Overview of Enteric Campylobacteriosis

Campylobacter spp are spiral or curved rods that exhibit a characteristic corkscrew darting motility, mediated by a single polar flagellum. These are slow growing, with a generation time of ~90 min, fastidious, and require enriched medium and microaerobic conditions with increased CO₂ (3%–15% O₂, 3%–10% CO₂, 85% N₂) for growth.

The family Campylobacteraceae consists of three genera, including Campylobacter and Arcobacter associated with animal and human diseases. Certain species are present commensally in animals as suspected reservoirs for human infections. The thermophilic Campylobacter spp, C jejuni, or C coli have the highest prevalence and disease impact. Campylobacter species causing diseases in livestock include C jejuni subsp jejuni (enteritis and abortion), C coli, C mucosalis (porcine enteritis), C upsaliensis, C helveticus (companion pet enteritis), C hyointestinalis subsp hyointestinalis (porcine and bovine enteritis), C sputorum (abortions in sheep), and C fetus subsp fetus (isolated from intestinal tracts of sheep and cattle, sporadic abortions). Certain species such as C jejuni, C hyointestinalis, and C fetus possess closely related subspecies with different disease foci. Initially, Arcobacter spp were considered to be aerotolerant campylobacters and are implicated in reproductive disorders, mastitis, gastric ulcers, and/or diarrhea in livestock, including A cryaerophilus (previously C cryaerophila), A skirrowii, A thereius, and A butzleri.

Transmission is food- or waterborne or via fecal-oral spread. Animals serve as reservoir hosts for Campylobacter spp infections in both animals and people throughout the world. The predominant ecologic niche for Campylobacter spp is the GI tract of a wide variety of domesticated and wild vertebrates, and zoonotic transmission from animals to people in meat of animal origin, especially chicken, is a food safety issue. Campylobacter spp are also commonly isolated from free-living birds, including migratory birds and waterfowl, crows, gulls, and domestic pigeons, which can contaminate environments of grazing animals. Wild rodents and insects such as flies have also been reported to harbor and transmit C jejuni. Fecal contamination of the environment provides a ubiquitous source of these organisms under appropriate conditions for their survival. Campylobacter spp can persist for long periods in feces, milk, water, and urine, especially at temperatures close to 4ºC. In adverse conditions, C jejuni jejuni converts to a viable nonculturable form that can be reactivated when ingested.

Human foods documented as contaminated with Campylobacter include chicken, turkey, beef, pork, fish, and milk. Domesticated poultry are the most significant reservoir of C jejuni jejuni for people, causing 50%–70% of cases; chicken meat is the number one source. Dogs and cats are commonly infected similar to their owners when they ingest undercooked poultry.

Bacterial motility, mucus colonization, toxin production, attachment, internalization, and translocation are among the processes associated with C jejuni jejuni virulence. Infection begins with ingestion of C jejuni jejuni in contaminated foods or water. Gastric acid provides a barrier, and the bacteria must reach the small and large intestines to multiply; C jejuni invades both epithelial cells and cells within the lamina propria.

Abdominal pain, fever, diarrhea, blood in feces, and inflammatory cells in feces demonstrate the inflammatory nature of the infection. Natural infections with C jejuni jejuni resulting in enteritis have been reported in juvenile macaques, weaning-age ferrets, dogs, cats, and swine. Chickens, rodents, ferrets, primates, rabbits, and pigs have been inoculated experimentally by various routes with C jejuni and subsequently developed enteritis. Clinical reports describe primary infections with systemic spread, infection with mucosal disease, infection without disease but with short-term bacterial persistence, and infection with resistance and no bacterial persistence. These reports support the idea that C jejuni jejuni produces a spectrum of disease scenarios, depending on the immune status of the host, bacterial virulence, gene expression, and other factors.

C jejuni jejuni, C coli, C jejuni, C upsaliensis, and C helveticus are the Campylobacter spp that have been associated with intestinal disease in companion animals. C jejuni jejuni causes diarrhea in dogs and cats, which are considered a significant source of the bacterium for the human population. Diarrhea is usually acute but can be recurrent. Diarrhea lasting 515 days is the most common clinical sign in dogs <6 mo old. It may be watery to bloody with mucus and is sometimes bile-stained. Occasionally, the diarrhea becomes chronic and may be accompanied by fever and increased WBC count. Cats <6 mo old commonly have diarrhea, which may be bloody. Some infected cats show no signs. Additionally, C jejuni jejuni has been isolated in the profuse and odorless hemorrhagic vaginal discharge from late-pregnancy abortions in dogs.

