Migratory birds play a dual role as potential reservoirs of tick-borne pathogens, and potential dispersers of pathogen-containing ticks during their migratory journeys. Ixodes ricinus, a prevalent tick species in Northern and Western Europe, serves as a primary vector for Anaplasma phagocytophilum-a bacterium with implications for human and animal health. There is limited information available regarding A. phagocytophilum in birds. Our investigation focused on A. phagocytophilum prevalence in ticks collected from migratory birds in southeastern Sweden. The identification of ticks involved both molecular analyses for species determination and morphological classification to ascertain the developmental stage. The presence of A. phagocytophilum was determined using real-time PCR. Of the 1115 ticks analyzed from 4601 birds, 0.9% (n = 10), including I. ricinus and Ixodes frontalis, tested positive for A. phagocytophilum. Notably, common blackbirds (Turdus merula) yielded the highest number of A. phagocytophilum-infected ticks. The findings suggest that A. phagocytophilum is present in a small proportion of ticks infesting migratory birds in southeastern Sweden. Consequently, the role of birds as hosts for ticks infected with A. phagocytophilum appears to be low, suggesting that birds seem to play a minor indirect role in the geographic dispersal of A. phagocytophilum.

Humans are radically altering global ecology, and one of the most apparent human-induced effects is urbanization, where high-density human habitats disrupt long-established ecotones. Changes to these transitional areas between organisms, especially enhanced contact among humans and wild animals, provide new opportunities for the spread of zoonotic pathogens. This poses a serious threat to global public health, but little is known about how habitat disruption impacts cross-species pathogen spread. Here, we investigated variation in the zoonotic enteric pathogen Campylobacter jejuni. The ubiquity of C. jejuni in wild bird gut micro- biomes makes it an ideal organism for understanding how host behavior and ecology influence pathogen transition and spread. We analyzed 700 C. jejuni isolate genomes from 30 bird species in eight countries using a scalable generalized linear model approach. Comparing multiple behavioral and ecological traits showed that proximity to human habitation promotes lineage diversity and is associated with antimicrobial-resistant (AMR) strains in natural populations. Specifically, wild birds from urban areas harbored up to three times more C. jejuni genotypes and AMR genes. This study provides novel methodology and much-needed quantitative evidence linking urbanization to gene pool spread and zoonoses.

Goose and swan populations have increased concurrently with environmental degradation of wetlands, such as eutrophication, vegetation losses, and decrease in biodiversity. An important question is whether geese and swans contribute to such changes or if they instead benefit from them. We collected data from 37 wetlands in southern Sweden April - July 2021 to study relationships between geese, swans and other waterbird guilds, macrophytes, invertebrates, as well as physical and water chemistry variables. Neither goose nor swan abundance was negatively correlated with other trophic levels (abundance, richness, or cover). On the contrary, goose or swan abundances were positively related to abundances of surface and benthic feeding waterbirds, cover of specific macrophytes, and to invertebrate richness and abundance. Moreover, invertebrates (number of taxa or abundance) were positively associated with abundance of several waterbird guilds and total phosphorous with surface feeders, whereas water colour was positively (surface feeders) or negatively (benthic feeders) related. We conclude that waterbirds are more abundant in productive wetlands and that geese and swans do not show clear deleterious effects on other trophic levels included in this study. However, patterns may be masked at the species level, which should be addressed in further studies, complemented with experimental studies of grazing impact.

