Infectious agents come in many shapes and sizes. Bacteria and protozoans are microscopic one-celled organisms. Viruses are even smaller. Fungi grow like plants. Helminths resemble worms.

Mar 5, 2024 · Bacteria Bacteria are one-celled life forms called organisms that can be seen only with a microscope. Not all bacteria are harmful. Some bacteria that live in the body are helpful. …

Apr 8, 2025 · Infectious diseases are illnesses that happen when tiny living beings get inside the body and multiply. Bacteria, viruses, fungi and parasites are examples of organisms that can …

Nov 25, 2025 · Bacteria cause bacterial infections. Viruses cause viral infections. Antibiotic medicines kill or keep many bacteria from growing but don't treat viruses. Antiviral medicines …

Sep 20, 2025 · Anthrax is a rare but serious illness caused by a spore-forming bacterium, called Bacillus anthracis. In the body, the spores form poisons that can destroy tissues. Anthrax …

Dec 22, 2021 · Repetitive douching disrupts the good organisms that live in the vagina and can increase your risk of vaginal infection. Douching won't clear up a vaginal infection.

Apr 8, 2025 · Anti-parasitics Some diseases, including malaria, are caused by tiny parasites. These organisms live in or on host organisms, which can include people. Parasites get their …

Feb 9, 2023 · Blastocystis is a microscopic parasite that can live in your digestive tract. Researchers don't fully understand the role blastocystis plays, if any, in causing disease. …

Nov 14, 2023 · Learn about different tick species and some of the diseases they may carry.

May 15, 2024 · Nail fungus is caused by various fungal organisms (fungi). The most common is a type called dermatophyte. Yeast, bacteria and molds also can cause nail infections. The …