Antibodies - The First Line of Defence

The following three animations illustrate, in a simplified form, the interaction of IBD virus and circulating neutralising antibodies.

The animations require a Flash player which is installed in most web browsers today. If they do not work, click here to download Flash or download and run the stand-alone executable version (MS Windows).

The animations are based on an infection with a virulent strain of IBD virus; however the same dynamics apply to vaccine strains. Vaccine strains must infect the bursa of Fabricius to induce immunity. If a high level of circulating antibodies (MDA – maternal derived antibody) neutralises the vaccine before reaching the bursa, the chicken is not immunized and thus remains susceptible to Gumboro infection at a later age.

Animation 1: IBDV - No Antibody

Animation sequence illustrates the course of infection of a pathogenic strain of Gumboro virus in a susceptible chicken, thus a chicken with no circulating antibodies to IBDV.

  • The virus is ingested.
  • Crosses the intestinal wall and enters the blood stream.
  • The virus is transported in the bloodstream to the different internal organs, including the bursa of Fabricius.
  • In the bursa there is massive viral replication, with subsequent bursal damage.
  • A secondary viraemia occurs with clinical symptoms and possible death. High levels of virus can be detected in allorgans.

Animation 1: IBDV - No Antibody (Start animation by clicking on play button)

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Animation 2: IBDV - Low Antibody

Animation sequence illustrates the course of infection of a pathogenic strain of Gumboro virus in a chicken with a low to moderate level of circulating antibody to IBDV.

  • The virus is ingested.
  • Crosses the intestinal wall and enters the blood stream. In the bloodstream the virus is exposed to circulating antibodies.
  • The antibodies neutralise a percentage of the virus. Thus less infectious virus is circulated to the different internal organs, including the bursa of Fabricius.
  • In the bursa there is viral replication. However due to an initial lower infectious dose the subsequent bursal damage is only partial.
  • A secondary viraemia occurs, but the level of virus circulating may be below that required to induce clinical symptoms.
  • The result is no clinical gumboro, however dependant on the degree of bursal damage there is still immunosuppression.

Animation 2: IBDV - Low Antibody (Start animation by clicking on play button)

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Animation 3: IBDV - High Antibody

Animation sequence illustrates the course of infection of a pathogenic strain of Gumboro virus in a chicken with a high level of circulating antibody to IBDV.

  • The virus is ingested.
  • Crosses the intestinal wall and enters the blood stream. In the bloodstream the virus is exposed to circulating antibodies.
  • The antibodies neutralise the virus. Thus no or insignificant levels of infectious virus is circulated to the different internal organs, including the bursa of Fabricius.
  • The result is no clinical gumboro or bursal damage. A healthy chicken!

Animation 3: IBDV - High Antibody (Start animation by clicking on play button)

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