4.3 Infection and Response

What is a pathogen

Pathogens are microorganisms that cause infectious disease.

What are the four types of pathogen

• Virus

• Bacteria

• Fungi

• Protist

How do viruses make us feel ill

They live and reproduce in cells which damages them

How do bacteria make us feel ill

Bacteria may produce poisons (toxins) that damage tissues and make us feel ill.

How can pathogens be spread

They may infect plants or animals and can be spread by direct contact, by water or by air.

Give an example of each pathogen in humans

• Virus- HIV, Measles

• Bacteria- Salmonella, Gonorrhoea

• Fungi- Athletes Foot

• Protist- Malaria

Describe Measles

• Virus

• Symptoms- rash all over body, trouble with kidneys, fever

• Method of transmission- inhalation of droplets from sneezes or coughs

• Long term consequences- can be fatal, struggle with lungs

• Treatment/Prevention- most children are vaccinated against it

Describe HIV

• Virus

• Symptoms- initially causes flu like illness, attacks the body’s immune cells

• Late stage HIV infection (AIDS) occurs when the body’s immune system is so badly damaged it can no longer deal with other infections or cancers

• Method of transmission- STD- sexual contact, or exchange of body fluids, like blood (e.g. when drug users share needles

• Long term consequences- can be fatal, AIDS, immune system failure

• Treatment/Prevention- antiretroviral drugs, drug users don’t share needles

Describe Salmonella

• Bacteria

• Symptoms- Fever, abdominal cramps, vomiting and diarrhoea are caused by the bacteria and the toxins they secrete.

• Method of transmission- spread by bacteria ingested in food, or on food prepared in unhygienic conditions.

• Long term consequences- dehydration, potential death in elderly people

• Treatment/Prevention- poultry vaccination, cooking and pasteurisation of food

Describe Gonorrhoea

• Bacteria

• Symptoms- a thick yellow or green discharge from the vagina or penis and pain on urinating

• Method of transmission- STD- sexual contact

• Long term consequences- infertility, 50% of women and 10% men are asymptomatic

• Was easily treated with the antibiotic penicillin until many resistant strains appeared

• Treatment/Prevention- The spread can be controlled by treatment with antibiotics or the use of a barrier method of contraception such as a condom.

Describe Malaria

• Protist

• The malarial protist has a life cycle that includes the mosquito

• Symptoms- Malaria causes recurrent episodes of fever and can be fatal.

• Method of transmission- mosquito bite

• Long term consequences- fatal

• Treatment/Prevention- mosquito nets to avoid being bitten, mosquito repellant, drain swamps with mosquitos to prevent breeding, vaccination

Give an example of a plant virus, bacteria and fungi

• Virus- Tobacco Mosaic Virus (TMV)

• Fungi- Rose Black Spot

Symptoms of Rose Black Spot and what it leads to

• Black purple spots

• Leaves turn yellow and droop early

• It affects the growth of the plant as photosynthesis is reduced

• Leads to less chlorophyll, which leads to less light absorption, which leads to less photosynthesis, which leads to less glucose, which leads to less bonding with nitrates to form amino acids (proteins) which leads to less growth.

• It is spread in the environment by water or wind

• Rose black spot can be treated by using fungicides and/or removing and destroying the affected leaves.

Symptoms of tobacco mosaic virus and what it leads to

• Tobacco mosaic virus (TMV) is a widespread plant pathogen affecting many species of plants including tomatoes

• It gives a distinctive ‘mosaic’ pattern of discolouration on the leaves which affects the growth of the plant due to lack of photosynthesis.

• Leads to less chlorophyll, which leads to less light absorption, which leads to less photosynthesis, which leads to less glucose, which leads to less bonding with nitrates to form amino acids (proteins) which leads to less growth.

How can plant disease be detected

Plant diseases can be detected by:

• stunted growth (e.g. nitrate deficiency)

• spots on leaves (e.g. black spot fungus on roses)

• areas of decay or rotting (e.g. black spots on roses, blights on potatoes)

• growths (e.g. crown galls caused by bacterial infections)

• malformed stems or leaves (e.g. due to aphid or nematode infestation)

• discolouration (e.g. yellowing or chlorosis in magnesium deficiency, mosaic patterns from TMV)

• the presence of visible pests (e.g. aphids, caterpillars)

How can plant diseases be identified

Identification can be made by:

• reference to a gardening manual or website for garden

• taking infected plants to a laboratory to identify the pathogen

• using testing kits that contain monoclonal antibodies.

