Role of Birds in Salmonellosis

Abstract

The main research question explores the role of birds in Salmonella transmission dynamics, highlighting the zoonotic potential for disease spread from birds to humans. Investigating bird salmonellosis uncovers a complex interaction of factors, including birds’ feeding habits and ecological behaviors, that facilitate disease dissemination. Utilizing epidemiological evidence, genomic analysis, and case studies, the research elucidates how salmonellosis is transmitted among birds and to humans. Significant findings identify garden birds as major Salmonella reservoirs, reveal genetic similarities between avian and human Salmonella strains, and underscore the role of environmental contamination. Notably, species like the Eurasian siskin and greenfinch are significant carriers, with bird-feeding practices and feeder congregations accelerating transmission. The research emphasizes a comprehensive management approach to salmonellosis, involving public education, wildlife management, and strategic interventions to reduce risks. It calls for improved hygiene practices in human-bird interaction zones and targeted bird population surveillance for Salmonella. Understanding birds’ role in salmonellosis epidemiology is vital for developing effective public health strategies, enhancing food safety, and wildlife conservation, and underscoring the interconnectedness of human, animal, and environmental health in tackling zoonotic diseases.

1. Introduction

1.1 Definition of salmonellosis

Bird salmonellosis is a complicated and multifaceted problem that affects equally domestic and wild bird populations. Primary transmission occurs through contaminated food, but environmental and direct contact vectors also play a role in the spread of the illness. The bacteria Salmonella enterica are the primary drivers of this disease, which can take numerous forms and frequently cause severe gastrointestinal illness, fever, diarrhea, stomach cramps, and, tragically, high rates of death. Serovars such as Salmonella Typhimurium are mainly retained in both domestic and wild birds [1]. Notably, certain serovars, such as Salmonella Typhimurium, have adapted to persist in bird populations, with phage types such as DT40 and DT56v identified as prevalent in these hosts [1]. The zoonotic potential of Salmonella makes its extensive presence in bird populations a major public health problem and an ongoing concern for wildlife conservation efforts. Zoonosis, or bird flu, can spread from birds to humans through many channels, such as coming into contact directly with sick birds, touching bird baths or feeders, or having a pet that comes into contact with sick animals [2].

Salmonellosis significantly threatens wild birds, particularly passerine species such as finches and sparrows, as evidenced by their elevated mortality rates [3]. This disease’s spread is notably facilitated by behaviors common among these birds, such as congregating in large numbers at feeding sites. These gatherings, often around bird feeders provided by humans, serve as prime venues for Salmonella transmission, effectively turning them into hotspots for the disease. The resulting rapid spread not only jeopardizes bird conservation efforts by affecting the health and survival of these species but also increases the zoonotic risk, bridging the gap between wildlife diseases and human infections. This risk is especially pronounced in areas where there is close contact between humans and wild birds [4].

The connection between Salmonella infections in wild bird populations and human cases has been firmly established through extensive epidemiological research, underscoring the zoonotic nature of this pathogen. In light of this, raising awareness about salmonellosis and promoting good hygiene practices in places frequented by wild birds are crucial steps toward mitigating the risk of transmission but also increasing zoonotic risk [5]. Furthermore, proactive measures to monitor and control the spread of Salmonella among bird populations are vital, particularly given the emerging status of this disease. Over the last four decades, there has been a notable increase in the incidence of salmonellosis among wild birds, a trend likely propelled by the increase in artificial feeding practices. The birds most at risk are those that feed on the ground or in contaminated water sources, including those that consume both plant and animal matter, highlighting the need for vigilant management of the environments we share with these animals [2].

1.2 Key insights into salmonellosis spread and prevention

The study conducted by Lawson et al. [4] provides critical insights into the role of garden birds as primary reservoirs in the transmission dynamics of salmonellosis. This research, focused on England and Wales, revealed the significant involvement of garden birds in the spread of zoonotic bacteria responsible for human salmonellosis cases. Lawson et al. [4] reported that garden birds are significant reservoirs for bacteria that cause salmonellosis in humans. This study highlighted the connection between the presence of these birds and the incidence of salmonellosis cases in human populations. Research on the species-specific aspects of transmission revealed that certain garden bird species including Greenfinches (Carduelis chloris) and House Sparrows (Passer domesticus) are more likely to harbor and spread the Salmonella bacteria. This finding is crucial for understanding the epidemiology of salmonellosis and designing targeted control measures. The study also considered the environmental and ecological factors that contribute to the prevalence of salmonellosis in garden birds. Factors such as bird-feeding habits, migration patterns, and interactions with human environments were explored to understand how they influence the spread of disease. The identification of garden birds as primary reservoirs for salmonellosis-causing bacteria has significant public health implications. This suggests the need for better management practices in urban and suburban gardens and parks where human interaction with these birds is frequent. Lawson et al. proposed recommendations for controlling the spread of salmonellosis from garden birds to humans. These include public awareness campaigns, safe bird-feeding practices, and enhanced surveillance of bird populations for Salmonella infections. This research also revealed the broader impact of salmonellosis on wildlife and domestic animal populations, suggesting that garden birds could be a source of infection for a wide range of animals, thereby impacting biodiversity and animal health.

