Abstract
BackgroundThe European perch, Perca fluviatilis L. is a common paratenic host of dioctophymatid nematodes belonging to the genus Eustrongylides. In this host, once infected oligochaetes, which serve as the first intermediate host, are ingested, Eustrongylides migrates through the intestine and is frequently encountered within the musculature, free within the body cavity, or encapsulated on the viscera. The current study details the first Italian record of Eustrongylides sp. with larvae reported in the muscle of P. fluviatilis.MethodsUninfected and nematode-infected muscle tissues of perch were fixed and prepared for histological evaluation and electron microscopy. Some sections were subjected to an indirect immunohistochemical method using anti-PCNA, anti-piscidin 3 and anti-piscidin 4 antibodies.ResultsA total of 510 P. fluviatilis (TL range 15–25 cm) from Lake Trasimeno, Perugia were post-mortemed; 31 individuals had encysted nematode larvae within their musculature (1–2 worms fish−1). Histologically, larvae were surrounded by a capsule with an evident acute inflammatory reaction. Muscle degeneration and necrosis extending throughout the sarcoplasm, sarcolemmal basal lamina, endomysial connective tissue cells and capillaries was frequently observed. Within the encapsulating reaction, macrophage aggregates (MAs) were seen. Immunohistochemical staining with the proliferating cell nuclear antigen (PCNA) revealed numerous PCNA-positive cells within the thickness of the capsule and in the immediate vicinity surrounding Eustrongylides sp. larvae (i.e. fibroblasts and satellite cells), suggesting a host response had been initiated to repair the nematode-damaged muscle. Mast cells (MCs) staining positively for piscidin 3, were demonstrated for the first time in response to a muscle-infecting nematode. The piscidin 3 positive MC’s were seen principally in the periphery of the capsule surrounding the Eustrongylides sp. larva.ConclusionsA host tissue response to Eustrongylides sp. larvae infecting the musculature of P. fluviatilis was observed. Numerous fibroblasts, MAs and MCs were seen throughout the thick fibroconnectival layer of the capsule enclosing larvae. PCNA positive cells within the capsule suggest that host repair of nematode damaged muscle does occur, while the presence of the antimicrobial peptide piscidin 3 is shown for the first time. This is first report of Eustrongylides sp. in an Italian population of P. fluviatilis.
Highlights
The European perch, Perca fluviatilis L. is a common paratenic host of dioctophymatid nematodes belonging to the genus Eustrongylides
The European perch, Perca fluviatilis L., is widely distributed throughout the Palaearctic region and serves as a common paratenic host to the third or fourth stage larvae of several species of nematode belonging to the genus Eustrongylides Jägerskiöld, 1909
The vast majority of larvae were encountered within the epaxial muscle and were evident by their large size (c. 30 mm in length), by their red coloration and by the distortion their presence imposed on the musculature (Figure 1)
Summary
The European perch, Perca fluviatilis L. is a common paratenic host of dioctophymatid nematodes belonging to the genus Eustrongylides In this host, once infected oligochaetes, which serve as the first intermediate host, are ingested, Eustrongylides migrates through the intestine and is frequently encountered within the musculature, free within the body cavity, or encapsulated on the viscera. Infections have been associated with epizootic episodes resulting in the significant mortality of a range of nestling ardeids (i.e. bitterns, egrets, herons etc.) and other wading birds [2,3,4] In those fish species that serve as a paratenic host, Eustrongylides spp. migrate into the body and are frequently encountered within the skeletal musculature and only occasionally are found free within the body cavity or encapsulated on the viscera [1]. 1822, have been reported to induce necrosis, resulting in a decrease in yolk formation, and, the disappearance of vitellogenic oocytes [5]
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