Abstract
White sturgeon (Acipenser transmontanus) is a native fish to the west coast of North America and a central part of the multimillion-dollar aquaculture industry in California and surrounding western states, being the primary species used for the production of globally recognized high quality caviar and sturgeon meat.1 These aquaculture practices provide substantial revenues to producers, generation of local employment opportunities, and wild population conservation by offering a sustainable alternative to wild caught sturgeon. Infectious diseases pose a major threat to aquaculture production, causing millions of dollars in annual losses. Acipenserid herpesvirus 2 (AciHV-2) is a large double stranded DNA virus in the family Alloherpesviridae that causes skin ulceration, lethargy, inappetence, erratic swimming, and death in white sturgeon, as well as other sturgeon species.2,3 Reports reveal that natural outbreaks can result in up to 10% mortality in adults and up to 50% mortality in juvenile white sturgeon,4 with mortalities of up to 80% seen in controlled laboratory challenges5. It is well established in mammals that herpesviruses have multiple pathways for regulating host cellular immune competency.6-9 In fish, few studies have been conducted to elucidate mechanisms of immune evasion employed by viruses.10 This is of particular interest because immunomodulation can result in infection facilitation for other opportunistic pathogens. Streptococcus iniae is a gram-positive, zoonotic bacterium known to infect a wide variety of farmed and wild fish species worldwide, with novel genotypes recently reported as disease agents in cultured white sturgeon in California. Streptococcosis has been reported to result in up to 50% mortality in subadult white sturgeon,11 and co-infections of AciHV-2 and S. iniae have been diagnosed in cultured sturgeon in California since 201512. However, little is known regarding disease pathogenesis and immune response during these co-infections in white sturgeon. To investigate the presence of potential immunomodulatory virulence genes, present in AciHV-2, whole-genome analysis of four isolates recovered from cultured fish in California from 1991–2020 was performed. Additionally, to investigate the role of AciHV-2 during co-infections with S. iniae, in vivo controlled co-infection challenges in white sturgeon fingerlings were conducted. A better understanding of the host immune response during infection is essential for the development of prophylactic, therapeutic, and biosecurity regimens.
Acknowledgements
The authors wish to thank the Center for Aquatic Biology and Aquaculture at UC Davis for their constant support with the housing and care of the fish used in this project. This work was supported in part through NIH T-32 OD011147 (EMQC).
*Presenting author
+Student presenter
Literature Cited
1. Mims SD, Lazur A, Shelton WL, Gomelsky B, Chapman F. 2002. Species profile: production of sturgeon. Southern Regional Aquaculture Center Publication No. 7200.
2. Lepa A, Siwicki AK. 2012. Fish herpesvirus diseases: a short review of current knowledge. Acta Vet Brno 81(4):383–9.
3. Goodwin A. 2012. Herpesviruses in fish. Southern Regional Aquaculture Center. Publication No. 4710.
4. Mugetti D, Pastorino P, Menconi V, Pedron C, Prearo M. 2020. The old and the new on viral diseases in sturgeon. Pathogens 9(2):146.
5. Watson L, Yun S, Groff J, Hedrick R. 1995. Characteristics and pathogenicity of a novel herpesvirus isolated from adult and subadult white sturgeon Acipenser transmontanus. Dis Aquat Org 22:199–210.
6. Crow MS, Lum KK, Sheng X, Song B, Cristea IM. 2016. Diverse mechanisms evolved by DNA viruses to inhibit early host defenses. Crit Rev Biochem Mol Biol 51(6):452–81.
7. Alcami A. 2003. Viral mimicry of cytokines, chemokines and their receptors. Nat Rev Immunol 3(1):36–50.
8. Gorshkova EA, Shilov ES. 2016. Possible mechanisms of acquisition of herpesvirus virokines. Biochem Mosc 81(11):1350–1357.
9. Rinaldo CR. 1990. Immune suppression by herpesviruses. Ann Rev Med 41:331–38.
10. Guo CJ, He J, He JG. 2019. The immune evasion strategies of fish viruses. Fish Shellfish Immunol 86:772–84.
11. Nguyen DT, Marancik D, Soto E. 2020. Intracoelomic and intramuscular injection challenge model of piscine streptococcosis in white sturgeon fingerlings. J Aquat Anim Health 32(3):133–8.
12. Soto E, Richey C, Stevens B, Yun S, Kenelty K, Reichley S, et al. 2017. Co-infection of Acipenserid herpesvirus 2 (AciHV-2) and Streptococcus iniae in cultured white sturgeon Acipenser transmontanus. Dis Aquat Org 124(1):11–20.