Dr Sanjay Singhal, Chief Operating Officer, Stallen South Asia Pvt. Ltd, Mumbai

Mycoplasma, contrary to many other organisms, lack a cell wall, making them smallest free-living organisms with respect to of both size and gene number. Pathogenic Mycoplasma species in chickens are Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS). MG is typically the more virulent species and results in substantial financial losses. On commercial layer farms across different age groups, MS is a prevalent pathogen and is more ubiquitous.

The ability of different strains of Mycoplasma synoviae (MS) to produce illness varies greatly, with numerous forms appearing moderate. In highly susceptible birds, more pathogenic MS strains can cause serious joint infections, respiratory illnesses, and reduced egg production.

MS often manifests as a mixed infection with other respiratory pathogens, which include the infectious bronchitis virus (IBV) and the Newcastle disease virus (NDV). MS may not necessarily be the primary the cause. These mixed infections can cause significant chronic respiratory illness, particularly under harsh environmental circumstances including high ammonia, low temperatures, and dust. Birds with MS may react more to other live vaccines. Layers of egg yolk peritonitis caused by E. coli have been linked to MS aetiology.

Transmission
Horizontal transmission occurs through direct contact. Birds carry the infection for the rest of their lives. In many respects, the spread appears to be like that of M. gallisepticum except that it is more rapid. Yet reports of slow spreading infections exist. Only a few percent of birds may show clinical symptoms, but most birds often acquire illness by respiratory transmission. Infection may also occur because of environmental contamination or fomites. In chickens and turkeys, vertical transmission is a crucial factor in the spread of MS. When commercial breeder flocks are infected during egg production, the rate of egg transmission seems to peak in the first 4-6 weeks following infection; beyond that, the transmission may stop, although the infected flock may shed at any moment.

Pathophysiology
The pathologic characteristics of synovitis induced by MS involve the joints’ synovial cells hypertrophy and become more proliferative. Activated synovial fibroblasts (SFs) are the primary constituents of hyperplastic synovial tissue in humans with arthritis and play a significant role in the pathophysiology of synovitis.

Matrix metalloproteinases, cathepsins, chemokines, and cytokines are produced by activated synovial fibroblasts, which worsen inflammation and degrade bone and cartilage. For arthritis, reducing the number of activated synovial fibroblasts is a potential treatment approach.

Clinical signs
In poultry, Mycoplasma synoviae usually manifests as upper respiratory tract infection; it may cause mild respiratory disturbances such as rales but is usually subclinical. When the infection spreads to the joints, certain strains of MS may cause a transition from the acute to the chronic phase. Exudative tenosynovitis, an inflammation of the tendons and synovial membranes brought on by invasion of the joint tissue, ultimately results in lameness. The keel bone bursa and the hock (tibial metatarsal) joints are the main regions affected; however other joints may also be damaged. Although this type can be observed in flocks as young as 4 weeks old, it usually manifests itself soon after mature pullets are transferred to the laying farm.

Generally, there is no impact on egg production if the flock is exposed to MS during the laying phase. Egg production may decrease, and desirable egg quality may decrease in flocks that face challenges throughout the laying season. A flock of MS-positive birds that are treated with periodic antibiotic feed therapy might display an irregular egg production curve. Due of restricted movement to feed, water, and nests, lameness from tenosynovitis might further affect egg production.

Oviduct tropism of MS strains have been found recently in commercial layers. It is noticed that flocks infected with certain strains of MS have a higher proportion of cracked and broken eggs. On the apex of the egg, or pointed end, there is a distinctive eggshell defect that may be seen. The rough surface of the eggshell, located 2 centimetres from the apex, is characterized by thinning and translucency, resembling glass eggs. These eggshells lack part of the palisade layer and the mammillary knob layer, according to scanning electron microscopy.

Diagnosis
Accurate diagnosis of mycoplasmosis is crucial for effective management. It is typically achieved through a combination of clinical signs, post-mortem examinations, and laboratory tests. These tests may include serology (blood tests), PCR (polymerase chain reaction), and bacterial isolation from affected tissues.

Treatment
Antibiotics can be administered to control the spread of the disease and manage clinical symptoms. Tetracyclines, tylosin, and lincomycin are commonly used antibiotics. However, it is important to note that these treatments are not curative and are used to suppress the disease.

Prevention and Control
Biosecurity Measures: Implement strict biosecurity measures to prevent the introduction and spread of mycoplasmosis. This includes limiting visitor access, maintaining separate footwear and clothing for workers, and disinfecting equipment and facilities regularly.
Cleanup Programs: Use of appropriate molecule for effective cleaning up of mycoplasmal infection prior to vaccination may provide better results.

Minimize Stress: Stress weakens the immune system, making birds more susceptible to infections. Provide a low-stress environment by ensuring proper nutrition, ventilation, and living conditions.

Surveillance: Regularly monitor your flock for any signs of illness. Early detection allows for prompt intervention and reduces the spread of the disease.

