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Published Date: 2012-10-28 20:19:15
Subject: PRO/AH/EDR> Vaccine combination, poultry - Australia: deadly
Archive Number: 20121028.1371043
VACCINE COMBINATION, POULTRY- AUSTRALIA: DEADLY
***********************************************
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: 12 Jul 2012
Source: Science [edited]
Scientists have found that 2 virus strains used to vaccinate chickens in Australia may have recombined to form a virus that is sickening and killing the animals. "This shows that recombination of such strains can happen, and people need to think about it," says Glenn Browning, a veterinary microbiologist at the University of Melbourne, Parkville in Australia and one of the co-authors on the paper.
Chickens worldwide are susceptible to a group of herpesviruses called ILTV, which target their upper respiratory tract. The resulting disease, called infectious laryngotracheitis, reduces egg production and can kill up to 1/5th of those infected. "The birds effectively choke to death on blood and mucus," says Browning. The disease is not known to infect any animals other than chickens and chicken-like birds.
To combat ILTV, farmers vaccinate their chickens with attenuated herpesviruses that can still infect and replicate but do not lead to disease. Australia has used 2 vaccines, which are produced by Pfizer and called SA2 and A20. In 2006, however, the country purchased a new vaccine from the European company Intervet called Serva. 2 years later, new strains of ILTV, called class 8 and 9, appeared. They are just as deadly as other strains. "But they seem to be dominating over the strains that were reported prior to 2007," says Browning.
Because the new strains appeared shortly after the European vaccine was introduced, scientists thought that the new vaccine strain might have reverted back to a disease-causing form. But when the researchers sequenced the genomes of the 2 new strains and the 3 vaccine strains, they found that the new viruses were actually stitched together from the European and Australian vaccines. Although it is not clear what mutations keep the vaccine strains from causing disease in the 1st place, they were probably lost when the viruses recombined, says Browning, whose team reports its findings online today [12 Jul 2012] in Science.
"This is quite possible but a bit surprising, since it would imply that both vaccines have gone into the same animal, which would be required for recombination to occur," Paul Farrell, a virologist at Imperial College London, wrote in a statement released by the Science Media Centre. Farmers do not deliberately vaccinate with both vaccines, Browning agrees. But the SA2 strain might have spread into an unvaccinated population that was later vaccinated with the Serva strain, he suggests.
The data for the recombination is "convincing," says Walter Fuchs, who heads the National Reference Laboratory for Infectious Laryngotracheitis of Poultry on the island of Riems in Germany. The combination of vaccine strains to form a new virus is "a problem that needs to be taken seriously," adds Thomas Mettenleiter, head of the Federal Research Institute for Animal Health also on Riems. Only well-characterized live vaccines rendered harmless by mutations in the same or overlapping regions should be used in order to minimize the risk of recombination to a new virulent strain, he argues.
Live-attenuated vaccines are also used in humans, but a lot less than in poultry, and their sequence is usually known. "This is not a panic-button on vaccines," says Browning. And Farrell stresses vaccines have been one of the great success stories of medicine. "The type of important technicality raised in this article should not be allowed to detract from the enormous health benefit generally provided by vaccines," he wrote.
--
Communicated by:
Thomas Monath
[This was only just brought to the attention of the moderator, who apologizes for the tardiness of this post.
What strikes me as most important is that there are modified live viruses in these vaccines. If vaccines with different strains can recombine to produce a different strain of the disease in chickens, then it stands to reason it could happen in any animal, including in people. Scientists at all levels should be looking at this when a vaccine with a new strain is introduced for any disease. Veterinarians and physicians need to be keeping accurate records of which strain was used for vaccination in a particular animal or human.
Furthermore, reversion of an ITLV vaccine to virulence has happened before; see ProMED-mail post 20050308.0689
Australia may be located on the interactive ProMED HealthMap at: http://healthmap.org/r/1z_*. - Mod.TG]
Subject: PRO/AH/EDR> Vaccine combination, poultry - Australia: deadly
Archive Number: 20121028.1371043
VACCINE COMBINATION, POULTRY- AUSTRALIA: DEADLY
***********************************************
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: 12 Jul 2012
Source: Science [edited]
Scientists have found that 2 virus strains used to vaccinate chickens in Australia may have recombined to form a virus that is sickening and killing the animals. "This shows that recombination of such strains can happen, and people need to think about it," says Glenn Browning, a veterinary microbiologist at the University of Melbourne, Parkville in Australia and one of the co-authors on the paper.
Chickens worldwide are susceptible to a group of herpesviruses called ILTV, which target their upper respiratory tract. The resulting disease, called infectious laryngotracheitis, reduces egg production and can kill up to 1/5th of those infected. "The birds effectively choke to death on blood and mucus," says Browning. The disease is not known to infect any animals other than chickens and chicken-like birds.
To combat ILTV, farmers vaccinate their chickens with attenuated herpesviruses that can still infect and replicate but do not lead to disease. Australia has used 2 vaccines, which are produced by Pfizer and called SA2 and A20. In 2006, however, the country purchased a new vaccine from the European company Intervet called Serva. 2 years later, new strains of ILTV, called class 8 and 9, appeared. They are just as deadly as other strains. "But they seem to be dominating over the strains that were reported prior to 2007," says Browning.
Because the new strains appeared shortly after the European vaccine was introduced, scientists thought that the new vaccine strain might have reverted back to a disease-causing form. But when the researchers sequenced the genomes of the 2 new strains and the 3 vaccine strains, they found that the new viruses were actually stitched together from the European and Australian vaccines. Although it is not clear what mutations keep the vaccine strains from causing disease in the 1st place, they were probably lost when the viruses recombined, says Browning, whose team reports its findings online today [12 Jul 2012] in Science.
"This is quite possible but a bit surprising, since it would imply that both vaccines have gone into the same animal, which would be required for recombination to occur," Paul Farrell, a virologist at Imperial College London, wrote in a statement released by the Science Media Centre. Farmers do not deliberately vaccinate with both vaccines, Browning agrees. But the SA2 strain might have spread into an unvaccinated population that was later vaccinated with the Serva strain, he suggests.
The data for the recombination is "convincing," says Walter Fuchs, who heads the National Reference Laboratory for Infectious Laryngotracheitis of Poultry on the island of Riems in Germany. The combination of vaccine strains to form a new virus is "a problem that needs to be taken seriously," adds Thomas Mettenleiter, head of the Federal Research Institute for Animal Health also on Riems. Only well-characterized live vaccines rendered harmless by mutations in the same or overlapping regions should be used in order to minimize the risk of recombination to a new virulent strain, he argues.
Live-attenuated vaccines are also used in humans, but a lot less than in poultry, and their sequence is usually known. "This is not a panic-button on vaccines," says Browning. And Farrell stresses vaccines have been one of the great success stories of medicine. "The type of important technicality raised in this article should not be allowed to detract from the enormous health benefit generally provided by vaccines," he wrote.
--
Communicated by:
Thomas Monath
[This was only just brought to the attention of the moderator, who apologizes for the tardiness of this post.
What strikes me as most important is that there are modified live viruses in these vaccines. If vaccines with different strains can recombine to produce a different strain of the disease in chickens, then it stands to reason it could happen in any animal, including in people. Scientists at all levels should be looking at this when a vaccine with a new strain is introduced for any disease. Veterinarians and physicians need to be keeping accurate records of which strain was used for vaccination in a particular animal or human.
Furthermore, reversion of an ITLV vaccine to virulence has happened before; see ProMED-mail post 20050308.0689
Australia may be located on the interactive ProMED HealthMap at: http://healthmap.org/r/1z_*. - Mod.TG]