Detection of tick-borne pathogens in wild birds and their ticks in Western Siberia and high level of their mismatch

Uropygial gland microbiota of nearctic-neotropical migrants vary with season and migration distance

Symbiotic microbiota are important drivers of host behaviour, health, and fitness. While most studies focus on humans, model organisms, and domestic or economically important species, research investigating the role of host microbiota in wild populations is rapidly accumulating. Most studies focus on the gut microbiota; however, skin and other glandular microbiota also play an important role in shaping traits that may impact host fitness. The uropygial gland is an important source of chemical cues and harbours diverse microbes that could mediate chemical communication in birds, so determining the factors most important in shaping host microbiota should improve our understanding of microbially-mediated chemical communication. Hypothesizing that temporal, geographic, and taxonomic effects influence host microbiota, we evaluated the effects of season, migration distance, and taxonomy on the uropygial gland microbiota of 18 passerine species from 11 families. By sampling 473 birds at a single stopover location during spring and fall migration and using 16S rRNA sequencing, we demonstrate that season, followed by migration distance, had the strongest influence on uropygial gland microbial community composition. While statistically significant, taxonomic family and species had only weak effects on gland microbiota. Given that temporal effects on gland microbiota were nearly ubiquitous among the species we tested, determining the consequences of and mechanisms driving this seasonal variation are important next steps.

Genome sequence of Ehrlichia muris from Ixodes ricinus collected in Italy on a migratory bird provides epidemiological and evolutionary insights

Ticks are prominent vectors of several zoonotic diseases. Tick-borne pathogens include the members of the genus Ehrlichia, which are obligate intracellular bacteria infecting immune and hematopoietic cells. Ehrlichia muris predominantly affects rodents, but was also reported to be a human pathogen. The known geographical distribution of this bacterium ranges from Asia, to the USA and eastern Europe. In the present work, we report the finding of E. muris in an Ixodes ricinus tick collected from a migratory bird (Turdus iliacus) in Italy, southern Europe. We sequenced the total DNA from this tick sample, and, thanks to a dedicated bioinformatic pipeline, selectively assembled the genome of the bacterium, which represents the first one for E. muris from Europe. Phylogenetic and comparative genomic analyses were then performed. Accounting for tick species distribution, bird migratory routes, and molecular phylogeny of the bacterium, it is likely that this bird transported the tick to Italy from an endemic area of E. muris, such as eastern Europe. In addition, comparative genomic analyses highlighted that E. muris and other Ehrlichia spp. display copy number variations in two families of membrane proteins, likely due to recent gene duplication, deletion and recombination events. These differences are probably a source of variability for surface antigens to evade host immunity, with a potential role in host adaptation and specificity. The present results underline the impact of migratory birds on the spread of tick-borne pathogens towards non-endemic areas, highlighting the need for further epidemiological surveillance at bird ringing stations in Italy, and advocating further investigations on possible local transmission of E. muris in competent mammalian hosts.

East-to-west dispersal of bird-associated ixodid ticks in the northern Palaearctic: Review of already reported tick species according to longitudinal migratory avian hosts and first evidence on the genetic connectedness of Ixodes apronophorus between Siberia and Europe

Birds are long-known as important disseminators of ixodid ticks, in which context mostly their latitudinal, south-to-north migration is considered. However, several bird species that occur in the eastern part of the northern Palaearctic are known to migrate westward. In this study, a female tick collected from the sedge warbler, Acrocephalus schoenobaenus, in Lithuania was identified morphologically and analyzed with molecular-phylogenetic methods. In addition, literature data were reviewed on ixodid tick species known to be associated with birds that have recorded east-to-west migratory route in the Palaearctic. The tick collected from A. schoenobaenus was morphologically identified as Ixodes apronophorus. Two mitochondrial genetic markers for this specimen showed 100% identity with a conspecific tick reported previously in Western Siberia, Russia. Based on literature data, as many as 82 bird species from 11 orders were found to have records of ringing in the easternmost part of the northern Palaearctic and recaptures in Europe. Of these bird species, 31 ixodid tick species were reported in the Euro-Siberian region. Nearly all passeriform bird species with east-to-west migration were reported to carry ticks, whereas no reports of tick infestation were documented from the majority of wetland-associated bird species, mostly from the orders Anseriformes and Charadriiformes. The first European sequences of bona fide I. apronophorus revealed genetic connectedness with conspecific ticks reported from Siberia. Since the principal hosts of this tick species are rodents which do not migrate large distances, the most likely explanation for genetic similarity in this direction is dispersal of this tick species via migratory birds. Given the high number of tick species that are known to associate with bird species migrating in westward direction, this appears to be an important means of the gene flow between geographically distant tick populations in the northern Palaearctic.

