Disheygirl
Songster
That sounds familiar….When NPIP was developed Mareks was common, but very,very mild did not kill or cripple birds. But it did cause problems in UK and US production farms that were growing in the 50s and 60s because production decreased when birds got it but eventually recovered
A vaccine was developed in 1970, but it was a leaky vaccine..so a once nonfatal disease has become virulent and deadly. https://www.healthline.com/health-n...072715#Preventing-More-Virulent-Virus-Strains