Researchers investigated the ecology and epidemiology of Koi Herpesvirus, a potential pathogenic biocontrol agent for invasive common carp. The team found the virus was widespread in Minnesota, species specific during experimental and natural outbreaks, highly transmissible by direct contact, and could result in high mortality for common carp.
Koi herpesvirus (KHV) is a highly lethal and species-specific virus of common carp, and the ornamental variety, koi, and has previously been found to be widespread in carp populations in Minnesota. Researchers investigated KHV as a potential pathogenic biocontrol agent for carp that could be used alone or as part of an integrated pest management (IPM) strategy. Through a series of laboratory trials and investigations of infected wild populations, the team made several important discoveries critical to biocontrol evaluation and application. Researchers have, for the first time in North America, isolated KHV from a wild carp population, which opened the door for research in this project and beyond. They then investigated the genetic epidemiology of 15 regional KHV strains and now hypothesize that KHV may have been introduced along with infected carp more than 100 years ago. They also confirmed the primary route of transmission requires direct social contact, early in the disease course prior to the development of clinical lesions. This confirms that the delivery of a KHV as a biocontrol agent would need to be by releasing infectious fish, not virus indirect exposure in water. The ecology of KHV was intensively monitored in Lake Elysian (KHV outbreaks in 2018, 2019) over multiple seasons to understand demographic patterns and persistence. It is clear now that KHV can persist within a population, most likely in surviving adult male fish and be transmitted to naïve carp returning from spawning habitats. Lastly the species specificity of KHV was confirmed through laboratory exposures and wild fish surveys – no replicating virus was found in a native fish, despite high prevalence and/or mortality in cohabitating carp. Altogether, this research supports continued investigation of KHV as a ‘augmentative biocontrol’ agent for IPM, leveraging the natural disease dynamics to induce large mortality events.
Phase III: Evaluation of koi herpes virus for use as a potential biocontrol agent for common carp in Minnesota
This is the third phase of a project working to identify and evaluate a safe and effective pathogenic biocontrol agent for carp. Following an extensive literature review, local and international consultation, and multiple seasons of region-wide fish disease surveillance, we have concluded that koi herpes virus (KHV) is a candidate pathogen worthy of further investigation. In the second phase of the project, we detected the virus in association with numerous mass mortalities of carp in Minnesota and surrounding states with no apparent effect on native species. However, key uncertainties remain in understanding the natural ecology of KHV in Minnesota, which is a pre-requisite to evaluating its potential safety and efficacy as a biocontrol agent. Phase III of this effort will:
- Isolate and characterize various strains of KHV from lakes in Minnesota
- Evaluate the pathogenicity of these strains in adult and juvenile carp
- Determine the prevalence of KHV in native fish and carp populations in lakes with histories of exposure using highly sensitive diagnostic tests.
We will also communicate our findings to scientific, management, and public stakeholders. This will advance our scientific understanding of KHV’s potential impacts on fishes in Minnesota and its potential value as a biocontrol agent.
Phase II: Virus discovery and evaluation for use as potential biocontrol agents
Phase I of this project provided initial baseline data on viruses of carp species in the region. Phase II will build upon this work for carp species and now include zebra mussels to utilize newly developed techniques to more strategically identify viral biocontrol candidates for control of invasive carp and zebra mussels. More specifically, Phase II will:
- Collect apparently healthy invasive carp and mussel species in the Midwest region;
- Collect samples from mortality events of native and invasive fish and mussel populations in the Midwest region;
- Conduct virus discovery by next generation sequencing and culture potential pathogens;
- Determine the disease causing potential of two selected viruses, one for native and invasive fish and the other for native and invasive mussels; and
- Communicate findings to scientific, management, and public stakeholders.
This will provide the scientific foundation to begin to evaluate specific pathogens for invasive species control. Furthermore, understanding the virome of invasive species will serve as a potential early indicator for the movement and distribution of pathogens that may threaten native species.
Phase I: Exploring whether native pathogens can be used to control AIS
This project is exploring the introduction or promotion of species-specific pathogens for controlling AIS. This high-risk, high-reward approach must be carefully assessed with thorough investigation and scientifically justified risk assessment. As a first step in Phase I of a multi-phase project, invasive carp species were surveyed to identify viruses circulating in these populations. Nearly 700 common carp were collected from Minnesota lakes, 120 silver carp from the Fox and Illinois Rivers, and a variety of carp species from eight mortality events. All fish were negative for cyprinid herpes viruses 1, 2, and 3, carp edema virus, and spring viremia of carp virus. However, advanced molecular approaches and virus isolation detected several known and unknown viruses of significance. This included novel viruses from at least seven RNA virus families: picornavirus, reovirus, hepatovirus, astrovirus, hepatitis virus, betanodavirus, and paramyxovirus. The novel carp paramyxovirus was associated with a mortality event and shows particular promise for further evaluation as a biocontrol agent. The standard operating procedures developed during Phase I will be essential to advance future work on this and related pathogen discovery research. Unfortunately, Phase I was met with several unforeseen challenges that hindered completion of all proposed activities, including laboratory renovation progress, service provider availability and delays, and access to mortality events. In spite of these setbacks, this project has significantly advanced our understanding of invasive carp viruses and positioned us well to for future research efforts. Phase I of this project provided researchers and managers with baseline data on viruses circulating in invasive carp populations in the region.
Dr. Phelps serves as both the Director of MAISRC and as a MAISRC research fellow. The review and administration of Dr. Phelps research proposals and projects with MAISRC are guided by the Managing Director Conflict of Interest in MAISRC Proposal Funding policy. Questions about this policy can be directed to MAISRC Associate Director, Cori Mattke.