16. Biological Knowledge and Society Flashcards
Epidemic
Outbreak of a contagious disease that spreads readily and extensively and effecting many individuals simultaneously in an area or a population
Pandemic
An epidemic over a wide geographic area and affecting a large proportion of the population
Conditions that support a pandemic
🔹 When a new pathogen or novel strain of an existing pathogen appears in geographic areas which humans have not come into contact with (little to no immunity)
🔹 Vaccine is unlikely to exist or the vaccine is available in limited amounts that are not sufficient to prevent the spread of the pathogen.
🔹 Pathogen causes serious illness in people and other species
🔹 Non human hosts act as reservoirs of the pathogen and pathogen moves from non human host to human host via suitable vector.
🔹 Pathogen easily transmitted from people by airborne particles or contact with blood or bodily fluids
🔹 Uncontrolled spread of pathogen occurs across wide geographic region, movement of infected individuals or migration of infected vectors that transmit pathogen from infected to non infected people.
What is the structure of the influenza A virus?
🔹 Two kinds of protein embedded in the lipid bilharziasis membrane forming outer envelope of the virus
🔹 Hemagglutinin (HA) and neuraminidase (NA)
🔹 19 different Hemagglutinin types have been identified and 11 different subtypes of neuraminidase (NA)
What is the size of the influenza virus?
Spherical particles with diameter in the range of 80-120 nm
Genome of influenza virus
Single stranded RNA molecule organised into eight separate segments encoding 11 proteins.
Three of the segments encode sub unit of RNA polymerase, enzyme that is needed when infected host cell makes copies of the viral genome
Role of Hemagglutinin (active at start of infection)
🔹 allows virus to attach to target cells
🔹 causes virus to fuse to cell membrane
🔹 allows viral genetic material to invade target cell where it will replicate
Role of neuraminidase (active at end of infection)
🔹 allows virus to diffuse through protective mucus
🔹facilitates the exit of virus progeny from infected cells.
🔹 necessary for release of the next generation of virions for efficient spread of infection
How do you name an influenza virus?
🔹 TYPE a b or c
🔹 STRAIN host, geographical origin and year of isolation
🔹 SUBTYPE applies to influenza only H1 to H15 and N1 to N9
Antigenic drift (gradual small changes)
🔹 RNA of infected virus continually undergoes frequent mutations as it replicates, can have nucleotide change or point mutation on one of its genes
🔹 Initially mutated viruses closely related to one another and have similar antigenic properties
🔹 Under these circumstances the memory cells of a person’s immune system will recognise and respond to these viruses.
🔹 Over time accumulation of small changes means antigenic properties of mutated viruses altered to major degree. New subtype identified.
🔹 virus no longer recognised by immune system memory cells so infected person has symptoms.
Antigenic shift (sudden BIG change)
🔹 Influenza A virus can undergo majors sudden change in HA and NA surface proteins
🔹 When one host is infected with 2 different kinds of influenza A virus a new combination of genetic material can be produced by reassortment and the virus cannot be identified by the immune system.
🔹 Influenza A genome not one long single stranded RNA chain but consists of 8 separate RNA segments that can be swapped.
🔹 Reassortment of viral genetic material commonly occurs when host becomes infected with two or more different influenza viruses at the same time. Can exchange genetic information so that the new influenza virus subtypes are formed.
What is the effect of antigenic shift
No one in the population is likely to have immunity to the new viral subtype so that if people are exposed to this new subtype of virus they will contract influenza which can develop into an epidemic or even a pandemic
Why is antigenic shift restricted to influenza A virus
They are the only influenza viruses that infected not only people but other species. As a result strains of influenza can become very different during their transmission within animal groups
Steps of reassortment
🔹 Virus coat breaks down and RNA genes move to the cell nucleus to be copied and transcribed
🔹 Viral genes are copied and prepared for packaging into new virus particles
🔹 Repackaging of genes creates a virus that can transfer from human to human
Define rational drug design
Construction of a drug to fit the active site of a molecule so that the natural action of the molecule cannot occur
Why are scientists able to design a drug that’s effective against ALL influenza strains
🔹 Neurominidase is a surface antigen which is an enzyme responsible for allowing newly formed virions ot exit from an infected body cell.
