Marek disease

Marek's Disease is a highly contagious viral disease affecting chickens. It is named after József Marek, a Hungarian veterinarian who first described the disease in 1907. Marek's Disease is caused by an alphaherpesvirus known as Marek's Disease Virus (MDV) or Gallid herpesvirus 2 (GaHV-2). The disease is characterized by the presence of T-cell lymphomas in various organs, leading to a wide range of clinical symptoms including paralysis, weight loss, and acute death. Marek's Disease poses a significant threat to poultry industries worldwide due to its impact on flock health and productivity.

Etiology

Marek's Disease is caused by the Marek's Disease Virus (MDV), which is a member of the Herpesviridae family. The virus has a double-stranded DNA genome and is highly cell-associated, spreading through dander, feather follicles, and respiratory secretions. There are several strains of MDV, varying in virulence from mild to highly virulent.

Transmission

The primary route of transmission is through inhalation of infected dust and dander. Once in the environment, the virus can remain infectious for months, making control and eradication difficult. Vertical transmission (from parent to offspring through eggs) is not considered a significant route of spread.

Clinical Signs

Clinical signs of Marek's Disease can vary but often include:

• Paralysis of the legs, wings, and neck
• Weight loss and anorexia
• Irregularly shaped pupils or blindness
• Visible tumors in the skin, muscles, or internal organs
• Depression and immobility

Diagnosis

Diagnosis of Marek's Disease is based on clinical signs, histopathological examination of tumors, and PCR detection of the virus. Serological tests can also be used to detect antibodies against MDV, indicating exposure to the virus.

Prevention and Control

Vaccination is the primary method of controlling Marek's Disease. Vaccines are usually administered to chicks at one day of age, either in ovo (in the egg) or immediately after hatching. Good biosecurity practices, including maintaining a clean environment and minimizing stress, are also important in controlling the spread of the disease.

Treatment

There is no treatment for Marek's Disease once clinical signs appear. Management practices focus on prevention through vaccination and biosecurity.

Economic Impact

Marek's Disease has a significant economic impact on the poultry industry due to mortality, reduced productivity, and the cost of vaccination. It is considered one of the most important diseases of chickens globally.

Research

Research on Marek's Disease continues to focus on understanding the virus's pathogenesis, improving vaccine efficacy, and developing strategies to manage virus resistance to vaccines.