Progress 07/01/20 to 06/30/24
Outputs
Target Audience:The research goal of this project is to address high-priority, industry-identified issues to enhance production efficiency and profitability in aquaculture throughout the southeastern United States by improving disease management. The target audience for the new information and technologies developed includes U.S. catfish farmers, research scientists, extension specialists, and fish health professionals. Ultimately, American consumers will benefit from the production of an inexpensive, safe, and domestically sourced seafood product, contributing to a reduction in the U.S. trade deficit in seafood commodities. Information derived from this project will be disseminated to user groups through a formal network of extension program specialists using workshops, seminars, advisory groups, and demonstration projects involving farmer user groups. Investigators will also share their findings with other scientists and aquaculture students through scientific publications and professional meetings. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This project supported a Master's level graduate student and provided partial resources for a Ph.D. student working on the characterization of catfish herpesviruses and the development of treatment strategies to prevent CCV outbreaks in commercially raised hybrid and channel catfish. How have the results been disseminated to communities of interest?The information generated from this project has been disseminated to stakeholders through a formal network of extension program specialists via workshops, seminars, advisory groups, and newsletters with farmer user groups. Investigators have also shared findings with other scientists and aquaculture students through scientific publications and professional meetings. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Screening of Channel Catfish Broodstock for IcHV1 Latency Commercial and research populations of channel catfish broodstock were tested for Ictalurid herpesvirus 1 (IcHV1), also known as CCV, to assess viral latency. Non-invasive tissue samples, specifically fin clips, were screened using PCR analysis, revealing a high prevalence of IcHV1 carrier states across all tested populations. These results indicated the absence of CCV-free fish populations, which prevented broodfish immunization studies proposed in Aims 1A and 2A. This finding prompted a survey of commercial catfish hatcheries to assess the prevalence of IcHV1 in catfish eggs and post-swim-up fry. The survey confirmed that all rearing populations carried IcHV1 in a latent state, highlighting virus's ubiquitous prevalence throughout catfish aquaculture in the southeastern United States. Genetic Characterization of Archived CCV Isolates. The genomes of archived viruses recovered from diseased fish were sequenced, revealing two variants of CCV, designated as IcHV1A and IcHV1B, which as consistent with previous work identifying two discrete genetic lineages of IcHV1 based on RFLP analysis. Challenge trials demonstrated IcHV1B may exhibit increased virulence compared to IcHV1A. Subsequent surveys of hatchery fish populations showed a higher prevalence of IcHV1A, possibly due to its lower virulence, which may lead to increased latency within the population. Both IcHV1 strains were further compared to an archived herpesvirus isolated from blue catfish to evaluate potential strain variations across different host species. Sequencing revealed significant genetic differences between the archived virus isolated from blue catfish and IcHV1A and IcHV1B strains, suggesting the virus isolated from blue catfish may represent a new species of alloherpesvirus. Since hybrid catfish (Blue catfish x Channel catfish) now represent over 60% of catfish produced in the southeastern United States, this herpesvirus, tentatively termed blue catfish alloherpesvirus (BCAHV) is considered a potential emergent pathogen with significant economic implications, requiring further investigation. The host specificity of blue catfish alloherpesvirus (BCAHV) was initially assessed in tissue culture by inoculating cell lines derived from various fish families, including Ictaluridae, Cyprinidae, Centrarchidae, and Clariidae with BCAHV. Viral replication and cytopathic effects (CPE) were observed exclusively in cell lines derived from Ictaluridae, indicating BCAHV has limited host preference specific to this family. Comparative challenge trials were also conducted to assess the virulence of blue catfish alloherpesvirus (BCAHV) in blue catfish, channel catfish, and blue x channel hybrid catfish. Following exposure to BCAHV, mortality rates were highest in blue catfish (82%), intermediate in hybrid catfish (26%), and lowest in channel catfish (7%). Infected catfish exhibited reduced feeding, excessive mucus production, abnormal swimming, and loss of body equilibrium. External clinical signs of infection included distended abdomen, mild to moderate exophthalmia, and hemorrhages at the base of the fins and the ventral portion of the abdomen. Internal clinical signs included an ascitic fluid-filled peritoneal cavity, dark and congested spleen, and pale, swollen anterior and posterior kidneys. Histopathological examination of BCAHV-infected fish revealed splenitis and severe erythrophagia. The virus was successfully re-isolated from infected fish and used to fulfill River's Postulates. Rechallenge studies with IcHV1A and IcHV1B isolates demonstrated cross-protective effects, indicating fish surviving the initial challenge developed a robust immune response, regardless of the viral lineage. Further investigations with these groups and blue catfish alloherpesvirus (BCAHV) revealed similar cross-protective effects between IcHV1A and IcHV1B isolates. While IcHV1 (A&B) have conserved epitopes that are absent in BCAHV, the cross-protection shown here suggests monovalent vaccines may protect against known Ictalurid alloherpesviruses. Intrinsic and Extrinsic Factors affecting BCAHV virulence. Challenge trials were conducted to evaluate intrinsic and extrinsic factors on BCAHV virulence in blue and blue x channel hybrid catfish. Fish were exposed to BCAHV between 30 and 120 days post hatch (dph). Age was shown to influence mortality of blue catfish with the greatest mortality observed at 60 dph. In agreement with the previous challenge trial, blue catfish