Biological control using sterilizing viruses: host suppression and competition between viruses in non‐spatial models

Abstract

Summary 1.Research is currently underway to develop genetically engineered viruses that can sterilize pest animals. The technique, known as viral-vectored immunocontraception (VVIC), promises to control mammalian pests such as the European rabbit, the house mouse and domestic cats. 2. Using host±parasite models we explored the degree of control of the host population that can be attained when hosts that recover from infection become permanently infertile. The models assume some demographic compensation for reduced fertility in the host population, and are tailored to address issues raised by the use of the myxoma virus as an agent to sterilize rabbits. A`pay-o' function is developed, which de®nes the degree to which host density is suppressed by a sterilizing agent. 3. The results show that sterilizing viruses can reduce host abundance, and that hosts with low birth rates and moderate mortality rates are the best targets for VVIC. High transmissibility increases the pay-o from VVIC, but because virulent parasites kill most of the hosts that they infect, the pay-o is highest if benign parasites are used as the vector of contraceptive antigens. We argue that appropriate pay-o functions should be developed as a basis for research and development on genetically modi®ed organisms. 4. The host±parasite models are extended to include a competing strain of virus that does not sterilize the host. We analysed these models using a general approach to the analysis of competition, which has not often been applied to epidemiological models. The extended model shows that host sterilization per se does not aect the competitive ability of viruses, a result that applies to a broad class of models in which the per capita growth rates of competing parasites are linear functions of limiting competitive factors.

Yield, compensation and fertility control: a model for vertebrate pests

“…The difference may be caused by the estimate of the intercept (Q T = r m /a) being negatively biased or the duration of the rabbit studies in Australia being too short. The estimate of r m (1.32 year -1 ) was lower than those reported (2.06 year -1 and 3.6 year -1 ) by Hone (1999) and Hood et al (2000) respectively for rabbits in Australia. Modelled equilibrium relationships between European rabbit abundance (P) and the proportion of females sterilised (Q) in the population.…”

“…Also the modelling assumes logistic growth of rabbit populations. Such growth has been reported for a rabbit population in New Zealand (Barlow and Kean 1998) and was assumed to occur in models for rabbits in Australia (Hood et al 2000). …”

Predicting the effect of immunocontraceptive recombinant murine cytomegalovirus on population outbreaks of house mice (Mus musculus domesticus) in mallee wheatlands

“…Simple models of this type have been used extensively and seem to capture essential features of host-disease dynamics (e.g. Barlow 2000;Hood et al 2000). Consequently, they provide a useful basis for making comparisons with other studies.…”

Modelling hunting strategies for the conservation of wild rabbit populations

“…These include general models on unspecific control strategies (Darwin and Williams, 1964;Smith and Trout, 1994;Smith, 1997) and, more recently, models in which disease is the control method (Pech and Hood, 1998;Hood et al, 2000). However, models focusing on rabbit conservation have received little attention (Calvete and Estrada, 2000;Fa et al, 2001).…”