Marek’s disease is caused by a herpesvirus. It is a very common highly contagious disease resulting in immune suppression and increased susceptibility to other diseases such as coccidiosis.  Marek’s disease has three different clinical manifestations:

1. Nervous (neurological) – paralysis of the legs, wings and eye lesions.
2. Visceral – tumours of the body organs and muscles.
3. Cutaneous – tumours of the skin and feather follicles.

The vaccine prevents the formation of tumours but it does not prevent the infection and shedding of the field virus by the chicken.  Prevention of clinical Marek’s disease requires good hygiene combined with an all-in/all-out production system along with vaccination.  It is essential to place the vaccinated day old chickens into a clean environment.  This allows them to develop immunity without a field challenge by Marek’s disease virus.

There are three types of vaccine available:

1. Rispens attenuated chicken strain
2. Non-pathogenic chicken strain
3. Herpesvirus of turkeys (HVT).

Due to the interfering effect of maternal antibody on the HVT it is advisable to alternate vaccine types in successive generations.

MD-Vac is a Type 3 vaccine and it is lyophilised (freeze dried) which allows for convenient storage (refrigeration) and handling.  MD-Vac is less effective than the cell associated vaccines in the presence of maternal antibodies and in the face of high field strain challenge of Marek’s disease virus.