Prospects for immunocontraceptive control of feral and stray cat (Felis catus) populations in Australia
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2025
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Melbourne Authors
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Veterinary Science Collected Works
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PhD thesis
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© 2025 Jemima Amery-Gale
Abstract
Domestic cats (Felis catus) have been introduced to most of the world, with feral cats now occurring across the Australian mainland and on the majority of the island land area around the continent. On average, Australia’s introduced cat populations kill over 1.5 billion native terrestrial vertebrates annually. Predation by feral cats is listed as a key threatening process in Australia, having contributed to the extinction of at least 30 mammal species and currently threatening over 120 indigenous species. Feral and stray cats are notoriously difficult to control, but given their catastrophic impacts on biodiversity, there is urgent need for more effective tools for their broadscale management.
Immunocontraception, or vaccinating against pregnancy, offers a humane, and potentially more target-specific method of population control than existing lethal methods. To investigate feline viruses that may have potential as contraceptive vectors, tissue samples were opportunistically collected from 393 culled feral or Indigenous community cats from widely spaced locations across Australia, and tested for Felis catus gammaherpesvirus 1 (FcaGHV1), feline dependoparvovirus (FDPV) and other dependoparvoviruses by targeted PCRs.
FcaGHV1 and FDPV were detected in all populations sampled. FcaGHV1, FDPV and non-FDPV dependoparvoviruses were detected at 14.2%, 16% and 5.9% prevalences respectively. Consistent with previous studies, FcaGHV1 infection was most common in adult male cats, and higher prevalences were obtained when a wider range of tissues were tested – suggesting that testing a single sample type may underestimate FcaGHV1 prevalence.
Feline dependoparvovirus was detected from 35.6% of subadults but only 2.5% of adult cats, with splenic tissue having the highest prevalence of detectable FDPV DNA. Australian feral cats may also be infected with other dependoparvoviruses, but further investigation is required to determine their identity and significance. The host range, prevalence and potential of FcaGHV1, FDPV and other dependoparvoviruses as vaccine or gene transfer vectors all represent promising areas of study in the field of virally vectored approaches to cat contraception.
Feline calicivirus (FCV) commonly causes upper respiratory tract, oral and ocular infections in felids. When synthesised in vitro, the capsid proteins of caliciviruses self-assemble into non-replicating virus-like particles (VLPs) that can stimulate robust immune responses. Recombinant VLPs incorporating reproductive epitopes may provide a potential strategy for inducing longer-term, albeit not likely host-specific, immunocontraception, with potential application as injectable fertility control tools. Chimeric FCV capsid proteins designed to incorporate feline reproductive epitopes were produced using mammalian cells, but no sign of self-assembling FCV VLPs was detected. Further work is required to optimise production of FCV-like particles incorporating foreign epitopes.
To investigate the prevalence of pre-existing antibodies that may interfere with the efficacy of a potential FCV-based vaccine, serum samples were opportunistically collected from 669 Australian feral, stray or Indigenous community cats. FCV-F9-neutralising antibodies were detected from 69.7% of cats tested, showing high risk of natural exposure to FCV. The prevalence and titres of anti-FCV antibodies were highest amongst adult cats living in highly modified environments, suggesting that any FCV-based vectors would be most efficacious on islands or amongst immature cats in remote Indigenous communities.
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immunocontraception, vectored contraception, fertility control, feral cats, free-roaming, domestic cats, reproductive antigens, virus-like particles, Feline calicivirus, seroprevalence, neutralising antibodies, Felis catus gammaherpesvirus 1, Dependoparvoviruses, Adeno-associated viruses, Feline dependoparvovirus