Feral pigeons: A reservoir of zoonotic Salmonella Enteritidis strains?

The microbiota in feces of domestic pigeons in Seoul, Korea

In Korea, feral pigeons pose significant public health risks because they carry various zoonotic pathogens. Human population density is a significant factor in zoonotic disease events. Seoul is one of the largest cities by population density among developed countries and where most of the homeless population in Korea exists. We designed this study to compare the microbiota of pigeon feces by regional characteristics and the presence of homeless individuals. Therefore, this study used 16S rRNA amplicon sequencing to detect possible pathogenic microbes and assess the current risk of zoonosis in Seoul, South Korea. Pigeon fecal samples (n = 144) obtained from 19 public sites (86 and 58 fecal samples from regions in and outside Seoul, respectively) were examined. Potentially pathogenic bacteria were also detected in the fecal samples; Campylobacter spp. was found in 19 samples from 13 regions, Listeriaceae was found in seven samples, and Chlamydia spp. was found in three samples from two regions. Principal coordinates analysis and permutational multivariate analysis of variance revealed a significant difference in bacterial composition between the regions in Seoul (n = 86) and outside Seoul (n = 58) and between the regions with (n = 81) and without (n = 63) homeless individuals. Overall, this study identified various potentially pathogenic microorganisms in pigeon feces at public sites in South Korea. Moreover, this study demonstrates that the microbial composition was influenced by regional characteristics and homelessness. Taken together, this study provides important information for public health strategic planning and disease control.

Regulated necrosis, a proinflammatory cell death, potentially counteracts pathogenic infections

Since the discovery of cell apoptosis, other gene-regulated cell deaths are gradually appreciated, including pyroptosis, ferroptosis, and necroptosis. Necroptosis is, so far, one of the best-characterized regulated necrosis. In response to diverse stimuli (death receptor or toll-like receptor stimulation, pathogenic infection, or other factors), necroptosis is initiated and precisely regulated by the receptor-interacting protein kinase 3 (RIPK3) with the involvement of its partners (RIPK1, TRIF, DAI, or others), ultimately leading to the activation of its downstream substrate, mixed lineage kinase domain-like (MLKL). Necroptosis plays a significant role in the host's defense against pathogenic infections. Although much has been recognized regarding modulatory mechanisms of necroptosis during pathogenic infection, the exact role of necroptosis at different stages of infectious diseases is still being unveiled, e.g., how and when pathogens utilize or evade necroptosis to facilitate their invasion and how hosts manipulate necroptosis to counteract these detrimental effects brought by pathogenic infections and further eliminate the encroaching pathogens. In this review, we summarize and discuss the recent progress in the role of necroptosis during a series of viral, bacterial, and parasitic infections with zoonotic potentials, aiming to provide references and directions for the prevention and control of infectious diseases of both human and animals.

Prevalence of multidrug resistance in Pseudomonas spp. isolated from wild bird feces in an urban aquatic environment

Antimicrobial resistance (AMR) has been detected in the microbiota of wildlife, yet little is known about the origin and impact within the ecosystem. Due to the shortage of nonepizootic surveillance, there is limited understanding of the natural prevalence and circulation of AMR bacteria in the wild animal population, including avian species. In this surveillance study, feces from wild birds in proximity to the River Cam, Cambridge, England, were collected and Pseudomonas spp. were isolated. Of the 115 samples collected, 24 (20.9%; 95% CI, 12.6%‒29.2%) harbored Pseudomonas spp. of which 18 (75%; 95% CI, 58%‒92%) had a multiple antibiotic resistance (MAR) index greater than 0.2. No Pseudomonas spp. isolate in this study was pansusceptible. Resistance was found among the 24 isolates against ciprofloxacin (87.5%; 95% CI, 74.3%‒100%) and cefepime (83.3%; 95% CI, 68.4%‒98.2%), both of which are extensively used to treat opportunistic Pseudomonas spp. infections. The prevalence of Pseudomonas spp. in the wild bird feces sampled during this study is greater than previous, similar studies. Additionally, their multidrug resistance profile provides insight into the potential risk for ecosystem contamination. It further highlights the importance of a One Health approach, including ongoing surveillance efforts that help to develop the understanding of how wildlife, including avifauna, may contribute and disperse AMR across the ecosystem.

