Eustrongylides species have been reported from various regions of China. In the present study, the morphology and molecular ecology of the Eustrongylides species have been investigated in order to clarify their life-cycle, pathology and host specificity.
In the present study, fourth-stage larvae isolated from naturally infected swamp eel (Monopterus albus) were used to infect domestic ducks (Anas platyrhynchos domestica (L.)). The male and female worms were observed underwent different developmental patterns in host ducks. In males, the fourth moult occurred on day 1–2 post-infection (p.i.), after which they became maturity on day 4 p.i., and died on day 7– 9 p.i. However, females underwent the fourth moult on day 2–4 p.i., produced eggs from day 9 to 17 p.i., and then degenerated and died. When compared to fourth-stage female larvae, adult females demonstrated a 151% considerable increase in total body size. However, the increase in size of the male was not as significant as that in females.
In order to clarify influence of Eustrongylides infection in their definitive hosts, prevalence, mortality and pathology in ducks of different ages, which were experimentally infected by E. ignotus from swamp eel, were investigated. It was found that E. ignotus caused mechanical deterioration and inflammatory reaction of ducks’ proventriculus. The infection could lead death of nestling ducks and the mortality decreased along with the increase of the age of ducks.
Eustrongylides larvae were collected from different fish species in different locations in China and phylogenetic relationship was studied to determine the host specificity of this parasites, by using ITS and COI as the molecular markers. The results showed that the prevelance differed significantly in different host species and habitats. Phylogenetic trees indicated that Eustrongylides was monophyletic when comparing with the outgroups. The specimens of Eustongylides under investigation could be divided into three well-supported clades. The genetic analysis also showed unequivocally that S. asotus and C. argus might harbour two genetic species of morphologically cryptic nematodes.