Skip to comments.Chicken Vaccines Combine to Produce Deadly Virus
Posted on 07/13/2012 9:28:04 PM PDT by neverdem
Vaccines aren't supposed to cause disease. But that appears to be what's happening on Australian farms. Scientists have found that two virus strains used to vaccinate chickens there 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, known as infectious laryngotracheitis (ILTV), reduces egg production and can kill up to one-fifth of those infected. "The birds effectively choke to death on blood and mucus," says Browning. The disease is not known to infect any other animals other than chicken 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 two vaccines, which are produced by Pfizer and called SA2 and A20. In 2006, however, the country purchased a new vaccine from European company Intervet called Serva. Two 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 two new strains and the three 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 first place, they were probably lost when the viruses recombined, says Browning, whose team reports its findings online today 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.
I’m thinking about making peace with God.
It can’t be much longer.
Besides the food situation. 0 will see that there is a war of some sort before the election. Maybe even a conspired one. It may not go well.
Now this is weird. Two tame viruses merge into one vicious virus.
The new virus kills chickens and related poultry. (I’d guess turkeys are vulnerable too.) Nothing else, and not people.
I have a very low immune system and can get sick very easy
so everything scares me.
Ping! (Thanks, neverdem!)
I can hear the WHO giggling uncontrollably crouched in a corner in a dark room rubiing thier hands together radically.
Nice going, Urkels. :(
Interesting. Fortunately there is a ready alternative.
An attenuated vaccine is a vaccine created by reducing the virulence of a pathogen, but still keeping it viable (or live). Attenuation takes an infectious agent and alters it so that it becomes harmless or less virulent. These vaccines contrast to those produced by killing the virus (inactivated vaccine).
While attenuated vaccines have several advantages, secondary mutation has long been known to result in a reversion to virulence.
This is I gather the first recorded instance of an RNA swap between two attenuated viruses, which normally happens between to normal viruses, especially influenza. But in future it means that farmers will need to use both attenuated and inactive vaccines to avoid this problem.
That, and wipe out any affected flocks right now, before the mutation can spread.
Bottom line: They have known that a secondary mutation could reactivate an attenuated virus; but now they know that two similar attenuated viruses can interact, so this needs to be avoided, not just in animals, but humans as well.
Brings to mind a picture of a child playing with the (now rabid) family pet.
Well, it's a good thing avian viruses have never demonstrated the ability to mutate into human infectious strains.
Thanks for the PING! I’d been hearing like stories on the radio on the internet from a woman engineer who keeps her eyes and ears open.
Thanks for the ping!
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