The hepatopancreatic microsporidian Enterocytozoon hepatopenaei (EHP) is an emerging pathogenthat affects cultured shrimp Penaeus vannameiin several SE Asian countries including China, Vietnam, Thailand, Indonesia, India and Malaysia. EHP infections are often accompanied by opportunistic infections of Vibrio spp. Laboratory challenges and a case control study were used to determine the effects of EHP infection on twoVibrio diseases:acute hepatopancreatic necrosis disease (AHPND) and septic hepatopancreatic necrosis (SHPN).To determine the effect of EHP on AHPND, two independent experimental infections were carried out. EHP-infected shrimp (EHP-AHPND group) and healthy shrimp (AHPND group)werechallenged with2.4 x 10 5 CFU/ml of AHPNDcausing Vibrioparahaemolyticus. The results of the experimental infections showed that EHP-AHPND group exhibited higher mortalities (60 and 44%) than the AHPND group (0 and 18%).Thepathological effects of AHPND vs. EHP-AHPND groups were compared during the first 12 hours post infection,57% of the EHP-AHPND group displayed severe hepatopancreas necrosisand sloughing, features characteristic of AHPND infectionwhile only 11% ofAHPND groupshowedthese features. This indicated that EHP-infected shrimp have a higher susceptibility to AHPND infection. To determine the effect of EHP on SHPN, we reviewed the histopathology of samples collected where EHP is endemic; and a case control study was carried out to determine the association between SHPN and EHP. We compared individual shrimp displaying histological signs of SHPN with the shrimp from the same pondswithout these signs.A strong association was found between SHPN and EHP, indicatingthat shrimp with EHPhave an increased susceptibility to SHPN. Thesefindings suggested that EHP infectionis a risk factor forboth AHPNDand SHPN.
Aquaculture of cobia has gained popularity in the last decade, and this species is now farmed in several countries in Latin America and Asia. Despite recent improvement in production techniques that allowed the expansion of the industry, little is known about the diseases that affect cobia during the larviculture stage. In this article we investigated the cause of mass mortalities occurring 13−20 d post-hatching in 3 cycles of cobia larviculture. Wet mounts from diseased larvae gills revealed the presence of cyst-like basophilic inclusions. DNA from the cysts was extracted and PCR amplified using the 16S rRNA gene universal primers for prokaryotes. The amplified products were sequenced and analyzed using BLAST, finding a similarity of 99% with Endozoicomonas elysicola, a Gram-negative bacterium. Confirmation of E. elysicola was conducted by designing a specific probe for in situ hybridization. Specific primers were also designed for diagnostic purposes. This is the first report of epitheliocystis in cobia larvae and also the first report of E. elysicola as an epitheliocystis-causing agent.
KEY WORDS: Epitheliocystis · Endozoicomonas elysicola · Cobia · Gill inflammation
Resale or republication not permitted without written consent of the publisherDis Aquat Org 106: [31][32][33][34][35][36][37] 2013 30%, at least 3 severe episodes of mortalities in larvae have occurred, with final survival in the range of 2 to 10%. Wet-mount analysis and histopathology of gills from diseased fish showed characteristic lesions of epitheliocystis. In this article we present the first description of epitheliocystis causing severe mortalities in cobia larvae.
MATERIALS AND METHODS
AnimalsCobia larvae were produced and reared at CENI-ACUA's laboratory in Punta Canoas Bolivar, Colombia. Mature breeders were held in captivity at CEINER (Center for Research, Education and Recreation) and fertilized eggs were shipped to CENI-ACUA. Larviculture was performed in circular larval rearing tanks (6−7 t) under flow-through production according to published protocols (Benetti et al. 2008).
BackgroundDuring cobia larviculture at CENIACUA, 3 independent cycles presented with sudden events of mortality starting at 13 to 22 dph. The first signs were detected in Outbreak A at 13 dph, in Outbreak B at 22 dph and in Outbreak C at 15 dph. Mortalities started 12 h after the initial symptoms appeared, reaching almost 100% by 7 d. After the first outbreak, screening was initiated on 9 dph animals by wet mount and histopathology of gill tissue in order to detect early pathological signs of the disease.
HistologyMoribund larvae from the 3 outbreaks were anesthetized using clove oil and necropsied. Whole larvae were fixed in neutral 10% buffered formalin for 24−48 h, embedded in paraffin, sectioned and stained with hematoxylin and eosin as described by Faulk et al. (2007). Selected sections were also analyzed by Gram-Twort staining (Ollett 1951). Each larva was examined, and the severity of the disease was determined with a grading system based on...
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