MYCOPLASMOSIS IN THE COMMERCIAL POULTRY

Avian mycoplasmosis which is an important disease condition in birds is caused by four (4) commonly recognized pathogens: Mycoplasmagallisepticum(MG), Mycoplasma synoviae(MS), Mycoplasma meleagridis(MM)and Mycoplasma iowae (MI). Other mycoplasmas have also been incriminated in mycoplasma infections in birds but are not pathogenic, so this review will focus mostly on MG and MS. This present review focused on clinical signs, transmission, economic significance, methods of diagnosis, treatment, prevention and control and researches done in Nigeria and it is aimed at increasing the research interest in avian mycoplasma in the country.

Avian mycoplasmosis is a disease which is worldwide in occurrence and is extremely important to both the broiler grower and the table-egg producer . It is caused by mycoplasma organisms of the Class Mollicutes. These organisms are different from other bacteria; they are of very small sizes and do not have a cell wall . These characteristics account for the “fried egg” type of colonial morphology exhibited by mycoplasmas, their complete resistance to antibiotics that affect cell wall synthesis and their complex nutritional requirements . Avian mycoplasmas are also host specific (for instance, Mycoplasmameleagridis infects turkeys only)

Mycoplasma in poultry is not a new disease. There is mention in the old books of similar symptoms from about 100 years ago but it has generally been called roup or a common cold. Treatment tended to be by culling only.

The disease acquired the name mycoplasma once the causative organism had been discovered. Mainly the respiratory system in poultry is affected and the disease may be becoming more common, spreading with increased travelling of stock, more people keeping chickens and mixing them from different sources. The incubation period before clinical signs appear can be as little as a few days – it is very infectious. It appears to thrive in the bird when other pathogens are present, such as E. coli or infectious bronchitis (IB is certainly now more common in free-range flocks) or if the birds are stressed or debilitated. Debilitating factors include nutritional deficiency, excessive environmental ammonia and dust and stressors such as changes in the pecking order or exhibitions.

The organism is neither a bacterium nor a virus in size, but part way between, having no cell wall but with a plasma membrane. Four out of the known 17 species of mycoplasma are pathogenic in poultry:

Mycoplasma gallisepticum: signs can include foamy eyes, sneezing, nasal discharge, swollen eyelids and sinuses, reduced egg production and gasping in chickens, turkeys and pheasants, swollen sinuses in waterfowl. This one is the main culprit in backyard flocks.

Mycoplasma synoviae: signs include swollen and hot joints in chickens and turkeys and/or respiratory signs as above, or thin, deformed shells at the broad (apical) end of the egg.

Mycoplasma meleagridis: signs include poor growth in turkey poults and lowered hatchability in turkey breeders.

Mycoplasma iowae: signs included reduced hatchability in turkey breeders, twisted legs in turkey poults.

When nasal discharge is evident, feathers become stained with this as the bird tries to clean its eyes and nostrils. There is a particular sweet smell associated with this discharge which to the sensitive nose is immediately apparent when entering a hen house.

Nasal discharge and cool temperatures are protective of the organism so any sneezing will deposit droplets which will remain infective for several days. Transmission is also through the egg, plus carried on the clothes and hands of people tending the birds. Mycoplasmas are transmitted laterally by contact , infectious aerosols coughed and sneezed by infected birds , through contaminated feed, water, contact personnel and communicant animals mainly birds and vertically through the eggs . Veneral transmission is particularly important in the case of MM . MS infection can also be through the conjunctiva and upper respiratory tract . It has beenreported by that M. gallinarum and M. gallinaceum have been isolated from the oviduct of chickens. This suggests that egg transmission of this species is possible.According to , infected birds carry MG for life and can remain asymptomatic until they are stressed.

All ages of chickens and turkeys are susceptible to avian mycoplasmosis although young birds are more prone to infection than the older ones ; it seems that some resistance develops with age

Economic Significance– MG has been ascribed to be the most economically important of the pathogenic mycoplasma species affecting poultry due to the significant losses occurring from decrease in egg production, decrease in egg quality, poor hatchability(high rate of embryonic mortality and culling of day old birds), poor feed efficiency, an increase in mortality and carcass condemnations and medication costs. Economic losses in the poultry industry caused by this infection have been noted to be significant the infection has been reported by to reduce egg production in layers and broiler breeder chickens by 10-20%.

