Chicken infectious anemia virus (CIAV) is a ubiquitous and highly resistant virus of chickens that causes anemia and death in chicks less than 3 wk of age and immunosuppression in chickens older than 3 wk of age. The production of specific-pathogen-free eggs free of CIAV is essential for research and vaccine production. Currently, flocks are screened for CIAV by antibody tests to ensure freedom from CIAV infection. Recent evidence, however, indicates that chickens may carry and vertically transmit CIAV DNA independently of their antibody status. In this study, we tested embryos and eggshell membrane residues by nested polymerase chain reaction (PCR) as a sensitive method of detecting CIAV DNA. CIAV DNA could be detected in the blastodisks and semen obtained from antibody-positive and -negative chickens. Examination of different tissues between 18 and 20 days of incubation indicated that many but not all organs of individual embryos were positive. The lymphoid organs and gonads had the highest incidence of CIAV DNA, which was significantly different (P < 0.05) from the incidence in the liver. Eggshell membrane samples from embryos or newly hatched chicks were an excellent noninvasive source for the detection of CIAV DNA, identifying significantly more positive embryos than did pooled lymphoid organs. The use of dexamethasone injections as a method to improve the detection of carrier birds did not result in an increase of vertical transmission or cause seroconversion in the treated hens. A combination of testing eggshell membrane residues at hatch and periodic testing of blood DNA by nested PCR can be used to identify chickens carrying CIAV DNA and may be used to eradicate carrier birds.
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Vol. 47 • No. 3