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Cryptosporidiosis

20160328-13

Very high magnification micrograph of cryptosporidiosis cryptosporidium infection). H&E stain. Colonic biopsy. Source: Nephron – Own work, CC BY-SA 3.0,

 

 

Ernest Edward Tyzzer (1875-1965) was an American physician and parasitologist, who first described the organism, cryptosporidiosis in 1907, and who recognized that it was a coccidian. Cryptosporidiosis, also known as crypto, is a parasitic 1) ___ caused by Cryptosporidium, a protozoan parasite in the phylum Apicomplexa. It affects the intestines of mammals and is typically an acute short-term infection. It is spread, mainly, through the fecal-oral route, often through contaminated water.

 

Human infection with cryptosporidium was first documented in 1976. Since that time, cryptosporidium has been recognized as a cause of gastrointestinal illness in both immunocompetent and immunodeficient people. Infection with cryptosporidium results in watery diarrhea associated with varying frequencies of abdominal cramping, nausea, vomiting, and fever. In immunocompetent people, cryptosporidiosis is a self-limited illness, but in those who are 2) ___, infection can be unrelenting and fatal. Infection occurs in a variety of settings; waterborne outbreaks of cryptosporidium infection have been documented in association with drinking water from a contaminated artesian well, untreated surface water, and filtered public water supplies. Cryptosporidiosis can also affect the respiratory tract in both immunocompetent (i.e., individuals with a normal functioning immune system) and immunocompromised (e.g., persons with HIV/AIDS) individuals, resulting in watery diarrhea with or without an unexplained cough. In immunocompromised individuals, the symptoms are particularly severe and can be fatal. Recent evidence suggests that it can also be transmitted via fomites in respiratory secretions. Fomite is a term for any inanimate object that can carry disease-causing organisms. Towels, bedding used by a person with an illness, or just the transfer of bacteria on a kitchen cutting board, kitchen sink, a public toilet, public railing or bannister, cat sand box, animal or human hair, etc. Consider forensic medicine and the clues that epidemiologists look for, those items are often 3) ___.

 

Cryptosporidium is the organism most 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 parasite is transmitted by environmentally hardy microbial cysts (oocysts) that, once ingested, exist in the small intestine and result in an infection of intestinal epithelial 4) ___. Cryptosporidiosis may occur as an asymptomatic infection, an acute infection (i.e., duration shorter than 2 weeks), recurrent acute infections in which symptoms reappear following a brief period of recovery for up to 30 days, and a chronic infection (i.e., duration longer than 2 weeks) in which symptoms are severe and persistent. It may be 5) ___ in individuals with a severely compromised immune system.

 

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 6) ___. 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. 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 among 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. 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 7) ___. 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. Cases of cryptosporidiosis can occur in a city that does not have a contaminated water supply. In a city with clean water, it may be that cases of cryptosporidiosis have different origins. Testing of water, as well as epidemiological study, are necessary to determine the sources of specific infections. Note that Cryptosporidium typically does not cause serious or fatal illness in healthy people. It may chronically sicken some children, as well as adults who are exposed and immunocompromised. As few as 2 to 10 oocysts can initiate an infection. The parasite is located in the brush border of the epithelial cells of the small intestine. They are mainly located in the jejunum. When the sporozoites attach the epithelial cells’ membrane envelops them. Thus, they are “intracellular but extracytoplasmic“. The parasite can cause damage to the microvilli where it attaches. The immune system reduces the formation of Type 1 merozoites as well as the number of thin-walled oocysts. There are many diagnostic tests for Cryptosporidium. They include microscopy, staining, and detection of antibodies.

 

Many treatment plants that take raw water from rivers, lakes, and reservoirs for public drinking water production use conventional filtration technologies. This involves a series of processes, including coagulation, flocculation, sedimentation, and filtration. 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 filters remove Cryptosporidium product-specifically. While Cryptosporidium is highly resistant to chlorine disinfection, with high enough concentrations and contact time, Cryptosporidium will be inactivated by chlorine dioxide and ozone treatment. The required levels of chlorine generally preclude the use of chlorine disinfection as a reliable method to control Cryptosporidium in drinking water. Ultraviolet (UV) light treatment at relatively low doses will inactivate Cryptosporidium. Water Research Foundation-funded research originally discovered 8) ___ efficacy in inactivating Cryptosporidium. One of the largest challenges in identifying outbreaks is the ability to identify Cryptosporidium in the laboratory. Real-time monitoring technology is now able to detect Cryptosporidium with online systems, unlike the spot and batch testing methods used in the past. The most reliable way to decontaminate drinking water that may be contaminated by Cryptosporidium is to boil it. In the US the law requires doctors and labs to report cases of 9) ___ to local or state health departments. These departments then report to the Center for Disease Control and Prevention. The best way to prevent getting and spreading cryptosporidiosis is to have good hygiene and sanitation. An example would be hand-washing. Prevention is through washing hands carefully after going to the bathroom or contacting stool, and before eating. People should avoid contact with animal feces. They should also avoid possibly contaminated food and water. Standard water filtration may not be enough to eliminate Cryptosporidium; boiling for at least 1 minute (3 minutes above 6,500 feet (2,000 m) of altitude) will decontaminate it. Heating milk at 71.7 0C (161 0F) for 15 seconds pasteurizes it and can destroy the oocysts’ ability to infect. Water can also be made safe by filtering with a filter with pore size not greater than 1 micrometer, or by filters that have been approved for “cyst removal“ by NSF International National Sanitation Foundation. Bottled drinking water is less likely to contain Cryptosporidium, especially if the water is from an underground source. The US CDC notes the recommendation of many public health departments to soak contaminated surfaces for 20 minutes with a 3% hydrogen peroxide (99% kill rate) and then rinse them thoroughly, with the caveat that no disinfectant is guaranteed to be completely effective against Cryptosporidium. However, hydrogen peroxide is more effective than standard bleach solutions.

 

Symptomatic treatment primarily involves fluid rehydration, electrolyte replacement (sodium, potassium, bicarbonate, and glucose), and antimotility agents (e.g. loperamide). Supplemental zinc may improve symptoms, particularly in recurrent or persistent infections or in others at risk for zinc deficiency. Cryptosporidiosis is found 10) ___ and causes 50.8% of water-borne diseases that are attributed to parasites. In developing countries, 8-19% of diarrheal diseases can be attributed to Cryptosporidium and 10% of the population excretes oocysts. In developed countries, the number is 1-3%. The age group most affected is children from 1 to 9 years old. As of 2010 cryptosporidiosis caused about 100,000 deaths down from 220,000 in 1990. Roughly 30% of adults in the United States are seropositive for cryptosporidiosis, meaning that they contracted the infection at some point in their lives.

 

ANSWERS: 1) disease; 2) immunocompromised; 3) fomites; 4) tissue; 5) fatal; 6) toxoplasmosis; 7) pools; 8) UV’s; 9) cryptosporidiosis; 10) worldwide

 

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