Mixed infections and the competitive fitness of faster‐acting genetically modified viruses

Abstract

Faster-acting recombinant baculoviruses have shown potential for improved suppression of insect pests, but their ecological impact on target and nontarget hosts and naturally occurring pathogens needs to be assessed. Previous studies have focused on the fitness of recombinants at the between-hosts level. However, the population structure of the transmission stages will also be decided by within-host selection. Here we have experimentally quantified the within-host competitive fitness of a fast-acting recombinant Autographa californica multicapsid nucleopolyhedrovirus missing the endogenous egt gene (vEGTDEL), by means of direct competition in single- and serial-passage experiments with its parental virus. Quantitative real-time PCR was employed to determine the ratio of these two viruses in passaged mixtures. We found that vEGTDEL had reduced within-host fitness: per passage the ratio of wild type to vEGTDEL was on average enhanced by a factor of 1.53 (single passage) and 1.68 (serial passage). There is also frequency-dependence: the higher the frequency of vEGTDEL, the stronger the selection against it is. Additionally, the virus ratio is a predictor of time to host death and virus yield. Our results show that egt is important to within-host fitness and allow for a more complete assessment of the ecological impact of recombinant baculovirus release.

Competition between wild-type and a marked recombinant baculovirus (Spodoptera exigua nucleopolyhedrovirus) with enhanced speed of action in insect larvae

“…Our results of reduced fitness of SeXD1 as compared to SeUS1 are in agreement with those of Zwart et al (2009b), who found that an egt deletion mutant of AcMNPV was less fit in competition experiments with wild-type AcMNPV in Trichoplusia ni. These findings collectively suggest that egt has a role in virus multiplication, spread or packaging in the insect.…”

Pathogen Growth in Insect Hosts: Inferring the Importance of Different Mechanisms Using Stochastic Models and Response-Time Data

“…Baculovirus biology suggests that the number of virus particles that initiates infections is probably small (Zwart et al 2009a(Zwart et al , 2009b, and so we used probabilistic models that inherently allow for demographic stochasticity. The models track the replication and destruction of virions, as well as the immune cells that are destroyed along with the virions.…”

Coevolution of virulence and immunosuppression in multiple infections

“…parasite‐induced host mortality) correlates with the extent of parasite resource exploitation. Adaptive benefits of resource exploitation include the positive correlation with transmission (Fraser et al ., ; de Roode et al ., ; Råberg, ), and a within‐host competitive advantage in coinfection (de Roode et al ., ; Bell et al ., ; Ben‐Ami et al ., ; Zwart et al ., ). Here, we focus on the latter adaptive benefit to study the evolution of virulence and immunosuppression.…”