Principles of infection 2 Flashcards
Herpes simplex virus
envelope? size? light microscope? other structures? dna?
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
Herpesviridae (class of viruses)
how is the two types transmitted?
Herpes simplex type 1 is transmitted by sex
Herpes simplex type 2 is transmitted by kissing
Transmission
how?
how can transmission be increased?
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
Latency + re-activation
what happens after infection?
what does this mean?
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
Examples of herpesviridae virus
2 examples and what they cause
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
Adenovirus
envelope?
DNA?
transmitted how?
what do they cause? (3)
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.
adenovirus transmission
what does mode of transmission depend upon?
describe the 3 modes
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
Papillomavirus
envelope?
Dna?
what can it cause? (2)
transmitted how? (2)
This also has no envelope and is a DNA virus, it can cause warts and cervical cancer
Skin contact.
Sexual contact
Human immunodeficiency virus
envelope?
Dna?
This is an enveloped virus containing RNA
Rotavirus
enevelope?
size?
symptom?
transmission?
Non-enveloped
Small
Diarrhoea
Transmission mainly faecal oral
Mumps virus
transmission?(2)
what is available?
Direct contact with saliva or respiratory droplets.
Vaccine available
Measles virus
what is available?
transmission?
Vaccines are available
Contact with infectious droplets
Airborne transmission
horizontal transmission
what is this?
example of viruses transmitted this way (5)
Human to human transmission
viruses which are transmitted this way include: measles, mumps, adenovirus, influenza, ebola
Early symptoms of Ebola infection
when can symtpoms appear after infection?
when can it spread?
symtoms>
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
Ebola
DNA?
envelope?
first infection?
tranmission? (3)
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
Ebola entering + effect
how can it enter the body? (3)
what will it do? where does it migrate?
effect of this?
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.
sexual transmission (2 examples)
Papilloma in genital tract
HIV
Mother to foetus vertical transmission - example
Rubella virus
insects bites - example (2)
Virus may enter via insects bites, for example haemorrhagic fevers and yellow fever
animal bites - example
rabies
Key structural points
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
vriuses that infect humans
examples
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
How do you diagnose infection
clinical
6 things to think about?
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
How do you diagnose infection
lab based
what do you look for? process called?
whats the 2 different types?
look for antibodies to the virus – method is called immunoassay
Two different types of antibody
IgM – recent infection
IgG – past infection
How do you diagnose infection
not used now
2 ways
Look for Virus by Electron Microscopy
Culture virus in cells – light microscopy looking for cytopathic effect
not used in diagnostic labs
why culture the virus in cells? what do you look for? what is the process called?
explain process
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.
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?
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.
