Microbes and diseases
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Microbes and Diseases PowerPoint PPT Presentation

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A microbe is anything too small to be seen without a microscope. Microbes are in the water you drink, the food you eat, and the air you breathe - they are everywhere. About 95% are good for us. Microbes and Diseases. These are called PATHOGENS. They include: Viruses Bacteria Fungi

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Microbes and Diseases

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A microbe is anything too small to be seen without a microscope

Microbes are in the water you drink, the food you eat, and the air you breathe -they are everywhere.

About 95% are good for us.

Microbes and Diseases

These are called PATHOGENS.

They include:

  • Viruses

  • Bacteria

  • Fungi

    The body’s natural barriers:

  • The skin stops microorganisms getting into the body

  • Sweat forms an extra protective layer over the skin

  • Tears contain chemicals that can kill bacteria

  • Stomach acid can kill bacteria in food and water

Microorganisms that cause Diseases

Microbes can cause diseases





influenza (flu)

food poisoning


sore throats

athlete’s foot


tuberculosis (TB)







German measles

whooping cough





These can be caused by cell damage or by toxins (poisons)

A rash Fever Swelling Vomiting Diarrhoea

SYMPTOMS–signs of a disease (illness) not normal



Cough Dizziness Pain Breathing problems




  • They infect cells and use them to make many more viruses. They cannot reproduce by themselves.

  • Once inside the cell, viral DNA replicates (makes an identical version of) itself 1000’s of times.

  • They then burst out of the host cell into the bloodstream, destroying the cell.

  • Examples: cold, flu, measles, mumps, rubella, HIV.

Viral Diseases

  • These diseases are caused by infections of viruses.

  • These infections cannot be cured by antibiotics e.g. penicillin.





  • Mumps is an infectious disease caused by the mumps virus.

  • Mumps normally affects children, but can occur at any age.

  • Immunisation is offered to all children in the UK. It is part of the MMR (Measles, Mumps and Rubella) vaccine. Two doses are usual - the first aged 15 months and the second about three years later.

  • MMR vaccine gives very good protection, and so mumps is now rare in the UK.

  • Possible complications – infertility in males over the age of 12 and miscarriage in 12-16 weeks of pregnancy.


Mumps Virus



Measles rash




Measles virus

  • Measles is one of the most contagious (it goes from one person to another easily) of all human viruses.

  • Measles causes rash, cough, and fever, and can lead to ear infection, pneumonia, conjunctivitis, diarrhoea, brain damage, and death.

  • Any doctor who suspects that a patient has measles is required by law to report it.

  • Measles infection can be prevented by a highly effective and safe vaccine which is part of the measles-mumps-rubella (MMR) immunisation.


  • Symptoms are a rash and fever for two to three days.

  • Complications - Birth defects if acquired by a pregnant woman.

  • Spread by contact with an infected person, through coughing and sneezing

  • Vaccine - Rubella vaccine (contained in MMR vaccine) can prevent this disease.




  • Chickenpox is caused by a virus.

  • Chickenpox is a mild, but highly infectious diseasethat most children catch between 2-8 years of age, although you can develop chickenpox at any age.

  • You are infectious from about two days before the rash appears until roughly five days after, when all of the blisters have fully crusted over.

  • Once you have had chickenpox, you will very rarely catch chickenpox for a second time.


More Viral diseases


Cold Sore










  • Single celled organisms that can multiply rapidly. They are bigger and more complex than viruses and can reproduce by themselves.

  • Attack tissues in host (person infected) and release toxins (poisons).

  • Examples: food poisoning, cholera and whooping cough.



Bacterial Infections

  • These diseases are caused by infections of bacteria.

  • These infections can be cured by antibiotics e.g. penicillin (unless resistant).

  • Antibiotics are substances that harm bacteria. Some antibiotics

    stop the bacteria reproducing

    and others kill the bacteria.


Antibiotic Resistance in Bacteria

  • Many bacteria have resistance to antibiotics (they are not killed by the antibiotic), so we need a range of antibiotics to fight diseases. We must use the best one for the job.

  • To slow down more antibiotic resistance developing in pathogenic bacteria we need to avoid over-using antibiotics or only use them when really necessary and always finish the course.

  • Tuberculosis (T.B.)is usually a disease of the lungs.

  • The risk factors for getting TB include poor diet and hygiene, close-contact situations, alcohol and drug abuse, certain diseases and occupations (e.g. health-care workers).


Tuberculosis bacteria


  • Salmonella is a type of bacteria. It is usually found in chicken, eggs, fish, meat and water.The salmonella bacteria attack the stomach and intestines. The bacteria attack all age groups and both sexes. Children, the elderly and people who are already ill are much more likely to get a serious infection.

  • Symptoms include vomiting, diarrhoea, strong stomach pain and fever.

Salmonella (Food Poisoning)

Salmonella bacteria




  • Gangrene is caused by a bacterial infection.

  • Gangrene can happen when a cut or surgical wound becomes infected with bacteria. The bacteria can spread under the skin or through the blood to cause a total body infection.

  • Some of these bacteria make poisons (toxins) that flow into the body, destroying tissues and causing severe illness or death.


Fungal Infections

  • These diseases are caused by infection by fungi.

  • These infections can be cured by fungicides



Athletes Foot

  • Athlete's Foot is a fungal infection. It is common in athletes or those taking part in sports regularly.

  • It is normally caught in changing rooms or showers because the fungus likes a moist (wet) environment.




  • The fungi that cause ringworm generally enter the body through a break in the skin.

  • Animals can have ringworm and can pass it on to humans. Children who come into close contact with their pets, farmers and people who work with animals, are more at risk.

  • Ringworm can also be caught through person-to-person contact.



  • = the body’s ability to resist infection

    The immune system’s job is to kill any organisms that enter the body

White blood cells are always used in fighting off microbes and are responsible for building up immunity to disease.

One type of white blood cell attacks anything that is ‘foreign’ or not meant to be there. It surrounds the microbe and digests (eats)it.

White Blood cells defend the body!


Another type of white blood cell attacks only certain microorganisms.

Every pathogen has unique molecules (antigens) on its surface; when white blood cells don’t recognise these antigens, they start to produce antibodies, which lock onto and kill the pathogens.


Once a white blood cell recognises the antigens on a pathogen, it divides quickly to make more antibodies to fight the infection. Some of these cells stay in the blood and ‘remember’ the antigens, so that they can quickly produce lots of antibodies if the body gets infected again – that’s why you are usually immune to most diseases you have had in the past.


  • A vaccine is usually made of the same or similar cells that could make you sick, but they are weak or inactive.

  • When a vaccine goes into the body, the immune system responds the same way it would to any germ. The vaccine is easier to fight than the illness you’re being vaccinated against and it won’t make you sick while your immune system fights it.

  • Once the immune system works out how to fight and kill the antigens, it remembers what works against them and protects your body in future.


It prevents disease

Big outbreaks of a disease (epidemic) can be prevented if many people have been vaccinated

Some diseases have been stopped completely

Vaccination – good or bad?


They cannot be completely safe for everyone.

Some people have side effects e.g. painful arm for a short time, high temperature


  • Some people are worried about possible side effects and refuse to let their children be vaccinated – even though getting the disease may be worse than the side effects

  • There must be enough people who are vaccinated to control the disease – people who refuse vaccination benefit because everyone else has been vaccinated. Is this fair?

  • Should people be forced to have vaccinations for the good of everybody?

Some people may not want to do what is best for society

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