Background: Haemonchus contortus (order Strongylida) is a common parasitic nematode infecting small ruminants and causing significant economic losses worldwide. Knowledge of genetic variation within and among H. contortus populations can provide a foundation for understanding transmission patterns, the spread of drug resistance alleles and might assist in the control of haemonchosis. Methods: 152 H. contortus individual adult worms were collected from seven different geographical regions in China. The second internal transcribed spacer (ITS-2) of the nuclear ribosomal DNA and mitochondrial nicotinamide dehydrogenase subunit 4 gene (nad 4) were amplified by polymerase chain reaction (PCR) and sequenced directly. The sequence variations and population genetic diversities were determined. Results: Nucleotide sequence analyses revealed 18 genotypes (ITS-2) and 142 haplotypes (nad 4) among the 152 worms, with nucleotide diversities of 2.6% and 0.027, respectively, consistent with previous reports from other countries, including Australia, Brazil, Germany, Italy, Malaysia, Sweden, the USA and Yemen. Population genetic analyses revealed that 92.4% of nucleotide variation was partitioned within populations; there was no genetic differentiation but a high gene flow among Chinese populations; some degree of genetic differentiation was inferred between some specimens from China and those from other countries. Conclusions: This is the first study of genetic variation within H. contortus in China. The results revealed high within-population variations, low genetic differentiation and high gene flow among different populations of H. contortus in China. The present results could have implications for studying the epidemiology and ecology of H. contortus in China.

Blastocystis is a common protist that can infect domestic and wild animals worldwide. Yak (Bos grunniens), an ancient species which can survive in alpine regions, has supplied necessities to local residents in plateau areas for generations. However, the infections with Blastocystis in yaks has been ignored for a long time. In the present study, the infections and genotypes of Blastocystis spp. in domestic yaks from Qinghai Province (northwestern China) were explored. Of 1027 faecal samples collected from yaks in seven regions of Qinghai Province, northwestern China, the total prevalence of Blastocystis was 27.07% (278/1027) targeting the small subunit ribosome rRNA (SSU rRNA) gene. This protist was detected in yaks within each examined age group, geographical origin and season. Significant difference in prevalence was found in yaks from different geographical origins. The highest prevalence (48.94%) was observed in animals from Haixi county. Sequence analysis revealed three animal-specific subtypes (ST10, ST12 and ST14) of Blastocystis spp. in these yaks, with ST10 being the predominant subtype widely distributed in all investigated regions, seasons and age groups. Interestingly, this is the first report about subtype ST12 infecting yaks. To our knowledge, this is the first systematic report on Blastocystis prevalence in yaks from China, and the findings provide fundamental data for establishing effective control measures for this protist in yaks as well as other animals in China.