Retrospective Analysis of the Impact of Vaccination with an Inactivated Vaccine on Toxoplasmosis-Associated Mortality in Captive Wildlife.

Abstract

Background/Objectives: Toxoplasma gondii is a major cause of zoonotic infections in both humans and animals, resulting in significant mortality in susceptible species, such as New World primates and marsupials. Toxoplasmosis is particularly concerning in zoos and wildlife reserves, where outbreaks threaten conservation efforts for endangered species. In the absence of a commercially available vaccine against toxoplasmosis for humans and captive wild animals, current prevention strategies are limited to restricting the access of cats to enclosures, controlling rodent populations, and maintaining strict food hygiene. Recent research has shown promising results with an intranasal vaccine (VXN-Toxo) composed of maltodextrin nanoparticles conjugated with a purified, inactivated T. gondii parasite. This experimental vaccine does not pose a risk of causing disease and offers advantages such as better stability compared with live pathogen-based vaccines. Methods: This study presents a large-scale evaluation of the effect of VXN-Toxo administered to captive wildlife across 20 zoos in Europe and the Americas between 2017 and 2025. Seven hundred and eighty-four animals, representing over 58 species (including primates, marsupials, rodents, and felids), were vaccinated without any adverse events reported. Results: Retrospective mortality data from 20 participating zoological institutions revealed an overall 96.7% reduction-and, in many cases, a complete elimination-of toxoplasmosis-associated deaths post vaccination. Conclusions: These results demonstrate, for the first time, consistent and broad-spectrum protection against T. gondii of different strains in a wide array of captive wildlife species. This universal vaccine represents a promising tool for toxoplasmosis prevention in zoological collections, with significant implications for animal health and conservation strategies.