What is the infectious agent (pathogen) that causes this infectious disease? For example, the name of the bacteria, virus, or parasite. Giardia is a flagellated (meaning to have whip-like appendages for movement) protozoan that attaches itself to the lining of the upper intestinal tract of a host animal. Giardia lamlia is the parasite also known as G. intestinalis or G. duodenalis and was first observed by Anton van Leeuwenhoek in 1681. Anton van Leeuwenhoek also invented the microscope. It was named in 1915 for the two scientists who studied it: Prof. A. Giard in Paris and Dr. F. Lambl in Prague.
There are species of Giardia other than Giardia lamblia that infect small rodents, amphibians, birds, and fish, but are not passed on to humans. Once Giardia attaches itself to the lining of the intestine it begins to feed and reproduce, causing Giardiasis (the infection). Giardia is a trophozoite that reproduces by dividing itself, which is called binary fission, about every 12 hours. One single parasite can theoretically result in more than a million in 10 days and a billion in 15 days. At some time, it releases its hold on the intestine and travels in the fecal stream.
The trophozoite then transforms into an egg-like structure called a cyst and eventually passed in the stool. This cyst excretion is called shedding and can last for months. Once outside the body the cyst is ingested by another animal. Stomach acid and digestive enzymes cause the cyst to “hatch” into trophozoites and the cycle repeats. How is this infectious agent transmitted through food or water? Infected people and animals pass Giardia cysts in their stool. The cysts can survive in the environment in water and food, and on surfaces and objects.
People get Giardiasis by ingesting the infectious stage (cysts) of the parasite. This can happen by swallowing water from a swimming pool, lake, river, pond, or stream contaminated with sewage from Giardia-infected people or animals. Giardiasis can be contracted by the unsanitary preparation of food in contact with contaminated water, surfaces, or people. The most common of these ways is through contaminated water (i. e. lakes and streams) which is why the nickname “beaver-fever” was first introduced. This was because of the presumed link between water-dwelling animals being known carriers.
Water-dwellers, such as beavers, can contaminate water more directly than an animal that defecates on the ground. What is an example of a real life outbreak of this foodborne illness in the United States? Giardiasis has been most often associated with travel to places like Latin America, Africa, Asia, and Russia. However, Giardia has always been present in wilderness streams and the water supplies of most cities around the world, including the United States.
A chief microbiologist at the EPA quoted in Backpacker magazine, Dec. 996, that before the 1930’s and 1940’s we were all ingesting Giardia all the time. This was before regulated municipal water treatment plants. To be classified as an “outbreak” the US Centers for Disease Control and Prevention (CDC) must implicate a source, and there must be multiple cases. The CDC estimates that as many as 2,500,000 cases occur in the US, or about one for every 100 persons every year. Approximately twenty percent of the world’s population has Giardiasis, and four to seven percent of Americans, most without any symptoms at all.
What are the clinical symptoms, duration of the disease, and treatment if any? The symptoms of Giardiasis vary. The most common symptoms, when they occur, are mild to moderate abdominal discomfort, increased intestinal gas (abdominal distention), sulfurous or “rotten-egg” burps, horrific flatulence, and mild to moderate diarrhea. Nausea, weakness, and loss of appetite can occur, but a fever is uncommon. Studies show that Giardiasis can be suspected when the illness lasts for seven or more days and at least two of the above symptoms. Most individuals infected, show no symptoms at all.
If an individual contracts Giardiasis with symptoms, the symptoms will most likely be gone in a little more than a week without treatment. However, they may still be carrying the cysts and can unknowingly spread the illness. Good personal hygiene is key to not spreading the sickness. Metronidazole (Flagyl) is the standard medication with about a 92 percent cure rate. This medication is recommended by the CDC, but is not approved by the US Food and Drug Administration because it can have some serious side effects and is potentially carcinogenic.
Quinacrine (Atabrine) and Furazolidone (Furoxone) are also prescribed. What steps can be taken to prevent further outbreaks? Include individual as well as environmental precautions and methods. Chlorine is not very effective for Giardia disinfection which is why swimming pools can be a primary source for the disease. High quality filters and Iodine are used in most water treatment. Methods are then taken to remove the taste of iodine from the water. Practice good sanitation and personal hygiene to protect yourself and animals.
Wash hands with soapy water after handling infected animals and feces. Bathe after recreational use of lakes and streams. When in wilderness areas, boil or purify water before drinking. Practice commonly recommended wilderness sanitary habits such as, defecating 100 feet away from water, bury or pack out feces and toilet paper, and wash before handling food. Being infected with Giardia may not be as much the problem, as to how your body reacts to the parasite, and how to get rid of it when the body does not react well to it.