Clinical signs are mainly seen in young birds of less than two weeks of age. Most outbreaks occur in broilers, followed by replacement pullets. Outbreaks in older birds (replacement pullets) have been reported when other immunosuppressive agents like Marek's Disease virus and/or Infectious Bursal Disease virus are involved.
Young chickens are depressed and huddle under the heat source. The birds appear less developed for their age and anaemic. CAV infection impairs the immune system as it multiplies in most lymphopoietic organs resulting in the depletion of lymphocytes.
CAV enhances the effect of other immunosuppressive agents such as Marek’s Disease virus and Infectious Bursal Disease virus. The reduction in the development of antibodies after vaccination against Newcastle Disease in CAV infected birds is common.