Pathogen transmission risk by opportunistic gulls moving across human landscapes

Rapid loss of maternal immunity and increase in environmentally mediated antibody generation in urban gulls

Monitoring pathogen circulation in wildlife sentinel populations can help to understand and predict the spread of disease at the wildlife-livestock-human interface. Immobile young provide a useful target population for disease surveillance, since they can be easily captured for sampling and their levels of antibodies against infectious agents can provide an index of localized circulation. However, early-life immune responses include both maternally-derived antibodies and antibodies resulting from exposure to pathogens, and disentangling these two processes requires understanding their individual dynamics. We conducted an egg-swapping experiment in an urban-nesting sentinel seabird, the yellow-legged gull, and measured antibody levels against three pathogens of interest (avian influenza virus AIV, Toxoplasma gondii TOX, and infectious bronchitis virus IBV) across various life stages, throughout chick growth, and between nestlings raised by biological or non-biological parents. We found that levels of background circulation differed among pathogens, with AIV antibodies widely present across all life stages, TOX antibodies rarer, and IBV antibodies absent. Antibody titers declined steadily from adult through egg, nestling, and chick stages. For the two circulating pathogens, maternal antibodies declined exponentially after hatching at similar rates, but the rate of linear increase due to environmental exposure was significantly higher in the more prevalent pathogen (AIV). Differences in nestling antibody levels due to parental effects also persisted longer for AIV (25 days, vs. 14 days for TOX). Our results suggest that yellow-legged gulls can be a useful sentinel population of locally transmitted infectious agents, provided that chicks are sampled at ages when environmental exposure outweighs maternal effects.

A spatial analysis of urban gulls contribution to the potential spread of zoonotic and antibiotic-resistant bacteria

Wildlife human interactions within cities are becoming more common with consequences for pathogen transmission and human health. Large gulls are opportunistic feeders, adapted to coexist with humans in urban environments, and are potential vectors for spread and transmission of pathogens, including antimicrobial-resistant bacteria. We investigated the potential role that urban gulls play in the spread and dispersal of these bacteria. We analysed 129 faecal swabs from yellow-legged gulls (Larus michahellis) of different ages (56 adults and 73 immatures) during the breeding period from three years in the highly populated city of Barcelona (northeastern Spain). Thirteen individuals tested positive for the pathogenic bacteria (Escherichia coli, Listeria monocytogenes, Campylobacter jejuni), including antibiotic-resistant strains. We modelled the potential spatial spread of pathogens using the GPS trajectories of 58 yellow-legged gulls (23 adults, 35 immature individuals), which included the thirteen individuals that tested positive for pathogenic bacteria. By overlapping the spatially explicit pathogen dispersal maps with the distribution of urban installations sensitive at risk of possible pathogen spillover (e.g. elder and medical centres, markets, food industries, kindergartens, or public water sources), we identified potential areas at risk of pathogen spillover. Pathogens may be potentially spread to municipalities beyond Barcelona city borders. The results revealed that immature gulls dispersed pathogens over larger areas than adults (maximum dispersal distances of 167 km versus 53.2 km, respectively). Recreational urban water sources were the most sensitive habitats visited by GPS-tagged gulls that tested positive, followed by schools. Combining GPS movement data with pathogen analytics allows spatially explicit maps to be generated using a One Health approach that can help urban and public health management within large cities, such as Barcelona, and identify areas used by humans that are sensitive to pathogen spillover from gulls.

Gulls in Porto Coastline as Reservoirs for Salmonella spp.: Findings from 2008 and 2023

Gulls act as intermediaries in the exchange of microorganisms between the environment and human settlements, including Salmonella spp. This study assessed the antimicrobial resistance and molecular profiles of Salmonella spp. isolates obtained from fecal samples of gulls in the city of Porto, Portugal, in 2008 and 2023 and from water samples in 2023. Antimicrobial susceptibility profiling revealed an improvement in the prevalence (71% to 17%) and antimicrobial resistance between the two collection dates. Two isolate collections from both 2008 and 2023 underwent serotyping and whole-genome sequencing, revealing genotypic changes, including an increased frequency in the monophasic variant of S. Typhimurium. qacE was identified in 2008 and 2023 in both water and fecal samples, with most isolates exhibiting an MDR profile. The most frequently observed plasmid types were IncF in 2008 (23%), while IncQ1 predominated in 2023 (43%). Findings suggest that Salmonella spp. circulate between humans, animals, and the environment. However, the genetic heterogeneity among the isolates from the gulls' feces and the surface water may indicate a complex ecological and evolutionary dynamic shaped by changing conditions. The observed improvements are likely due to measures to reduce biological contamination and antimicrobial resistance. Nevertheless, additional strategies must be implemented to reduce the public health risk modeled by the dissemination of pathogens by gulls.

