Wildlife susceptibility to infectious diseases at global scales.

Disease transmission prediction across wildlife is crucial for risk assessment of emerging infectious diseases. Susceptibility of host species to pathogens is influenced by the geographic, environmental, and phylogenetic context of the specific system under study. We used machine learning to analyze how such variables influence pathogen incidence for multihost pathogen assemblages, including one of direct transmission (coronaviruses and bats) and two vector-borne systems (West Nile Virus [WNV] and birds, and malaria and birds). Here we show that this methodology is able to provide reliable global spatial susceptibility predictions for the studied host-pathogen systems, even when using a small amount of incidence information (i.e., [Formula: see text] of information in a database). We found that avian malaria was mostly affected by environmental factors and by an interaction between phylogeny and geography, and WNV susceptibility was mostly influenced by phylogeny and by the interaction between geographic and environmental distances, whereas coronavirus susceptibility was mostly affected by geography. This approach will help to direct surveillance and field efforts providing cost-effective decisions on where to invest limited resources.

Mining increases the prevalence of avian haemosporidian parasites in Northeast Amazonia.

Studies contrasting parasite prevalence and host-parasite community structure between pristine and disturbed environments will improve our understanding of how deforestation affects disease transmission and parasite extinction. To determine how infection rates of a common and diverse group of avian blood parasites (Plasmodium and Haemoproteus) respond to changes in avian host composition after mining, we surveyed 25 bird communities from pristine forests (two forest types: plateau and hillside) and reforested sites in Northeast Amazonia. Infection rates and both parasite and avian host community structure exhibited considerable variation across the deforestation gradient. In opposition to the emerging pattern of lower avian haemosporidian prevalence in disturbed tropical forests in Africa, we show that secondary forests had higher haemosporidian prevalence in one of the largest mining areas of Amazonia. The dissimilarity displayed by bird communities may explain, in part, the higher prevalence of Haemoproteus in reforested areas owing to the tolerance of some bird species to open-canopy forest habitat. On the other hand, deforestation may cause local extinction of Plasmodium parasites due to the loss of their avian hosts that depend on closed-canopy primary forest habitats. Our results demonstrate that forest loss induced by anthropogenic changes can affect a host-parasite system and disturb both parasite transmission and diversity.

Culex quinquefasciatus (Diptera: Culicidae) survivorship following the ingestion of bird blood infected with Haemoproteus sp. parasites.

Arthropod vectors are frequently exposed to a diverse assemblage of parasites, but the consequence of these infections on their biology and behavior are poorly understood. We experimentally evaluated whether the ingestion of a common protozoan parasite of avian hosts (Haemoproteus spp.; Haemosporida: Haemoproteidae) impacted the survivorship of Culex quinquefasciatus (Say) (Diptera: Culicidae). Blood was collected from wild northern cardinals (Cardinalis cardinalis) in College Station, Texas, and screened for the presence of Haemoproteus spp. parasites using microscopic and molecular methods. Experimental groups of Cx. quinquefasciatus mosquitoes were offered Haemoproteus-positive cardinal blood through an artificial feeding apparatus, while control groups received Haemoproteus-negative cardinal blood or domestic canary (Serinus canaria domestica) blood. Culex quinquefasciatus mosquitoes exposed to Haemoproteus infected cardinal blood survived significantly fewer days than mosquitoes that ingested Haemoproteus-negative cardinal blood. The survival of mosquitoes fed on positive cardinal blood had a median survival time of 18 days post-exposure and the survival of mosquitoes fed on negative cardinal blood exceeded 50% across the 30 day observation period. Additionally, mosquitoes that fed on canary controls survived significantly fewer days than cardinal negative controls, with canary control mosquitoes having a median survival time of 17 days. This study further supports prior observations that Haemoproteus parasites can be pathogenic to bird-biting mosquitoes, and suggests that Haemoproteus parasites may indirectly suppress the transmission of co-circulating vector-borne pathogens by modulating vector survivorship. Our results also suggest that even in the absence of parasite infection, bloodmeals from different bird species can influence mosquito survivorship.

COMPARISON BETWEEN STANDARD ZOO QUARANTINE PRACTICES AND RISK-BASED MANAGEMENT OF ANIMAL TRANSFERS: A RETROSPECTIVE ANALYSIS OF AVIAN ACQUISITION MORBIDITY AND MORTALITY (2013-2018).

