Colibacillosis in Chickens

Definition

Localized or systemic infections caused by Escherichia coli in diverse tissues and organs including omphalitis (picture 1), peritonitis, salpingitis, cellulitis, synovitis, coligranuloma, meningitis, and septicemia.

Introduction

This infection is one of the most common bacterial diseases affecting poultry, and thus it is associated with a large economic cost. In sharp contrast to mammals, it is generally accepted that, in poultry, a primary agent is needed to weaken the host's defenses for E. coli to cause disease. Thus, viral infections that otherwise could go unnoticed can get contaminated with E. coli, generating a lingering disease often associated with elevated mortality.

Etiology

Avian pathogenic E. coli, is a gram-negative, non-spore-forming bacillus. Somatic (O) and capsular (K) antigens are often used to designate serotypes. Serotypes with the somatic antigens 1, 2, 35, and 78 are frequently associated with disease in poultry. Most of the strains are motile.

Susceptibility of the agent

E. coli is inactivated at 60 °C for 30 min. The organism is sensitive to desiccation. Washing and drying surfaces eliminates the bacteria. However, E. coli can also be inactivated in wet litter by heat treatment, especially in the presence of free ammonia. Reproduction of the bacteria is inhibited at pH < 4.5. Chlorine can be used to treat water. E. coli can acquire resistance against disinfectants when subjected to environmental pressure. The mechanisms for resistance are encoded in plasmids that can be shared between bacteria.

Occurrence

Colibacillosis has a worldwide presence. It affects all types of poultry, wild birds, and mammals. Infections in poultry are generally linked to suboptimal sanitation in the hatchery and/or poor environmental conditions in the barn, or it occurs after birds have been affected by another primary agent or immunosuppressive disease. Association with mycoplasma and the infectious bronchitis virus are common.

Pathogenesis

E. coli is present in the intestinal tracts of birds and mammals and is widely disseminated through fecal material into the environment. If susceptible birds (immunosuppressed) or damaged tissues get exposed, E. coli may colonize and cause disease.

Clinical manifestations

Vary according to the location of the infected tissue or nature of the compromised organs: respiratory distress in airsacculitis (picture 2); weakened young birds with distended abdomens in omphalitis; lameness and frequent dehydration in synovitis; upright position and cessation of egg production in chronic salpingitis; sudden death of well-fleshed animals in acute septicemia; dimpling and yellowing of the skin in cellulitis; and diarrhea in enteritis (E. coli enteritis is rare in poultry).

Picture 1. Omphalitis. Picture credit. Dr. I. Rojas.

Necropsy findings

Variable depending on the infected tissue or compromised organs: air sacs are thickened and caseous exudate is present in airsacculitis; swollen navel and a congestive yolk sack with abnormal material in omphalitis (picture 3); swelling of joints and tendon sheets with accumulation of exudate inside the joints in synovitis; deposition of yellowish caseous exudate in subcutaneous tissue in cellulitis; accumulation of fibrinous material around the heart (pericarditis, picture 4), on the liver (perihepatitis, picture 5) and inside the abdominal cavity (peritonitis, picture 5); petechia and swollen organs can be detected in acute septicemia; distended oviduct with caseous exudate in salpingitis (which normally appears combined with peritonitis as salpingo-peritonitis, picture 6); and nodules along the mesentery, intestinal tract, and liver in coligranuloma. E. coli enteritis does not differ from unspecific bacterial enteritis, appearing often with congestion, edema, cellular sloughing, mucus and excess liquid in the lumen.

Picture 2. Airsacculitis. Picture credit. Dr. G. Lorenzoni.

Picture 3. Omphalitis. Picture credit. Dr. I. Rojas.

Picture 4. Pericarditis. Picture credit. Dr. I. Rojas.

Picture 5. Polyserositis (pericarditis, perihepatitis, peritonitis). Picture credit. Dr. I. Rojas.

Picture 6. Salpingo-peritonitis. Photo credit. Dr. M. Jimenez.

Diagnosis 

Isolation of serotypes of E. coli associated with disease in poultry in the absence of other primary pathogens and their serological fingerprints. Diagnosis based on sole presence of E. coli is rarely accepted as a definitive diagnosis due to the well-documented ability of the organism to act as an opportunistic pathogen.

Relevant differential diagnosis

Mycoplasmosis, infectious bronchitis, laryngotracheitis, Newcastle. Refer to the enteritis section for details on differential diagnostics for enteritis.

Prevention

Strengthen measures to clean and disinfect fertile eggs from the breeder flocks. Avoid incubating floor eggs. Increase sanitation in the hatchery. Reduce the risk of primary pathogens using biosecurity and vaccination in poultry flocks. Reducing ammonia and dust levels in the barns may help reduce the environmental insult that E. coli commonly needs to gain access into a flock.

Treatment

Antibiotics such as tetracyclines, sulfas, ampicillin, and streptomycin have been successfully used to control some E. coli. Early treatment is advised, with a follow-up considering antibiotic sensibility testing using the specific isolate. As the organism gets encapsulated or sequestered into caseous exudate, the antibiotic treatment will be less effective; thus, chronic stages of infection have a lower chance of being successfully treated.

References

• Avian Diseases Manual. 7^th ed. The American Association of Avian Pathologists.
• Diseases of Poultry, 13th ed. AAAP. Whiley-Blackwell.