Backyard zoonoses: The roles of companion animals and peri-domestic wildlife

The spillover of human infectious diseases from animal reservoirs is now well appreciated. However, societal and climate-related changes are affecting the dynamics of such interfaces. In addition to the disruption of traditional wildlife habitats, in part because of climate change and human demographics and behavior, there is an increasing zoonotic disease risk from companion animals. This includes such factors as the awareness of animals kept as domestic pets and increasing populations of free-ranging animals in peri-domestic environments. This review presents background and commentary focusing on companion and peri-domestic animals as disease risk for humans, taking into account the human-animal interface and population dynamics between the animals themselves.

Detection and Phylogenetic Analysis of Extended-Spectrum β-Lactamase (ESBL)-Genetic Determinants in Gram-Negative Fecal-Microbiota of Wild Birds and Chicken Originated at Trimmu Barrage

Extended-spectrum β-lactamases (ESBL) give rise to resistance against penicillin and cephalosporin antibiotics in multiple bacterial species. The present study was conducted to map genetic determinants and related attributes of ESBL-producing bacteria in three wild aquatic bird species and chickens at the "Trimmu Barrage" in district Jhang, Punjab province, Pakistan. To study the prevalence of ESBL-producing bacteria, a total of 280 representative samples were collected from wild bird species; cattle egrets (Bubulcus ibis), little egrets (Egretta garzetta) and common teals (Anas crecca) as well as from indigenous chickens (Gallus gallus domesticus) originating from a local wet market. The isolates were confirmed as ESBL producers using a double disc synergy test (DDST) and bacterial species were identified using API-20E and 20NE strips. A polymerase chain reaction (PCR) was used to detect ESBL genetic determinants and for genus identification via 16S rRNA gene amplification. A phenotypic antimicrobial susceptibility test was performed for ESBL-producing isolates against 12 clinically relevant antibiotics using the Kirby-Bauer disk diffusion susceptibility test. A phylogenetic tree was constructed for the sequence data obtained in this study and comparative sequence data obtained from GenBank. The overall prevalence of ESBL-producing bacteria was 34.64% (97/280). The highest percentage (44.28%; 31/70) of ESBL-producing bacteria was recovered from chickens (Gallus gallus domesticus), followed by little egrets (Egretta garzetta) (41.43%; 29/70), common teal (Anas crecca) (28.57%; 20/70) and cattle egrets (Bubulcus ibis) (24.28%; 17/70). Five different ESBL-producing bacteria were identified biochemically and confirmed via 16S rRNA gene sequencing, which included Escherichia coli (72; 74.23%), Enterobacter cloacae (11; 11.34%), Klebsiella pneumoniae (8; 8.25%), Salmonella enterica (4; 4.12%) and Pseudomonas aeruginosa (2; 2.06%). Based on PCR, the frequency of obtained ESBL genes in 97 isolates was blaCTX-M (51.55%), blaTEM (20.62%), blaOXA (6.18%) and blaSHV (2.06%). In addition, gene combinations blaCTX-M + blaTEM, blaTEM + blaOXA and blaCTX-M + blaSHV were also detected in 16.49%, 2.06% and 1.03% of isolates, respectively. The ESBL gene variation was significant (p = 0.02) in different bacterial species while non-significant in relation to different bird species (p = 0.85). Phylogenetic analysis of amino acid sequence data confirmed the existence of CTX-M-15 and TEM betalactamases. The average susceptibility of the antibiotics panel used was lowest for both Klebsiella pneumoniae (62.5% ± 24.42) and Salmonella enterica (62.5% ± 31.08) as compared to Enterobacter cloacae (65.90% ± 21.62), Pseudomonas aeruginosa (70.83% ± 33.42) and Escherichia coli (73.83% ± 26.19). This study provides insight into the role of aquatic wild birds as reservoirs of ESBL-producing bacteria at Trimmu Barrage, Punjab, Pakistan. Hence, active bio-surveillance and environment preservation actions are necessitated to curb antimicrobial resistance.

