Synonymas
Chronic respiratory disease, infectious sinusitis and mycoplasmosis.
Aetiology
Mycoplasma gallesepticum is an avian pathogen within the genus mycoplasma. They lack cell wall and are self duplicating. They stain very well in geimsa and by light microscopy, the organism appear coccoid.
Age/species affected
Chickens, turkeys, ducks, pigeons, peafowl and passerine birds of all ages are susceptible to the infection. The infection is more severe in younger than in adult chickens and turkeys.
Transmission
By direct or indirect contact with birds through exudates, aerosols, airborne dust feathers contaminated food and water.
Vertical transmission through infected breeders to the chicks
Recovered birds remain infected for life; subsequent stress may cause returning of disease
Clinical signs
The incubation period for the infection varies from 6-10 days, morbidity is usually high up to 90% or more while mortality is low rarely above 20%.
Clinical signs observed include ocular and nasal discharge, coughing, tracheal rales, , conjunctivitis with facial skin edema, lowered egg producton, slow growth, inappetence, occasional encephalopathy and abnormal feathers, swollen sinusis, reduced hatchabilty and chick viability. The disease in chicken can cause dwarfing, airsacculitis and death.
Forms of the disease in turkeys
There are two forms of the disease in turkey: the upper form and the lower form.
In the upper form, the birds have watery nostrils and eyes, the infraorbitals become swollen and the exudates becomes caseous and firm. The birds have respiratory rales, breathing problems and looks depressed.
In the lower form, infected turkeys form airsacculitis without outward signs of the infection. Thus, the condition may go undetected until the birds are slaughtered and the typical lesions are observed.
Post-mortem lesions
Airsacculitis: Airsacs are filled with fibrinous caseous exudates serofibrinous pneumonias.
Unilateral or bilateral swelling of periorbital sinuses with nasal discharge and conjunctivitis are observed.
Catarrhal inflammation of nasal cavities,passages, sinuses, trachea and bronchi.
Occasional arthritis, tenosynovitis and salpingitis in chickens.
Diagnosis
Tentative diagnosis is based on characteristic clinical signs and post-mortem lesions while positive diagnosis is by culture and isolation of the organism. Serology- ELISA is accepted as the primary screening test. PCR is possible if it is urgent to determine the flock status.
Differential diagnosis
Infectious coryza, Aspergillosis, vitamin A deficiency, viral respiratory diseases, mycoplasma infections such as Mycoplasma meleagridis(turkeys) and Mycoplasma synoviae.
Treatment
The following products are effective against mycoplasma infection. They are tilmicosin, tylosin, spiramycin, tetracyclines and fluoroquinolones.
Control
Since the disease can be transmitted, control can only be effective if directed towards vertical transmission. This is achieved by testing and elimination of the reactors to Mycoplasma gallesepticum test until subsequent test yield 100% negative.
Breeders can be treated strategically at specific periods with tylosin to reduce egg transmission.
Dipping of eggs in tylosin before hatching also reduces egg transmission.
Other methods of control include purchase of uninfected chicks, all-in/all-out practice.