M meleagridis causes vertically transmitted (transovarian) disease of turkeys.
Disease primarily impacts newly hatched poults with airsacculitis but has also been associated with decreased hatchability from infected breeder flocks and with poor growth and skeletal abnormalities in progeny.
M meleagridis is a host-specific pathogen of turkeys (not chickens). With successful control programs (eg, National Poultry Improvement Plan in the US), turkey primary breeders have eliminated the infection from their stocks, producing eggs and poults free of M meleagridis. Thus, M meleagridis has not been reported in the commercial turkey industry for quite some time.
Marked differences in the pathogenicity of various strains of M meleagridis result in variable clinical manifestations, with airsacculitis in poults being the most common.
Epidemiology and Transmission of Mycoplasma meleagridis Infection in Poultry
Before control programs, turkeys worldwide were commonly infected with Mycoplasma meleagridis.
Infection of progeny occurs primarily through vertical (egg) transmission with rates that vary over the laying season. At the hatchery, organisms may be spread horizontally via aerosols from the respiratory tract or to the vent on contaminated hands during vent-sexing. Respiratory tract infection also leads to horizontal transmission among birds within young, growing flocks and may be a factor in the spread to flocks previously free of infection (flock-to-flock transmission).
In some infected turkeys, organisms localize in the reproductive tract. Thus, the source of vertical transmission in hens is organisms incorporated in eggs. In toms, the phallus and adjacent tissues (cloaca) become infected and contaminate the semen.
Artificial insemination of turkey hens with infected semen is another important method of transmission. Additionally, indirect transmission may result from poor biosecurity practices, such as vaccination, whereby mycoplasmas are transferred directly from infected to noninfected turkeys via contaminated hands, clothing, and equipment.
Clinical Findings and Lesions of Mycoplasma meleagridis Infection in Poultry
Vertical transmission and embryo infection with M meleagridis leads to decreased hatchability (due to late embryo death), poult quality, and growth rate. Only mild respiratory signs are present, despite high rates of airsacculitis in poults from infected hens.
Egg-borne infections may impact early rapid growth of hock joints, periarticular tissues, cervical vertebrae, and adjacent bone, producing skeletal abnormalities such as torticollis ("crooked neck" or "wry neck") or leg deformities.
Adult breeders usually show no clinical signs of venereal or respiratory infection.
Hatched poults may have airsacculitis with variable degrees of thickening, turbidity, foamy yellow exudate, and caseous flecks (see image of airsacculitis in poult). These lesions recede with age.
Poults with torticollis may have cervical airsacculitis and osteomyelitis of adjacent vertebrae. The generalized skeletal lesions that may develop in poults 1–6 weeks old are characterized by chondrodystrophy or by varus deformities and perosis.
Courtesy of American Association of Avian Pathologists.
Microscopic lesions in the reproductive tract of hens consist of lymphocytic foci in the fimbria, uterus, and vagina, with plasma cells and heterophils in the lamina propria. Infected embryos and young poults show inflammatory lesions of airsacculitis and occasionally pneumonia.
Diagnosis of Mycoplasma meleagridis Infection in Poultry
Serological testing, culture, or real-time PCR assay
A high prevalence of airsacculitis in day-old poults suggests M meleagridis infection.
Serological testing by agglutination (tube or plate) or ELISA can demonstrate antibody. Confirmation was historically by hemagglutination-inhibition assay or by culture, isolation and identification of isolated colonies; however, real-time PCR assay is now used to detect M meleagridis DNA from ante- or postmortem specimens as well as isolates.
Infection with other Mycoplasma spp and poor poult quality must be considered in the differential diagnosis.
Treatment, Control, and Prevention of Mycoplasma meleagridis Infection in Poultry
Sourcing eggs or poults from breeders free of M meleagridis
Turkey eggs or poults should be obtained from breeder flocks free of M meleagridis and monitored by serological testing. Additionally, vertical transmission can be monitored by examining pipped embryos or cull poults for airsacculitis. Semen used for insemination must be free of M meleagridis.
Dipping eggs in tylosin or another antimicrobial decreases the incidence of transmission in infected flocks. However, this practice has been generally eliminated with the eradication of M meleagridis from primary breeder flocks and is only used by multiplier breeders when there is an outbreak.
Injection of a suitable antimicrobial at 1 day old or water medication for the first 5–10 days appears to decrease infection and airsacculitis caused by M meleagridis and improve weight gain.
Key Points
M meleagridis is vertically transmitted, causing embryo and young poult death, skeletal abnormalities, and growth retardation.
M meleagridis has been eradicated from all primary turkey breeders in the US.
M meleagridis–free breeding stock and antimicrobial treatment are the most effective means of control and prevention.
For More Information
Ferguson-Noel N. Other mycoplasmal infections. In: Swayne DE, ed. Boulianne M, Logue CM, McDougald LR, Nair V, Suarez DL, associate eds. Diseases of Poultry. 14th ed. Wiley Blackwell; 2020:933-939.
Kempf I. Avian mycoplasmosis. In: Brugère-Picoux J, Vaillancourt J-P, Shivaprasad HL, Venne D, Bouzouaia M, eds. Manual of Poultry Diseases. Association francaise pour l’avancement des science; 2015:278-285.
