Density-independent Infection during in vitro Interaction of Mesocyclops edax and Second-stage Larvae of Gnathostoma turgidum

摘要

While infection by Gnathostoma turgidum (Stossich) in the definitive host, the Virginian opossum, Didelphis virginiana (Kerr), has been described in wildlife, the complete life cycle of the parasite is unknown. Development of early third-stage larvae of Gnathostoma spp. in vitro-infected cyclopoids has been evaluated previously. However, factors involved in viability of copepods as first-intermediate hosts for G. turgidum and that maintain the life cycle of the parasite in endemic areas of gnathostomosis have not been well studied. In this study, in vitro capability of Mesocyclops edax (Forbes) to ingest second-stage larvae of G. turgidum, and density-dependence relationship with the parasitic load were determined. Average ingestion of 1:5, 1:10, and 1:15 densities were 3.5 +/- 0.3, 7.5 +/- 0.6, and 10.8 +/- 1.0, respectively; whereas parasitic loads of each density in M. edax after interaction were 1.7 +/- 0.3, 2 +/- 0.3, and 1.8 +/- 0.3. Parasitic loads of copepods exposed to each density of second-stage larvae were not statistically different. Ingestion capacity by M. edax in vitro for larvae was directly proportional to density of larvae. However, the parasitic load tended to remain constant regardless of density of larvae to which the copepod was exposed. The behavior might be limited by the size of the host or co-evolutionary strategies that favor viability and maintenance of the life cycle of the parasite in wildlife.