{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,27]],"date-time":"2026-05-27T14:14:57Z","timestamp":1779891297107,"version":"3.53.1"},"reference-count":41,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2021,12,10]],"date-time":"2021-12-10T00:00:00Z","timestamp":1639094400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Animals"],"abstract":"<jats:p>In spring 2019, diseased four-month-old tilapia (Oreochromis spp.) from an aquaculture farm in Southern California, USA were received for diagnostic evaluation with signs of lethargy, anorexia, abnormal swimming, and low-level mortalities. At necropsy, non-specific external lesions were noted including fin erosion, cutaneous melanosis, gill pallor, and coelomic distension. Internal changes included ascites, hepatomegaly, renomegaly, splenomegaly, and multifocal yellow-white nodules in the spleen and kidney. Cultures of spleen and kidney produced bacterial colonies identified as Francisella orientalis. Homogenized samples of gill, brain, liver, spleen, and kidney inoculated onto Mozambique tilapia brain cells (OmB) developed cytopathic effects, characterized by rounding of cells and detaching from the monolayer 6\u201310 days post-inoculation at 25 \u00b0C. Transmission electron microscopy revealed 115.4 \u00b1 5.8 nm icosahedral virions with dense central cores in the cytoplasm of OmB cells. A consensus PCR, targeting the DNA polymerase gene of large double-stranded DNA viruses, performed on cell culture supernatant yielded a sequence consistent with an iridovirus. Phylogenetic analyses based on the concatenated full length major capsid protein and DNA polymerase gene sequences supported the tilapia virus as a novel species within the genus Megalocytivirus, most closely related to scale drop disease virus and European chub iridovirus. An intracoelomic injection challenge in Nile tilapia (O. niloticus) fingerlings resulted in 39% mortality after 16 days. Histopathology revealed necrosis of head kidney and splenic hematopoietic tissues.<\/jats:p>","DOI":"10.3390\/ani11123524","type":"journal-article","created":{"date-parts":[[2021,12,10]],"date-time":"2021-12-10T08:17:58Z","timestamp":1639124278000},"page":"3524","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":15,"title":["Isolation, Identification and Characterization of a Novel Megalocytivirus from Cultured Tilapia (Oreochromis spp.) from Southern California, USA"],"prefix":"10.3390","volume":"11","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-4912-6427","authenticated-orcid":false,"given":"Khalid","family":"Shahin","sequence":"first","affiliation":[{"name":"Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA"},{"name":"Aquatic Animal Diseases Laboratory, Aquaculture Department, National Institute of Oceanography and Fisheries, Suez P.O. Box 43511, Egypt"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kuttichantran","family":"Subramaniam","sequence":"additional","affiliation":[{"name":"Department of Infectious Diseases and Immunology, College of Veterinary Medicine, University of Florida, Gainesville, FL 32611, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alvin C.","family":"Camus","sequence":"additional","affiliation":[{"name":"Department of Pathology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zeinab","family":"Yazdi","sequence":"additional","affiliation":[{"name":"Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Susan","family":"Yun","sequence":"additional","affiliation":[{"name":"Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Samantha A.","family":"Koda","sequence":"additional","affiliation":[{"name":"Department of Infectious Diseases and Immunology, College of Veterinary Medicine, University of Florida, Gainesville, FL 32611, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Thomas B.","family":"Waltzek","sequence":"additional","affiliation":[{"name":"Department of Infectious Diseases and Immunology, College of Veterinary Medicine, University of Florida, Gainesville, FL 32611, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Felipe","family":"Pierezan","sequence":"additional","affiliation":[{"name":"School of Veterinary Medicine, Federal University of Minas Gerais, Belo Horizonte 31270-010, Brazil"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ruixue","family":"Hu","sequence":"additional","affiliation":[{"name":"Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Esteban","family":"Soto","sequence":"additional","affiliation":[{"name":"Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,12,10]]},"reference":[{"key":"ref_1","unstructured":"Food and Agriculture Organization of the United Nations (FAO) (2021, March 31). Cultured Aquatic Species Information Program Oreochromis niloticus (Linnaeus, 1758). Available online: http:\/\/www.fao.org\/fishery\/culturedspecies\/Oreochromis_niloticus\/en."