Molecular characterisation and phylogeny of two nematode parasites recovered from the amphibian host Schlerophrys regularis sampled in Lagos metropolis, Nigeria

Abstract

Research on amphibian parasites has been on the increase because of the noticeable decline of amphibians. Studies on these parasites  have been limited to their prevalence and infection patterns, and there is still a dearth of knowledge on the phenotypic variations. To  characterise and investigate the genetic variability and relatedness of amphibian nematode parasites, two nematode parasites– suspected Cosmocerca sp. and suspected Rhabdias sp.–of the toad Schlerophrys regularis were investigated. One hundred and sixty- eight S. regularis were collected from three study areas: Ikorodu, Ojota and Badagry. Intestines were dissected to obtain the enteric parasites, and lungs were washed in saline solution. Parasites were labelled according to the location of collection (Badagry 5A-5I,  Ikorodu 5J–5O, Ojota 5P and 5S) and were then preserved for further identification. Eighteen parasites were identified morphologically  using standard keys and by amplification of the 18S small subunit (SSU) ribosomal DNA sequence. Phylogenetic analysis was done using  the Neighbour-Joining method. From the sequence homology and phylogenetic analysis, the suspected Cosmocerca sp. shared the  closest genetic relatedness with Aplectana chamaeleonis isolate AC3 with 100% similarities while the suspected Rhabdias sp. shared the  closest genetic relatedness with Rhabditoides regina isolate DF5012 with 100% similarities. Based on location, four Aplectana  chamaeleonis (5E, 5F, 5G, 5H) and five Rhabditoides regina (5A, 5B, 5C, 5D, 5I) were from Badagry, four Aplectana chamaeleonis (5J, 5M,  5N, 5O) and two Rhabditoides regina (5K, 5L) from Ikorodu, one Aplectana chamaeleonis (5S) and two Rhabditoides regina (5P, 5Q) from  Ojota. We report that Rhabditoides regina, a parasite known to be associated with insects, was recovered in the lungs of toads. Further  investigations to resolve the complexities of superfamily Cosmocercoidea are recommended. Relatedness was not influenced by collection location as parasites were not unique to a specific environment.