THE MERCK VETERINARY MANUAL
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Overview of Enterococcosis in Poultry

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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; infections are usually secondary to another disease. Enterococcus infections can result in either an acute or subacute/chronic form.

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 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. E cecorum has been associated with arthritis in broiler chickens.

Transmission 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. 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. 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.

Lesions:

Acute enterococcosis lesions include splenomegaly, hepatomegaly, enlarged kidneys, and congestion of subcutaneous tissue. 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 pericarditis, perihepatitis, airsacculitis, arthritis and/or tenosynovitis, osteomyelitis, myocarditis, and valvular endocarditis. 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.

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 includes bacterial septicemic diseases such as staphylococcosis, streptococcosis, colibacillosis, pasteurellosis, and erysipelas.

Antibiotics, including penicillin, erythromycin, novobiocin, oxytetracycline, chlortetracycline, or tetracycline, have been used to treat acute and subacute infections. 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 sources.

A high percentage of ready-to-eat poultry products are contaminated with Enterococcus spp; however, food poisoning in people has not been reported.

Last full review/revision March 2015 by Teresa Y. Morishita, DVM, MPVM, MS, PhD, DACPV

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