Herpesviruses are latent viruses- no news here. Herpesviruses integrate into host genomes to move into a latent stage- again, no news here. Herpesvirus vaccine integrates into host genome- wait, what?
Researchers were shocked when it was recently discovered that the vaccine to a deadly chicken herpesvirus, Marek's disease virus, also integrated into the chicken genome. Marek's disease is highly contagious and causes cancer in chickens. Considering that chicken is a major source of meat (and eggs!), farmers have for many years vaccinated their breeding stocks to keep them healthy.
The three vaccines developed for Marek's disease virus, and used for the past 40 years, are live, related, but weaker strains of virus. The vaccine works because there is cross-reactivity of immunity against the vaccine virus and Marek's disease virus. While the vaccine prevents tumor formation, it doesn't prevent infection of Marek's disease virus. The mechanism has so far remained a mystery, so when researchers monitored vaccinated chicks and found that all of the vaccine virus strains also integrated into the chicken genome-- in less than a day-- it was quite unexpected.
Researchers are now continuing tests to see if the vaccine viruses can emerge from their latent states and allow for long-lasting protection, or prevent latency by competing with Marek's disease virus for locations in the genome. More to come!
-- Sharon Kam