## 4 Discussion  
In the current study, we observed the occurrence of the zoonotic pathogens _Cryptosporidium_ spp., _E. bieneusi_, and _G. duodenalis_ in domestic Bactrian camels inhabiting on Qinghai-Tibet Plateau. High prevalence was detected in _E. bieneusi_ (45%) infection, followed by _Cryptosporidium_ spp. (15%) and _G. duodenalis_ (7.5%). The intestinal-colonizing parasites _G. duodenalis_ was considered the most common pathogenic parasite in humans and animal species [32; 33; 34; 35; 36]. Although _G. duodenalis_ infection in yaks [37] and sheep [38] living in high-altitude environment had been reported, there were very few reports on the prevalence of _G. duodenalis_ infection in camels. The infection rate of _G. duodenalis_ in Bactrian camels observed in our study was comparable to that reported in yaks and sheep [38]. Inconsistency with the study to report _G. duodenalis_ infections in sheep, which was found in the plain area with a higher infection rate of 6.7% [39] might be a result of altitude influence. The infection rate of _Cryptosporidium_ spp. in camels observed in this study was close to that reported by others [16; 40; 41]. We also found that infection rate of _E. bieneusi_ in this study was comparable to those reported by others [40; 41; 42]. Besides, individuals were concurrently infected with _Cryptosporidium_ spp. and _E. bieneusi_ (5/40), _G. duodenalis_ and _E. bieneusi_ (1/40), but not _Cryptosporidium_ spp. and _G. duodenalis_. Even though no study on mixed infected with _Cryptosporidium_ spp. and _G. duodenalis_ in camels was reported, co-infection of _Cryptosporidium_ spp. and _G. duodenalis_ was still found in yaks [37], children [43], and goat [44]. Concurrent infection with _Cryptosporidium_ spp. and _E. bieneusi_ in dromedary camel [40], as well as co-infection of _G. duodenalis_ and _E. bieneusi_ in dairy cattle was proposed [45] in an early study. A recent study indicated that the maintenance of homeostasis between the gut microbiota and the rest of the body was crucial for health. Intestinal parasites, particularly the protozoans, may cause an alteration in the structure of the gut microbiota, resulting in gastrointestinal upset or systemic diseases [46]. In this study, we analyzed the interaction between intestinal protozoans and bacterial community composition and diversity to understand whether eukaryote microbes modulate the microbiota in camels. The results showed that, by alpha diversity analysis, bacterial community diversity was not significantly different between Control and other groups; however, the higher Chao1 index and similar Shannon diversity index in Control indicated negative samples with higher species richness and lower evenness than Group A (_E. bieneusi_ positive samples). It was also observed that _Frimicutes_ and _Bacteroidetes_ were the predominant phyla, accounting for more than 81% of the bacteriophyta presented in all groups. Although other phyla presented in low abundance, _Spirochaetes_ was detected in relatively highest abundance in Group E than in the other five groups, followed was Group A. The phylum _Verrucomicrobia_ was found in lower abundance in Groups A, C, E than in the other three groups. These results demonstrated that the genera of _Verrucomicrobia_ phylum were negatively correlated with _E. bieneusi_ and _G. duodenalis_, while _Spirochaetes_ was positively correlated with co-infection with _E. bieneusi_ and _G. duodenalis_ in the camel host. From the literature available, there has been no report on the state of the relationship of _E. bieneusi_, _G. duodenalis_, and intestinal _Spirochaetes_; only a previous study mentioned that _G. duodenalis_ provides bearable conditions for concurrent spirochetal diarrhea developing potentially [47]. According to our results, there is more possibility that infection with _E. bieneusi_ and co-infection by _G. duodenalis_ might contribute to the growth of bacteria that belong to _Spirochaetes_. Samples from animals harboring _Cryptosporidium_ spp.