Clinical, histopathological, and phylogenetic studies on Oreochromis niloticus and Procambarus clarkii affected with Myxosporea in Egypt

The myxosporean infection and its phylogenetic analysis were investigated in tilapia (Oreochromis niloticus) with average weight (70 ± 5 g) and crayfish (Procambarus clarkii) with average weight (20 ± 6 g). The prevalence of myxosporean infection was 100% for tilapia gills and internal organs without any specific clinical signs. Gross examination of affected tilapia showed enlargement of posterior kidney with macroscopic white nodules in kidneys and gills while crayfish gills showed black spots. Microscopic examination of the fresh preparation of kidneys of tilapia showed spores of Myxosporea. Moreover, the hepatopancreas fresh samples of crayfish demonstrated myxosporean spores. The gene sequencing of 18S gene from tilapia kidneys followed by phylogenetic analysis revealed that the isolated parasite had the highest sequence similarity to Myxobolus sp. ram SR-2018 [MK203074.1] giving 89.77% identity and was named Myxobolus sp. Egy1. In crayfish, histopathological examination showed the developmental stages of Myxosporea in the lumen and stroma of gill lamellae with degeneration of lining epithelium. In addition, different developmental stages of Myxosporea were scattered in the lining epithelium and lumen of hepatopancreas with vacuolation and multifocal deformation. In tilapia, histopathology revealed severe degenerative changes in the gill lamellae and renal tubules with presence of different developmental stages of Myxosporea. These findings support the high prevalence of myxosporean infection, particularly Myxobolus, in tilapia that induced histopathological damage in gills, and internal organs. Interestingly, we detected myxosporean spores in gills and hepatopancreas of crayfish which is considered a first report that needs further phylogenetic and epidemiological investigations.