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

Document Type : Original Article

Authors

Central Laboratory for Evaluation of Veterinary Biologics, Abbasia, Cairo Egypt

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 in
vaccination failure recently noticed in broiler flocks, is lacking in Egypt. So, the present
study aimed to characterize CAV isolate-collected from a commercial broiler flock
suffered from severe anemia and high mortality based on sequence and phylogenetic
analysis of partial VP1 gene as well as to study pathogenicity and immunosuppressive
potential in one day-old SPF chicks. The CAV isolate proved to be positive by PCR. The
PCR product was sequenced and submitted to the gene bank under the accession
number KX171350 and the CAV strain was designated as CLEVB-Zag2. Phylogenetic
analysis 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 highly
pathogenic for the experimentally inoculated SPF- chicks showing depression, severe
anemia in almost all chicks in two infected groups beginning at the 7th day post
infection (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 infected
group. Blue wings were observed in few chicks in each infected group at the 14th day PI.
Macroscopic lesions consisting of subcutaneous and muscular hemorrhages are
observed with pale bone marrow, significant atrophy of thymus, spleen and bursa,
hepatomegally with mottled liver and paleness of the carcasses were detected 7 days PI
Those findings were evident and increased in severity until the day 14 PI. Concerning the
CLEVB-Zag2 CAV, it was found to be highly immunosuppressive in the infected SPFchicks vaccinated with a commercial potent inactivated H5N1 vaccine as manifested by
a significant reduction (protection 50%). The variance in the titer of the shieded
challenge H5N1 virus was 1.45 log10 and the mean HI titer at the 4th week post
vaccination was 1.5 log2 compared with the non-infected vaccinated group where these
values were 90%, 2.35 log10 and 5.3 log2; respectively. In conclusion, the present study
revealed that the CLEVB-Zag2 CAV isolate is highly pathogenic and immunosuppressive.

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