Pathogens and Disease

Pathogens and Disease


A pathogen is a micro-organism that causes diseases. They are parasitic and can be in the form of bacteria, fungi, viruses and protozoa.





* Microscopic single-celled organisms

* Can be seen with a light microscope

* No cell wall

* No nucleus

* Reproduce asexually by binary fission (splitting into two)

* Produce spores in poor conditions, which are resistant to variations in temperature and pH

Examples: Staphylococcus, Salmonella, Spirillum

Diseases caused: whooping cough, tetanus, food poisoning, diphtheria, typhoid.

* Most are many-celled

* Many can be seen without a microscope

* They are similar to plants but have no chlorophyll

* They consist of hyphae (fine threads) that grow to form mycelium

* They reproduce asexually by producing spores, which are carried by wind or insects.

Examples: Mucor, Aspergillus

Diseases caused: athlete's foot, ringworm, many plant diseases such as mildew.

* Much smaller than bacteria

* Cannot be seen with a light microscope, only with an electron microscope

* Non-living

* Consist of a protein coat containing genetic information

* Reproduce asexually by injecting DNA into a living cell

* The viral genetic material instructs the cell to stop its normal activity and make copies of the virus.

Examples: Adenovirus, Herpes, Influenza

Diseases caused: common cold, influenza, chicken pox, AIDS, smallpox.

* Single-celled organisms

* Nearly all live in water and in the body fluids of animals

* Are different from bacteria because they have a definite nucleus and they feed in a variety of ways.

Examples: Amoeba, Euglena, Paramecium

Diseases caused: amoebic dysentery, malaria, sleeping sickness.

Sasha TaylorPage 4

Biology 1 – Level 3


Using information from this unit and unit 11 plus your own research, write an essay under the title: The body is like a castle under siege, discuss:

Your essay will need to:

1. Analyse both the specific and non specific defences against diseases in terms of antigens and anti bodies (limited to lgG and lGm antibodies)

2. Compare the immune response shown by B lymphocytes with that shown by T lymphocytes.

3. Analyse the primary and secondary responses to antigens with reference to the role of memory cells.


Immunisation is an artificial method of producing immunity.

Passive immunisation involves the injection of antibodies made by another organism. It is useful in circumstances where the body would not have enough time to produce antibodies of its own. For example, if you cut yourself, you may be given an injection of ready-made tetanus antibodies.

Active immunisation involves stimulating the body to produce its own antibodies. This is achieved when a vaccine triggers the immune system to produce antibodies against the disease as though the body had been infected with it. This also teaches the body's immune system how to produce the appropriate antibodies quickly. If the immunised person then comes into contact with the disease itself, their immune system will recognise it and immediately produce the antibodies needed to fight it.

A newborn baby has a natural immunity to several diseases, such as measles, mumps and rubella, from antibodies that are passed from the mother to baby via the placenta.

Natural immunity only lasts for a few weeks or months. In the case of diphtheria, tetanus, whooping cough and polio, the natural immunity only lasts for about 2 – 3 months. In the case of measles, mumps and rubella it may last for up to one year in infants – this is why MMR is given just after a child's first birthday.

The timescales given for vaccinations are intended to increase your child's protection as their natural immunity wears off.


Influenza is a highly infectious illness caused by a flu virus. The virus infects your lungs and upper airways, causing a sudden fever, headache and general aches and pains. You couldalso lose your appetite, feel nauseous and havea dry, chesty cough.

The flu virus is spread in the small droplets of saliva coughed or sneezed into the air by an infected person. If you breathe in these droplets, you may become infected. It can also be spreadifsomeone with the virus touches commonsurfaces such as door handleswith unwashed hands. The spread of the virus usually happens in small outbreaks or very rare cases, in epidemics. Outbreaks tend to occur mostly in winter and it spreads rapidly, especially in schools and old peoples' homes.

There are three types of influenza virus's called, A, B and C. Influenza A viruses infect mammals and birds, whereas the Influenza B and C viruses infect only humans. The A type of the influenza virus is the type most likely to cause epidemics and pandemics, due to the fact that the virus can undergo antigenic shift, this is when two strains of the virus combine to form a new strain with a combination of the antigens on its surface. The virus can also mutate naturally in an attempt to resist the body's defenses such as the human immune system. Populations tend to have more resistance to influenza B and C because they cannot change by antigenic shift and can only change by natural mutation; therefore influenza B and C is usually similar to its predecessor and similar enough to be destroyed by the immune system.

A person who has been attacked by virus C needs antibodies (proteins made by the immune system). They should provide immunity against the virus for life. Type C only causes a mild illness that is not much different from a common cold and none of the symptoms apply to type C except weakness.

If you have been suffering from type B you would have been feeling very run down and tired. This is because you will have suffered all of the above symptoms. The type B virus is quite stable but it occasionally alters just like the cold virus. A new strain can often cause small outbreaks of infection, for example Swine Flu.