The study by Mather et al. [6] on the genomic analysis of Salmonella enterica in wild passerines provides profound insights into the transmission dynamics of salmonellosis. The research identified genetic similarities between the Salmonella strains found in wild birds and those that infect humans. These similarities suggest that the same or closely related strains of Salmonella are capable of infecting both birds and humans, pointing to a shared pathway or common source of infection. The researcher conducted a genomic analysis of the Salmonella strains isolated from birds. They found notable genetic overlaps with strains that infect humans. This finding implies that the same or closely related strains of Salmonella are capable of infecting multiple species. This shared genetic profile suggests a common evolutionary pathway or a shared environmental reservoir that facilitates cross-species transmission or similar mechanisms to cause disease in different hosts. This can include similarities in how bacteria invade host cells, evade the immune system, or produce toxins. Another aspect of the genetic basis could be related to antimicrobial resistance. The presence of similar resistance genes in both bird and human Salmonella strains is a matter of concern for treatment and public health, as it suggests the potential for the spread of resistance traits across species. The findings of the genetic study conducted by Mather et al. [6] contribute to molecular epidemiology, which helps trace the origins and spread of infections by examining the genetic makeup of pathogens. Understanding the genetic similarities allows for better tracking of infection sources and pathways. The genetic analysis tools used in the study are crucial for public health surveillance. These methods enable health authorities to identify and respond to outbreaks more effectively by understanding.

The 2014 study by Krawiec et al. [7] significantly advanced our understanding of how certain garden birds, specifically the Eurasian siskin and greenfinch, act as significant carriers and reservoirs for Salmonella spp., playing a critical role in the transmission dynamics of salmonellosis. The transmission cycle involves the birds acquiring the Salmonella bacteria, likely from their environment or through interaction with other infected birds or animals. Once infected, these birds can shed the bacteria through their feces, which can then contaminate their surroundings, including food sources, water, and areas where they congregate. This transmission cycle is particularly concerning because it provides multiple opportunities for the spread of Salmonella to other birds, wildlife, and potentially to humans, especially in settings where there is close interaction between humans and these bird species. This research has considerable implications for public health and wildlife management, especially in areas where Eurasian siskins and greenfinches are common, as it focuses on controlling the spread of Salmonella within bird populations. This study enables more targeted surveillance and intervention efforts. Such efforts can include monitoring bird populations for signs of infection, implementing measures to mitigate the spread of bacteria in bird habitats, and educating the public about safe practices for bird feeding and handling. Furthermore, the study contributes significantly to the One Health approach, emphasizing the interconnected nature of human, animal, and environmental health.

2. Epidemiology of Salmonellosis

2.1 Prevalence and incidence

Salmonellosis is a worldwide health issue that impacts millions of people each year. Its occurrence varies by region and is affected by factors such as food hygiene practices and interactions between animals and humans. This variety is a result of the many situations under which Salmonella can propagate and impact populations [8]. Enhanced food handling and sanitation measures have reduced salmonellosis in certain areas, but in other regions, interactions between humans and animals contribute to disease transmission. Comprehending these dynamics is essential for creating efficient public health interventions to lessen the impact of salmonellosis on a global scale.

2.1.1 Subclinical salmonellosis in wild birds near pig farms

Andrés et al. [9] reported that Salmonella was more prevalent in birds near pig farms. The study detected Salmonella in 1.85% of bird fecal samples, with Salmonella Typhimurium being the most prevalent serotype. This indicates that pig farms may amplify Salmonella infection among wild birds, with non-migratory birds being particularly affected [9].

2.1.2 Salmonellosis in garden birds and human transmission in England and Wales

Lawson et al. [4] reported that garden birds are a significant source of human salmonellosis in England and Wales. This study linked the phage types of Salmonella found in birds to those found in humans, supporting the hypothesis that garden birds act as the primary reservoir of these zoonotic bacteria Lawson et al. [4].

2.1.3 Salmonella in wild birds and retail food in Singapore

Aung et al. [10] found a 0.99% prevalence of Salmonella in wild birds in Singapore, suggesting that avian Salmonella isolates are subject to less antimicrobial selection pressure than those from food sources. This study helps to elucidate the epidemiology of human salmonellosis in wild birds [10].

2.1.4 Salmonella typhimurium O:4-12 infection in Norway linked to wild birds

Kapperud et al. [11] reported that the epidemic strain of Salmonella typhimurium O:4-12 in Norway often causes fatal salmonellosis among wild passerine birds. The study indicated a clear seasonal pattern and an epidemiologic link between avian and human cases [11].

Salmonellosis is a global health concern, with millions affected annually. Its incidence varies geographically and is influenced by factors such as food hygiene practices and animal-human interactions [12].

2.2 Common Salmonella serovars

The study conducted by Şik et al. [13] in Turkey provided a comprehensive analysis of Salmonella serovars across various animal species. They examined 1047 Salmonella spp. strains collected between 2015 and 2020, revealing a diverse range of serovars: 19 serogroups and 75 different serovars. The most commonly isolated serovar was Salmonella Infantis, which is primarily found in chickens. Other notable findings included Salmonella montevideo in calves, Salmonella darle in tortoises, and Salmonella typhimurium in lambs. Of particular interest was the identification of Salmonella Hessarek in wild birds, emphasizing the prevalence of this serovar in avian species. This study highpoints the intricate distribution of Salmonella serovars in various animal populations, highlighting the need for targeted surveillance and control strategies [13].

