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Aivlosin® in Poultry
Mycoplasmosis
Mycoplasmosis, caused by both Mycoplasma gallisepticum (Mg) and Mycoplasma synoviae (Ms), is prevalent in the commercial poultry industry in many parts of the world.
Mycoplasma gallisepticum (Mg)
Clinical signs
Spread of the disease
Diagnosis
Treatment
Management and control
Mycoplasma synoviae (Ms)
Clinical signs
Spread of the disease
Diagnosis
Management and control
Mycoplasma gallisepticum (Mg)
Mg generally causes chronic respiratory disease in broilers. The mycoplasma attaches to the cilia on the respiratory epithelial cells and may even cause the cilia to stop beating. Other strains may become invasive and escape from the respiratory tract to other sites, such as the reproductive tract or leg joints.
Clinical signs
Chronic respiratory signs such as coughing, snicking and tracheal rales are more evident in chickens whilst sinusitis and conjunctivitis are the main signs in turkeys. Gross signs can consist of mucus in the nares, trachea and lungs. Enlargement of the infraorbital sinus, especially in turkeys, may be evident as a result of mucus and later caseous material accumulation.
Mg is a primary pathogen in its own right but disease can be exacerbated if other respiratory pathogens are present or the bird is debilitated for other reasons. Lesions will be increased in severity as a result of concurrent infections, such as IBV, NDV, TRT and
E. coli. The "reaction" to respiratory viral vaccines can be exacerbated if mycoplasma is present.
Birds with infected leg joints, such as the hock joint, may have difficulty walking due to excess joint fluid swelling the joint.
Mg infection in laying birds can cause a reduction in egg production and a decrease in egg quality together with reduced hatchability.
Spread of the disease
Mycoplasma can be transmitted via the egg; some developing embryos may be killed but enough infected chicks hatch to allow for transmission of the disease within the flock.
The main source of spread within the flock is the aerosol transmission of infected material from bird to bird, especially in high density flocks. Spread between flocks can be via fomites (e.g. boots and equipment) and possibly windborne over small distances.
Diagnosis
Although there are problems with the sensitivity and specificity of the rapid slide agglutination test, it is commonly used to screen a flock and to indicate that the poultry have been infected. It is a relatively cheap and easy test to perform and rapid results for a large number of sera can be produced. Generally speaking the more samples tested from a flock the greater the accuracy.
Another alternative for serology is the ELISA, but this also has similar drawbacks as the slide agglutination test (sensitivity and specificity). It can be used as part of an automated system and large numbers of sera can be tested.
In situations where serology is not clear- cut, disease is diagnosed by identification of the organism or its DNA, which may be achieved by culture or by the use of a PCR (polymerase chain reaction).
Suitable sites for taking swabs include the choanal slit, oropharynx, and cloaca. Care should be taken with the transport of the material (use moist swabs, courier if possible) as mycoplasma are relatively sensitive organisms. Growing mycoplasma can be difficult and requires some expertise. The identification of this relatively slow growing organism is usually done using an immunofluorescence test which incorporates a mycoplasma-specific antiserum.
Treatment
Treatment of infected birds (principally layers and broilers) with antibiotics is practiced in the field. The antibiotic should be present at the mucosal sites in the respiratory tract. Previously, it was thought that the mycoplasmas were solely located in the respiratory tract closely associated with the epithelial cell surface but recent evidence has shown that Mg can enter the cells and even replicate intracellularly. An effective intracellular antibiotic offers advantages over an antibiotic that does not penetrate cells.
Vaccine is also used in layers, in order to prevent drops in egg production and effects on the egg quality. Inactivated and live vaccines (F, ts-11 and 6/85) have both been used in the field. F vaccine is more virulent whilst the other two are less so and they may not induce a detectable antibody response, although they are in the main protective. Vaccines are not registered for use in either broilers or turkeys.
Management and control
In some instances, such as primary breeding birds and commercial breeding flocks, it is possible to eradicate the disease and breeding stocks are often maintained as disease- free. A small nucleus of chickens is tested and maintained disease -free. The flocks are expanded from this clean nucleus. Antibiotic treatment of embryonated eggs to establish mycoplasma-free birds is possible and is practiced.
It has proven much more difficult to maintain table egg layers and broilers as disease–free.
Mycoplasma synoviae (Ms)
In general, all aspects of the disease are similar to those of Mg.
Initially, the organism was associated with synovitis whereas nowadays it is more commonly associated with a mild respiratory disease. Experimentally, those strains with a haemagglutinin are more frequently associated with synovitis.
M.synoviae is extremely common in commercial layers with mortality usually less than 10%. The economic importance of this disease is difficult to determine as documented evidence is rare.
Clinical signs
Clinical signs are often not apparent, but when present they can present as both respiratory and arthritic signs.
In the respiratory form, only slight tracheal rales may be present.
In the acute arthritic form of the disease there is marked depression, growth retardation, loss of condition together with swelling of the foot and hock joints that causes lameness.
The effect on egg production varies, some reports state that a drop in egg production of 5-10% occurs but in other studies none is reported.
Broilers may be severely affected but this appears to be limited to pathogenic strains of Ms.
Spread of the disease
Ms is spread in a similar manner to Mg. However, it appears that respiratory transmission of Ms may be quicker than Mg.
Diagnosis
Similar to Mg, the diagnosis of Ms is based on serology and/or the detection of the organism or its DNA. There is a rapid plate agglutination test and an ELISA for serology. Although Ms is associated with arthritis, swabs of the trachea are used for isolation of the organism. The conditions for growth of Ms are more fastidious than Mg and the fragility of Ms appears to be greater, especially in acidic conditions.
Management and control
Ms has been stated to be more resistant to antimicrobials than Mg, but remains fully susceptible to Aivlosin®.
Control measures are also the same as for Mg.
Control measures are also the same as for Mg.
