Marek’s Disease (MD) is a highly contagious disease caused by an Alphaherpesvirus that mainly affects chickens, but it can also be found in turkeys.
Virus may survive for months in poultry house litter or dust. Dust or dander from infected chickens is particularly effective in transmission. Once the virus is introduced into a chicken flock, regardless of vaccination status, infection spreads quickly from bird to bird. Young chicks are particularly susceptible to horizontal transmission.
Mortality usually occurs between 10 and 20 weeks of age and can reach up to 50% in unvaccinated flocks.
Paralysis of neck, wings and neck
Skin around feather follicles raised and roughened
Diagnosis based only on clinical findings might be difficult, as tumours in liver, spleen, kidneys or other tissues might also be indicative of lymphoid leucosis. One of the main characteristics of MD is swelling of the sciatic nerves. However, a proper diagnosis requires histological examination. Virus isolation or PCR from fresh blood samples and affected organs can confirm the infection.
Currently there is no treatment for affected flocks.
In order to increase the protection of the birds against Marek’s, it is a good idea to combine different vaccine types. The most commonly used vaccines in commercial birds contain a combination of Rispens (CVI) and HVT strains. Currently in some longer lived broilers and backyard laying hens a vaccine composed of just a HVT strain is used.
Vaccination is usually performed at the hatchery. There are two different routes of the vaccine application: In–ovo injection or subcutaneous injection at day of age.