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)
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)
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)