In Central Spain, Martín-Maldonado et al. [14] investigated the presence and antimicrobial resistance of Salmonella in urban birds. They found that 12.3% of the 300 sampled birds were Salmonella positive, with white storks feeding in landfills showing the highest prevalence. This study identified zoonotic serovars such as Salmonella enteritidis and S. typhimurium, including their monophasic variants. A significant finding was the high resistance rate to antibiotics, with 40.5% of Salmonella strains being resistant to ciprofloxacin, nalidixic acid, and colistin. These results demonstrate the potential role of urban birds as reservoirs and disseminators of antimicrobial-resistant Salmonella strains, posing a public health concern [14].

Fu et al. [15] conducted a study in the United States to examine the resistance of Salmonella enterica strains in wild birds. They sequenced 375 S. enterica strains collected from wild birds in 41 states from 1978 to 2019. The dominant serovar found was Typhimurium, comprising 68.3% of bird isolates. Notably, the proportions of isolates identified as multi-antimicrobial resistant (1.87%) or multi-heavy metal resistant (1.87%) were low. These findings suggest that wild birds in the United States do not serve as significant reservoirs for multi-resistant S. enterica strains, although continuous surveillance is necessary due to the potential transmission of resistant bacteria to humans and domestic animals [15].

Wales and Lawes [16] focused on Salmonella Gallinarum, a serovar that specifically affects avian species like such as chickens and turkeys. This serovar causes invasive and septicemic diseases, often leading to high mortality rates. S. Gallinarum has two biovars, Pullorum and Gallinarum, both of which cause severe disease in poultry but with different transmission dynamics. This study underscores the importance of clean breeding practices for controlling this pathogen, though sporadic outbreaks still occur even in countries with stringent control measures [16].

Smith et al. [17] identified the bar-tailed godwit, a migratory shorebird, as a reservoir for Salmonella Hvittingfoss in Australia. This serovar was responsible for a foodborne outbreak in 2016–2017 linked to tainted cantaloupes. The study found a genetically similar strain of S. Hvittingfoss in the godwit population, highlighting the potential role of migratory birds in the long-distance transmission of foodborne pathogens. This discovery is significant in understanding the dynamics of Salmonella transmission and the potential environmental reservoirs of foodborne pathogens [17].

Numerous serovars of Salmonella exist, with some such as Typhimurium and Enteritidis being particularly prevalent in human infections [18].

2.2.1 Human health impact

The disease can range from mild gastroenteritis to severe systemic infections, especially in vulnerable populations such as children and immunocompromised individuals (Figure 1) [19].

Figure 1.

Graphs showing the incidence of salmonellosis over time in different region.

3. Zoonotic transmission

Zoonotic diseases, also known as zoonoses, are infections that can be transmitted from animals to humans, either through direct contact with infected animals, indirectly through environmental exposure, or by consuming contaminated food products. These diseases encompass a wide range of health implications, from mild symptoms to severe illnesses, and are a significant concern in both public health and veterinary medicine.

One notable zoonotic disease is salmonellosis, which is caused by Salmonella bacteria. Salmonella is widely distributed in the animal kingdom, particularly in birds and reptiles, as well as in mammals and amphibians. Research by Ellis in 1969 highlighted birds as significant reservoirs for Salmonella, emphasizing the risk of transmission to humans. Salmonella infections can lead to gastrointestinal illnesses and more severe conditions, especially in individuals with weakened immune systems [12].

The primary sources of human infection with Salmonella include contaminated food products such as poultry, eggs, meat, and dairy products derived from infected animals. Direct contact with infected animals or their fecal matter is another significant source of transmission, posing a particular risk in settings like farms, veterinary clinics, or even in households with pets like turtles and birds. Additionally, environmental contamination is an increasingly recognized vector for salmonellosis. Contaminated water sources, soil, or surfaces can harbor Salmonella bacteria, broadening the scope of potential exposure beyond animal products and direct animal contact [20].

In 2011, Hoelzer, Moreno Switt, and Wiedmann noted out the growing importance of environmental contamination, including contaminated produce, as a source of human salmonellosis. This acknowledgment necessitates a comprehensive approach to controlling outbreaks, which includes monitoring potential animal reservoirs and environmental contamination, in addition to food safety measures [21].

The study of zoonotic transmission, particularly of Salmonella, is crucial for developing preventive strategies and managing public health risks associated with these diseases. Understanding the diverse transmission pathways helps in implementing targeted interventions to reduce the incidence and impact of zoonotic diseases (Figure 2).

Figure 2.

Flowchart depicting the zoonotic transmission cycle of salmonellosis.

4. Birds as carriers of Salmonella

Birds, encompassing a wide range of wild and domesticated species, play a significant role as reservoirs for the Salmonella bacteria. These avian hosts can harbor and disseminate various serovars of this bacterium, contributing to the spread of salmonellosis.

4.1 Avian reservoirs of Salmonella

The presence of Salmonella in birds is a well-documented phenomenon. Studies have shown that both wild and domesticated bird populations can carry and transmit different serovars of Salmonella. Lawson et al. [4] specifically highlighted the role of garden birds as sources of human salmonellosis in England and Wales, indicating the direct link between avian carriers and human infections. This relationship underscores the importance of birds in the epidemiology of Salmonella, not only as carriers but also as potential sources of transmission to other species, including humans [4].

