The stakes are considerable. The global movement of live animals, meat, milk, semen, embryos, feed ingredients, and biological materials has created expanding routes by which pathogens of high epidemic potential can be translocated into countries lacking the biosecurity capacity to intercept them. The review catalogues the primary culprits: transboundary animal diseases such as highly pathogenic avian influenza, African swine fever virus, foot-and-mouth disease virus, lumpy skin disease virus, and peste des petits ruminants virus. These pathogens circulate at elevated intensity in exactly the regions that host most of the world’s livestock, sustain extensive informal cross-border trade, and contain critical wildlife interfaces—yet often lack the institutional, technical, and financial resources to run quarantine systems to international standards. The intersection of high pathogen pressure, porous borders, and thin institutional capacity, the authors write, makes LMIC border quarantine the most consequential and simultaneously the most constrained node in global biosecurity.

Conceptually, the review distinguishes quarantine from its neighbors in the animal health governance architecture. Import risk analysis generates probabilistic estimates of pathogen entry for given commodities and trading partners; internal movement control regulates redistribution within national territories after an introduction; surveillance detects pathogens already circulating. Quarantine, by contrast, is the procedural intervention that converts regulatory authority into physical action at the border—the officer who inspects, the laboratory that tests, the facility that detains, and the mandate that authorizes destruction or re-export. Its epidemiological rationale is that interrupting pathogen introduction before domestic amplification is far more resource-efficient than controlling spread after establishment, a principle of particular importance for pathogens with high transmission rates and short generation intervals, where a single undetected infected consignment can seed an outbreak requiring enormous national resources to contain.

The legal scaffolding for this work rests on three principal international instruments. The World Trade Organization’s Agreement on the Application of Sanitary and Phytosanitary Measures permits quarantine measures that are scientifically justified, proportional to assessed risk, and applied consistently across trading partners. The World Organisation for Animal Health (WOAH) Terrestrial Animal Health Code provides the risk-based technical reference for import permits, veterinary certification, and disease-free status recognition, while the WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals underpins laboratory confirmation. The International Health Regulations govern notification and response for zoonotic pathogens at points of entry, and the Convention on International Trade in Endangered Species adds a parallel permit layer for wildlife consignments—one whose documentation requirements, the review notes, sometimes conflict with veterinary quarantine procedures at busy airports and seaports, demanding inter-agency coordination that is frequently absent in LMIC border management.

Yet the evidence assembled shows that underperformance in LMIC quarantine is driven less by the absence of standards than by what happens, or fails to happen, beneath them. Weak governance independence emerges as the binding constraint: where the veterinary authority lacks legal independence from political influence, adequate funding, or authority to act against powerful trading interests, quarantine integrity is compromised regardless of technical capacity. Thin diagnostic capacity compounds the problem—centralized veterinary laboratories capable of processing quarantine samples are often distant from border posts, with transit times exceeding the stability of labile pathogens, promoting prolonged detention or, worse, informal clearance without testing. Many LMIC systems, the review observes bluntly, can inspect visually but cannot test diagnostically. Workforce shortages, fragmented data systems, and the absence of compensation mechanisms for traders whose consignments are destroyed add further friction, creating disincentives for compliance and enforcement alike.

The structural dominance of informal trade looms largest of all. In sub-Saharan Africa, the majority of cross-border livestock movements occur outside formal channels, bypassing official points of entry entirely and rendering quarantine inspection structurally inapplicable to the bulk of introduction risk. Network analysis of small ruminant movements in Uganda documented extensive trade through informal routes with minimal veterinary oversight, concluding that strategies depending exclusively on official border quarantine will miss most transboundary disease pathways. Cross-border camel circuits in the Horn of Africa, informal cattle movement across Yunnan Province’s borders in China, and the intercontinental flow of unregulated meat imports through European checkpoints all illustrate the same mismatch: quarantine systems calibrated to formal trade volumes are addressing a minority share of the actual risk. Notably, stochastic modeling of foot-and-mouth disease risk at the Thailand–Myanmar border found that complete elimination of informal trade channels was more effective than formal inspection procedures under conditions of high smuggling prevalence, though even partial quarantine compliance substantially reduced introduction risk.

