Detection of the amoebic parasite (order Dactylopodida) in cultured Pacific white shrimp (Litopenaeus vannamei)

This study describes the amoeba (order Dactylopodida) infection in Pacific white shrimp Litopenaeus vannamei cultured in an anonymous shrimp hatchery, located in North America. The diseased shrimp grossly exhibited reduced appetite, lethargy, respiratory distress, eroded carapace, and blackened gill. Histopathology examination revealed a massive amoeba infection (mostly in trophozoite form) mainly in the gill, but also other organs, such as the antennal gland, lymphoid organ, appendages, and nerve cord of the studied shrimp. The irregular-shaped trophozoites, with the prominent centrally located nucleolus and the basophilic parasome, suggested that this parasite is related to the Paramoeba sp. (order Dactylopodida). Analysis of the small subunit rRNA sequence showed 100% sequence similarity with Paramoeba spp. (or Neoparamoeba spp.) from several aquatic crustaceans and echinoderm species, such as sea urchins, crabs, and lobsters. The sequence also matched with other amoeba species, such as Korotnevella sp. and Pseudoparamoeba sp. (order Dactylopodida). Diagnostic in situ hybridization and PCR assays were developed as the initial screening methods for the detection of the amoebic infection in cultured shrimp. This report is the first to describe the amoeba (Paramoeba-like sp.) infection in penaeid shrimp.