Researchers have discovered that herpes virus, like the ones responsible for causing Marek's disease in poultry, could be the source of more-virulent virus that endanger those unvaccinated from severe illness.

In a study published in the journal PLoS Biology, researchers pointed out the future challenge of identifying other vaccines that could be allowing virus to not just survive but to evolve as well to become more harmful. Andrew Read, one of the authors for the study, explained that an example of a perfect vaccine is one that keeps those vaccinated from getting sick and prevents them from spreading the virus to others.

The less-than-perfect vaccines discovered by the researchers work by creating "leaky" barriers against a virus, sometimes getting vaccinated individuals sick but with milder symptoms. Since the vaccinated individual survives long enough to spread the virus to others, the virus also survives and latches on other hosts.

"Our research demonstrates that the use of leaky vaccines can promote the evolution of nastier "hot" viral strains that put unvaccinated individuals at greater risk," said Venugopal Nair, who led the study.

Back in the 1950s, Marek's disease used to be a minor illness that doesn't do a lot of harm in chickens. But when the virus became virulent, it evolved, becoming capable of wiping out all unvaccinated birds in a flock in just 10 days. Today, the virus may be in its nastiest form but it is also increasingly becoming rare, so much so that it is a minor problem when a flock has been vaccinated. Read added that it does not matter whether or not a virus becomes highly virulent as long as a vaccine's effectiveness does not drop.

The researchers' work may use chickens as examples but it also has implications for human health. In the case of Ebola, for instance, researchers have to guarantee that vaccines being developed are not leaky, preventing the virus from not only being transmitted to other people but evolving as well.

To ensure vaccines are perfect, rigorous testing will be needed, alongside vigilant monitoring. The researchers also recommended individual vaccinations for personal protection as some protection will still be better than none.

The study received funding support from the the U.K. Biotechnology and Biological Sciences Research Council and the National Institutes of Health's Institute of General Medical Sciences. Other authors include: Stephen Walkden-Brown, David Kennedy, Lorraine Smith, Luke Blackwell, Lydia Kgosana, Claire Powers and Susan Baigent.

Photo: U.S. Army Corps of Engineers Europe | Flickr