Modelling the koi herpesvirus (KHV) epidemic highlights the importance of active surveillance within a national control policy
Summary
1. Koi herpesvirus can cause serious disease in carp Cyprinus carpio populations globally. Populations of carp exposed to the virus are already widespread across England and Wales, and there is a need to determine whether and how to control its spread. This study evaluates potential management options and provides recommendations applicable to many infected countries.

2. The influences of the main drivers of the epidemic were investigated using simple compartment based models, and the effectiveness of several potential control options were evaluated. Models were parameterized using recorded fish movement, field and experimental data.

3. Experimental studies suggested the risk of transmitting the virus between waters on angling equipment was low. Data from previous studies suggested live fish movements between fisheries, and the introduction of imported ornamental fish to be the most likely routes by which a fishery could be infected.

4. The models suggest that fish movements between fisheries alone could not have led to the number of exposed sites known to exist in 2007. An additional external infection pressure such as the introduction of imported ornamental fish would have been required, and is likely to have been the main driver of the epidemic in its early stages.

5. Predictions of future scenarios suggest that fish movements between fisheries have taken over as the main driver of the epidemic, and consequently restricting imports to reduce the external infection pressure is unlikely to have much impact on its own.

6. Due to the small proportion of infected waters currently detected, increasing the duration of movement restrictions placed on infected sites from four years to permanent was predicted to have little effect on the epidemic.

7. Synthesis and applications. Given the current stage of the koi herpesvirus epidemic, reducing the spread of the virus between fisheries is likely to be challenging, but may be possible by conducting an active surveillance programme and placing permanent movement restrictions on exposed sites. However, this will only be effective if the external infection pressure can also be reduced, possibly through restrictions on the import of fish from koi herpesvirus infected countries.