Final report: Phase 3 of the carp herpesvirus project (CyHV-3)

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This report represents the culmination of work conducted in Phase 3 of a study to investigate the potential of Cyprinid herpesvirus 3 (CyHV-3; also known as koi herpesvirus, or the carp herpesvirus) as a biological control agent for carp in Australia. Following encouraging results from the initial studies, the aim of the current phase (Phase 3) was to extend the earlier results in order to be confident that use of CyHV-3 would be a safe and effective biocontrol agent for carp in Australia.

Perhaps the most significant results from Phase 3 relate to further susceptibility testing of non-target species. Following clinical, molecular and histological observations, we now know that CyHV-3 does not infect (and therefore cannot affect) a wide taxonomic range of non-target animals including: 14 species of fish (13 native species, and the introduced rainbow trout); yabbies; a species of lamprey; two amphibian species; two reptile species; chickens; and mice. These results strongly suggest that both spillover infections and species jumps are highly unlikely with CyHV-3, and, therefore, the results encourage further work on the use of CyHV-3 as a potential biocontrol agent for carp in Australia.

Very importantly, we have also made good progress on the development of a mathematical model for CyHV-3 to determine a release strategy for the virus in the Lachlan River catchment (LRC). In the course of developing the model, limitations in the availability of hydrological and carp demographic data became obvious, and while these deficiencies slowed progress, they were overcome in a variety of ways including the use of a Bayesian Belief Network workshop (to generate data on the distribution and abundance of carp in the waterways of the Murray-Darling Basin, MDB). The final mathematical model, which will be focused on the LRC, will allow the following questions to be addressed: (1) when will it be best to release the virus (what season and what part of the El Nino Southern Oscillation (ENSO) cycle)? (2) where will it be best to release the virus (upstream or downstream or in recruiting grounds)? (3) will supplementary regional controls – for example, fishing, trapping, netting – be needed? (4) if they are (which is probable), what will be the best way to apply these (before or after releasing the virus).

Transferring the Indonesian strain of CyHV-3 (the C07 strain) from the secure to the non-secure area at AAHL has been an important achievement in order to allow future progress of the project. As an extension of this process, production of aliquots of freeze-dried (f-d) virus, and subsequent testing of the virulence of reconstituted f-d virus, was also an important achievement. It is likely that, if the virus is eventually used in the field in Australia, it will be delivered to the sites of distribution throughout the MDB in a f-d form. While concentrations of virus in the f-d preparations fell below useful levels, subsequent lessons learned from an experienced overseas organization should result in a better outcome. In the meantime, we have determined the decay rate of CyHV-3 in tissue culture supernatant fluid held at 4 oC as an alternative means of delivering virus to the field if necessary.

Sequencing and annotating the complete genome sequence of Indonesian CyHV-3 (C07 strain) has been a significant achievement in allowing ultimate recognition of the potential biocontrol virus in Australia. Additional studies, firstly, on the expression of immune-related genes of carp during CyHV-3 infection (assisting our understanding of the carp-virus interaction), and, secondly, in attempting to identify a marker of persistent/latent infection in carp, have also allowed further characterization of this potential future virus for biocontrol of carp in Australia.

Recommendations

The findings that are documented in this Report provide great encouragement for further work on the use of CyHV-3 as a potential biocontrol agent for carp in Australia. Particular recommendations for future work include:

  • Completion of the non-target species (NTS) testing (2 Western Australian and 3 Queensland species of fish).
  • Extension of the modelling work from the LRC to the MDB at large.
  • Development of tools (particularly a serological test) for monitoring the effect of the virus on carp populations to recognize when, and if, modifications are required to the virus or to control programs that will complement the effect of the virus.
  • Development of a quantitative measure of stress in carp in order to address animal ethics issue associated with the release of the virus.
  • Modification of the protocol for the production of freeze-dried virus.
  • Susceptibility testing of carp from throughout the entire MDB to the virus to ensure that CyHV-3 (C07 strain) will be effective.
  • Selection and development of a genetic strategy to complement the effect of CyHV-3 as a biocontrol agent.
Author McColl K
Year 2016
Place published Canberra
Publisher Invasive Animals CRC
Pages 51
ISBN/ISSN Online ISBN 978-0-9924083-3-6
Control method Biological Control
Region Australia - national
Documents

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Links

PestSmart toolkit: Carp