Infectious Diseases - Pathogens

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Viruses

Viruses are very tiny – they are much smaller than bacteria or fungi . They measure only a few thousand millionths of a metre (nanometres).

All natural viruses cause disease including the common cold, influenza (flu), measles, mumps and rubella. They are not living cells themselves, and they can only reproduce inside other living cells.

Viruses can attack all different types of living organisms – they invade animal, plant and even bacterial cells. Different viruses attack specific cells – so the 'flu virus attacks the cells of the respiratory system while the virus which causes meningitis attacks the cells of the membranes which cover your brain.

Scientists have started to use viruses to benefit people. They are an important tool in genetic engineering. They are used to carry new genes into the DNA of the cells of other organisms.

The flu virus
Photo provided by CDC/ Dr. Erskine. L. Palmer; Dr. M. L. Martin

The structure of viruses

Protein coat
this attaches to and penetrates the host cell. It surrounds and protects the genetic material
Genetic material
This can be DNA or another similar chemical called RNA. It contains the information needed to take over the host cell DNA and make new viruses

The structure of a virus

Antibiotic

Medicine that acts against bacterial infections. Penicillin is an example of an antibiotic.

Antibody

Protein that is produced by lymphocytes (white blood cells) and that attaches to a specific antigen.

Antigen

Molecule on the surface of a pathogen that identifies it as a foreign invader to the immune system.

Bacteria

Single-celled organism. Has a cell wall, cell membrane, cytoplasm. Its DNA is loosely-coiled in the cytoplasm and there is no distinct nucleus.

Biotechnology

The use of biological organisms or enzymes to create, break down or transform a material

Dissect

To cut apart, or separate, tissue especially for anatomical study.

Exponential growth

If something is growing exponentially the larger the quantity gets, the faster it grows

Fungus

Micro-organism that can grow in long tubes called hyphae or as single cells. Fungi have a nucleus, cytoplasm and a cell wall.

Herd immunity

If a high percentage of a population is immune to a disease the disease cannot be passed on because it cannot find new hosts.

HIV/AIDS

Infection caused by the human immunodeficiency virus (HIV). It attacks and destroys the immune system.

Hybridoma

Hybridoma cells are formed by fusing a specific antibody-producing cell with a type of cancer cell that grows well in tissue culture

Immune system

The body's natural defence mechanism against infectious diseases.

Immunisation

A process which gives immune resistance to a particular disease. The human or animal is exposed to a harmless antigen in order to raise antibodies and provide an immune memory.

Lymphocyte

A type of white blood cell that make antibodies to fight off infections.

Macrophage

A type of white blood cell that consumes dead pathogens that have been killed by antibodies.

Parasite

Organism that feeds off another living host and causes it some damage. An example of a parasite is a tapeworm that lives in the digestive system of a host organism.

Pathogen

A micro-organism that causes disease.

Phagocyte

Phagocytes are the white blood cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells.

Protein

A polymer made up of amino acids joined by peptide bonds. The amino acids present and the order in which they occur vary from one protein to another.

Protozoa

Protozoa are one-celled animals

Spore

A spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavourable conditions.

Toxin

A poisonous or toxic substance - produced by pathogens.

Vaccination

A small amount of dead or weakened pathogen is introduced into the body. It prepares the immune system to prevent future infections with the live pathogen.

Vaccine

Medicine that contains a dead or weakened pathogen. It stimulates the immune system so that the vaccinated person has an immunity against that particular disease.

Virus

The smallest of living organisms. Viruses are made up of a ball of protein that contains a small amount of the virus DNA. They can only reproduce after they have infected a host cell.

Opportunistic Infections

An infection that would not normally cause disease in a healthy person but which can take hold when a person's normal immune defences are reduced.