Topic 16 Flashcards
epidemic
- contagion, infection or illness that spreads to many people in one specific geographic region
- epidemic occurs un excess number of cases that would usually be expected of infection or illness
pandemic
contagion, infection or illness, not limited to one geographic location- potential to spread to millions of people in many countries across the globe
conditions that support pandemic
- novel strain appears in geographic area
- human population hasn’t come into contact with pathogen previously- little to no immunity
- vaccine unlikely to exist or in limited quantity- can’t prevent pathogen spread
- pathogen is cause of serious illness in humans and other species
- various non-human hosts acts a reservoirs, pathogen moves from non-human to human host via vectors
- pathogen is easily transmitted- airborne particles or bodily fluid contact
- uncontrolled spread of pathogen occurs across wide geographic area- movement of infected individuals to non-infected area
influenza structure
- neuraminidase and haemagglutinin determine antigenic properties
- genome contains 8 separate segments of RNA- code for 11 proteins- 3 code for RNA polymerase
haemagglutinin
- active at start of infection
- causes virus to attach to target cells
- allows virus to fuse with cell membrane
- allows virus genetic material to invade target cell where it is replicated
neuraminidase
- active at end of infection
- allows virus to diffuse through protective mucus
- facilitates exit of virus progeny from infected cells
- necessary for release of next generation of virions for efficient infection spread
antigenic drift- small gradual changes
RNA of virus undergoes frequent mutation as it replicates
- can have point mutation in one of its genes
- at start, mutated viruses have similar antigenic properties-immune system can still recognise them
- overtime, mutations accumulate- major changes to antigenic properties occur- new subtype identified
- virus is no longer recognised by immune system- can’t stop infection
antigenic shift-sudden big change
-restricted to influenza a virus- only type that can infect both humans and other species
When one host is infected with two different kinds of influenza A virus- a new combination of genetic material can be produced by re-assortment- new virus cannot be identified by the immune system.
This re-assortment is made possible because the influenza A genome is not one long single-stranded RNA chain- eight separate RNA segments that can be swapped.
When this occurs, the influenza viruses can mix and exchange genetic information- new influenza virus subtypes are formed.
As a result, no one in the population is likely to have immunity to this new viral subtype- if people are exposed to this new subtype of virus, they will contract influenza which can develop into an epidemic, or even a pandemic.
reassortment steps
carrier organism becomes infected with two different subtypes of influenza a virus
- inside carrier cells, virus coat breaks down and RNA genes move to nucleus to be copied/transcribed
- viral genes are then prepared for packaging into new virus particles
- repackaging of genes creates virus contains new HA and NA combinations
identifying viruses
X-ray crystallography - determines the structure of viruses.
Electron microscopy - images that distinguish various kinds of virus.
Immunological methods:
ELISA technique can be used to detect the presence of a specific viral antigen in a cell
-Or it can be used to detect presence of antibody to a specific viral disease in body fluids.
In situ hybridisation with DNA probes- detect and locate specific genetic sequences, diagnostic of particular DNA viruses.
Reverse transcriptase techniques can be used to identify RNA viruses.
Restriction enzymes- used to differentiate between different strains of same DNA virus.
ELISA- presence of antigens
A ‘capture antibody’ bound to a solid surface, such as is used to identify the presence of a specific viral antigen through an antigen-antibody reaction.
All unbound material washed away.
A second antibody with enzyme indicator is then added, along with a substrate for this enzyme- enables production of coloured complex.
If colour appears, the specific viral antigen is present; if no colour appears, the specific viral antigen is absent.
ELISA for antibodies
To detect antibodies to viruses, viral protein is linked to the solid support, and then the clinical specimen is added.
If antibodies against the virus are present in the specimen, they will bind to the immobilized antigen.
The bound antibodies are then detected by using a secondary antibody that binds to the first antibody.
identifying bacteria
Phenotypic methods:
Use of microscopy- differentiate bacteria on the basis of differences in cell wall, size and response to gram stain, physical features such as the presence or absence of a capsule.
Use of different media- differentiate bacteria on variation in growth patterns, which can distinguish aerobic bacteria from facultative anaerobic.
Use of a range of biochemical tests eliciting different bacterial responses.
Immunological methods:
Monoclonal antibodies.
ELISA
Immunofluorescence
Genotypic and molecular methods:
The examination of the genetic material of bacteria using:
-sequence analyses
-plasmids
antibiotics
- used to treat bacterial infections
- act by killing bacteria/inhibiting their growth
- some are narrow spectrum- limited variety of bacteria
- broad spectrum- many kinds of bacteria
antivirals
type of medication used to treat viral infections
- only effective when virus is in cell and replicating
- do not kill virus but inhibit development
- different antivirals target different stages of replication
