Molecular taxonomic study of Strongyloides spp. in Sri Lanka with emphasis on Strongyloides fuelleborni on the premises of a Sri Lankan university.

Strongyloides stercoralis is the main cause of human strongyloidiasis, but increasingly, presumably mostly zoonotic, human infections with S. fuelleborni are reported. Recently, a number of studies investigated the population structures, host specificities and zoonotic potentials of these two species, using molecular taxonomy. This is the first such study from Sri Lanka. We collected stool samples from humans, dogs and monkeys and used the Baermann after culture method to isolate individual live Strongyloides worms and determined parts of the cox-1 (mitochondrial) and the 18S rDNA (nuclear) and, for a subset, whole genome sequences. Despite a predicted high prevalence, we did not detect any Strongyloides in 126 human stool samples from the plantation sector. This may reflect the impact of improvements in sanitation and hygiene, reducing the worm burden to below our detection threshold. On the other hand, we observed a rather high incidence of S. fuelleborni in monkeys from within a university campus. Unexpectedly, also the two Strongyloides positive dogs we found on campus passed S. fuelleborni, one along with the expected S. stercoralis. Based on the mitochondrial sequences, the S. fuelleborni formed three subclusters within the previously described Asian clade. At the nuclear 18S rDNA locus, all S. fuelleborni carried haplotypes that had previously been described in Asia but some were heterozygous for one Asian allele and one that had so far been considered Africa specific. This suggests that Sri Lanka might be a hybridization zone for the two clades. The S. stercoralis found in this study clustered with the previously proposed 'human and dog shared' type of S. stercoralis. The presence of possible hybrids between the African and the Asian clade of S. fuelleborni and the presence of this species in dog faeces are interesting findings that need to be confirmed in additional studies. The presence of S. stercoralis and S. fuelleborni in animal faeces within the University premises, including the dormitory and the swimming pool area, raises concerns of possible exposure of the University community to these parasites in spite of sanitary conditions that render human to human transmission unlikely.