Can domestic pigeon be a potential carrier of zoonotic Salmonella?

Salmonellosis is one of the most important bacterial diseases in pigeons. This study aimed to estimate the prevalence of Salmonella spp. in domestic pigeons (Columba livia f. domestica) in Poland, its antimicrobial susceptibility (both phenotypic and genotypic), and its capability for biofilm formation. The presence of selected virulence genes, nucleotide homology of selected genes, and susceptibility to bacteriophages were investigated as well. From the 585 pigeons tested, 5.47% turned out positive. All isolated strains were recognized as Salmonella enterica ser. Typhimurium. The asymptomatic pigeons were carriers of 37.5% of the isolates. The dominant variants were as follows: 1,4,[5],12,:i:1,2 (53.13%) and 1,4,[5],12,:‐:‐ (31.25%). Most of the strains analysed showed the ability to produce biofilm after 24 and 48 hr of incubation (59.38% and 53.13%, respectively). Over 90% of the strains were confirmed for lpfA, agafA, invA, sivH, and avrA virulence genes. Also, of the thirteen antimicrobial susceptibility genes, the following were confirmed: sul1, tet(A), bla_TEM‐1, floR, strA, and strB. The most common were the strB (18%) and tet(A) (12%) genes that are responsible for coding resistance to aminoglycosides and tetracyclines, respectively. Most of the strains were phenotypically resistant to oxytetracycline (46.88%), neomycin (53.13%) and tylosin (100%). The susceptibility of the investigated Salmonella strains to the bacteriophages was between 33% and 100%. MLST, PCR MP and ERIC PCR analyses indicated a very high genetic similarity of the investigated strains (over 99%). Results of our study indicate that Salmonella enterica ser. Typhimurium is still an important agent in domestic pigeons and that its antimicrobial resistance increases. Alarming is also the confirmation of a single‐phase variant 1,4,[5],12:i,‐, which could have increased virulence and multi‐drug resistance encoded on the plasmid. Most importantly, however, such strains have been isolated from humans with clinical symptoms of Salmonella infection.

Antimicrobial susceptibility and detection of virulence-associated genes of Escherichia coli and Salmonella spp. isolated from domestic pigeons (Columba livia) in Brazil

Overpopulation of domestic pigeons is considered to be one of the major problems of urban centers, as these birds are responsible for the dissemination of relevant pathogens to animal and human health. The aim of this study was to detect potentially pathogenic Escherichia coli and Salmonella spp. in domestic pigeons captured in areas near silos used for grain and feed storage, analyzing the antimicrobial sensitivity and the presence of virulence-associated genes. We evaluated 41 pigeons. From each bird, cecal contents and a pool of viscera (heart, spleen, and liver) were collected. Fifty strains of E. coli and three strains of S. Typhimurium were isolated. The antimicrobial susceptibility assay showed that 2% of the isolates of E. coli were resistant to chloramphenicol and the combination of sulfamethoxazole + trimethoprim and 4% to tetracycline, doxycycline, and sulfonamide. The three S. Typhimurium strains were sensitive to all antimicrobials tested. The pathogenicity profile demonstrated that no E. coli isolates showed a STEC compatible profile. Regarding the APEC pathotype, all genes were observed in 8% of E. coli, 6% had only the iss gene and 4% presented ompT, hlyF, and iutA genes. invA, hilA, avrA, and lpfA genes were detected in 100% of Salmonella isolates. The sitC and pefA genes were only present in one strain and the remaining genes were detected in two. In conclusion, it was found that pigeons living in the vicinity of silos are carriers of important pathogens, and control measures should be taken to minimize animal and human health risks.

