Mortalities accompanied with symptoms similar to vibriosis were observed in farmed greater amberjack Seriola dumerili immunized with a commercial Vibrio anguillarum vaccine (serotype J-O-3). The symptoms of infection included exfoliation of the head epithelium, ragged caudal fin, accumulated ascites, and ophthalmitis. Bacteria isolated from infected fish were positive in species-specific PCR assays for V. harveyi. A phylogenic analysis based on topA (DNA topoisomerase I) and mreB (rod shape-determining protein mreB) concatenated gene sequence provided further confirmation of the isolated bacteria as V. harveyi. Experimental infection revealed that the isolate was pathogenic to greater amberjack. In a vaccine trial, mortality of fish immunized with formalin-killed cells (FKC) of the isolate was significantly lower than that of control fish, suggesting that FKC of the isolate prevents greater amberjack from V. harveyi infection.
Pathogenic studies using model animals for diseases that are found in similar diagnosis as in humans are widespreading and medaka fish Oryzias latipes is one of such animal models, however, histological studies on their diseases are still limited. In this study, we applied whole body serial tissue sectioning to adult medaka; it is similar to whole body computed tomography (CT) scanning to decide the lesion (s) location, furthermore, it can give us more precisely microscopic histological information. When adult medaka collected from a wild population were examined, we found cystic lesion (s) in their testis with a diameter of about 500 μm, filled with serous material. Because each of cysts was covered with epithelium, the lesion was found to be a true cyst. Cysts with the same histological appearance were also found adjacent to ovary and liver, and some of the medaka showed polycystic condition. This condition was seen at a high frequency in wild medaka, but it had not been found in laboratory-reared medaka. Although number of observations is small for giving conclusion, these results suggest that cysts could be a common lesion in wild medaka and whole body sectioning can be a powerful methodology for pathological examination of model animal like medaka.
Cyprinid herpesvirus 3 (CyHV-3), also named koi herpesvirus (KHV), is a lethal pathogen of koi and common carp Cyprinus carpio. In the present study, we described a procedure to generate monoclonal antibodies (mAbs) against the envelope protein pORF132 of CyHV-3 and application of the mAb. Three recombinant plasmids targeting the expression of one complete pORF132 and two truncated pORF132 were constructed, respectively. After induction, a truncated pORF132 was successfully expressed in a soluble form and the purified recombinant protein was used in the preparation of mAbs. Two hybridoma cell clones, 4E11 and 4B11, were obtained and mAb 4E11 reacted to CyHV-3 infected cells and not to CyHV-2 (goldfish hematopoietic necrosis virus) and IcHV-1 (channel catfish virus) infected cells. An antigen-capture ELISA based on the pair of mAb 4E11 and anti-CyHV-3 IgY was primarily constructed. This antigen-capture ELISA could distinguish between the CyHV-3 infected and uninfected fish samples.
Kudoa septempunctata infecting the muscle of the olive flounder Paralichthys olivaceus has been recently demonstrated to cause food poisoning in humans who eat the raw flesh of flounder. In the present study, we assessed the effective treatments of a water supply to prevent K. septempunctata infection in a flounder hatchery where the parasite was enzootic. The prevalence of infection in a positive control fish group exposed to unfiltered seawater was 33% at 3 months post-exposure, whereas no infection was observed in the treated fish groups exposed to sand-filtered seawater, sand- and cartridge (5 μm)-filtered seawater or sand-filtered seawater followed by ultraviolet (UV) irradiation at a dose of 46 mJ/cm2. Additionally, treatment with UV irradiation alone was effective for the prevention of K. septempunctata infection. To ensure complete protection from K. septempunctata infection, we recommend double treatments of a water supply with sand filtration and UV irradiation in olive flounder hatcheries.
Cyprinid herpesvirus 3 (CyHV-3) is the causative agent of koi herpesvirus disease and poses a significant threat to common and koi carp. Since its first description, the virus has spread worldwide. In 2010 and 2011, mass mortality of common carp was reported in a hatchery and several ponds in northern Vietnam. CyHV-3 was detected in infected tissues by PCR, confirmed by sequencing of the thymidine kinase gene. Duplex PCR demonstrated that the virus belonged to the genetic lineage (I++/II-) previously described in Indonesia. This suggests CyHV-3 as the causative agent of the disease outbreak and constitute the first report of CyHV-3 in Vietnam.
Passive immunization was performed to determine whether serum antibodies were involved in protection for red sea bream iridoviral disease (RSIVD) in Pagrus major, Seriola quinqueradiata, S. lalandi, S. dumerili and Oplegnathus fasciatus. When fish were experimentally challenged, significantly lower mortality was noted in the fish received the convalescent serum than control fish, except for O. fasciatus. The administration of serum from fish immunized with a commercial vaccine, significantly suppressed mortality of the recipient, except for S. lalandi and O. fasciatus. The results suggest that serum antibodies play a primary role in the protection against RSIVD in red sea bream and the genus Seriola.