},{"key":"ref_2","unstructured":"Lim, C.E., and Webster, C.D. (2006). Biology. Tilapia: Biology, Culture, and Nutrition, Taylor and Francis. [1st ed.]."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1115","DOI":"10.1111\/jfd.13237","article-title":"Tilapia Lake virus: The story so far","volume":"43","author":"Surachetpong","year":"2020","journal-title":"J. Fish. Dis."},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Liu, W., Zhang, Y., Ma, J., Jiang, N., Fan, Y., Zhou, Y., Cain, K., Yi, M., Jia, K., and Wen, H. (2020). Determination of a novel parvovirus pathogen associated with massive mortality in adult tilapia. PLoS Pathog., 16.","DOI":"10.1371\/journal.ppat.1008765"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"253","DOI":"10.3354\/dao02985","article-title":"Megalocytivirus infection in cultured Nile tilapia, Oreochromis niloticus","volume":"119","author":"Subramaniam","year":"2016","journal-title":"Dis. Aquat. Organ."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"1550","DOI":"10.1111\/tbed.13825","article-title":"First detection of Infectious Spleen and kidney Necrosis Virus (ISKNV) associated with massive mortalities in farmed tilapia in Africa","volume":"68","author":"Paley","year":"2021","journal-title":"Transbound. Emerg. Dis."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"521","DOI":"10.3390\/v4040521","article-title":"Megalocytiviruses","volume":"4","author":"Kurita","year":"2012","journal-title":"Viruses"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"890","DOI":"10.1099\/jgv.0.000818","article-title":"ICTV Virus Taxonomy Profile: Iridoviridae","volume":"98","author":"Chinchar","year":"2017","journal-title":"J. Gen. Virol."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"1","DOI":"10.3354\/dao02594","article-title":"Megalocytivirus infection in orbiculate batfish Platax orbicularis","volume":"105","author":"Sriwanayos","year":"2013","journal-title":"Dis. Aquat. Organ."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"19","DOI":"10.3147\/jsfp.27.19","article-title":"Iridovirus infection of cultured red-sea bream, Pagrus major","volume":"27","author":"Inouye","year":"1992","journal-title":"Fish Pathol."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1229","DOI":"10.1111\/jfd.12815","article-title":"A natural infection by the red sea bream iridovirus-type Megalocytivirus in the golden mandarin fish Siniperca scherzeri","volume":"41","author":"Kim","year":"2018","journal-title":"J. Fish. Dis."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"95","DOI":"10.1111\/j.1365-2761.2009.01110.x","article-title":"Irodovirus infections in finfish\u2014Critical review with emphasis on ranaviruses","volume":"33","author":"Whittington","year":"2010","journal-title":"J. Fish. Dis."},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Kibenge, F.S.B., and Godoy, M.G. (2016). Chapter 8\u2014Iridoviruses of fish. Aquaculture Virology, Academic Press.","DOI":"10.1016\/B978-0-12-801573-5.00019-X"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"401","DOI":"10.1111\/jfd.12134","article-title":"The first case of infectious spleen and kidney necrosis virus (ISKNV) infection in aquarium-maintained mandarin fish, Siniperca chuatsi (Basilewsky), in Japan","volume":"37","author":"Tanaka","year":"2014","journal-title":"J. Fish. Dis."