Preventive Measures Against Koi Herpesvirus Disease in Fancy Carp 
in Niigata Prefecture

Kazuo Yamada

Niigata Prefecture Inland-water Fisheries Experimental Station, Niigata940-1137, Japan

ABSTRACT

[Objectives] Following outbreaks of koi herpesvirus (KHV) that occurred in many regions worldwide, including Israel, many areas of Europe, the United States and Indonesia, the Fisheries Division of the Niigata Prefectural Government started implementing PCR tests on the prefecture's carp in October 2001.The aims of the test were to (1) prevent the entry of KHV into the prefecture and (2) prevent the spread of KHV within and out of the prefecture, both domestic and abroad, if the virus is detected in carp in Niigata.

Although there has been no report of KHV outbreak in Niigata's fancy carp, the prefecture's fancy carp industry has voluntary suspended all of its shipments temporarily. This measure has been taken to prevent the possible transfer of the virus following the detection of KHV in common carp in Niigata in November 2003 (Note: these KHV-affected fish, originally transferred from Ibaraki Prefecture, were obtained from an entertainment fishing pond and a breeder of common carp in Niigata Prefecture).

[Method] PCR tests were conducted in Niigata Prefecture during the following three periods: from October to November 2001 for fancy carp owned by twenty carp breeders, in December 2002 for fancy carp owned by thirty carp breeders, and from July to August 2003 for fancy carp owned by 114 breeders that export fancy carp overseas. (Note: many of the breeders have participated in the PCR tests in multiple years). These PCR tests were conducted on young fish that were less than a year old and of little product value, and were kept in water that was maintained between 20⁰C and 25⁰C. These fish, which were maintained by designated staff members who conducted PCR tests under the supervision of the Niigata Prefectural Inland-water Fisheries Experimental Station, were kept for a three-week period in the same pool with adult fish that would be shipped for commercial purposes. Afterwards sample from the gill, spleen, kidney and heart tissues (sometimes just a sample from the gill tissue) were taken from two to five of these fishes. These tissues were homogenized to extract DNA, which was obtained by using a DNA extraction kit. Each sample was mixed with an agent that contained types of primers such as 9/5 and Sph1-5. After this stage, the samples received an agarose gel electrophoresis treatment to examine the DNA fragments. A KHV DNA sample, which Niigata had received from Dr. R.P. Hedrick, was used to compare the results of the samples taken from Niigata.

[Results] All the fish that were examined by PCR tests during the previous period were negative. Also during these test periods, Niigata provided carp business owners in the region with meetings and lectures about KHV to enable the breeders to detect KHV-affected carp at an early stage of the disease and thus minimize the risk of spreading the virus. 

Currently PCR tests are being conducted on the largest scale ever in Niigata with the participation of 150 carp breeders, each of which presented tissue samples from 31 fish taken from their farm. Originally, the voluntary policy to temporary suspend ornamental carp shipments prohibited any shipments of fancy carp until the test results of the fish from all the breeders concerned were confirmed; however, the voluntary policy to temporary suspend fancy carp shipments has been revised to allow overseas shipments of fish upon confirmation of favorable test results of the fish from each individual breeder.

Upon Niigata Prefectural Government's request, the carp industry in Niigata is creating a KHV prevention policy that instructs carp breeders how to avoid exposing fish to the virus. Under this policy, any fish that is shipped from another breeder will have to be isolated from other fishes in a low-temperature tank for three weeks during which time the breeder will check to see whether or not the fish is infected with the virus. It also advises the breeder to avoid using river water when maintaining the fish and to sanitize all equipment that comes in contact with fish water of the fish themselves, including staff's boots and gloves. Staff members are also required to wash their hands at their facility and to keep a detailed journal of the conditions of their fish.