Beginning 01 January 2016, for all animals transferred into the collection, Disney's Animal Kingdom used a risk-based process that relies on pathogen hazard identification and then assessment and mitigation of the risk for each identified pathogen hazard. Data on morbidity, mortality, and disease introduction was compared for birds transferred in pre- and post-risk-based processes used during the period 2013-2018. When assessing morbidity within 3 mo of acquisition, logistic regression revealed that birds entering "straight to collection" had lower morbidity rates than those entering with either "standard quarantine" or "risk-based standard quarantine" methods (P = 0.032). Mortality within 3 mo of acquisition was not significantly different between straight-to-collection and standard quarantine or risk-based standard quarantine methods (P = 0.40). In addition, no transmissible pathogens of concern were introduced with acquired birds using either method. Implementation of a risk-based approach to animal transfers between zoos and aquariums may be an alternative method that does not pose a greater risk to animal morbidity or mortality while still protecting the collection from disease introduction.

BLOOD PARASITE INFECTIONS IN STRIGIFORMES AND PSITTACIFORMES SPECIES IN CAPTIVITY WITH A NEW RECORD OF POTENTIAL FATAL BLOOD PARASITE TRANSMISSION TO PARROTS.

Although parrot species are infrequently infected by hemoparasites in the wild, some fatal infections have been reported in captive individuals. Conversely birds of prey are frequently infected by hemoparasites. In this study, 193 captive birds from Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) centers in Madrid, Spain, belonging to orders Psittaciformes, Accipitriformes, Strigiformes, and Falconiformes, were blood-sampled in search of parasite infections. Molecular and microscopic analyses were conducted to detect parasites of the following genera: Haemoproteus, Plasmodium, Leucocytozoon, Trypanosoma, Babesia, and Lankesterella. Infections by microfilariae and Coccidia were also searched in blood samples. Surprisingly, infections by Haemoproteus syrnii, a common parasite from owls, were detected in the cadavers of two species of parrots, Trichoglossus haematodus and Psittacula cyanocephala. The same haplotype was also detected in the cadavers of two owl species, Tyto alba and Strix rufipes. All these birds were housed and died in the same center. Infections by species of Plasmodium, Leucocytozoon, and Trypanosoma were also found in different species of raptors. Nocturnal raptors (Strigiformes) show significantly higher prevalence of infection by blood parasites than diurnal raptors (Falconiformes and Accipitriformes). In conclusion, a potential fatal transmission of Haemoproteus syrnii, from Strigiformes to Psittaciformes species, is reported and several infections by different blood parasites were detected in birds of prey. These results emphasize the importance of increasing prevention measures to avoid or reduce the transmission of blood parasites among birds from different species housed in these types of centers.

Complete sporogony of the blood parasite Haemoproteus nucleocondensus in common biting midges: why is its transmission interrupted in Europe?

Haemoproteus species (Haemoproteidae) are widespread blood parasites and are transmitted by Culicoides biting midges and Hippoboscidae louse flies. Although these pathogens may cause morbidity or mortality, the vectors and patterns of transmission remain unknown for the great majority of avian haemoproteids. Haemoproteus nucleocondensus has been frequently reported in Europe in great reed warblers Acrocephalus arundinaceus after their arrival from African wintering grounds, but this infection has not been found in juveniles at the breeding sites. The factors that prevent its transmission remain unclear. This study was designed to test whether the sporogony of H. nucleocondensus (lineage hGRW8) can be completed in Culicoides impunctatus, one of the most abundant European biting midge species. Wild-caught females were infected with H. nucleocondensus from great reed warblers. Microscopic examination and PCR-based methods were used to detect sporogonic stages and to confirm species identity. This study showed that H. nucleocondensus completes sporogony in C. impunctatus, suggesting that there are no obstacles to its transmission from the point of view of vector availability and average temperature in Northern Europe. We discuss other ecological factors which should be considered to explain why the transmission of H. nucleocondensus and some other Southern origin haemosporidians are interrupted in North Europe.

Crimean-Congo Hemorrhagic Fever Virus Genome in Tick from Migratory Bird, Italy.

We detected Crimean-Congo hemorrhagic fever virus in a Hyalomma rufipes nymph collected from a whinchat (Saxicola rubetra) on the island of Ventotene in April 2017. Partial genome sequences suggest the virus originated in Africa. Detection of the genome of this virus in Italy confirms its potential dispersion through migratory birds.

Mosquito-borne epornitic flaviviruses: an update and review.