Vaccination: There are vaccines available for both MG and MS, Stallen has killed vaccines against both MG and MS named as MYC Vac and MS Vac respectively, which provides better protection against avian mycoplasmosis. Our MS Vac is the only killed vaccine against Mycoplasma synoviae available in Indian Market. Recommended dose of both vaccines by parenteral route 0.5ml/ bird.

For better results, proper cleanup program with effective anti- mycoplasmal drug is recommended. The above-mentioned vaccines can also be used in midlay vaccination if the priming is done with the live vaccines.

Recommended vaccination schedule

Introduction
Avian mycoplasmosis was primarily described in turkeys in 1905 and in chickens in 1930. There are 23 named species of mycoplasma recovered from avian sources but only two of them are established pathogens for domestic poultry as Mycoplasma gallisepticum (MG), Mycoplasma synoviae (MS) causes ‘Chronic Respiratory Disease’. Mycoplasma pathogens cause upper respiratory and locomotory illness in chickens and other avian species. They are responsible not only for clinical diseases but also for decreased weight gain, lowered feed conversion efficiency, reduced hatchability, and downgrading at slaughter (Bradbury, 2001).

Mycoplasma gallisepticum (MG) infection in the commercial poultry industry is common in many areas. Despite the great efforts by poultry breeding companies made towards eradication of pathogenic mycoplasmas from poultry flocks, Still Mycoplasma gallisepticum infection is of continuing economic concern in commercial broiler breeder chicken flocks. Failure in eliminating the disease in grandparent (GP) stock, it persists in broiler breeders and broilers through vertical transmission. The continued presence of MG in commercial broiler breeder flocks suggests that efforts at eradication were not highly successful. This organism is smaller than common bacteria and larger than viruses, but lacks a cell wall. This characteristic makes MG extremely fragile (no cell wall) and difficult to culture (specialised growth requirement) and host adapted (avian only).
Respiratory tract infections are of great importance in poultry industry, causing heavy economic losses. Mycoplasma gallisepticum and Mycoplasma synoviae are the most pathogenic organisms of the respiratory tract.

Other respiratory tract infections include both viral pathogens (Newcastle disease virus, Infectious bronchitis virus, avian influenza virus) and bacterial pathogens (Salmonella pullorum, Escherichia coli, Avibacterium paragallinarum, etc) cause disease independently and in association with each other and causes Complex Chronic Respiratory Disease (CCRD).

Mycoplasma control for any companies requires integrated approach involving diligent biosecurity, animal husbandry & disease survivallance. The consequences of wide spread infection in breeder operation can be devastating result of both as direct and indirect losses occurring throughout the production cycle (Ley,2003).

Transmission
MG and MS can spread through horizontally and vertically route of susceptible birds with infected chickens; spread may also occur by contaminated airborne dust, droplets, or feathers (Ley and Yoder, 1997). It can be transmitted through the chicken hatching egg to the offspring. MG has been isolated from the oviduct of infected chickens and semen of infected roosters (Yoder and Hofstad, 1964).

Clinical Sign
Both diseases are economically important, egg transmitted, and hatchery disseminated diseases. They lead to tremendous economic losses in poultry production as a result of decreased hatchability and egg production, reduced quality of day-old chicks, reduced growth rate. Chicken showed swelling of the facial skin, and the eyelids, increased lacrimation, congestion of conjunctival vessels, and respiratory rales.

Mycoplasma synoviae (Ms) infection is usually known as infectious synovitis, an acute-to-chronic infectious disease for chickens involving primarily the synovial membranes of joints and tendons sheaths. However, during recent years, MS has less frequently been associated with synovitis but more frequently associated with airsacculitis in chicken.

Pathogenesis
It is presumed that MG enters the respiratory tract by inhalation of aerosols or via the conjunctiva and attaches to mucosal cells by its well-organized terminal organelles, which remains and spread in respiratory system.

As MG & MS are exhibiting with no cell wall, it is readily killed by most of the disinfectants, heat, and sunlight, and does not survive for prolonged periods outside the host. MG can remain viable
1. Chicken faeces for 1-3 days at 20°C,
2. Muslin cloth 3 days at 20°C or 1 day at 37°C,
3. In egg yolk 18 week at 37°C or 6 week at 20°C.

It only remains viable in the environment, outside the chicken, for typically up to 3 days. For this reason, MG is fairly easy to eliminate on single age, all-in all-out poultry farms Since MG can be transmitted vertically. Establishing the MG-clean status of breeder flocks and maintaining that status can be accomplished by participation in control programmes. An MG eradication programme may be initiated by treatment of breeders and their hatching eggs to reduce egg transmission. Attempts to eliminate egg transmission of MG by medication of breeder flocks or their progeny with antimycoplasmal prevention drug have generally been able to produce considerable reduction in rate of MG infection but generally were not adequate to obtain entirely infection-free flocks. Previously successful methods were the treatment of hatching eggs with heat and/or antimycoplasmal. For heat treatment eggs were gradually heated in a forced-air incubator to reach an internal temperature of 46.10C over 12-14 hour and then allowed to return to room temperature (Yoder, 1970). Hatchability was sometimes reduced 8-12%, but MG and MS appeared to be inactivated. Egg dipping with a temperature or pressure differential has been used by several researchers as a means of getting antibiotics into hatching eggs to eliminate egg transmitted MG (Alls et al., 1963;Hall et al., 1963; Stuart and Bruins, 1963).

