الفهرس 
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Abstract
Enteric protozoan parasites remain the most commonly encountered parasitic diseases that continue to cause significant morbidity and mortality worldwide especially in developing countries. The Cryptosporidium parasite represents one of the most important enteric parasites as its infection corresponds to a disease of a major socioeconomic importance.
Cryptosporidiosis is predominantly a gastrointestinal disease of humans and other animals, caused by various species of protozoan parasites representing the genus Cryptosporidium. Cryptosporidiosis is becoming most prevalent in both developed and developing countries particularly among immunocompromised patients and among children aged less than five years. Despite exhaustive attempts at chemotherapy, no efficacious treatment for cryptosporidiosis has been identified; however some agents may be promising. Several Cryptosporidium outbreaks have been reported during the last decades. Spread of these protozoan parasites in developing countries occurs mostly through faecal contamination as a result of poor sewage and poor quality of water. Food and water-borne outbreaks of these protozoan parasites have been favored by the fact that the infectious oocyst form of the parasites is relatively resistant to chlorine.
Currently, there are 21 Cryptosporidium species recognized as valid and at least eight of them have been reported in humans. The majority of human infections however, are either caused by the zoonotic species Cryptosporidium parvum that infects animals as well as humans or by the anthroponotic species Cryptosporidium hominis.
Despite the fact that Cryptosporidium has been identified as a prevalent and virulent agent of childhood diarrhea in the Nile River, Very little is known about the genetic structure of Cryptosporidium spp. in Egypt.
The present study aims to analyze the prevalence of Cryptosporidium spp in Egyptian patients, as well as to study the genotypes heterogeneity of Cryptosporidium isolated cases.
In this study a total of 391 stool samples were collected from Egyptian patients suffering from diarrheal symptoms. Samples were collected from 8 different public hospitals in Cairo and 2 medical camps organized by the faculty of Medicine, Ain Shams University.
For the detection of Cryptosporidium positive cases, initial screening was performed by immunochromatograhic detection that resulted in 23 possible positive cases showing immunoreactivity against anti-cryptosporidial antibodies in addition to 89 cases that showed reactivity against the anti-giardial antibodies. The microscopic examination of the 23 Cryptosporidium detected samples confirmed Cryptosporidium oocysts in 20 samples only after repeated examination of modified Ziehl–Neelsen-stained smears, including 5 cases with very low parasitic load. Nested PCR amplification resulted in the detection of 12 cases only targeting the small subunit of rRNA gene (SSU rRNA). On the other hand, the Cryptosporidium oocyst wall protein gene (COWP) detected 18 cases after several optimization trials to overcome the possible feacal PCR inhibitors. Based on the collective data, 21 isolates were confirmed at least by two of the three detection methods used (the Immunochromatography, the microscopic examination and the PCR amplification), so the Cryptosporidium prevalence may be estimated to be (21/391; 5.37%).
The determination of the genotyping heterogeneity was performed using PCR-RFLP analysis targeting both the SSU rRNA and COWP genes for the amplified cases, (3 cases gave weak amplified product in COWP gene amplification that couldn’t be involved in subsequent RFLP analysis).
Genotyping analysis for 12 cases targeting the SSU rRNA gene demonstrated the predominance of C. hominis infection in 75% versus 25% of the cases with C. parvum infection.
The results of the PCR-RFLP analysis targeting the COWP gene confirmed the genotypes determined by the SSU rRNA gene for each of the 12 cases. Additionally, 3 more cases were genotyped targeting the COWP gene only. The additional 3 isolates showed an apparent combination between C. hominis and C. parvum patterns indicating the presence of mixed infection with C. hominis and C. parvum genotypes in those cases. Based on the COWP gene PCR-RFLP analysis the prevalence of C. hominis infection was (80%; 12/15) compared to C. parvum infection which was (40%; 6/15), where both values included the 3 isolates which exhibited mixed infection (20%; 3/15).
In conclusion, the data obtained from the PCR-RFLP analysis targeting both the SSU rRNA and COWP genes confirmed the predominance of C. hominis infection over that of C. parvum in the studied cases. Such data elucidate the fact that anthroponotic transmission of Cryptosporidium infection is the predominant mode of transmission in Cairo, Egypt, Furthermore, the presence of up to 40% of samples infected with C. parvum demonstrate the need for further investigation to determine the subgenotypes of C. parvum aiming to clarify the mode of transmission in order to improve the possible control measures