A Herpesvirus Associated with Mass Mortality of Juvenile and Adult Koi, a Strain of Common Carp

Abstract

A herpesvirus was isolated from adult koi, a strain of common carp Cyprinus carpio, suffering mass mortality in two outbreaks-one in the mid-Atlantic region of the United States and the second in Israel. The principal external signs of dying fish were pale and irregularly colored gills. There were few consistent internal signs in either outbreak. The most prominent microscopic lesions were in the gills, where hyperplasia and necrosis of the epithelium were severe. Other lesions included interstitial nephritis, splenitis, and enteritis. Affected cells often contained nuclei with marginated chromatin and faint intranuclear inclusions. Typical herpesvirus particles were present in branchial epithelial cells, hepatocytes, and among circulating leukocytes. Inoculations of the koi fin (KF-1) cell line with tissue extracts from the gill and kidney-spleen resulted in cytopathic effects characterized by severe vacuolation first detected after 7 d incubation at 20°C. Exposures of adult koi to the herpesvirus as propagated in KF-1 cells by bath or intraperitoneal injections resulted in 80-100% mortality during a 26-d period, and the virus was reisolated from the gill, kidney, liver, spleen, intestine, and brain of dead fish. The viral agents from koi in Israel and the United States appear to be similar if not identical; both could be distinguished from Herpesvirus cyprini by indirect fluorescent antibody tests with rabbit anti-H. cyprini serum. Other factors should be examined but we strongly suspect that this newly recognized koi herpesvirus (KHV) has the potential to be a significant cause of mortality among koi and presumably common carp.

Koi Herpes Virus: A Review and Risk Assessment of Indian Aquaculture

“…The nomenclature of KHV is based on its icosahedral structure which resembles herpesviruses and its host range appears to be limited to koi species of cyprinidae [34]. It is also named as cyprinid herpesvirus 3 (CyHV-3), following the nomenclature of other cyprinid herpesviruses: CyHV-1 (carp pox virus, fish papilloma virus) and CyHV-2 (goldfish haematopoietic necrosis virus) [85].…”

“…KHV is a large, linear, double-stranded DNA virus with an icosahedral core of 100-110 nm [34,37]. DNA molecule consists of a central portion flanked by two 22-kb repeat regions, called the left and right repeats.…”

“…Structural proteins consists of capsid (3), envelope (13), tegument (2) and unclassified (22) structural proteins [51]. ORF092 and ORF136 are predicted to encode a major capsid protein (MCP) and a First reported occurrence of KHV [34] viral envelope protein, respectively [3,51]. ORF81 encodes a highly immunogenic type 3 membrane protein expressed on the envelope of CyHV-3 [70].…”

“…Cell lines derived from koi fin (KF-1), C. carpio carp brain (CCB), and C. carpio carp gills (CCG) are suitable for in vitro cultivation of KHV [34,58,69]. Other common fish cell lines such as FHM, RTG-2, CHSE-214 and EPC do not support the growth of KHV [14,60,65].…”

“…Koi, a subspecies of the common carp, is a colorful ornamental fish that is traded worldwide for display in aquaria [47]. In 1998, a viral disease outbreak was first noticed in cultured common carp in Israel and USA [34,62] and in Germany in 1997-1998 [11]. This disease has been termed as Koi herpes virus disease (KHVD) and the disease causing agent was identified as Koi herpes virus (KHV).…”