疫苗結合會產生致命病毒

疫苗結合會產生致命病毒
Vaccines combine to produce deadly virus
Last updated 08:04 13/07/2012
Science
Translation by Autumnson Blog

Vaccines aren't supposed to cause disease. But that appears to be what's happening on Australian farms.
疫苗假定不應該引起疾病，但那似乎正是在澳大利亞農場發生的東西。
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.
科學家們已發現，兩種被用於接種雞隻的病毒株有可能重新組合，來形成一種病毒使動物不適和殺害。
"This shows that recombination of such strains can happen and people need to think about it," said Glenn Browning, a veterinary microbiologist at the University of Melbourne, Parkville, in Australia and one of the co-authors on the paper.
“這顯示這些菌株的重組可以發生及人們需要想一想，”一位在澳洲帕克維爾墨爾本大學的獸醫微生物學家及論文的合著者格倫布朗寧說。
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.
全世界的雞隻都對一組皰疹病毒被稱為傳染性喉氣管炎病毒(ILTv)敏感，這專門針對牠們的上呼吸道。由此產生的疾病稱為傳染性喉氣管炎（ILTV），減低雞蛋的生產並能殺死五分之一的受感染者。
"The birds effectively choke to death on blood and mucus," said Browning. The disease is not known to infect any other animals other than chicken and chicken-like birds.
“鳥類有效地在血液和粘液上窒息致死，”布朗寧說，這種疾病仍不知道能否感染雞隻和類似雞隻鳥類以外的任何其他動物。
To combat ILTV, farmers vaccinate their chickens with attenuated herpesviruses that can still infect and replicate but do not lead to disease.
為打擊傳染性喉氣管炎病毒，農民以細長的皰疹病毒接種雞隻，那仍然能感染和複製但並不引致疾病。
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.
澳洲已使用兩種疫苗，那都是由輝瑞公司生產並被稱為SA2和A20。然而，在2006年，該國從歐洲一家名為賽瓦特威購買一種新的疫苗
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," said Browning.
兩年之後，雞傳染性喉氣管炎病毒的新菌株出現，被稱為第8和9類。它們尤如其它菌株一樣致命， “但它們似乎將主導到2007年之前報告的菌株，”布朗寧說。
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 was not clear what mutations kept the vaccine strains from causing disease in the first place, they were probably lost when the viruses recombined, said Browning, whose team reports its findings online 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 agreed. But the SA2 strain might have spread into an unvaccinated population that was later vaccinated with the Serva strain, he suggested.

The data for the recombination is "convincing," said 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," added Thomas Mettenleiter, head of the Federal Research Institute for Animal Health also on Riems.

Only well-characterised live vaccines, rendered harmless by mutations in the same or overlapping regions, should be used in order to minimise the risk of recombination to a new virulent strain, he argued.

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," said Browning.

And Farrell stressed vaccines had 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.

Science Now
http://www.stuff.co.nz/science/7272611/Vaccines-Combine-to-Produce-Deadly-Virus