Colibacillosis

Colibacillosis is a broad term used to describe localized or systemic infections caused wholly or in part by avian pathogenic Escherichia coli (APEC). This condition encompasses a range of clinical disease manifestations in poultry. Chickens of all ages are susceptible; however, young birds—including developing embryos—are more frequently and severely affected. Colibacillosis commonly occurs alongside other diseases, which can complicate diagnosis and management.

The most common manifestations of E. coli infection in chickens include:

• Cellulitis: A bacterial skin infection characterized by inflammation of the subcutaneous tissues, most often affecting the lower abdomen and upper legs.
• Colisepticemia: A systemic infection (septicemia) that occurs when E. coli enters the bloodstream, leading to rapid dissemination throughout the body. This is a life-threatening condition associated with acute, nonspecific signs such as lethargy, depression, weakness, and decreased appetite.
• Omphalitis (yolk sac infection): A common, typically non-contagious infection of the navel in newly hatched chicks, often caused by bacterial invasion, including E. coli.
• Egg peritonitis, salpingitis, and oophoritis: Frequently associated with E. coli ascending from the cloaca or spreading from infected air sacs. Affected hens may have a recent history of egg binding, usually within the past six months.
• Coligranulomatosis (Hjarre’s disease): A rare, sporadic form of colibacillosis characterized by granuloma formation, often secondary to prior intestinal mucosal damage. Capsular components of E. coli, such as galactans, are thought to contribute to the granulomatous response.

E. coli infections often occur concurrently with other pathogens, including bacteria, fungi, protozoa, and viruses. Common co-infections include:

• Chronic respiratory disease (CRD): Typically associated with Mycoplasma gallisepticum, this condition develops gradually and is characterized by chronic respiratory signs such as tracheitis, sinusitis, airsacculitis, and conjunctivitis.
• Swollen head syndrome (SHS): An acute, highly contagious upper respiratory disease caused by avian metapneumovirus (AMPV).

Clinical Signs

Clinical signs of colibacillosis are highly dependent on the form of the disease and severity of infection. Disease expression is influenced by factors such as age, duration of infection, environmental conditions, and the presence of concurrent disease.

Treatment

Mild intestinal infections may respond to antibiotics administered orally or via drinking water; however, most cases require parenteral antimicrobial therapy. Selection of appropriate antibiotics should be guided by culture and sensitivity testing, as many E. coli strains exhibit resistance to commonly used drugs, including tetracyclines, sulfonamides, aminoglycosides, beta-lactams, and others. Effective treatment also depends on the drug’s ability to penetrate affected tissues or granulomas.

Adjunct therapies—such as probiotics to support gut health and certain plant-derived compounds (e.g., baicalin, yucca, Schisandra chinensis, Echinacea purpurea, and oregano)—have shown potential benefits in reducing bacterial load or modulating inflammation in some studies, though their use should complement, not replace, appropriate medical treatment.