Cryptosporidium Parvum Drinking Water Protozoan
Written by Mr. Brian Oram, PG
Featured Training Programs
Drinking Water - Disinfection
Cryptosporidium is a protozoan organism which causes the parasitic infection, cryptosporidiosis. It exists in either the free-swimming (trophozoite) form or the oocyst (dormant) form. Cryptosporidium parvum is now recognized as a human pathogen which can cause severe diarrheal illness.
Members of the genus Cryptosporidium are placed taxonomically within the phylum Apicomplexa, order Eucoccidiorida, suborder Eimeriorina, and family Cryptosporidiidae. Species infect epithelial surfaces, especially those along the gut, and can be found in a wide range of vertebrates, including humans. Cryptosporidium parvum infects the small intestine of an unusually wide range of mammals, including humans (Tyzzer, 1912).
Ingestion of drinking water contaminated with viable Cryptosporidium oocysts, the environmentally resistant form of the organism, is the major mode of transmission. Cryptosporidium is introduced into the water supply via animal excreta containing oocysts. Important reservoirs of the oocysts include cattle, sheep and pigs. Cryptosporidium is also found in wild animal populations. The organism is more prevalent in ruminants such as deer, elk, moose and caribou and is primarily found in neonates of these species. Person to person transmission is common, especially in child daycare settings. Direct contact with infected animals, especially calves and lambs, can cause illness in exposed persons. Contaminated food can also cause infections.
For example, typical oocyst shedding in Holstein calves that were each infected orally at 4 days of age with 25 million oocysts of C. parvum. No oocysts were detected until 4 days post-infection (DPI). Peak oocyst production occurred 6-8 following exposure and as few as 2 billion and as many as 20 billion oocysts can be collected during a single 24 hr period from calves during peak oocyst shedding. A single calf can easily produce 50 billion oocysts within a period of one week.
The life cycle of C. parvum is depicted below and begins with ingestion of the sporulated oocyst, the resistant stage found in the environment. Each oocyst contains 4 infective stages termed sporozoites, which exit from a suture located along one side of the oocyst. The preferred site of infection is the ileum, and sporozoites penetrate individual epithelial cells in this region. Parasites reside on the lumenal surface of the cells, and they were once thought to occur extracellularly. However, ultrastructural observations have clearly shown these parasites to be intracellular, enclosed by a thin layer of host cell cytoplasm. A unique, desmosome-like attachment organelle, plus accessory foldings of the parasite membranes, develop at the interface between the parasite proper and the host cell cytoplasm. This attachment organelle is sometimes referred to as the "feeder organelle." Multiple fission (=merogony; =schizogony) occurs, resulting in the formation of 8 merozoites within the meront. These meronts are termed Type I meronts and rupture open, releasing free merozoites. Once these merozoites penetrate new cells, they undergo merogony to form additional meronts. Type I merozoites are thought to be capable of recycling indefinitely and, thus, the potential exists for new Type I meronts to arise continuously.
It is thought that some Type I merozoites are somehow triggered into forming a second type of meront, the Type II meront, which contains only 4 merozoites. Once liberated, the Type II merozoites appear to form the sexual stages. Some Type II merozoites enter cells, enlarge, and form macrogametes (=macrogametocyte). Others undergo multiple fission once inside cells, forming microgametocytes containing 16 non-flagellated microgametes. Microgametes rupture from the microgametocyte and penetrate macrogametes, thus forming a zygote. A resistant oocyst wall is then formed around the zygote (the only diploid stage in the life cycle), meiosis occurs, and 4 sporozoites are formed in the process. Formation of sporozoites is termed sporogony. These oocysts are passed in the feces and into the environment.
Approximately 20% of the oocysts produced in the gut fail to form an oocyst wall and only a series of membranes surround the developing sporozoites. These "oocysts," devoid of a wall, are sometimes termed "thin-walled oocysts." It is believed that the resulting sporozoites produced from thin-walled oocysts can excyst while still within the gut and infect new cells. Thus, C. parvum appears to have two autoinfective cycles: the first by continuous recycling of Type I meronts and the second through sporozoites rupturing from thin-walled oocysts.
