Pathogens are organisms that cause disease. Some bacteria, some fungi, a few single celled animals and all viruses can only live by invading another living thing. As they feed off their host, they cause damage to the host and release toxic materials. At best, the result is hardly noticeable, at worst it results in death.

Most pathogens can only live in a particular host. So, remember when all the family had flu, your dog still wanted to be taken for a walk and your cat was still hunting for mice and birds. Our influenza virus causes disease in humans, but does not affect cats or dogs. Yes, cats can get flu, but a different kind from he one that affects humans.

Some pathogens can affect more than one kind of host. Malaria in monkeys can be transmitted to humans and vice versa. This makes it much more difficult to control since wild animals act as a pool of malaria ready to be transmitted to humans.

Some examples of pathogenic diseases in humans:

  • Malaria and sleeping sickness (caused by single celled animals)
  • Common cold, AIDs and flu (influenza) (caused by viruses)
  • Ringworm (caused by a fungus)
  • Tuberculosis(TB), gastroenteritis and syphyllis (caused by bacteria)

Controlling disease depends on knowing how the disease is cause and how it is transmitted. Malaria was though to be caused by breathing bad air, hence the name. Now that we know it is caused by plasmodium (a single celled animal|) and that this is passed from one person to another by a mosquito bite, we can attempt to eradicate it.

Pathogens are parasites, that means they live at the expense of another living thing. However, not all parasites are pathogens; a tapeworm is a parasite, and it does cause damage to its host, but we don’t call it a pathogen. Similarly, we don’t call ecto-parasites such as ticks, lice and fleas. Ecto-parasites live on the surface of their host, whereas endo-parasites live inside their hosts.