Cross-species transmission of influenza A virus (IAV) from wild waterfowl to poultry is the first step in a chain of events that can ultimately lead to exposure and infection of humans. Herein, we study the outcome of infection with eight different mallard-origin IAV subtypes in two different avian hosts: tufted ducks and chickens. We found that infection and shedding patterns as well as innate immune responses were highly dependent on viral subtypes, host species, and inoculation routes. For example, intraoesophageal inoculation, commonly used in mallard infection experiments, resulted in no infections in contrast to oculonasal inoculation, suggesting a difference in transmission routes. Despite H9N2 being endemic in chickens, inoculation of mallard-origin H9N2 failed to cause viable infection beyond 1 day postinfection in our study design. The innate immune responses were markedly different in chickens and tufted ducks, and despite the presence of retinoic acid-inducible gene-I (RIG-I) in tufted duck transcriptomes, it was neither up nor downregulated in response to infection. Overall, we have revealed the heterogeneity of infection patterns and responses in two markedly different avian hosts following a challenge with mallard-origin IAV. These virus-host interactions provide new insights into important aspects of interspecies transmission of IAV.IMPORTANCE Our current findings highlight important aspects of IAV infection in birds that have implications for our understanding of its zoonotic ecology. In contrast to mallards where the intestinal tract is the main site of IAV replication, chickens and tufted ducks show limited or no signs of intestinal infection suggesting that the fecal-oral transmission route might not apply to all bird IAV host species. Our results indicate that mallard-origin IAVs undergo genetic changes upon introduction into new hosts, suggesting rapid adaptation to a new environment. However, similar to the mallard, chickens and tufted ducks show a limited immune response to infection with low pathogenic avian influenza viruses. These findings and future studies in different IAV hosts are important for our understanding of barriers to IAV transmission between species and ultimately from the wild reservoir to humans. Our current findings highlight important aspects of IAV infection in birds that have implications for our understanding of its zoonotic ecology. In contrast to mallards where the intestinal tract is the main site of IAV replication, chickens and tufted ducks show limited or no signs of intestinal infection suggesting that the fecal-oral transmission route might not apply to all bird IAV host species.

BackgroundIn mammals, the gut microbiota has important effects on the health of their hosts. Recent research highlights that animal populations that live in captivity often differ in microbiota diversity and composition from wild populations. However, the changes that may occur when animals move to captivity remain difficult to predict and factors generating such differences are poorly understood. Here we compare the bacterial gut microbiota of wild and captive Damaraland mole-rats (Fukomys damarensis) originating from a population in the southern Kalahari Desert to characterise the changes of the gut microbiota that occur from one generation to the next generation in a long-lived, social rodent species.ResultsWe found a clear divergence in the composition of the gut microbiota of captive and wild Damaraland mole-rats. Although the dominating higher-rank bacterial taxa were the same in the two groups, captive animals had an increased ratio of relative abundance of Firmicutes to Bacteroidetes compared to wild animals. The Amplicon Sequence Variants (ASVs) that were strongly associated with wild animals were commonly members of the same bacterial families as those strongly associated with captive animals. Captive animals had much higher ASV richness compared to wild-caught animals, explained by an increased richness within the Firmicutes.ConclusionWe found that the gut microbiota of captive hosts differs substantially from the gut microbiota composition of wild hosts. The largest differences between the two groups were found in shifts in relative abundances and diversity of Firmicutes and Bacteroidetes.

In social species, group members commonly show substantial similarity in gut microbiome composition. Such similarities have been hypothesized to arise either by shared environmental effects or by host relatedness. However, disentangling these factors is difficult, because group members are often related, and social groups typically share similar environmental conditions. In this study, we conducted a cross-foster experiment under controlled laboratory conditions in group-living Damaraland mole-rats (Fukomys damarensis) and used 16S amplicon sequencing to disentangle the effects of the environment and relatedness on gut microbiome similarity and diversity. Our results show that a shared environment is the main factor explaining gut microbiome similarity, overshadowing any effect of host relatedness. Together with studies in wild animal populations, our results suggest that among conspecifics environmental factors are more powerful drivers of gut microbiome composition similarity than host genetics.

