Dogs are reservoir hosts for possible transmission of human strongyloidiasis in Thailand: molecular identification and genetic diversity of causative parasite species

Human strongyloidiasis is a deleterious gastrointestinal disease mainly caused by Strongyloides stercoralis infection. We aimed to study the possible transmission of S. stercoralis between humans and pet animals. We isolated Strongyloides from humans and domestic dogs in the same rural community in north-east Thailand and compared the nucleotide sequences of derived worms using portions of the mitochondrial cytochrome c oxidase subunit 1 (cox1) and 18S ribosomal RNA (18S rRNA) genes. Twenty-eight sequences from the 18S rRNA gene were obtained from worms derived from humans (n = 23) and dogs (n = 5), and were identical with S. stercoralis sequences (from Thailand, Cambodia, Lao PDR and Myanmar) published in the GenBank database. The 28 cox1 sequences from humans and dogs showed high similarity to each other. The available published cox1 sequences (n = 150), in combination with our 28 sequences, represented 68 haplotypes distributed among four clusters. The 28 samples from the present study represented eight haplotypes including four new haplotypes. Dogs and humans shared the same haplotypes, suggesting the possibility of zoonotic transmission from pet dogs to humans. This is of concern since dogs and humans live in close association with each other.