Mycoplasma in Chickens and Poultry: What Bird Owners Need to Know
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Mycoplasma is one of those pathogens that most poultry keepers will encounter, or at least hear about, eventually.
Mycoplasmas occur worldwide and are particularly important in chickens and turkeys, although infections can also occur in ducks, geese, guinea fowl, pheasants, quail and some companion bird species.
What Is Mycoplasma?
Mycoplasmas are unusual bacteria because they do not have a cell wall.
This distinction is important. Many commonly used antibiotics work by targeting bacterial cell walls, so these medications will not work against Mycoplasma.
Mycoplasmas are relatively fragile outside the host but can be much more difficult to manage once established within a flock.
Infected birds can become long-term carriers, sometimes without showing obvious signs of disease.
How Does Mycoplasma Spread?
Transmission occurs primarily through close contact and respiratory secretions.
Mycoplasma can also be transmitted vertically through the egg, allowing infection to pass from breeding birds to their offspring.
Once introduced into a flock, infected birds may remain carriers and can shed the organism, particularly during periods of stress.
This makes introducing new birds one of the major opportunities for Mycoplasma to enter an established flock.
What Are the Signs of Mycoplasma?
The clinical signs depend partly on the Mycoplasma species involved.
Respiratory Signs
Respiratory disease is commonly associated with Mycoplasma gallisepticum (MG).
Signs can include:
- Rales or raspy breathing
- Sneezing
- Nasal discharge
- Excess mucus
- Swelling around the eyes or sinuses
- Reduced activity and appetite
- Reduced egg production
More severely affected birds may become pale or develop bluish discolouration associated with respiratory compromise.
Lameness and Swollen Joints
Mycoplasma synoviae (MS) is particularly associated with synovitis and joint disease.
Affected birds may show:
- Lameness
- Reluctance to walk
- Spending more time sitting
- Swollen joints
- Fluid accumulation around joints or tendon sheaths
- Sternal bursitis, sometimes called a breast blister
However, MS infection does not always cause obvious joint disease and may also be associated with respiratory infection.
Eggshell Changes
Mycoplasma synoviae has also been associated with eggshell apex abnormalities, sometimes described as "glass top" eggs.
The shell around the pointed end of the egg may appear translucent, thin, roughened or unusually fragile.
This can be an important clue in laying flocks, although abnormal eggshells can have many other causes.
Diagnosing Mycoplasma
Clinical signs can make us suspicious of Mycoplasma, but they cannot reliably confirm the diagnosis.
Respiratory disease and lameness have numerous possible causes, so laboratory testing can be particularly useful.
Testing may include:
- PCR testing
- Serology
- Post-mortem examination
- Additional testing to rule out other infectious diseases
Serology can provide evidence that a bird or flock has been exposed to Mycoplasma, but it does not necessarily tell us whether the organism is responsible for the current clinical disease.
Can Mycoplasma Be Treated?
Antibiotics can be useful for managing clinical Mycoplasma disease, but there is an important distinction between treating the disease and eliminating the infection.
Appropriate antibiotics may reduce bacterial activity and improve clinical signs, but treatment does not necessarily eliminate Mycoplasma from the bird.
Recovered birds may therefore remain carriers.
Antibiotic selection should also be appropriate for Mycoplasma. Because these organisms lack a cell wall, antibiotics that rely on disrupting bacterial cell wall synthesis are ineffective.
Why Carrier Birds Matter
A chicken can look completely healthy and still carry Mycoplasma.
Problems may reappear during periods of stress, such as:
- Introducing new birds
- Moving or transporting birds
- Changes in housing
- Poor weather
- Other illness
- The onset of lay
- High stocking pressure
Carrier birds can also introduce Mycoplasma to previously unaffected birds.
This is why flock history and biosecurity become particularly important once Mycoplasma has been identified.
Managing Mycoplasma in a Backyard Flock
Management depends on the species involved, severity of disease and purpose of the flock.
Useful measures can include:
- Quarantining new birds before introduction
- Investigating respiratory disease rather than repeatedly treating blindly
- Testing where appropriate
- Reducing overcrowding and environmental stress
- Maintaining good ventilation
- Avoiding unnecessary movement between flocks
- Treating clinically affected birds under veterinary guidance
- Considering carrier status when breeding, selling or introducing birds
Mycoplasma does not automatically mean disaster for a backyard flock. Many infected birds can remain clinically well with good management.
The important thing is understanding that once Mycoplasma becomes established, managing the flock is often more realistic than assuming a course of antibiotics has eliminated the organism.
The Takeaway
Mycoplasma is common, contagious and capable of remaining within a flock long after the obvious clinical signs have disappeared.
Respiratory disease, swollen joints, lameness and characteristic eggshell abnormalities can all raise suspicion, but testing is valuable because several other diseases can produce similar signs.
If Mycoplasma is confirmed, treatment can help control clinical disease, while good biosecurity and flock management help reduce transmission and future flare-ups.
Written by Dr Sam Hurley, BSc, BVSc, MAHM