West Nile Virus, Usutu virus, Bagaza virus, Israel turkey encephalitis virus and Tembusu virus currently constitute the five flaviviruses transmitted by mosquito bites with a marked pathogenicity for birds. They have been identified as the causative agents of severe neurological symptoms, drop in egg production and/or mortalities among avian hosts. They have also recently shown an expansion of their geographic distribution and/or a rise in cases of human infection. This paper is the first up-to-date review of the pathology of these flaviviruses in birds, with a special emphasis on the difference in susceptibility among avian species, in order to understand the specificity of the host spectrum of each of these viruses. Furthermore, given the lack of a clear prophylactic approach against these viruses in birds, a meta-analysis of vaccination trials conducted to date on these animals is given to constitute a solid platform from which designing future studies.

Discovery and Sequence Analysis of Four Deltacoronaviruses from Birds in the Middle East Reveal Interspecies Jumping with Recombination as a Potential Mechanism for Avian-to-Avian and Avian-to-Mammalian Transmission.

The emergence of Middle East respiratory syndrome showed once again that coronaviruses (CoVs) in animals are potential source for epidemics in humans. To explore the diversity of deltacoronaviruses in animals in the Middle East, we tested fecal samples from 1,356 mammals and birds in Dubai, The United Arab Emirates. Four novel deltacoronaviruses were detected from eight birds of four species by reverse transcription-PCR (RT-PCR): FalCoV UAE-HKU27 from a falcon, HouCoV UAE-HKU28 from a houbara bustard, PiCoV UAE-HKU29 from a pigeon, and QuaCoV UAE-HKU30 from five quails. Complete genome sequencing showed that FalCoV UAE-HKU27, HouCoV UAE-HKU28, and PiCoV UAE-HKU29 belong to the same CoV species, suggesting recent interspecies transmission between falcons and their prey, houbara bustards and pigeons, possibly along the food chain. Western blotting detected specific anti-FalCoV UAE-HKU27 antibodies in 33 (75%) of 44 falcon serum samples, supporting genuine infection in falcons after virus acquisition. QuaCoV UAE-HKU30 belongs to the same CoV species as porcine coronavirus HKU15 (PorCoV HKU15) and sparrow coronavirus HKU17 (SpCoV HKU17), discovered previously from swine and tree sparrows, respectively, supporting avian-to-swine transmission. Recombination involving the spike protein is common among deltacoronaviruses, which may facilitate cross-species transmission. FalCoV UAE-HKU27, HouCoV UAE-HKU28, and PiCoV UAE-HKU29 originated from recombination between white-eye coronavirus HKU16 (WECoV HKU16) and magpie robin coronavirus HKU18 (MRCoV HKU18), QuaCoV UAE-HKU30 from recombination between PorCoV HKU15/SpCoV HKU17 and munia coronavirus HKU13 (MunCoV HKU13), and PorCoV HKU15 from recombination between SpCoV HKU17 and bulbul coronavirus HKU11 (BuCoV HKU11). Birds in the Middle East are hosts for diverse deltacoronaviruses with potential for interspecies transmission.IMPORTANCE During an attempt to explore the diversity of deltacoronaviruses among mammals and birds in Dubai, four novel deltacoronaviruses were detected in fecal samples from eight birds of four different species: FalCoV UAE-HKU27 from a falcon, HouCoV UAE-HKU28 from a houbara bustard, PiCoV UAE-HKU29 from a pigeon, and QuaCoV UAE-HKU30 from five quails. Genome analysis revealed evidence of recent interspecies transmission between falcons and their prey, houbara bustards and pigeons, possibly along the food chain, as well as avian-to-swine transmission. Recombination, which is known to occur frequently in some coronaviruses, was also common among these deltacoronaviruses and occurred predominantly at the spike region. Such recombination, involving the receptor binding protein, may contribute to the emergence of new viruses capable of infecting new hosts. Birds in the Middle East are hosts for diverse deltacoronaviruses with potential for interspecies transmission.

Louse flies of Eleonora's falcons that also feed on their prey are evolutionary dead-end hosts for blood parasites.

