3.2.3 Controlling communicable diseases

what are the 3 types of vaccines

1. live attenuated

2. dead microorganisms/killed inactivated

3. pathogen fragments (subunit)

what is live attenuated vaccine

• modified strains of bacteria/virus that cannot cause disease (non pathogenic)

• e.g MMR

PROS and CONS of live attenuated vaccine

PROS:

• provides strongest immune response

• immunity can be passed on —> herd immunity

CONS:

• no suited for immunocompromised people

• bacteria/virus may revert back to pathogenic

• harder to store/transport —> need specific conditions

what is killed inactivated/dead microorganism vaccine

• bacteria/virus killed by heat or chemicals

• but the antigens remain and can initiate an immune response

• e.g flu, hep A

PROS and CONS of killed inactivated vaccine

PROS:

• safer than live attenuated

• easier to store/transport

• not possible for microorganisms to revert back to pathogenic

CONS:

• weaker immune response than live attenuated —> need booster vaccine

• needs adjuvant (chemical added to increase immune response)

what is a pathogen fragment/subunit vaccine

• specific antigens that cause an immune response are extracted and used in the vaccine

• e.g Hep B

what are pros of using a pathogen fragment/subunit vaccine

• can be used to make vaccines for many different strains

• stimulates both cellular + humoral immune response

what is the importance of booster vaccines

• no memory cells produced after first injection

• boosters ensure there’s high numbers of memory cells in the blood

• so upon a 2nd/3rd exposure to pathogen, memory cells will divide rapidly into lots of plasma cells —> more antibodies produced at faster rate

what is the role of vaccination programmes

• protect the population from a wide range of diseases with the aim to achieve herd immunity

what is herd immunity and why’s it important in preventing epidemics

when 80%+ of the population is vaccinated against a certain disease —> prevents infection spreading from infected to non-infected person —> may lead to disease being eradicated —> prevents epidemics

risks of trying to establish herd immunity

• live attenuated vaccines may become pathogenic again and cause disease

• people may have allergic reactions to vaccine

• controversy in effectiveness of vaccines e.g MMR —> people don’t get vaccinated

what are the biological problems in the development of vaccines

1. high mutation rates —> new strains develop —> not recognised by memory cells —> so each new strain needs a new vaccine which TAKES TIME TO DEVELOP

2. antigen variability —> there’s variation in antigens on pathogen —> antibodies can’t bind to antigens as not specific —> new strains of pathogen are formed —> memory cells can’t recognise antigens —> new vaccines needed

EXAMPLE: there’s many sub-types of HIV virus due to variation in antigens

why’s it hard to use and distributed vaccines?

1. storage/production of vaccines - must be in sterile conditions —> must have no contamination —> some vaccines need to be stored in very specific conditions —> expensive

2. nutritional status of target population - malnutrition affects strength of immune response e.g protein deficiency —> aa used as respiratory substrate —> lack of proteins + energy to make antibodies

EXAMPLE: live attenuated vaccines - hard to store/transport + risk of microorganism becoming pathogenic/virulent again

2. distribution - some areas are remote

what are the ethical issues in developing vaccines

• tests on both animals and unaffected humans

• very expensive

• takes a long time

what are the ethical issues in using vaccines

• people need to consent —> balance between people’s right to refuse vaccines whilst still protecting population

• parental consent for childhood vaccines —> HPV VACCINE (see flashcard)

• unknown side effects

ethical issues in HPV vaccine for girls

• HPV = subunit/pathogen fragment vaccine

• offered to all 12-14yo girls —> reduces risk of cervical cancer

• should it be offered to boys as well

• may encourage unprotected sex

• needs parental consent

• vaccine may have side effects

what are the modes of action of antibiotics (how do they work)

• prevent cell wall synthesis - water enters bacterial cell by osmosis —> rupture + cell contents leak out

• prevent transcription/translation —> prevent protein synthesis

• prevent semi-conservative replication —> prevent bacteria reproducing by binary fission

• prevent synthesis of folic acid - folic acid needed for DNA/RNA synthesis

what are the 3 types of antibiotics

1. bactericidal

2. bacteriostatic

3. sulfonamides

why don’t antibiotics work on viruses

• virus has no cell wall

• viruses have no csm membranes

• viruses have no ribosomes

• viruses reproduce inside host cells so can’t be reached by antibiotics

• viruses don’t metabolise

• viruses have viral protein coat/capsid —> antibiotics don’t work on them

what do bactericidal antibiotics do

• kills bacteria

• prevents cell wall synthesis —> water enters bacterial cell by osmosis —> ruptures

what do bacteriostatic antibiotics do

• prevents reproduction/growth of bacteria by preventing protein synthesis

• bacteria survives but can’t reproduce —> can’t make new proteins

what do sulfonamides do

• act as COMPETITIVE INHIBITORS for bacterial enzymes

• prevent folic acid synthesis —> can’t make DNA

how does kirby bauer test work

• work in sterile conditions - bunsen burner to create upward convection current to carry away microorganisms, disinfect surfaces using VirKon

• sterilise all equipment e.g wave inoculating loop in open flame

• use inoculating loop to uniformly spread bacteria across agar plate

• add discs soaked in antibiotics

• tape only 2 sides of petri dish and store upside down - condensation collects on lid not agar

• incubate at temperatures below 25oC so no harmful pathogens are cultured

• after a few days, remove and measure zone of inhibition

how does antibiotic resistance occur

• variation in bacteria population

• some bacteria have a mutation which makes them resistant to antibiotic

• antibiotics are a selection pressure

• antibiotic resistance provides a selective advantage

• bacteria with antibiotic resistance have a higher chance of surviving and reproducing

• advantageous alleles passed on

• continues over many generations

what can cause antibiotic resistance

• spontaneous mutations

• antibiotics given for viral infections

• people don’t finish course of antibiotics

• only broad spectrum antibiotics used when pathogen isn’t known

• use of antibiotics in livestock

EQ: why may an antibiotic that’s effective on gram negative bacteria not work on gram positive

can’t reach cell membrane due to thick peptidoglycan cell wall

what is a vaccine

weakened/dead form of a microorganism that triggers an immune response

EQ: describe how hospital staff and medical professionals can help to prevent the spread of these resistant strains.

• isolation of infected patients

• disinfect hands/wear disposable gloves

• regularly clean the wards

• regularly clean bedding/tables/equipment

why do antibiotics not harm human cells

human cells don’t have cell walls