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Streptococcosis: Introduction |  |
| Streptococcosis in avian species is worldwide in distribution, 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, including wild birds, and are commonly found in various poultry environments. |
| Streptococci were previously classified in both Lancefield antigenic serogroups C and D. Lancefield group D
Streptococcus
spp
are commonly referred to as “fecal streps.” The application of new bacteriologic techniques, especially DNA-DNA and DNA-rRNA hybridization has led to the reclassification of the Lancefield group D streptococci to the
Enterococcus
spp
. Bacteria identified by genus only in earlier reports could have been classified as
Enterococcus
spp
in current nomenclature instead of
Streptococcus
spp
. For diseases caused by the Lancefield antigenic serogroup D, see
enterococcosis,
Enterococcosis: Introduction. |
| Etiology and Epidemiology: |
| The genus
Streptococcus
is 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.
Streptococcus
spp
isolated from avian species and associated with disease include
S
zooepidemicus
(occasionally referred to as
S
gallinarum
),
S
bovis,
and
S
dysgalactiae
.
S
mutans
, 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 of
S
bovis
causing acute septicemia and joint infections have been found in racing pigeons.
S
dysgalactiae
has been cultured from broiler chickens with cellulitis, a condition observed on the skin and subcutaneous tissue at processing.
Streptococcus
spp
have 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
S
zooepidemicus
can result in acute septicemia in chickens. |
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| Clinical Findings: |
|
S zooepidemicus
is 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
S
zooepidemicus
infections, clinical signs are typical of an acute septicemic infection and include lassitude, bloodstained tissue and feathers around the head, yellow droppings, emaciation, and 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%.
Streptococcus
spp
have also been isolated in cases of acute fibrinopurulent conjunctivitis. In pigeons,
S
bovis
infection produces acute onset of mortality with occasional lameness, inappetence, diarrhea, and the inability to fly. |
Lesions:
| Gross lesions of
S
zooepidemicus
in 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 serosanguineous. Bloodstained feathers around the mouth and head with blood coming from the mouth may occur. In broilers, cellulitis involving the skin and subcutaneous tissues can be observed at processing and has been associated
with both
Escherichia
coli
and
S
dysgalactiae
. 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
Streptococcus
spp
from 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 from
S
zooepidemicus
and 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. |
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| 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 to
S
bovis
in 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 of
Streptococcus
spp
in hatchers by as much as 86%. |
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