Cryptosporidiosis

Cryptosporidiosis, sometimes informally called crypto, is a parasitic disease caused by '' Cryptosporidium'', a genus of protozoan parasites in the phylum Apicomplexa. It affects the distal small intestine and can affect the respiratory tract in both immunocompetent (i.e., individuals with a normal functioning immune system) and immunocompromised (e.g., persons with HIV/AIDS or autoimmune disorders) individuals, resulting in watery diarrhea with or without an unexplained cough. In immunosuppressed individuals, the symptoms are particularly severe and can be fatal. It is primarily spread through the fecal-oral route, often through contaminated water; recent evidence suggests that it can also be transmitted via fomites contaminated with respiratory secretions.

''Cryptosporidium'' is commonly isolated in HIV-positive patients presenting with diarrhea. Despite not being identified until 1976, it is one of the most common waterborne diseases and is found worldwide. The infection begins when a human consumes food or water containing cysts of the ''Cryptosporidium'' organism.

Signs and symptoms

Cryptosporidiosis may occur as an asymptomatic infection, an acute infection (i.e., duration shorter than 2 weeks), as recurrent acute infections in which symptoms reappear following a brief period of recovery for up to 30 days, and as a chronic infection (i.e., duration longer than 2 weeks) in which symptoms are severe and persistent. It may be fatal in individuals with a severely compromised immune system. Symptoms usually appear 5–10 days after infection (range: 2–28 days) and normally last for up to 2 weeks in immunocompetent individuals; symptoms are usually more severe and persist longer in immunocompromised individuals. Following the resolution of diarrhea, symptoms can reoccur after several days or weeks due to reinfection. The likelihood of is high in immunocompromised adults, and low in those with normal immune systems.

In immunocompetent individuals, cryptosporidiosis is primarily localized to the distal small intestine and sometimes the respiratory tract as well. In immunocompromised persons, cryptosporidiosis may disseminate to other organs, including the hepatobiliary system, pancreas, upper gastrointestinal tract, and urinary bladder; pancreatic and biliary infection can involve acalculous cholecystitis, sclerosing cholangitis, papillary stenosis, or pancreatitis.

Intestinal cryptosporidiosis

Common signs and symptoms of intestinal cryptosporidiosis include:
* Moderate to severe watery diarrhea, sometimes contains mucus and rarely contains blood or leukocytes
** In very severe cases, diarrhea may be profuse and cholera-like with malabsorption and hypovolemia
* Low-grade fever
* Crampy abdominal pain
* Dehydration
* Weight loss
* Fatigue
* Nausea and vomiting – suggests upper GI tract involvement and may lead to respiratory cryptosporidiosis
* Epigastric or right upper quadrant tenderness

Less common or rare signs and symptoms include:
* Reactive arthritis (may affect the hands, knees, ankles, and feet)
* Jaundice – suggests hepatobiliary involvement
* Ascites – suggests pancreatic involvement

Respiratory cryptosporidiosis

Symptoms of upper respiratory cryptosporidiosis include:
* Inflammation of the nasal mucosa, sinuses, larynx, or trachea
* Nasal discharge
* Voice change (e.g., hoarseness)

Symptoms of lower respiratory cryptosporidiosis include:
* Cough
* Shortness of breath
* Fever
* Hypoxemia

Reason

'' Cryptosporidium'' is a genus of protozoan pathogens which is categorized under the phylum Apicomplexa. Other apicomplexan pathogens include the malaria parasite '' Plasmodium'', and ''Toxoplasma'', the causative agent of toxoplasmosis. A number of ''Cryptosporidium'' infect mammals. In humans, the main causes of disease are ''C. parvum'' and ''C. hominis'' (previously ''C. parvum'' genotype 1). ''C. canis'', ''C. felis'', ''C. meleagridis'', and ''C. muris'' can also cause disease in humans. ''Cryptosporidium'' is capable of completing its life cycle within a single host, resulting in microbial cyst stages that are excreted in feces and are capable of transmission to a new host via the fecal-oral route. Other vectors of disease transmission also exist.

