Marek’s Disease in Chickens: Causes, Symptoms & Prevention

Chickens worldwide are impacted by Marek’s disease, a highly contagious viral illness caused by Marek’s disease virus (MDV), a type of herpesvirus. This disease mostly affects young birds aged 6 to 20 weeks, although infection can occur as early as 3–4 weeks old or later in life. Backyard keepers and commercial poultry farmers alike face challenges due to its ability to cause tumours, nerve damage, and immune suppression.

The History and Cause of Marek's Disease

This disease was first identified in 1907 by the Hungarian vet Jozsef Marek, who suspected it was caused by an infectious agent, later confirmed as a virus decades later with modern techniques. MDV forms cancerous tumours called T cell lymphomas which invade organs such as the kidneys, liver, and spleen, as well as nerves controlling wings and legs, notably the brachial plexus and sciatic nerves.

Recognising Symptoms Early

The hallmark signs, often called 'fowl paralysis', include leg weakness, paralysis, and drooping wings caused by nerve infiltration. Sometimes symptoms are subtle, such as weight loss despite normal appetite, diarrhoea, dehydration, and pale wattles indicating anaemia. Outbreaks can be distressing due to rapid spread and multiple birds affected simultaneously. Severely virulent strains may cause sudden death with few clinical signs.

Diagnosis and Confirming Marek's Disease

Suspicion arises when young birds present neurological symptoms. Definitive diagnosis requires a post mortem examination to identify thickened nerves or tumours in organs and skin. Laboratory testing of tumour tissues confirms diagnosis, distinguishing Marek’s disease from similar conditions. Veterinary assistance is advisable for accurate diagnosis.

Transmission and Contagion Risks

Marek’s disease spreads easily through feather dander contaminated with the virus, which infected birds shed for life. Chicks usually become infected shortly after hatching from environmental dust. The virus can remain infectious for at least a year in poultry housing environments, underscoring the need for thorough cleaning and disinfection. Stress from mixing birds or approaching laying age may trigger disease symptoms in infected birds.

Effective Prevention and Control Measures

Vaccination represents the best defence and is routinely administered to day-old chicks in commercial settings. Vaccines do not prevent infection but almost always stop clinical disease. For home hatchers, cleaning incubators and brooders thoroughly is crucial. Rearing chicks separately from adults can help reduce early infection. Genetic resistance breeding is a promising future approach, with some breeds like Fayomi showing greater resilience.

Conclusion

Marek’s disease remains a distressing issue for chicken keepers. Understanding its symptoms, transmission, and control means flock keepers can better protect their birds. Although treatment options are limited, compassionate care and strict management practices can reduce losses and improve bird welfare.