Genetic characterization and zoonotic potential of Blastocystis from wild animals in Sichuan Wolong National Natural Reserve, Southwest China

Towards minimizing second-generation mis-identification of Blastocystis

At least 1-2% of DNA sequences annotated as Blastocystis in GenBank represent organisms other than Blastocystis or sequence artefacts. As well as being biologically incorrect, such practice can lead to overestimates of genetic diversity, underestimated host specificity, and incorrect classification of samples tested for Blastocystis using DNA-based methods.

Marked genetic diversity within Blastocystis in Australian wildlife revealed using a next generation sequencing-phylogenetic approach

Blastocystis is a genus of intestinal stramenopiles that infect vertebrates, and may cause disease of the alimentary tract. Currently, at least 40 genotypes ("subtypes") of Blastocystis are recognised worldwide based on sequence data for the small subunit of the nuclear ribosomal RNA (SSU-rRNA) gene. Despite the numerous studies of Blastocystis worldwide, very few studies have explored Blastocystis in wild animals, particularly in Australia. Here, we used a PCR-based next generation sequencing (NGS)-phylogenetic approach to genetically characterise and classify Blastocystis variants from selected wildlife in the Australian state of Victoria. In total, 1658 faecal samples were collected from nine host species, including eastern grey kangaroo, swamp wallaby, common wombat, deer, European rabbit, canines and emu. Genomic DNA was extracted from these samples, a 500 bp region of the SSU-rRNA gene amplified by polymerase chain reaction (PCR) and, then, a subset of samples sequenced using Illumina technology. Primary PCR detected Blastocystis in 482 of the 1658 samples (29%), with the highest percentage in fallow deer (63%). Subsequent, Illumina-based sequencing of a subset of 356 samples revealed 55 distinct amplicon sequence variants (ASVs) representing seven currently-recognised subtypes (STs) [ST13 (prominent in marsupials), ST10, ST14, ST21, ST23, ST24 and ST25 (prominent in deer)] and two novel STs (ST45 and ST46) in marsupials. Mixed infections of different STs were observed in macropods, deer, emu and canids (fox, feral dog or dingo), but no infection was detected in rabbits or wombats. This study reveals marked genetic diversity within Blastocystis in a small number of species of wild animals in Australia, suggesting complexity in the genetic composition and transmission patterns of members of the genus Blastocystis in this country.

Extensive prevalence and significant genetic differentiation of Blastocystis in high- and low-altitude populations of wild rhesus macaques in China

BACKGROUND

Blastocystis is a common intestinal protist with a wide range of hosts. Thus far, 38 subtypes have been identified. In recent years, wild animals have been confronted with habitat fragmentation as well as an increasing risk of zoonotic disease transmission due to human disturbance. Only limited data are available on Blastocystis infection and subtype distribution in wild rhesus macaques in China. The aim of the present study was to investigate the prevalence and genetic diversity of Blastocystis in nine wild rhesus macaque populations in China.

METHODS

A total of 276 faecal samples were collected from five high-altitude populations (high-altitude group [HAG]; 2800-4100 m a.s.l.) and four low-altitude populations (low-altitude group [LAG]; 5-1000 m a.s.l) of rhesus macaques. PCR-based analysis, using a new primer pair for the amplification of a 1690-bp sequence of the small subunit ribosomal RNA (SSU rRNA) gene, was used for prevalence and genetic diversity analysis.

RESULT

Analysis of faecal samples revealed that Blastocystis infection was common in rhesus macaques, with an infection positivity rate of 80.1% (n = 221/276 samples). There was no significant difference (P = 0.121) in positivity rate between the LAG (84.3%) and HAG (76.8%). Overall, 33 haplotypes were obtained and classified into four subtypes (STs), of which three were potentially zoonotic subtypes (ST1, 29.7%; ST2, 16.7%; ST3, 31.9%) and one that was first identified in this study and named ST39 (12.0%). The STs were distributed differently among the rhesus macaque populations, except for ST3, which was found in all populations. Phylogenetic analyses revealed two major divergent clades of ST3 for the HAG and LAG. Genetic diversity analysis showed a high genetic diversity of ST3 (haplotype diversity: 0.846; nucleotide diversity: 0.014) in the rhesus macaques, but a high genetic differentiation (F_ST > 0.25) and a low gene flow (Nm = 0.09) between the HAG and LAG.

CONCLUSION

Our study, which is the first investigation on Blastocystis infection in multiple wild rhesus macaque populations in China, indicates a potential risk of zoonotic transmission of Blastocystis in the study areas. Blastocystis ST3 showed high genetic diversity in wild rhesus macaques and significant genetic differentiation between the HAG and LAG. Our results provide fundamental information on the genetic diversity and prevalence of Blastocystis in wild rhesus macaque populations.