Scientists have found that n some Australian farms, vaccines are causing diseases, due to the effect of two virus strains present in chicken vaccination, recombining to form a deadly virus. Glenn Browning says that this shows that indeed recombination can happen and that people should be wary of it.
All around the world chickens are vulnerable to a class of herpesviruses known as ILTV, which attack the bird’s upper respiratory system. When this happens, it results to infectious laryngotracheitis, reduces the number of eggs produced and may kill around one-fifth of the infected chicken. Browning says that this death is caused by choking on mostly mucus and blood. Current knowledge indicates that the deadly virus infects only chickens and other similar birds.
Farmers can fight ILTV by vaccinating their chickens with less virulent herpesviruses that don’t cause the disease. Australia has been using SA2 and A20 vaccines produced by Pfizer. However, in 2006 the country bought a new vaccine called Serva from the Europe-based Intervet. In 2008, new ILTV strains called class 8 and 9, showed up. According to Browning, these were similarly harmful as the other strains but seemed dominant over pre-2007 strains.
Initially, scientists were led to believe that the new vaccine had reverted to its diseases-causing form because of the introduction of the European vaccine. However, when scientists arrayed the genomes of the 3 vaccine strains by order with the new strains, it was discovered that the new virus strains were in fact sewn together from the Australian and European vaccines. It’s yet to be known the kind of mutations that prevent the vaccine strains from causing diseases but Browning argues that maybe this ability was lost when recombining.
Another scientist, Paul Farrell at Imperial College, wrote that the findings could be possible, although a bit surprising and that it would mean that both vaccines had gone through the same animal as that would be a requirement for recombination to take place. Browning agrees that although farmers don’t intentionally inoculate with both vaccines, there might be a way that the SA2 strain spread into the vaccinated population which is afterwards inoculated with the Serva strain.
Other scientists add their opinion and views on the deadly virus. Walter Fuchs, a specialist on the disease in Germany, states that he was “convinced” by the data on recombination. Thomas Mettenleiter, a head researcher on animal health in Germany, feels that scientists should take the problem of vaccine strains combining to form deadly viruses seriously. He argues further that, in order to mitigate on the possibility of a new deadly virus strain due to recombination, well-characterized live vaccines, that are harmless after mutating in the same areas need to be used.
Live and less virulent vaccines are used in human beings, although less often as compared to poultry and in a sequence that is normally known. Browning says that this use is not a reason to push the panic button on vaccines. Farrell stresses that vaccines are indeed a great medical success and also writes that the kind of vital technicalities raised in this article should not act as detraction from recognizing the huge benefits of vaccines to our health.