Host shifts are widespread among avian haemosporidians, although the success of transmission depends upon parasite-host and parasite-vector compatibility. Insular avifaunas are typically characterized by a low prevalence and diversity of haemosporidians, although the underlying ecological and evolutionary processes remain unclear. We investigated the parasite transmission network in an insular system formed by Eleonora's falcons (the avian host), louse flies that parasitize the falcons (the potential vector), and haemosporidians (the parasites). We found a great diversity of parasites in louse flies (16 Haemoproteus and 6 Plasmodium lineages) that did not match with lineages previously found infecting adult falcons (only one shared lineage). Because Eleonora's falcon feeds on migratory passerines hunted over the ocean, we sampled falcon kills in search of the origin of parasites found in louse flies. Surprisingly, louse flies shared 10 of the 18 different parasite lineages infecting falcon kills. Phylogenetic analyses revealed that all lineages found in louse flies (including five new lineages) corresponded to Haemoproteus and Plasmodium parasites infecting Passeriformes. We found molecular evidence of louse flies feeding on passerines hunted by falcons. The lack of infection in nestlings and the mismatch between the lineages isolated in adult falcons and louse flies suggest that despite louse flies' contact with a diverse array of parasites, no successful transmission to Eleonora's falcon occurs. This could be due to the falcons' resistance to infection, the inability of parasites to develop in these phylogenetically distant species, or the inability of haemosporidian lineages to complete their development in louse flies.

Zoonotic diseases from birds to humans in Vietnam: possible diseases and their associated risk factors.

In recent decades, exceeding 60% of infectious cases in human beings are originated from pathogenic agents related to feral or companion animals. This figure continues to swiftly increase due to excessive exposure between human and contaminated hosts by means of applying unhygienic farming practices throughout society. In Asia countries-renowned for lax regulation towards animal-trading markets-have experienced tremendous outbreaks of zoonotic diseases every year. Meanwhile, various epidemic surges were first reported in the residential area of China-one of the largest distributor of all animal products on the planet. Some noticeable illnesses comprising of A/H5N1 or H7N9-known as avian influenza which transmitted from poultry and also wild birds-have caused inevitable disquiet among inhabitants. Indeed, poultry farming industry in China has witnessed dynamic evolution for the past two decades, both in quantity and degree of output per individual. Together with this pervasive expansion, zoonotic diseases from poultry have incessantly emerged as a latent threat to the surrounding residents in entire Asia and also European countries. Without strict exporting legislation, Vietnam is now facing the serious problem in terms of poultry distribution between the two countries' border. Even though several disease investigations have been conducted by many researchers, the disease epidemiology or transmission methods among people remained blurred and need to be further elucidated. In this paper, our aim is to provide a laconic review of common zoonotic diseases spread in Vietnam, outstanding cases and several factors predisposing to this alarming situation.

Usutu virus: A new threat?

Usutu virus (USUV) is an emerging arbovirus that was first isolated in South Africa in 1959. This Flavivirus is maintained in the environment through a typical enzootic cycle involving mosquitoes and birds. USUV has spread to a large part of the European continent over the two decades mainly leading to substantial avian mortalities with a significant recrudescence of bird infections recorded throughout Europe within the few last years. USUV infection in humans is considered to be most often asymptomatic or to cause mild clinical signs. Nonetheless, a few cases of neurological complications such as encephalitis or meningoencephalitis have been reported. USUV and West Nile virus (WNV) share many features, like a close phylogenetic relatedness and a similar ecology, with co-circulation frequently observed in nature. However, USUV has been much less studied and in-depth comparisons of the biology of these viruses are yet rare. In this review, we discuss the main body of knowledge regarding USUV and compare it with the literature on WNV, addressing in particular virological and clinical aspects, and pointing data gaps.

Experimental model of oral transmissible AA amyloidosis in quails.

In poultry and zoo birds, mass outbreaks of amyloid A (AA) amyloidosis are often reported, and horizontal transmission is considered as one of the causes. However, oral transmission of avian AA amyloidosis in nature has been unclear. In order to clarify the horizontal transmission of avian AA amyloidosis, basic research using an appropriate oral transmission model is necessary. In this study, we developed an oral transmission model of AA amyloidosis using quails, and assessed the oral transmission efficiency of AA amyloidosis in quails and mice. Young quails, adult quails, and young mice received inflammatory stimulation with lipopolysaccharide; simultaneously, homogeneous amyloid fibrils were orally or intravenously administered. By histological examination, induction of amyloidosis by oral or intravenous administration of amyloid was confirmed in all species. Furthermore, both quail and murine AA amyloidosis were orally transmitted in a dose-dependent manner. These results support the possibility of horizontal transmission of avian AA amyloidosis in nature. This model will be able to contribute to the elucidation of spontaneous horizontal transmission of avian AA amyloidosis in the future. RESEARCH HIGHLIGHTS Quail AA amyloidosis was orally transmitted in a dose-dependent manner. Oral transmission was less efficient than intravenous transmission. In-cage horizontal transmission did not occur during 4-week cohabitation. Amyloid deposition in tissues of quail was grossly visible.

