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Mark Jackwood

Genetic drift & shift

Changes in the infectious bronchitis (IB) virus occur due to mutations or recombination:

  • Mutations occur when the virus replicates its genome, but errors occur in the genetic code, resulting in “genetic drift.” These are variant viruses.

  • Recombination occurs when two or more similar viruses infect the same cell, which leads to a rapid change in the genetic makeup of the virus. This is called “genetic shift” and constitutes a new viral serotype.
  • The virus-neutralization test, which requires live virus, is used to group IB virus isolates into serotypes. It cannot, however, compare viruses from different geographic areas. This is now possible with molecular techniques, which examine the spike gene that is routinely used to identify IB virus types.

    The two molecular procedures used for IB-virus diagnostics are real-time polymerase chain reaction (PCR) and genetic sequencing. Real-time PCR allows researchers to rapidly screen field samples for IB viruses; it also determines the amount of virus in the sample. However, it does not identify the IB-virus type; the type of IB virus is determined by genetic sequencing.

    According to the University of Georgia’s Mark Jackwood, PhD, surveillance and identification of new variant viruses by sequence analysis are key steps for improved control of IB. other steps include determining if new variants are pathogenic (not all are), using clinical-case data and surveys to determine how widespread the variant has become and discovering whether commercially available vaccines are effective, he said.

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