Sustained multi-year contraceptive efficacy of single-dose GonaCon in synanthropic female capybaras.

Capybaras (Hydrochoerus hydrochaeris) are increasingly synanthropic throughout South America, where their rapid population growth in human-altered landscapes heightens conflicts and, critically, elevates the public health risk of Brazilian Spotted Fever (BSF), a lethal Rickettsia rickettsii zoonosis transmitted by Amblyomma sculptum ticks. Since capybara density is tightly coupled with pathogen circulation, non-lethal, scalable management strategies are essential. We evaluated the long-term efficacy and safety of the single-dose GonaCon™ immunocontraceptive vaccine in free-living, sexually mature female capybaras (n=6 treated, n=3 control) ~ 33 months. All treated females demonstrated sustained reproductive suppression (absence of parturition or estrus behavior; p < 0.01). Efficacy was confirmed by multi-modal evidence: plasma progesterone (P4) and estradiol (E2) concentrations were significantly suppressed, showing reductions of 41% and 36% by Day 27 post-vaccination, respectively (p < 0.005; Cohen's d > 1.5). Histological analysis validated HPG axis disruption, revealing significantly lower ovarian weights (p=0.002) and suppressed folliculogenesis, with treated ovaries possessing drastically fewer antral follicles (mean 2.3 ± 0.5 vs. 12.7 ± 1.2 in controls; p<0.001). The treatment was safe, with the only adverse effect being a transient, localized swelling in 4/6 animals that resolved within two weeks. Importantly, treated females maintained critical social behaviors, including alloparental care. These findings provide strong evidence for the sustained, multi-year efficacy of GonaCon in a large wild rodent, supporting its use as a humane, non-surgical tool for density management and BSF risk mitigation under the One Conservation Paradigm.