High susceptibility of the laboratory-reared biting midges Culicoides nubeculosus to Haemoproteus infections, with review on Culicoides species that transmit avian haemoproteids.

Haemosporidian parasites belonging to Haemoproteus cause avian diseases, however, vectors remain unidentified for the majority of described species. We used the laboratory-reared biting midges Culicoides nubeculosus to determine if the sporogonic development of three widespread Haemoproteus parasites completes in this insect. The midges were reared and fed on one common blackbird, white wagtail and thrush nightingale naturally infected with Haemoproteus minutus, Haemoproteus motacillae and Haemoproteus attenuatus, respectively. The engorged females were dissected in order to follow their sporogonic development. Microscopic examination was used to identify sporogonic stages. Bayesian phylogeny based on partial cytochrome b gene was constructed in order to determine phylogenetic relationships among Culicoides species-transmitted haemoproteids. All three parasites completed sporogony. Phylogenetic analysis placed Culicoides species transmitted haemoproteids in one well-supported clade, proving that such analysis readily indicates groups of dipteran insects transmitting avian haemoproteids. Available data show that 11 species of Culicoides have been proved to support complete sporogony of 18 species of avian haemoproteids. The majority of Culicoides species can act as vectors for many Haemoproteus parasites, indicating the low specificity of these parasites to biting midges, whose are globally distributed. This calls for control of haemoproteid infections during geographical translocation of infected birds.

The global biogeography of avian haemosporidian parasites is characterized by local diversification and intercontinental dispersal.

The biogeographic histories of parasites and pathogens are infrequently compared with those of free-living species, including their hosts. Documenting the frequency with which parasites and pathogens disperse across geographic regions contributes to understanding not only their evolution, but also the likelihood that they may become emerging infectious diseases. Haemosporidian parasites of birds (parasite genera Plasmodium, Haemoproteus and Leucocytozoon) are globally distributed, dipteran-vectored parasites. To date, over 2000 avian haemosporidian lineages have been designated by molecular barcoding methods. To achieve their current distributions, some lineages must have dispersed long distances, often over water. Here we quantify such events using the global avian haemosporidian database MalAvi and additional records primarily from the Americas. We scored lineages as belonging to one or more global biogeographic regions based on infection records. Most lineages were restricted to a single region but some were globally distributed. We also used part of the cytochrome b gene to create genus-level parasite phylogenies and scored well-supported nodes as having descendant lineages in regional sympatry or allopatry. Descendant sister lineages of Plasmodium, Haemoproteus and Leucocytozoon were distributed in allopatry in 11, 16 and 15% of investigated nodes, respectively. Although a small but significant fraction of the molecular variance in cytochrome b of all three genera could be explained by biogeographic region, global parasite dispersal likely contributed to the majority of the unexplained variance. Our results suggest that avian haemosporidian parasites have faced few geographic barriers to dispersal over their evolutionary history.

Linked seasonal outbreaks of Salmonella Typhimurium among passerine birds, domestic cats and humans, Sweden, 2009 to 2016.

In 2016, an outbreak of Salmonella Typhimurium (STm) with multilocus variable-number tandem repeat analysis (MLVA) profiles historically associated with passerine birds (2-[11-15]-[3-4]-NA-212) occurred among passerines, cats and humans in Sweden. Our retrospective observational study investigated the outbreak and revisited historical data from 2009-16 to identify seasonality, phylogeography and other characteristics of this STm variant. Outbreak isolates were analysed by whole-genome single nucleotide polymorphism (SNP) typing. The number of notified cases of passerine-associated STm among passerines, cats and humans per month and county, and their MLVA profiles, were compared to birdwatchers' counts of passerines. Seasonal trend decomposition and correlation analysis was performed. Outbreak isolates did not cluster by host on SNP level. Passerine-associated STm was seasonal for birds, cats and humans, with a peak in March. Cases and counts of passerines at bird feeders varied between years. The incidence of passerine-associated STm infections in humans was higher in the boreal north compared with the southern and capital regions, consistent with passerine population densities. Seasonal mass migration of passerines appears to cause STm outbreaks among cats certain years in Sweden, most likely via predation on weakened birds. Outbreaks among humans can follow, presumably caused by contact with cats or environmental contamination.

