About 7 years ago, hundreds of people were getting sick in Milwaukee, Wisconsin. These people were complaining of diarrhea and stomach upset. What was this terrible plague? Eventually, it was determined that a parasite called Cryptosporidium parvum was the culprit. This organism normally bothers wild animals and occasionally people. Fortunately, for the people of Milwaukee the source of the infection was located in the city's water filtration devices. Only by proper sand filtration was the epidemic halted.
Most parasites by definition are leeching off other living beings to survive. The parasite injures and gets nutrients from the host it lives in. Some organisms called parasites live in a host but don't cause any problems for the host. They are called commensals (for example, Entamoeba coli).
Parasitologists study parasites. Imagine all your life devoted to freeloaders. Parasitology is an interdisciplinary field. To study these critters you need to know a good bit about microbiology, immunology, biochemistry, and other life sciences. Billions of parasitic infections occur in humans every year. Infections can be fatal, however, most result in few if any symptoms. Parasites are a major health concern. Approximately 30 percent of the world's population is infected with the worm called Ascaris lumbricoides.
Parasites can be found everywhere. A common misconception is that these parasitic infections only occur in hot tropical areas of the world. Even though most parasitic infections occur in the tropics, many people in the United States and Canada become infected (note Milwaukee example above). If you have ever visited a tropical country you may also bring back a parasite along with your souvenirs. To find out what parasites are common in your place in this world go to the McGill University site.
Do you want to know more about parasites? Dr. Baron's Medical Microbiology book contains a lot of information about parasites that infect humans. The above link takes you to the table of contents. Scroll down to get to the parasite chapters. However, If you are impatient this link will take you right to the information. If you want some great images this link is truly fantastic. This website contains a lot of images of different
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