glandular fever which is transmitted by kissing and Can also be transmitted through blood and semen

Question 6

Adenovirus

envelope?
DNA?
transmitted how?
what do they cause? (3)

Answer 6

There is no envelope and it is a DNA virus.
It is transmitted by coughing or sneezing etc.
There are different serotypes (variations based on antigens) of adenovirus.
They may cause an eye infection, respiratory infection or gastrointestinal infection.

Question 7

adenovirus transmission

what does mode of transmission depend upon?
describe the 3 modes

Answer 7

Mode of transmission depends on the virus serotype.
Respiratory infection – droplets
Gastrointestinal infection – ingestion of contaminated food or water.
Eye infection – contact with contaminated objects

Question 8

Papillomavirus

envelope?
Dna?
what can it cause? (2)

transmitted how? (2)

Answer 8

This also has no envelope and is a DNA virus, it can cause warts and cervical cancer

Skin contact.
Sexual contact

Question 9

Human immunodeficiency virus

envelope?
Dna?

Answer 9

This is an enveloped virus containing RNA

Question 10

Rotavirus

enevelope?
size?
symptom?
transmission?

Answer 10

Non-enveloped
Small
Diarrhoea
Transmission mainly faecal oral

Question 11

Mumps virus

transmission?(2)
what is available?

Answer 11

Direct contact with saliva or respiratory droplets.

Vaccine available

Question 12

Measles virus

what is available?
transmission?

Answer 12

Vaccines are available
Contact with infectious droplets
Airborne transmission

Question 13

horizontal transmission

what is this?
example of viruses transmitted this way (5)

Answer 13

Human to human transmission

viruses which are transmitted this way include: measles, mumps, adenovirus, influenza, ebola

Question 14

Early symptoms of Ebola infection

when can symtpoms appear after infection?
when can it spread?

symtoms>

Answer 14

Symptoms can appear from 2 to 21 days after exposure – only spreads after symptoms begin
Fever
Headache
Diarrhoea
Vomiting
Stomach pain
Muscle pain
Unexplained bleeding or bruising

Question 15

Ebola

DNA?
envelope?
first infection?
tranmission? (3)

Answer 15

RNA virus
Enveloped
Natural reservoir not yet identified
Possible that first patient infected through contact with infected animal – bats or primates
Then person to person transmission
Direct contact with blood or body fluids
Contaminated objects – needles syringes

Question 16

Ebola entering + effect

how can it enter the body? (3)
what will it do? where does it migrate?
effect of this?

Answer 16

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 17

sexual transmission (2 examples)

Answer 17

Papilloma in genital tract

HIV

Question 18

Mother to foetus vertical transmission - example

Answer 18

Rubella virus

Question 19

insects bites - example (2)

Answer 19

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

Question 20

animal bites - example

Answer 20

rabies

Question 21

Key structural points

Answer 21

Size - small
You can’t see the virus under light microscope. Need electron microscope
Can be enveloped or non enveloped
The nucleic acid – DNA or RNA

Question 22

vriuses that infect humans

examples

Answer 22

	Herpes simplex type 1
	Herpes simplex type 2
	Varicella zoster
	Epstein Barr virus
	Rubella
	Measles
	Mumps
	Rabies
	HIV
	Poxvirus
	Influenza
	Rhinovirus
	Rotavirus
	Ebola virus
	Adenovirus

Question 23

How do you diagnose infection
clinical

6 things to think about?

Answer 23

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 24

How do you diagnose infection
lab based

what do you look for? process called?
whats the 2 different types?

Answer 24

look for antibodies to the virus – method is called immunoassay
Two different types of antibody
IgM – recent infection
IgG – past infection

Question 25

How do you diagnose infection
not used now

2 ways

Answer 25

Look for Virus by Electron Microscopy

Culture virus in cells – light microscopy looking for cytopathic effect

Question 26

not used in diagnostic labs

why culture the virus in cells? what do you look for? what is the process called?

explain process

Answer 26

Another way could be by culturing the virus in cells and look for viral proteins in the cell cultures. To do this you would use an immunofluorescence labeling method.

First you’d use an antibody directed against viral proteins and you’d label that antibody with an immunofluorescence tag. When they bind to the viral proteins you’ll be able to see the viral proteins.

Question 27

What are the current strategies?How do we diagnose infection?

2 methods?
why can’t you detect RNA/DNA? what can be done about this?

Answer 27

Look for viral proteins in patient’s tissue/blood
Use immunoassay

It 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 which amplifies nucleic acids. These can then be run on a gel (gel electrophoresis) and the amplified product can be seen as a band.