Streptococci are nonmotile, gram-positive, catalase-negative coccoid bacteria that occur singly, in pairs, or in short chains when observed on stained smears. The genetic diversity of Streptococcus spp is expansive and multiple species have been reclassified to the closely related genus Enterococcus or their nomenclature has been updated.
Streptococcus spp associated with disease in avian species include:
Streptococci have been associated with:
Transmission is via oral or aerosol routes as well as through skin injuries.
Streptococcal infections can be localized or septicemic. Endocarditis and lameness occur during the subacute or chronic stage of the infection. In S equi zooepidemicus infections, clinical signs are typical of an acute septicemic infection, and lethargic birds are often prostrate. In affected layers, egg production may drop by 15%. In pigeons, S gallolyticus infection produces acute mortality with lameness, inappetence, diarrhea, and the inability to fly. Acute fibrinopurulent conjunctivitis has been noted in infections caused by other Streptococcus spp.
Lesions in the acute septicemic form of streptococcosis include:
There may also be serosanguineous fluid in the subcutaneous space and in the pericardium. Bloodstained feathers around the mouth and head due to blood from the oral cavity have been reported occasionally. Cellulitis involving the skin and subcutaneous tissues has been associated with both Escherichia coli and S dysgalactiae.
Chronic streptococcal infections result in:
Lesions on the heart valves appear as small, yellowish-white or tan, raised areas on the valvular surface. Focal granulomas, as a result of septic emboli, can be found in many tissues. Gram-positive bacterial colonies are readily observed in thrombosed vessels and within necrotic foci microscopically.
History, clinical signs, and lesions, along with demonstration of Streptococcus-like bacteria in blood films or impression smears of affected tissues, allows for a presumptive diagnosis of streptococcosis. Isolation of Streptococcus spp from lesions confirms the diagnosis. Streptococci can be cultured easily on blood agar.
Differential diagnoses of streptococcosis include other bacterial septicemic diseases, including:
and when blood is noted coming from the mouth:
Antibiotics, including erythromycin and chlortetracycline, have been used to treat acute and subacute infections of streptococcosis. When treating poultry, always use current FDA-approved food animal drugs. Clinically affected birds respond well early in the course of the infection, but this response decreases as the disease progresses within a flock. Antimicrobial susceptibility testing should be performed to select a suitable antibiotic.
Because streptococcosis often occurs secondary to other diseases, it is important to prevent immunosuppressive diseases and conditions. In addition, because skin wounds can provide an entry for Streptococcus, it is important to reduce this risk factor. Proper cleaning and disinfection, including water sanitation, can reduce environmental sources of infection.
To date, although there has been no conclusive evidence of Streptococcus spp transmission between poultry and humans, it has been reported that an isolate from a human case of Streptococcus galllolyticus subsp. gallolyticus endocarditis shared similar characteristics to those isolates found in a layer flock under the patient's care. The specific transmission route needs to be further elucidated.