Riemerella anatipestifer is a bacterial pathogen that affects ducklings, gosling, turkeys, and other fowl. Clinical signs include ocular and nasal discharge, mild coughing and sneezing, watery green feces, and neurologic signs progressing to obtundation and death. Diagnosis is based on typical neurologic signs, pathological lesions, and identification of the causative organism. Careful management practices are important for prevention.
Riemerella anatipestifer (formerly Pasteurella anatipestifer) is a highly contagious, widely distributed bacterial pathogen that primarily affects young ducklings and, less frequently, older developer-aged and, rarely, breeder-aged ducks, as well as turkeys and geese. Other waterfowl, chickens, and pheasants occasionally may be affected. In commercial duck and geese operations, mortality can be significant. Surviving ducklings may grow poorly and be condemned at time of slaughter.
Courtesy of Dr. Gavin Hitchener.
Courtesy of Dr. Gavin Hitchener.
Etiology and Transmission of Riemerella anatipestifer Infection in Poultry
Riemerella anatipestifer is gram-negative, nonsporulating, catalase and oxidase positive, and nonmotile. It grows microaerophilically in enriched media. Given that R anatipestifer possesses few characteristic phenotypic properties, isolation and identification procedures should be polyphasic. Definitive diagnosis should include genotypic identification (PCR array amplification of a partial region of the rpoB or the 16S rRNA gene with subsequent sequencing is recommended).
Similar to Pasteurella multocida, R anatipestifer has many (>20) immunotypes (or serotypes). This complicates efforts at widespread prevention using bacterins because of limited and mostly ineffective cross-protection between serotypes. Cross-protective vaccine candidates using an immunoproteomics approach are in development. Efforts are also underway to molecularly sequence the known serotypes to reduce the need to rely on serology, which can be susceptible to error, for differentiating field infections.
The epidemiology and pathogenesis of R anatipestifer infection are poorly understood, and no definitive virulence factors are readily identified for all serotypes at this time. Ducks are believed to be infected from the environment by the respiratory route or when R anatipestifer is introduced into lesions of the webbed foot. Turkeys may be infected by injuries or by the respiratory route when another pathogen disrupts the respiratory epithelium. Once the infection is established on a farm, it frequently becomes endemic. It is common for multiple serotypes to be present on a single facility, with co-infections possible. Use of bacterins or vaccines for specific serotypes may not provide cross-protection from serotypes not included in these biologics.
Clinical Findings and Lesions of Riemerella anatipestifer Infection in Poultry
Clinical signs of Riemerella anatipestifer infection usually develop after an incubation period of 2–5 days. Affected ducklings, usually 1–7 weeks old, often have ocular and nasal discharges, mild coughing and sneezing, tremors of the head and neck, depression, and incoordination progressing to obtundation and death. In typical cases, affected ducklings in the terminal stages of disease lie on their backs, paddling their legs. Stunting may occur in survivors, with scarring of air sacs and the pericardium resulting in condemnation at slaughter. Necrotic dermatitis on the lower back or around the vent may also occur. Fibrinous exudate in the pericardial cavity and over the surface of the liver is the most characteristic lesion. Fibrinous airsacculitis is common, and infection of the CNS can result in fibrinous meningitis. The spleen and liver may be swollen. Pneumonia may occur. Mortality in ducks is usually 2%–50%. A high proportion of affected birds develop mucopurulent or caseous salpingitis. Affected breeding stock should be slaughtered.
Affected turkeys, usually 5–15 weeks old, often exhibit dyspnea, droopiness, hunched back, lameness, and a twisted neck. Fibrinous pericarditis and epicarditis are the most pronounced lesions. There may also be fibrinous perihepatitis, airsacculitis, and purulent synovitis. Osteomyelitis, meningitis, and focal pneumonia occur occasionally. Mortality in turkeys is 5%–60%, and rates of condemnations are in the range of 3%–13%.
Diagnosis of Riemerella anatipestifer Infection in Poultry
Clinical findings, age of disease onset, gross findings, and aerobic culture are definitive for most field infections.
Brain, heart, liver, spleen, air sac, and lung are preferred organs to harvest samples for culture testing (listed in order of importance for sampling).
