One of the most economically damaging diseases of game birds in the UK is mycoplasmosis - better known as ‘bulgy eye’ disease. With the introduction of the first licensed treatment, SARAH ROGERS takes a closer look at new management options for game bird breeders and rearers.

Mycoplasmosis has been recognised in pheasants and partridges since the 1950s. The disease is most often seen in adult birds, though all ages may be affected and the high death rate among 7-to-14-day-old chicks can be devastating to game farmers.  

Typically, Mycoplasma gallisepticum bacterial infections are associated with slow onset chronic respiratory signs which include severe sinusitis, sneezing, conjunctivitis, watery eye, nasal discharge, poor productivity, slow growth and a marked reluctance to move. They often occur alongside other respiratory diseases and can increase their severity.

Routes of infection

The disease is passed between birds by close contact through air droplets, infected litter and equipment, and from hen to chick through the egg.  Unfortunately, recovered birds remain carriers, meaning that once a flock is infected it remains infected and subsequent stress such as breeding may cause a new outbreak.

Spread is slow between houses and pens suggesting that aerosols are not normally a major route of transmission. However, any inanimate object is capable of carrying infectious organisms. Consequently equipment, vehicles or articles taken to pens appear to play a significant factor in spreading the disease between farms.

Chicks and poults in rearing pen: feed should be supplied regularly and on dry ground

The bacteria can survive for a number of days outside the bird, and prolonged survival has been reported in eggs. Survival seems to be improved on hair and feathers. Importantly, co-infection with respiratory viruses such as infectious bursal disease and Newcastle disease, or virulent bacterial infections including E. coli, Pasteurella spp. Haemophilus, and inadequate environmental conditions are all factors for clinical disease.

The most obvious signs of infection are:

• Coughing
• Nasal and eye discharge
• Sinus swelling
• Poor productivity
• Slow growth
• Leg problems
• Depression
• Lack of appetite
• Reduced hatchability and chick viability
• Occasional brain disease and abnormal feathers

Diagnosis

Your vet will take swabs for testing in a number of ways. Suspect flocks should be re-sampled after two to three weeks and it should be noted that some inactivated vaccines for other diseases can induce 'false positives' in testing for three to eight weeks. The use of modern DNA-based techniques can quickly confirm diagnosis if it is urgent to determine the flock status.

Prevention by biosecurity and management 

Most countries’ official poultry health programmes are focused on eradicating the disease, so Mycoplasma gallisepticum infection status is important for trade in birds, hatching eggs and chicks. These programmes are based on making sure chicks are sold free from infection, all-in/all-out production, biosecurity, and routine monitoring. In the case of known infected flocks preventative medication is usually beneficial.

Vaccines, many of which are not licensed for use in pheasants, using live attenuated or naturally mild strains of the bacterium are used in some countries and may be helpful in gradually displacing field strains on multi-age sites. However, productivity in challenged and vaccinated birds is not as good as in Mycoplasma-free stock. Good management techniques, avoiding stress and overcrowding are most important factors for keeping birds healthy and disease-free.

Healthy hen   

Hen with ‘bulgy eye’ symptoms

Biosecurity measures

• Place disinfectant footbaths at all main entrances and change them regularly
• Clean, disinfect and dry out housing between batches of birds
• Quarantine all sick birds and any day-old chicks
• Ensure housing is in good condition, clean and kept at an appropriate steady temperature, especially during the first three weeks.
• Ideally batch sizes should be small enough to ensure that groups can be isolated should a problem arise
• Ensure pens are large enough to ensure there is no overcrowding that can lead to stress. Higher stocking densities are more likely to result in the spread of infection
• Make sure clean water is available and the area surrounding drinkers is clean and dry
• Ensure feed is supplied regularly and on dry ground so that it does not become contaminated.
• Control exposure to wild birds and pests
• Nominate a veterinary practice to handle any disease problem
• Work with your vet to develop a health management programme

Prevention by vaccination

A study carried out for the Game and Wildlife Conservation Trust suggests that a Mycoplasma vaccine used in chickens is not effective in day-old game birds.

Other research suggests that Mycoplasma infection can be enhanced by the presence of certain viruses, notably coronaviruses such as infectious bronchitis, avian pneumovirus and even infectious larygotracheitis.  The author concluded that whilst vaccinating with the Mg vaccine alone provided little improvement, definite improvements in bird health using antibiotic programmes to control the disease as an assessor were seen when breeder birds were vaccinated for all four diseases.

Game farmers or keepers who use caught-up pheasants should be particularly vigilant as these birds are more likely to suffer from or to be carrying the disease. 

Treatment

Various antibiotics have been used to treat Mycoplasma infections including tylan, tiamulin, tetracyclines, lincospectin but none were licensed specifically for use in pheasants or game birds. Recently a new oral antibiotic tylvalosin (Aivlosin) has received a full marketing authorisation through the European Regulatory Authorities.  Antibiotics should be seen as a control measure and will not under normal circumstances eradicate the disease. Mycoplasma infection is in the environment and birds can and will become re-infected or wild birds will spread the disease back in to flocks. However, recent studies have shown that the Aivlosin offers unsurpassed control of Mycoplasma gallisepticum, statistically bettering the historical treatment of choice in closely monitored trials with Liverpool University.

Aivlosin is the first and only fully European Medicines Agency (EMA) licensed product for the treatment of bulgy eye, caused by Mycoplasma gallisepticum in pheasants and should be used at the first sign of infection.  Research shows that it quickly reduces all the classical signs of bulgy eye and treated birds feed better and gain weight faster compared with un-medicated birds and those subject to standard treatment.

Aivlosin granules dissolve in cold water and don’t need sugary additives to make them palatable to the birds. The Aivlosin treatment period is a convenient three-day programme and the meat withdrawal period is only two days.

Conclusion

Mycoplasmosis can be spread both through the egg and through direct contact with infected birds (commercial or wild). It can have a serious effect on egg production and it is essential that action is taken as early as possible to control it. If the infection levels in the breeding birds are reduced at the start of the season it will help minimise the levels of infection transmitted via the eggs and through direct contact.
The breeding and rearing seasons are also one of the most stressful times of the year for the birds and as a consequence it is at these times that the birds are most vulnerable. Reduction of stress through sound management practices can help reduce the levels of Mycoplasma infection.

Sarah Rogers is a consultant for ECO Animal Health www.ecoanimalhealth.com

Key points

1. Avoid stress
2. Have a good biosecurity programme in place
3. Select birds from a known source not just caught- up birds
4. Speak to your vet about a farm health scheme.