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| HISTORY | ||||
Cryptosporidium
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 six
microns in diameter. The oocyst is a "suitcase" for the infectious material inside.
Cryptospofidium is widespread in the environment. Oocysts 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, cats, etc.) are
able to infect humans. Conversely, organisms from humans can infect animals. Consequently,
animals typically found in watersheds may serve as sources of infection. 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 excreted in the feces.
The Cryptosporidium infection causes an illness called cryptospopidiosis. 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 isn't 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 two- and under. A cure for Cryptospotidiosis has not been found. Recovery depends
on the patient's immune system. The disease can be fatal for those with AIDS.
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 filters. Also, the cyst is much more difficult to kill using chlorine than normal
coliform found in drinking water.
Since Doulton ceramic water filters are manufactured so that they remove pathogenic bacteria
down to I micron in size; they are effective in the removal of Cryptosporidium. The Sterasyl
ceramic filter elements have been tested and certified by the National Sanitation Foundation to
meet their Standard 53 for the removal of cysts.