Chicken vaccines merged to form live viruses and caused outbreaks of irony

Since 2008, Australian chickens have been suffering from intense outbreaks of a disease called infectious laryngotracheitis (ILT). Their eyes become red and swollen, they cough and gasp for air, and they sometimes bleed from their noses. The survivors produce fewer eggs, leading to severe losses for farmers. The disease is caused by a highly contagious virus called ILTV. It’s a herpesvirus, one of the group that causes herpes, chickenpox, and glandular fever in humans. It’s a problem for poultry the world over, but the recent outbreaks in New South Wales and Victoria have been unusually severe, killing up to 18 per cent of infected chickens. They also have an ironic origin – they’re the result of vaccines. Chickens are often vaccinated against ILTV, using weakened versions of the virus. Now, Sang-Won Lee from the University of Melbourne has found that two such vaccines have merged together to create the live ...