Characterization of Salmonella enterica Isolates from Diseased Poultry in Northern China between 2014 and 2018

Salmonella infection not only causes acute and chronic diseases in poultry flocks, but the infected poultry are among the most important reservoirs for a variety of Salmonella serovars frequently transmitted to humans. This study aimed to investigate the occurrence of Salmonella spp. in local poultry farms in China. Samples (n = 4255), including dead-in-shell embryos, culled day-old-hatchings and 1- to 4-week-old diseased birds, were collected for Salmonella culture from broiler chicken, meat-type duck and pigeon farms in northern China between 2014 and 2018. A total of 103 Salmonella were isolated. S. enterica serovar Enteritidis and S. Typhimurium were the most prevalent serovars, representing 53.4% and 34.9% of the isolates, respectively. Serovar diversity was the highest in ducks, with the S. Apeyeme being isolated for the first time from duck tissues. All isolates were characterized by multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). MLST showed that all S. Enteritidis isolates shared the same sequence type (ST11), and Typhimurium showed several rare STs in addition to ST19. In comparison, PFGE showed better discrimination for S. Enteritidis and S. Typhimurium isolates, with nine distinct pulsotypes being observed. The isolates exhibited varying degrees of resistance to 15 tested antimicrobials and identified S. Enteritidis isolates (98.18%) with multiple antimicrobial resistance were a cause for concern. Our data on invasive Salmonella infection in meat-type poultry in local farms can be used to identify sources and factors associated with Salmonella spread in poultry and the associated food chain.

Are we overestimating risk of enteric pathogen spillover from wild birds to humans?

Enteric illnesses remain the second largest source of communicable diseases worldwide, and wild birds are suspected sources for human infection. This has led to efforts to reduce pathogen spillover through deterrence of wildlife and removal of wildlife habitat, particularly within farming systems, which can compromise conservation efforts and the ecosystem services wild birds provide. Further, Salmonella spp. are a significant cause of avian mortality, leading to additional conservation concerns. Despite numerous studies of enteric bacteria in wild birds and policies to discourage birds from food systems, we lack a comprehensive understanding of wild bird involvement in transmission of enteric bacteria to humans. Here, we propose a framework for understanding spillover of enteric pathogens from wild birds to humans, which includes pathogen acquisition, reservoir competence and bacterial shedding, contact with people and food, and pathogen survival in the environment. We place the literature into this framework to identify important knowledge gaps. Second, we conduct a meta‐analysis of prevalence data for three human enteric pathogens, Campylobacter spp., E. coli, and Salmonella spp., in 431 North American breeding bird species. Our literature review revealed that only 3% of studies addressed the complete system of pathogen transmission. In our meta‐analysis, we found a Campylobacter spp. prevalence of 27% across wild birds, while prevalence estimates of pathogenic E. coli (20%) and Salmonella spp. (6.4%) were lower. There was significant bias in which bird species have been tested, with most studies focusing on a small number of taxa that are common near people (e.g. European starlings Sturnus vulgaris and rock pigeons Columba livia) or commonly in contact with human waste (e.g. gulls). No pathogen prevalence data were available for 65% of North American breeding bird species, including many commonly in contact with humans (e.g. black‐billed magpie Pica hudsonia and great blue heron Ardea herodias), and our metadata suggest that some under‐studied species, taxonomic groups, and guilds may represent equivalent or greater risk to human infection than heavily studied species. We conclude that current data do not provide sufficient information to determine the likelihood of enteric pathogen spillover from wild birds to humans and thus preclude management solutions. The primary focus in the literature on pathogen prevalence likely overestimates the probability of enteric pathogen spillover from wild birds to humans because a pathogen must survive long enough at an infectious dose and be a strain that is able to colonize humans to cause infection. We propose that future research should focus on the large number of under‐studied species commonly in contact with people and food production and demonstrate shedding of bacterial strains pathogenic to humans into the environment where people may contact them. Finally, studies assessing the duration and intensity of bacterial shedding and survival of bacteria in the environment in bird faeces will help provide crucial missing information necessary to calculate spillover probability. Addressing these essential knowledge gaps will support policy to reduce enteric pathogen spillover to humans and enhance bird conservation efforts that are currently undermined by unsupported fears of pathogen spillover from wild birds.

