Marek's disease is one of the most common chicken diseases, so much so that the virus is assumed to be present in nearly all commercial flocks worldwide. The virus comes in various forms which affect the nervous system (Neural), eyes (Ocular), skin (Cutaneous), and the organs (Visceral). Skin tumors can also be found in the feather follicles. Symptoms vary depending on the form of the illness. Growing birds under the age of 6 months are most commonly affected by Marek's, however it can affect birds at any age.
Where: Worldwide (Extremely common - prevalent anywhere poultry is raised)
When: Any age but typically at 3 to 6 months.
Why: Herpes Virus (no cure)
Common Symptoms: (vary by the form of Marek's)
Treatment: None. Many recommend culling birds that show symptoms.
Vaccine: Yes (click here for more information)
Also Known As:
Affects: Muscles, neurological tissue ,organs, skin.
Clinical Diagnosis: Definite diagnosis us by necropsy through the presence of swollen organs and tumors in affected tissues. Additional diagnosis by laboratory testing of blood/plasma.
Diseases with similar symptoms: Lymphoid Leukosis has similar symptoms, however it generally affects birds that are 6-9 months old, whereas Marek's generally affects birds that are 3-6 months old. Botulism can also cause paralysis.
Duration of symptoms: 7 to 21 days, however it can be longer.
Incubation: As little as 14 days.
Morbidity: Moderate (10-49%) occurrence in birds that have not been vaccinated. Low (<10%) occurrence in vaccinated birds.
Mortality: Up to 100%.
Transmission to people: No.