Assessment of Virally Vectored Autoimmunity as a Biocontrol Strategy for Cane Toads

Abstract

BackgroundThe cane toad, Bufo (Chaunus) marinus, is one of the most notorious vertebrate pests introduced into Australia over the last 200 years and, so far, efforts to identify a naturally occurring B. marinus-specific pathogen for use as a biological control agent have been unsuccessful. We explored an alternative approach that entailed genetically modifying a pathogen with broad host specificity so that it no longer caused disease, but carried a gene to disrupt the cane toad life cycle in a species specific manner.Methodology/Principal FindingsThe adult beta globin gene was selected as the model gene for proof of concept of autoimmunity as a biocontrol method for cane toads. A previous report showed injection of bullfrog tadpoles with adult beta globin resulted in an alteration in the form of beta globin expressed in metamorphs as well as reduced survival. In B. marinus we established for the first time that the switch from tadpole to adult globin exists. The effect of injecting B. marinus tadpoles with purified recombinant adult globin protein was then assessed using behavioural (swim speed in tadpoles and jump length in metamorphs), developmental (time to metamorphosis, weight and length at various developmental stages, protein profile of adult globin) and genetic (adult globin mRNA levels) measures. However, we were unable to detect any differences between treated and control animals. Further, globin delivery using Bohle iridovirus, an Australian ranavirus isolate belonging to the Iridovirus family, did not reduce the survival of metamorphs or alter the form of beta globin expressed in metamorphs.Conclusions/SignificanceWhile we were able to show for the first time that the switch from tadpole to adult globin does occur in B. marinus, we were not able to induce autoimmunity and disrupt metamorphosis. The short development time of B. marinus tadpoles may preclude this approach.

Development and Disease: How Susceptibility to an Emerging Pathogen Changes through Anuran Development

“…The fully aquatic life cycle of X. laevis may result in unique immunological adaptations that are not shared with amphibian species that live terrestrially after metamorphosis. Pallister et al [50] suggested that differences in larval development might contribute to differences in immune function. Indeed, comparative immunological studies between X. laevis and other anuran species are needed.…”

Is Typhoid Mary a good role model?

“…So far, efforts to identify a truly cane toad‐specific pathogen for use as a biological control agent have been unsuccessful, as have been efforts to induce autoimmunity and disrupt metamorphosis (Pallister et al ., ). Alarm pheromones and translocation of parasitic lungworms to the invasion front may provide new tools in the management of this damaging pest species (Saunders et al ., ).…”

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

“…Such strategies were explored for the management of vertebrate pests, such as rodents, rabbits, cane toads, and carp, in Australia [53]. However, major challenges regarding efficacy (i.e., insufficient duration of sterility) and delivery (i.e., ineffective transmission of the viral vector) were reported for such applications [54][55][56][57]. Most of these approaches have been abandoned in the meantime, and only the use of pathogenic non-GM viruses to control invasive fish species, such as tilapia or carp, is still being evaluated [58,59].…”