Most illness in humans is caused by viruses, bacteria or parasites. Here is a breakdown of how each of these affects humans and what type of diseases they spread.
Viruses and Infection in Humans
Viruses are the smallest of the infectious organisms and do not respire, move or grow. However, they can reproduce but only inside a living cell. Some viruses spread rapidly amongst humans and cause illnesses such as influenza, AIDS, herpes, hepatitis, rabies, yellow fever, chicken pox and ebola. Viral diseases are generally not easy to treat and preventative measures such as vaccination and improved sanitation may be introduced if an epidemic threatens. Some viruses such as rabies and ebola have an extremely high mortality rate.
Bacteria and Infection in Humans
Bacteria are responsible for a wide range of unpleasant diseases in humans. They are described as microscopic, single-cell organisms. They come in a variety of different shapes and some have flagella which help them to move. Bacterial infections can be treated with a wide range of antibiotics but some strains have become resistant to many antibiotics. This is a particular problem in certain diseases such as tuberculosis. Bacterial diseases include cholera, pneumonia, Chlamydia, leprosy, syphilis, anthrax, diphtheria and some types of meningitis.
Protozoa and Infection in Humans
Protozoa are defined as single-celled microscopic organisms and include amoebas, ciliates, flagellates, and sporozoans. They are commonly spread by water, food, domestic animals and insects. Among the diseases caused by protozoa are sleeping sickness, malaria, trichomoniasis and toxoplasmosis.
Worms and Infection in Humans
Humans are susceptible to worm infections and can pick these up from food, water, contact with contaminated surfaces and from insects. Worms range in size from microscopic to many feet long and are responsible for some nasty parasitic infections such as bilharzia. The worms include tapeworm, pinworm, hookworm, roundworm and threadworm.
Fungi and Infection in Humans
Fungi are single or multicellular organisms that grow and multiply in moist warm places. They can be passed on by physical contact and may cause itching, rashes and inflammation. Common fungal infections include ringworm, thrush, athlete’s foot.
Understanding what is causing an illness is part of the solution to the problem. Viruses, bacteria, protozoa, worms, and fungi all affect humans in different ways and cause a wide spectrum of diseases and sicknesses. In some cases prevention is the best way to handle the organism, and vaccinations, prophylactic treatment and basic hygiene go a long way towards keeping a number of diseases at bay.
Killer Diseases , Hazel Richardson, Dorling Kindersley, 2002