British beef blues

Curious cause

Down deer, ill elk

Can't happen here?

Laughing death in New Guinea

Identifying disease agents

Menacing microbes

Glossary

Meet the pathogens
PAGE POSTED 23 OCTOBER, 1996

Ameba
A one-celled animal that changes shape as it moves about. It's propelled by pseudopodia, temporary "feet" that form from bulges from the cell membrane. Causes amebic dysentery, an intestinal disease, and other illnesses.

Bacterium (plural: bacteria)
A free-living organism, with or without a distinct nucleus, that causes such diseases as strep throat, scarlet fever, typhoid, bubonic plague, tetanus, and other serious illnesses. Bacteria may form clumps or colonies. They have no nucleus, and reproduce by dividing. Some are bacteria older than your great-grandfather.

Fungus
Organisms that contain no chlorophyll, and live as single cells (like yeasts) or multi-cellular organisms (mushrooms). A least 40 species of fungi cause disease in humans, including athlete's foot, ringworm, thrush (particularly in AIDS patients), and histoplasmosis, an infection of the lungs.

Parasite
A wide range of pathogens cause such diseases as malaria, schistosomiasis and scabies. These multicellular organisms generally have complex life cycles and must live part of their lives in another organism. Malaria parasites spend part of their life cycle in certain mosquitoes.

Protein
The only infection protein known at this point is the prion. When its shape is altered, this normal protein can "infect" other proteins, causing them to change shape as well. Scientists think prions can cause TSE diseases (Want The Why Files guide to mad-cow lingo?) in people, sheep, cows, mink, rats, mice, hamsters and possibly monkeys.

Viroid
A small string or circle of RNA (with only about 300 nucleotides) that infects mainly plants. Unlike viruses, viroids do not encode for a protein; rather, their structure causes damage and disease.

Virus
The smallest agent (aside from the prion) able to cause an infection. Viruses are not cells; they direct cells to make more viruses but seldom contain the organelles found in bacteria and other cells. Most viruses are short strings of DNA. "Retroviruses" including herpes and HIV, are composed of RNA, a similar genetic material). Viruses are between 20 and 250 billionths of a meter in length.

Mucho readings in our bibliography.