What is chlorosis

Lack of chlorophyll cause by a lack of magnesium ions

What are the three types of plant defences

• Physical

• Chemical

• Mechanical

Give an example of a physical defence

• Bark/dead cell layers which fall off- protective layer, hard for pathogens to penetrate; when the layers fall off, pathogens fall off with them

• Tough waxy cuticle on leaves- barrier to entry of pathogens; stomata are only way into the cell

• Cellulose cell wall- strengthen cells, prevent invasion from microorganisms- this is why aphids piercing cell wall is dangerous as it gives pathogens a way into the cell

• Leaf fall- any infected leaves, such as those infected with rose black spot, will fall off the tree and be lost

Give an example of a chemical defence

• Antibacterial chemicals.

• Poisons to deter herbivores.

Give an example of a mechanical defence

• Thorns and hairs deter animals- make eating them painful or painful, and hairs deter insects from laying their eggs in the stems

• Leaves which droop or curl when touched- dislodges insects and frightens animals

• Mimicry to trick animals- trick animals not to eat them, or trick insects not to lay their eggs in them

What are aphids

• Insects with sharp mouths which extract the glucose rich sap of the phloem

• They attack in huge numbers, depriving the plants of the products of photosynthesis

• They also act as vectors- they carry disease, and transfer it with their mouth

What will a nitrate deficiency cause

• Less nitrate ions means, less proteins can be produced by combined them with glucose

• This is seen by stunted growth

What does a magnesium deficiency cause

• Less magnesium means not enough chlorophyll is produced, referred to as chlorosis, causing less photosynthesis

• This is seen by yellowing of the leaves

What does the skin do to stop pathogens entering the body

• Acts as a barrier

• Secretes sebum- antimicrobial

• Dry

What are some non specific human defences

• Tears- antimicrobial properties

• Earwax- trap bacteria

• Skin

• Goblet cells and cilia

• Stomach acid- kills pathogens

• Platelets- form seals by getting stuck in protein fibres and drying

What are the two specialised cells in the trachea that stop pathogens, and what do they do

• Goblet Cell- Produces mucus which traps pathogens

• Ciliated Epithelial Cell- Has hairs called cilia which waft the mucus up the throat and out the nose or mouth

What does smoking do to cilia

It paralyzes it

What are the main two types of white blood cells

Phagocytes and lymphocytes

What do phagocytes do

It engulfs, destroys and kills the pathogens. This is called phagocytosis

What do lymphocytes do

• Release Antibodies - These are proteins which have complimentary shapes to the antigens (markers) on pathogens. They bind to the antigens which destroys and kills the pathogen

• Release antitoxins- These bind to toxins release by bacteria and neutralise them

What is a vaccine

• Contains small quantity of a dead or inactive form of the pathogen

• The spread of pathogens can be reduced by immunising a large proportion of the population.

• They provide a controlled exposure to the pathogen, training and strengthening it so it can fight off the disease in future and help with immunisation

• By stimulating the white blood cells to produce antibodies, and simulating an infection, the immune system is better equipped for a real infection in future

• Memory cells remain in the blood which recognise the pathogens upon secondary infection

• If the same pathogen re-enters the body the white blood cells respond quickly to produce the correct antibodies, preventing infection

What is different between vaccine exposure and secondary infection

• Vaccines have a lag before antibody production begins, infection doesn't

• More antibodies are produced during secondary infection

• Antibodies are produced at a faster rate during secondary infection

• Concentration of antibodies in blood depletes slower after secondary infection

What is a memory cell

Memory cells are lymphocytes that stay in the blood for many years. On exposure to a pathogen they can produce antibodies very quickly

Who discovered the first antibiotic

Alexander Flemming- peniciliin

What are antibiotics used to treat and what are the issues with over use of antibiotics

• Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body.

• It is important that specific bacteria should be treated by specific antibiotics.

• The use of antibiotics has greatly reduced deaths from infectious bacterial diseases.

• However, the emergence of strains resistant to antibiotics is of great concern.

