Respiratory infections in chickens are seen worldwide, but especially in temperate poultry-producing areas in winter months. A number of respiratory viruses, bacteria, mycoplasma & fungi may be involved. Dust, ammonia and other factors associated with poor ventilation, may act as predisposing factors. Live vaccines can also contribute to respiratory diseases in poultry. Morbidity is typically 10 – 20% and mortality 5 – 10%.

M gallisepticum is commonly involved in the polymicrobial “chronic respiratory disease” in broiler chickens, leading to increased condemnations in the processing plant. In layers and breeders, it is usually subclinical, but causes a reduction in the number of eggs laid per hen over the production cycle. Turkeys are more susceptible to M gallisepticum, frequently resulting in swollen infraorbital sinuses and is thus called “infectious sinusitis.” These diseases affect chickens and turkeys worldwide, causing the most significant economic losses in large commercial operations, and are commonly seen in noncommercial flocks. Infection also occurs in pheasants, chukar partridges, peafowl, pigeons, quail, ducks, geese, and psittacine birds. Songbirds are generally resistant, although there is a widespread outbreak of M gallisepticum causing conjunctivitis and mortality in wild house finches (and some similar species) in North America

M synoviae was first recognized as an acute to chronic infection of chickens and turkeys that produced an exudative tendinitis and synovitis (infectious synovitis), with increased condemnation in the processing plant; it occurs most commonly as a subclinical infection of the upper respiratory tract, especially in multi-age layer flocks. M synoviae infection is also a complication of airsacculitis in association with Newcastle disease or infectious bronchitis. It is distributed worldwide and is seen primarily in chickens and turkeys, but ducks, geese, guinea fowl, parrots, pheasants, and quail may also be susceptible. M synoviae is even more fastidious than M gallisepticum. Serum (preferably swine) and nicotinamide adenine dinucleotide (NAD) are required for growth in M synoviae culture media.

M synoviae isolates vary widely in virulence, and suspected virulence factors include adhesins, sialidase, nitric oxide, cell invasion, and antigenic variation and immune evasion.

Economic impact

Mycoplasma galliceptum reduces production by an average of 15 eggs per chick.

Carpenter et al (1981)

Mycoplasma synovii reduces production by 8-10 eggs per chick.

Mallinson (1985)

Economic losses of mycoplasma are estimated at a rate of 0.60 – 0.75 cents per chicken.

Hussni et al (1987)