Pathogenicity and immunosuppressive potential of an Egyptian field isolate (2015) of the chicken anemia virus (CAV) in chickens

Abstract

Chicken anemia virus (CAV) is the causative agent of chicken infectious anemia (CIA).Studying CAV isolates in Egypt and their genetic diversity and its potential role invaccination failure recently noticed in broiler flocks, is lacking in Egypt. So, the presentstudy aimed to characterize CAV isolate-collected from a commercial broiler flocksuffered from severe anemia and high mortality based on sequence and phylogeneticanalysis of partial VP1 gene as well as to study pathogenicity and immunosuppressivepotential in one day-old SPF chicks. The CAV isolate proved to be positive by PCR. ThePCR product was sequenced and submitted to the gene bank under the accessionnumber KX171350 and the CAV strain was designated as CLEVB-Zag2. Phylogeneticanalysis at the nucleotide and amino acids level classify CLEVB-Zag2 CAV under group III(genotype III) of CAVs. On the other hand, the CLEVB-Zag2 CAV was found to be highlypathogenic for the experimentally inoculated SPF- chicks showing depression, severeanemia in almost all chicks in two infected groups beginning at the 7th day postinfection (PI) and reached the peak of severity at the 14th day (hematocrit value,hemoglobin conc. and RBCs counts) are significantly reduced in chicks of the infectedgroup. Blue wings were observed in few chicks in each infected group at the 14th day PI.Macroscopic lesions consisting of subcutaneous and muscular hemorrhages areobserved with pale bone marrow, significant atrophy of thymus, spleen and bursa,hepatomegally with mottled liver and paleness of the carcasses were detected 7 days PIThose findings were evident and increased in severity until the day 14 PI. Concerning theCLEVB-Zag2 CAV, it was found to be highly immunosuppressive in the infected SPFchicks vaccinated with a commercial potent inactivated H5N1 vaccine as manifested bya significant reduction (protection 50%). The variance in the titer of the shiededchallenge H5N1 virus was 1.45 log10 and the mean HI titer at the 4th week postvaccination was 1.5 log2 compared with the non-infected vaccinated group where thesevalues were 90%, 2.35 log10 and 5.3 log2; respectively. In conclusion, the present studyrevealed that the CLEVB-Zag2 CAV isolate is highly pathogenic and immunosuppressive.