The review also surveys a technological frontier that could reshape border quarantine within the decade. Portable nucleic acid amplification platforms, including isothermal amplification and miniaturized PCR systems, now enable field-deployable detection of priority pathogens at border posts, cutting test turnaround from days to hours and allowing perishable samples to be tested before biological degradation. Digital veterinary health certificates, cryptographically secured and verifiable in real time against issuing-authority databases, could suppress the fraudulent documentation that systematic reviews have identified as a persistent pathway for unregulated product movement. Risk-based targeting—directing inspection intensity toward consignments with the highest estimated introduction probability, informed by trade volumes, disease status, commodity hazards, and interception histories—has demonstrated measurable detection gains in well-resourced settings, including a validated systems analysis of Australian biosecurity borders. Machine learning applied to biosecurity assessment data has uncovered risk profiles invisible to conventional analysis, and whole-genome sequencing of intercepted pathogens can phylogenetically attribute outbreak strains to specific trade routes, creating an evidentiary basis for adjusting import conditions.

The authors are careful, however, to flag a specific and uncomfortable evidence gap: none of these tools—portable diagnostics, digital certification, AI-assisted targeting—has published field validation data from LMIC border posts under routine operating conditions. Their demonstrated performance comes from higher-resource settings; whether the gains transfer to contexts where power supply, connectivity, and maintenance capacity differ substantially is an immediate priority for field research. The review also acknowledges its own limits: it is a purposive narrative synthesis rather than a systematic review, and the underlying literature itself remains geographically concentrated, with Central Africa beyond Cameroon, most of Latin America outside Brazil, and much of Southeast Asia underrepresented.

The conceptual heart of the paper is its reframing of quarantine as One Health infrastructure. The One Health Joint Plan of Action, developed jointly by the FAO, UNEP, WHO, and WOAH, positions strengthened border biosecurity as integral to pandemic prevention, explicitly endorsing investment in LMIC veterinary capacity as a global health security priority—with an implementation timeline through 2026 that the authors describe as an immediate policy window. The review argues that inspection protocols addressing both the animal health status of consignments and the zoonotic risk they pose are more faithful to One Health principles than livestock-only screening, and that veterinary and public health border functions should be coordinated rather than run in parallel siloes. An assessment at the Libya–Tunisia border documented exactly the cost of non-integration: incomplete surveillance integration, restricted information sharing, and inadequate coordination for shared zoonotic threats, even where both countries were formally committed to One Health.

Ultimately, the authors make an economic as much as a scientific argument. Cost-benefit analyses of national veterinary service preparedness have found that returns to prevention investment substantially exceed the costs of outbreak response, yet preparedness funding consistently falls below optimal levels—most acutely at border posts, where capital investment in facilities, diagnostic equipment, and information technology must be sustained alongside recurrent personnel and consumables spending. Evidence from the COVID-19 pandemic adds a sobering lesson in enforcement: adherence and consistency of application were stronger determinants of epidemic control than the formal stringency of the measures themselves, suggesting that well-enforced moderate quarantine measures outperform nominally strict ones with poor compliance. Reframing border quarantine as strategic infrastructure—comparable to national laboratory systems or emergency response capacity—rather than administrative overhead, the review concludes, is the necessary condition for attracting the development bank instruments, global health security funds, and pandemic preparedness financing that LMIC systems need. Governance reform, the authors insist, is a precondition for returns on technical investment, not a parallel priority: without legal independence, enforcement authority, and accountability, no portable PCR machine or digital certificate will deliver the protection that formal regulatory mandates promise.

It is a mystery that has puzzled scientists for years. How can the world’s only winged mammals carry viruses that cause severe disease while rarely becoming seriously ill themselves?

Now researchers at Tulane University, with collaborators at Stanford University and the Centers for Disease Control, may have found a reason.

In a study published in Science Advances, the research team found that the world’s largest family of bats has two distinct copies of the genes that produce antibodies, the specialized proteins that help the immune system recognize and fight infections. Every other known mammal has only one such set. The discovery opens new avenues for understanding the evolution of immunity and how animals respond to disease.

“We’ve never seen anything like this in a mammal before,” said Hannah Frank, associate professor of ecology and evolutionary biology at Tulane University School of Science and Engineering and corresponding author of the study. “This completely changes our understanding of how mammalian immune systems can be organized and raises exciting new questions about why bats have been so evolutionarily successful and how they respond to viruses.”