Molecular identification of potential intermediate hosts of Aulonocephalus pennula from the order Orthoptera.

Aulonocephalus pennula is a heteroxenous nematode that commonly infects a declining game bird, the northern bobwhite quail (Colinus virginianus). There is a lack of information on the life cycle of A. pennula and the potential effects of infection on bobwhites. In order to better understand the life cycle of this parasite, various species from the order Orthoptera were collected from a field site in Mitchell County, Texas. Using polymerase chain reaction (PCR), nine potential intermediate hosts were identified from the 35 orthopteran species collected. Later, ten live specimens were collected to identify larvae within the potential intermediate hosts. Larvae were present in three of these and were sent for sequencing. Similarly, the presence of larvae was confirmed from extra tissues of samples identified as positive with PCR. This was the first study to document potential intermediate hosts, but future studies are needed to confirm that these species are capable of transmitting infection to bobwhite. However, this study demonstrates that PCR has increased sensitivity and may be a valuable tool when determining intermediate hosts.

Wild waterfowl as potential vectors of Vibrio cholerae and Aeromonas species.

OBJECTIVE: To study the hypothesis that migratory waterfowl are possible disseminators of Vibrio cholerae and Aeromonas. METHODS: We monitored the presence of V. cholerae and Aeromonas in three wild waterfowl species. RESULTS: V. cholerae and Aeromonas species were isolated and identified from intestine samples of little egrets and black-crowned night herons. Only Aeromonas species were isolated from black-headed gulls. The majority of Aeromonas isolates were A. veronii. Twenty-three V. cholerae serogroups were identified. V. cholerae serogroup O1 was found in the intestine DNA extractions from four little egrets and black-crowned night herons; six birds carried cholera toxin subunit A gene. CONCLUSION: Wild waterfowl species may carry pathogenic V. cholerae O1 and non-O1 serogroups and Aeromonas species in their intestine. The migration of waterfowl is a potential mechanism for global distribution of V. cholerae and Aeromonas.

Flanders hapavirus in western North America.

Flanders virus (FLAV; family Rhabdoviridae) is a mosquito-borne hapavirus with no known pathology that is frequently isolated during arbovirus surveillance programs. Here, we document the presence of FLAV in Culex tarsalis mosquitoes and a Canada goose (Branta canadensis) collected in western North America, outside of the currently recognized range of FLAV. Until now, FLAV-like viruses detected in the western United States were assumed to be Hart Park virus (HPV, family Rhabdoviridae), a closely related congener. A re-examination of archived viral isolates revealed that FLAV was circulating in California as early as 1963. FLAV also was isolated in Nebraska, Colorado, South Dakota, North Dakota, and Saskatchewan, Canada. Phylogenetic analysis of the U1 pseudogene for 117 taxa and eight nuclear genes for 15 taxa demonstrated no distinct clustering between western FLAV isolates. Assuming the range of FLAV has been expanding west, these results indicate that FLAV likely spread west following multiple invasion events. However, it remains to be determined if the detection of FLAV in western North America is due to expansion or is a result of enhanced arbovirus surveillance or diagnostic techniques. Currently, the impact of FLAV infection remains unknown.

Molecular characterization of fowl aviadenoviruses species D and E associated with inclusion body hepatitis in chickens and falcons indicates possible cross-species transmission.

During the period from 2015 to 2017, frequent outbreaks of inclusion body hepatitis (IBH) were observed in broiler chickens and falcons in Saudi Arabia. Fifty samples were collected from both species. The histopathological examination and polymerase chain reaction confirmed the IBH infection in eight samples (five samples from chickens and three samples from falcons). The genomic sequence and phylogenetic analysis based on nucleotide and amino acid sequences of Saudi strains, reference fowl aviadenoviruses (FAdVs) and field viruses available in Genbank revealed that all investigated FAdVs clustered into FAdV-2 (species D) and FAdV-6 (species E). The host-dependent characterization revealed that falcon origin strains showed low identity (∼35%) with falcon adenoviruses isolated from USA, which clustered into a separate group. The identification of FAdV-D and FAdV-E in diseased falcons and chickens indicates cross-species transmission although falcons and chickens are phylogenetically different. The control of IBH infection in falcons and chickens should be based on the separation of carriers and susceptible chickens as well as falcons to prevent cross-species contact. Vaccination is an important method for prevention of IBH. The characterization of newly emerging FAdV strains provides valuable information for the development of an efficacious control strategy based on the molecular structure of current circulating FAdV strains in different species of birds.