Staphylococcosis

   All avian species appear to be susceptible to staphylococcosis, which is common worldwide wherever poultry are reared. Staphylococcus aureus is usually the causative agent, but there is increasing evidence that other Staphylococcusspecies may also be involved. The disease condition can vary depending on where and how the bacteria enter the host; infections have been reported in the bones, joints, tendon sheaths, skin, sternal bursa, navel, yolk sac, liver, lungs, and eyelids. Septicemic infection has also been seen in laying chickens, with death occurring very quickly.

Etiology:

S aureus is a gram-positive coccus that appears in grape-like clusters on a stained smear. It is usually isolated on blood agar, on which it produces circular, smooth, white to orange colonies, 1-3 mm in diameter, within 24 hr. Saureus is facultatively anaerobic, β hemolytic, catalase positive, fermentative for glucose and mannitol, and coagulase positive. For many years, only coagulase-positive strains were considered to be of any clinical significance; however, in recent years, S hyicus , S epidermidis , and S gallinarum have been isolated from clinical materials.

Transmission, Epidemiology, and Pathogenesis:

S aureus and other Staphylococcus species are part of the normal flora on the skin and mucous membranes and are not thought to produce disease unless there is some breakdown in an environmental or immune system barrier and immunodepression. Most infections occur because of a wound, damage to the mucous membranes, or both. Infection can also occur in the hatchery as a result of contamination of an open navel. Staphylococcal septicemia is usually seen in laying chickens only in very hot weather. Once in the host, S aureus usually travels to the metaphyseal area of a nearby joint and causes osteomyelitis with subsequent spread to the joint. S aureus can produce disease locally at the site of entry, but the tendency to spread to the bones and joints is probably the most important feature of this disease.

Clinical Findings:

Infection most often manifests as a synovitis, with lameness being the most common clinical sign. The bones and associated joints most frequently affected are the proximal tibiotarsus and proximal femur; the proximal tarsometatarsus, distal femur, and tibiotarsus are also involved when infection is extensive. Other common lesions include navel and yolk sac infections. Lesions that have been reported include green liver in turkeys, and liver spots and granulomas. In acute infections, mortality may be the only clinical observation.

Lesions:

Lesions in the bone are focal yellow areas of necrosis, while lesions in joints consist of purulent exudates. Chicks with navel infection have navel areas that are dark and wet. Infected yolk sacs are retained longer than normal and are abnormal in color, consistency, and odor. Gangrenous dermatitis is seen in chickens that are immuno-suppressed and is a combination of S aureus and Clostridium septicum . Affected areas are usually dark (hemorrhagic) and crepitant. Green liver has been a problem in turkeys and has been associated with osteomyelitis and synovitis at the processing plant. Liver spots and granulomas have been a cause of liver condemnation. In acute infections, necrosis and vascular congestion is observed in the liver, spleen, and/or kidneys.

Diagnosis:

S aureus is easily isolated from stab swabs of affected material on sheep or bovine blood agar. Most strains of Saureus are β hemolytic, while most other strains of Staphylococcus are not. Swabs can be streaked onto selective media such as mannitol-salt agar or phenylethyl alcohol agar. These media inhibit the growth of gram-negative bacteria. The coagulase test is used to establish the significance of an isolate; only coagulase-positive isolates are considered to be pathogenic. Differential diagnosis includes Escherichia coli and Pasteurella multocida .

Treatment and Prevention:

Staphylococcosis can be successfully treated with antibiotics, but a sensitivity test should be performed because antibiotic resistance is common. Antibiotics used to treat Staphylococcus infections include penicillin, erythromycin, lincomycin, and spectinomycin. Because wounds are a major cause of infection, it is important to reduce all potential sources of injury (eg, sharp objects) to the bird. Splinters in litter, sharp rocks, wire from cages, sharp edges or nails on floor slats, and fighting have been associated with the disease, as well as beak and toe trimming procedures in young chickens and turkeys. Good litter management is important in controlling foot- pad erosions to prevent infection. Hatchery sanitation is also important to reduce the numbers of bacteria, including S aureus, which is a hearty bacterium that can be difficult to kill using normal sanitation procedures. Bacterins have not been effective against S aureus , but there have been reports that competitive exclusion using a strain of S epidermidis has been effective in young, growing turkeys.

Zoonotic Risk:

S aureus can cause food poisoning. Enterotoxin-producing strains are found on poultry, and proper precautions should be taken during handling and cooking.

Reference :- Merck Veterinary Manual

 
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