4.2 Factors contributing to Salmonella carriage in birds

Several factors influence the likelihood of birds carrying Salmonella. These include:

1. Diet: the type of food consumed by birds can affect their risk of Salmonella infection. Birds that feed on a diet rich in seeds or those scavenging for food in human-inhabited areas or farms may be more likely to encounter and ingest Salmonella bacteria [7].

2. Environmental exposure: birds living in or near contaminated environments, such as agricultural lands with livestock or areas with poor sanitation, have higher chances of coming into contact with Salmonella [22].

3. Interactions with other animals or humans: birds that interact with other infected animals or with humans, particularly in settings such as poultry farms, petting zoos, or households, can acquire and spread Salmonella. The interaction does not need to be direct or indirect contact through contaminated surfaces or equipment, which can also facilitate transmission [22].

Meade and Barrow [23] discussed these factors, emphasizing the complexity of Salmonella transmission in avian populations. They pointed out that the interaction of these factors creates a dynamic environment where the risk of Salmonella carriage can vary significantly among different bird populations and environments [23].

In summary, the role of birds as carriers of Salmonella is a multifaceted issue influenced by various ecological and environmental factors. Understanding these dynamics is crucial for developing strategies to control the spread of salmonellosis and protect public health (Table 1).

Species	Commonly identified serovars	References
Eastern Bluebird	Typhimurium, other serovars	[22]
Chipping Sparrow	Typhimurium, other serovars	[22]
Cattle Egret (Bubulcus ibis)	Typhimurium, other serovars	[22]
House Sparrow (Passer domesticus)	Typhimurium, other serovars	[22]
Fish Crows (Corvus ossifragus)	Typhimurium, Panama, other serovars	[22]
Cormorants, Pelicans, Herons	Typhimurium, other serovars	[7]
Gulls and Terns	Typhimurium, other serovars	[7]
Eurasian Siskins	Typhimurium	[7]
Greenfinches	Typhimurium	[7]
Asian Pied Starling (Gracupica contrasta)	Not specified	No relevant data provided
House Crow (Corvus splendens)	Not specified	No relevant data provided
Seabirds	Panama, Typhimurium, other serovars	[7]

Table 1.

List of bird species and their associated Salmonella serovars.

5. Salmonella in wild birds

Salmonella in wild birds is an area of significant interest due to the role these birds play in the transmission of the bacterium. Wild birds, including various garden and marine species, have been identified as carriers of Salmonella, and they can act as vectors, facilitating the spread of this pathogen [24].

5.1 Prevalence in wild bird populations

The prevalence of Salmonella in wild bird populations varies depending on numerous factors, including geographical location, bird species, and local environmental conditions. A study by Tardone et al. [25] highlighted the presence of Salmonella in both garden and marine bird populations, demonstrating the widespread nature of this issue. These birds can pick up Salmonella from various sources and potentially spread it over long distances, especially in the case of migratory specie [25].

5.2 Risk factors for wild birds

Several factors contribute to the risk of wild birds harboring and spreading Salmonella:

1. Foraging habits: birds that forage in areas where they can come into contact with Salmonella, such as agricultural lands or places with poor waste management, are at a higher risk of infection.

2. Habitat overlap with humans and domestic animals: birds living near human habitations or domestic animals are more likely to encounter sources of Salmonella. This is particularly true for birds that frequently live in urban areas or farm environments.

3. Environmental contamination: areas contaminated with Salmonella, whether through industrial activities, sewage, or other means, can serve as hotspots for birds to acquire the bacterium.

Minette [26] discussed these risk factors, indicating that the likelihood of wild birds carrying Salmonella is influenced by their interactions with both natural and anthropogenic environments. For example, birds that feed in contaminated areas or interact with domestic animals are more likely to become carriers of Salmonella [26].

In summary, wild birds play a significant role in the epidemiology of Salmonella due to their prevalence in diverse bird populations and the various risk factors that facilitate bacterial transmission. Understanding these dynamics is crucial for assessing the potential public health risks and for developing effective strategies to mitigate the spread of Salmonella from wild birds to humans and other animals (Figure 3).

Figure 3.

Map showing the prevalence of salmonellosis in wild birds across different continents [27].

6. Salmonella in domesticated birds

6.1 Salmonella in poultry

One of the most significant reservoirs for Salmonella is poultry flocks, and the products of poultry flocks are frequently the source of human infections. Salmonella can be passed on to people through contact with infected birds, feces, or contaminated goods such as eggs and meat. Salmonella can also be spread through cross-contamination [22].

6.2 Measures to prevent the spread of Salmonella in poultry farms

Salmonella poses a notable threat to chicken farms, and it is imperative to implement control measures to prevent its dissemination. Several strategies can be implemented to manage Salmonella in poultry farms:

6.2.1 Measures to ensure biosecurity

Implementing biosecurity measures is crucial to prevent the entry of Salmonella into the farm. Implementing biosecurity measures is crucial for preventing Salmonella from entering farms. These methods include regulating entry to farms, sterilizing equipment and trucks, and preventing interactions between wild birds and poultry [9]. Ensuring limited entry to farms is a crucial concern, and the provision of shower and changing room amenities for both workers and tourists can effectively mitigate the transmission of Salmonella.

