Diseases: Chronic Respiratory Disease

Introduction

• Caused by infection with Mycoplasma gallisepticum; often complicated by the presence of other organisms, especially the bacterium Escherichia coli.
• Other mycoplasmas also cause disease in poultry

Clinical Signs

• Clinical disease is long lasting and spreads slowly through a flock
• Chickens of all ages are susceptible
• Uncomplicated disease is usually mild with nasal discharge, cough and respiratory sounds
• Signs are more severe with physical stress or a secondary infection
• Reduced egg production
• Low mortality

Post Mortem Lesions

• Sinusitis and tracheitis with mucoid discharge
• Thickened air sacs
• Cheese-like deposits on air sacs
• Fibrin on heart, liver and peritoneum in cases with secondary infection

Diagnosis

• Clinical signs and post mortem lesions allow a presumptive diagnosis
• Organism is difficult to grow and requires complicated media

Samples

• Exudates from areas with lesions, if there is access to a laboratory with a diagnostic capacity

Transmission

• Usually spread by direct contact between susceptible chickens and carrier chickens
• Recovered chickens can become carriers
• Infection with inhaled droplets containing organisms occurs readily
• Transmitted from hen to chick through the egg

Treatment

• Treatment with antibiotics is probably not warranted under village conditions

Prevention and Control

• Good husbandry - avoid conditions that will cause stress, for example cold and bad ventilation