Streptococcosis

    Streptococcosis in avian species has spread worldwide, occurring as both acute septicemic and chronic infections with mortality ranging from 0.5% to 50%. Infection is considered secondary, because streptococci may form part of the normal intestinal and mucosal flora of most avian species.

Streptococci were previously classified in both Lancefield antigenic serogroups C and D. Lancefield group DStreptococcussppare commonly referred to as “fecal streps.” The application of new bacteriologic techniques, especially DNA-DNA and DNA-RNA hybridization has led to the reclassification of the Lancefield group D streptococci to theEnterococcusspp.

Etiology and Epidemiology:

The genus Streptococcusis composed of gram-positive, spherical bacteria occurring singly, in pairs, or in short chains, which are nonmotile, nonsporeforming, facultative anaerobes. They are catalase-negative and ferment sugars, usually to lactic acid. Streptococcuss ppisolated from avian species and associated with disease include Szooepidemicus (occasionally referred to asSgallinarum), Sbovis, and S dysgalactiae. Smutans, a common bacterium in the human oral cavity, has been associated with septicemia and mortality in geese; contaminated drinking water and poor quality litter were possible predisposing factors. Naturally occurring infections ofSboviscausing acute septicemia and joint infections have been found in racing pigeons. Sdysgalactiaehas been cultured from broiler chickens with cellulitis, a condition observed on the skin and subcutaneous tissue at processing. Streptococcusspphave been isolated from lesions of osteomyelitis in turkeys. Naturally occurring and experimental poultry infections resulting in bacterial endocarditis are commonly associated with streptococci and other bacteria. Transmission occurs most commonly via oral and aerosol routes. However, transmission can occur through skin injuries, especially in caged layers. Aerosol transmission of Szooepidemicuscan result in acute septicemia in chickens.

Clinical Findings:

S zooepidemicusis found almost exclusively in mature chickens but has been documented as a cause of mortality in wild birds. Incubation periods range from 1 day to several weeks, with 5-21 days most common. Endocarditis occurs when septicemic streptococcal infection progresses to a subacute or chronic stage. Lameness may also be observed in subacute or chronic infections. In Szooepidemicusinfections, clinical signs are typical of an acute septicemic infection and include weariness bloodstained tissue and feathers around the head, yellow droppings, emaciation, pale combs and wattles. Cyanosis in the terminal stages has been described. Mortality varies, but may reach 50%. In layers, egg production may drop as much as 15%. Streptococcusspphave also been isolated in cases of acute fibrinopurulent conjunctivitis. In pigeons, Sbovisinfection causes acute mortality with occasional lameness, inappetence, diarrhea, and the inability to fly.

Lesions:

Gross lesions of Szooepidemicusin acute disease include splenomegaly, hepatomegaly (with or without miliary to 1-cm foci that are red, tan, or white), enlarged kidneys, congestion of subcutaneous tissue, and peritonitis. Subcutaneous and pericardial fluid may appear sero-sanguineous. Blood stained feathers around the mouth and head with blood coming from the mouth . In broilers, cellulitis involving the skin and subcutaneous tissues can be observed at processing and has been associated with both EscherichiacoliandSdysgalactiae. Lesions of chronic streptococcal infections include fibrinous arthritis and/or tenosynovitis, osteomyelitis, salpingitis, fibrinous pericarditis, necrotic myocarditis, and valvular endocarditis. Vegetative valvular lesions are usually yellow, white, or tan small, raised rough areas on the valvular surface. Valve lesions are most consistently found on the mitral valve but may be found on other valves. Microscopically, valvular lesions consist primarily of fibrin with bacteria, heterophils, macrophages, and fibroblasts. Focal granulomas can be found in virtually any tissue as a result of septic emboli. Gram-positive bacterial colonies are readily observed in thrombosed vessels and within necrotic foci with tissue Gram stains.

Diagnosis:

Demonstration of bacteria typical of streptococci in blood films or impression smears of affected heart valves or lesions from birds with typical signs and lesions allows a presumptive diagnosis of streptococcosis. Isolation of Streptococcussppfrom typical lesions in poultry with appropriate clinical signs confirms the diagnosis. Streptococci are easily isolated in blood agar. Fermentation of mannitol, sorbitol, arabinose, and growth on MacConkey agar can also aid in differentiation of streptococci in Lancefield serogroup D fromSzooepidemicusand other Lancefield serogroup C streptococci. Preferred tissues for culture include liver, spleen, blood, yolk, embryo fluids, or any tissue with lesions. Bacterial endocarditis can be diagnosed based on valvular vegetations with secondary infarcts of myocardium, liver, and/or spleen. In suspected cases, it is important to culture lesions to establish a definitive diagnosis and rule out other bacteria. A rapid detection test by latex agglutination has been described for identification of antigenic serogroup C streptococci in animals.

Differential diagnosis includes other bacterial septicemic diseases, eg, staphylococcosis, enterococcosis, colibacillosis, pasteurellosis, and erysipelas.

Treatment and Control:

Treatment includes use of antibiotics such as penicillin, erythromycin, novobiocin, oxytetracycline, chlortetracycline, and tetracycline in acute and subacute infections. Clinically affected birds respond well early in the course of the disease. As the disease progresses within a flock, treatment efficacy decreases. Antibacterial sensitivity should be performed on bacterial isolates. There is no treatment for poultry with bacterial endocarditis. In vitro sensitivity toSbovisin pigeons has been demonstrated with penicillins, macrolides, lincomycin, tetracyclines, chloramphenicol, and nitrofurans.

Prevention requires reducing stress and preventing immunosuppressive diseases and conditions. Proper cleaning and disinfection can reduce environmental streptococcal resident flora to minimize external exposure. The use of formaldehyde reduces the total count ofStreptococcussppin hatchers by as much as 86%.

Reference :- Merck Veterinary Manual

 
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