Summer 2012 Newsletter
Mycoplasma gallisepticum infection of Backyard and Commercial Poultry Operations
by Dr. Daniel A. Wilson
edited by Dr. Pat Wakenell
ABSTRACT

Mycoplasma gallisepticum (MG) is an important disease of backyard and commercial poultry flocks in Indiana and the US. As a target disease of the National Poultry Improvement Plan (NPIP) the incidence of MG has been greatly reduced over the last 50 years, however, the disease still has a continuing significance. MG is the causative agent of Chronic Respiratory Disease of chickens and Infectious Sinusitis of turkeys, both of which can result in varying rates of morbidity and mortality. An increasing number of mycoplasmosis cases in backyard flocks have been identified as backyard flock ownership has increased and owners of these flocks continue to trade birds at "swap meets" and through online trading websites. Treatment of MG positive flocks with antibiotic therapy is either not feasible or unsuccessful. If necessary, depopulation of backyard flocks as a result of clinical mycoplasmosis can be very emotional and detrimental to flock owners. Mycoplasmosis carries a significant economic importance to commercial poultry operations through death loss, condemnations, and reduced egg production. Prevention of MG in both backyard and commercial flocks is achievable by appropriate bio-security methods and surveillance programs like the NPIP. Subsidized testing for MG and other avian diseases is available through the Indiana State Poultry Association Test-12 program. After requesting paperwork from ispa@purdue.edu owners may submit one dozen eggs to the Purdue Animal Disease Diagnostic Lab and receive free test results. In addition to surveillance testing, education of backyard owners concerning bio-security is essential to prevent mycoplasmosis and other infectious diseases of poultry.

INTRODUCTION

Mycoplasma gallisepticum (MG) was first described in turkeys in the United States in 1905 but has since become the most economically significant mycoplasma in the poultry industry. MG is worldwide in distribution and represents a disease of concern for a variety of commercial poultry operations. As commercial poultry operations in the United States grew over the last century and moved to more vertically integrated confinement operatios, MG became a significant economic concern. Economic issues of MG are due largely to potential for large death losses, increased condemnation at processing plants, and reduced egg production in commercial egg production facilities. Additional costs can be incurred from MG vaccination, depopulation of affected flocks, and surveillance programs. MG incidence in the United States has been greatly reduced since the disease was added to the National Poultry Improvement Plan (NPIP) 50 years ago. Cases of MG in backyard flocks in Indiana have become more frequent in recent years. This could be due to increased surveillance methods or an actual increase in MG transmission as more backyard flock owners trade birds at "swap-meets" and through online trading websites.

MG is a gram-negative coccoid intracellular organism. Natural hosts of MG are gallinaceous birds (chickens, turkeys, etc.) although MG has been found naturally occurring in other avian species. MG is rarely isolated from wild turkeys but some have been found to be sero-positive by surveillance studies.

TRANSMISSION

MG is readily transmitted horizontally from both clinically infected and carrier birds through direct contact. Mycoplasma organisms can survive off of the host bird for approximately 24 hours and fomites can serve as an infectious route. Vertical transmission from some carrier birds occurs through trans-ovarian transmission. Poultry can carry the MG organisms with no clinical signs until a stressful event triggers clinical disease. Incubation period varies from 6-21 days and presentation of clinical signs can be highly variable.

DIFFERENTIAL DIAGNOSES

Respiratory signs present in MG infection can resemble infections with other respiratory organisms such as Infectious Coryza (Haemophilus paragallinarum) and Infectious Bronchitis Virus in chickens or fowl cholera (Pasteurella multocida) in chickens or turkeys. As with any birds with respiratory disease. Exotic Newcastle and Avian influenza should always be included as possible differentials.

CLINICAL SIGNS

Chickens are much less susceptible to MG infections than turkeys and suffer less severe clinical signs than that of turkeys. Some chickens may seroconvert to MG with little to no outward signs of infection. For this reason, MG infection of chickens is often referred to as Chronic Respiratory Disease. In some cases chickens may only exhibit clinical signs of anorexia, weight loss, and reduced egg production. Younger chickens are more likely to exhibit classic MG signs of tracheal rales, nasal discharge, and coughing. Chickens can occasionally have more severe clinical signs of swelling of eyelids, conjunctivitis, increased lacrimation, and sinusitis. In an acute infection, turkey flocks are much more likely to show outward respiratory signs including severe sinusitis with facial distortion and general respiratory distress. These acute signs contribute to anorexia, depression, and varying amounts of mortality in an exposed flock. The severe distension of the infraorbital sinus that occurs with MG infection has led to this disease being referred to as Infectious Sinusitis in turkeys.

Swollen infraorbital sinus in a turkey with Mycoplasma Gallisepticum

Figure 1: Swollen infraorbital sinus in a turkey with Mycoplasma Gallisepticum

Environmental stressors can cause a more clinical disease picture in both backyard and commercial poultry. As flocks are housed in conditions with poor air quality the morbidity and mortality of a flock may increase. Poor ventilation during winter months often contributes to increased incidence of MG outbreaks. Other stressors such as moving flocks, shipping birds, or adding new birds to a flock can further worsen the clinical picture of MG.

