Scanning the Horizon for Environmental Applications of Genetically Modified Viruses Reveals Challenges for Their Environmental Risk Assessment

The release of novel genetically modified (GM) virus applications into the environment for agricultural, veterinary, and nature-conservation purposes poses a number of significant challenges for risk assessors and regulatory authorities. Continuous efforts to scan the horizon for emerging applications are needed to gain an overview of new GM virus applications. In addition, appropriate approaches for risk assessment and management have to be developed. These approaches need to address pertinent challenges, in particular with regard to the environmental release of GM virus applications with a high probability for transmission and spreading, including transboundary movements and a high potential to result in adverse environmental effects. However, the current preparedness at the EU and international level to assess such GM virus application is limited. This study addresses some of the challenges associated with the current situation, firstly, by conducting a horizon scan to identify emerging GM virus applications with relevance for the environment. Secondly, outstanding issues regarding the environmental risk assessment (ERA) of GM virus applications are identified based on an evaluation of case study examples. Specifically, the limited scientific information available for the ERA of some applications and the lack of detailed and appropriate guidance for ERA are discussed. Furthermore, considerations are provided for future work that is needed to establish adequate risk assessment and management approaches.

The transmission rate of MCMV in house mice in pens: implications for virally vectored immunocontraception

Pest mammals have severe economic, environmental and social impacts throughout the world. Fertility control could reduce these impacts. Murine cytomegalovirus (MCMV) is being considered as an immunocontraceptive vector to control outbreaks of house mice (Mus domesticus) in Australian grain-growing regions. For successful control, a modified MCMV must transmit at a sufficient rate to keep populations of house mice below acceptable economic thresholds. We used disease models developed previously by using observations of free-ranging wild-mouse populations to assess the transmission rate of two laboratory strains of MCMV (N1 and G4) collected in a previous experiment. Mice contained in pens were deliberately infected with the N1 strain only, or with the N1 strain followed by the G4 strain. If we assume density-dependent transmission, which is the more likely mode of transmission, we found the N1 strain of MCMV transmitted at a rate ~1/300 of the rate of field strains, and hence too slowly for successful virally vectored immunocontraception (VVIC). If transmission was frequency-dependent, the rate of transmission was ~1/3 of the rate of field strains, and hence may allow successful VVIC. The G4 strain transmitted at least as slowly as the N1 strain, and possibly much more slowly; however, we could not determine whether this was an inherent property of the G4 strain or whether it was caused by competition with the N1 strain. Given the reliance of successful VVIC on rapid transmission, we recommend that future work in any VVIC system explicitly quantifies the transmission rate of recombinant viruses relative to field strains, both in the presence and absence of competing strains.

Delivering and registering species-tailored oral antifertility products: a review

Technologies that induce infertility in wildlife are advancing rapidly. This is due largely to our increasing understanding of reproductive physiology, as well as the demand for management techniques that reduce fertility rather than increase mortality. However, transferring wildlife fertility control from the laboratory into landscape-scale utility for free-ranging animal populations will be highly dependent on products possessing oral activity and cost-effectiveness. A significant challenge to the delivery process is providing the international regulators in each jurisdiction with the most relevant data packages they need to assess new products. An essential part of any product registration for free-ranging animals will be the development of species-tailored delivery systems, especially so for non-specific antifertility actives. This review examines the current range of orally deliverable antifertility options, broadly classifies them according to overall risk compared with alternative vertebrate pesticides, outlines a species-tailoring process that reduces identified risks, and encompasses the data requirements for their registration for sale in Australasia, the USA and Europe.

Prospects for virally vectored immunocontraception in the control of wild house mice (Mus domesticus)

The wild house mouse (Mus domesticus) is not native to Australia and was introduced from Europe with early settlement. It undergoes periodic population explosions or plagues, which place significant economic and social burdens on agricultural communities. Present control mechanisms rely on improvements to farm hygiene and the use of rodenticides. This review covers over a decade of work on the use of virally vectored immunocontraception (VVIC) as an adjunct method of controlling mouse populations. Two viral vectors, ectromelia virus (ECTV) and murine cytomegalovirus (MCMV) have been tested as potential VVIC vectors: MCMV has been the most widely studied vector because it is endemic to Australia; ECTV less so because its use would have required the introduction of a new pathogen into the Australian environment. Issues such as efficacy, antigen choice, resistance, transmission, species specificity and safety of VVIC are discussed. In broad terms, both vectors when expressing murine zona pellucida 3 (mZP3) induced long-term infertility in most directly inoculated female mice. Whereas innate and acquired resistance to MCMV may be a barrier to VVIC, the most significant barrier appears to be the attenuation seen in MCMV-based vectors. This attenuation is likely to prevent sufficient transmission for broad-scale use. Should this issue be overcome, VVIC has the potential to contribute to the control of house mouse populations in Australia.

Prospects for the future: is there a role for virally vectored immunocontraception in vertebrate pest management?

Virally vectored immunocontraception (VVIC) has been studied and promoted as an alternative to lethal methods for vertebrate pest control in Australia and New Zealand. Virally vectored immunocontraception offers a potentially humane and species-specific control method with potential for a good benefit–cost outcome, but its applicability for broad-scale management remains unknown. We present case studies for the house mouse, European rabbit, red fox and common brushtail possum and describe the current status of research into the use of VVIC as a broad-scale pest-management tool. All case studies indicated that there are significant problems with delivery and efficacy. The current state of development suggests that VVIC is not presently a viable alternative for the management of these vertebrate pests, and it is highly unlikely that this will change in the foreseeable future. An absence of benefit–cost data also hinders decision-making, and until benefit–cost data become available it will not be clear if there are short- or long-term benefits resulting from the use of VVIC for broad-scale pest management.

Pest or prized possession? Genetically modified biocontrol from an international perspective

This article provides an overview of current research, regulations and international issues concerning genetically modified (GM) organisms for use as biological controls of vertebrates. There is increasing interest in using biotechnology to solve vertebrate pest problems around the world. A major issue lies in the fact that individual countries focusing on internal problems of pest management may overlook the potential of transborder entry. Animals considered a pest in one country may well be prized possessions in another, and research and management strategies should consider the adverse effects of biocontrol agents entering the ‘wrong’ country. There is a wealth of guidance in the form of national and international regulations and ethics guidelines. However, current legislation and agreements may not be adequate to ensure that all risks of GM biocontrols, particularly disseminating agents, have been considered from an international perspective. Major issues include concerns of transboundary movement, non-target effects and the need for an international body to consult with and regulate the use of GM biocontrols. We live in a finite and interconnected world: it is vital that impacts of potential control strategies are assessed at a local and international level, and from social, environmental and economic perspectives.