[2] The disease is characterized by the presence of T cell lymphoma as well as infiltration of nerves and organs by lymphocytes.

[3] Viruses related to MDV appear to be benign and can be used as vaccine strains to prevent Marek's disease.

A step-wise process has been proposed for diagnosis of Marek's disease, which includes: The demonstration of peripheral nerve enlargement along with suggestive clinical signs in a bird that is around three to four months old (with or without visceral tumors) is highly suggestive of Marek's disease.

Histological examination of nerves reveals infiltration of pleomorphic neoplastic and inflammatory lymphocytes.

[8] The presence of nodules on the internal organs may also suggest Marek's disease, but further testing is required for confirmation.

Key clinical signs as well as gross and microscopic features that are most useful for differentiating Marek's disease from lymphoid leukosis and reticuloendotheliosis include: In addition to gross pathology and histology, other advanced procedures used for a definitive diagnosis of Marek's disease include immunohistochemistry to identify cell type and virus-specific antigens, standard and quantitative PCR for identification of the virus, virus isolation to confirm infections, and serology to confirm/exclude infections.

The World Organisation for Animal Health (OIE) reference laboratory for Marek's disease is Avian Viral Oncogenesis group (led by Professor Venugopal Nair OBE) at The Pirbright Institute, UK.

Strict biosecurity and proper cleaning is essential, using products like Activated Oxine or Virkon S and reducing dander buildup in the environment.

Proper diet, regular deworming and vitamin supplements can also help keep infected flocks healthier.

The evolution of Marek's disease due to vaccination has had a profound effect on the poultry industry.

Highly virulent strains have been selected to the point that any chicken that is unvaccinated will die if infected.