The environment abounds with potential sources of infectious diseases. Without the protection of the immune system, infections would quickly overwhelm the body. Certain viruses, bacteria, fungi and a variety of parasites possess mechanisms to skirt surface immune defenses and infect the human body. Some infectious diseases prove self-limiting, resolving quickly as the immune system regains the upper hand. More serious types of infectious diseases require medical treatment to assist the immune system in restoring health.
Viral Diseases
Viral illnesses prove the most common type of infectious disease. Throughout life, viruses infect the body causing a variety of illnesses. The common cold repeatedly afflicts humans throughout life. Colds are the leading cause of work and school absenteeism in the United States, according to the National Institute of Allergy and Infectious Diseases. Many other viral illnesses of wide-ranging severity may occur during a lifetime, including influenza, viral gastroenteritis, chickenpox, shingles, viral pneumonia, aseptic meningitis, viral encephalitis, infectious mononucleosis, measles, viral hepatitis, genital herpes and warts, yellow fever, dengue, fifth disease and AIDS.
Bacterial Diseases
Bacteria cause diverse infectious illnesses, which may localize to a specific body location or disseminate throughout the body. Types of bacterial infectious diseases include strep throat, sinusitis, bacterial pneumonia, food poisoning, septic arthritis, skin and soft tissue infections, bacterial meningitis, urinary tract infections, gonorrhea, syphilis, pelvic inflammatory disease, bloodstream infections and toxic shock syndrome. Some of the many bacterial species noted in the medical reference text "Principles and Practice of Infectious Diseases" as possible agents of infectious diseases include Staphylococcus aureus, meningococcus, pneumococcus, groups A and B streptococcus, Klebsiella, Escherichia coli, Proteus, Pseudomonas, Enterobacter, Clostridium, Salmonella, Shigella, Bacillus anthracis, Mycobacterium tuberculosis, Treponema pallidum and Chlamydia.
Fungal Diseases
Various forms of fungi can cause infectious diseases. In contrast to most viral and bacterial infections, fungal diseases typically develop gradually and clear slowly. Surface fungal infections occur frequently, including jock itch, scalp ringworm, athlete's foot, thrush, fungal nail infections and vaginal yeast infections. "Principles and Practice of Infectious Diseases" notes that inhaled fungal spores can cause sinus and lung infections, including aspergillosis, mucormycosis, coccidioidomycosis, blastomycosis and cryptococcosis. People with a weakened immune system prove susceptible to widespread fungal infections that rarely occur in those with robust immune function. Pneumocystis pneumonia, caused by the fungus Pneumocystis jirovec, most commonly occurs in people with AIDS.
Parasitic Diseases
The Centers for Disease Control and Prevention explains that parasites are organisms that infect another living being to gain a source of food. Parasites range in size from single-celled protozoans to infectious worms that reach more than 20 feet long. Protozoal infectious diseases include amoebic dysentery, babesiosis, intestinal giardiasis and cryptosporidiosis, vaginal trichomoniasis and malaria. Parasitic worms favor infection of the gastrointestinal tract, causing illnesses such as ascariasis, ancylostomiasis, cysticercosis, river blindness, intestinal tapeworms, elephantiasis and pinworms.
References
- "Principles and Practice of Infectious Diseases, Sixth Edition"; Gerald L. Mandell, M.D., et al., Editors; 2004
- National Institute of Allergy and Infectious Diseases: Common Cold, Overview
- Medline Plus: Fungal Infections
- Medline Plus: Pneumocystis Infections
- Centers for Disease Control and Prevention: About Parasites
