Introductory Chapter: The Significance of Campylobacter as Foodborne Pathogen

1. Introduction

1.1 Campylobacter

Campylobacter is related to Arcobacter, Helicobacter, and Wolinella and is classified as proteobacteria in the order Campylobacteriales and the family Campylobacteraceae [1, 2]. Sebald and Veron (1963) were the first to propose the genus Campylobacter, which now has 27 species and 8 subspecies [3]. Campylobacter is gram-negative bacteria that are curved, spiral, or rod-shaped and do not produce spores. They are tiny (0.2–0.9 μm in width and 0.2–5 μm in length). With the exception of the nonmotile Campylobacter gracilis and Campylobacter showae, which possess numerous flagella, most species have a corkscrew-like movement through a single polar flagellum or bipolar flagella [4]. This genus of bacteria is chemoorganotroph, meaning they get their energy from amino acids and tricarboxylic acid cycle intermediates. They have high dietary requirements and need a variety of nutritional settings, including anaerobic or micro-aerobic conditions. Some species of this genus are considered commensal organisms. However, they are linked to a broad range of illnesses in animals and humans. The three species of the genus, including Campylobacter jejuni, Campylobacter coli, and Campylobacter lari, which are usually referred to as thermophilic species, account for the bulk of human infections. C. coli is the second most prevalent Campylobacter species related to human sickness, and it is often found in pigs. C. jejuni subspecies jejuni (also known as C. jejuni) and C. jejuni subspecies doylei are the two subspecies of C. jejuni. C. jejuni is a pathogen that is found as a commensal in chickens and is considered a major foodborne pathogen. C. jejuni subspecies doylei is distinct from C. jejuni in that it does not have any animal hosts [5, 6]. Since its discovery, Campylobacter has been recognized as a significant human gastrointestinal pathogen globally. According to the Emerging Pathogens Institute’s Foodborne Illness Risk Ranking Model (FIRRM), Campylobacter is the most prevalent foodborne pathogen in the United States, posing the greatest public health burden [7]. Since 2013, Campylobacter infection has been the most frequently detected infection in FoodNet locations, and the rate of infection seems to be rising. The poultry industry is a significant source of Campylobacter. Campylobacter is a zoonotic-causing commensal bacteria found in the gastrointestinal tracts of many wild animals (birds like ducks and gulls), agricultural animals (cattle and pigs), and companion animals (dogs and cats) [8]. C. jejuni causes the majority of cases within a vast and varied collection of species, while C. coli causes 1–25% of Campylobacter-related disorders [9]. Due to occasional exposure to this disease, vulnerable populations of Campylobacter have been found to be concentrated in the United States and European nations [10]. Campylobacteriosis has been shown to be seasonal, with a surge in the summer months, perhaps due to an increase in flies and other vectors [11]. In flocks, the infection passes horizontally from the environment to 2- or 3-week-old chicks due to protective maternal antibodies retained in serum for a week after hatching. Then progressively reduce it until the third week is complete. Campylobacter infection quickly spreads horizontally among the population, with an incidence rate of 2.37 cases per day. One infected bird may spread Campylobacter to 20,000 chickens within a week. Numerous investigations have shown that vertical Campylobacter infection is possible. Campylobacter was recovered from the internal and external surfaces of eggshells, the maternal reproductive system, and rooster sperm [12]. The majority of human illnesses are caused by eating raw, infected animal products, including meat and milk, particularly chicken meat. People may be infected by drinking contaminated water, coming into contact with animals, and other environmental causes [11]. Campylobacteriosis is characterized by acute diarrhea that is often accompanied by abdominal cramping, headache, and fever [13]. Campylobacteriosis is a self-limiting illness with a latent phase of 2–5 days and a clinical duration of up to 2 weeks [14]. However, the symptoms may persist for many weeks, and in 10% of reported cases, medical intervention is necessary [15]. Guillain-Barre syndrome (GBS), a life-threatening autoimmune illness that causes peripheral neurological injury and has a death rate of 2–7% and a poor prognosis, is attributed to C. jejuni infection [16, 17].

1.2 Human campylobacteriosis

Recent advances in epidemiological monitoring, including the use of genetic techniques, have resulted in the detection of at least ten additional Campylobacter spp., other than C. jejuni and C. coli, in gastroenteritis patients; these have been designated as emerging Campylobacter pathogens [18]. Campylobacter concisus and Campylobacter upsaliensis have the greatest incidence among them. Furthermore, in samples obtained from southern Ireland, Campylobacter ureolyticus seems to have surpassed C. coli as the second most prevalent causal agent of campylobacteriosis. Except for ten Campylobacter species, all have been linked to human sickness, and infections are most often induced by the eating of infected meat, especially chicken, milk, or water, or by contact with the environment [19]. Infections with Campylobacter usually induce acute gastroenteritis, but they may potentially cause severe extra-intestinal sickness or long-term neurological or gastrointestinal problems (Figure 1, [20]).

Figure 1.

Campylobacter infections in humans: Sources and clinical symptoms. The main sources and pathways of Campylobacter transmission are shown on the left side of the figure. Arrows indicate transmission routes that are still under investigation. The variety of clinical symptoms of Campylobacter infections documented in humans is shown on the right-hand side of the figure.

