Cryptosporidium is distributed worldwide.Of the 20 species that are known to exist, only Cryptosporidium parvum infects human beings.Infection appears to occur primarily through water or food contaminated with infected feces and through transmission from person to person.Immunocompromised persons are at risk of contracting this parasite, such as those infected with AIDS.Other potentially at-risk populations include immunocompetent children in tropical areas, children in day care centres, animal handlers and those traveling outside.
Morphology of Cryptosporidium parvum
The roundish Cryptosporidium oocysts are often confused with yeast, measuring only 4 to 6 μm. The mature oocyst is composed of four small sporozoites, although not always visible.
Schizonts and Gametocytes
The other morphological forms required to complete Cryptosporidium ‘s life cycle include schizonts containing 4 to 8 merozoites, microgametocytes and microgametocytes. The mean size of these forms is only between 2 and 4 μm. It should be noted that these morphological forms are not commonly used or seen
Life Cycle of Cryptosporidium parvum
Cryptosporidium infection usually occurs after a mature oocyst is ingested. Sporozoites appear in the upper gastrointestinal tract after excystation, where they reside in the epithelial cell membrane.There may then be asexual and sexual multiplication. Sporozoites break from the resulting oocysts and invade new epithelial cells to initiate autoinfection. Many of the resulting oocysts remain intact, pass through the feces and serve as a new host’s infection stage.
Interestingly, two forms of oocysts are thought to be involved in the life cycle of Cryptosporidium.The thin-shelled version is most likely responsible for auto infections because it always appears to rupture while still in the host.The thick oocyst is usually left intact and discharged from the body.This form is believed to occasionally initiate auto infections.
Clinical symptoms of Cryptosporidiosis
Otherwise, healthy people infected with Cryptosporidium typically suffer from self – limiting diarrhea that lasts about 2 weeks.Episodes of 1 to 4 weeks of diarrhea were reported in day care centres.There may also be fever, nausea, vomiting, loss of weight, and abdominal pain.If fluid loss is severe due to diarrhea and/or severe vomiting, this condition can be fatal, especially in infants.
Infected immunocompromised persons, especially patients with AIDS, usually have severe diarrhea and one or more of the symptoms described above.Malabsorption in these patients may also be associated with infection.In addition, infection can migrate to other areas of the body, such as the stomach and the breathing system.A debilitating condition leading to death may result in these patients. Estimated infection rates in patients with AIDS range from 3 to 20% in the United States and from 50 to 60% in Africa and Haiti. Cryptosporidium infection is considered to be a cause of morbidity and mortality.
Laboratory Diagnosis of Cryptosporidium parvum
The preferred specimen for the recovery of Cryptosporidium oocysts is stool.Several methods have been found to successfully identify these organisms.Oocysts can be seen with iodine or modified acid-fast stain.Furthermore, formalin fixed smears stained with Giemsa can also be use to recover the oocysts.As noted, it is important to make a distinction between yeast and real oocysts. Oocysts were also detected using the following methods: Enterotest, immunosorbent enzyme-linked test (ELISA) and indirect immunofluorescence. Concentration via modified zinc sulfate flotation or sugar flotation in Sheather has also proven to be successful, especially when the treated sample is examined under a phase contrast microscopy.Merozoites and gametocytes are usually recovered only in the intestinal biopsy material.
Treatment of Cryptosporidiosis
Numerous experiments have been conducted to treat cryptosporidium with a wide variety of medications.Unfortunately, most of these possible treatments have proven to be ineffective.However, the use of spiramycin, although still in the experimental stage, has proved to be helpful in removing Cryptosporidium ‘s host.More research is needed on this treatment and on new antiparasitic medicines to develop effective medicines.
Prevention and Control of Cryptosporidiosis
Proper treatment of water supplies, handling of known infected material by using gloves and wearing a jacket (if applicable), proper hand washing and properly disinfecting potentially infected equipment with full – strength commercial bleach or 5 to 10% household ammonia are essential for the prevention and control of cryptosporidium.
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