Mycoplasmosis is a collective term for infectious diseases caused by the micro-organisms called mycoplasmas. There are a number of mycoplasmas that can infect poultry, with Mycoplasma gallisepticum (MG) (which affects a number of bird species including chickens, turkeys, gamebirds and pigeons), M. synoviae (MS) (which affects chickens and turkeys), and M. meleagridis (MM) (which only affects turkeys) being the main species.
MG can cause chronic respiratory disease and decreased growth or egg production and affected carcasses sent to slaughter may be downgraded. Some chickens may not show symptoms. Observable clinical signs may include rales, coughing, sneezing, nasal discharge, frothiness and swelling around the eyes or difficulty breathing. Signs are often more severe in turkeys. MS can cause respiratory disease similar to MG but if it becomes systemic it can cause lameness, swollen joints, loss of weight and breast blisters. Greenish diarrhoea can also be present in dying birds. MM is a venereal disease that can result in high mortality of young poults through starvation. Signs in young poults include unthriftiness, difficulty breathing, poor growth and neck and leg deformations. Breeder flocks may experience a drop in egg production and hatchability.
All of these mycoplasmas can be transmitted vertically and so can be introduced into the flock through infected eggs, including venereal transmission by males for MM. Vertical transmission has been greatly reduced through the establishment and maintenance of MG, MS and MM-free breeder flocks. They can spread through bird-to-bird contact and contact with exhaled respiratory droplets either as aerosols or on equipment, people and surroundings. Birds recovered from MG and MM remain carriers of the organisms and continue shedding for life.
All of these mycoplasmas are sensitive to several antibiotics, however, vaccines for some mycoplasmas are also available. Good biosecurity procedures are critical for prevention. Mycoplasmas are destroyed by disinfectants and sunlight.