Strongyloides stercoralis: detection of parasite-derived DNA in serum samples obtained from immunosuppressed patients.

Strongyloidiasis is an important neglected disease, which is life threatening in immunocompromised patients. This study aimed to evaluate the frequency of Strongyloides stercoralis infection among immunosuppressed subjects living in endemic communities by conventional PCR of the 18S rRNA and Cox1 genes to detect cell-free DNA in the patients' serum samples. Fresh stool and serum samples were obtained from participants. The stool samples were examined using parasitological methods. Total DNA was extracted from the serum samples and S. stercoralis larvae isolated from patient fecal samples. Conventional PCR to amplify a 101 bp fragment of the 18S rRNA gene was carried out for all extracted DNA, and then positive samples were further evaluated for a 121 bp fragment of the Cox1 gene. The PCR products of selected samples were sequenced and BLAST analysis was performed. Out of 120 patients, 57 and 63 cases had autoimmune disorders and cancer, respectively. The 101 bp fragments of the 18S rRNA were successfully amplified in 36 out of 120 (30%) serum samples. The PCR products of five samples were sequenced and compared with reference sequences in GenBank, which showed 97% identity and 90% coverage. In conclusion, to the best of our knowledge, this is the first molecular study for the detection of S. stercoralis cell-free DNA in human serum samples. These results provide useful insights for future studies and show that serum is an alternative specimen and may be useful in molecular diagnosis of diseases, particularly in immunosuppressive patients.