Genetic identification of Stephanofilaria sp. isolated from ulcerative dermal lesions in black rhinoceros.

Abstract

Stephanofilaria is a genus of nematodes that cause ulcerative dermal lesions in large mammals. However, there is a dearth of knowledge on the molecular genetics of Stephanofilaria species infecting critically endangered rhinoceros. This study employed genetic barcoding genes to identify Stephanofilaria species and to determine its genetic diversity and evolution. Phylogenetic analyses on partial genes of the second internal transcribed spacer Ribosomal DNA (ITS-2) and cytochrome c oxidase subunit 1 (Cox-1), revealed a 77% and 93% bootstrap support at the Cox-1 and ITS-2 loci respectively to a clade containing previously identified Stephanofilaria species. Morphological examination also confirmed features diagnostic of Stephanofilaria dinniki previously known to infect rhinoceros. Gene diversity of Cox-1 was 0.931 ± 0.030 and 0.579 ± 0.104 for the ITS-2, whereas nucleotide diversity was 0.008 ± 0.002 and 0.00197 ± 0.0016 for the Cox-1 and ITS-2 genes respectively. Neutrality tests (Fu and Li's D* and Fu and Li's F*) were significantly negative (p<0.05) at all loci, whereas Tajima D and Fu's FS were each statistically significant (p<0.05) at the Cox-1 and ITS-2 loci respectively. The high gene diversity, low nucleotide diversity and negative neutrality tests are consistent with positive selection at the Cox-1 gene. Stephanofilaria infection among rhinoceros is currently restricted to highland sanctuaries compared to a widespread distribution in both lowlands and highlands in the 1960s suggesting an adaptation to vectors thriving in cooler highland temperatures. This is the first genetic identification of S. dinniki, in rhinoceros and will aid in diagnosis, treatment, studies, and rhinoceros conservation.