Role of cellular response in elimination of the monogenean Neoheterobothrium hirame in Japanese flounder Paralichthys olivaceus

Abstract

Adult worms of the blood-feeding monogenean parasite Neoheterobothrium hirame, which cause anemia in the Japanese flounder Paralichthys olivaceus, attach to the host fish by embedding their posterior part deeply into the host tissue. To investigate the possibility that cellular responses of the host fish can eliminate N. hirame, flounder were experimentally infected with N. hirame larvae and reared in either fed or starved conditions. Mature parasites were identified on the buccal cavity wall of the fish 33 d post-infection (Day 33). Monocytes/macrophages and granulocytes increased rapidly in the blood and infected sites after the appearance of mature parasites. These cells adhered to the tegument of the parasites. In addition, a few cells with large electron-dense granules (DGCs) were observed in the inflammatory foci. On Day 47, the tegument of some parasites collapsed partially and were phagocytosed by the infiltrated host cells. Some infiltrated cells adhered directly to the inner tissues of the parasites. On Day 54, in the fed fish group, the loss of the tegument led to damage of the parasites' inner tissue by a large number of infiltrated cells. In this group, the elimination of the parasites was noted from Day 47 to 54. These observations probably suggest that the cellular response of the host fish destructed the parasite's posterior part embedded in the tissue, thereby eliminating the parasites. On the other hand, a high mortality was observed in the starved group. The starved fish developed much more severe anemia than the fed fish, and the elimination of the parasites was not observed in this group. The results of the present study suggest that flounder can eliminate N. hirame if they are fed sufficiently. KEY WORDS: Flounder · Leucocytes response · Neoheterobothrium hirame · Monogenean parasiteResale or republication not permitted without written consent of the publisher

Seasonal and spatial variations in prey utilization and condition of a piscivorous flatfish Paralichthys olivaceus

“…This parasite has serious impacts (anemia and reduction in somatic condition) on Japanese flounder populations in other localities (Shirakashi et al 2006). Japanese flounder can resist N. hirame infection by feeding sufficiently (Nakayasu et al 2005), and our results reflect the high food availability in the study area. The presence of anchovy and sandlance strongly support the production of piscivorous fishes.…”

Microarray analyses of gene expression in Japanese flounder Paralichthys olivaceus leucocytes during monogenean parasite Neoheterobothrium hirame infection

“…These cells communicate to eliminate the parasites through various cytokines, which results in the production and release of hostile molecules (Buchmann 1999). As reported by Nakayasu et al (2005), N. hirame induces inflammatory reactions at the infected site. Further study focusing on the reaction at the site of infection should be conducted to improve our understanding of the host-parasite interaction.…”

“…The parasite causes necrosis and intensive infiltration of inflammatory cells in tissues around the attachment sites. Nakayasu et al (2005) suggested that monocytes/macrophages, granulocytes and cells with large, electron-dense granules may possibly be involved in the elimination of the parasite by cellular response, because these cells infiltrated and directly adhered to the parasites, and destroyed the integument and inner tissue of the parasites. There is no doubt about the involvement of leucocytes in the host response, but their role in the defense activity against N. hirame is unclear.…”

Haematological and parasitological assessment of silver catfish Rhamdia quelen farmed in Southern Brazil

“…This would explain the significant monocytes increase in the cold season. Monocytes play an important role in host defense against parasites, by infiltrating the damaged tissue and by adhering to the pathogen (NAKAYASU et al, 2005). Considering the negative correlation between the number of monocytes and parasitism by Monogenea in cold season, it can be assumed that this relationship is due to the migration of monocytes to the injured site when parasitism increases.…”