Phylogenetic analysis of Blastocystis isolates from animal and human hosts in the Philippines

To study the genetic diversity and cross-transmissibility of Blastocystis species in naturally infected hosts, 12 Blastocystis isolates from animal and human hosts in the Philippines were analyzed by sequencing the full-length small subunit ribosomal RNA (SSU rRNA) genes. Each sequence showed very high similarity (from 97% to 100%) to homologous sequences of other Blastocystis isolates reported previously. Phylogenetic analysis revealed that the 12 isolates were classified into 4 genetically distinct subtypes: 1, 2, 3, and 6. Results showed that Blastocystis subtypes 1, 2, and 3 were shared by isolates from varied hosts. This study confirms the remarkable heterogeneity of SSU rRNA gene among different Blastocystis isolates. The findings of this study agree with previous reports that the different Blastocystis subtypes have low host-specificity, comprising isolates from humans and various animal hosts. This study also suggests evidence for zoonotic transmission of the parasite and cross-transmissibility among heterogeneous hosts.