Chronic respiratory disease is an upper respiratory infection caused by Mycoplasma gallisepticum
. The disease occurs very commonly in backyard chicken flocks worldwide. Young birds less than 4 months of age, and roosters, tend to have more severe infections than older or adult birds. The characteristic signs include tracheal rales or gurgling sounds, nasal discharge, sneezing, gaping, and coughing. Conjunctivitis and eye discharge may be present in one or both eyes. There can less commonly be facial swelling and head shaking.
Transmission of Chronic Respiratory Disease in Chickens
Sources of infection include latently and chronically infected birds (domestic chickens and turkeys or wild birds). It spreads vertically (from breeding parents to offspring) and horizontally both directly from bird to bird and can be indirectly spread by living and inanimate vectors. Within a flock the spread of the pathogen is normally slow. M. gallisepticum
doesn't survive for very long in the environment, and only remains infective for a couple of hours to days. The incubation period is typically 4 to 10 days.
Diagnosis of Chronic Respiratory Disease
There are several different types of tests available for detection of M. gallisepticum
in chickens, offered by veterinary diagnostic laboratories. Two of the most popular include:
- A real-time polymerase chain reaction (rtPCR) procedure which is conducted on tracheal and/or oropharyngeal swabs of clinically ill birds. This provides direct confirmation of the presence of the M. gallisepticum pathogen.
- Hemagglutination inhibition (HI) which is an indirect test that's performed on serum samples collected from birds that usually have been ill for a short period or have had clinical symptoms from which they have recovered. If the test comes back positive for antibodies, a presumptive diagnosis of chronic respiratory infection can be made.
Treatment for Chronic Respiratory Disease
Several antibiotics can be used to treat mycoplasma infections in chickens: macrolides, lincosamides, aminoglycosides, tetracyclines, floroquinolones, and pleuromutilins.