Vaccination on the Fly: The Use of Mosquitoes to Vaccinate Bat Populations That Harbor Human Pathogens

Monica Borucki | 19-DR-014

Project Overview

The vast majority of emergent human diseases are caused by zoonotic viruses, which jump from animal reservoirs and infect humans. As climate change progresses and causes shifts in the distribution of zoonotic disease reservoir species, new outbreaks of human and veterinary disease are inevitable as viruses host-jump from wildlife reservoirs. Thus, a novel strategy needs to be implemented to deliver vaccines to wildlife species known to harbor potentially emergent viruses. The objective of this project was to use mosquitoes to deliver vaccines to bats, which are known to serve as reservoirs of significant pathogens such as rabies virus, coronaviruses, Nipah virus, and Ebola virus, and thus decrease the threat of viral emergence from these animals. Because bats are blood-fed upon by various species of mosquitoes, one can speculate that mosquitoes can be exploited to deliver vaccines during natural host feeding activities.

We hypothesized that bacterial species known to inhabit the salivary gland of mosquitoes could be genetically manipulated to produce vaccine antigens that are secreted into the saliva of the mosquito thereby enabling immunization of bats by route of mosquito bite. To create a vaccination system, symbiotic bacterial species that colonize the salivary glands of mosquitoes were genetically modified to express a vaccine protein from rabies virus and fed to mosquitoes. To test the ability of vaccine proteins generated by bacteria to produce a bat immune response, bats were inoculated with different rabies vaccine proteins generated by recombinant (genetically modified) E. coli bacteria. Testing of sera from the inoculated bats showed production of a moderate immune response to the bacteria-derived vaccine. Three species of symbiotic bacteria were genetically modified to produce rabies vaccine proteins and tested for protein expression and secretion. These bacterial species were also tested for the ability to reliably translocate from the mosquito gut to the salivary glands. Results of the experimental efforts from this project indicate that while the antigens of interest are likely to result in a moderate immune response in bats, the three different species of symbiotic bacteria tested were not able to secrete intact vaccine antigens, and surprisingly, none of these bacterial species were able to travel from the mosquito gut to the salivary glands.

Mission Impact

If this system of vaccine delivery had proved to be feasible it could have been used to vaccinate many different animal species that have important roles in disease transmission but are not generally considered for vaccination due to difficulty in capture and high population turnover. Use of blood-feeding arthropods such as mosquitoes as a vaccine delivery system to wildlife would be a significant step towards control of zoonotic pathogens that cause a constant threat to global health. Despite the fact the goal was not met, a novel mosaic peptide that included different immunogenic regions of the rabies virus was designed and when tested in Jamaican fruit bats, gave a moderate immune response, thus has the potential as a vaccine for wildlife. Importantly, this project forged a collaboration with mosquito and bat experts at Colorado State University that may be useful for future Lawrence Livermore National Laboratory projects that address the role of mosquitoes and bats in disease transmission.

Publications, Presentations, and Patents

E. K. Harris, T. H. Lee, M. Franco, M. C. Yung, V. Lao, E. M. Borland, N. M. Collette, B. R. Borlee, T. Schountz, R. C. Kading, M. K. Borucki, "Genetically engineered endosymbionts of mosquitoes for use in paratransgenesis," The American Society for Tropical Medicine and Hygiene: November 15-19, 2020.