Ducks have recently received a lot of attention from the research community due to their importance as natural reservoirs of avian influenza virus (AIV). Still, there is a lack of tools to efficiently determine the immune status of ducks. The purpose of this work was to develop an automated differential blood count for the mallard duck (Anas platyrhynchos), to assess reference values of white blood cell (WBC) counts in this species, and to apply the protocol in an AIV field study. We established a flow cytometry-based duck WBC differential based on a no-lyse no-wash single-step one-tube technique, applying a combination of newly generated monoclonal antibodies with available duck-specific as well as cross-reacting chicken markers. The blood cell count enables quantification of mallard thrombocytes, granulocytes, monocytes, B cells, CD4(+) T cells (T helper) and CD8(+) cytotoxic T cells. The technique is reproducible, accurate, and much faster than traditional evaluations of blood smears. Stabilization of blood samples enables analysis up to 1 week after sampling, thus allowing for evaluation of blood samples collected in the field. We used the new technique to investigate a possible influence of sex, age, and AIV infection status on WBC counts in wild mallards. We show that age has an effect on the WBC counts in mallards, as does sex in juvenile mallards. Interestingly, males naturally infected with low pathogenic AIV showed a reduction of lymphocytes (lymphocytopenia) and thrombocytes (thrombocytopenia), which are both common in influenza A infection in humans.IMPORTANCE Outbreaks of avian influenza in poultry and humans are a global public health concern. Aquatic birds are the primary natural reservoir of avian influenza viruses (AIVs), and strikingly, AIVs mainly cause asymptomatic or mild infection in these species. Hence, immunological studies in aquatic birds are important for investigating variation in disease outcome of different hosts to AIV and may aid in early recognition and a better understanding of zoonotic events. Unfortunately, immunological studies in these species were so far hampered by the lack of diagnostic tools. Here, we present a technique that enables high-throughput white blood cell (WBC) analysis in the mallard and report changes in WBC counts in wild mallards naturally infected with AIV. Our protocol permits large-scale immune status monitoring in a widespread wild and domesticated duck species and provides a tool to further investigate the immune response in an important reservoir host of zoonotic viruses. Outbreaks of avian influenza in poultry and humans are a global public health concern. Aquatic birds are the primary natural reservoir of avian influenza viruses (AIVs), and strikingly, AIVs mainly cause asymptomatic or mild infection in these species.

The Little Stint Calidris minuta is an Arctic wader species that migrates through the Baltic Sea region towards wintering areas in North and West Africa and the Mediterranean region. We use a 75-year trapping series, comprising 4,791 Little Stints on autumn migration, from Ottenby Bird Observatory in Sweden to illustrate long-term trends in abundance, phenology, and morphometrics. Numbers of trapped juveniles dropped from median 31 (mean 74) in 1946–1999 to median 1.5 (mean 3.5) birds in 2000–2020, while the number of adults was generally low and without trends. Rolling window analyses showed that the drop in juveniles started around 1984, and from 1993 onward the median never exceeded seven juveniles/year (25 %-quantile: 0–1; 75 %-quantile: 4–55). Moreover, adult birds advanced their passage on average 0.48 days per year, passing 26 days earlier in 2020 than in 1946. Earlier migration of adults and decreased numbers of juveniles suggest low reproductive output in recent decades. Morphometric data of recaptured birds show that Little Stints on stopover at Ottenby gain fuel at a speed close to the theoretical maximum, strongly indicating that the conditions at the trapping site remain favourable for foraging waders.

Analysis of long-term datasets on bird populations can be used to answer ecological and management questions that are useful for conservation. Tanguar Haor (9500 ha) is one of the major freshwater wetlands in Bangladesh and supports a large number of migratory and resident waterbirds. Because of its unique ecological and economic values, it is arguably the most notable wetland in the floodplains of northeast Bangladesh and in the region. This Ramsar site supports globally important populations of threatened waterbirds, such as the Baer's Pochard Aythya baeri, Common Pochard Aythya ferina, Falcated Duck Mareca falcata, Ferruginous Duck Aythya nyroca, Oriental Darter Anhinga melanogaster, and Black-tailed Godwit Limosa limosa. Considering the international significance of this site, knowledge gaps on waterbird population trends, and key ecological factors, we conducted waterbird census between 2008 and 2021 to identify priority sites for conservation, population trends of resident and migratory waterbirds, and environmental factors that influence their abundances. We recorded a total of 69 species of waterbirds (maximum count of 166,788 individuals in 2013) and assessed population trends of 47 species. Of these, peak counts of 15 species exceeded the 1% threshold of their Asian-Australian Flyway population estimates. Most species (59%) showed a declining trend, including the critically endangered Baer's Pochard and the vulnerable Common Pochard, and 16 species (41%) showed an increasing trend. Based on the abundance and species diversity, we have identified Chotainna beel and Lechuamara beel as conservation priority sites within the Haor complex and discuss key threats to these areas. We also offer evidence that adjusting water-level management to annual rainfall patterns could be a useful intervention for waterbird management. Involving local communities in conservation efforts by creating bird sanctuaries within the Haor complex will strengthen waterbird conservation in the country and along the East Asian-Australian Flyway.