112 Unit 1 Introduction to Healthcare Copyright Goodheart-Willcox Co., Inc. Bacteria can cause major illness in our bodies. Here are some examples: • Hospital stays can be prolonged by the bacterium called Staphylococcus aureus (S. aureus). The infections caused by these bacteria are commonly called staph infections. • The Black Death that killed approximately 25 million people in fourteenth-century Europe was a plague caused by the rod-shaped bacterium, Yersinia pestis. Today, Yersinia pestis is easily treated with antibiotics. • Syphilis is a bacterial infection caused by a spiral bacterium called a spirochete. Bacterial infections are treated with antibiotics—drugs that kill the disease-inducing microorganism. Viruses Much smaller than bacteria, viruses depend on a living cell to sur- vive because they cannot reproduce on their own. Viruses are the cause of the common cold, smallpox, chicken pox, measles, infl uenza, human papillomavirus (HPV), herpes simplex, and AIDS. Many more illnesses are caused by viruses. Antibiotics do not kill viruses. Usually, time and rest are necessary to let most of these illnesses run their course. Doctors will advise patients to stay home, take non-aspirin pain relievers, and get plenty of rest. However, vaccines have been developed against many viral diseases. A vaccine intro- duces small amounts of the microorganism into the system in an effort to boost the immune system against the microorganism. An increasing num- ber of antiviral remedies are being developed. These remedies prevent the virus from replicating, or reproducing itself. Fungi Microscopic fungi include yeasts and molds. Some fungi can cause dis- ease, especially if the immune system has already been compromised by a different disease or disorder. Examples of fungal infections include athlete’s foot, thrush (an infection of the mouth or throat), vaginitis, and certain lung diseases. Fungal infec- tions are treated with topical, oral, or injectable medications. Protozoa Although they are larger than viruses, protozoa also depend on a host cell to survive and replicate. Protozoa are found in water and soil and cause amoebic dysentery, an infl ammation of the colon that results in fever, abdom- inal pain, and severe diarrhea. They also cause amoebiasis, trichomoniasis, and malaria (a disease contracted via a mosquito bite). In a malaria patient, the protozoan lives in red blood cells. Protozoal infections are treated with oral and injectable anti-protozoal medications. protozoa microorganisms that depend on a host cell to survive and replicate can cause serious illness