Mycoplasma Synoviae in Chickens: Symptoms, Causes and Treatment

Mycoplasma synoviae is a small, wall-less bacterium that evades many common antibiotics and is naturally resistant to beta-lactams (penicillin, amoxicillin).

• Vertical transmission: MS infects the ovary and oviduct, contaminating eggs before shell formation. Infected chicks hatch and can develop synovitis from this maternally acquired infection when stressed.
• Respiratory horizontal spread: MS spreads between birds through respiratory secretions (aerosol and contact). Flock-level seroprevalence can reach 90%+ in commercial operations.
• Stress triggers: Concurrent infections, vaccination reactions, temperature stress, or dietary deficiencies can activate latent MS infection into clinical synovitis. Many birds carry MS subclinically until a stressor precipitates joint disease.
• Eggshell apex abnormality: Certain MS strains (particularly the "MS-H" strain and some European isolates) infect the uterus and deposit material at the egg apex during the final stage of shell formation, creating the characteristic thin, pale band at the pointed end of the egg.

Swollen, creamy exudate-filled joints in growing or adult chickens, especially hock joints, are the classic MS synovitis presentation.

• Joint aspiration: The creamy white exudate from affected joints is pathognomonic for MS synovitis. Culture of joint fluid on PPLO media grows Mycoplasma within 7-14 days.
• Serology (ELISA, HI test): Detects MS antibodies in the flock. Seroconversion confirms exposure. Used for flock-level surveillance and breeder flock monitoring.
• PCR: Rapid, sensitive detection of MS from joint fluid, respiratory swabs, or reproductive tract samples. Can differentiate MS from M. gallisepticum.
• Eggshell apex QC: Candling or visual inspection of hatching eggs for apex abnormalities can trigger MS investigation in breeder flocks.

Antibiotics suppress MS infection and reduce clinical signs but do not eliminate the organism from the flock. Treated birds remain carriers.

Tylosin (drug of choice): Tylosin phosphate 50-100 mg/gallon in drinking water for 5-7 days provides good MS suppression. Repeat courses may be needed when clinical signs recur under stress.

Oxytetracycline: 200-400 mg/gallon in water for 5-7 days as an alternative to tylosin. Also effective against Mycoplasma species.

Tiamulin: 250 mg/gallon for 3-5 days is highly effective against MS and may produce longer remissions than tylosin. Requires a veterinary prescription in the US.

Enrofloxacin: Under veterinary prescription for fluoroquinolone-sensitive isolates. Reserve for cases where first-line options fail.

Physical management of synovitis: In individual pet birds, joint aspiration to remove the creamy exudate combined with antibiotic treatment provides rapid relief. Provide soft bedding and easy food and water access to prevent secondary starvation in lame birds.

• Source birds from MS-free or MS-monitored breeder flocks. Ask for serology records (ELISA negative). MS-free flocks require regular testing to maintain certification.
• Vaccinate with live MS vaccine (available in some countries) to reduce colonization rates and vertical transmission in breeder flocks.
• Minimize stressors that activate latent MS infection: maintain optimal temperature, avoid overcrowding, and keep vaccination schedules current to prevent concurrent infections that trigger synovitis outbreaks.
• All-in, all-out management and thorough disinfection between flocks. MS survives poorly in the environment and is susceptible to standard disinfectants, making thorough cleaning effective at reducing flock-to-flock carryover.