The discovery was made in vesper bats, which includes more than 500 species found on every continent except Antarctica. Their remarkable evolutionary success has long intrigued scientists, and this newly discovered antibody system may offer one explanation.

Antibodies are Y-shaped proteins made of two heavy protein chains and two light protein chains. In humans and every other known mammal, those heavy chains are built from a single set of genes. Frank and her collaborators discovered that vesper bats instead possess two separate heavy-chain gene systems, giving them an entirely new way to generate antibody diversity. 

While researchers have traditionally focused on bats’ innate immune systems, Frank said this study highlights the importance of looking more closely at their adaptive immune system— the part responsible for producing antibodies.

“We think this discovery is an important piece of the puzzle,” Frank said. “It doesn’t fully explain why bats are such effective viral reservoirs, but it reveals a level of immune variety we didn’t know existed and gives us an entirely new direction to explore.”

Bats are critical pollinators, seed dispersers and natural pest controllers but also serve as natural hosts for many viruses, Frank said. Understanding how they coexist with those viruses without becoming ill may eventually help scientists better understand immune responses across species and improve strategies for preventing disease spillover.

“We’ve learned an enormous amount about immunity by studying humans and laboratory mice,” Frank said. “But the natural world is far more varied than that. Every time we study a species that has evolved differently, we have the opportunity to discover something entirely new.”

Journal

Science Advances

DOI

10.1126/sciadv.aeb6714

Avian influenza H5N1 has been a persistent threat to both wild and captive bird populations globally, with fatality rates soaring above 50% in some outbreaks. The virus’s propensity for rapid mutation and wide host range complicates traditional vaccine design, which often offers limited cross-protection and requires frequent updates to keep pace with viral evolution. By contrast, RNA replicon vaccines leverage self-amplifying RNA technology that enables robust antigen expression within host cells, eliciting potent and durable immune responses without the risks associated with live-attenuated or inactivated virus preparations. This study represents one of the first large-scale applications of RNA replicon vaccination in diverse avifauna, signaling a paradigm shift in veterinary vaccine development.

The researchers employed a replicon derived from alphaviruses, engineered to express hemagglutinin (HA) proteins specifically from H5N1 avian influenza strains. HA is a critical viral surface glycoprotein involved in host cell entry and a primary target for neutralizing antibodies. Upon administration, the RNA replicon is taken up by avian host cells, where it autonomously replicates and translates the encoded HA antigen. This in situ production of viral proteins mirrors natural infection, thereby stimulating both humoral and cellular branches of the immune system with exceptional efficiency. Importantly, the replicon system lacks the viral structural genes necessary for particle formation, eliminating the possibility of vaccine-derived infection or reversion to virulence.

The study’s scope encompassed an unprecedented spectrum of species, ranging from small passerines to large raptors and waterfowl, reflecting the heterogeneity inherent in global zoological collections. Each species received intramuscular injections of the RNA replicon vaccine, followed by rigorous monitoring for clinical signs, immune parameters, and viral shedding post-experimental challenge with pathogenic H5N1 strains. Remarkably, vaccinated birds exhibited significant protection, with a dramatic reduction in morbidity and mortality compared to controls. This efficacy surpassed previously reported benchmarks of traditional vaccination efforts, underscoring the replicon’s enhanced immunogenic profile.

Kinetics of the immune responses were characterized by early onset of neutralizing antibodies as well as sustained memory B and T cell activity. The durability of protection was especially notable: follow-up assessments at six and twelve months post-vaccination revealed persistent immunity, an essential feature for zoo populations where repeated vaccination may be logistically challenging. Additionally, the vaccine induced cross-reactive immunity against divergent H5N1 clades, hinting at the potential for broader-spectrum protection against evolving viral variants. These findings hold immense promise for simplifying vaccination regimens and reducing the logistical burden on wildlife health teams.

From a safety perspective, the RNA replicon platform demonstrated an excellent profile. No adverse reactions beyond mild and transient local inflammation were observed across species, an important consideration given the sensitivity of many exotic and endangered birds to stress and invasive procedures. The replicon’s non-integrative mechanism and rapid degradation by host nucleases further bolster its safety credentials. Concurrently, the absence of adjuvants, which can sometimes provoke unwanted side effects, makes this RNA-based strategy more tolerable and animal-friendly compared to conventional vaccine formulations.