Why will antibiotics not work for viral infections

• Viruses operate and reproduce inside cells

• So will not be e

How are viral infections treated

• Antibiotics cannot kill viral pathogens.

• Painkillers and other medicines are used to treat the symptoms of disease but do not kill pathogens.

• It is difficult to develop drugs that kill viruses without also damaging the body’s tissues.

What are antiseptics

Substances which kill bacteria on surfaces- should not be used in the body

What are anti-inflammatory drugs

Drugs which reduce swelling

Where do drugs traditionally come from

Traditionally drugs were extracted from plants and microorganisms.

• The heart drug digitalis originates from foxgloves.

• The painkiller aspirin originates from willow.

• Penicillin was discovered by Alexander Fleming from the Penicillium mould.

Most new drugs are synthesised by chemists in the pharmaceutical industry. However, the starting point may still be a chemical extracted from a plant.

Where does aspirin come from

willow bark

Which drug comes from foxgloves

Digitalis

What are the stages of developing new drugs

New medical drugs have to be tested and trialled before being used to check that they are safe and effective.

New drugs are extensively tested for toxicity, efficacy and dose.

Preclinical testing is done in a laboratory using cells, tissues and live animals.

Clinical trials use healthy volunteers and patients.

• Very low doses of the drug are given at the start of the clinical trial.

• If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug.

• In double blind trials, some patients are given a placebo.

What is involved in preclinical trials

• Tests on live cells, then animals

• Tests for toxicity

What are the stages of clinical trials

• Phase 1- Low dosage on healthy individuals- Toxicity

• Phase 2- Low dosage on individuals with the disease, may include placebo- Efficacy

• Phase 3- Variety of doses on individuals with the disease, may include placebo and/or double blind test- Dosage and Efficacy

• Peer review- another company or group of scientists check findings, avoids bias, and checks for validity

What is a double blind trial

A trial in which neither the doctors or the patients know which treatment they will receive

What is a placebo

A substance which has no medical effect, used as a control in testing new drugs. It contains no active ingredient

What is a monoclonal antibody

• Monoclonal antibodies are produced from a single clone of cells.

• The antibodies are specific to one binding site on one protein antigen and so are able to target a specific chemical or specific cells in the body.

What is a hybridoma

A hybrid/fusion of a B-Lymphocyte and a tumor cell

How are monoclonal antibodies produced?

• They are produced by stimulating mouse lymphocytes to make a particular antibody.

• The lymphocytes are combined with a particular kind of tumour cell to make a cell called a hybridoma cell.

• The hybridoma cell can both divide and make the antibody.

• Single hybridoma cells are cloned to produce many identical cells that all produce the same antibody.

• A large amount of the antibody can be collected and purified.

What are some ways monoclonal antibodies can be used

• For diagnosis such as in pregnancy tests.

• In laboratories to measure the levels of hormones and other chemicals in blood, or to detect pathogens.

• In research to locate or identify specific molecules in a cell or tissue by binding to them with a fluorescent dye.

• To treat some diseases: for cancer the monoclonal antibody can be bound to a radioactive substance, a toxic drug or a chemical which stops cells growing and dividing. It delivers the substance to the cancer cells without harming other cells in the body.

How can monoclonal antibodies treat cancer

• Monoclonal antibodies can have signals put on that alert white blood cells, when they bind to the antigens of cancer cells

• Monoclonal antibodies can bind to antigens on cancer cells in order to stop growth stimulating proteins binding, which stops the tumour spreading and growing

• Monoclonal antibodies can have radioactive substances or drugs attached to them, which attacks the cancer cell when they bind to the antigens.

What are the advantages and disadvantages of using monoclonal antibodies

Advantages

• Don’t harm other cells, only the harmful ones, because of their specific shape

• Their specificity means they can be used to treat a wide range of diseases

Disadvantages

• Because they are mouse antibodies, they can trigger and immune response in humans, making us feel ill

• Monoclonal antibodies create more side effects than expected. They are not yet as widely used as everyone hoped when they were first developed.

Who are some key individuals in the development of preventing and reducing the spread of disease

• Ignaz Semmelweis- discovered that washing hands between medical procedures reduces the spread of disease

• Louis Pasteur- showed that microorganisms cause disease, and developed vaccines against anthrax and rabies

• Joseph Lister- used antiseptic chemical to sterilise operating rooms before operations