MYCOPLASMA GALLISEPTICUM Dr. Salah M. Hassan, MSc, PhD College of Veterinary Medicine University of Mosul
Common Names
Mycoplasma gallisepticum infection, MG, Mycoplasmosis, Chronic Respiratory Disease (CRD), PPLO Infection, Airsaculitis.Definition
A contagious disease primarily of chickens and turkeys, characterized by respiratory signs and lesions and a prolonged course in the flockEtiology
1) Mycoplasma gallisepticum is the causal agent. Mycoplasma are the smallest free-living organisms (smaller than the bacteria). They do not possess cell walls and grow rather slowlyEtiology (Continued)
2) MG seldom survives for more than a few days outside the chicken. Carrier birds are required for survival.
Transmission
1) Vertically (transovarian). MG is transmitted in some eggs laid by inapparent carriers.Transmission (Continued)
2) Horizontally. Infected chickens transmit MG through: aerosols contaminated feed and water other avian species, domestic and wildTransmission (Continued)
3) Mechanically. MG is spread by contact with contaminated equipment, on shoes and fomites (feed sacks, crates, etc.).Transmission (Continued)
The MG organism infects poultry which often become long term carriers. These chickens then contaminate the farm and infect other MG free birds.
Occurrence
MG is of worldwide incidence and is of considerable economic importance to all segments of the commercial poultry industry.Occurrence
MG causes: Breeders-decreased egg production Fertile Eggs-reduced hatchability due to late embryo mortality Chicks- reduced livabilityOccurrence
MG plays a role in the respiratory complex of diseases resulting in downgrading of carcasses MG + E. Coli + IBD Immunosuppression + IB and ND Vaccine/Field VirusesOccurrence
Laying Hens The main problem associated with MG infection is a 5-10% drop in egg production.Production Losses
MG free hens laid 15.7 more eggs per hen housed than unvaccinated MG infected birds over a 45 week laying period. MG infected layers, vaccinated with F-strain or bacterin, produced 7 more eggs per hen housed as compared to unvaccinated group. _____________ Avian Diseases 25:406-415, 1984Occurrence
Effect on egg production (quantity and quality) depends on: virulence of the strain of MG degree of stress placed on birds.Occurrence
Increased medication costs and poor feed conversions are additional factors that make this one the costliest disease problems confronting the poultry industry.Clinical Signs
Commercial Layers tracheal rales ocular and nasal discharge coughing feed intake reduced weight loss egg production drops, usually maintained at a lower levelClinical Signs
Broilers usually between 3 and 8 weeks of age more pronounced than in adult birds severe cases frequently associated with stress factors-poor ventilation, concurrent diseases, vaccine reactionsClinical Signs (Continued)
Broilers feed intake and growth rates reduced male birds more severely affected illness more pronounced during winter- ammonia, dust,...Clinical Signs(Continued)
MG infection may be dormant in infected chickens and cause no disease until triggered by stress (poor husbandry, dust, ammonia, temperatures extremes, disease challenge, vaccine reactions, immunosuppression, etc)
Clinical Signs (Continued)
MG is often associated with the following pathogens: IBV and NDV (field and vaccine viruses), E. coli, H. paragallinarum, making the condition more severeLesions
Primarily catarrhal exudate in nasal passages, trachea, and bronchiearly- air sac exudate has a “soap suds” or “beaded” appearancelater- exudate becomes caseous and yellowLesions (Continued)
MG infection alone- only slightly detectable lesions complicated cases of MG- fibrinous perihepatitis, pericarditis, and severe airsaculitisMortality
adult flocks- negligable broilers - low in uncomplicated cases - up to 30% if poor management and other stress factors mortality may be low, but cull rate high
Diagnosis
1) Tentative diagnosis of MG made based on history, clinical signs, and lesions.Diagnosis (Continued)
2) Serology Positive plate test for MG from suspect flock strengthens diagnosis False positive reactions may occur with plate test, confirm suspicious results with HI or ELISA testDiagnosis (Continued)
3) A definitive diagnosis would include isolation and identification of MG (often is difficult and time consuming)Diagnosis(Continued)
Serum Plate Agglutination (SPA): Detects IgM class of antibodies Detects antibodies within 7 days of infection Test is easy to perform, rapid, inexpensive, and sensitive Test is prone to false positive reactions (screening test)Diagnosis (Continued)
Causes of false positive SPA results: Serum from MS infected chickens Contaminated serum Freezing of serum Freezing of SPA antigenDiagnosis (Continued)
Causes of false positive SPA results: Prolonged storage of serum at 4 C Infection of chickens with S .aureus Vaccination with inactivated oil- emulsion vaccines, 2-8 weeks post vaccinationDifferential Diagnosis
MG infection- differentiated from other common respiratory diseases of chickens, including NDV, IBV, infectious coryza, fowl cholera, TRT, ORT, and MS
Prevention and Control
Biosecurity Strict isolation to prevent introduction of MG into a clean flockPrevention and Control (Continued)
Prevention of MG in commercial layers is difficult because hens are commonly maintained on multiple-age farmsPrevention and Control (Continued)
Preferred method for eliminating MG infection- depopulation of infected flocks Complete depopulation of MG (+) farms is necessary to eradicate infectionPrevention and Control (Continued)
The MG organism is fragile and lives only a short time outside the chicken A house can be easily freed of MG by cleaning and disinfecting between flocks after all chickens are gone
Prevention and Control (Continued)
Avoid multiple age farms All in & all-out grow-out programs Careful traffic control and good sanitation Maintain biosecurity on single age farmsPrevention and Control (Continued)
In multiple-age farms where depopulation and disinfection are impractical, options include: Medication VaccinationGeneral Comments
Pullets raised MG (-) often become infected when placed in MG (+) multiple-age laying operations When beginning production and reaching peak productionGeneral Comments (Continued)
Flocks may have serologic evidence of infection with no clinical signs, especially if infected at an early age. These birds may have some immunity, but remain carriers and transmit the disease to susceptible chickens by contact or egg transmission, especially after a stressor.Medication
Commonly used antibiotics include tylosin, gallimycin, tetracyclines, Baytril, Pulmotil, others Treatment will partially alleviate symptoms, lesions, and egg production lossesMedication
Disadvantages: Cost of antibiotics Development of antibiotic-resistant MG organisms MG infection not eliminated MG shed continuesVaccination
Vaccine types: F-strain MG - live product Mycovac-L - strain 6/85 of MG TS-11 MG bacterin - inactivated product