},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Figueiredo, P., Tavares, G.C., Dorella, F.A., Rosa, J.C.C., Marcelino, S.A.C., Pierezan, F., and Pereira, F.L. (2021). First report of infectious spleen and kidney necrosis virus infection in Nile tilapia in Brazil. Transbound Emerg. Dis., 1\u20138.","DOI":"10.1111\/tbed.14217"},{"key":"ref_16","unstructured":"OIE (2021, June 20). Chapter 2.3.7. Red Sea Bream Iridoviral Diseases. Available online: https:\/\/www.oie.int\/fileadmin\/Home\/eng\/Internationa_Standard_Setting\/docs\/pdf\/2.3.07_RSIVD.pdf."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"201","DOI":"10.3354\/dao02041","article-title":"Influence of temperature shifts on the onset and development of red sea bream iridoviral disease in rock bream Oplegnathus fasciatus","volume":"84","author":"Jun","year":"2009","journal-title":"Dis. Aquat. Organ."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"11","DOI":"10.1016\/S0044-8486(01)00639-1","article-title":"Experimental transmission, pathogenicity and physical-chemical properities of infectious spleen and kidney necrosis virus (ISKNV)","volume":"204","author":"He","year":"2002","journal-title":"Aquaculture"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"193","DOI":"10.3354\/dao064193","article-title":"Phylogenetic analysis of the major capsid protein gene of iridovirus isolates from cultured flounders Paralichthys olivaceus in Korea","volume":"64","author":"Do","year":"2005","journal-title":"Dis. Aquat. Organ."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"140","DOI":"10.1016\/j.aquaculture.2006.04.033","article-title":"Experimental transmission, and virulence of a Megalocytivirus (Family Iridoviridae) of dwarf gourami (Colisa lalia) from Asia in Murray cod (Maccullochella peelii peelii) in Australia","volume":"258","author":"Go","year":"2006","journal-title":"Aquaculture"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"306","DOI":"10.1177\/104063870902100302","article-title":"Systemic iridovirus infection in the Banggai cardinalfish (Pterapogon kauderni Koumans, 1933)","volume":"21","author":"Weber","year":"2009","journal-title":"J. Vet. Diagn. Investig."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"697","DOI":"10.1128\/jb.173.2.697-703.1991","article-title":"16S ribosomal DNA amplification for phylogenetic study","volume":"173","author":"Weisburg","year":"1991","journal-title":"J. Bacteriol."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Gardell, A.M., Qin, Q., Rice, R.H., Li, J., and K\u00fcltz, D. (2014). Derivation and osmotolerance characterization of three immortalized tilapia (Oreochromis mossambicus) cell lines. PLoS ONE, 9.","DOI":"10.1371\/journal.pone.0095919"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"184","DOI":"10.1016\/j.aquaculture.2018.07.060","article-title":"A TaqMan RT-qPCR assay for tilapia lake virus (TiLV) detection in tilapia","volume":"497","author":"Waiyamitra","year":"2018","journal-title":"Aquaculture"},{"key":"ref_25","doi-asserted-by":"crossref","unstructured":"Hanson, L.A., Rudis, M.R., Vasquez-Lee, M., and Montogomery, R.D. (2006). A broadly applicable method to characterize large DNA viruses and adenoviruses based on the DNA polymerase gene. Virol. J., 3.","DOI":"10.1186\/1743-422X-3-28"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"199","DOI":"10.3354\/dao02204","article-title":"Development of a real-time PCR assay for identification and quantification of the fish pathogen Francisella noatunensis subsp","volume":"89","author":"Soto","year":"2010","journal-title":"orientalis. Dis. Aquat. Organ."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"1972","DOI":"10.1093\/bioinformatics\/btp348","article-title":"trimAl: A tool for automated alignment trimming in large-scale phylogenetic analyses","volume":"25","year":"2009","journal-title":"Bioinformatics"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1530","DOI":"10.1093\/molbev\/msaa015","article-title":"IQ-TREE 2: New models and efficient methods for phylogenetic inference in the genomic era","volume":"37","author":"Minh","year":"2020","journal-title":"Mol. Biol. Evol."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"119","DOI":"10.1111\/jfd.12915","article-title":"Mortality from scale drop disease in farmed Lates calcarifer in Southeast Asia","volume":"42","author":"Senapin","year":"2018","journal-title":"J. Fish. Dis."