الفهرس 
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Abstract
The present work was initiated to study the incidence, morphology, molecular identification, host specificity and life cycle by light and electron microscope of Cryptosporidium spp. infecting ducks. Examination of 915 intestinal fecal samples and 870 bursal impression smears collected from Giza, Cairo and El-Dakhlia governorates by M.Z.N stain revealed that the total incidence of Cryptosporidium spp. was 36.4% and 42% in intestinal and bursal samples respectively. Cairo governorate showed the highest incidence of Cryptosporidium spp. infection (49% and 95%) of the intestinal fecal samples and bursal impression smears respectively. Examination of each of 549 intestinal fecal samples and bursal impression smears of ducks at young age (1W-2M) revealed that 66.5% were infected with Cryptosporidium spp. While the older one (˃2 to 6 M) were Cryptosporidium spp. negative. Seasonal incidence showed that the highest rate was in winter (69.6% &78.7%) while the lowest one was in autumn was 5.3% & 7.3% of intestinal fecal samples and bursal impression smears respectively. Comparative study between M.Z.N. and ELISA showed that examination of intestinal fecal samples and bursal impression smears of each of 100 Muscovy ducks by M.Z.N. stain revealed that 28 and 33% were Cryptosporidium spp. positive respectively. While ELISA showed that 55% of these ducks had antibodies against Cryptosporidium species. characterization and immunoblotting of Cryptosporidium spp. antigens of ducks revealed that the bands at the MW 68, 38-42, 20 and that lower than 15 KDa considered to be specific for duck strain as they react versus Cryptosporidium positive duck serum only. Analysis of PCR amplified fragments on agarose gel electrophoresis revealed that 435 bp was detected for Cryptosporidium spp. of ducks. Sequencing of the PCR products revealed that the investigated species was C. meleagridis in ducks (the accession number in gene bank was KM581271). Studying the host specificity of Cryptosporidium spp. revealed that oocysts could be transmitted from ducks to chickens and vice versa but not transmitted from ducks to rabbits and mice. Also C. parvum were not transmitted from calves to ducklings. Histopathological changes from bursa of fabricius and intestine of experimentally infected ducklings with C. meleagridis were described. Result of life cycle by light and transmission electron microscope showed presence of different developmental stages of cryptosporidia (trophozoites, schizonts, macrogametocytes, developing micrgamony and oocyst).