Changes in the feeding ecology of an opportunistic predator inhabiting urban environments in response to COVID-19 lockdown

Urban-dwelling species present feeding and behavioural innovation that enable them to adjust to anthropogenic food subsidies available in cities. In 2020, the SARS-CoV-2 virus outbreak resulted in unprecedented reduction in the human activity worldwide associated with the human lockdown. This situation opened an excellent opportunity to investigate the capability of urban wildlife to cope with this anthropopause event. Here, we investigated the effects of the COVID-19 lockdown on the feeding strategies of the urban yellow-legged gull (Larus michahellis) population inhabiting the highly dense city of Barcelona (NE Spain). We compared the diet of chicks (through stomach content and stable isotope analyses) sampled randomly around the city of Barcelona before (2018 and 2019), during (2020) and after (2021) the COVID-19 lockdown. The results revealed that the anthropopause associated with the lockdown had an effect on the diet of this urban-dwelling predator. The diversity of prey consumed during the lockdown was lower, and consumption of urban birds (pigeons and parakeets) and marine prey (fishery discards and natural prey) decreased during the year of lockdown. Although it was not analysed, these diet changes probably were associated with variations in the availability of these resources due to the decrease in human activity during the lockdown. These results demonstrate the trophic flexibility of urban-dwelling species to cope with the changes in the availability of human-related anthropogenic resources in urban marine ecosystems.

Multiresistant Enterobacteriaceae in yellow-legged gull chicks in their first weeks of life

Wild animal species living in anthropogenic areas are commonly carriers of antimicrobial‐resistant bacteria (AMRB), but their role in the epidemiology of these bacteria is unclear. Several studies on AMRB in wildlife have been cross‐sectional in design and sampled individual animals at only one point in time. To further understand the role of wildlife in maintaining and potentially transmitting these bacteria to humans and livestock, longitudinal studies are needed in which samples are collected from individual animals over multiple time periods. In Europe, free‐ranging yellow‐legged gulls (Larus michahellis) commonly live in industrialized areas, forage in landfills, and have been found to carry AMRB in their feces. Using bacterial metagenomics and antimicrobial resistance characterization, we investigated the spatial and temporal patterns of AMRB in a nesting colony of yellow‐legged gulls from an industrialized area in southern France. We collected 54 cloacal swabs from 31 yellow‐legged gull chicks in 20 nests on three dates in 2016. We found that AMRB in chicks increased over time and was not spatially structured within the gull colony. This study highlights the complex occurrence of AMRB in a free‐ranging wildlife species and contributes to our understanding of the public health risks and implications associated with ARMB‐carrying gulls living in anthropogenic areas.

Gulls living in cities as overlooked seed dispersers within and outside urban environments

The yellow-legged gull is an opportunistic and generalist bird that has colonised urban areas, where it has found very favourable trophic resources but also causes disturbance to humans and damage to infrastructure. Here, we investigated the potential role that gulls play in the dispersal of plants in Barcelona, a highly populated city of north-eastern Spain. We analysed the stomach contents of 145 chicks collected in urban nests and reported the presence of seeds of 27 plant taxa. We then developed a plant dispersal model based on the movements of 20 GPS-tracked yellow-legged gulls breeding in the city of Barcelona. We estimated seed dispersal distances, seed shadows and percentage of seeds reaching habitats suitable for seeds regurgitated in pellets and those excreted in faeces. Seven of the 27 plant taxa found in the stomachs were alien taxa to Spain. Average dispersal distances of plant seeds by gulls were around 700 m, but maximum dispersal distances reached up to 35 km. Dispersal distances and seed spatial patterns did not differ between faeces and pellet models, as most strongly depended on gull movements. About 95% of the seeds were dispersed within urban environments and between 20 and 30% reached suitable habitats for seed deposition (urban woodlands, green urban parks and urban grasslands). Urban gulls frequently dispersed seeds (including alien species) within urban habitats, both via direct consumption or via secondary dispersal after consuming granivorous birds that had ingested the seeds, such as pigeons or parakeets. Urban planning for Barcelona is based on native plant species, and thus, special attention should be paid to alien plants dispersed by birds, which could pose a risk to native biodiversity in urban ecosystems.

