Infection and response

what is a communicable disease?

diseases caused by microorganisms (pathogens) they can be transmitted from person to person

cell structures for bacteria?

• loop of DNA

• plasmids (resistance)

• antigen

• flagella

what is a virus not?

LIVING OR A CELL

structure of virus?

• protein coat

• genetic material

what is an antigen

foreign molecule, usually protein, recognised by WBC

how do bacteria reproduce?

• bacteria enter body

• feed on nutrients

• divide by binary fission - large numbers

how do viruses reproduce?

• enter the body and invade body cells

• cause host cells to make more virus

how do bacteria cause symptoms?

• produce waste products which are poisonous

• toxins which damage/destroy body cells

who do viruses cause symptoms?

• take over cells, therefore cells get DAMAGED

4 methods of pathogen transmission

1. direct contact

   • STD

   • re-using dirty needles

   • through a cut

2. Water/food

   • humans - contamination (salmonella/cholera)

   • plants - fungal spores via water

3. air (droplet infection)

   • coughing/sneezing when ill in humans - breathed in

   • plants - fungal spores by wind

4. Animals spread pathogens as vector - rabid dog/mosquito

4 primary and non specific defence systems

• skin - covers the body acting as a barrier

• nose - hair and mucus trap pathogens

• trachea/bronchi also produce mucus. moved by cilia to throat (mexican wave) swalled to stomach

• stomach - produces HCl to destroy pathogens

Measles

• type of pathogen

• symptoms

• method of transmission

• treatment/prevention

• virus

• red skin rash, fever

• droplets from infected person’s cough/sneeze

• vaccination, no treatment

HIV

• type of pathogen

• symptoms

• method of transmission

• treatment/prevention

• virus

• flu like symptoms for a few weeks

• sexual contact, exchanging bodily fluids (sharing needles)

• Antiretroviral prevents development of AIDS. no cure/vaccine. use of condoms/not sharing needles

TMV

• type of pathogen

• symptoms

• method of transmission

• treatment/prevention

• virus

• mosaic pattern on leaves of plants - discoloured

• contact disease/healthy plant - insect vectors

• no treatment, good field hygiene + pest control to prevent

salmonella

• type of pathogen

• symptoms

• method of transmission

• treatment/prevention

• bacteria

• fever, abdominal cramps, vomiting, diarrhoea

• eating undercooked poultry/eggs, eating food prepared in unhygienic places

• vaccinate poultry, cook poultry thoroughly

gonorrhoea

• type of pathogen

• symptoms

• method of transmission

• treatment/prevention

• bacteria

• green/yellow discharge from penis/vagina, pain when urinating

• sexual contact

• treated with antibiotics, use condoms

rose black spot

• type of pathogen

• symptoms

• method of transmission

• treatment/prevention

• fungus

• purple/black spots on rose leaves

• spores of fungus carried by wind

• cut off leaves - burn, fungicides

malaria

• type of pathogen

• symptoms

• method of transmission

• treatment/prevention

• protist

• episodes of fever/shaking

• mosquito - vector

• treated using combination of drugs, prevent with antimalarial drugs, insecticides, preventing breeding

4 methods to prevent spread of disease

1. isolate infected individuals

2. hygiene

3. vaccination

4. destroying vectors

how does isolating individuals work/prevent spread of disease?

• stay at home until no longer infectious

• remove infected plants + burn them to prevent spread

how does destroying vectors work/prevent spread of disease?

• use insecticides to destroy insects that may transmit disease

• avoid/kill animals that have rabies

• kill mosquitos - repellent spray, sleep in insect net

how does hygiene work/prevent spread of disease?

• washing hands/sanitise

• face masks

• clean surfaces

• cook food thoroughly

how does vaccination work/prevent spread of disease?

• makes people immune to that disease so they can’t pass it on

• herd immunity

• poultry vaccinated against salmonella

immune response on first infection?

slow response, time for the pathogens to increase and cause symptoms, get ill

3 things WBC do

1. Phagocytosis

2. antibody production

3. antitoxin production

how does phagocytosis work?

