Overview of Avian Campylobacter Infection
Campylobacteriosis is a significant enterocolitis of people frequently acquired through consumption of undercooked poultry meat contaminated with Campylobacter jejuni. It is the leading bacterial cause of sporadic enteritis in developed countries. It can also be acquired from handling backyard poultry as well as diarrheic companion animals and from contaminated water. The organism colonizes the intestine of chickens, turkeys, and waterfowl but is generally nonpathogenic in birds. Some strains of C jejuni have been reported to cause enteritis and death in newly hatched chicks and poults; however, it has not been possible to satisfy Koch’s postulates and reproduce the syndrome previously termed “avian vibrionic hepatitis” by administering isolates of C jejuni to chickens.
Commercial poultry and free-living birds are natural reservoirs of the thermophilic campylobacters (C jejuni, C coli, and C lari) and other poorly defined species. It is estimated that more than half of all commercial broiler and turkey flocks harbor C jejuni, although the prevalence can vary from 0% to100% depending on season (lowest in fall and winter and highest in summer). The organism has been isolated from numerous birds, including Columbae and domestic and free-living Galliformes and Anseriformes.
C jejuni has been found in all areas of commercial poultry production. Isolation of the organism is a function of surveillance and ability of laboratory personnel to culture and identify Campylobacter spp.
C jejuni is the predominant species associated with foodborne infection derived from poultry. C coli and C lari can also be recovered from the intestinal tract of poultry and have also been implicated in foodborne infection.
Environmental contamination is probably the most common source of infection for poults, chicks, and ducklings. Litter can remain infective for long periods, subject to at least a 10% moisture level and neutral pH. Exposed chicks and poults become colonized and can continue to excrete C jejuni for their lifetimes. Contaminated water may introduce infection into poultry flocks, and nonchlorinated water derived from a dam, river, or shallow well should be regarded as a possible source. Rats, mice, wild birds, darkling beetles, and houseflies can infect flocks; equipment and footwear contaminated with feces from an infected source may also serve as a vehicle of transmission. Once C jejuni has been introduced into the environment, rapid transmission within the flock occurs, with subsequent colonization of a high proportion of exposed breeders, commercial-meat, or laying-strain poultry. Some strains of Campylobacter can be transmitted vertically, either on the surface of eggs or by transovarial transmission. It has been isolated from the reproductive tracts of hens and roosters.
Many chicks are colonized with Campylobacter spp early in life with no associated clinical signs or pathology.
Most chicks display no lesions associated with Campylobacter infection. Some studies have reported that challenged chicks may exhibit distention of the jejunum, disseminated hemorrhagic enteritis, and in some cases, focal hepatic necrosis. Microscopic lesions of infected chicks include edema of the mucosa of the ileum and cecum with C jejuni in the brush border of enterocytes. Mononuclear infiltration of the submucosa and villous atrophy occur, with intraluminal accumulation of mucus, erythrocytes, and mononuclear and polymorphonuclear cells. However, infected flocks seldom exhibit increased mortality rates or decreased feed conversion. It is unclear whether these findings represent a true clinical syndrome in chicks, because challenge studies frequently result in no lesions.
Fecal specimens should be collected using swabs, then placed in Cary-Blair transport medium. Alternatively, cecal droppings can be collected into sterile laboratory sampling bags and packed on ice. Enrichment culture of specimens in semisolid motility medium facilitates isolation when small numbers of C jejuni are present. Campylobacter can be cultured on many different selective media, but commonly available formulations contain Brucella agar base and bovine blood with as many as seven antibiotics that inhibit overgrowth of Enterobacteriaceae. They also can be cultured on blood agar by selective filtration; bacteria in a 1/10 diluted fecal sample are allowed to penetrate a filter (0.45 µm pores) placed on the surface of a blood agar plate. After the liquid is absorbed into the plate, the filter is removed. Thermophilic Campylobacter spp should be cultured at 42°C under humid, microaerophilic conditions (85% nitrogen, 10% carbon dioxide, and 5% oxygen) for 48 hr. Some strains require a hydrogen-enriched atmosphere (5%). Campylobacter spp of significance in poultry are oxidase- and catalase-positive, indole-negative, and reduce selenite. The thermophilic species may be characterized on the basis of hippurate hydrolysis; nalidixic acid sensitivity is no longer reliable because of the increasing prevalence of fluoroquinolone-resistant C jejuni. The Penner or Lior serotyping schemes can be used to classify C jejuni ribotyping, or pulsed-field gel analysis can distinguish among various C jejuni isolates.
Because C jejuni is not found as a specific pathogen under commercial conditions, treatment of poultry flocks is not a consideration. If C jejuni is considered a problem in companion bird aviaries or in exotic species, antibiotics such as erythromycin can be administered in drinking water. Galliformes should receive a dosage of 10–30 mg/kg for 4 consecutive days, and Psittaciformes and exotics should be medicated at 30–40 mg/kg. Because of the zoonotic risk associated with C jejuni and its ability to rapidly develop antibiotic resistance, antibiotics should be used with caution in companion birds. Fluoroquinolones and erythromycins are the classes of antimicrobials used to treat people for campylobacteriosis.
Preharvest prevention of Campylobacter infection in commercial species is based on strict biosecurity, decontamination of housing between successive flocks, exclusion of rodents and wild birds, and insect eradication. Chlorination of drinking water to 2 ppm and operation of farms on a strict “all-in/all-out” basis occasionally reduces the prevalence of infection. In the context of commercial production in the USA where earth-floored housing is used and litter is recycled, preharvest control of C jejuni is impractical. Innovative methods of prevention, such as competitive exclusion, bacteriophage therapy, bacteriocins, and the use of vaccines, are under intensive investigation. Withholding feed from broilers and turkeys for at least 12 hr before slaughter and thorough decontamination of transport coops and modules reduce fecal contamination and lower the level of C jejuni introduced into processing plants.
C jejuni is a major source of foodborne enteritis in people; contaminated, undercooked poultry is responsible for >50% of cases investigated. The condition was recognized in the mid-1970s, and the significance of the organism has become apparent with improved methods of isolation and identification. Nonchlorinated ground water, unpasteurized milk, young diarrheic pets, and contaminated beef and pork products are also responsible for infection of people.
Improved washing of carcasses, use of counter-flow scalding, elimination of immersion chillers, and reduction in manual handling by installation of advanced automated equipment can reduce C jejuni contamination on poultry meat. Chemical disinfectants, such as chlorine, peracetic acid with hydrogen peroxide, and trisodium phosphate, glutaraldehyde and succinic acid, and organic compounds, such as lactic and acetic acids, may effectively reduce C jejuni on poultry carcasses in the processing plant. Some research indicates that bacteriophages and bacteriocins may also be useful. However, the regulations regarding chemical or biological sanitizers that can be used in processing plants and the performance standards for Campylobacter in the plant are currently in flux.
Gamma irradiation at levels of 1–3 kGy effectively eliminates C jejuni from poultry carcasses and products. Irradiation has been endorsed by a number of international health agencies, but irradiated foods are not widely available in the USA because of consumer concerns. The risk of foodborne C jejuni infection can be reduced through cooking of poultry to achieve a core temperature of 74°C for 1 min. Concurrent hygienic storage, handling, and preparation are necessary to prevent contamination of prepared foods, work surfaces, and utensils by raw poultry and other meats.