Cysts: Real pests in our Drinking Water
Cryptosporidium, “Beaver Fever”, Giardia Lambia
This organic sporozoan, first described in 1907, wasn’t recognized as a cause of human illness until 1976. It is a protozoan parasite that can infect a variety of animals. In the environment, Cryptosporidium exists as a resilient, infectious, round oocyst about four to six microns in diameter. The cyst is a “suitcase” for the infectious material inside.
Cryptosporidium is widespread in the environment. Oocysts (cysts) have been found in rivers, streams, lakes, reservoirs, sewage, and treated surface water. Once introduced to water, the oocyst can survive for weeks, even at low temperatures. The organism has been found in humans, cattle, sheep, swine, goats, cats, and dogs as well as deer, raccoons, foxes, coyotes, beavers, muskrats, rabbits and squirrels. Oocysts infecting certain species can infect another (referred to as cross-transmission). For example, organisms from domestic animals (cattle, dogs, eats, etc.) are able to infect humans, Conversely, organisms from humans can infect animals. Consequently, animals which typically reside in or around watersheds may serve as hosts to the cysts and continuous sources of infection. This is where the nick name “Beaver Fever” was born. Beavers carry the organisms and through their feces spread it throughout surface water supplies without becoming ill themselves. Moreover, infection can occur not only from drinking contaminated water but also from eating contaminated food and from exposure to fecally contaminated environmental surfaces.
When ingested, the Oocysts pass through the stomach into the small intestine. There the Oocysts split open, releasing sporozoites which invade the cells lining the gastrointestinal tract. Infected cells lining the intestine appear normal, but their ability to absorb water and nutrients is severely impaired. The water and food ingested simply passes through the digestive system. Additional Oocysts are formed in the intestine and either split open to release additional sporozoites to continue the infection or are excreted in the feces.
The Cryptosporidium infection causes an illness called cryptosporidiosis. After the Oocysts are ingested, the incubation period typically varies from two to 12 days with an average of seven days. Disease symptoms include diarrhea, abdominal cramps, nausea, occasional vomiting and low grade fever.
The number of Oocysts that must be ingested to cause infection in humans is not conclusively known. Studies indicate that as few as ten and perhaps as many as 500 Oocysts are required to initiate infections in mammals. The infectious dose for humans is thought to be fewer than ten.
Cryptosporidiosis typically last 10 to 14 days. However, it may linger off and on for up to 30 days and infrequently can persist for extended periods. Children may be the most susceptible, particularly six year olds and under. A rapid cure for Cryptosporidiosis has not been found. Recovery depends on the patient’s overall health and immune system. The disease can be fatal for those who are already in a fragile state such as someone with AIDS or any others weakness to their immune system.
There are two varieties of the oocyst; (1) a sphere of about 4.5 micron in diameter and (2) an ellipse of about 7 x 5 micron. The thick walls of the Oocysts make it difficult, almost impractical, to kill with the UV systems in most domestic water treatment systems. Also, the cyst is much more difficult to kill using chlorine than normal coliform bacteria found in water supplies.