Koi herpes virus
| Koi herpes virus | ||||||||||||||||||
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| Cyprinid herpesvirus 3 | ||||||||||||||||||
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| CyHV-3 | ||||||||||||||||||
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The Koi herpesvirus ( KHV ), scientifically cyprinid herpesvirus 3 (CyHV-3), out of date Carp nephritis and gill necrosis virus , (CNGV) is a highly infectious virus , which is an epidemic, acutely to subacutely progressing viral infectious disease of carp and koi - Carp - which causes koi herpes virus infection ( Koi Herpes Disease ).
The incubation period is between a week and several months, depending on various factors such as stress and the condition of the fish. If the disease breaks out, the mortality rate is usually between 80% and 100% over a period of 24 hours to 14 days.
Pathogen
The pathogen was described as a herpes virus in 2000 by Ron Hedrick at the University of California, Davis .
The virus is a close relative of the herpes virus cyprini (officially Cyprinid herpesvirus 1 ), which was described in Japan in 1990. Both species are classified as DNA viruses , belonging to the genus Cyprinivirus in the virus family Alloherpesviridae . The virus first appeared and was described in 1997 in Germany and 1998 in Israel. The approx. 296 kbp double-stranded DNA genomes of three Koi herpesvirus isolates were published in 2007 by Takashi Aoki in Japan, completely sequenced, with only slight sequence homologies to other herpesvirus genomes (genus Herpesviridae ) being found. These differences ultimately led to the International Committee on Taxonomy of Viruses (ICTV) placing them in a family of their own.
So far, no information is available on the importance of individual virus genes for the virulence of the pathogen and for the host's immune defense . Therefore z. For example, at the Friedrich Loeffler Institute, large parts of the KHV genome were cloned in bacteria using plasmid and cosmid vectors . The purpose of these clones is to determine further viral DNA sequences which, among other things, could contribute to the establishment of sensitive PCR methods for diagnostic virus detection. By in vitro - expression of the cloned genes immunogenic viral proteins to be identified and used for serological diagnosis. Attempts are also being made to produce recombinant koi herpesviruses through targeted gene deletions , which can be used as attenuated live virus vaccines .
Occurrence
The KHV infection is diagnosed as a disease only in koi fish and carp ( Cyprinus carpio ). Related cyprinid breeds such as grass carp ( Ctenopharyngodon idella ), crucian carp ( Carassius carassius ) or goldfish ( Carassius auratus ) do not always appear to be unaffected by the virus. This information is secured insofar as KHV has already been detected in goldfish, but they do not fall ill but can certainly act as carriers.
infection
Like most viruses, the Koi herpes virus is transmitted through direct contact. This can be the fish themselves through skin contact and gill excretions, water (e.g. transport water) or other liquids that have come into contact with infected fish. Fiddling in the water with your hands or working with objects such as nets, nets or contact with footwear are sufficient to transmit the virus. Waterfowl can also introduce the virus into water, although the virus does not survive outside of its habitat for more than two hours. Especially cormorants are blamed for the spread. Without a susceptible fish as a host, the virus survives in the water for a maximum of 14 days. In most cases, the virus is introduced into the stock by new fish.
proof
Analyzes of fish for diseases are usually detected in cell cultures . This method can only be used to a limited extent with the Koi herpes virus. Different characteristics and the mutability of the virus lead to inaccurate or incorrect results despite precisely defined cell lines. The polymerase chain reaction (PCR) is more sensitive. For this purpose, fragments of the virus genome are detected in a molecular-biological test. The combination of this examination with the clinical assessment allows a statement to be made about the possible presence of the virus. In the event of a negative result, this method does not offer 100% security either.
Another detection method is the so-called LAMP test ( Loop-mediated Isothermal Amplification ). Put simply, LAMP works according to the principle that a primer is used to search for parts of the CyHv-3 gene. The result can then be read off very easily thanks to a result that is displayed in color, which causes a color change when a reagent is added. Green means there is a LAMP reaction, orange means the sample shows no infection with KHV. Due to the short diagnosis time, less than two hours, the LAMP method is ideal for a quick diagnosis of KHV. Despite the short diagnosis time, the LAMP-based diagnosis is just as reliable as the far more complex PCR analysis. However, LAMP is a test that is not easy to carry out, as a certain amount of laboratory experience is also required here. However, in contrast to the established PCR, it is suitable for use “on site”. In contrast to PCR, which can only be carried out in special laboratories, the LAMP method can be used in private clinics and veterinary practices to diagnose the Koi herpes virus.
Since the negative evidence does not rule out an infection, an organ sample should be taken from the gills, liver, kidneys, spleen and brain of dead animals and this should be examined according to the requirements of the test laboratory.
Investigation bodies
The following institutions specialize in fish examinations
- Friedrich Loeffler Institute (FLI), Federal Research Institute for Animal Health, National Reference Laboratory for KHV infection on the island of Riems
- Institute for Zoology, Fisheries Biology and Fish Diseases Munich (Veterinary Faculty of the Ludwig Maximilians University Munich )
- Fish Health Service Bavaria
- Tauros diagnostics from Bielefeld University
- University of Veterinary Medicine Hannover , specialization in fish diseases
- Lower Saxony State Office for Consumer Protection and Food Safety (LAVES) - Veterinary Institute Hanover
- Landesbetrieb Hessisches Landeslabor - Veterinary medicine
Individual evidence
- ↑ a b c d e ICTV: ICTV Taxonomy history: Human alphaherpesvirus 1 , EC 51, Berlin, Germany, July 2019; Email ratification March 2020 (MSL # 35)
- ↑ Waltzek TB, Kelley GO, Stone DM, Way K, Hanson L, Fukuda H, Hirono I, Aoki T, Davison AJ, Hedrick RP: Koi herpesvirus represents a third cyprinid herpesvirus (CyHV-3) in the family Herpesviridae , in: J Gen Virol. 86 (Pt 6), June 2005, pp. 1659-1667, doi: 10.1099 / vir.0.80982-0
- ↑ ICTV : Master Species List 2018a v1 MSL including all taxa updates since the 2017 release. Fall 2018 (MSL # 33)