Evidence of the role of free-living birds as disseminators of Salmonella spp

ABSTRACT This study aimed to review aspects of Salmonella spp. in free-living birds and their potential as disseminators for domestic animals, man, and the environment. Isolation of Salmonella spp. have been reported in several species of wild birds from Passeridae and Fringillidae, among other avian families, captured in countries of North America and Europe, where Salmonella ser. Typhimurium is the most frequently reported serotype. The presence of pathogens, including Salmonella, may be influenced by several factors, such as diet, environment, exposure to antibiotics, infection by pathogenic organisms and migration patterns. Researches with wild birds that live in urbanized environment are important, considering that birds may participate in the transmission of zoonotic pathogens, which are more prevalent in cities due to the human activity. Based on the information collected, this article concludes that wild birds are still important disseminators of pathogens in several geographic regions and may affect man, domestic animals, and other birds.

Chlamydia psittaci and C. avium in feral pigeon (Columba livia domestica) droppings in two cities in the Netherlands

Background: Feral pigeons (Columba livia domestica) live and breed in many city centres and contact with their droppings can be a hazard for human health if the birds carry Chlamydia psittaci.

Objective: The aim of this study was to establish whether pigeon droppings in two Dutch cities (Utrecht and Haarlem) contain C. psittaci and/or C. avium, which could be a potential hazard for transmission to humans.

Methods: In May 2017 seven feral pigeon ‘hot spots’ with between 5 and 40+ pigeons present were identified in two cities by visual observations over two days. During the following ten days fresh droppings were collected at these hot spots and the samples were pooled per three droppings to achieve 40–41 samples per city. Samples were analysed for Chlamydia DNA with a broad range 23S Chlamydiaceae Real-Time PCR and positive samples were tested with a specific C. psittaci and C. avium Real-Time PCR. Positive C. psittaci samples were genotyped.

Results:C. psittaci and C. avium were detected in both cities. For C. psittaci the prevalences in Utrecht and Haarlem were 2.4% and 7.5%, respectively; for C. avium 36.6% and 20.0%, respectively. One sample contained both species. All C. psittaci samples belonged to genotype B.

Conclusion:C. psittaci and C. avium are present in feral pigeon droppings in Utrecht and Haarlem. Human contact with droppings from infected pigeons or inhalation of dust from dried droppings represent a potential hazard to public health.

Free-Ranging Synanthropic Birds (Ardea alba and Columba livia domestica) as Carriers of Salmonella spp. and Diarrheagenic Escherichia coli in the Vicinity of an Urban Zoo

The presence of free-ranging urban birds is a risk factor for transmitting pathogens to captive animals and humans alike, including Salmonella spp. and diarrheagenic Escherichia coli. Cloacal swabs from 156 synanthropic Great egrets (Ardea alba) and feral pigeons (Columba livia domestica) that inhabit the surroundings of an urban zoo were processed for the identification of Salmonella spp. and diarrheagenic E. coli pathotypes. Bacterial species identification and genotypic characterization employed the matrix-assisted laser desorption ionization-time of flight mass spectrometry and PCR techniques, respectively, comparing their phylogenetic profiles through amplified fragment length polymorphism (AFLP) analysis. A total of 11 birds were positive for Salmonella Typhimurium (7%) and 9 individuals (5.8%) for diarrheagenic E. coli (enteropathogenic E. coli/Shiga-toxin producing E. coli [EPEC/STEC]) strains. S. Typhimurium strains presented highly similar AFLP profiles (85-100%), whereas EPEC/STEC strains showed more polymorphism. The results show free-ranging birds as carriers for both microorganisms in a zoo environment in Brazil for the first time and suggest these species as possible sources of infection to other animals as well as exposing personnel and visitors to potential zoonotic microorganisms. The presence of carriers highlights the importance of a surveillance system and the need for preventive measures to avoid attracting growing number of synanthropic avian species.

