Staphylococcosis in Chickens

Description of bacterial infections caused byStaphylococci in chickens

IntroductionStaphylococcal infection of poultry. This infection iscommonly associated with infection of skin, bones, joints, andnavel. There is a potential risk for human food poisoning.

EtiologyStaphylococcus aureus is the most common species that causesdisease in poultry. However, other species may also be found. Among the most frequently isolated species are S. lentus, S.simulans, S. cohnii, S. gallinarum, and S. capit

Features of the agentStaphylococcus is a genus of coccoid, facultative anaerobicbacteria. In stained smears, it tends to aggregate, giving theappearance of clusters of grapes. Staphylococcus species areGram-positive, although cultures older than 24h may stainGram-negative. They are readily isolated in blood agar after astandard culture period of 24h. The colonies are generallyb-hemolytic, 1-3 mm in diameter, and often white or creamy incolor (but can also appear orange). Some poultry isolates arecapable of human food poisoning.

Susceptibility of the agentStaphylococcus species are fairly resistant to chemical andphysical agents. In particular, they are very resistant to highconcentrations (7.5%) of common table salt (NaCl), which canbe used to isolate the agent from heavily contaminatedmaterial. Disinfectants containing chlorine are effectiveagainst the organism (in the absence of abundant organicmatter).

Occurrence Infections with Staphylococcus occur worldwide and affect allspecies of birds. Outbreaks are generally more important inchickens and turkeys.

PathogenesisMost species of Staphylococcus are considered benignorganisms on skin and mucosal membranes. Coagulasepositive isolates of these bacteria are considered pathogenicfor poultry. The pathogenesis and port of entry of thesebacteria have not been completely understood. It is almostcertain that bacteria can gain entry inside tissues through cuts,lacerations, scratches, injections contaminating the skin(localized abscesses, cellulitis, and also gangrenousdermatitis). In addition, it is thought that Staphylococcus cantranslocate into the blood through mucosal surfaces affectedby severe inflammation (enteritis). From the blood, thesebacteria can reach articular surfaces (causing arthritis andsynovitis), and bones (causing osteomyelitis). In the case ofcontamination of the navel in the hatchery, newly hatchedchicks will develop omphalitis. The incubation period is ingeneral short (2-3 days). However, when hard tissues areaffected the incubation period can be longer. Some cases ofStaphylococcus have been linked to previous infections withimmunosuppressive agents (infectious bursal disease,infectious anemia, Marek's disease).

Clinical manifestationsThey depend on the affected system.

• Locomotor system: Swollen joints and tendons arecommon; lameness or gait alterations may develop. Osteomyelitis of the femur and/or tibiotarsus can producelameness. In severe cases, the birds can be prostrated. Ifthe developing abscess in the thoracolumbar vertebraecompresses the spinal cord, paraplegia mayoccur. Reduction of body weight and dehydration can beexpected due to increased difficulty to access feed andwater.

• Skin: localized abscess or diffuse cellulitis may developwith the accumulation of purulent exudate. Inimmunosuppressed birds, the dermal infection mayprogress to a gangrenous dermatitis. When the skininfection occurs through cuts in the skin of the feet, aplantar abscess with a very large inflammatory componentmay develop (bumblefoot).

• Omphalitis: In case of navel contamination, the navelappears wet and may fail to heal. Abdominal distentionmay be apparent. Affected chicks fail to thrive, and many

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will die during the first week of life.

Picture 1. Swelling of the joints. Picture credit. Dr. I. Rojas

Picture 2. Bumblefoot. Picture credit Dr. E. Pendleton

Necropsy findingsNecrosis and congestion may be present in the internalorgans. In osteomyelitis, the head of the femur may benecrotic or partially degenerated due to septic necrosis. Fracture of the femoral head is a common finding. Purulentmaterial and necrotic tissue are evident at the site of thefracture. Caseous material may also be found in the proximalend of the tibiotarsus and sometimes in the thoracolumbarvertebra.

In young animals with omphalitis, there is congestion of thesubcutaneous blood vessels. The yolk inside the abdominalcavity is not absorbed and blood vessels irrigating the yolkappear engorged. Lumps of purulent material may be presentin the yolk.

Picture 3. Bacterial chondronecrosis with osteomyelitis(BCO). Picture credit. Dr. I. Rojas

Picture 4. Bacterial chondronecrosis with osteomyelitis(BCO). Note the caseous exudate in the proximal tibia. Picturecredit. Dr. G. Lorenzoni

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DiagnosisLesions are suggestive. Culture of the organism from affectedtissue is necessary for diagnosis.

Relevant differential diagnosesE. coli, Mycoplasma synoviae, Reoviruses, Salmonella,Pasteurella.

Prevention and treatmentTo reduce the incidence of Staphylococcosis, it helps to use anappropriate vaccination program to protect chickens fromimmunosuppressive diseases. There is a vaccine available forturkeys that is produced with an avirulent strain ofstaphylococcus (S. epidermidis 115) that has shown someefficacy on reducing the incidence of the disease in the field.

Minimize the risk of skin lesions by eliminating sharp objectsfrom the area used by birds. If toe trimming is a regularpractice in your operation, make sure to properly disinfectblades and skin. Provide sufficient feeder space to preventbirds from climbing on each other's backs to gain access tofeed. Scratches are a common port of entry for Staphylococcus. Control intestinal diseases or respiratorydiseases that could compromise the epithelial barriers. Antibiotic treatment may be effective if the infection is in softtissue but is largely ineffective for osteomyelitis andomphalitis.

ReferencesDiseases of Poultry, 13 th ed. D. E. Swayne. Wiley-Blackwell.

Avian Diseases Manual. 7 th ed. The American Associationof Avian Pathologists.

AuthorsGino LorenzoniAssistant Professor, Poultry Science and Avian Healthagl20@psu.edu814-863-7302

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