Vaccines used to protect chickens against herpes have combined to form a deadly virus that is killing birds in Australia, scientists have revealed.
To combat infectious laryngotracheitis (ILTV), Australian poultry producers were using two types of vaccine produced by pharmaceutical company Pfizer, called SA2 and A20.
But in 2006 the country purchased a new vaccine called Serva from Europe-based Intervet. Subsequently new strains of ILTV have appeared, known as class eight and nine.
Researchers from the University of Melbourne tested the genomes and found the new strain had been “stitched together” from the three herpesvirus vaccines.
The new strain is more prevalent than previous strains of the herpes virus.
Paul Farrell, a virologist at Imperial College London said, as farmers do not deliberately vaccinate with both vaccines, the recombination suggests the vaccine strain first spread to a non-vaccinated population, before moving into a flock vaccinated with a different strain.
“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,” he explained.
The research paper was first published by Science Magazine.
Infectious laryngotracheitis symptoms:
- A respiratory disease which affects the upper respiratory tract
- Signs include gasping and coughing in an effort to clear blood-stained mucus from the trachea
- The disease causes a reduction in egg production
- It can kill up to one fifth of birds affected
- Birds often die from suffocation if the windpipe becomes completely blocked