Molecular analyses provided insights into the mechanistic underpinnings of protection. Quantitative PCR and immunohistochemistry confirmed that the replicon-driven HA antigen was robustly expressed in muscle tissues without dissemination to distal organs, mitigating concerns about off-target effects. Furthermore, vaccinated birds showed elevated upregulation of interferon-stimulated genes and cytokine markers consistent with antiviral innate immune activation. This dual stimulation of innate and adaptive defenses likely contributes to the observed rapid viral clearance upon challenge, underscoring the replicon’s capacity to orchestrate a comprehensive immunological assault.

The implications for avian conservation are profound. Many species housed in zoos are threatened by habitat loss and disease outbreaks, and H5N1 remains a persistent obstacle to sustaining captive breeding programs aimed at species recovery. The ability to immunize multiple bird taxa effectively with a single vaccine platform streamlines protective efforts and enhances resilience against unforeseen influenza incursions. Moreover, controlling H5N1 in zoo environments reduces spillover risks to wild birds and ultimately to humans, contributing to global One Health strategies aimed at preempting zoonotic pandemics.

Unexpectedly, the study also revealed intriguing interspecies differences in vaccine uptake and immune magnitude, reflective of the diverse immune system architectures among avian orders. While most species responded robustly, subtle variations in antibody titers and T cell subsets suggest that tweaking dosage regimens or delivery methods could further optimize outcomes for certain taxa. These nuances highlight the importance of species-specific immunological research to maximize vaccine utility and underscore the replicon’s adaptability as a modular platform.

Furthermore, the technological advantages of RNA replicon vaccines extend beyond avian influenza. Their modular design facilitates rapid antigen swapping, offering a versatile toolkit for confronting emerging infectious diseases in wildlife. The cold-chain independence, scalability, and synthetic nature of replicon production streamline manufacturing and distribution, enabling timely responses to outbreaks. Future research could harness this platform to target other viral pathogens affecting critical wildlife or agricultural species, potentially revolutionizing veterinary and conservation vaccinology.

In regulatory and ethical terms, the adoption of RNA replicon vaccines aligns with evolving standards emphasizing animal welfare and biosafety. The minimal environmental impact due to non-replicating vaccine particles and absence of genetic modification in host genomes reduces ecological concerns. Zoos can integrate such vaccines into health management protocols with confidence that they do not pose risks to non-target species or disrupt ecological balances, fostering sustainable practices in biodiversity preservation.

From a translational perspective, this landmark study opens avenues to engineer next-generation nucleic acid vaccines tailored to zoological species’ unique immunological landscapes. The robust protection documented in this multi-species trial affirms RNA replicon technology as a potent weapon in the fight against avian influenza. It lays the groundwork for larger field trials in diverse geographies, extended monitoring of immune memory, and development of multi-valent formulations encompassing multiple influenza subtypes to preempt antigenic drift.

The scientific community also heralds this work as a major step toward One Health integration. By intervening at the wildlife interface, the RNA replicon vaccine strategy could break chains of viral transmission that have historically precipitated global flu pandemics. Conservationists, veterinarians, and public health experts are poised to collaborate in deploying such innovations to safeguard both animal and human populations, fulfilling a critical nexus in pandemic preparedness.

In sum, the pioneering application of RNA replicon vaccination in 23 zoo bird species signals a transformative chapter in avian disease control. This elegant approach combines molecular precision, immunological potency, and pragmatic applicability across taxonomic boundaries to offer durable, broad-spectrum protection against high-consequence avian influenza strains. The approach promises not only to safeguard vulnerable avian collections from devastating disease outbreaks but also to contribute meaningfully to global efforts aimed at mitigating emergent infectious threats at the human-animal-environment interface. As research advances and field implementation scales, RNA replicon vaccines may well become the cornerstone of resilient strategies protecting biodiversity and public health alike.

Subject of Research: RNA replicon vaccination against H5N1 avian influenza in diverse zoo bird species

Article Title: RNA replicon vaccination confers long-lasting protection against H5N1 avian influenza in 23 zoo bird species

Article References:
Stettler, M., Hoby, S., Wenker, C. et al. RNA replicon vaccination confers long-lasting protection against H5N1 avian influenza in 23 zoo bird species. Nat Commun 16, 9245 (2025). https://doi.org/10.1038/s41467-025-64301-5

Image Credits: AI Generated