1. Cryptosporidium:

2. Cryptosporidium species are protozoan parasites that infect a broad range of hosts including humans, domestic and wild animals, causing asymptomatic, mild to severe gastrointestinal disease in their host species. The most common species reported in humans worldwide are Cryptosporidium parvum and Cryptosporidium hominis.

3. Oocyst morphology:
Round to oval oocyst 4-6 ㎛ in diameter. Oocyst seems often refractile at wet smear. They appear as black dots or small vacuoles seen after modified acid fast staining.

4. Cryptosporidium Oocyst stained by modified acid-fast stain.

5. Life cycle
Cryptosporidium species exist as multiple cell types, which correspond to different stages during the infection (e.g., a sexual and asexual stage). Cryptosporidium oocyst is hardy, thick-walled, can survive in the environment for months and is resistant to many common disinfectants, particularly chlorine-based disinfectants.

6. After being ingested, the oocysts exist in the small intestine
After being ingested, the oocysts exist in the small intestine. They release sporozoites that attach to the microvilli of the epithelial cells of the small intestine. They become trophozoites that reproduce asexually by multiple fission (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 and develop into new trophozoites and multiply a sexually. 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

7. Type II merozoites changed to either macrogamonts or microgamonts
Type II merozoites changed to either macrogamonts or microgamonts. These are the female and male sexual forms, respectively. This stage, when sexual forms arise, is called gametogony. Zygotes are formed by microgametes from the microgamont penetrating the macrogamonts. The zygotes develop into oocysts of two types. 20% of oocysts have thin walls and so can reinfect the host by rupturing and releasing sporozoites that start the process over again. 80% of the oocysts are thick-walled oocysts, which are excreted into the environment. The oocysts are mature and infective upon being excreted.

9. Transmission of oocysts:
Infected individuals shed large numbers of oocysts (infective stage), which are environmentally resistant to inactivation by commonly used drinking water disinfectants including chlorine treatment and are able to survive routine wastewater treatments. Cryptosporidium oocysts are highly infectious as few as 10 or less Cryptosporidium oocysts can produce disease in healthy adults.

10. Mode of transmission:
1-The faecal–oral route, either directly or indirectly.
For humans, direct transmission can be from person to person due to poor hygiene in overcrowded areas as day care centres, aged care facilities, schools, kids nurseries and other institutions, or from animals to persons such as farmworkers and pet owners.
Most indirect transmission is from contaminated drinking or recreational water. Contaminated food can also be a source of transmission.
2- Cryptosporidium is rarely transmitted via inhalation of aerosolized droplets or by contact with fomites contaminated by coughing.

11. Pathogenesis:
Two to ten oocysts are enough to initiate an infection. The parasite is located in the brush border of the epithelial cells of the small intestine. The parasite can cause damage to the microvilli where it attaches. The most pronounced morphologic alteration is villous atrophy, although villous blunting and fusion might also occur. The severity of mucosal injury correlates with the numbers of infecting organisms. Moderate to severe infections can be accompanied by a patchy or prominent neutrophil and mononuclear infiltrate in the lamina propria and numerous intraepithelial neutrophils.

12. Pro-inflamatory cytokines such as interleukin IL-1, IL-6, IL-8, and tumour necrosis factor (TNF) are released during the infection and they could induce leucocytes chemotaxis increasing inflammatory response in the wall of the intestine. Prostaglandins level increases leads to increase excretion of NaCl leading to increase severity of diarrhoea.

13. The immune status of the host, both innate and adaptive immunity, has a major impact on the severity of the disease and its prognosis. In immunocompetent hosts, disease–parasite development and replication is relatively confined to the terminal jejunum and ileum. In immunocompromised hosts, the entire gastrointestinal tract, as well as biliary and pancreatic ducts could be infected. Less frequently there could also be involvement of the respiratory tree.

14. Clinical picture:
The incubation period for symptomatic cryptosporidiosis is 1–2 weeks.
Human cryptosporidiosis is frequently accompanied by abdominal pain, fever, vomiting, malabsorption and diarrhoea, which may sometimes be profuse and prolonged. Immunocompetent individuals typically experience self-limiting disease.

15. Immunocompromised individuals, including HIV/AIDS patients often suffer from intractable diarrhoea, which can be fatal. Immune compromised patients may get extra intestinal cryptosporidiosis as biliary involvement, or pancreatitis. Pulmonary infection in immunocompromised patients leads to respiratory tract infection symptoms. Rarely, conjunctival irritation is also present.

16. Cryptosporidium is second only to rotavirus as a major cause of severe diarrhoea in children. Cryptosporidium spp. is one of the five highest attributable burdens of diarrhoea in the first year of life. Globally, cryptosporidiosis is estimated to be responsible for the majority of deaths among children less than 5 years of age. Cryptosporidium infection in children is also associated with malnutrition, persistent growth retardation, impaired immune response and cognitive deficits.

17. Diagnosis:
Detection of Cryptosporidium in clinical pathology laboratories is based mainly on microscopic detection by stains and/or fluorescent antibodies (IFA) and other antigenic detection methods.
1- Acid-fast (AF)-modified Ziehl–Neelsen staining is one of the most common differential staining techniques used for detection of Cryptosporidium. Three separate faecal samples should be examined for immunocompetent patients and two samples for patients with AIDS for confident diagnosis of cryptosporidial infections using acid-fast staining

18. 2- IFA is superior to acid-fast modified Ziel-Neelson staining method for detection of cryptosporidium, but it is more expensive than acid-fast staining and requires a fluorescence microscope and well-trained staff. Three separate faecal samples should be examined for immunocompetent patients and two samples for patients with AIDS for confident diagnosis of cryptosporidial infection by this method.

19. 3- Other detection techniques that depends on antigen detection as enzyme-linked immunosorbent assays (ELISAs), enzyme immunoassays (EIAs) and immunochromatographic assay for Cryptosporidium are also available and have the advantage of reducing assay times with disadvantage of variable diagnostic sensitivities.
Major limitation of both conventional microscopy and antigen detection methods is that they cannot identify to species or subtype level, which is essential for understanding transmission dynamics and outbreaks, in particular for zoonotic species.

20. 4- Serology for detection of anti-cryptosporidium antibodies as IgG and IgM antibodies may be used, however these antibodies may stay for long time in the circulation. A finding of sero-conversion from negative to positive or titter rising in two successive tests reflects active infection.
5- PCR as Real-time or quantitative PCR (qPCR) or multiplex PCR assays have been developed to quantitate the numbers of Cryptosporidium oocysts present in human and animal faecal and water samples with 100% specificity and sensitivities as low as 200 oocysts per gram of faeces.

21. Treatment:
Nitazoxanide is licensed for children and adults. It can be prescribed for all patients ≥ 1 year of age.

22. Prevention of cryptosporidiosis:
Wash hands thoroughly with soap and warm water: before preparing and eating food, after handling raw food, after going to the toilet or changing a baby’s nappy, after working, feeding, or playing with pets and other animals.
Do not drink untreated water and always wash fruits and vegetables before eating them.
Take care of toilets hygiene.
Do not allow patients who have had cryptosporidiosis to go to swimming pools at least two weeks after being free from diarrhoea.