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Diseases of Aquatic Organisms

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DAO 48:101-108 (2002)  -  doi:10.3354/dao048101

Initial characteristics of koi herpesvirus and development of a polymerase chain reaction assay to detect the virus in koi, Cyprinus carpio koi

Oren Gilad1, Susan Yun1, Karl B. Andree1, Mark A. Adkison1, Amir Zlotkin2, Herve Bercovier2, Avi Eldar3, Ronald P. Hedrick1,*

1Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, California 95616, USA
2Institute of Microbiology, Department of Clinical Microbiology, The Hebrew University-Hadassah Medical School, Ein Karen, Jerusalem, Israel
3Department of Poultry and Fish Diseases, The Kimron Veterinary Institute, Beit Dagan, Israel
*Corresponding author. E-mail:

ABSTRACT: Since 1998, episodes of mass mortality have occurred in populations of common carp Cyprinus carpio carpio in Israel and in populations of koi Cyprinus carpio koi in Israel and the USA. A herpesvirus isolated from infected fish has been shown in experimental studies to induce disease and mortality similar to those observed in outbreaks at infected farms. Initial characteristics of the virus show that it is clearly different from Herpesvirus cyprini (CHV), the most commonly known her- pesvirus from cyprinid fish. The koi herpesvirus (KHV) has 31 virion polypeptides. Twelve of the virion polypeptides of KHV have similar molecular weights to those of CHV and 10 are similar to those of channel catfish virus (CCV). Both virion polypeptide and restriction fragment length poly- morphism analyses of genomic DNA showed that the first KHV isolates from Israel and the USA were identical. In contrast, the genomic DNA restriction fragments clearly distinguish KHV from CHV and CCV. A polymerase chain reaction (PCR) assay to detect the virus in koi tissues was developed with sequences obtained from 1 restriction fragment of KHV DNA. The PCR assay effectively detected a 484 base pair sequence from KHV but did not amplify genomic DNA from either CHV or CCV. The PCR assay detected as little as 1 pg of KHV DNA mixed with 100 ng of host DNA. Viral sequences were amplified from koi obtained from field collections and from koi that were experimentally exposed to 102 TCID50 ml–1 of KHV via the waterborne route. All KHV exposed fish dying of infection between 8 and 10 d post exposure or surviving to 14 d post exposure were found to be positive by PCR, while unexposed control koi were all negative. The assay also showed the presence of KHV DNA in tissues of koi obtained from farms in Israel. The PCR assay should assist virus isolation pro- cedures and histologic and electron microscopic analyses now commonly used to detect KHV infection. Current studies are examining the possibility of using the PCR to detect KHV DNA in live fish and the relative sensitivity and specificity of the KHV PCR assay compared with other diagnostic tests.

KEY WORDS: Koi · Common carp · Herpesvirus · Koi herpesvirus · Polymerase chain reaction

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Cite this article as: Gilad O, Yun S, Andree KB, Adkison MA and others (2002) Initial characteristics of koi herpesvirus and development of a polymerase chain reaction assay to detect the virus in koi, Cyprinus carpio koi. Dis Aquat Org 48:101-108.

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