6.2.2 Vaccination

Vaccination is a highly efficient and economical approach to mitigate the consequences of clinical Salmonella infections in chickens. Vaccines can decrease the occurrence of Salmonella in groups of chicken and hinder the transmission of the pathogen to humans [28, 29].

6.2.3 Flock surveillance for infection

Surveillance of chicken flocks is essential for identifying the presence of Salmonella infection. Sampling of regular chicken flocks should be monitored to oversee the production chain, and prompt measures should be implemented upon detection of Salmonella [28]. Identifying the source of the illness is crucial for preventing the dissemination of bacteria.

6.2.4 Sanitization and sterilization

Thoroughly cleaning and disinfecting poultry houses and equipment is crucial for preventing the transmission of Salmonella. It is essential to exercise caution when cleaning and disinfecting. Additionally, before replenishing the facility, it is necessary to conduct a bacteriological investigation [30].

6.3 Salmonella-free birds

The crucial initial step in preventing illnesses is introducing birds free from Salmonella [31]. Incoming avian specimens must exhibit optimal health conditions, and the relocation of poultry groups after their production cycle should exclusively be permitted for slaughter. Poultry farms can mitigate the occurrence of Salmonella in their flocks and hinder the transmission of the infection to humans by implementing these management methods (Figure 4).

Figure 4.

Diagram of biosecurity measures in a poultry farm setup. 1. The biosecurity plan should include the separation of domestic species, their removal, and testing for any diseases. 2. As a biosecurity precaution, the human factor attempts to minimize indirect transmission by discouraging equipment sharing and supporting thorough disinfection of shared equipment. Additionally, visitors should be provided with personal protective equipment when in close contact with animals. 3 and 4. Utilizing detergents for on-farm washing will enhance the efficiency of debris and biofilm removal. 5. The veterinarians must maintain a sanitary atmosphere. 6. Preventive environmental measures on farms should encompass the implementation of physical barriers or fences, monitoring programs, vaccination protocols, and mandated testing of natural fauna. 7. Wastes from diseased animals and any biological wastes from wild animals must undergo proper disposal procedures. Water management and environmental contamination in the range of 8–9 restrict animals from accessing natural water sources such as streams and creeks, which could potentially contain infections [32].

7. Transmission routes

Salmonella, a prevalent and possibly lethal bacterium, can infect humans through different means, including direct interaction with birds, pollution of the environment, and transmission through food. Understanding these transmission pathways is essential for implementing efficient preventive strategies. New research has provided insight into the many mechanisms by which Salmonella can be transmitted from birds to humans.

7.1 Transmission of diseases from birds to humans

Salmonella can be transmitted to humans by direct contact with birds or their excrement. This transmission mode is most pertinent in environments where people are close to avian species, such as in domestic poultry-rearing or bird-feeding endeavors. Research has demonstrated that Salmonella can be transferred among hens, cattle, and pigs through infected feed or the environment in free-range situations. Moreover, wild avian species have the potential to transmit Salmonella to humans by direct contact or through exposure to their excrement and saliva, particularly in settings where birds congregate, such as bird feeders [33, 34].

7.2 Environmental contamination

The transmission of Salmonella from birds to people, resulting in indirect human contact, is a significant problem in terms of environmental contamination. Both wild and domestic birds have the potential to contaminate diverse surroundings, such as agricultural settings, with Salmonella, so endangering human health. By deposition, Salmonella can contaminate water supplies, soil, or surfaces near avian habitats. Studies have emphasized the significance of environmental pollution in the transmission of Salmonella from birds to humans, underscoring the need to reduce environmental exposure in regions with large bird populations. Moreover, the presence of Salmonella in water sources has raised concerns due to its potential to affect the microbiological integrity of water and compromise food safety. The primary sources of Salmonella contamination on produce include soil, manure, irrigation water, and exposure to reptiles, birds, or other small animals. It has garnered significant attention as a potential reservoir of Salmonella contamination, and research has linked it to Salmonella contamination [22, 35].

7.3 Transmission of pathogens through food

Contaminated poultry products are a significant means of transmitting Salmonella to humans. Poultry goods, including eggs and meat, can potentially be infected with Salmonella, which presents a substantial hazard to consumers. Ensuring the appropriate management, preparation, and preservation of chicken products is crucial for preventing the spread of Salmonella through food. Research has shown that Salmonella is commonly found in birds that live in urban areas, indicating there is a risk of spreading the bacteria through the consumption of contaminated chicken products [36, 37].

To summarize, Salmonella can be transmitted from birds to humans through different pathways, such as direct contact, environmental pollution, and transmission through contaminated food. It is crucial to implement measures restricting exposure to various transmission modes, such as maintaining excellent hygiene, following safe food handling practices, and addressing environmental contamination. Various actions are necessary to decrease the risk of Salmonella infection in humans (Figure 5).

Figure 5.

Infographic showing different transmission routes from birds to humans.