showed significantly higher mortality compared to hybrid catfish, but age did not significantly influence mortality in Channel catfish. The effects of temperature and crowding were evaluated to determine risk factors associated with BCAHV outbreaks. Both temperature and stocking density significantly influenced mortality following BCAHV exposure in channel and hybrid catfish. At 25°C, mortality rates were 81% in blue catfish and 30% in hybrid catfish. In contrast, negligible losses were observed at 32°C, with no mortality in hybrid catfish, establishing a temperature threshold for BCAHV. However, when blue catfish were exposed to BCAHV at 25°C followed by a rapid rise in temperature to 28°C and 32°C, mortality rates were similar across all temperature treatments. This suggests that once fish are infected within the optimal temperature window, elevated temperatures do not inhibit viral replication, and ensuing death. Additionally, crowding was shown to increase mortality following BCAHV exposure, highlighting the importance of hatchery management strategies in preventing or minimizing losses. Virkon Treatment A cell line from the fin of hybrid catfish (HCF) was developed using explant techniques and enzymatic dissociation to evaluate the effectiveness of Virkon in preventing viral replication and cytopathic effects (CPE) in tissue culture. Both BCAHV and IcHV1 were found to cause CPE in the HCF cell line. In contrast, no CPE was observed after HCF cells were inoculated with Koi Herpes Virus, demonstrating host specificity. Treatment of HCF cells with 0.005% Virkon was effective in inactivating IcHV1 and preventing CPE in the hybrid cell line. Subsequently, channel and hybrid catfish were exposed simultaneously to IcHV1 and Virkon at graded concentrations. A Virkon concentration of 10 ppm, administered for 120 minutes, was shown to inactivate IcHV1, thereby preventing horizontal transmission. Control fish exhibited pathology consistent with CCV infection, while no histological changes were observed in fish treated only with Virkon. These results suggest Virkon could be an effective treatment to minimize horizontal transmission of BCAHV and CCV during hatchery outbreaks, with low potential toxicity to fish. Viral Attenuation An IcHV1 isolate was attenuated through repetitive passages on CCO cell lines in tissue culture. Attenuation was confirmed after the 41st passage, and the attenuated isolate was subsequently evaluated as a potential vaccine candidate for controlling CCV in hybrid and channel catfish. Following exposure (10³.? TCID??/ml) to the attenuated isolate, a significant reduction in mortality was observed in both channel and hybrid catfish when later exposed to the parental wild-type isolate. Additionally, the use of BCAHV as a vaccine candidate, which has shown protective effects and low virulence in channel catfish, is also being explored.
Publications
- Type:
Theses/Dissertations
Status:
Published
Year Published:
2021
Citation:
Dharan, Vandana. (2021). Development of cell cultures from the tissues of ictalurid catfish and investigation into the pathogenesis of blue catfish alloherpesvirus. Thesis. Mississippi State University. Mississippi State, MS.
- Type:
Journal Articles
Status:
Published
Year Published:
2024
Citation:
Venugopalan, A., White, D., L�pez?Porras, A., Ford, L., Ware, C., Lewis, M. A., ... & Hanson, L. A. (2024). Diversity in clinical isolates of Ictalurid herpesvirus 1 (IcHV1) from US farm?raised catfish and virulence assessment in channel and channel� blue catfish hybrids. Journal of Fish Diseases, e14005.
- Type:
Journal Articles
Status:
Published
Year Published:
2021
Citation:
Venugopalan, A., Griffin, M. J., Wise, D. J., White, D., Ford, L., L�pez?Porras, A., ... & Hanson, L. A. (2021). Virulence and immunogenicity of blue catfish alloherpesvirus in channel, blue and blue� channel hybrid catfish. Journal of Fish Diseases, 44(9), 1399-1409.
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Progress 07/01/22 to 06/30/23
Outputs
Target Audience:The research goal of this project is to address high-priority, industry-identified issues to enhance production efficiency and profitability in aquaculture throughout the southeastern United States by improving disease management. The target audience for the new information and technologies developed includes U.S. catfish farmers, research scientists, extension specialists, and fish health professionals. Ultimately, American consumers will benefit from the production of an inexpensive, safe, and domestically sourced seafood product, contributing to a reduction in the U.S. trade deficit in seafood commodities. Information derived from this project will be disseminated to user groups through a formal network of extension program specialists using workshops, seminars, advisory groups, and demonstration projects involving farmer user groups. Investigators will also share their findings with other scientists and aquaculture students through scientific publications and professional meetings. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?One Master of Science student continues to work on the objectives. How have the results been disseminated to communities of interest?Results to date have been shared informally with stakeholders but more results will be disseminated when final results are analyzed. What do you plan to do during the next reporting period to accomplish the goals?We plan to complete the aims and compile results for publication and dissemination.
Impacts
What was accomplished under these goals?
Significant progress was made on aim 3 of this project.
Publications
- Type:
Theses/Dissertations
Status:
Published
Year Published:
2023
Citation:
Venugopalan, Arun. (2023). Evolution and epidemiology of channel catfish virus (CCV). Dissertation. Mississippi State University, Mississippi State, MS.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2023
Citation:
Aarattuthodi S, Khoo L, Bosworth B, Kumar G. Catfish viruses: profiling aids and management strategies. Aquaculture America 2023, Feb 23-26, 2023. New Orleans, LA Abstract # 5
- Type:
Other
Status:
Published
Year Published:
2022
Citation:
Aarattuthodi, S. et al. 2022. Catfish viruses: Profiling aids management strategies. National warmwater Aquaculture Center. Fall Seminar. November 17, 2022. Stoneville. MS
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