Molecular characterization of Strongyloides stercoralis in Mazandaran Province, North of Iran

Strongyloides stercoralis is a parasitic nematode that lives in the mucosa of the small intestine and causes strongyloidiasis in humans. Mazandaran is among the endemic areas of this parasite in Iran. For detecting S. stercoralis larvae in stool samples, various techniques, such as PCR technique have been used. The present study was conducted to determine the molecular characteristics of S. stercoralis collected from residents of Mazandaran, Northern Iran. From April to September 2017, a number of 2,195 samples of human feces were collected from different regions of Mazandaran province. First, all stool samples were tested using the formalin-ether method. Then, S. stercoralis-positive stool samples and 300 random samples were selected for molecular study. A set of primer pairs for conventional PCR was used in a PCR reaction to amplify the mitochondrial cytochrome c oxidase subunit 1 (Cox1) gene. To confirm the results of PCR, positive samples were sent for sequencing. The sequence was compared with reference sequences from GenBank. Phylogenetic relationships of the Cox1 gene of S. stercoralis inferred by the maximum likelihood algorithm. According to our results, in the stool test with the formal ether method, 21 (0.95%) stool samples were found to be positive for S . stercoralis, and 162 (38.7%) samples were positive for other parasites. All 21 positive samples were confirmed as S . stercoralis by PCR method. The sequence of the samples overlapped 99% with S . stercoralis in the Genbank. Our results showed that conventional PCR could detect all the microscopically positive samples.