8. Salmonella strains and serovars in birds

8.1 Common Serovars in birds

Serovars like Typhimurium and Enteritidis are commonly found in birds [38]. Salmonella enterica serovars, including Typhimurium and Enteritidis, are frequently present in various bird species, whether they are wild or domestic. These serovars are especially problematic since they can cause illness in birds and humans. These serovars have been classified as host-specific and linked to salmonellosis in avian species, such as pigeons and passerines. Moreover, the rise of antibiotic-resistant Salmonella strains in avian species is becoming increasingly problematic, as it could compromise the efficacy of antimicrobial therapy for avian and human illnesses [7, 39].

Studies have demonstrated that various forms of Salmonella, such as Typhimurium, can infect a wide range of hosts. Nevertheless, they may also adapt to specific hosts, with different lineages linked to particular bird species. An investigation of 131 S. Typhimurium isolates obtained from wild birds in the United States revealed that isolates from various taxonomic host groups, such as passerine birds, water birds, and larids, belonged to three separate lineages. This suggests that genetic characteristics are associated with adaptability to different hosts [40].

8.2 Antimicrobial resistance in Avian-associated Salmonella

The emergence of antimicrobial-resistant strains in birds is a growing concern [41]. The increase in antimicrobial-resistant strains of Salmonella in avian species is a burgeoning concern that substantially impacts the well-being of animals and humans. Poultry-associated Salmonella isolates have developed antimicrobial resistance (AMR) due to the extensive use of antimicrobial agents on farms. Consequently, the emergence of antibiotic-resistant Salmonella strains has presented a formidable obstacle in effectively treating Salmonella infections in both avian and human populations [8].

An analysis of antibiotic resistance in Salmonella spp. obtained from poultry worldwide revealed a significant prevalence of resistance (60.7%) in Salmonella isolates against routinely employed antibiotics in poultry farming, including nalidixic acid and ampicillin. The study also identified significant antibiotic resistance levels toward streptomycin, amoxicillin/clavulanic acid, and trimethoprim/sulfamethoxazole. The results emphasize the extensive occurrence of antibiotic resistance in Salmonella strains obtained from poultry, emphasizing the immediate requirement for efficient approaches to control the dissemination of antimicrobial resistance in bird populations [42].

The appearance of Salmonella strains that are resistant to antimicrobial drugs in broiler chickens has also sparked worries about the consequences of using antimicrobial agents in the production of food animals. The detection of antibiotic-resistant Salmonella in meat products has increased worries regarding the potential ramifications of antimicrobial usage in the poultry sector. As a result, there has been a demand for the adoption of antimicrobial agents and the development of alternative approaches to decrease antibiotic dependence in chicken farming [43].

8.3 Salmonella strain in birds reported from different countries

Research has been conducted in several areas to examine the occurrence and genetic traits of Salmonella in birds that live in the wild. This has yielded vital knowledge on the specific strains and serovars linked to salmonellosis in birds. Notable discoveries derived from the given sources include the following:

8.4 Incidence and serotypes in Poland

A study conducted in Poland has revealed that Salmonella ser. Typhimurium as a causative agent of salmonellosis in pigeons and passerines. This finding confirms that certain wild bird species serve as reservoirs for Salmonella serotypes, particularly Salmonella ser. Typhimurium [7].

8.5 Molecular characterization in the United States

A study conducted in the United States revealed that Salmonella enterica serovar Typhimurium isolates obtained from wild birds exhibited unique lineages that were determined by the kind of bird. Some of these isolates displayed genetic characteristics indicating adaptability to their specific hosts. Genetic sequencing of 131 S. Typhimurium samples obtained from wild birds in 30 states across the United States was performed. The samples were collected between the years 1978 and 2019 [39].

8.6 Incidence and variety in environments of fresh produce

Studies have demonstrated a significant amount of diversity in bird feces, with the identification of up to three serovars of Salmonella from a single sample, indicating a wide range of variations. The culture-based investigation confirmed the presence of a wide range of serovars among the isolates, thereby indicating a high level of diversity [22].

8.7 Salmonella in wild birds in Bangladesh

A study conducted in Bangladesh found that 65% of Corvus splendens (house crow) and 67% of Gracupica contra (Asian Pied Starling) were infected with Salmonella. This highlights the potential public health importance of salmonellosis transmitted by birds (Figure 6) [45].

Figure 6.

Chart illustrating the antimicrobial resistance patterns of avian Salmonella strains. The antimicrobial resistance phenotypes and genotypes of the Salmonella isolates were analyzed for the distribution of resistance to different antibiotics. The abbreviations used are as follows: TET for tetracycline, GEN for gentamicin, CIP for ciprofloxacin, ENR for enrofloxacin, SXT for sulfamethoxazole/trimethoprim, AMP for ampicillin, CRO for ceftriaxone, and FOX for cefoxitin [44].

9. Public health concerns

The transmission of salmonellosis from birds can cause substantial health hazards, particularly during outbreaks. The increasing prevalence of antibiotic-resistant strains in avian populations is problematic since it can compromise the efficacy of antimicrobial therapy for avian and human illnesses [46]. Public health must track and manage outbreaks associated with avian sources, as they have the potential to cause the transmission of Salmonella to people and other animals [47].