Climate Change Impacts on Microbiota in Beach Sand and Water: Looking Ahead

Beach sand and water have both shown relevance for human health and their microbiology have been the subjects of study for decades. Recently, the World Health Organization recommended that recreational beach sands be added to the matrices monitored for enterococci and Fungi. Global climate change is affecting beach microbial contamination, via changes to conditions like water temperature, sea level, precipitation, and waves. In addition, the world is changing, and humans travel and relocate, often carrying endemic allochthonous microbiota. Coastal areas are amongst the most frequent relocation choices, especially in regions where desertification is taking place. A warmer future will likely require looking beyond the use of traditional water quality indicators to protect human health, in order to guarantee that waterways are safe to use for bathing and recreation. Finally, since sand is a complex matrix, an alternative set of microbial standards is necessary to guarantee that the health of beach users is protected from both sand and water contaminants. We need to plan for the future safer use of beaches by adapting regulations to a climate-changing world.

Occurrence and antimicrobial resistance of zoonotic enteropathogens in gulls from southern Europe

Campylobacter spp. and Salmonella spp. are the two most frequent zoonotic bacteria involved in human enteric infections in the European Union. Both enteropathogens have been isolated from a diversity of wild birds in Northern Europe, but there is limited information about gulls as potential reservoirs in Southern Europe. A broad sampling of fledglings from nine colonies of yellow-legged gull (Larus michahellis, N = 1222) and Audouin's gull (Larus audouinii, N = 563) has been conducted in Spain and Tunisia during the late chick-rearing period. Overall, the occurrence of Campylobacter spp. and Salmonella spp. was 5.2% (93/1785, CI_95%: 4.2-6.2%) and 20.8% (371/1785, CI_95%: 18.9-22.7%), respectively. The most predominant Campylobacter species was C. jejuni (94.6%). A high diversity of Salmonella serovars was isolated and the most frequent were those also reported in human outbreaks, such as Salmonella Typhimurium. A high proportion of Campylobacter and Salmonella isolates showed resistance to at least one antimicrobial agent (20.2% and 51.5%, respectively), while 19.2% of Salmonella isolates were multidrug-resistant. These results show the relevance of gulls as reservoirs of Campylobacter and Salmonella by maintaining and spreading these bacteria, including resistant and multidrug resistant strains, in the environment. Our results suggest that gulls can serve as sentinel species for antibiotic pressure in the environment.

Prevalence and Antimicrobial Resistance of Enteropathogenic Bacteria in Yellow-Legged Gulls (Larus michahellis) in Southern Italy

Wild birds may host and spread pathogens, integrating the epidemiology of infectious diseases. Particularly, Larus spp. have been described as responsible for the spread of many enteric diseases, primarily because of their large populations at landfill sites. The aim of this study was to examine the role of yellow-legged gulls as a source of enteropathogenic bacteria such as Campylobacter spp., Salmonella spp., Shiga toxin-producing Escherichia coli and Yersinia spp., with particular attention to antibiotic-resistant strains. Enteropathogenic bacteria were isolated from 93/225 yellow-legged gulls examined from April to July, during a four-year period (2016-2019). Specifically, Campylobacter spp. was isolated from 60/225 samples (26.7%), and identified as C. coli (36/60) and as C. jejuni (24/60). Salmonella spp. was isolated from 3/225 samples (1.3%), and identified as Salmonella arizonae. Shiga toxin-producing E. coli were isolated from 30/225 samples (13.3%) samples, and serotyped as E. coli O128 (12/30) O26 (9/30), O157 (6/30) and O11 (3/30); Yersinia spp. was never detected. Isolated strains exhibited multidrug resistance, including vitally important antibiotics for human medicine (i.e., fluoroquinolones, tetracyclines). Our study emphasizes the importance of yellow-legged gulls as potential reservoirs of pathogenic and resistant strains and their involvement in the dissemination of these bacteria across different environments, with resulting public health concerns.