Enterococcosis in Poultry
Enterococcosis has been reported in a variety of avian species worldwide. Enterococcus spp are normal microflora found in the intestinal tract of poultry and other bird species. Enterococcus infections usually occur secondary to another disease. However, in recent years, Enterococcus cecorum has become an emerging pathogen in poultry, especially broilers. These pathologic changes have resulted in increased mortality, poor production, and increased condemnation. Enterococcus infections can result in either an acute or subacute/chronic form. Diagnosis is confirmed by isolation of the organism.
Enterococci are nonmotile, gram-positive, catalase-negative coccoid bacteria that appear singly, in pairs, or in short chains on stained smears. Enterococcus spp isolated from birds with clinical disease include E avium, E cecorum,E durans, E faecalis, E faecium, and E hirae. E faecalis affects birds of all ages, but infection is especially devastating for embryos and young chicks. In addition, E cecorum has been associated with osteomyelitis, including femoral head necrosis, spondylitis, and arthritis in adult broiler chickens.
There is a succession of Enterococcus species within the chicken intestinal tract that appears to be age dependent. E faecalis usually colonizes the intestines first, followed by E faecium, and then E cecorum. In recent years, E cecorum has emerged as a major cause of skeletal disease in adult broiler chickens.
Transmission of enterococcosis is via the oral and/or aerosol routes as well as from skin wounds. Infection may result in septicemia. Endocarditis can occur when the infection progresses to a subacute/chronic stage. Brain necrosis and encephalomalacia in young chickens have been reported in enterococcosis. The transmission route for E cecorum is not entirely understood, although oral and/or aerosol routes have been proposed, as for other enterococcal species. The horizontal transmission of E cecorum is rapid in commercial operations. Although enterococcosis has been reported in poultry species, it should also be noted that some strains of Enterococcus have a beneficial effect on growth and feed efficiency and are used as probiotics.
In the acute form of enterococcosis, clinical signs are related to septicemia and include depression, lethargy, ruffled feathers, diarrhea, and a decrease in egg production. In the subacute/chronic form, depression, lameness, and head tremors may be noted. If untreated, most affected birds die. The most prominent sign of pathogenic E cecorum is paralysis due to inflammation in the spinal column, especially at the free thoracic vertebra. Chickens will characteristically sit with both legs extended cranially. Because these affected chickens are lame, they often become dehydrated, which also increases mortality rates. Egg transmission or fecal contamination of hatching eggs can often lead to late embryo mortality, and an increased number of hatchlings are unable to “pip” through the shell at hatch.
Acute enterococcosis lesions include:
Multifocal, whitish-tan areas of necrosis may be observed on the liver and spleen. Omphalitis or enlarged yolk sacs may be seen in infected chicks or poults.
In the subacute/chronic form, lesions include:
An enlarged, flaccid heart with pale to hemorrhagic areas in the myocardium has also been reported, along with infarcts throughout the internal organs. Focal granulomas can be found in many tissues as a result of septic emboli. Gram-positive bacterial colonies are readily seen in thrombosed vessels and within areas of necrosis.
For commercial flocks, lesions have resulted in increased condemnation losses.
History, clinical signs, lesions, and demonstration of enterococci in blood or on impression smears are suggestive of enterococcosis. Isolation of Enterococcus spp from lesions will confirm the diagnosis. Enterococci are easily isolated on blood agar.
Differential diagnoses include bacterial septicemic diseases such as:
Prevention of enterococcosis requires preventing underlying immunosuppressive disorders.
Antibiotics, including erythromycin and chlortetracycline, have been used to treat acute and subacute infections of enterococcosis. Always consult the current FDA-approved drugs for poultry when considering treatment. Clinically affected birds respond well early in the course of the disease, but treatment efficacy decreases as the disease progresses. Antimicrobial susceptibility testing should be performed to ensure that the most efficacious antibiotic is used.
Prevention and control require preventing immunosuppressive diseases and conditions, because enterococcosis often occurs secondary to another disease. In addition, ensuring proper cleaning and disinfection of the facilities can reduce environmental reservoirs of the bacteria. Water sanitation helps to reduce the incidence. Enterococcal species are resistant to drying, so they can survive for prolonged periods in the environment.
Enterococcus spp are part of the normal flora in poultry but can cause secondary infections, so treatment of primary diseases can prevent enterococcal infections.
Clinical signs of enterococcosis are related to septicemia, and treatment is effective if provided in the early stages of the disease.
If enterococcosis becomes chronic, skeletal diseases have been reported, and treatment efficacy decreases with chronicity.