For the most part, Campylobacter infections are self-limiting gastroenteritis with no long-term repercussions. Campylobacter jejuni is the most commonly encountered cause of Campylobacter gastroenteritis worldwide, followed by Campylobacter coli. “Emerging Campylobacter species, “ which include Campylobacter concisus, Campylobacter lari, Campylobacter ureolyticus, and Campylobacter upsaliensis, have also been found often in patients with gastroenteritis [20]. Complicated cases of campylobacteriosis, including extra-intestinal infections and long-term sequelae, contribute significantly to the total illness burden of Campylobacter, even though they are very uncommon. Individuals who are immunocompromised, pregnant, or old are more likely to get extra-intestinal infections. Campylobacter-associated bacteremia, septicemia, meningitis, spontaneous abortion, neonatal sepsis, abscesses, soft tissue infections, cardiovascular problems, and periodontal disease have all been reported. A tiny percentage of individuals with Campylobacter gastroenteritis suffer long-term post-infectious sequelae, such as Guillain-Barré syndrome (0.07%), reactive arthritis (2.86%), and IBS (irritable bowel syndrome) (4.01%) [21]. Guillain-Barré syndrome (GBS) is the most severe post-infectious consequence, with immediate flaccid paralysis and ophthalmoplegia, while Miller Fisher syndrome (MFS), a clinical variation of GBS, causes ophthalmoplegia and cerebellar-like ataxia [22]. While immunological diseases are well-known long-term effects of campylobacteriosis, there is also mounting evidence of a link between Campylobacter infection and chronic gastrointestinal illnesses, including inflammatory bowel disease (IBD), IBS, celiac disease, esophageal disease, and colon cancer [21, 23].

1.3 Campylobacter in livestock

The species Campylobacter fetus, which was most likely the first Campylobacter identified, is primarily responsible for the clinical relevance of Campylobacter infection in animals. C. fetus subsp. fetal and C. fetus subsp. veneralis are the two subspecies of the species. C. fetus subsp. the fetus has been found in a variety of animals, including poultry, reptiles, and humans, but is most often related to sheep and bovine miscarriage [24, 25]. Immunocompromised humans, as well as instances of neonatal sepsis and septic abortion, have all been discovered to have the pathogen. Bovine genital campylobacteriosis and infected venereal illness are caused by C. fetus subsp. veneralis, which may cause infertility, abortion, and embryo mortality [26]. Campylobacter is present in a broad spectrum of birds and animals as an asymptomatic colonizer and is regarded as a public health issue when identified in cattle and pets [8, 20]. Campylobacter spp., such as C. jejuni and C. coli, but also C. upsaliensis, C. concisus, C. lari, and Campylobacter lanienae, are often found as colonizers in the digestive tracts of chickens, pigs, and cattle. Once Campylobacter has been introduced to a flock, it may quickly spread. It usually leads to the life-long colonization of poultry [8].

1.4 Campylobacter in poultry

Campylobacter infection has been the most commonly found infection in FoodNet sites since 2013, and the prevalence of infection seems to be increasing. According to the Emerging Pathogens Institute’s FIRRM, Campylobacter is the most common foodborne pathogen in the United States, causing the highest public health risk [7]. According to epidemiologic research based on molecular epidemiology, chicken may be the leading cause of human campylobacteriosis [27]. In the meanwhile, owing to its greater feeding efficiency and quicker development rate than pork and beef, poultry is one of the world’s most significant animal protein resources [28]. The consumption of meat has shifted to poultry. This reflects the cheaper price of chicken compared to other meats in low-income developing nations, while it demonstrates a growing preference for white meats in high-income countries, which are easier to cook and seen as a healthier dietary option. Poultry meat is expected to account for 41% of total protein derived from meat sources worldwide in 2030, an increase of 2% from the baseline period (OECD/FAO, 2021–2030). Campylobacter is commensal bacteria that cause chronic infections in birds, causing little or no visible symptoms despite extensive colonization. Poultry is extensively colonized by Campylobacter, particularly C. jejuni and C. coli, and serves as a natural reservoir for these bacteria. C. jejuni infection is the most common cause of food-borne gastroenteritis in individuals worldwide [29]. When the first bird in a flock gets colonized, illness quickly spreads throughout the flock [11]. Campylobacter spreads rapidly throughout the flock, most likely as a consequence of fecal-oral transmission exacerbated by shared water and feed [15]. C. jejuni can also survive in feather follicles and pores on chicken skin at a depth of 20–30 m upon contact with its poultry host, which gives C. jejuni an appropriate microenvironment with little exposure to oxygen, appropriate humidity, and temperature to endure stress conditions [30]. C. jejuni colonization may continue throughout the broiler’s lifecycle, resulting in carcass contamination at the slaughter site. Although Campylobacter may be detected in the mucous layer of broiler chickens’ intestines, it is more often found in the cecal and cloacal crypts, where it does not attach to epithelial cells [31]. Broiler chickens may harbor C. jejuni at concentrations of up to 10⁶ to 10¹⁰ CFU per gram of feces [15]. C. jejuni discovery in tissues other than the intestine, such as the spleen, lung, heart, and liver, shows that this virus may translocate intestinal epithelial cells and become systemic [32]. Epidemiological tests suggest that a two-log unit decrease in C. jejuni contamination in chicken carcasses may result in a 30-fold reduction in the risk of human infection [33]. Additionally, this shows that eradicating C. jejuni on farms would have a major influence on the lowering of campylobacteriosis in humans.