Marek's disease

A viral disease affecting chickens

Marek's disease is a highly contagious viral disease in chickens caused by an alphaherpesvirus known as Gallid alphaherpesvirus 2. It is characterized by the presence of lymphomas, immunosuppression, and neurological symptoms. The disease is named after the Hungarian veterinarian József Marek, who first described the condition in 1907.

Virology

Marek's disease is caused by a herpesvirus that primarily affects chickens, although it can also infect other poultry species. The virus is classified into three serotypes:

• Serotype 1: Oncogenic strains that cause the disease.
• Serotype 2: Non-oncogenic strains found in chickens.
• Serotype 3: Non-oncogenic strains found in turkeys.

The virus is transmitted through aerosols and fomites, with infected birds shedding the virus in feather dander.

Pathogenesis

The pathogenesis of Marek's disease involves several stages:

• Early infection: The virus infects the respiratory tract and spreads to lymphoid tissue.
• Latent infection: The virus establishes latency in T cells.
• Reactivation: The virus reactivates, leading to lymphoproliferative disease.

Clinical Signs

Ocular Marek's disease showing irregular pupil shape and color changes.

Clinical signs of Marek's disease vary depending on the form of the disease:

• Neurological form: Paralysis, ataxia, and torticollis.
• Visceral form: Tumors in organs such as the liver, spleen, and kidneys.
• Ocular form: Changes in the iris leading to "gray eye" or ocular Marek's disease.
• Cutaneous form: Nodular lesions on the skin.

Diagnosis

Diagnosis of Marek's disease is based on clinical signs, histopathology, and polymerase chain reaction (PCR) testing. The presence of lymphoid tumors and enlarged nerves are indicative of the disease.

Prevention and Control

The primary method of controlling Marek's disease is through vaccination. Vaccines are typically administered to day-old chicks and provide protection against the oncogenic strains of the virus. Good biosecurity practices are also essential to prevent the spread of the virus.

Related pages

• Avian diseases
• Herpesviridae
• Vaccination in poultry