Salmonella Typhimurium DT193 and DT99 are present in great and blue tits in Flanders, Belgium

Endemic infections with the common avian pathogen Salmonella enterica subspecies enterica serovar Typhimurium (Salmonella Typhimurium) may incur a significant cost on the host population. In this study, we determined the potential of endemic Salmonella infections to reduce the reproductive success of blue (Cyanistes caeruleus) and great (Parus major) tits by correlating eggshell infection with reproductive parameters. The fifth egg of each clutch was collected from nest boxes in 19 deciduous forest fragments. Out of the 101 sampled eggs, 7 Salmonella Typhimurium isolates were recovered. The low bacterial prevalence was reflected by a similarly low serological prevalence in the fledglings. In this study with a relatively small sample size, presence of Salmonella did not affect reproductive parameters (egg volume, clutch size, number of nestlings and number of fledglings), nor the health status of the fledglings. However, in order to clarify the impact on health and reproduction a larger number of samples have to be analyzed. Phage typing showed that the isolates belonged to the definitive phage types (DT) 193 and 99, and multi-locus variable number tandem repeat analysis (MLVA) demonstrated a high similarity among the tit isolates, but distinction to human isolates. These findings suggest the presence of passerine-adapted Salmonella strains in free-ranging tit populations with host pathogen co-existence.

First detection and characterization of Salmonella spp. in poultry and swine raised in backyard production systems in central Chile

Little is known about Salmonella serovars circulating in backyard poultry and swine populations worldwide. Backyard production systems (BPS) that raise swine and/or poultry are distributed across Chile, but are more heavily concentrated in central Chile, where industrialized systems are in close contact with BPS. This study aims to detect and identify circulating Salmonella serovars in poultry and swine raised in BPS. Bacteriological Salmonella isolation was carried out for 1744 samples collected from 329 BPS in central Chile. Faecal samples were taken from swine, poultry, geese, ducks, turkeys and peacocks, as well as environmental faecal samples. Confirmation of Salmonella spp. was performed using invA-polymerase chain reaction (PCR). Identification of serovars was carried out using a molecular serotyping approach, where serogroups were confirmed by a multiplex PCR of Salmonella serogroup genes for five Salmonella O antigens (i.e., D, B, C1, C2-C3, and E1), along with two PCR amplifications, followed by sequencing of fliC and fljB genes. A total of 25 samples (1·4% of total samples) from 15 BPS (4·6 % of total sampled BPS) were found positive for Salmonella. Positive samples were found in poultry (chickens and ducks), swine and environmental sources. Molecular prediction of serovars on Salmonella isolated showed 52·0% of S. Typhimurium, 16·0% of S. Infantis, 16·0% S. Enteritidis, 8·0% S. Hadar, 4·0% S. Tennessee and 4·0% S. Kentucky. Poor biosecurity measures were found on sampled BPS, where a high percentage of mixed confinement systems (72·8%); and almost half of the sampled BPS with improper management of infected mortalities (e.g. selling the carcasses of infected animals for consumption). Number of birds other than chickens (P = 0·014; OR = 1·04; IC (95%) = 1·01-1·07), mixed productive objective (P = 0·030; OR = 5·35; IC (95%) = 1·24-27·59) and mixed animal replacement origin (P = 0017; OR = 5·19; IC (95%) = 1·35-20·47) were detected as risk factors for BPS positivity to Salmonella spp. This is the first evidence of serovars of Salmonella spp. circulating in BPS from central Chile. Detected serovars have been linked to human and animal clinical outbreaks worldwide and in Chile, highlighting the importance of BPS on the control and dissemination of Salmonella serovars potentially hazardous to public health.