Colibacillosis

Colibacillosis refers to any localized or systemic infection caused partly or entirely by avian pathogenic Escherichia coli (APEC), which include several clinical disease manifestations. Chickens of all ages are susceptible to colibacillosis, but young birds are more frequently and more severely affected, including developing embryos. Colibacillosis often occurs concurrently with other diseases, making it more difficult to diagnose.

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

• Cellulitis: Cellulitis is a bacterial skin infection resulting in inflammation of the subcutaneous tissue of birds, typically seen in the lower abdomen and upper legs.
• Colisepticemia: Septicemia, also known as blood poisoning, occurs when E. coli have invaded the chicken's bloodstream. Once in the bloodstream, the infection quickly spreads throughout the body. It is a serious, life-threatening condition which is associated with acute onset of very generalized clinical signs of sickness, such as listlessness, depression, weakness, and loss of appetite.
• Omphalitis: Omphalitis, also known as yolk sac infection, is an infectious, non-contagious, common condition affecting the naval of newly hatched chicks. It is caused by invasion by several bacterial, with one of the most common being E. coli.
• Egg peritonitis: Egg peritonitis, salpingitis, and oophoritis are frequently caused by E. coli, which ascended from the cloaca or by imprint metastases from infected air sacs. Affected hens may have a history of egg binding, usually within the past six months.
• Coligranulomatosis: Also referred to as Hjaerre's disease, a rare form of colibacillosis that occurs sporadically. Coligranulomas are thought to occur secondary, following damage to the intestinal mucosa by other agents. It is thought that the galactans found in the E. coli capsule that stimulate the granulomatous reaction.

E. coli infections often occur concurrently with other bacteria, fungi, protozoa, and viruses. The most common co-infections documented to occur with E. coli include:

• Chronic respiratory disease (CRD): Chronic respiratory disease (CRD), also known collectively as mycoplasma gallisepticum (MG) infection, is considered to be one of the major pathogens that cause respiratory disease in poultry. It tends to develop slowly in flocks and associated with progressive and chronic respiratory signs. Chickens with chronic respiratory disease often show clinical signs associated with the respiratory system, which include mild tracheitis, sinusitis, airsacculitis and conjunctivitis.
• Swollen head syndrome (SHS): Swollen head syndrome (SHS) is an acute, highly contagious upper respiratory tract infection of poultry. SHS is caused by infection with the avian metapneumovirus (AMPV), a type of pneumovirus which is classified into four subtypes (A, B, C, and D).

Clinical Signs

Clinical signs of colibacillosis are usually nonspecific and vary depending on the manifestation of the infection. The severity varies depending on the age of the bird, duration of infection, management conditions, and concurrent diseases present.

Treatment

Antibiotics that are administered orally or in the drinking water may be effective in treating mild E. coli infections of just the intestinal mucosa. Most E. coli infections require parenteral antibiotics for successful treatment. The drug selected needs to be able to penetrate the target tissues or granulomas.

Most E. coli strains are resistant to many commonly sold antibiotics for chickens, including cephradine, tetracyclines, chloramphenicol, amino-glycosides, beta-lactam antibiotics, and sulfonamides.