Mass drug administration for the prevention human strongyloidiasis should consider concomitant treatment of dogs

Strongyloides stercoralis is the causative agent of strongyloidiasis, which affects more than 300 million people worldwide [1]. Canine strongyloidiasis is also caused by the same species, S. stercoralis of an animal origin with up to 50% worldwide prevalence [2–5]. It is known that human S. stercoralis strains can infect dogs in laboratory settings (dogs have to be immunosuppressed to maintain infection) [6–8]. Increasing evidence suggests that S. stercoralis could be a potential zoonotic pathogen [2, 5, 9–11]. A study by Goncalves et al. [9] examined 181 kennels and 11 dog keepers responsible for kennel cleaning in the southeastern region of Brazil. The serological analysis (ELISA) found that 24.3% (44 out of 181) and 33% (3 out of 9) of dogs and humans were infected with S. stercoralis, respectively [9]. In another study, stool examination identified rhabditiform larvae in the feces of an animal handler. Examination of his wife and his domesticated pet dog found no larvae present in their stools. However, one-third of the dogs under his charge had S. stercoralis larvae in their feces [10]. Another recent study identified S. stercoralis in dog using the S. stercoralis species-specific primers and probes commonly used to identify human S. stercoralis identification [12]. These studies suggest that dogs may play a role in human strongyloidiasis and/or that humans may play a role in canine strongyloidiasis. There are a few studies describing the role of dogs in the spread of human strongyloidiasis. A study from Anima Islands, Japan, assessed more than 600 humans and their dogs and found no strongyloidiasis cross-contamination [13]. However, further studies are needed to explore the effect of differing interactions and behaviours between humans and dogs in different communities and cultures. Genetic studies are useful for exploring the differences between dog and human S. stercoralis strains and provide insight into the potential for cross infection. The whole genome S. stercoralis sequence (accession number PRJEB528) described by Hunt et al. [14] was from a canine fecal sample. There are 2 regions of S. stercoralis that have been of a particular interest for nucleotide sequencing. Hyper-variable regions ([HVR] I-IV) in 18s ribosomal DNA and a cytochrome c-oxidase subunit 1 gene (cox1) region in mitochondrial DNA (mtDNA) are generally considered to be inter and intraspecific and are used to examine S. stercoralis populations of different geographic locations or hosts [15, 16]. A study by Hasegawa et al. [15] evaluated the HVR-I-IV regions among different species of Strongyloides. They found that for the HVR-I-III regions, multiple species frequently shared the same sequence. In HVR-I they describe minor sequence variations within S. stercoralis sampled from different hosts and locations. These differences, however, did not indicate the host of origin of the particular worm. HVR-IV appeared more species-specific, but did not show intra-specific variations in some Strongyloides spp., including S. stercoralis. In a following study Hasegawa et al. [16] sequenced