Chicken Vaccines Combine to Produce Deadly Virus | Wired Science | Wired.com

Chicken Vaccines Combine to Produce Deadly Virus | Wired Science | Wired.com

“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.

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

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.

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.

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.