Molecular comparison of isolates of an emerging fish pathogen, koi herpesvirus, and the effect of water temperature on mortality of experimentally infected koi

Abstract

Koi herpesvirus (KHV) has been associated with devastating losses of common carp (Cyprinus carpio carpio) and koi (Cyprinus carpio koi ) in North America, Europe, Israel and Asia. A comparison of virion polypeptides and genomic restriction fragments of seven geographically diverse isolates of KHV indicated that with one exception they represented a homogeneous group. A principal environmental factor influencing the onset and severity of disease is water temperature. Optimal growth of KHV in a koi fin cell line occurred at temperatures from 15-25 6C. There was no growth or minimal growth at 4, 10, 30 or 37 6C. Experimental infections of koi with KHV at a water temperature of 23 6C resulted in a cumulative mortality of 95?2 %. Disease progressed rapidly but with lower mortality (89?4-95?2 %) at 28 6C. Mortality (85?0 %) also occurred at 18 6C but not at 13 6C. Shifting virus-exposed fish from 13-23 6C resulted in the rapid onset of mortality.

Transmission dynamics of an emerging infectious disease in wildlife through host reproductive cycles

“…CyHV-3 displays optimal growth at 15-25 1C in vitro, whereas growth is very low at o10 1C and undetectable at 430 1C (Gilad et al, 2003). As expected from the temperature dependence, CyHV-3 increased in host tissues in the spring after the water temperature exceeded 15 1C (Figure 4a).…”

“…However, an increasing number of experimental studies have investigated fluctuations of CyHV-3 in hosts and its possible transmission routes. In vitro experiments with carp cell lines have demonstrated that CyHV-3 growth depends on host cell temperature; optimal growth occurs at 15-25 1C, whereas temperatures lower than 10 1C or higher than 30 1C result in very low or undetectable virus replication (Gilad et al, 2003). Such temperature dependence also occurs in another viral pathogen of common carp, the spring viremia of the carp virus (Ahne et al, 2002).…”

“…Sexually matured common carp (4c.350 mm) form groups in breeding habitats for mating when females spawn (Barus et al, 2002). Interestingly, the breeding season coincides with a rise in water temperature to over 15-18 1C in the spring (Barus et al, 2002), which is optimal for the growth of CyHV-3 (Gilad et al, 2003). Furthermore, a survey of the prevalence of CyHV-3 antibodies in the common carp population of Lake Biwa in 2006 indicated that infection occurred primarily in adult fish (Uchii et al, 2009).…”

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

“…Other common fish cell lines such as FHM, RTG-2, CHSE-214 and EPC do not support the growth of KHV [14,60,65]. The optimal temperature for viral propagation in KF-1 cells is 15-25°C; at 30°C these cells do not produce virus [26]. The virus induces typical plaques in 3-4 days after inoculation in the cultured cells along with the formation of syncytia and increase in cytoplasmic vacuoles.…”

“…Massive mortalities occur within a week of onset of clinical signs, with the mortality rate reaching 80-100 % [84]. At temperatures above 30°C or below 13°C, KHV becomes dormant and clinical signs generally cease [12,26]. Viral DNA can be detected in the blood and kidney, 1 day after virus exposure [17,65].…”