Causes and effective ways to prevent Marek’s disease in chickens

Marek’s disease in chickens is a highly contagious viral disease, often manifested by symptoms such as leg or wing paralysis, visceral tumors, and immunosuppression in the flock. In this article, Vemedim will explain the disease mechanism, recognizable signs, and practical prevention-control strategies to help farmers manage their flocks more proactively. Let’s take a look!

Causes of Marek’s disease in chickens

Marek’s disease is one of the dangerous diseases in chickens, first detected in Vietnam in 1978 under names such as chicken leg atrophy, chicken cancer, or tumor syndrome. It is caused by Herpes virus type B, which can spread rapidly through the respiratory and digestive routes.

This virus can survive in the scales and feathers of infected chickens for more than a year, making chicks especially susceptible. The incubation period lasts at least 28 days, usually around 2 months, and the mortality rate can reach 60–70% in a flock. There is currently no specific treatment, so early detection and prevention are vital.

The herpes virus that causes Marek’s disease is highly infectious and affects all types of chickens. Scientists have isolated three viral types that cause the disease:

Serotype 1: Tumor-causing, highly virulent strains that can mutate. This is the main virus type causing severe disease.
Serotype 2: Naturally occurring strains that do not cause tumors, often used in research and as vaccines.
Serotype 3: Low-virulence, non-pathogenic strains, mainly in turkeys, used in preventive vaccines.

*Chickens infected with Marek’s disease caused by Herpes virus type B, easily spread through the respiratory and digestive routes*

The incidence rate ranges from 10–60%, and mortality can reach 100%. Chickens usually become infected after 6 weeks of age, most commonly between 8 and 24 weeks. In some rare cases, the disease has also been reported in waterfowl and other birds. Marek’s disease in chickens is characterized by excessive lymphocyte proliferation, forming tumors in peripheral nerves, internal organs, skin, and muscles, leading to movement disorders and paralysis.

Marek’s virus spreads very quickly within a flock because it exists in the feather follicles of chickens. Just 14 days after infection, chicks can already transmit the disease to one another. The virus can survive for months in the environment at 20–25°C and up to a year at 4°C. It spreads directly through the respiratory route or indirectly via feed, drinking water, farming equipment, and hatcheries containing the pathogen. However, the virus does not spread through the chicken embryo.

>> See also:

Symptoms of Marek’s disease in chickens

Marek’s disease progresses in two forms: acute and chronic (classic), with the following symptoms:

Acute form

It usually occurs in chickens 4–8 weeks old, sometimes earlier. Symptoms are atypical, mainly sudden death with a mortality rate of 20–30%. Before death, chickens may show lethargy, weakness, loss of appetite, difficulty walking, paralysis, drooping of one wing due to inflammation of the motor nerves, and loose droppings.

Chronic (classic) form

Appears in chickens 4–8 months old and includes two forms:

Nervous form: Chickens have difficulty walking, initially with mild paralysis and then complete paralysis. The tail droops or deviates to one side, and the wings droop on one or both sides.
Ocular form: Begins with mild eye inflammation; chickens become sensitive to light and have clear watery eyes. As the disease progresses, the conjunctiva becomes inflamed, the iris is inflamed, and white pus accumulates in the corners of the eyes. Chickens see poorly, have difficulty pecking food accurately, and may eventually become completely blind.

*The acute form of Marek’s disease in chickens occurs at 4–8 weeks of age, with a mortality rate of 20–30%*

Prevention and treatment of Marek’s disease in chickens

Currently, Marek’s disease has no specific treatment, so prevention is the main measure:

When no outbreak has occurred

Vaccinate 1-day-old chicks against Marek’s disease.
Strictly implement veterinary biosecurity measures, collect chicken feathers daily, and burn the feathers because the virus persists for a long time in feather follicles.
In industrial poultry farming, separate laying hens and chicks into different areas, and follow the “all-in, all-out” principle.
After flock removal, disinfect houses and equipment with disinfectants such as Vemedim BKC (GSGC) and leave the house empty for at least 1 month.
For flocks that have previously been infected, leave the house empty for at least 3 months and clean regularly.
Apply biosecure farming practices and avoid raising adult chickens together with chicks.

*To prevent Marek’s disease in chickens, chicks and adult chickens should be raised separately, along with other hygiene principles*

When an outbreak occurs

Monitor closely and detect the disease early.
Isolate the infected flock and do not transport sick chickens বাইরে.
Destroy the entire diseased flock by burning and burying, and treat residual waste such as manure and trash.
Clean and disinfect the house regularly 1–2 times per week with disinfectants such as Vemedim Disina.
Do not bring in new chicks during the period of flock treatment.
Leave the house empty for at least 3 months before restocking.

*If Marek’s disease is detected in home-raised chickens, the sick chickens should be destroyed and the house cleaned and disinfected with disinfectants*

Effective prevention and control of Marek’s disease in chickens requires the simultaneous application of multiple measures. When farmers fully follow these guidelines, combined with the knowledge and recommendations from Vemedim, the flock will be better protected, economic losses from sick chickens will be reduced, and farming efficiency will be maintained.