In cattle and sheep, Campylobacter spp can cause enteritis and abortion, including C jejuni jejuni, C fetus subsp fetus, C hyointestinalis subsp hyointestinalis, and C sputorum (abortions in sheep). However, in studies that compared C jejuni prevalence in healthy cattle and in cattle considered “sick” because of diarrhea, the frequency of Campylobacter spp was not significantly different. Beef and dairy cattle can have significant levels of Campylobacter, with prevalences of 2.5%–60%. In a number of studies, cattle checked at slaughter harbored Campylobacter in gallbladders, large and small intestines, and liver. Fecal shed in cattle leads to contamination of milk and beef.

Campylobacters can contribute to colitis in weaning aged pigs. Swine commonly carry C coli and C jejuni jejuni as intestinal commensals, and studies in the USA, Netherlands, Great Britain, and Germany show that more than half of commercially raised pigs excrete the organisms. C coli strains comprise most isolates from pigs, causing first watery, then inflammatory diarrheal disease. Pigs have anorexia, fever, and diarrhea for 1–5 days followed by remission of clinical signs but continue to shed C jejuni jejuni in the feces. C hyointestinalis hyointestinalis and C mucosalis are also implicated as causes of enteritis in pigs. Concurrent infections with viruses, other bacteria (eg, Escherichia coli), and parasites increase the disease and pathology caused by Campylobacter spp in swine. C hyointestinalis subsp lawsonii has been isolated from pig stomachs; however, this subspecies has not been implicated in disease.

Birds, including intensively farmed poultry, appear to have a higher infection rate and carriage of Campylobacter spp, especially C jejuni jejuni, than other animals. In broilers, the organism may colonize the palatine lymphoid tissues and the crop, leading to extremely rapid transmission through communal water troughs and standard fecal-oral spread. However, the organism has been isolated from the small intestines of clinically ill birds, especially psittacines (parrots) and passeriforms (finches and canaries), with hepatitis, lethargy, loss of appetite, weight loss, and yellow diarrhea. Mortality may be high. Campylobacter spp have also been isolated from free-living birds, including migratory birds and waterfowl, crows, gulls, and domestic pigeons; however, disease due to C jejuni jejuni, for example in naturally infected birds, is rare.

Campylobacter GI disease has been reported in exotic pets (eg, ferrets, mink, primates, hamsters, guinea pigs, mice, and rats). Although clinical signs vary in these species, they generally include mucoid, watery, bile-streaked diarrhea (sometimes with blood), anorexia, vomiting, and fever. Prolonged infections are possible but uncommon; most infections are self-limiting with mild signs.

The following species have been isolated from birds, shellfish, reptiles, marine mammals, and livestock not known to be associated with disease symptoms: C avium, C hyointestinalis lawsonii, C fetus subsp testudinum, C canadensis, C peloridis, C insulaenigrae, C subantarcticus, C volucris, and C ureolyticus (previously Bacteroides ureolyticus). Several of these are implicated in human diseases.

Arcobacter spp infecting animals include A cryaerophilus (livestock abortion), A butzleri (livestock diarrhea, bovine and porcine abortions), A skirrowii (sheep diarrhea, livestock abortions), and A thereius (porcine abortion). Disease status is unknown, although these species have been isolated from food animals: A cibarious (chicken meat, piggery effluent), A trophiarum (fattening pigs), and A suis (pork meat). Approximately 11 additional Arcobacter spp found in shellfish, sewage, seawater, sediments, and salt marsh plants are not known to cause diseases in animals or people.

Campylobacter spp can be found in both healthy and diarrheic animals; thus, clinical signs and postmortem findings depend on the species and the host animal and its age. Diagnosis of enteric campylobacteriosis relies on isolation of the causative agent using selective media under microaerophilic conditions. Fresh fecal samples should be collected and transported to the laboratory preferably on the same day and within at least 2 days for processing. If transport to the laboratory is delayed, transport media and storage at 4°C produce the best results. Campylobacters are very sensitive to environmental conditions, including dehydration, atmospheric oxygen, sunlight, and increased temperature. Organisms are thin (0.2–0.8 µm × 0.3–5 µm), gram-negative, motile, curved rods. The cells are S-shaped or curved but are occasionally long (8 µm) spiral rods. They exhibit a typical spiraling motility. In unfavorable growth conditions, spiral rods undergo a degenerate conversion to coccoid forms. Campylobacters can be quickly outgrown by contaminating microbes during prolonged transport to the laboratory, and isolation of pure colonies for downstream testing can be difficult. Filtration using 0.45 µm filters can help because campylobacters will pass through.

