Investigation of the unstable attenuation exhibited by a chicken anaemia virus isolate

Abstract

An attenuated chicken anaemia virus (CAV) isolate, cloned isolate 10, which was molecularly cloned from the Cuxhaven-1 CAV after 173 cell-culture passages, was shown previously to recover pathogenicity following 10 passages in young chicks. The consensus nucleotide sequence of the 'revertant' (Rev) virus, present as a tissue homogenate, differed from cloned isolate 10 at a single nucleotide residue (nucleotide 1739) that changed amino acid 287 of the capsid protein from alanine to aspartic acid. Subjecting Rev virus to 10 cell-culture passages reselected viruses with an alanine at this amino acid position. Experimental infections using a molecularly cloned Rev virus isolate demonstrated that the mutation at nucleotide 1739 was not in itself responsible for the recovery of pathogenicity exhibited by the Rev virus. Additional sequence analyses of cloned amplicons provided evidence that the Rev virus population comprised minor, genetically different subpopulations, and provided an indication of CAV's potential for genetic change.

Genetic Heterogeneity among Chicken Infectious Anemia Viruses Detected in Italian Fowl

“…However, the level of attenuation does not usually prevent vertical or horizontal transmission of the vaccines to and between offspring [49]. This vaccine behavior could consequently be a hazard for young chicks, since it has been demonstrated that attenuated CIA strains have the potential to revert to virulent phenotypes after chicken-to-chicken transmission in the field [50,51]. Vaccine persistence, circulation and reversion to virulence have also been frequently reported for other empirically attenuated avian vaccines developed to control immunosuppressive or respiratory diseases [52][53][54].…”

Epidemiology and molecular characterization of chicken anaemia virus from commercial and native chickens in Taiwan

“…In the current investigation, the sequences of five Taiwanese field isolates were highly similar to those of the vaccine strain 26P4 or Del‐Ros with only two or three nucleotide substitutions in the VP1 gene. Attenuated CAV can revert to be virulent by serial passages in chickens (Todd et al., ). In addition, a previous report showed that some field CAV strains derived from 26P4 vaccine strain were circulating in South Korea (Kim et al., ).…”

Evolutionary reversion of live viral vaccines: Can genetic engineering subdue it?

“…Even more problematic, attenuation by this method may yield genetically polymorphic strains, and reversion to high virulence may involve variants at low frequencies, something not easily identified or interpreted from sequences ( Badgett et al. 2002 ; Todd et al. 2003 ; Depledge et al.…”