infection and response

• pathogens

  pathogen: any microorganism that carries a disease

  the four types of pathogen, and examples in animals and plants

  • virus
  • eg: animals - HIV (could become AIDS) plants - tobacco mosaic virus
  • bacteria
  • eg: animals - salmonella, plants - agrobacterium
  • fungi
  • eg: animals - athlete's foot plants - rose black spot
  • protists
  • eg: animals - malaria plants - downy mildew
• pathogens

  all pathogens live simple lifecycle:

  infect a host

  reproduce or (if a virus) replicate

  spread from their host and infect other organisms
• all diseases caused by pathogens are communicable diseases: they can be transferred from one organism to another
• pathogens

  types of non communicable diseases and examples

  • inherited disorders - cystic fibrosis
  • defficiency diseases (lack of essential minerals or vitamins) - scurvy
  • diseases like cancer which happen due to exposure to carcinogens or occur naturally due to an error during cell replication
• transmission

  these are the ways pathogens are spread

  • direct contact - sex, shaking hands
  • water - cholera
  • air - when an infected person sneezes or coughes, droplets
  • unhygenic food preperation - under cooked or reheated food can cause escherichia coli (cause of food poisoning)
  • vector - any organism that can spread a disease, mosquitoes
• viral diseases

  • viruses are not alive (do not complete MRS GREN)
  • we say strains of viruses and not species
  • made of short length DNA and are surrounded by a protien coat
  • their lifecycle is the same as other pathogens
  • they can survive outside of the host for long periods
  • when they have infected a suitable host cell(s) they replicate inside the cell
  • they do not divide and reproduce they replicate their dna and coat these are then assembled into new viruses
  • host cell(s) burst and can infect nearby cells
  • cannot be treated with antibiotics
• tobacco mosaic virus

  effects tobacco and other closely related species - peppers, tomatoes

  transmitted by contact

  > either naturally between the plants or from farmers hands

  it infects the chloroplasts of the plant, changing them from green to yellow or white

  it can aslo make the leaves crinkle or curl up

  > reduces plants ability to photosynthesise

  ~ farmer's yield reduces

  there is no cure, instead farmers have to reduce the spread of it
• HIV (human immunodefficiency virus)

  transmitted by body fluids

  > unprotected sex, sharing needles, cuts

  immediately after the patient will experience flu - like symptoms, these will go away, the patient may not know they are infected

  AIDS (aquired immune deficiency syndrome)

  when HIV becomes active again and starts attacking the body's immune system

  there is no cure for HIV / AIDS

  patients are given antiviral treatment to stop HIV progressing into AIDS
• measles

  very infectious viral disease often caught by young children

  transmitted through air, when someone infected sneezes

  causes fever and a rash

  many children are given vaccines, but this isn't available everywhere

  it causes more serious effects such as infertility if caught by an adult who did not have it when younger
• gonorrhoea - bacterial diseases

  common bacterial disease transmtted through sex (STD)

  causes: burning pain when weeing, thick yellow / green discharge from someones naughty bits (male or female)

  if untreated can result in infertility

  prevention: dont have oral or anal and use a condom

  many antibiotics which used to be effective are now not because it is evolving resistance

  scientists are constantly trying to find new antibiotics
• salmonella - bacterial disease

  salmonella is a genus of bacteria which causes food poisoning

  causes: abdominal cramps, vomiting and diarrhoea

  found in unhygenic kitchens, undercooked or unproperly reheated foods (meat, eggs, poulty)

  prevention: in the UK all poultry are vaccinated against it

  cook food thoroughly, after preparing it in hygenic conditions is the best way to avoid it
• Protist diseases

  Protists are a group of microorganisms that have features that belong to animals, plants and fungi.

  They are all eukaryotic, which means they have a nucleus
• Malaria

  Malaria is spread by mosquitos which carry the Plasmodium protist.

  > found in higher temperatures (Africa, Asia, and South and Central America)

  Mosquitos suck blood containing the protists from an infected person. They pass the protist, to other people they suck blood from.

  they're vectors because they transmit it without being effected
• malaria

  symptoms: a fever, sweats and chills, headaches, vomiting and diarrhoea.

