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Mycoplasma gallisepticum and M. synoviae are the two significant species affecting commercial chickens.
Occurrence and Economic Significance
Chronic respiratory disease caused by M. gallisepticum and synovitis and airsacculitis due to M. synoviae infection, occur world-wide. These conditions are responsible for extensive losses in broiler operations especially where flocks are exposed to concurrent viral respiratory diseases and environmental stress. The economic impact of mycoplasmosis in broilers includes severely depressed growth rate and feed conversion efficiency, elevated mortality, and condemnation at processing. In commercial layers and breeders, liveability and egg production are depressed.

Mycoplasmosis is transmitted by the vertical route from infected parent flocks to progeny.
Lateral transmission occurs by direct contact between clinically affected or recovered carriers and susceptible flocks.
Indirect infection occurs through contact with contaminated equipment, feed bags, and personnel.
Wild birds and rodents may transmit the disease to susceptible flocks.
Mycoplasmas do not survive outside the host for longer than 24 hours.

Clinical Signs
Mycoplasmosis is characterized by chronic respiratory signs including ocular discharge, tracheal rales (“gurgling and snicking”), markedly reduced growth rate and an increased susceptibility to intercurrent respiratory diseases. Chronic cases are emaciated and show purulent nasal discharge.
M. synoviae infection results in acute arthritis especially of the hock and stifle joints.

Affected birds show congestion of the upper respiratory tract, mild tracheitis, and in chronic cases airsacculitis and colibacillosis. Acute cases of M. synoviae infection show serous arthritis. In advanced cases, seropurulent exudate may be present in affected joints.

Two to three weeks following infection, chickens demonstrate antibodies which can be detected using the serum plate agglutination test or the automated ELISA technique. These highly sensitive tests are used to screen flocks. The hemagglutination inhibition test is applied to confirm the provisional serologic diagnosis.
Mycoplasma spp can be isolated and identified by inoculating tracheal swabs or serous joint exudate from acute cases onto special selective media. This procedure may require up to 30 days and may be inconclusive due to technical problems including contamination. The polymerase chain reaction assay can be applied as a commercially available, sensitive and specific test procedure. Kits are available for M. gallisepticum and/or M. synoviae respectively.

Clinical signs can be suppressed by administering tylosin or a fluoroquinolone compound in drinking water. Chicks derived from known infected parent flocks can be treated with a suitable antibiotic during the first 48 hours after placement and re-treated subsequently at 20 to 24 days of age for a 24 to 48 hour period. It is emphasized that treatment does not eliminate the carrier state in infected flocks but will suppress excretion of the organism in respiratory exudate and vertical transmission through eggs.

The world’s primary breeders of broilers and commercial layers have eliminated mycoplasmosis. Infection of grandparent and parent level breeders occurs in developing industries due to deficiencies in biosecurity on farms operated by multipliers. It is essential to purchase parent and commercial stock from known mycoplasma-free breeder flocks. Strict biosecurity will prevent lateral introduction of infection. Live M. gallisepticum vaccines are available for immature egg-production flocks which will be transferred to multi-age, infected layer farms. The live attenuated F-strain vaccine administered in drinking water has been largely replaced in the USA by the milder TS-11 and 6/84 products. Inactivated vaccines administered as oil emulsions are available commercially but are of limited value. A pox-vectored recombinant Mg vaccine (“Vectormune”) has recently been licenced for administration to immature egg-production pullets in the USA. It is noted that vaccination will suppress clinical signs of infection but will not eliminate the carrier state.

Fowl Cholera

Fowl cholera is a contagious, bacterial disease that affects domestic and wild birds worldwide. It usually occurs as a septicemia of sudden onset with high morbidity and mortality, but chronic and asymptomatic infections also occur.

Newcastle Disease

Newcastle disease is an infection of domestic poultry and other bird species with virulent Newcastle disease virus (NDV). It is a worldwide problem that presents primarily as an acute respiratory disease, but depression, nervous manifestations, or diarrhea may be the predominant clinical form. Severity depends on the virulence of the infecting virus and host susceptibility. Occurrence of the disease is reportable and may result in trade restrictions.

Fowl cholera is the reason for great economic loss of poultry in bangladessh

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