Development of Cryptosporidium occurs more rapidly than many textbooks imply, and each generation can develop and mature in as little as 12-14 hours. Due to the rapidity of the life cycle, plus the autoinfective cycles, huge numbers of organisms can colonize the intestinal tract in several days. The ileum soon becomes crowded and secondary sites are often infected, such as the duodenum and large intestine. In immunosuppressed individuals, parasites can sometimes be found in the stomach, biliary and pancreatic ducts, and respiratory tract. Diarrhea, weight loss, and abdominal cramping are clinical signs of the disease and in immunosuppressed individuals electrolyte imbalance may occur.
The prepatent period, which is the interval between infection and the first appearance of oocysts in the feces, is generally 4 days (3 days in heavy infections). Patency, which is the length of time oocysts are shed in the feces, generally lasts 6-12 days in immunocompetent individuals but may be prolonged in immunosuppressed patients.
Infections are most common in young children and immunocompromised individuals. (AIDS/HIV patients, chemotherapy patients and organ transplant patients.) Symptoms of cryptosporidiosis usually appear within two to ten days after ingestion of the parasite. Symptoms include watery diarrhea, headache, abdominal cramps, nausea, vomiting and low grade fever. These symptoms may lead to weight loss and dehydration. In otherwise healthy individuals, symptoms usually last from one to two weeks, at which time the immune system is able to stop the infection. In the immunocompromised, the infection may continue and become life-threatening. At present, there is no effective drug therapy for cryptosporidiosis.
Water treatment for Cryptosporidium relies on properly designed and operated filtration systems. Chlorine disinfection of the organism is ineffective, as it has been shown that even one oocyst can withstand pure bleach (50,000 ppm chlorine) for 24 hours and still cause an infection, but UV / Ozone Disinfection with filtration is very promising. Filter systems usually consist of several filters. A "roughing filter" containing a 5µ - 10µ (micron) cartridge filter is installed to remove any large diameter sediments, such as iron sediments, sand, salt , etc. Downstream from the roughing filter, a "polishing filter" containing a <1µ absolute cartridge filter is installed to remove small particles including Cryptosporidium, from the water. Most reputable water system vendors are currently recommending a filter porosity of <1µ to submicron or membrane filters to remove Cryptosporidium cysts and trophozoites from drinking water. Testing for Groundwater Sources and Potential for Surface Water Influence.
Testing procedures are available for detecting Cryptosporidium oocysts in both raw and treated drinking water. The testing procedure involves filtering a large volume of water through a 1 micron, yarn-wound, polypropylene filter. The filter is then treated to remove any oocysts which may be present and the sample is concentrated. A monoclonal antibody to Cryptosporidium is added to the sample to bind to oocyst wall antigens. The reaction can be visualized by the addition of fluorescein isothiocyanate (FITC) - conjugated anti-immunoglobulin and scanning with an epifluorescence microscope.
Great Books on Giardia
New Approaches for Isolation of Cryptosporidium and Giardia
Evaluation of Antibodies to Cryptosporidium and
Giardia Using Flow Cytometry
Giardia and Giardiasis: Biology, Pathogenesis, and Epidemiology (This is a Great Reference !)
Whole House Treatment System for Protozoans, plus a
Sediment Filter Fitted with a 0.2 micron Filter
UV Disinfection Systems (6 to 12 gpm) and
other water treatment systems
In-line Ozonation System
Water, Wastewater, and Stormwater Design, Operation, and Management
Water Treatment I
Iron/ Managanese Treatment, Coagulation and Flocculation, Sedimentation,
Disinfection, and an Introduction to Regulations
Water Treatment II
Corrosion Control, Taste and Odor Control, Water
Softening, and Reservoir Management
Water Distribution Systems Water Analysis
Metering, Disinfection, and More
UV Systems for Water Treatment
Industrial Wastewater Treatment
Wastewater Treatment I