The pattern of ''Cryptosporidium'' life cycle fits well with that of other intestinal homogeneous coccidian genera of the suborder '' Eimeriina'': macro- and microgamonts develop independently; a microgamont gives rise to numerous male gametes; and oocysts serving for parasites' spreading in the environment. Electron microscopic studies made from the 1970s have shown the intracellular, although extracytoplasmic localization of ''Cryptosporidium'' species.

These species possess a number of unusual features:
* an endogenous phase of development in microvilli of epithelial surfaces
* two morphofunctional types of oocysts
* the smallest number of sporozoites per oocyst
* a multi-membraneous "feeder" organelle

DNA studies suggest a relationship with the gregarines rather than the coccidia. The taxonomic position of this group has not yet been finally agreed upon.

The genome of ''Cryptosporidium parvum'' was sequenced in 2004 and was found to be unusual amongst Eukaryotes in that the mitochondria seem not to contain DNA. A closely related species, ''C. hominis'', also has its genome sequence available. CryptoDB.org is a NIH-funded database that provides access to the ''Cryptosporidium'' genomics data sets.

Transfer

Infection is through contaminated material such as earth, water, uncooked or cross-contaminated food that has been in contact with the feces of an infected individual or animal. Contact must then be transferred to the mouth and swallowed. It is especially prevalent amongst those in regular contact with bodies of fresh water including recreational water such as swimming pools. Other potential sources include insufficiently treated water supplies, contaminated food, or exposure to feces. The high resistance of '' Cryptosporidium'' oocysts to disinfectants such as chlorine bleach enables them to survive for long periods and still remain infective. Some outbreaks have happened in day care related to diaper changes.

The following groups have an elevated risk of being exposed to ''Cryptosporidium'':
* Child care workers
* Parents of infected children
* People who take care of other people with cryptosporidiosis
* International travelers
* Backpackers, hikers, and campers who drink unfiltered, untreated water
* People, including swimmers, who swallow water from contaminated sources
* People who handle infected cattle
* People exposed to human feces through sexual contact

Cases of cryptosporidiosis can occur even in cities that have a properly de-contaminated water supply. In a city with clean water, it may be that cases of cryptosporidiosis have other origins. Testing of water, as well as epidemiological study, are necessary to determine the sources of specific infections. ''Cryptosporidium'' is causing serious illness more frequently in immunocompromised than in apparently healthy individuals. It may chronically sicken some children, as well as adults who are exposed and immunocompromised. A subset of the immunocompromised population is people with AIDS. Some sexual behaviors can transmit the parasite directly.

Life cycle

'' Cryptosporidium'' spp. exist as multiple cell types which correspond to different stages in an infection (e.g., a sexual and asexual stage). As an oocyst – a type of hardy, thick-walled spore – it can survive in the environment for months and is resistant to many common disinfectants, particularly chlorine-based disinfectants. After being ingested, the sporozoites within oocysts excyst (i.e., are released) in the small intestine. The released sporozoites subsequently attach to the microvilli of the epithelial cells of the small intestine. From there they become trophozoites that reproduce asexually by multiple fission, a process known as schizogony. The trophozoites develop into Type 1 meronts that contain 8 daughter cells.

These daughter cells are Type 1 merozoites, which get released by the meronts. Some of these merozoites can cause autoinfection by attaching to epithelial cells. Others of these merozoites become Type II meronts, which contain 4 Type II merozoites. These merozoites get released and they attach to the epithelial cells. From there they become either macrogamonts or microgamonts. These are the female and male sexual forms, respectively. This stage, when sexual forms arise, is called gametogony.Murray, Patrick R., Ken S. Rosenthal, and Michael A. Pfaller. Medical Microbiology. 5th ed. Philadelphia: Elsevier Inc., 2005: 855–856.

Zygotes are formed by microgamete

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