Losses Can Occurs as Result of
1. Decreased egg production
2. Decreases egg hatchability
3. Decreased day old chick quality and chick viability
4. Increase chick mortality
5. Higher FCR and low weight gain
6. Costly control measures involving biosecurity, vaccination & medication.

Control of pathogenic avian mycoplasma can consist of one of three general approaches, according to Kleven (2008): The mycoplasma infection are transmitted both horizontally and vertically and it’s remained in the flock constantly as sub clinical form. To control MG infection in broiler breeder, laying hens and commercial broilers chicken the major specific focus is given on vaccination and medication.

1. Maintenance of Flocks, which are Free of Infection.
To keep a flock free of infection is difficult, especially in areas where large populations of chickens have grown up, as the industry has expanded. To maintain freedom from mycoplasma requires a mycoplasma free source, on a single age, ‘all in all out’ site, with good biosecurity and an effective monitoring system.

2. Control by Vaccines
The use of mycoplasma vaccines in breeding & laying hens has grown over recent years to reduce the impact of infections, but these can confuse the usual serological monitoring systems. They may control an infection in the chicken clinically but there is still a potential risk of vertical transmission to the egg and chick. Vaccination could not completely prevent the occurrence of EAA, although a significant reduction of EAA egg production (approximately 50%) was recorded. Moreover, a delay in the onset of egg production was observed in the vaccinated birds (Feberwee et.al. 2009).

1. Killed/Inactivated Vaccines
– These are M. gallisepticum killed organisms with oil emulsion adjuvants to protect the birds from infection with virulent M. gallisepticum.
– Several adjuvant enhanced bacterin vaccines but they are expensive and administration is difficult because they need to be injected twice with a 4-6 week interval (Ley, 2003).
– Killed vaccines have been shown to reduce, but not eliminate the M. gallisepticum infection and are not effective in long term control of infection in multiple age farms.
Killed vaccination did not reduce horizontal spread of M. gallisepticum (Levisohn et. al.,2000).
– These are more stable and safer than live vaccine.

2. Live/Attenuated Vaccine
There is three type of live vaccines is available for M. gallisepticum viz.
A. Connecticut F-Strain
B. MG 6/85 Strain
C. TS-11 Strain (temperature Sensitive Mutants)

A. Connecticut F-Strain
– Live F-strain M. gallisepticum vaccine is a relatively mild strain that originate from the Connecticut F strain of United States. Despite the advantages of the f-strain vaccine it has many of the disadvantages of the inactivated vaccines.
– MG free chickens tend to lay better than F-strain immunised ones.
– F-strain is too virulent for young chicks.
– F-strain is capable of lateral spread in the flock.
– F-strain does not completely block trans ovarian transmission when birds are challenged with virulent MG.

B. MG 6/85 STRAIN
– The 6/85 strain of MG is in lyophilised form and originate from United States.
– It has low virulence in chicken.
– Vaccinates were protected against airsacculitis and colonisation of the trachea was detectable from 4 to 8 weeks after vaccination (Ley, et. al., 1997).

C. TS-11 STRAIN
– ts-11 is a live chemically induced mutant strain of MG is in frozen form and developed from Australian MG field isolate (Whithear et. al.,1990a).

3. Control by Special Antibiotics
Medication of a flock but can prevent subsequent losses in breeders & laying hens. MS Infections could be treated with antimicrobial use in breeders, layers flock and eggs to prevent vertical transmission.
Control of MG and MS infection in broiler chicken by medication is the most practical way to minimize the transmission of disease and economic losses.
– The most important macrolide agent used for treatment and control of mycoplasma infection is Tilmicosin Phosphate.
– Tilmicosin is a broad-spectrum bacteriostatic synthesized from tylosin molecule which is having 75 percent more intra alveolar concentration in the lungs tissue to work efficiently against mycoplasma as organism remain intracellular in the cell and tissue.

In Broiler Breeder & Commercial Layers
– It is very important to treat chicks from day first of life to combat against mycoplasma, Tilmicosin Phospate-25% @ dose rate of 15-20mg/kg body weight through drinking water for 3 successive days every 5 weeks up to for 16th to 20th weeks.

– After 20th or 24th week incorporate Tiamulin through feed as per recommendation of veterinarian.

– It is emphasized to follow best antimycoplasmal drug prevention programme through feed.

In Commercial Broilers
– It is suggested to use Tylosin Tartarate 100% through drinking water for first 3 days @ dose rate of 65 mg/kg of BW.

– In high risk or known source of infected breeders it is suggested to use Tilmicosin Phosphate-25% through drinking water for first 3 days @ dose rate of 15mg/kg of BW.

The medication can be repeated on a monthly, three weekly or two weekly basis depending on the mycoplasma status of the flock or the ‘risk’ of breakdown from the proximity of infected neighbours.