Effect of Water Temperature on Mortality and Virus Shedding in Carp Experimentally Infected with Koi Herpesvirus

Abstract

ABSTRACT-Common carp Cyprinus carpio were experimentally exposed to koi herpesvirus (KHV) under water temperature regimes ranging from 16∞C to 28∞C. Fish maintained at 16∞C, 23∞C and 28∞C died due to infection at 21 -52, 5 -20 and 7 -14 days post-virus exposure (dpe), respectively. Cohabitation experiments in which KHVinfected common carp were kept with naive koi carp revealed that infectious virus was continuously shed from the infected common carp for 34 days (7-40 dpe) at 16∞C, for 14 days (1-14 dpe) at 23∞C and for 12 days (3-14 dpe) at 28∞C. The relatively extended duration of virus shedding observed at 16∞C suggests the potential risk of infection from fish maintained under low-temperature conditions as a source of viral inocula.Key words: koi herpesvirus, KHV, carp, water temperature, virus transmission, virus shedding tally exposed to KHV between 18∞C and 28∞C, but not at 13∞C. St-Hilaire et al. 7) reported that KHV-infected fish maintained at 12∞C exhibited no mortality for 30 weeks, but began dying after water temperature increased to 23∞C. In the present study, common carp were experimentally infected with KHV at water temperatures of 16∞C, 23∞C and 28∞C -the presumed permissive range of water temperatures for infection -and observed for mortality. We also examined the duration of virus shedding from the KHV-infected common carp under different water temperatures using cohabitation experiments. Materials and MethodsCommon carp brain (CCB) cells 8) were cultured in MEM supplemented with 5% fetal bovine serum. The KHV strain NRIA0308, isolated from diseased common carp in Japan in 2003, was used to inoculate CCB cells. After incubation at 20∞C for 14 days, the culture supernatant was used as a virus source for infecting common carp. The infective titer of the KHV virus stock determined using CCB cells was 10 3.6 TCID 50 /mL.KHV-free common carp (average 4.4 g in body weight, total 240 fish) from the National Research Institute of Aquaculture (NRIA) were divided into three groups consisting of 80 fish and acclimatized in 200 L aquaria adjusted to 16∞C, 23∞C or 28∞C (± 0.5∞C) over a 7-day period. Each group was separately infected with KHV by immersion in a 10 L aquarium containing 10 mL of the virus stock solution for 1 h, and 10 fish from each group were transferred to a 60 L aquarium adjusted to each water temperature and monitored for mortality for 60 days.For virus shedding experiments, common carp from each of the KHV-infected groups were cohabited with naive koi carp (average 3.7 g, total 81 fish). Twenty common carp from the KHV-infected group at 16∞C were transferred to a 28 L aquarium maintained at 16∞C (cohabitation aquarium), and three individual koi carp were introduced at intervals of 1, 3, 5, 7, 14, 21, 28, 40 and 60 days after the common carp were exposed to KHV. After cohabitation with infected common carp for 24 h, the koi carp were transferred to nine 10 L-aquaria adjusted to 23∞C and observed for mortality over a twoweek period. In order to maintain a constant number of fish in the...

Ostreid Herpesvirus 1 Infection among Pacific Oyster (Crassostrea gigas) Spat: Relevance of Water Temperature to Virus Replication and Circulation Prior to the Onset of Mortality

“…High seawater temperatures appear to be one of the potential factors likely to induce OsHV-1 infection. This hypothesis is consistent with observations on koi herpesvirus, for which temperatures between 18°C and 28°C favored the onset and severity of disease in fish (35)(36)(37)(38)(39)(40). Field surveys conducted in Japan showed that the lowest water temperature at which outbreaks occurred was 15.5°C to 16°C (36,39).…”

Cyprinid Herpesvirus 3

“…Experimentally, KHVD has been reproduced in temperatures ranging from 16 to 28°C (Gilad et al, 2003(Gilad et al, , 2004Yuasa, Ito, & Sano, 2008) and the lowest temperature associated with a CyHV-3 outbreak was 15.5°C in a field survey in Japan (Hara, Aikawa, Usui, & Nakanishi, 2006). Interestingly, CyHV-2 induces mortalities in goldfish at a slightly enlarged temperature range from 15 to 30°C (Ito & Maeno, 2014) suggesting a similar but adaptable temperature range in cyprinid herpesviruses.…”

“…Interestingly, CyHV-2 induces mortalities in goldfish at a slightly enlarged temperature range from 15 to 30°C (Ito & Maeno, 2014) suggesting a similar but adaptable temperature range in cyprinid herpesviruses. In CyHV-3 infections, the onset of mortality was affected by the water temperature; the first mortalities occurred between 5-8 and 14-21 dpi when the fish were kept between 23-28 and 16-18°C, respectively (Gilad et al, 2003;Yuasa et al, 2008). Moreover, daily temperature fluctuations of AE3°C induce important stress in fish, which increases cortisol release in the water and also their susceptibility to CyHV-3 (higher mortality rate and viral excretion) (Takahara et al, 2014).…”

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

“…The infected fish begin to die within 1 or 2 days after the onset of the symptoms [34]. During infection, virulent virus is shed continuously via feces, urine, gills and skin mucus for a longer period from infected common carp at 16°C than those at 23-28°C [90]. Massive mortalities occur within a week of onset of clinical signs, with the mortality rate reaching 80-100 % [84].…”