Reduced egg production and reduced weight gain in chickens, turkeys, waterfowl and pheasants.

History, clinical signs, and typical gross lesions may be suggestive of M gallisepticum infection. Serology by agglutination and ELISA methods are commonly used for surveillance. Hemagglutination-inhibition is used as a confirmatory test, because nonspecific false agglutination reactions may occur, especially after injection of inactivated oil-emulsion vaccines or infection with M synoviae. M gallisepticum should be confirmed by isolation from swab samples of infraorbital sinuses, nasal turbinates, choanal cleft, trachea, air sacs, lungs, or conjunctiva. Primary isolation is made in mycoplasma medium containing 10%–15% serum. Colonies on agar medium are used for species identification by immunofluorescence with species-specific antibodies. PCR can also be used for detection of M gallisepticum DNA using swabs taken directly from infected sites (choana, sinuses, trachea, air sacs) or after growth in culture.

Mycoplasma isolates must be identified by species, because birds may also be infected with nonpathogenic mycoplasmas. E coliinfection, Newcastle disease, avian influenza, and other respiratory diseases (eg, infectious bronchitis in chickens) should be considered in the differential diagnosis and can act as inciting or contributing pathogens.

On post mortem examination, lesions may be found throughout the upper and lower respiratory tracts. Catarrhal exudates may be present in the nasal passages, infra orbital sinuses, trachea and bronchi . Mild sinusitis, tracheitis and air sacculitis are observed in uncomplicated cases of mycoplasmosis in chickens. Thickening and turbidity of the air sacs, Exudative accumulations, fibrinopurulent pericarditis and perihepatitis may be seen in cases where the chicken is concurrently infected with E. coli . In turkeys severe mucopurulent sinusitis may be found with variable severe tracheitis and air sacculitis . Interstitial pneumonia and Salpingitis are often seen in chickens and turkeys ; other findings may include conjunctivitis, corneal opacities and peri ocular edema . The severity of these lesions is variable depending on the virulence and pathogenicity of the infecting strain, concurrent respiratory pathogens and stress factors .

Differential diagnosis in poultry includes respiratory diseases such as infectious bronchitis, mild Newcastle disease and avian influenza . Other pathogens to be considered include Hemophilusparagallinarum, and Pasteurellamultocida, while avian pneumovirus, Pasteurellamultocida and Chlamydia are also to be considered in turkeys. Mixed infections with Mycoplasma gallisepticum and other organisms can occur

It has been reported that the treatment of mycoplasma infected breeders with anti microbials decreases the rate of clinical manifestations and consequently also decreases the risk of transovarian transmission. It was stated that although this procedure is recommended for laying hens, it doesn’t eliminate MG,MS OR even MM from the flock. Many antimicrobial agents such as oxytetracycline, amino glycosides, lincosamides, fluoroquinolones, tylosin and tiamulin have been shown to possess different degrees of in vitro activity against various veterinary mycoplasmas .An impressive effect of tylosin on Mycoplasma infected chickens has been recently reported . However, increasing resistance of mycoplasma against tetracyclines, macrolides and quinolones has been reported in animal and human species. Mycoplasmas have higher mutation rates than conventional bacteria which mean that they can rapidly develop resistance to other drugs including the oxytetracyclines and tylosin as has been reported in Europe . The massive use of antimycoplasma drugs resulted in development of antimycoplasma drug resistant MS and MG strains .However, the carrier status of infected flocks is not eliminated by treatment. It only suppresses the excretion of the micro organism in respiratory exudates and eggs

Antibiotic treatment will not completely cure the disease but will reduce the incidence to a tolerably low level. Tylan Soluble is licensed for the treatment of mycoplasma and is probably the best treatment. Baytril Oral should not be used in laying hens as it will take them out of the food chain. Tylan Soluble is effective in young stock but seems to be less effective in older stock unless given at the acute (early) stage of the disease. If still showing signs after treatment the bird must be culled as the organism will be too deeply entrenched within the airsacs and hollow bones to be removed, the bird remaining a carrier which will infect others. (Denagard is sometimes prescribed for chickens: this drug combined with the coccidiostat in a grower ration becomes fatal, so only use it in adults on a layer ration).

Reference-on request