9.1 Outbreaks and surveillance

Tracking and managing outbreaks linked to avian sources are critical for public health [38]. CDC [48] Salmonella infections associated with avian sources have been documented in different environments, such as in backyard poultry farming and bird-feeding activities. In the United States, health authorities have examined numerous outbreaks of Salmonella, including Enteritidis, Indiana, Infantis, Mbandaka, and Typhimurium, which have been connected to contact with backyard poultry. These widespread occurrences emphasize the significance of closely observing and monitoring Salmonella infections to prevent their dissemination [48].

9.2 Impact on public health

Salmonellosis from avian sources poses significant health risks, especially in outbreak scenarios [49]. Avian-related salmonellosis can result in various symptoms, such as diarrhea, abdominal cramps, and fever, which can potentially lead to severe illness and mortality in some instances. The presence of harmful microorganisms in poultry meat and its by-products poses a significant threat to public health, as it can transmit zoonotic diseases through contaminated food. Furthermore, the emergence of antimicrobial-resistant strains of Salmonella in birds can complicate the treatment of Salmonella infections in both avian and human populations [46].

To summarize, Salmonella infections from avian sources pose substantial public health issues due to their potential to cause outbreaks, severe disease, and mortality. The presence of antimicrobial-resistant strains in birds adds complexity to the issue, requiring thorough monitoring, preventive, and control strategies to reduce the danger of transmission to people and other animal species (Figure 7).

Figure 7.

Timeline of major salmonellosis outbreaks associated with birds [8, 50].

10. Preventive measures

10.1 Strategies for reducing bird-related salmonellosis

Includes wildlife management, improving food hygiene, and public education [51]. Controlling Salmonella in chicken is paramount for public health, as it primarily contributes to human foodborne illnesses. It is crucial to employ efficient techniques to decrease the occurrence of salmonellosis caused by birds, hence minimizing the potential for transmission to humans and other animals. Various crucial strategies have been found to tackle this problem, such as implementing wildlife management, enhancing food cleanliness, and promoting public education.

10.2 Biosecurity practices in poultry farms

Critical for preventing the spread of Salmonella in poultry products [52]. Implementing biosecurity measures in poultry farms is crucial for mitigating the transmission of Salmonella in poultry products. Stringent biosecurity measures, such as thorough cleaning and disinfection, are crucial for minimizing disease occurrence in chicken farms and food processing facilities. Incorporating comprehensive hygiene and biosecurity measures into the whole poultry management strategy is crucial. The foremost step in preventing infections is the introduction of birds that are free from Salmonella. Furthermore, implementing limited entry, consistent surveillance of chicken populations, and prompt response upon identification of Salmonella are crucial elements of efficient biosecurity measures [53].

10.3 Non-antibiotic approaches

Administering postbiotics, which are non-antibiotic methods, has been proven to significantly decrease Salmonella-related infections in chickens. Using non-antibiotic options like probiotics, synbiotics, phytobiotics, and vaccinations has proven productive in managing Salmonella infections in laying hens, broilers, turkeys, and quails. It is crucial to use these non-antibiotic measures to avoid sickness and enhance the productive performance of birds while decreasing the dependence on antibiotics in poultry production [28].

10.4 Public education and awareness

Raising awareness about transmission risks and preventive measures is vital. Promoting an understanding of the hazards of transmitting salmonellosis through birds and taking preventive steps to minimize these risks is crucial. Public education programs should prioritize promoting proper hygienic practices, including regularly cleaning feeders, ensuring various food sources, and monitoring bird behavior. Furthermore, it is crucial to educate poultry farmers and workers on the significance of implementing rigorous biosecurity protocols and exercising judicious practices when using antimicrobial agents. This is necessary to effectively curb the dissemination of Salmonella within chicken populations and mitigate the potential for foodborne transmission to people [9]. To summarize, it is crucial to employ all-encompassing approaches, such as efficient biosecurity measures, immunization, non-antibiotic substitutes, and public awareness campaigns, to diminish avian-associated salmonellosis and mitigate the likelihood of human transmission. These procedures must be implemented at every stage of chicken meat and egg production to guarantee the safety and excellence of poultry products and safeguard public health (Figure 8).

Figure 8.

Flowchart of the implementation of preventive measures at different levels.

11. Research and future directions

11.1 Ongoing research in bird-associated Salmonella

Research focuses on understanding transmission dynamics, developing vaccines, and improving surveillance. Current investigations on bird-associated Salmonella have focused on understanding transmission dynamics, formulating vaccines, and enhancing surveillance. Research has been undertaken to ascertain the frequency and genetic makeup of Salmonella in wild birds across different areas. Research conducted in the western and southwestern regions of the United States discovered that the incidence of Salmonella in wild birds ranged from 0.5% to 6.5%. This study detected 24 avian species, with the eastern bluebird being the most prevalent [22]. The ability to detect Salmonella in wild birds to acquire and spread the pathogen has emphasized the significance of monitoring and managing efforts.

11.2 Innovations and technologies

Technological advancements in detection and control measures are ongoing. Continuous progress is being made in the technology field to identify and manage Salmonella. An area of innovation is the advancement of non-antibiotic approaches to manage Salmonella illness in chickens. Empirical research has substantiated that ingesting postbiotics through the mouth substantially diminishes Salmonella-related illnesses in chickens [28]. This provides a promising non-antibiotic option for reducing Salmonella infections in laying hens, broilers, turkeys, and quails facing challenges. Furthermore, progress in omics sciences has facilitated a more profound comprehension of Salmonella’s genetic and molecular attributes, thereby aiding in the creation of inventive control strategies.

