Purpose of Vaccination: To prevent vertical transmission of the Chicken Anaemia Virus from breeder hens infected during egg production to their progeny. Progeny may develop a severe anemic and immunosuppressive disease as a result of infection.
Cux-1 isolate: is a virulent strain. Vielitz E. et al. (J. Vet. Med. 34, 533-557, 1987) report the evaluation of a live CAA vaccine derived from the Cux-1 strain. However, no attenuated CAA strain is used therein. This vaccine comprising virulent CAA is administered to 9-15 weeks old chickens and showed no pathogenicity in the inoculated birds. In view of the known age resistance to experimentally induced disease due to CAA, which is essentially complete by the age of 2 weeks, the level of attenuation of the live vaccine virus for the inoculated birds themselves is of less importance in this case.
26P4 strain: This isolate still display some rest-virulence for one-day-old chicks and, hence, are not particularly suited for vaccinating chicks younger than 1 week-of-age. In addition, this attenuated CAV isolate induce lesions in chicken embryos that make these vaccine virus less suited for in ovo vaccination.
Del-Ros strain: This isolate was characterized by John K. Rosenberger and Sandra Cloud. It is an isolate from Delaware, USA (Av Dis 33:707-713, 1989). The Del Ros strain of CAV was isolated from livers of "Delmarva", USA broilers characterized by low hematocrits, excessive early mortality, pale fatty bone marrow and subcutaneous hemorrhages. The virus was initially propagated in immunosuppressed SPF leghorns, but was subsequently adapted after a few passages, to grow in MSB-1 cell cultures. Antigenically the virus is indistinguishable from the Cux-1 strain.
The virus was attenuated by multiple passages in MSB-1 cells for use as a vaccine for seroconverting broiler breeders. The vaccine virus prepared from the Del Ros strain is less pathogenic than the original Cux-1 embryo propagated vaccine produced in Europe but is more aggressive than the CAV vaccine developed and produced by Intervet. The Del Ros strain derived vaccine virus can be applied in drinking water, but is more efficacious if injected well before the onset of egg production.