Diseases are caused by pernicious microbes (microscopic agents which facilitate basic life functions such as digesting and breathing). Microbes come in many formats and most are beneficial to health. However, certain categories of microbe can carry illness:
Viruses replicate living cells of other organisms and are the smallest of all the infectious agents. Well-known viruses include the common cold, measles and chicken pox.
Bacteria have an excellent ability to reproduce and thereby cause illness to spread. Bacteria-based diseases include tuberculosis and pneumonia.
Fungi, responsible for such afflictions as thrush and athlete’s foot, are parasitic agents which feed off healthy tissue and introduce infection.
Disease is spread when one of these harmful microbes is transmitted in one, or a combination, of the following ways:
- by air
- by water
- through touch
- through consumption of contaminated food
Injurious particles, having been expelled by sneezing or coughing, may be disseminated through the air and inhaled by healthy individuals. Airborne illnesses include the flu, mumps and whooping cough.
Waterborne disease such as cholera and giardisis may be contracted after swallowing infected water.
Direct person-to-person contact can result in the spread of such illnesses as glandular fever, scabies, Hepatitis B and gonorrhoea. “Contact” includes such contact between skin, membranes, blood, saliva, semen and other discharges. Certain diseases, described as zoonotic, may be transmitted following contact with an animal. Zoonotic diseases include malaria, rabies and toxoplasmosis.
Finally, a disease may be contracted by consuming or handling a contaminated object, commonly food. Well-known illnesses transmitted by food include E. coli infection, norovirus and botulism.