11.3 Challenges and opportunities

The evolving nature of Salmonella strains and changing environmental conditions present both challenges and opportunities for research. The dynamic characteristics of Salmonella strains and shifting environmental circumstances pose obstacles and prospects for scientific investigation. The occurrence of Salmonella in wild birds exhibits regional and temporal variability, with swings in prevalence observed throughout different years and geographic areas [22]. This fluctuation presents difficulty in monitoring and control endeavors. Nevertheless, it also provides a chance to obtain a more profound understanding of the elements that influence the incidence of Salmonella in wild bird populations. The rise of antimicrobial-resistant strains in avian species poses a substantial obstacle. Nevertheless, it has also stimulated the advancement of non-antibiotic approaches and the investigation of cutting-edge technology for managing Salmonella infections in poultry (Figure 9).

Figure 9.

Graphical representation of the research landscape of bird-associated salmonellosis. Maximum-likelihood phylogeny of 914 poultry, human, and other isolates from 46 countries. The tree is midpoint-rooted. There are three main lineages: Global, Atlantic, and United States. Each continent-originating isolate is color-coded. Human and poultry (chickens and eggs) isolates were included. In Chile, Brazil, and Mauritius poultry, Salmonella enteritidis clades were identified. Isolates with publicly available phage types are arrow-headed. The Atlantic. The scale bar shows 50 SNPs. b circular cladogram of the maximum-likelihood phylogeny of 914 isolates. Internal nodes with a spearman or Pearson correlation between isolation years and branch lengths > 0.4 are shown by colored circles. The circle sizes are proportional to the R² values (0.4–0.9). Gray shading indicates high temporal SNP increases in the global and Atlantic lineages [54].

12. Conclusion

12.1 Summary of key findings

Birds play a significant role in the epidemiology of salmonellosis, serving as both reservoirs and vectors. The studies on the role of garden birds in the transmission of salmonellosis reveal a multifaceted issue that intersects wildlife ecology, public health, and environmental science. The research underscores the need for a holistic approach to managing this public health challenge, involving careful monitoring of bird populations, public education on safe bird interaction practices, and strategic wildlife management to mitigate the risks of salmonellosis transmission.

12.2 Extended analysis of key studies and findings

• Comprehensive view: this study was not limited to identifying garden birds as reservoirs. It also explored how human interaction with these birds, particularly in urban and suburban gardens, potentially increases the risk of salmonellosis transmission. The research suggested a more nuanced understanding of bird-human interactions and their implications for disease spread [4].

• Beyond genomic analysis: the genomic analysis provided by this study gave insights into the genetic similarities of Salmonella strains in birds and humans. This has broader implications for tracking the evolution of bacteria and understanding their spread across species. This finding also underscores the need for hygiene and safety in human interactions with wild birds [6].

• Specific bird species as reservoirs: by focusing on specific species like the Eurasian siskin and greenfinch, this study highlighted the varied susceptibility of different bird species to Salmonella. It paved the way for targeted public health advisories and wildlife management strategies, especially in regions where these species are common [55].

• Host resistance and poultry breeding: investigating host resistance at the genetic level opens up potential pathways for breeding disease-resistant poultry. This could have significant implications for the poultry industry and food safety, reducing the risk of salmonellosis transmission from poultry to humans [49].

• Seasonal dynamics and disease monitoring: understanding the seasonal patterns of Salmonella in wild birds such as greenfinches provides critical information for timely surveillance and intervention strategies. This research is vital for planning public health initiatives and wildlife conservation efforts [56].

• Risks of supplementary feeding: the study on supplementary feeding practices sheds light on how human activities can inadvertently increase disease transmission risks. It emphasizes the need for responsible wildlife feeding and the design of bird feeders that minimize the spread of pathogens [5].

• Diversity of Salmonella strains: the discovery of host-adapted Salmonella phage types in British garden birds suggested that the interaction between Salmonella and its bird hosts is more complex than previously thought. This finding is crucial for understanding the disease ecology and for developing more effective control measures [1].

• Environmental contamination: highlighting the risk of environmental contamination at public events like agricultural fairs, this study illustrates how Salmonella can spread in communal settings. This finding underscores the importance of sanitation and public awareness to prevent outbreaks [57].

12.3 The ongoing importance of studying birds in salmonellosis

Consistent surveillance and investigation are crucial for effectively addressing the public health hazards linked to avian salmonellosis. The continued significance of researching salmonellosis in birds lies in their capacity to acquire and disseminate the bacterium, which presents a potential threat to human well-being. Human sickness outbreaks have been linked to direct interactions with untamed avian species. Moreover, wild birds can act as reservoirs for zoonotic infections, such as Salmonella. The continued significance of investigating avian involvement in salmonellosis is in the capacity of these birds to acquire and disseminate the bacterium, hence constituting a potential hazard to human well-being. Continuous surveillance and research are crucial for effectively managing the public health concerns linked to bird-associated salmonellosis. These efforts aid in assessing the extent of the danger of Salmonella transmission from wild birds to humans and in devising efficient ways for monitoring and controlling the spread of the disease (Figure 10).

Figure 10.

Conceptual diagram summarizing the interconnectivity of the chapter’s key points.