Common clinical signs of coccidiosis can include:

Clinical signs of Marek's disease vary depending on which tissues and organs are affected. Some birds may show only mild signs, while others develop severe paralysis or rapidly progressive disease.

• Paralysis or weakness of one or both legs, often with one leg stretched forwards and the other backwards
• Wing droop or paralysis
• Difficulty standing, walking, or perching
• Respiratory signs can occur when paralysis affects the nerves controlling the glottis, leading to rattling breathing sounds, coughing, sneezing, and honking as the bird attempts to clear its airway.
• Digestive signs can include slow crop emptying, reduced gut motility, weight loss, and undigested food in the droppings as tumours infiltrate the intestines and interfere with normal digestion.
• Depression and lethargy
• Pale comb and wattles
• Reduced growth rates in young birds
• Vision changes, irregular pupils, grey eyes, or blindness (ocular Marek's disease)
• Skin lesions or enlarged feather follicles
• Sudden death with few or no warning signs

In some birds, Marek's disease causes tumours within internal organs such as the liver, spleen, kidneys, heart, lungs, ovaries, or intestines. These birds may show vague signs of illness including weight loss, weakness, reduced appetite, and poor performance before deteriorating rapidly.

Young birds often experience the most severe clinical signs, particularly paralysis and rapid disease progression. However, Marek's disease can affect birds of any age, and adult birds are not immune to developing clinical disease.

While vaccination remains an important tool for reducing the impact of Marek's disease, vaccinated birds can still become infected and may still develop clinical signs. The duration of protection in backyard poultry is not fully understood, and cases are occasionally seen in vaccinated birds several years after vaccination.

Chickens

*infection has occasionally been reported in other bird species, clinical disease is overwhelmingly seen in chickens.

Marek's disease is caused by Marek's disease virus (MDV), a highly contagious herpesvirus that infects chickens. Once infected, birds carry the virus for life and can continue to shed it into the environment.

The virus is primarily spread through infected feather dander and dust. As birds preen and shed feathers, microscopic particles containing the virus become airborne and can be inhaled by other birds. Infection can occur even without direct contact between birds.

The virus is extremely resilient and can survive in poultry houses, coops, sheds, and soil for many months, making eradication difficult once it has become established in an environment.

Stress, overcrowding, poor biosecurity, and the introduction of infected birds can increase the risk of disease within a flock. While vaccination can significantly reduce the severity of disease, it does not completely prevent infection or viral shedding.

1. Feather Dander & Dust

Marek's disease virus is shed from the feather follicles of infected birds and spreads through contaminated feather dander and dust. Chicks can become infected from as early as one day of age by inhaling virus particles present in their environment.

2. Carrier Birds

Infected birds typically remain carriers for life, even if they never develop clinical signs. These birds continue to shed virus into the environment and can infect susceptible flock mates.

3. Environment

Marek's disease virus is highly resilient and can survive for months to years in poultry houses, litter, dust, equipment, and other contaminated surfaces, creating a long-term source of infection.

4. Movement Between Flocks

The virus can be spread between properties through infected birds, contaminated equipment, transport crates, clothing, footwear, and other items that have been exposed to infected feather dust and dander.

Diagnosing Marek's disease can be challenging as many of the clinical signs overlap with other conditions affecting the nervous system, muscles, eyes, and internal organs.

1. Clinical Signs

Marek's disease may be suspected based on clinical signs such as paralysis of one or both legs, wing weakness, weight loss, vision changes, poor growth, or sudden death. However, these signs alone are not sufficient for a definitive diagnosis.

2. Physical Examination

A veterinarian may identify findings consistent with Marek's disease during a physical examination, including nerve enlargement, paralysis, muscle wasting, or changes to the iris and pupil of the eye.

3. Post-Mortem Examination

Post-mortem examination can reveal tumours affecting organs such as the liver, spleen, kidneys, heart, lungs, reproductive tract, skin, and nerves. While these findings can strongly suggest Marek's disease, further testing is often required to confirm the diagnosis.

4. Laboratory Testing

Polymerase Chain Reaction (PCR) testing can detect Marek's disease virus in tissues, feather follicles, or environmental samples. Histopathology performed on affected tissues can identify the characteristic tumour and nerve changes associated with the disease and is often considered the gold standard for confirmation.

There is currently no cure for Marek's disease. However, treatment and supportive care can help improve comfort, quality of life, and in some cases allow affected birds to regain function. Outcomes vary considerably depending on the severity of disease and the organs affected.