  Damage caused to the blood and liver.

  first malaria vaccine in 2021

  preventions: sleep under mosquito nets and wear insect repellent to avoid bites 

  Antimalarial drugs are also taken, which treat the symptoms and can prevent infection.
• fungal diseases

  Not all fungi cause disease. 

  Not all fungi are single-celled

  Fungal cells have a nucleus and so are eukaryotic.
• Athlete's foot

  a rash caused by a fungus that is usually found between people's toes. >causes: dry, red and flaky or white, wet and cracked skin.

  It is often found in communal areas (like swimming pool changing rooms or gyms).

  transmitted by touching infected skin or surfaces that have been previous contaminated.

  It is treated by antifungal medication.
• Rose black spot

  caused by a fungus which infects roses.

  >It infects leaves and causes black or purple spots on the leaves.

  The rest of the leaves often turn yellow and can drop off the plant.

  >reduces that plant's ability to photosynthesise and reduces growth.

  It can be transmitted in air or water, as well as through direct contact by gardeners.

  It is treatable using fungicides and by removing and destroying infected leaves.
• preventing spread of disease

  • Sterilising water (cholera)
  • Chemicals or UV light kill pathogens in unclean water
  • Suitable hygiene (salmonella)
  • Cooking foods thoroughly and preparing them in hygienic conditions kills pathogens.
  • personal hygiene (athlete's foot)
  • Washing surfaces with disinfectants kills pathogens.
  • vaccination (measles)
  • Vaccinations introduce a small / weakened version of a pathogen into your body, immune system learns how to defend itself
  • contraception (HIV / AIDS)
  • Using barrier contraception (condoms) stops the transfer of bodily fluids and STD.
• first lines are general defences, and are not specific to fight against certain types of pathogen.

  They are called non-specific, and they can be physical or chemical barriers.
• skin

  The skin covers almost all parts of your body to prevent infection from pathogens.

  If it is cut or grazed it immediately begins to heal itself, often by forming a scab, which prevents infection as the skin acts as a physical barrier.

  Parts of the body that do not have skin have developed other ways to prevent infection.

  > the eyes produce tears, which contain enzymes, and these are chemical barriers.

  
• Nose

  The nose has internal hairs, which act as a physical barrier to infection. Cells in the nose produce mucus.

  > This traps pathogens before they can enter the lungs.

  When the nose is blown, mucus is removed and any pathogens are trapped within it.
• Trachea and bronchi

  The trachea runs from the nose towards the lungs.

  The cells that line the trachea also have hairs called cilia, which are much smaller than those in the nose (ciliated cells).

  The ciliated cells waft their hairs and move mucus and pathogens upwards towards the throat where it is swallowed into your stomach.

  Other cells called goblet cells create the mucus in order to trap pathogens.

  The production of mucus in your airways is a physical barrier.
• Stomach

  Stomach acid is part of the body's non-specific first line of defence.

  It is hydrochloric acid and while it does us no harm, it is strong enough to kill any pathogens that have been caught in mucus in the airways or consumed in food or water.

  Stomach acid is a chemical barrier against infection.
• phagocytes

  Phagocytes surround any pathogens in the blood and engulf them.

  They are attracted to pathogens and bind to them.

  The phagocytes membrane surrounds the pathogen and enzymes (inside the cell) break down the pathogen and destroy it.

  As phagocytes do this to all pathogens that they encounter, they are called 'non-specific'.

  process is called phagocytosis
• antigen: A protein on the surface of a substance (often a pathogen) that triggers an immune response.
• Lymphocytes

  type of white blood cell.

  recognise proteins on the surface of pathogens called antigens. Lymphocytes detect these are foreign not naturally occurring and produce antibodies.

  > can take a few days, (may feel ill)

  • The antibodies cause pathogens to stick together and make it easier for phagocytes to engulf them.

  pathogens produce toxins which make you feel ill.

  • Lymphocytes also produce antitoxins to neutralise these toxins.
  • Both the antibodies and antitoxins are highly specific to the antigen on the pathogen, thus the lymphocytes that produce them are called 'specific'.
• Vaccinations

  Pathogens are microbes that cause diseases. 

