May 11, 2013 by
Filed under: Parasites 

Life Cycle

Cryptosporidium is taxonomically classified as a Sporozoa, since its oocyst releases four sporozoites (its motile infectious agents) upon excystation. However, it differs from related parasites such as Toxoplasma by its monoxenous life cycle–completing its entire cycle within a single host (Flanigan and Soave, 1993). The life cycle is complex; there are both sexual and asexual cycles, and there are six distinct developmental stages. One of the most common causes of waterborne disease in humans and animals is the parasitic protozoan of the genus’ Cryptosporidium. This microscopic parasite lives and multiplies itself in the intestine of humans and animals. Cryptosporidium parvum known as Crypto spreads through the stool of an infected animal or a person or drinking recreational water. The Cryptosporidium cyst shell is extremely tough and durable. It survives in chlorine treated water, and can make it through to tap water. The shell-like cover dissolves in the stomach and in return cause damage to the intestines by multiplying itself by millions.

Cryptosporidium lives in dirt, food, water, and many surfaces that are exposed to contaminated feces. The infection occurs when one swallows the parasite accidentally; from swallowing recreational water, such as swimming pools, fountains, lakes, ponds, hot tubs, Jacuzzi, and shallow ponds. One can also become infected by eating raw foods without washing them thoroughly. Cryptosporidium can be picked up by touching infected toys, bathroom surfaces and dipper pales. All it takes is rubbing or touching one’s, mouth with a contaminated hand, and the parasite finds a new home.

  1. Excystation of the orally ingested oocyst in the small bowel with release of the four sporozoites
  2. Invastion of intestinal epithelial cells via the differentiated apical end of the sporozoite within a vacuole formed of both host and parasite membranes and the initiation of the asexual intracellular multiplication stage
  3. Differentiation of microgametes and macrogametes
  4. Fertilization initiating sexual replication
  5. Development of oocysts
  6. The formation of new, infectious sporozoites within the oocyst, which is then excreted in the stool

The cycle begins anew when these oocysts are ingested by a new host. Below is a visual representation of the Cryptosporidium life cycle (Heyworth, 1992):

Clinical manifestations

Cryptosporidium symptoms include stomach cramps or pain, dehydration, nausea, vomiting, fever, blood in the stool, and weight loss. For a person with an average immune system; Cryptosporidium symptoms last about two weeks. Cryptosporidium symptoms emerge two to ten days after being infected. The infection seems to get better for a few days, and then returns to feel worse before the whole infection ends. Cryptosporidium symptoms appear the same ways in humans as they do in animals. Outdoor cats are more likely to catch the parasite than indoor cats. Cryptosporidium is highly contagious and can infect one’s entire family, including animals very quickly. The various symptoms of cryptosporidiosis differ greatly between immunocompetent and immunocompromised individuals. In immunocompetent patients, cryptosporidiosis is an acute, yet self-limiting diarrheal illness (1-2 week duration), and symptoms include:

  • Frequent, watery diarrhea
  • Nausea
  • Vomiting
  • Abdominal cramps
  • Low-grade fever

For immunocompromised persons, the illness is much more severe (Juranek, 1995):

  • Debilitating, cholera-like diarrhea (up to 20 liters/day)
  • Severe abdominal cramps
  • Malaise
  • Low-grade fever
  • Weight loss
  • Anorexia

Due to lack of tissue specificity, C. parvum infection has also been identified in the biliary tract (causing thickening of the gallbladder wall) and the respiratory system (Casemore, et al., 1994).



Cryptosporidium can infect all people. If one has a healthy immune system the symptoms last for about two weeks with no serious damage. However, for persons with severely declining immune system, there is a greater risk for more serious life-threatening infections. Persons with autoimmune diseases who are taking immunosuppressive drugs and those who are young babies are more venerable to the Cryptosporidium symptoms.

One’s healthcare provider handles diagnoses for Cryptosporidium symptoms. Providing a stool sample is the only way to identify the actual cause of the infection. The testing for Cryptosporidium can be difficult and may require several stool specimens for definite results. One’s doctor has to request the testing of Cryptosporidium symptoms. Most labs do not routinely test for Cryptosporidium. There is no effective treatment to Cryptosporidium symptoms; people with a healthy immunity system will recover on their own. Rapid loss of water from vomiting and diarrhea can be life threatening in babies, and need fluid replacement.

Cryptosporidium symptoms are highly contagious avoid spreading it to others by following basic guidelines. Washing one’s hand with soap and water every time after using the toilet, or changing diapers. Washing ones hand before preparing foods and washing all raw foods prevents the spreading of the parasite.Infection by C. parvum has been reported in six continents and identified in patients aged 3 days to 95 years old (Flanigan and Soave, 1993). Transmission is usually fecal-oral, often through water contaminated by livestock mammal feces. Persons most likely to be infected by Cryptosporidium are:

  • infants and younger children in day-care centers
  • those whose drinking water is unfiltered and untreated
  • involved in farming practices such as lambing, calving, and muck-spreading
  • engaging in sexual practices that brings a person into oral contact with feces of an infected individual
  • patients in a nosocomial setting with other infected patients or health-care employees
  • veterinarians who come in contact with farm animals
  • travelers to areas with untreated water
  • living in densely populated urban areas
  • owners of infected household pets (rare)


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