While birds with severe disease often have a poor prognosis, recovery is not always black and white. Through our telemedicine service and rehabilitation experience, we have seen some birds with neurological signs improve over time, ranging from partial recovery of movement through to regaining sufficient function to return to a relatively normal life within their flock. Unfortunately, there is limited published information regarding recovery rates, making it difficult to predict outcomes for individual birds. As a result, treatment decisions should be based on the severity of clinical signs, quality of life, and the bird's response to supportive care.

1. Supportive Care

• Supportive care is the cornerstone of treatment. Ensuring birds remain warm, hydrated, well-nourished, and protected from bullying can significantly improve their chances of recovery. Birds struggling to eat or drink may require assist feeding, nutritional supplementation, and ongoing nursing care.
• Birds affected by weakness or paralysis may benefit from physiotherapy, gentle range-of-motion exercises, and environmental modifications to help maintain muscle strength and mobility. Soft bedding, easy access to food and water, and supportive housing can improve comfort and reduce complications.
• Birds requiring extended periods of supportive care should also have their mental wellbeing considered. Providing opportunities for social interaction, environmental enrichment, and normal species-specific behaviours can help reduce stress and improve quality of life during recovery.

2. Pain Relief & Management of Secondary Disease

• Birds showing signs of discomfort may benefit from veterinary assessment and appropriate pain relief. In some cases, anti-inflammatory medications may also be used to help reduce inflammation associated with nerve involvement and improve comfort.
• Marek's disease can suppress the immune system, making affected birds more susceptible to secondary bacterial, viral, fungal, and parasitic infections. Identifying and treating these conditions may improve overall health and quality of life.

3. Quality of Life Assessment

• Birds that remain bright, comfortable, and able to access food and water can often be successfully managed with supportive care. However, birds experiencing severe paralysis, an inability to eat or drink, significant weight loss, respiratory distress, or a poor quality of life may require humane euthanasia to prevent unnecessary suffering.

Important Note:

There is limited scientific information available regarding recovery rates in backyard poultry. Some birds with mild neurological signs can stabilise or improve with supportive care, while others may continue to deteriorate. Each case should be assessed individually.

Managing Marek's disease relies on vaccination, biosecurity, and good flock management. Prevention is far more effective than treatment, as there is currently no cure.

1. Vaccinate Chicks

• Vaccination is the most effective preventative measure.
• Chicks should be vaccinated before exposure to infected environments.
• Vaccination reduces clinical disease but does not prevent infection or shedding.

2. Source Birds Carefully

• Purchase birds from reputable suppliers that vaccinate against Marek's disease.
• Quarantine new birds for at least 30 days before introducing them to the flock.

3. Maintain Good Biosecurity

• Limit visitors and use dedicated footwear and equipment.
• Clean and disinfect housing, feeders, and drinkers regularly.
• Reduce the movement of birds and equipment between flocks.

4. Reduce Dust & Feather Dander

• Marek's virus spreads through infected feather dander.
• Maintain good ventilation and routinely remove dust, feathers, and debris from poultry housing.

5. Avoid Overcrowding

• Overcrowding increases stress and exposure to infectious disease.
• Provide adequate space, feed, and water access for all birds.

6. Support Bird Health

• Feed a balanced diet and provide constant access to clean water.
• Minimise stress and maintain good parasite control and general flock health.

7. Monitor for Early Signs

• Watch for paralysis, weakness, weight loss, vision changes, or increased mortality.
• Seek veterinary advice if Marek's disease is suspected.

Vaccination combined with good biosecurity and husbandry remains the most effective approach to reducing the impact of Marek's disease in poultry flocks.

When to Seek Veterinary Advice

Seek veterinary advice if you notice:

• Birds developing leg or wing paralysis, weakness, or difficulty standing.
• Progressive weight loss despite a normal appetite.
• Signs of vision loss.
• Respitory signs.
• Birds becoming lethargic, depressed, or reluctant to move.
• Unexplained deaths, particularly in young birds between 8 and 30 weeks of age.
• Multiple birds within the flock showing similar neurological signs.
• Enlarged feather follicles or unusual skin lesions.
• Signs continue to worsen despite supportive care.
• You suspect Marek's disease but are unsure, as several conditions can cause similar signs, including nutritional deficiencies, injury, toxins, and other infectious diseases.

A definitive diagnosis often requires post-mortem examination and, in some cases, laboratory testing to distinguish Marek's disease from other causes of paralysis and wasting.