  Vaccines allow a dead or altered form of the disease causing pathogen to be introduced into the body, which contain a specific antigen (protien which triggers immune response) .

  >causes the immune system, specifically the white blood cells, to produce complementary antibodies (target and attach to the antigen)

  When a white blood cell engulfs and digests a pathogen it is called phagocytosis.
• vaccinations

  During the primary infection the antibodies slowly increase, peak at around ten days and then gradually decrease.

  A second exposure to the same pathogen causes the white blood cells to respond quickly in order to produce lots of the relevant antibodies, which prevents infection.

  
• Herd immunity

  Following a vaccination, a person can become immune to the specific disease.

  > immunity gives protection against illness in an individual.

  The majority of the population must be vaccinated against serious diseases ---> reduces the chance of people coming into contact with specific pathogens ---> leading to herd immunity.
• three scenarios in relation to herd immunity. 1

  The majority of the population are not vaccinated against a specific disease, however, a few people are ill and contagious.

  >This can develop easily into a mass infection because the majority of the population are not vaccinated.
• three scenarios in relation to herd immunity. 2

  Most of the population are not vaccinated against the specific disease and are healthy, some are vaccinated and healthy, and a few are not vaccinated, but ill and contagious.

  Mass infection can result again, but a small number of vaccinated individuals remain healthy and some that are not vaccinated will also be healthy.
• three scenarios in relation to herd immunity. 3

  The majority of the population are vaccinated and healthy against a specific disease, a few are not vaccinated but well.

  A few are not vaccinated and they are ill and contagious.

  The result is that the majority are protected due to the high level of vaccination.

  A few individuals will still become ill, but the large number of vaccinated individuals gives protection.
• painkillers

  Painkillers are chemicals that relieve the symptoms but do not kill the pathogens. (paracetamol and aspirin)

  As the symptoms are treated, your immune system still needs to combat the pathogen.
• Antibiotics

  Antibiotics are substances that slow down or stop the growth of bacteria.

  They are commonly prescribed medicines, (penicillin and amoxicillin)

  These can be taken to cure the disease by killing the pathogen, but only cure bacterial diseases and not viral ones.
• penicillin

  1928: Penicillin was the first antibiotic discovered in by Alexander Fleming.

  He noticed that some bacteria he had left in a petri dish had been killed by the naturally occurring Penicillium mould.
• how antibiotics work

  • Antibiotics damage the bacterial cells but do not damage the host cells.
  • They have the ability to cure some bacterial diseases that would have previously killed many people.
  • Since their introduction, they have had a large influence on the world's health and death rate.
  • Different bacteria cause different diseases.
  • One antibiotic may only work against one type of bacteria, or a few types. This means that a range of different antibiotics is needed for the treatment of the whole range of bacterial diseases.
• treating viral diseases

  Viral diseases cannot be cured by antibiotics, as they reproduce inside the host cells.

  It is very difficult to develop antiviral drugs, as they might damage the host cell whist killing the virus.

  Antiviral drugs only slow down viral development, and viruses change their antigens quickly which means new drugs have to be generated regularly.
• antibiotic resistance

  Commonly prescribed antibiotics are becoming less effective due to a number of reasons:

  • overuse of antibiotics
  • failing to complete the fully prescribed course by a doctor
  • use of antibiotics in farming

  These can lead to the effectiveness of antibiotics being reduced, and the incidence of antibiotic resistance increasing. These bacteria are commonly known as superbugs.
• antibiotic resistance - over use

  People feel unwell and when going to the doctors, they expect antibiotics to be prescribed.

  If patients have viral infections (such as the common cold) and not a bacterial one, the antibiotics are ineffective and unnecessary.
• anitbiotic resistance - failing to complete the course

  Patients should always fully complete the prescribed course of antibiotics, every time they are taken.

  • This ensures all bacteria are killed, and so none survive which can subsequently mutate and produce resistant strains.
  • Patients begin to feel well after a few days of taking the medicine, and stop taking them.
  • This is potentially very harmful, as random mutations can occur which can lead to antibiotic resistance.
  • The resistant bacteria reproduce quickly, and the resistance spreads.