Cryptosporidium

Life cycle

Cryptosporidium has three developmental stages: meronts, gamonts and oocysts. They reproduce within the intestinal epithelial cells. The Cryptosporidium spore phase (oocyst) can survive for lengthy periods outside a host. It can also resist many common disinfectants, including chlorine-based disinfectants.

Immune system evasion

A Cryptosporidium infection in the intestine causes epithelial cells to activate multiple defense mechanisms. They secrete chemokines and cytokines to mobilize immune cells to the infection site. They also release antimicrobial peptides that are capable of targeting and killing parasite-free stages. Cryptosporidium has evolved to evade these host immune defenses to ensure survival throughout their life cycle.

The location at which Cryptosporidium reside, within an intracellular yet extra-cytoplasmic area in the parasitophorous vacuole (P.V.), limits the direct exposure of parasite antigens to immune cells, protects against phagocytosis, and prevents targeting by guanylate-binding proteins.

Cryptosporidium has also evolved mechanisms to regulate apoptosis and epithelial cell turnover in a stage-specific manner, which promotes the parasite's own growth and ensures completion of its life cycle. The role of NF-kB in the host cell response is critical, as this transcription factor is involved in both pro-apoptotic and anti-apoptotic signaling pathways.

Water treatment and detection

Many treatment plants that take raw water from rivers, lakes, and reservoirs for public drinking water production use conventional filtration technologies. Direct filtration, which is typically used to treat water with low particulate levels, includes coagulation and filtration but not sedimentation. Other common filtration processes including slow sand filters, diatomaceous earth filters, and membranes will remove 99% of Cryptosporidium. Membranes and bag- and cartridge-filter products remove Cryptosporidium specifically.

Cryptosporidium is highly resistant to chlorine disinfection; but with high enough concentrations and contact time, Cryptosporidium inactivation will occur with chlorine dioxide and ozone treatment. In general, the required levels of chlorine preclude the use of chlorine disinfection as a reliable method to control Cryptosporidium in drinking water. Ultraviolet light treatment at relatively low doses will inactivate Cryptosporidium.

One of the largest challenges in identifying outbreaks is the ability to verify the results in a laboratory. The oocytes may be seen by microscopic examination of a stool sample, but they may be confused with other objects or artifacts similar in appearance. Most cryptosporidia are 3–6 μm in size, although some reports have described larger cells.

Boiling is believed to be the safest option for water contaminated by Cryptosporidium.

Diagnosis

The most common approach in diagnosing cryptosporidiosis is detection of the Cryptosporidium oocysts, oocyst antigens, or oocyst DNA in stool samples. Due to the difficulty surrounding detection of these oocysts, there should be a minimum of three stool samples collected on three separate days to rule out the parasitic infection in patients with severe diarrhea. For a higher chance of detection, the stool sample should be concentrated using the formalin-ether sedimentation method prior to microscopy.Acid-fast or phenol-auramine staining on unconcentrated fecal smears can be used to stain the oocysts red or bright yellow, but oocysts have the ability to appear as "ghost" cells. These methods for the identification of oocysts in fecal smears have overall low sensitivities, so the use of ELISA and immunochromatographic tests for diagnosis are deemed more useful;The latter options also allow for specificity of Cryptosporidium antigens. Considered the gold standard for detection of this parasite in stool samples, polymerase chain reaction (PCR) is the most convenient method due to its lower cost, higher sensitivity, and higher specificity for identifying Cryptosporidium species.

Epidemiology

Exposure risks

• People who swim regularly in pools with insufficient sanitation (certain strains of Cryptosporidium are chlorine-resistant)
• Child-care workers
• Parents of infected children
• People caring for other people with cryptosporidiosis
• Backpackers, hikers, and campers who drink unfiltered, untreated water
• People who visit petting farms and open farms with public access
• People, including swimmers, who swallow water from contaminated sources
• People handling infected cattle
• People exposed to human feces
• People who turn compost that has not gone through its phase where temperatures over 50 °C are reached

Dealing with stabilized compost – composting material that has gone through the phases where micro-organisms are digesting the organic matter and the temperature inside the composting pile has reached temperature up to 50–70 °C – poses very little risk as these temperatures kill pathogens and make oocysts unviable.

Like many fecal-oral pathogens, the disease can also be transmitted by contaminated food, poor hygiene or turning compost in a local compost site. Testing of water, as well as epidemiological study, are necessary to determine the sources of specific infections. Cryptosporidium typically does not cause serious illness in healthy people. It may chronically sicken some children, as well as adults exposed and immunocompromised.

Species

• Cryptosporidium andersoni
• Cryptosporidium bailey
• Cryptosporidium bovis
• Cryptosporidium cervine
• Cryptosporidium canis
• Cryptosporidium cuniculus
• Cryptosporidium ducismarci
• Cryptosporidium fayeri
• Cryptosporidium felis
• Cryptosporidium fragile
• Cryptosporidium galli
• Cryptosporidium hominis
• Cryptosporidium marcopodum
• Cryptosporidium meleagridis
• Cryptosporidium molnari
• Cryptosporidium muris
• Cryptosporidium parvum
• Cryptosporidium ryanae
• Cryptosporidium saurophilum
• Cryptosporidium serpentis
• Cryptosporidium suis
• Cryptosporidium ubiquitum
• Cryptosporidium viatorum
• Cryptosporidium wrairi
• Cryptosporidium xiaoi