32 SEP TEMBER 2022 • WORLD AQUACULTURE • WWW.WA S .ORG Interference betweenTSVandYHV Another known virus interference phenomenon in shrimp is that between Taura syndrome virus (TSV) and yellow-head virus (YHV, Fig. 7). TSV is an icosahedral virion of » 40 nm diameter enclosing a single stranded, positive-sense linear RNA genome of » 9000 bases that replicates in cytoplasm (Valles et al. 2017). It infects epithelia and connective tissues of integument, gills, foregut and hindgut of shrimp (Hasson et al. 1999) and has caused massive mortalities in wild and farmed Pacific white shrimp in Latin American and Asian countries (Escobedo-Bonilla 2016). Yellow-head virus (YHV) is an enveloped rod-shaped virion of size between 160-200 nm long and 34-63 nm wide (Munro and Owens 2007). It has a single-stranded positive sense RNA genome of » 26,000 nucleotides and also replicates in cytoplasm (Walker et al. 2021). It causes systemic infection of gills, lymphoid organ, head soft tissues, eyestalk, nerve tissues, heart, midgut, hepatopancreas, connective tissues and muscle of shrimp (Duangsuwan et al. 2008). This virus also causes mortality of infected shrimp. These viruses have similar cell tropism, indicating that they may compete for the same tissues and cell types upon coinfection. An experiment was done using specific pathogen-free shrimp inoculated first by feeding them with TSV-infected tissues to produce chronically-infected shrimp. Then, after 27, 37 or 47 dpi, shrimp were challenged intramuscularly with a lethal dose (104 genome copies) of YHV. Interference occurred between TSV and YHV, resulting in significant higher survival of shrimp treated with TSV than YHV-positive controls at the different times evaluated. The highest survival occurred when YHV was inoculated 27 d after TSV inoculation (Aranguren et al. 2012). In situ hybridization assays showed that shrimp were infected with the two viruses but their tissue distribution was different. Presence of TSV was restricted to lymphoid organ due to its chronic stage, whereas YHV was found in cuticular epithelium, connective tissues and lymphoid organ. In this organ, TSV was mostly present in tubules while YHV was distributed in adjacent areas of the tubules, and severe necrosis by YHV was not seen in the shrimp with virus interference (Aranguren et al. 2012). Perspectives on Virus Interference in Shrimp Aquaculture Virus interference is a natural event occurring in various hosts from bacteria to animals, between viruses that are genetically related but also between viruses that are totally different. The mechanisms driving this phenomenon may be diverse. Virus interference may be relevant as a way to naturally fight lethal virus infections given that some less pathogenic viruses are able to curb replication and infection in the host. In crustaceans, virus diseases have been recorded even before the appearance of crustacean farming in aquaculture. Since the dawn of crustacean farming, the number of virus pathogens reported have dramatically increased as the result of intensification of culture and the decline of environmental and physiological conditions in such cultures. Some viral diseases have produced huge losses of farmed crustaceans, mainly marine shrimp. In time, some of those pathogens have dwindled in pathogenicity and become endemic in some regions. An example of this is the virus formerly known as IHHNV. In Northwest Mexico, this virus is widely spread throughout hatcheries and farms. Its impact is mild compared to that of WSSV, which still continues to cause mortality. This impact to farmed shrimp makes it necessary to find novel methods aimed at curbing the disease, including virus interference. The fact that shrimp previously infected with IHHNV may induce a reduction in severity of WSSV disease and/or mortality makes this phenomenon a potential natural control method against WSSV. The virus interference between TSV and YHV may have a similar effect and application as that between IHHNV and WSSV. As TSV has also declined in prevalence and severity of disease in L. vannamei worldwide, its efficacy to curb YHV infection and mortality in regions where YHV is endemic would be worth evaluating. Hence, virus interference in shrimp hosts may be an alternative and natural control method against two highly pathogenic viruses such as YHV or WSSV. Superinfection exclusion interference may be common in viruses infecting animals and it could be the mechanism observed in the interference between different viruses infecting farmed shrimp. As sequencing technology advances, better knowledge of environmental and crustacean virus diversity and virus genome organization will be gained. Understanding gene interactions between host - pathogen and virus - virus may help elucidate the mechanisms that drive virus interference. Notes Cesar M. Escobedo-Bonilla, Instituto Politecnico NacionalCIIDIR Sinaloa, Blvd. Juan de Dios Batiz Paredes 250. Col. San Joachin. C.P. 81101, Guasave, Sinaloa cesar_escobedomx@yahoo. com Acknowledgments The author acknowledges financial support from project SIP20220112 from IPNMexico. References Aranguren, L.F., K.L. Tang and D.V. Lightner. 2012. Protection from yellow head virus (YHV) infection in Penaeus vannamei preinfected with Taura syndrome virus (TSV). Diseases of Aquatic Organisms 98:185-192. Bonami, J.R., B. Trumper, J. Mari, M. Brehelin and D.V. Lightner. 1990. Purification and characterization of the infectious hypodermal and haematopoietic necrosis virus of penaeid shrimps. Journal of General Virology 71:2657-2664. Bonnichon, V., D.V. Lightner and J.R. Bonami. 2006. Viral interference between infectious hypodermal and hematopoietic necrosis virus and white spot syndrome virus in Litopenaeus vannamei. Diseases of Aquatic Organisms, 72:179-184. Couch, J.A. 1974. An enzootic nuclear polyhedrosis virus of pink shrimp: Ultrastructure, prevalence, and enhancement. Journal of Invertebrate Pathology 24:311-331. DaPalma, T., B.P. Doonan, N.M. Trager and L.M. Kasman. 2010. A systematic approach to virus-virus interactions. Virus Research 149:1-9. Delbrück, M. 1945. Interference Between Bacterial Viruses. III. The mutual exclusion effect and the depressor effect. Journal of Bacteriology 50:151-170. Delbrück, M. and S.E. Luria. 1942. Interference between bacterial
RkJQdWJsaXNoZXIy MjExNDY=