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Beak and feather disease virus (BFDV), the aetiological agent of Psittacine beak and feather disease (PBFD), is a significant threat to both wild and captive parrot populations globally. In Australia it has been recognised as a Key Threatening Process for endangered psittacine species. As a multi-host pathogen with structural and phenotypic constraints, BFDV provides an effective model for investigating virulence without confounding genetic effects. Virulence in infectious organisms emerges through complex selective pressures acting on both pathogens and their hosts. Shaping of these dynamics depends on host density, immunity, environmental factors, infectious load, distribution, and transmissibility, yet empirical evidence for the role of ecological specialisation remains limited. In this study naturally occurring BFDV spillover events were analysed using cophylogenetic approaches based on five years of passive surveillance data derived from submitted diagnostic samples and viral genome data which revealed novel insights into host-pathogen coevolution and transmission ecology. Phylogenetic and co-phylogenetic analyses showed a strong directional spillover pattern from psittacine hosts, particularly <i>Cacatuidae </i>and <i>Loriini</i>, into distant avian taxa such as raptors, with no evidence of reverse transmission. Furthermore, these spillover events were shaped by ecological and behavioural factors allowing evolution of virulence in cockatoos to enhance host fitness through gregarious and high-density behaviours that promote their role as symptomatic superspreaders, while non-psittacine predators likely serve as ecological dead-end hosts. <br/><br/>Arthropod insects represent one of the major pathways for viral transmission in natural ecosystems. However, avian circoviruses have received limited attention in this context. High viral loads in parasitic mites and haematophagous flies further suggest that these ectoparasites could facilitate the mechanical transmission of BFDV. Hippoboscid flies from the natural nesting sites of ten psittacine and non-psittacine hosts were screened in this study for the presence of BFDV DNA using sensitive qPCR in this study, where all samples found to be negative. Experimental feeding trials with houseflies (<i>Musca domestica</i>) and house crickets (<i>Acheta domesticus</i>) demonstrated that BFDV rep DNA persisted in houseflies across transstadial stages for up to 20 days, with virions detectable for 2 days post-feeding. In crickets, viral DNA also persisted for 20 days but declined sharply after Day 5, consistent with a lack of replication. These results revealed prolonged, non-propagative viral carriage in insects, highlighting their potential for mechanical transmission under natural conditions.<br/><br/>Effective early-life immunisation of nestlings and fledglings is essential to achieve seroconversion and protect against high environmental viral loads. Current experimental PBFD vaccines, which rely on recombinant capsid proteins delivered via injection, are poorly suited for large-scale deployment and early-life administration. This study developed a spray-dried vaccine formulation aimed at improving thermostability, shelf-life, and mucosal delivery in juvenile birds. Using a Design of Experiment approach, spray-drying parameters were optimised to produce recombinant capsid macroparticles of 3.1-9.5 µm size, facilitating efficient uptake by antigen-presenting cells. The resulting virus-like particle (VLP)-based vaccine maintained safe moisture content, preserved protein stability and antigenicity for 12 months at room temperature, and demonstrated superior thermostability and extended shelf life, confirming both its stability and strong immunogenic potential.<br/><br/>Compared to conventional parenteral vaccines, spray-dried formulations offer improved thermostability, longer shelf life, and the potential for alternative administration routes, including oral, oculonasal, and mucosal delivery. Existing experimental PBFD subunit vaccines rely on water-in-oil emulsions and intramuscular injection, which can be challenging in very young birds and are limited by cold chain requirements. Hence, the novel spray-dried VLP based BFDV subunit vaccine was evaluated in experimental chicken model for seroconversion and safety following intramuscular, oculonasal, and intra-cloacal administration. After the first booster, intramuscular vaccination induced a strong seroconversion, 3.3-3.5 times higher than controls (<i>p <</i> 0.005), whereas oculonasal and intra-cloacal routes showed no detectable response. Following the second booster, moderate humoral responses appeared in some oculonasal individuals, but the highest immunity was achieved intramuscularly, with anti-BFDV antibody binding titres reaching 1:409,600. Histopathological and haematological analyses showed no adverse effects, confirming the safety and immunogenicity of this spray-dried vaccine formulation. Collectively, these results integrate insights from viral ecology with applied conservation, providing a proof-of-concept platform for the development of effective mucosal immunisation strategies.<br/>