The Epizootiology Of Mareks Disease I. Incidence Of Antibody, Viraemia And Marek'S Disease In Six Flocks

Abstract

Six flocks consisting of the female grandparent line of a well known broiler strain were studied in an effort to determine the important aetiological factors in Mareks disease. Each flock was hatched in the same hatchery but at intervals of six weeks. Chicks of each flock were reared to between 8 and 9 weeks of age on a rearing site after which they were moved to a production site. Mortality was recorded to house and pen in all flocks. In addition six pens of about 300 chickens on each of the production sites were selected for special examination. Blood samples were collected at intervals from birds in these pens for determination of the incidence of precipitating antibody and viraemia, and a high proportion of birds dying in these pens were examined post mortem. All six flocks were infected with Mareks disease virus. Although the levels of mortality from Mareks disease varied greatly from flock to flock (0.6 to 23.4%) and as greatly between houses used by a single flock, and between pens within a house, there was little relationship between the pathogenicity of the viruses present in a flock or group of chickens and the subsequent mortality from Mareks disease. Maternal antibody was present in 90.0% of day old chicks, 66.7% of chicks at 7 days of age, 23.9% of chicks at 14 days of age and 2.1 % of chicks at 21 days of age. Active antibodies were present in all flocks but the time at which they were detected varied from flock to flock and from pen to pen within a flock. © 1972, American Industrial Hygiene Association. All rights reserved.