Ixodes ricinus as potential vector for Usutu virus

Usutu virus (USUV) is an emerging flavivirus that is maintained in an enzootic cycle with mosquitoes as vectors and birds as amplifying hosts. In Europe, the virus has caused mass mortality of wild birds, mainly among Common Blackbird (Turdus merula) populations. While mosquitoes are the primary vectors for USUV, Common Blackbirds and other avian species are exposed to other arthropod ectoparasites, such as ticks. It is unknown, however, if ticks can maintain and transmit USUV. We addressed this question using in vitro and in vivo experiments and field collected data. USUV replicated in IRE/CTVM19 Ixodes ricinus tick cells and in injected ticks. Moreover, I. ricinus nymphs acquired the virus via artificial membrane blood-feeding and maintained the virus for at least 70 days. Transstadial transmission of USUV from nymphs to adults was confirmed in 4.9% of the ticks. USUV disseminated from the midgut to the haemocoel, and was transmitted via the saliva of the tick during artificial membrane blood-feeding. We further explored the role of ticks by monitoring USUV in questing ticks and in ticks feeding on wild birds in the Netherlands between 2016 and 2019. In total, 622 wild birds and the Ixodes ticks they carried were tested for USUV RNA. Of these birds, 48 (7.7%) carried USUV-positive ticks. The presence of negative-sense USUV RNA in ticks, as confirmed via small RNA-sequencing, showed active virus replication. In contrast, we did not detect USUV in 15,381 questing ticks collected in 2017 and 2019. We conclude that I. ricinus can be infected with USUV and can transstadially and horizontally transmit USUV. However, in comparison to mosquito-borne transmission, the role of I. ricinus ticks in the epidemiology of USUV is expected to be minor.

Molecular evidence of Bartonella spp. in tropical wild birds from the Brazilian Pantanal, the largest wetland in South America

Despite the worldwide occurrence of bartonellae in a broad range of mammal species, in which they usually cause a long-lasting erythrocytic bacteremia, few studies reported Bartonella spp. in avian hosts. The present work aimed to investigate the occurrence and molecular identity of Bartonella spp. infecting birds in the Pantanal wetland, central-western Brazil using a multigene approach. For this purpose, blood samples were collected from 517 individuals from 13 avian orders in the states of Mato Grosso and Mato Groso do Sul. DNA was extracted from avian blood and 500/517 (96.7%) samples were positive in a conventional PCR targeting the avian β-actin gene. Nineteen (3.8%) out of 500 avian blood samples were positive in a qPCR assay for Bartonella spp. based on the nuoG gene. Among 19 avian blood DNA samples positive in the qPCR for Bartonella spp., 12 were also positive in the qPCR for Bartonella based on the 16S-23S RNA Intergenic region (ITS). In the PCR assays performed for molecular characterization, one 16S rRNA, three ribC, and one nuoG sequences were obtained. Based on BLASTn results, while 1 nuoG, 2 ribC, and 2 ITS sequences showed high identity to Bartonella henselae, one 16S rRNA and 2 ITS showed high similarity to Bartonella machadoae in the sampled birds. Bartonella spp. related to B. henselae and B. machadoae were detected, for the first time, in wild birds from the Brazilian Pantanal.

Transboundary determinants of avian zoonotic infectious diseases: challenges for strengthening research capacity and connecting surveillance networks

As the climate changes, global systems have become increasingly unstable and unpredictable. This is particularly true for many disease systems, including subtypes of highly pathogenic avian influenzas (HPAIs) that are circulating the world. Ecological patterns once thought stable are changing, bringing new populations and organisms into contact with one another. Wild birds continue to be hosts and reservoirs for numerous zoonotic pathogens, and strains of HPAI and other pathogens have been introduced into new regions via migrating birds and transboundary trade of wild birds. With these expanding environmental changes, it is even more crucial that regions or counties that previously did not have surveillance programs develop the appropriate skills to sample wild birds and add to the understanding of pathogens in migratory and breeding birds through research. For example, little is known about wild bird infectious diseases and migration along the Mediterranean and Black Sea Flyway (MBSF), which connects Europe, Asia, and Africa. Focusing on avian influenza and the microbiome in migratory wild birds along the MBSF, this project seeks to understand the determinants of transboundary disease propagation and coinfection in regions that are connected by this flyway. Through the creation of a threat reduction network for avian diseases (Avian Zoonotic Disease Network, AZDN) in three countries along the MBSF (Georgia, Ukraine, and Jordan), this project is strengthening capacities for disease diagnostics; microbiomes; ecoimmunology; field biosafety; proper wildlife capture and handling; experimental design; statistical analysis; and vector sampling and biology. Here, we cover what is required to build a wild bird infectious disease research and surveillance program, which includes learning skills in proper bird capture and handling; biosafety and biosecurity; permits; next generation sequencing; leading-edge bioinformatics and statistical analyses; and vector and environmental sampling. Creating connected networks for avian influenzas and other pathogen surveillance will increase coordination and strengthen biosurveillance globally in wild birds.

The Viromes of Mosquitoes from the Natural Landscapes of Western Siberia

The metagenomic analysis of mosquitoes allows for the genetic characterization of mosquito-associated viruses in different regions of the world. This study applied a metagenomic approach to identify novel viral sequences in seven species of mosquitoes collected from the Novosibirsk region of western Siberia. Using NGS sequencing, we identified 15 coding-complete viral polyproteins (genomes) and 15 viral-like partial sequences in mosquitoes. The complete sequences for novel viruses or the partial sequences of capsid proteins, hypothetical viral proteins, and RdRps were used to identify their taxonomy. The novel viral sequences were classified within the orders Tymovirales and Picornavirales and the families Partitiviridae, Totiviridae, Tombusviridae, Iflaviridae, Nodaviridae, Permutotetraviridae, and Solemoviridae, with several attributed to four unclassified RNA viruses. Interestingly, the novel putative viruses and viral sequences were mainly associated with the mosquito Coquillettidia richardii. This study aimed to increase our understanding of the viral diversity in mosquitoes found in the natural habitats of Siberia, which is characterized by very long, snowy, and cold winters.