Chicken infectious anemia virus: immunosuppression, transmission and impact on other diseases

Abstract

1. Original Objectives. The original broad objectives of the grant were to determine A) the impact of CAV on the generation of cytotoxic T lymphocytes (CTL) to reticuloendotheliosis virus (REV) (CU), B). the interactions between chicken anemia virus (CAV) and Marek’s disease virus (MDV) with an emphasis on horizontal spread of CAV through feathers (KVI), and C) the impact of CAV infection on Salmonella typhimurium (STM) (HUJI). During the third year and the one year no cost extension the CU group included some work on the development of an antigen-antibody complex vaccine for CAV, which was partially funded by the US Poultry and Egg Association. 2. Background to the topic. CAV is a major pathogen causing clinical disease if maternal antibody-free chickens are infected vertically or horizontally between 1 and 14 days of age. Infection after 3 weeks of age when maternal antibodies are not longer present can cause severe subclinical immunosuppression affecting CTL and cytokine expression. The subclinical immunosuppression can aggravate many diseases including Marek’s disease (MD) and several bacterial infections. 3. Major conclusions and achievements. The overall project contributed in the following ways to the knowledge about CAV infection in poultry. As expected CAV infections occur frequently in Israel causing problems to the industry. To control subclinical infections vaccination may be needed and our work indicates that the development of an antigen-antibody complex vaccine is feasible. It was previously known that CAV can spread vertically and horizontally, but the exact routes of the latter had not been confirmed. Our results clearly show that CAV can be shed into the environment through feathers. A potential interaction between CAV and MD virus (MDV) in the feathers was noted which may interfere with MDV replication. It was also learned that inoculation of 7-day-old embryos causes growth retardation and lesions. The potential of CAV to cause immunosuppression was further examined using CTL responses to REV. CTL were obtained from chickens between 36 and 44 days of age with REV and CAV given at different time points. In contrast to our earlier studies, in these experiments we were unable to detect a direct impact of CAV on REV-specific CTL, perhaps because the CTL were obtained from older birds. Inoculation of CAV at one day of age decreased the IgG antibody responses to inactivated STM administered at 10 days of age. 4. Scientific and Agricultural Implications The impact of the research was especially important for the poultry industry in Israel. The producers have been educated on the importance of the disease through the many presentations. It is now well known to the stakeholders that CAV can aggravate other diseases, decrease productivity and profitability. As a consequence they monitor the antibody status of the breeders so that the maternal antibody status of the broilers is known. Also vaccination of breeder flock that remain antibody negative may become feasible further reducing the negative impact of CAV infection. Vaccination may become more important because improved biosecurity of the breeder flocks to prevent avian influenza and Salmonella may delay the onset of seroconversion for CAV by natural exposure resulting in CAV susceptible broilers lacking maternal antibodies. Scientifically, the research added important information on the horizontal spread of CAV through feathers, the interactions with Salmonella typhimurium and the demonstration that antigen-antibody complex vaccines may provide protective immunity.