🔹 Although there are many differ subtypes of Neurominidase with varying structures, all the subtypes have the SAME ACTIVE SITE
What must scientists do when designing a drug against the influenza virus?
🔹 Work out shape and structure of active site
🔹 Identify the spatial arrangements of atoms surrounding active site
🔹 Note key amino acids that form the active site
🔹 Design inhibitor with complementary shape that could occupy the active site
🔹 Ensure the designed drug has charged groups on the molecule that would bind more tightly to the active site than the normal substrate
How does relenza work?
🔹 Relenza = zanamivir
🔹 Relenza works by binding to the active site of Neurominidase so that the viruses are trapped on the surface of the cell.
🔹 With the active site blocked, the Neurominidase cannot cut the sialic acid attachment between cell and virus.
🔹 Therefore virus cannot be freed to invade other body cells so it reduces the number of viruses in the body, thus reduced symptoms
What are physical methods of identifying VIRUSES
🔹 X Ray crystallography - determines the structure of viruses
🔹 Electron microscopy - images that distinguish various kinds of virus
What is an immunological method of identifying viruses?
ELISA technique can be used to detect presence of specific viral antigen in a cell or sample of body fluid, serum. Or to detect presence of antibodies to a specific viral disease in body fluids
How is ELISA used to detect for the presence of antigens?
🔹 A capture antibody bound to a solid surface, such as plastic, is used to identify the presence of a specific viral antigen through an antibody-antigen reaction
🔹 All unbound material is washed away.
🔹 A second antibody with an enzyme indicator is added, along with substrate for this enzyme that enables production of a coloured complex.
🔹 If colour appears the specific viral antigen is present, if no colour appears the specific antigen is absent
How can ELISA be used to detect for the presence of 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 immobilised antigen.
🔹 The bound antibodies are then detected by using a second antibody that binds to the first antibody
What are some molecular techniques for identifying viruses?
🔹 In situ hybridisation with DNA probes to detect and locate specific genetic sequences that are diagnostic of particular DNA viruses
🔹 Reverse transcriptase techniques can be used to identify RNA viruses
🔹 Restriction enzymes can be used to differentiate between different strains of the same DNA virus
Phenotypic methods for identifying BACTERIA
🔹 Use of microscopy to differentiate bacteria on the basis of differences in cell wall, size and response to gram stain and physical features such as the presence or absence of a capsule.
🔹 Use of different media to differentiate bacteria on the basis of variation in growth patterns which can distinguish aerobic bacteria from facultative anaerobes
🔹 Use of range of biochemical tests eliciting different bacterial responses
Shape
Spherical (coccus)
Rod like (bacillus)
Spiral (spirochaetae)
Organisation
Single
In pairs
In chains (strepto)
Clustered (staphylo)
Gelatinous external capsule
Present or absent
Mobility
Motile (with flagella)
Immotile (no flagella)
Gram positive
🔹 Thick peptidogylcan (disaccharide and amino acid) cross linked layers and teichoic acid (polysaccharide)
🔹 Turn violet when treated with gram stain
🔹 Effective antibiotics are penicillin and sulfonamide
Gram negative
Thin peptidoglycan and lipid
When treated with gram stain remains pink
Effective antibiotics are streptomycin tetracycline
Phagocytosis by wbc difficult
Immunological methods of identifying bacteria
Monoclonal antibodies
ELISA
Immunofluroescence
Genotypes and molecular methods of identifying bacteria
Gene probes
Sequence analyses
Plasmid fingerprinting
Antibiotics define
🔹 Class of antimicrobial drug used in the treatment and prevention of bacterial infections
🔹 Act by either killing pathogenic bacteria or by inhibiting their growth
Antiviral drugs
Drugs only effective only when the viruses are located within cells and are undergoing replication
Antiviral drugs do not kill their target pathogen and instead inhibit their development
Different antiviral drugs target different stages of development in different viruses
