All-in-One Infection and Response

Communicable disease

A disease caused by a pathogen which can be passed from organism to organism

Pathogen

A infectious disease-causing microorganism

How do bacteria cause disease

Once inside the body, they divide rapidly by binary fission.

• They damage cells and produce harmful toxins.

How do viruses cause disease

They invade and reproduce inside host body cells.

• Leads to cell bursting → making us feel ill

• releases copies into bloodstream

How do protists cause disease

Parasitic, meaning they use body cells as host cells

• Cause damage to body cells

How do fungi cause disease

Produce spores which can be spread to other organisms

Ways pathogens can be spread

• By air → Pathogens carried in the air and breathed in: droplet infection → when sneezing, coughing or talking expels pathogens

• By water - drinking or coming into contact with dirty water

• By direct contact - touching contaminated surfaces: contact with bodily fluids, microorganisms, infected material

ways to reduce spread of pathogens/disease

• Hygiene - handwashing, disinfectants, tissues when sneezing

• Sterilising water

• Barrier contraception - condoms

• Reducing contact with infected individuals - quarantine.

• Removing vectors - use of pesticides and insecticides, removal of habitats

• Vaccination

importance of preventing viral diseases

Scientists have not yet developed cures for many viral diseases.

• Dangerous pathogens: can enter all types of cells

Measles (Virus)

• Symptoms: Fever, red skin rash → lung infection, brain infection, blindness

• Spread by: Droplet infection: coughs, sneezes

• Prevented: Vaccination for young children → reducing transmission

HIV/AIDS (Virus)

• Symptoms: Initial flu-like symptoms → virus attacks immune system → AIDS

• Spread by: Sexual contact, exchange of bodily fluids: e.g. blood (injections)

• Prevention: Using condoms, no sharing needles, blood screening

  → Development of AIDS: antiretroviral drugs (stops virus replicating in body → must be taken for rest of life)

TMV (tobacco mosaic virus) (Virus)

Plant pathogen

• Symptoms: Discolouration of leaves → leaf cannot photosynthesise properly → reduced yield

• Spread by: Contact between diseased plants and healthy ones, vectors

• Prevention: Field hygiene, pest control, growing TMV-resistant strains

Salmonella food poisoning (Bacteria)

Bacteria living in guts of different animals

• Symptoms: Fever, stomach cramps, vomiting, diarrhoea

• Spread by: uncooked/under cooked meat and eggs, unhygienic conditions

• Prevention: Poultry vaccinated, separating raw and cooked food, hygiene when handling, cooking food thoroughly

Gonorrhoea (Bacteria)

• Symptoms: Yellow discharge from vagina/penis, pain when urinating

• Spread by: Unprotected sexual contact

• Prevention: Using condoms, antibiotics (resistance strains developing)

Rose black spot (Fungi)

• Symptoms: Purple/black spots on leaves → reduces area for photosynthesis → leaves turn yellow

• Spread by: Spores of fungus spread in water or wind

• Prevention: Fungicides, cutting off infected parts

Malaria (Protist)

Protist pathogens enter red blood cells and damage them.

• Symptoms: Fevers, shaking

• Spread by: Vectors (mosquitos) puncturing skin to feed on blood → protists enter bloodstream via saliva

• Prevention: Insect nets when sleeping, removal of stagnant waters to prevent breeding of vectors, antimalarial drugs when travelling, insect sprays

Skin's role in pathogen prevention

• Physical barrier

• Produces antimicrobial secretions → kill pathogens

Respiratory system's role in pathogen prevention

Nose:

• has hairs and mucus → trap pathogens → prevents from travelling to lungs

trachea and bronchi:

• have mucus → traps pathogens

• Ciliated cells → waft mucus upwards to be swallowed

Stomach's role in pathogen prevention

• Produces hydrochloric acid → kills pathogens in mucus, food and drink

Phagocytosis

White blood cells (phagocytes) engulfs and digests pathogens so they cannot infect more cells.

