Genetic diversity and identity of Ascaris worms from human and pig hosts in Thailand

Abstract

Ascaris roundworms are of public health and socio-economic importance worldwide. They are conventionally attributed to two taxa - A. lumbricoides infecting principally human and A. suum infecting principally pig. Phylogenomic analysis has revealed that Ascaris worms from both human and pig are represented in Clades A and B. A recent study indicates that the Ascaris worms from human and pig in Thailand belong to Clade A. We examined adult Ascaris worms from human and pig in Thailand by means of the partial sequences of three mitochondrial genes (cox1, cox2 and nad1) and concatenation of these genes. Phylogenomic analysis indicates that two isolates (H1,H2) of A. lumbricoides from human belonged to Clade B; one isolate (H3) belonged to Clade A (based on cox1, cox2 and concatenated sequences) or as an outlier to Clades A and B (based on nad1 sequences). All the eight isolates of A. suum from pig clustered in Clade A. The partial nad1 and the concatenated sequences revealed two lineages of A. suum isolates which were distinct from the two A. lumbricoides isolates of Clade B. It is evident that greater genetic diversity, and a more robust phylogeny, could be uncovered by the application of multiple genes. In sum, the present study reveals the presence in Thailand of A. lumbricoides from human in Clades A and B which necessitates appropriate treatment and control measures; Clades A and B have been reported to contain haplotypes of Ascaris worms from both human and pig in other parts of the world. A country wide study is needed to elucidate the identity, distribution, prevalence, cross transmission, genetic diversity and phylogeny of the Ascaris worms in Thailand.

Keywords: A. suum; Ascaris lumbricoides; Mitochondrial gene; Molecular identification; Thailand.