The type A version of influenza is the worst out of all three, not only do you suffer all the above symptoms, but it is highly unstable. It is very rare for a person to die from flu unless it keeps resisting the antibodies; however a common complication of seasonal flu is a bacterial chest infection. Occasionally, this can become serious and develop into a severe case of pneumonia. A course of antibiotics usually cures the bacterial infection, but itcan very occasionallybecome life-threatening, particularly in the frail and elderly.

New strains appear constantly around the world and some of these strains can also sometimes develop in to major epidemics like the Spanish Flu in 1918, the Asian Flu in 1957 and the Hong Kong Flu in 1968. The Spanish Flu killed millions of young adults in all countries of the world.

Anti-Influenza vaccines are available free of charge at the GP Surgery, but they only have a 60–70% success rate in preventing infection. The vaccination must be repeated each year just before the 'flu season' begins. Older people are recommended to have a vaccination and anyone suffering from respiratory or circulatory diseases, especially if they are living in institutions or old people's homes.

Antiviral medicationcan also be prescribed by your GP if you are in a high risk group. And have flu like symptoms. Antiviral medication will not cure flu but will help to reduce the length of time you are ill by around one day, relieve some of the symptoms, and reduce the potential for serious complications. Antiviralswork bystopping the virus from multiplying in your body. The differenttypes of antiviral medication are Zanamivir (Relenza), Oseltamivir (Tamiflu) and Amantadine.

In all but the mildest cases, a person with Flu should get plenty of rest in a warm well ventilated room. Painkillers can be taken to relieve aches and pains and also to reduce fever. Warm fluids soothe a sore throat and inhaling steam has a soothing effect on the lungs.

Some over-the-counter treatments can be given to children who have flu, according tothe instructions supplied with each medicine. Under-16s must not takeaspirin or ready-made flu remedies containing it.


Looking more generally at infectious diseases what are the main features in their control.

A disease is a medical condition which arises when something goes wrong with the normal working of the body. Non-infectious diseases are caused by microscopic organisms that invade the body, but does not spread from person to person and do not have, or are not known to involve, infectious agents. Infectious diseases are caused by microscopic organisms that invade the body and can spread from one person to another.

Diseases can be transmitted in various ways, such as:

Ø Droplets

— when an infected person coughs or sneezes, their droplet contains pathogens which will transmit the disease if breathed by an uninfected person

Ø Dust

— some diseases, like diphtheria and scarlet fever, can be spread by dust. Germs stick to the dust particles and float through the air. People can atchj the disease by breathing in the dust.

Ø Touch

— when an infected person touches an uninfected person, the pathogen can enter through the skin.

Ø Cuts

— Pathogens enter the body where the skin is cut by a contaminated object.

Ø Food or water

— pathogens in contaminated food and or water can enter the body through the soft gut wall.

Ø Sexual intercourse — sexually transmitted diseases gain entry through the soft mucous membranes of the penis and vagina.

Ø Insects

— blood sucking insects inject their mouthparts through the skin, and can transmit pathogens that they sucked from an infected person

Our bodies are protected from germs in many ways. Some of the ways arise from the body's own defence mechanisms and others are man-made.

Man-made solutions include:

Ø Immunisation — Immunisation is a vaccine triggers the immune system to produce antibodies against the disease as though the body had been infected with it. This also teaches the body's immune system how to produce the appropriate antibodies quickly. If the immunised person then comes into contact with the disease itself, their immune system will recognise it and immediately produce the antibodies needed to fight it.

Ø Ready-made antibodies

— this is when the body is given antibodies rather than producing them itself. For example, if you cut yourself, you may be given an injection of ready-made tetanus antibodies.

Ø Antibiotics

— Antibiotics are agents that destroy bacteria: a substance that is able to kill or inactivate bacteria in the body. Antibiotics are derived from micro-organisms, especially fungi, or are synthetically produced.

There is also the Non Specific Immunity & Specific Immunity Defense against Infectious Disease. Non Specific immunity is a quick-response system, which is present from birth. It is very effective against a wide range of pathogens and foreign substances, and it always gives the same type of response. Specific immunity is an immunity system which is effective against specific pathogens, but reacts slowly. This includes cells and protein within the blood and lymph, which attack, disarm, destroy and remove foreign bodies.

The body's own defence mechanisms:

The body has its own defence mechanisms, known as the barriers to infection, which are features of the human body that prevent micro-organisms from entering the body.




Forms membranes that prevent most cells from entering the body. The outer layer of the skin is tough and rough and forms a physical barrier. The sebaceous gland secretes lactic and fatty acids, which prevents the growth of most pathogenic bacteria.


Lysozyme, an enzyme found in mucous membranes, destroys bacteria.


Cilium/cilia are microscopic hair-like projections on the cell.


The tear fluid lubricates and protects the eyes from foreign matter and infection — the latter because it contains salt and lysozyme, an enzyme that destroys microorganisms.

Stomach Acid

Hydrochloric acid in the stomach destroys microorganisms that may have been ingested in the food. + Mucin coats the stomach, protecting it from the effects of the acid and pepsin.


Write an essay discussing the use of antibiotic drugs to treat bacterial diseases and the problems posed by the emergence of strains of bacteria resistant to certain anti bodies.

Sasha TaylorPage 4

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