Polymorphic marker regions support divergence of Mansonella sp. "DEUX" and M. perstans

Though being prevalent worldwide, Mansonella parasites are among the most neglected filarial nematodes. The true prevalence and genetic diversity of this genus have yet to be fully understood. Mansonella sp. "DEUX" is a recently described filarial nematode infecting humans and other primates in Gabon and Cameroon, although its status as distinct species has been controversial. We investigated four different polymorphic regions to further explore the genetic differences between Mansonella species and to support their status as distinct species.

We screened whole blood samples collected in EDTA tubes from individuals from rural areas in Gabon for mono-infections with only one Mansonella species, either Mansonella sp. "DEUX" or Mansonella perstans, as determined by quantitative polymerase chain reaction (qPCR) targeting the ITS1 region. We also included nine blood samples from Togo that had been collected as dried blood spots on 903™ protein saver cards and identified as M. perstans mono-infection. We further amplified, sequenced, and analyzed three molecular marker regions cox1, 12S rDNA, and 28S rDNA for their potential to discriminate between the two Mansonella species.

In total, 93 mono-infected blood samples were identified. Distinct single-nucleotide polymorphism (SNP) patterns for the two investigated Mansonella species were consistently detected in all four loci. The observed nucleotide divergences were comparable to other Onchocercidae family members. Species identification based on the ITS1 marker region was fully concordant with the SNP patterns in all samples. A complete genetic dimorphism could be observed in each of the four marker regions investigated.

The four polymorphic markers, ITS1, cox1, 12S rDNA, and 28S rDNA, consistently demonstrated clear dimorphism between the two Mansonella species. Our results support the classification of Mansonella sp. "DEUX" as a distinct, nonrecombining Mansonella species within the Onchocercidae family.