الفهرس 
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Abstract
During the period extended from September 2017 to March 2018, heart tissue specimens (90) were obtained from slaughtered one-humped camels at Al Bassatein abattoir, Cairo, Egypt. In addition, 101 fecal samples were collected from camels awaiting slaughter. Samples were screened using different genetic markers in order to investigate the genetic structure of T. gondii, Sarcocystis, Cryptosporidium and trichostrongyle parasites. Single positive T. gondii camel isolate was successfully typed using Mn- PCR-RFLP for three markers: 5′-SAG2 (type II), 3′-SAG2 (type II) and alt. SAG2 (type II). Furthermore, sequencing of the 3′-SAG2 amplicon confirmed the presence of HhaI restriction site, which classify this isolate as belonging to type II. A higher infection rate with Sarcocystis spp. was detected in the investigated samples (64.4%). RFLP analysis of PCR products yielded two different profiles for XbaI; one of them was not completely digested forming three fragments (mixed infection) and other one was slightly digested (mixed infection) or not (single infection). Meanwhile, MboI gave the same electromorph for all positive products. Notably, all positive samples were suspected to harbor two molecularly distinct Sarcocystis genotypes indicating a mixed infection. The identifiable reverse sequence fragments varied by a one nucleotide substitution in the enzyme recognition site (TCTAGA to TCTAAA) generating a restriction site for XbaI (TCTAGA) in one of the two genotypes. Additionally, two peaks were detected at the variable nucleotide site (G to A) in some isolates, confirming a mixed infection . Sarcocystis spp. isolated from dromedary camels in this study and previous isolate were clustered together with S. masoni from new world camelids (llama and guanaco) in one main branch in the phylogenetic tree separated from other species which strongly suggested a potential genetic relationship of the species infecting new-world and old-world camelids.Six samples (5.9%) were found to be positive for Cryptosporidium spp. infection after nested PCR screening. Sequencing of the partial SSU rRNA gene revealed the infection with C. parvum (two isolates, 834 bp), Cryptosporidium rat genotype IV (one isolate, 830 bp) and an unknown genotype designated as camel genotype (three isolates, 827 bp). Two haplotypes of C. parvum were detected in this study with a single nucleotide polymorphism at position 435 (T to C). Similarly, two haplotypes were detected of the camel genotype but with two nucleotide polymorphisms at positions 307 (G to A) and 494 (C to T). Moreover, sequence analysis of the gp60 gene of C. parvum revealed two subtypes, IIdA19G1 (860 bp) and IIaA15G1R1 (866 bp). Notably, phylogenetic analysis showed that Cryptosporidium species formed two clusters; one group contained C. parvum and the new genotypes which detected in this study (intestinal group), meanwhile the other group contained C. muris and C. andersoni (gastric group). Cryptosporidium spp. designated as camel genotype in this assay formed a separate branch on phylogenetic analysis (novel genotype) . Trichostrongyle type eggs were detected microscopically in 35 floats out of 101 examined samples (34.6%). Conventional PCR screening using the ITS2 generic primers detected only 23 positive samples (22.7%). The species contribution of nematodes was ordered as follows: Haemonchus sp. (95.6%), Trichostrongylus colubriformis (65.2%), Cooperia oncophora (60.8%) and Trichostrongylus axei (26%). The ITS-2 sequences revealed a higher frequency of minor differences represented by substitutions of one or more nucleotides, while no insertions or deletions were detected. A total of 15 haplotypes were recorded comprising T. axei (four haplotypes, two of 377 bp and two of 186 bp), H. longistipes (three haplotypes, 379 bp), T. colubriformis (five haplotypes, 232 bp) and C. oncophora (three haplotypes, 173 bp). In case of Haemonchus infection, tested positive samples using the generic primer pair were identified as H. longistipes and sharing 99%–100% homology with species-specific sequences in the GenBank database. Maximum genetic diversity was noted in the T.colubriformis ITS-2 partial sequences (232 bp) with up to five nucleotide substitutions. These data provided clues that camels are promising animals in parasitology research and more efforts are needed to characterize parasites infecting dromedary camels by molecular methods. Our molecular approach revealed unique Cryptosporidium genotypes infecting camels as well as high genetic diversity of the investigated parasites. Furthermore, this study gave more insights on the role of dromedaries in the transmission of these parasites to other animals and humans, as some parasites were found to be of zoonotic importance (e.g., T. gondii, C. parvum, T. axei and T. colubriformis).