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The Role of Immunosuppression in On-Farm Food Safety

Jeffrey, Johnson; Cardona, Carol
University of California - Davis
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  1. Characterize the effect of immunosuppression on the prevalence of food safety pathogens. We hypothesize that the immunosuppression caused by CIAV infection will increase the prevalence and load of Salmonella spp. and Campylobacter spp. in commercial broiler chickens.
  2. Characterize the effect of breeder vaccination for chicken infectious anemia virus on the prevalence of food safety pathogens. We will test the working hypothesis that the practice of vaccinating breeders for CIAV leads to progeny flocks hatched with high, even antibody titers to CIAV and thus reduces the risk for early colonization by food safety pathogens.
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  1. We will culture broilers in a commercial setting for Campylobacter spp. and Salmonella spp. weekly for the lives of the flocks. Chicken infectious anemia virus antibody titers will be measured concurrently as will relative immune organ weights. Four of eight flocks will be maintained without intervention and four of eight flocks will be given a commercially available live oral CIAV vaccine. We will compare the prevalence of Campylobacter spp. and Salmonella spp. in the flocks with CIAV immunosuppression to that in the flocks protected by vaccination.
  2. We will assess the prevalence and load of food safety pathogens in the progeny of both vaccinated and unvaccinated breeder flocks. As for objective 1, we will culture birds from each flock weekly for Salmonella spp. and Campylobacter spp, test them for CIAV antibodies, and measure relative immune organ weights. We will compare results from the progeny of breeder flocks that are vaccinated and those that are not vaccinated.
A Immunity can prevent the colonization of animals with food safety pathogens.
B Chicken infectious anemia virus is widespread and causes immunosuppression in chickens.
C The impact of chicken infectious anemia virus infections on the prevalence of food safety pathogens is not known.

A The purpose of this project is to characterize the role of immune suppression caused by CIAV on the prevalence of food safety pathogens in commercial broilers.

We have completed a vaccination trial in broiler chickens with a modified live chicken anemia virus (CAV) vaccine given orally in the drinking water. This CAV vaccine is commercially available for use in egg laying chickens and broiler breeder but had not been tested for safety or efficacy in broiler chickens. In order to test the safety of this vaccine, we inoculated 20 birds at 14 days of age and maintained a negative control group of 20 birds. Both groups originated from the same commercial broiler flock, were maintained in isolation after 10 days of age, and were treated identically before vaccination and during the entire experimental period. All birds were necropsied at 40 days of age and data was collected on body mass as well as relative immune organ weights. Tissues were collected for histopathology and for DNA extraction and PCR. Sera were collected throughout the experimental period and at necropsy and tested for antibodies to CAV. The trial has been completed but the data has not been completely analyzed to date. The birds in the vaccinated group did not show any clinical signs of disease nor did they have any gross lesions at necropsy that would suggest the CAV vaccine was not safe for use in broilers. Serology, histopathology, PCR and analysis of the data collected at necropsy is pending. Once complete, this data will be used as preliminary data for Specific Aim 1 in which we will vaccinate two commercial broiler flocks and compare their performance with two unvaccinated commercial broiler flocks. We are in the process of completing the sample collection for one unvaccinated broiler flock. We will complete sampling on a second unvaccinated flock in May, 2003. We have not yet begun to collect materials to complete Specific Aim 2.

On farm food safety is critically important in the prevention of human illness. We expect to identify chicken anemia virus infections in broilers as major contributors to the increased prevalence and load of food safety pathogens immediately prior to slaughter. We further expect to identify practical methods to ameliorate this problem.
Funding Source
Nat'l. Inst. of Food and Agriculture
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Bacterial Pathogens