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Editorial Information

Victoria Roberts BVSc MRCVS

Diseases of Farmyard Poultry
Part 1 - Mycoplasmosis


Disease background

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.

Fig 1:  Normal turkey head (note quite sunken appearance): Bourbon Red female

Fig 2:  Normal chicken head:  Australorp female

Causes and clinical signs

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.


Fig 3:  Nebraskan Spotted Turkey with Mycoplasma. Note swollen sinus (arrowed)

Transmission

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.

Economic impact

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

Diagnosis

Diagnosis is on clinical signs, see above.

 

Fig 4

Apical shell deformities

Fig 5
Swollen hock (Fig 4) and Apical eggshell deformities (Fig 5) both due to Mycoplasma synoviae

Fig 6 White Orpington with severely swollen sinuses and nasal discharge

Treatment

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).

Prevention

  • Keep stressors to a minimum or if a known stressor such as a show is imminent, give vitamin supplementation. There are several useful products on the market which contain probiotics and/or vitamins, administered in the water.
  • Use a suitable disinfectant for both huts and equipment such as Virkon or F10.
  • Keep dust and ammonia levels low by having (vermin-proof) ventilation on two sides of the hut at the top and never closing it off. Ammonia paralyses the small hairs (cilia) which act like an escalator to move normal mucus up the trachea before being swallowed.
  • Feed high quality commercial food for the stage of growth and the species of bird.
  • Monitor weather changes and take steps to minimise any effects.
  • When attending to the stock, begin with the youngest at the start of the day (i.e. with clean clothes).
  • Either quarantine new stock for 2-3 weeks or treat with Tylan Soluble as soon as the birds are obtained if there has been mycoplasma in your flock.
  • Do not buy from auctions.
  • If adult stock are kept symptom-free the risk of passing mycoplasma on through the egg is reduced.
  • If young stock happen to be exposed to a mild bout of mycoplasma they will acquire a certain amount of immunity as long as there are no other pathogens (such as E.coli) present.
  • Cider vinegar (10ml:500ml, plastic drinker only to avoid zinc toxicity) helps strengthen the immune system and keeps drinkers cleaner. Use one week a month, more often if diseases are present.
  • Biosecurity.

Vaccination

There is a mycoplasma vaccine marketed by MSD but it is recommended not to use it in breeding chickens. This appears to be because the manufacturers do not know how long the vaccine is effective.

With vigilance, mycoplasma can be kept at a low level in backyard flocks thus increasing the welfare of the birds.

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