Effects of certain stress factors on the re-excretion of infectious laryngotracheitis virus from latently infected carrier birds

Experiments were set up to assess the effects of ‘natural’ and ‘artificial’ stresses on the re-excretion of infectious laryngotracheitis (ilt) virus in latently infected chickens recovered from the acute phase of the disease. The stresses were rehousing with the addition of ilt-free contact birds, corticosteroid treatment and the onset of lay. The contact birds were also monitored for transmission of the virus from the carrier birds. Rehousing with unfamiliar birds induced ilt virus shedding in one of five birds and there was evidence of transmission from this bird to its mate. The onset of lay had a significant effect on the overall shedding rates of the carrier birds. Nine of 10 birds shed virus after onset of lay compared with only two in the three-and-a-half weeks before, and there was a highly significant increase (P<0·001) in the overall number of virus isolations during this period. Corticosteroid treatment did not affect virus shedding. These results may explain some of the apparently spontaneous outbreaks of ilt which occur in the field.