b1.1.2

a) Microorganisms that cause infectious disease are called pathogens.

b) Bacteria and viruses

• may reproduce rapidly inside the body and
• may produce poisons (toxins) that make us feel ill.
• Viruses damage the cells in which they reproduce.

The body has different ways of protecting itself against pathogens.

- White blood cells help to defend against pathogens by:

• ingesting pathogens
• producing antibodies, which destroy particular bacteria or viruses
• producing antitoxins, which counteract the toxins released by the pathogens.

- The immune system of the body

• produces specific antibodies to kill a particular pathogen.
• This leads to immunity from that pathogen.
• In some cases, dead or inactivated pathogens stimulate antibody production.
• If a large proportion of the population is immune to a pathogen, the spread of the pathogen is very much reduced.

Semmelweis recognised the importance of hand-washing in the prevention of spreading some infectious diseases.

• By insisting that doctors washed their hands before examining patients, he greatly reduced the number of deaths from infectious diseases in his hospital.

- Some medicines, including painkillers, help to relieve the symptoms of infectious disease, but do not kill the pathogens.

Antibiotics, including penicillin, are medicines that help to cure bacterial disease by killing infectious bacteria inside the body.

• Antibiotics cannot be used to…