→ Digest pathogens using enzymes

Antibody production (Lymphocytes)

White blood cells produce antibodies which are complementary to a specific antigen on a pathogen.

• binding of antibodies to antigens → pathogens clump together → easier to destroy

In the case of a second infection:

• correct antibodies can be produced at a faster rate → preventing person getting the same disease + symptoms again → immunity

Antitoxin production

Antitoxins bind to toxins released by pathogens and neutralise them.

Vaccination

Contains a dead or inactivated form of the pathogen which stimulates white blood cells to produce complementary antibodies to the pathogen.

Vaccination steps / how it works (6-Marker)

1. Dead/inactive/weak/ form of pathogen introduced into the body

2. (which) stimulates white blood cells / lymphocytes

3. (to) produce antibodies complementary to antigens of specific pathogen

4. antibodies made quickly on re-infection

5. (because of) memory cells that stay in bloodstream post infection

6. antibodies made in larger numbers and persist in bloodstream for longer

7. (so) pathogens rapidly killed before illness

Herd immunity

Limitation of spread of disease when a high proportion of a population is immune to a disease through vaccination.

Advantages of vaccinations

• Eradicated many deadly diseases: e.g. smallpox.

• Reduced occurrence of many: e.g. rubella

• Epidemics can be prevented (herd immunity)

Disadvantages of vaccinations

• Not guaranteed to work - might not protect against multiple strains of a pathogen

• Side effects or adverse reactions: e.g. fevers

• Take long time to develop

Antibiotics

Medicines that kill bacterial pathogens inside the body without damaging body cells.

• Cannot kill viruses: cannot reach inside of human host cells

Antibiotics characteristics: E.g. Penicillin

• Taken as a pill, syrup or injected directly

• Different antibiotics are effective against different types of bacteria → receiving correct one is crucial

• Use had decreased number of deaths from bacterial disease

Painkillers

Only treat symptoms of a disease, rather than the cause.

Antibiotic resistance

Occurs when mutations lead to individual bacteria being resistant to an antibiotic.

1. These bacteria survive

2. non-resistant bacteria die

3. resistant bacteria reproduce and pass on their gene → leading to a greater proportion of antibiotic-resistant bacteria

4. antibiotics no longer effective

Preventing antibiotic resistance

• Avoid overuse and unnecessary use of antibiotics: e.g. use on viral infections, mild colds

  → Reduces unnecessary exposure of antibiotics to bacteria

• Finish antibiotic courses - ensure all bacteria is killed

Plant digitalis is extracted from

Foxgloves.

Painkiller from willow bark

Aspirin.

Penicillin

Antibiotic discovered by Alexander Fleming

1. Was growing bacteria on plates

2. Found mould (penicillium mould) on culture plates with clear rings around mould → indicating bacteria no longer there

3. Found mould was producing a substance that killed bacteria (penicillin)

Three main factors tested for in drug development

• Toxicity - side effects on humans

• Efficacy - how efficient they are

• Dose - how much of drug is needed

Through preclinical testing and clinical trials

Preclinical testing

Carried out in a laboratory - uses cells, tissues and live animals.

Clinical testing

Uses healthy volunteers and patients after preclinical testing.

1. Tested on healthy volunteers with low dose → for no harmful side effects

2. Tested on patients to find most effective dose

3. Patients split: one group given actual drug, one given a placebo → effect of drug observed

   → Can be single-blind - only doctor knows

   → Can be double-blind - neither patient or doctor knows → removing bias when recording results

4. Peer-reviewed by other scientists → check for repeatability.

Aphids

Insects / vectors that weaken a plant and can transfer pathogens from diseased plants to healthy plants.

Reducing aphids

• Chemical pesticides

• biological pest control - using ladybirds.

Nitrate ions: Why plants need them

• convert sugars into proteins → required for the plant to grow

Nitrate deficiency

Growth of the plant will be stunted.

