Morphological, pathological and molecular investigation of equine filariasis in Assiut Governorate, Egypt

Abstract

Background

Filariasis poses a major global problem, affecting the overall health of equine. This study aimed to determine the occurrence of equine filariasis, studying the seasonal behavior of the infection, and perform morphological and molecular identification of the recovered adult and microfilariae.

Methods

A total of 120 equine blood samples collected from Assiut Governorate were subjected to microscopic examination, as well as histopathological sections were performed. Polymerase Chain Reaction amplification of the targeted regions (12S rRNA and 18S rRNA) and phylogenetic analysis were conducted from adult worms and infected tissues.

Results

The microscopy revealed that, Setaria spp. microfilariae in 10 donkeys and 3 horses (10.83%). Additionally, Onchocerca spp. microfilariae were detected in 2 donkeys (1.66%), however, none of the examined horses showed microfilariae of both species. Mixed infection with Setaria spp., and Onchocerca spp. microfilariae were observed in only 2 donkeys (1.66%). Post-mortem examination of 34 equine showed the presence of adult Onchocerca spp. and S. equina with infection rates of 17.64% and 26.47%, respectively. Parasitological examination of skin snips at the umbilical region from these animals revealed Onchocerca microfilariae in five donkeys (14.7%); however, no microfilariae were detected in horses. The peak of occurrence of Setaria spp. microfilariae was recorded in the summer season (17.5%), while the peak of the intensity of Onchocerca spp. infection was detected during the summer and autumn (5%). Films stained with Giemsa and Harris hematoxylin stains displayed enhanced details of microfilarial structures compared to Leishman’s stain. To date, no information available regarding the genetic diversity and phylogeny of Onchocerca cervicalis in Egypt. In the present study, phylogenetic analysis based on the nematode-specific 12S rRNA region was performed to determine the genetic diversity of Setaria spp. The BLAST results of the sequences of two samples were 100% identical with the reference sequences of S. digitata and one sample was 100% identical to S. equina. Likewise, phylogenetic analysis based on the nematode-specific 18S rRNA, revealed five samples were showing 99.8% identity to O. cervicalis reference sequence.

Conclusions

This study represents the first phylogenetic analysis of O. cervicalis in Egypt. Higher infection rates need urgent attention and control strategies, including vector control and suitable management practices. Giemsa and Harris hematoxylin stains are the staining methods of choice for microfilarial examination.