GROSS LESIONS

As with clinical signs, the gross lesions in chickens are much less prominent than those present in turkeys. Chickens may exhibit sings of catarrhal exudate in the nasal passages, trachea, and bronchi with additional caseous exudate present in air sacs. Conjunctivitis may be present in one or both eyes. Inflammation and accumulation of caseous exudate in the infraorbital sinus can be severe in turkeys causing facial distortion.

DIAGNOSIS

As with other bacterial diseases, diagnosis by isolation and identification culturing methods is ideal. Samples submitted for isolation can include lungs, tracheal or air sac exudates, fluid or sinus exudate, or by swabbing the trachea or choanal cleft of live birds. Serological testing of affected birds offers a rapid diagnostic tool which can aid in diagnosis of an acute MG infection while bacterial cultures are performed. Serum plate agglutination techniques are commonly employed to detect presence of antibodies for MG. This test is relatively inexpensive to perform and the test is sensitive when used as a screening tool. The plate agglutination technique often has false positive reactors due to cross-reactivity; however, tests can be confirmed by hemagglutination inhibition testing to rule out these false positives. An alternative to submission of sera of flocks is submission of whole eggs from a flock. Antibodies can be collected from the yolk of submitted eggs and a plate agglutination test can be performed in a similar fashion. Eggs are often an easy solution for sample submission when owners or veterinarians are uncomfortable collecting blood from poultry. The Indiana State Poultry Association currently offers a subsidized T-12 Program ("Test 12") which allows owners of backyard flocks to submit a dozen eggs to the Indiana Animal Disease Diagnostic Lab and receive free testing for Mycoplasma gallisepticum in addition to other diseases monitored by the National Poultry Improvement Plan. Contact ISPA at ispa@purdue.edu to receive additional information about the T-12 Program.

MG Serum Plate Agglutination test with negative (left) and positive (right)

Figure 2: MG Serum Plate Agglutination test with negative (left) and positive (right).
PREVENTION AND TREATMENT

Ideal prevention methods for MG include sourcing birds from flocks which monitored under the National Poultry Improvement Plan (NPIP). Preventing vertical transmission of MG from parent flocks is a critical step in the overall reduction of MG in flocks. Most commercial hatcheries are NPIP monitored and therefore parent stock are tested to be Mycoplasma free on a regular basis. Backyard poultry owners should be advised that sourcing birds from NPIP participating flocks can help reduce the likelihood of MG outbreaks. Owners of backyard flocks should avoid purchasing birds with unknown histories (swap meets, online ads, etc.) or at a minimum should quarantine and/or test new additions to a flock . Bio-security is important to both backyard and commercial operations as MG organisms can be transmitted between flocks by fomites such as clothing, boots, and equipment. Educating owners on the necessity of bio-security is essential to prevent not only MG, but also other infectious diseases.

Commercial chickens can be vaccinated with a variety of available killed and live MG vaccines to varying success rates. In geographic areas near large commercial turkey operations the usage of live vaccines may be restricted or even illegal. MG vaccines have not proven effective in turkeys as they are either too pathogenic or will not colonize the turkeys at all. Many commercial multi-age egg complexes that become MG positive will be left to remain MG positive while vaccination is used to prevent clinical disease. Commercial turkey flocks which experience infectious sinusitis are often depopulated to prevent spread to other flocks within the immediate area.

Treatment in commercial chicken and turkey flocks is usually not beneficial or feasible given meat and egg withdrawal times. MG is shown to be sensitive to macrolides, tetracyclines, fluoroquinolones, but are resistant to penicillins. Antibiotic treatment of affected flocks may reduce morbidity and mortality but it is unlikely to eliminate MG from the flock. Therefore, depopulation is often the only long-term solution to prevent spread of the MG from flock to flock.

RESOURCES
  • American Association of Avian Pathologists. (2006). Avian Disease Manual. 6th Edition. Mycoplasmosis.
  • Indiana State Poultry Association. http://inpoultry.org/
  • Kleven, SH. (2008). A Laboratory Manual for the Isolation, Identification, and Characterization of Avian Pathogens. 5th edition. Mycoplasmosis. Pg. 59-64.
  • National Poultry Improvement Plan. http://www.aphis.usda.gov/animal_health/animal_dis_spec/poultry/
  • Saif, YM. (2003). Diseases of Poultry. 11th edition. Mycoplasmosis. Pg. 719-774.
  • Shane, SM. (2005). Handbook of Poultry Disease. Mycoplasmosis. Pg. 95-98
  • Wakenell PS and DA Wilson. (2011). Diagnosis: MG/MS in a Backyard Flock. Is Control Possible? Proceedings of the Annual Meeting of the American Association of Avian Pathologists.
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