},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"de Groof, A., Guelen, L., Deijs, M., van der Wal, Y., Miyata, M., Ng, K.S., van Grinsven, L., Simmelink, B., Biermann, Y., and Grisez, L. (2015). A novel virus Causes Scale Drop Disease in Lates calcarifer. PLoS Pathog., 11.","DOI":"10.1371\/journal.ppat.1005074"},{"key":"ref_31","unstructured":"Soto, E., Lopez-Porras, A., Kenelty, K., Yun, S., and Pierezan, F. (2019, January 17\u201320). Analysis of the Nile tilapia (Oreochromis niloticus) immune response during Francisella noatunensis subsp. orientalis infection. Proceedings of the 2019 AFS Fish Health Section Annual Meeting and 60th Western Fish Disease Workshop, Ogden, UT, USA."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"451","DOI":"10.2754\/avb200170040451","article-title":"Pathogenesis of iridovirus: In vitro influence on macrophage activity and cytokine-like protein production in fish","volume":"70","author":"Siwicki","year":"2001","journal-title":"Acta Vet. Brno"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1489","DOI":"10.1099\/jgv.0.000811","article-title":"Fish miR-146a promotes Singapore grouper iridovirus infection by regulating cell apoptosis and NF-\u03baB activation","volume":"98","author":"Ni","year":"2017","journal-title":"J. Gen. Virol."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"19","DOI":"10.1111\/j.1365-2761.2011.01319.x","article-title":"The pathology of \u2018scale drop syndrome\u2019 in Asian seabass, Lates calcarifer Bloch, a first description","volume":"35","author":"Chee","year":"2012","journal-title":"J. Fish Dis."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"149","DOI":"10.1046\/j.1365-2761.1998.00082.x","article-title":"Systemic disease involving an iridovirus-like agent in cultured tilapia, Oreochromis niloticus L. A case report","volume":"21","author":"McGorgan","year":"1998","journal-title":"J. Fish. Dis."},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Wirth, W., Schwarzkopf, L., Skerratt, L.F., and Ariel, E. (2018). Ranaviruses and reptiles. PeerJ, 6.","DOI":"10.7717\/peerj.6083"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"173","DOI":"10.1016\/S0065-3527(05)65006-3","article-title":"A decade of advances in iridovirus research","volume":"Volume 65","author":"Maramorosch","year":"2005","journal-title":"Advances in Virus Research"},{"key":"ref_38","unstructured":"King, A.M.Q., Adams, M.J., Carstens, E.B., and Lefkowitz, E.J. (2012). Family Iridoviridae. Virus Taxonomy: Ninth Report of the International Committee on Taxonomy of Viruses, Elsevier Academic Press."},{"key":"ref_39","doi-asserted-by":"crossref","unstructured":"Huang, Y., Cai, S., Jian, J., Liu, G., and Xu, L. (2020). Co-infection of infectious spleen and kidney necrosis virus and Francisella sp. in farmed pearl gentian grouper (\u2640Epinephelus fuscoguttatus \u00d7\u2642E. lanceolatus) in China\u2014A case report. Aquaculture, 526.","DOI":"10.1016\/j.aquaculture.2020.735409"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"117","DOI":"10.1016\/j.fsi.2020.07.012","article-title":"Impact of Aeromonas hydrophila and infectious spleen and kidney necrosis virus infections on susceptibility and host immune response in Chinese perch (Siniperca chuatsi)","volume":"105","author":"Liu","year":"2020","journal-title":"Fish Shellfish Immunol."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"89","DOI":"10.3354\/dao02625","article-title":"Co-infection by alveolate parasites and frog virus 3-like ranavirus during an amphibian larval mortality event in Florida, USA","volume":"105","author":"Landsberg","year":"2013","journal-title":"Dis. Aquat. Organ."}],"container-title":["Animals"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2076-2615\/11\/12\/3524\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T07:45:02Z","timestamp":1760168702000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2076-2615\/11\/12\/3524"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,12,10]]},"references-count":41,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2021,12]]}},"alternative-id":["ani11123524"],"URL":"https:\/\/doi.org\/10.3390\/ani11123524","relation":{},"ISSN":["2076-2615"],"issn-type":[{"value":"2076-2615","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,12,10]]}}}