Magnesium ions: Why plants need them

• required to synthesise chlorophyll → absorbs light energy during photosynthesis

Magnesium deficiency

Causes chlorosis (leaves appearing yellow)

• Leaves cannot photosynthesise properly

Symptoms of disease in plants

• Stunted growth (lack of nitrate ions)

• spotted leaves (rose black spot fungus)

• decay/rotting (rose black spot fungus)

• abnormal growths

• malformation of stems/leaves (aphid infestations)

• discolouration (magnesium deficiency/TMV)

• presence of pests (caterpillars)

Identifying plant disease

• Reference to a gardening website or manual

• laboratory testing to identify pathogen

• monoclonal antibody test kits to identify pathogen

Physical defence responses in plants

• Cellulose cell walls - physical barrier into entering cells

• tough waxy cuticle - physical barrier into entering leaves

• outside layer on stems (bark) - stops pathogens entering

• leaf fall - cells fall off with pathogens

Chemical defence responses in plants

• Poisons - deter herbivores

• Antibacterial compounds - kill pathogens

Mechanical defence responses in plants

• Thorns and hairs - deter animals

• leaves that droop/curl on contact - moving away from pathogens or insects

• mimicry to trick animals - droop to look unhealthy → animals avoid them

Monoclonal antibodies (mAbs)

Antibodies that are clones from one parent cell, specific to one type of antigen.

• ability to bind to only one protein antigen → target chemicals and cells in the body

Production of monoclonal antibodies

1. Specific antigen injected into an animal (e.g. mouse)

2. Mice lymphocytes producing complementary antibodies extracted

3. Lymphocytes fused with myeloma cells (tumour cells → divide rapidly) to form hybridoma cells

4. Hybridoma cells divide to produce clones of itself → produce same antibody

5. Monoclonal antibodies collected and purified.

Uses of monoclonal antibodies

• Detection of pathogens

• Location of cancer cells and blood clots

• Used in pregnancy test kits

Myeloma cells

Type of tumour cell.

Uses of monoclonal antibodies - Pregnancy kit tests

Used to detect a hormone, hCG, in the urine of pregnant women

How pregnancy test works

There are two sections of the stick:

→ first section: mobile mAbs complemetary to hCG hormone - attached to blue beads

→ second section: stationary mAbs which are stuck to the stick

1. Individual urinates on first section: If hCG present, it binds to mobile mAbs attached to blue beads to form hCG / antibody complexes

2. Carried in the flow of liquid to second section

3. Stationary mAbs bind to hCG / antibody complexes

4. As each are bound to a blue bead, results shown as blue line → indicating pregnancy

Pregnancy test results if pregnant - simple

• hCG in urine binds to mAbs attached to a blue bead

• mAbs with hCG diffuse up the stick

• mAbs fixed to the stick bind to hCG

• Blue line forms

Pregnancy test results if not pregnant

No hCG in urine so a blue line is not formed.

Uses of monoclonal antibodies - Measure and monitor

Used to measure and monitor levels of hormones or chemicals in the blood.

• mAbs modified to bind to molecule wanted

• mAbs bound to fluorescent dye

• if molecules present, the mAbs bind to it, and dye can be observed

E.g. Blood screening for HIV infections

Uses of monoclonal antibodies - Cancer treament

1. Producing mAbs that bind to tumour markers to stimulate immune system to attack that cell.

2. Using mAbs to bind to receptor sites on cell membrane of cancer cells → growth-stimulating molecules cannot bind → stops cell divison

3. Using mAbs to transport toxic drugs, chemicals or radioactive substances → only damage cancer cells

Advantages of monoclonal antibodies

• Specific to one particular antigen - healthy cells not affected

• Can treat many different conditions

Disadvantages of mAbs

• Difficult too attach mAbs to drugs

• expensive to develop

• produced from mice lymphocytes - trigger immune response in humans