Serotyping is typically performed for vaccine and bacterin selection or epidemiological studies.
Diagnosis of Riemerella anatipestifer is based on typical CNS signs (if present), lesions, and isolation and identification of the causative organism (using traditional biochemical characterization). Other diseases (eg, colibacillosis, salmonellosis, Pasteurella multocida infection, and chlamydiosis) may produce similar lesions.
Tryptic soy or chocolate agar medium is recommended for isolation, although blood agar is also used, with incubation at 37°C under 5% carbon dioxide or, less optimally, in a candle jar. Recently, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been used successfully for identification and is quickly becoming the preferred diagnostic method for most larger laboratories.
Several PCR array-based diagnostic tests to detect R anatipestifer have been described, including assays for the ompA gene, 16S rRNA, rpoB gene, and an ERIC fragment. Due to a high rate of false-positive results, PCR amplification of a partial region of the rpoB or the 16S rRNA gene with subsequent sequencing is recommended to confirm identification.
The isolate should be serotyped or have whole genomic sequencing performed with single nucleotide polymorphism (SNP) analysis because the information may be useful for vaccine selection and epidemiological studies. Plate agglutinations are rapid and convenient for most facilities; however, this method is subject to cross-reactions, with the consequence of bacterin protection being inadequate at times. Unless titrations are carried out, only absorbed sera should be used because of the existence of multiple antigenic factors within a single strain. Biochemical characteristics can be used to differentiate this organism from other bacteria that cause important diseases of ducks and turkeys, particularly Escherichia coli, P multocida, Salmonella enterica, Coenonia anatina, Avibacterium gallinarum, and Bordetella avium. Impression smears help to determine whether Chlamydia is involved; however, PCR array-based diagnostic testing is preferred due to the health risk to humans associated with chlamydiosis.
Prevention and Control of Riemerella anatipestifer Infection in Poultry
Strict biosecurity should be maintained, with regular cleaning and disinfection of facilities.
Appropriate vaccines or bacterins (guided by serotyping or whole genomic sequencing) should be administered in naive ducklings and breeder birds on most commercial duck and goose farms.
All-in/all-out management systems should be used when applicable and down time should be allotted between flocks.
Careful management practices are important for prevention of Riemerella anatipestifer infection. A high level of biosecurity is essential. Cleaning and disinfection between flocks and separation of flocks on multiple-age farms are other factors of major importance. Rigid sanitation and depopulation are necessary for elimination of the disease on endemically infected farms. Allowing facilities to dry out and be exposed to hot dry air can reduce pathogen burdens on some facilities.
A bacterin and a live vaccine, both including the three most common serotypes of R anatipestifer (ie, serotypes 1, 2, and 5), are available for use in ducks and naive ducklings, respectively. Autogenous bacterins for other serotypes are available from multiple vaccine makers. An autogenous oil-emulsion bacterin can be used in turkeys. Breeder ducks can be vaccinated with a bacterin or live vaccine to provide protection to the ducklings that may last until duckings are 2–3 weeks old.
Sulfaquinoxaline or a combination of penicillin and streptomycin can be used for initial treatment; however, antimicrobial susceptibility testing should be performed because multidrug-resistant strains are becoming more prevalent due to antimicrobial use and development of antimicrobial gene resistance. Enrofloxacin is highly effective in preventing death in ducklings when administered in the drinking water; however, use of quinolones or most other antimicrobials in poultry operations is not allowed in many countries. Antimicrobial restrictions and development of antimicrobial gene resistance make biosecurity and prevention of introduction of disease critical to commercial operations.
Key Points
Riemerella anatipestifer causes acute bacterial septicemia of young ducklings and goslings and, less commonly, turkeys and other fowl.
Clinical signs include neurologic disease and watery green feces; mortality approaches 30–50% with virulent serotypes in commercial flocks.
Grossly, R anatipestifer infection is indistinguishable from E coli, Salmonella, or P multocida infections and requires aerobic culture for diagnosis.
Because of increasing antimicrobial resistance, vaccination and strong biosecurity are essential for control on commercial operations.
