No limit in interspecific hybridization in schistosomes: observation from a case report

Schistosomiasis is one of the most significant parasitic diseases of humans. The hybridization of closely related Schistosoma species has already been documented. However, hybridization between phylogenetically distant species is unusual. In the present study, we characterized the causative agent of schistosomiasis in a 14-year-old patient with hematuria from Côte d'Ivoire, using morphological and molecular approaches. A 24-hour parasitological examination of urine showed the presence of numerous eggs (150 μm long × 62 μm wide) with a lateral spine (25 μm), identified morphologically as Schistosoma mansoni. Examination of stools performed on the same day found no parasites. The urine and stool examinations of the patient's family members performed two weeks later showed neither parasites nor hematuria; but in contrast, many S. mansoni eggs were found again in the patient's urine, but never in his stools. Conventional PCRs were performed, using two primer pairs targeting 28S-rDNA and COI mtDNA. The 28S-rDNA sequence of these eggs, compared with two reference sequences from GenBank demonstrated a hybrid with 25 double peaks, indicating clearly hybrid positions (5.37%) between S. mansoni and S. haematobium. Similarly, we identified a unique S. mansoni COI sequence for the two eggs, with 99.1% homology with the S. mansoni reference sequence. Consequently, this case was the result of hybridization between an S. haematobium male and an S. mansoni female. This should be taken into consideration to explore the elimination of ectopic schistosome eggs in the future.