Enrichment is required for most clinical sampling unless material can be transported to the laboratory immediately. When samples are collected in swabs, the use of commercially available transport tubes containing medium, such as Amies, is recommended. The medium can be plain agar or charcoal-based. Several transport media have been described for transport of fecal specimens, including Cary-Blair, modified Cary-Blair, modified Stuart medium, Campy thioglycolate medium, alkaline peptone water, and semisolid motility test medium. Other media are recommended for the isolation of campylobacters associated with reproductive losses.

Campylobacter spp do not ferment carbohydrates, and other biochemical characteristics are thus used to identify different species. Thermophilic/thermotolerant Campylobacter spp, including C jejuni jejuni, C coli, C upsaliensis, C lari, C mucosalis, C sputorum, C hyointestinalis, and C helveticus grow best at 42°C, although they are capable of growth at 37°C. C fetus do not grow or grow poorly at 42°C. Alternatively, this species grows well at 25°C, whereas the thermophilic campylobacters do not (except C mucosalis, which can grow at 42° and 25°C, weak growth for C hyointestinalis at 25°C). C jejuni is differentiated on its ability to hydrolyze hippurate, and C upsaliensis has negative or weak catalase production and is differentiated from other campylobacters because of its sensitivity to nalidixic acid. C helveticus is also catalase negative but can be difficult to differentiate biochemically from C upsaliensis relying on distinctive colony morphologies.

Differentiation of subspecies can be necessary for identification of significant pathogens. C jejuni subsp jejuni is the main cause of enteritis, whereas C jejuni subsp doylei has been isolated only from enteritis cases of children and not animals. They can be differentiated by the ability of C jejuni doylei to reduce nitrate. Similarly, C hyointestinalis subsp hyointestinalis can cause bovine and porcine enteritis; however, C hyointestinalis subsp lawsonii has been isolated from the porcine stomach, but it is not known to cause disease. The subspecies can be differentiated by testing the intolerance of C hyointestinalis lawsonii to 1.5% bile and/or 0.1% potassium permanganate.

Arcobacter spp (previously known as aerotolerant campylobacters) can also be associated with human and animal diarrhea and with animal abortions. Arcobacters are usually not thermophilic but can be confused with the nonthermophilic Campylobacter spp if aerotolerance is confirmed using standardized suspensions of organisms. Although most cases of human enteritis are attributed to C jejuni jejuni, C coli, C lari, and C upsaliensis, it has been suggested that the importance of other species also associated with GI illness may be significantly underdiagnosed as a consequence of inappropriate isolation and identification methods.

Immunodiagnosis (ELISA) is unsuitable to diagnose intestinal Campylobacter infections.

PCR-based methods effectively identify infection, especially if cultivation is difficult or if the sample has been somewhat mishandled. However, a positive test is not sufficient evidence to determine causation and must be considered in conjunction with clinical signs.

Clindamycin, gentamicin, tetracyclines, erythromycin, cephalosporins (eg, cephalothin), and fluoroquinolones (eg, nalidixic acid) are effective against C jejuni, C helveticus, and C upsaliensis. C fetus, C hyointestinalis, C mucosalis, and C sputorum are usually resistant to the fluoroquinolones yet sensitive to cephalosporins. C coli are sensitive to fluoroquinolones but resistant to cephalosporins. Susceptibilities to penicillins and trimethoprim are variable across Campylobacter spp. Resistance to the fluoroquinolones, tetracycline, kanamycin, and some other antibiotics has been documented among the Campylobacter spp, mediated by both chromosomal and plasmid mechanisms. Culture-dependent diagnosis can provide isolates for antibiotic sensitivity testing. However, some animals remain colonized and become persistent shedders despite antibiotic therapy. If the goal of treatment is to decrease the risk of zoonotic transmission to a susceptible household member, antibiotic treatment alone may be inadequate. Control involves treatment, removal to a clean environment, and prospective fecal testing to ascertain shedding status; even so, low infective doses and the ubiquitous distribution of the organism pose significant challenges.