The current study first revealed that the predominant fluke species and the prevalence of fluke invasion in yaks and Tibetan sheep around Qinghai Lake on the QTP of China. To our knowledge, there were no published data of liver fluke and/or rumen fluke invasion in yak and Tibetan sheep in this area. The environmental conditions and geographic location of Qinghai Lake are easy to form a complete life cycle of fluke.
In this study, the eggs of Fasciola spp. and Paramphistomum spp. were detected in faecal samples from yaks and sheep, which is consistent with of liver fluke or rumen fluke eggs of a previous microscopic observation [19]. Morphological identification of eggs is rapid and convenient for distinguishing the fluke species, however, their eggs are very similar in morphological characters which may lead to misdiagnosis and subsequent failure treatment [20, 21, 22]. The molecular identification might avoid the shortcomings, which are powerful instrumental in the species identification and differentiation of fluke species [23, 24, 25, 26, 27, 28]. Therefore, this study was mainly based on morphological characteristics of the eggs for the initial identification of Fasciola spp. and Paramphistomum spp., and further confirmed by the molecular methods for their species. The eggs amplicons in this study were completely identical to those of the representative F. hepatica or P. leydeni registered in GenBank, and the resulting phylogenetic tree showed the F. hepatica and P. leydeni identified in the present study formed well defined clusters with their respective reference sequences. Obviously, F. hepatica and P. leydeni were major parasitic flukes of the yak or Tibetan sheep in this area.
In the present study, the overall prevalence of fluke infection in ruminants around Qinghai Lake was high, indicating serious fluke invasion in this area. In addition, P. leydeni was more prevalent (31.60%) than F. hepatica (14.98%) (Table 1), which was consistent with the prevalence trends of the previous studies for the predominant fluke species from the same environmental conditions [2, 29]. There was no association between P. leydeni invasion and breed of ruminant, similar to the findings of the previous studies [30]. However, the prevalence of F. hepatica was significant differences (p < 0.05) for yak and Tibetan sheep, which indicates that the tropism of fluke species might exist in breed of ruminants. Nevertheless, some studies have shown that there was no association between sex of ruminants and prevalence of fluke species [31]. It is interesting to note that some studies showed the prevalence rate of fluke infection was increased with the age of ruminants [32], which might be the adult ruminants are more likely to prolonged exposure time to infective stage of a fluke than those of young ruminants. Adult ruminants were detected and the high prevalence of fluke infection presented in this study, which was consistent with the previous findings [2]. Importantly, the prevalence rate of fluke infection is believed that contributed to the presence of related definitive hosts and the snail along with the favor environmental conditions, which could be the key factors influenced the successive completion of fluke life cycle [6, 33]. Therefore, future studies are needed to carry out environmental etiology surveillance of fluke infection around Qinghai Lake.
In conclusion, these findings provide the current data of fluke invasion in yak and Tibetan sheep around Qinghai Lake. The occurrence of F. hepatica and P. leydeni implies the suspected opportunity of these fluke spreading and contaminating in this area, probably exist in risk for fluke infection of other ruminants and human. Therefore, it is imperative to require further epidemiological investigations of fluke infection in this area.