WBC engulf and digest pathogens

how does antibody production work(+immunity)?

• produced by lymphocytes ( WBC)

• able to bind to pathogens as complimentary shape to antigen

• each wbc can make one antibody

• if invaded by pathogen, correct wbc is selected and divides by mitosis

• release millions into blood

• antibodies attach to pathogens and destroy them

• large number of specific wbc stay in blood as memory cells

• if same pathogen invades again, memory cell found quickly and produce many antibodies before symptoms (immune to this pathogen)

how does producing antitoxins work?

• antibodies called antitoxins bind to toxins (released by bacteria) to make them harmless

how do vaccines work?

• vaccine contains antigens of either dead or weakened pathogens

• stimulates same specific lymphocytes, which stay in blood as memory cells

what is herd immunity?

approx 90% of pop vaccinated - so few vulnerable people that spread of disease is reduced

what happens at each stage?

• INITIAL - primary response is slow, takes time to select specific and divide by mitosis

• person develops symptoms

• PRIMARY RESPONSE - pathogen destroyed

• SECONDARY EXPOSURE(same pathogen) - most antibodies broke down, memory cells remain

• much quickER response, produces MORE antibodies to destroy pathogen quickly due to memory cells = no symptoms = immune

• SECONDARY RESPONSE - pathogen destroyed

2 main treatment methods

1. relieve symptoms - doesn’t destroy pathogens - paracetamol, ibuprofen

2. destroy pathogens- anti- viral drugs, antibiotics

what are anti-viral drugs?

few exist, difficult to develop drugs that destroy viruses without damaging body’s tissues

what are antibiotics?

• used to kill bacteria in body → NOT VIRUSES

• decreased deaths from bacterial infections greatly

• some antibiotics treat some bacteria, others needed to be treated with different ones

• must be used carefully to prevent resistance(mutation

how do bacteria become resistant, what is an example?

MRSA

• bacteria divide by binary fission, one undergoes a mutation of DNA

• bacteria not resistant killed by antibiotics

• bacteria with resistant allele divides many times by binary fission - survives and reproduce

3 ways to reduce development of antibiotic resistant strains?

1. doctors should not prescribe antibiotics inappropriately

   • for viral infections

   • non serious infections

2. patients must complete full course of antibiotics so ALL bacterial pathogens are killed

3. limit use of antibiotics in agriculture

is it possible to keep up with emergence of new resistant strains?

no, development of new antibiotics is costly and slow

what drug is extracted from willow, what does it do?

Aspirin - painkiller, treats fevers

what drug is extracted from foxgloves, what does it do?

Digitalis - treats heart conditions

what drug is extracted from mould, what does it do?

Penicillin - kill bacteria, treat infections

conditions needed for bacteria to reproduce?

• oxygen

• warmth

• nutrients

4 parts of aseptic technique

• petri dishes and culture must be sterilised before use - kills unwanted microorganisms

• inoculating loop/glass spreader sterilised by heating in roaring bunsen flame

• lid of petri dish secured with adhesive tape to prevent microorganisms from contaminating, store upside down to stop condensation falling on agar surface

• school/college - incubated max temp 25 degrees, reduces likelihood of harmful pathogens

formula for calculating number of bacteria in population

bacteria at end of growth = bacteria at beginning x 2^{number of divisions}

7 stage of drug development

1. disease is targeted. chemical extracted from a plant or microorganism, or synthesis of new drugs

2. drugs tested in lab to see if they are toxic and if they work

3. Preclinical testing in lab - cells, tissues, organs

4. testing carried out on live animals - efficacy, dosage and side effects

5. Clinical trials carried out using healthy volunteers then patients. scientists start with a low dose. if drug is safe, more trials carried out to find optimum case. may be double blind with placebo

6. peer review to prevent false claims

7. results are published

What is a double blind trial?

Patients randomly allocated to drug or placebo group

• Scientists and patients DO NOT know whether they are getting drug or placebo

• avoids bias

what is a placebo?

• a drug with no therapeutic effect (e.g. sugar pill)

• act as a control so you can see how effective the new drug is