A form of the soil-borne Strongyloides nematode that infects humans has been identified for the first time in canine carriers in northern Australia. The findings by Flinders University environmental health researchers, along with experts in the United States, were published in PLOS Neglected Tropical Diseases.

The infective larval form of the Strongyloides spp resides in soil contaminated by feces of an infected person. Individuals encountering this soil are then susceptible to the larva burrowing through the skin where they then migrates to the lungs and ultimately the gut where they develop into adults.

Gut infections remain hidden, but symptoms can include abdominal pain, diarrhea, and bloating. Chronic infections can cause persistent skin and chest symptoms, but the condition often goes unchecked.

This study screened 273 samples of dog feces to compare with 4 samples from humans. Researchers conducted real-time polymerase chain reaction (PCR) of 47 dog and 4 human DNA samples, and then amplified results by conventional PCR with further sequencing. The complete set of amplified sequence variants was then analyzed. As a result of poor amplification in some canine samples, complete sequencing data were obtained on 20 samples.

According to Flinders doctoral candidate Mira Beknazarova, “ultimately, we were able to confirm for the first time that potentially zoonotic S stercoralis populations are present in Australia and suggest that dogs might represent a potential reservoir of human strongyloidiasis in remote Australian communities.”2 The results also independently supported previous reports of at least 2 genetically distinct groups of the nematode: one that infects humans and dogs and another that is specific to dogs. Further, researchers identified 2 new haplotypes (VIII and X). The PCR analysis also allowed for improved analysis of existing Strongyloides spp, and reassignment of 2 haplotypes detected in 4 Australian dog samples were assigned to hypervariable region IV.

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According to investigators, the results did not show direct transmission of the nematode from dogs to humans or the inverse. However, results do build on the need for further work aimed at preventative measures such as improved sanitation.

Reference

1. Beknazarova M, Barratt JLN, Bradbury RS, Lane M, Whiley H, Ross K. Detection of classic and cryptic Strongyloides genotypes by deep amplicon sequencing: a preliminary survey of dog and human specimens collected from remote Australian communities. PLoS Negl Trop Dis. 2019;13:e0007241.

2. Parasitic worms infect dogs, humans: infective nematodes found in canines in remote Australia [news release]. Adelaide, Australia: Flinders University: August 26, 2016. https://www.eurekalert.org/pub_releases/2019-08/fu-pwi082619.php. Accessed Septemeber 4, 2019.