Previous studies have shown that viruses can pick up genes from the vaccines designed to fight them, allowing the viruses to evolve in ways that sometimes boost virulence. This leaves room for the natural virus and the modified viral vaccines to interact in ways that may promote viral evolution or infectiousness. Vaccines made from live viruses do a better job than other vaccines in training the immune system to recognize Marek's disease virus, but these vaccines do not lead to eradication of the virus, Jarosinski said. The use of live vaccines that have been modified so that they're not infectious is the most effective strategy for controlling symptoms of the disease, which include failure to thrive, tumors and death. Some even vaccinate chicks in the egg, Jarosinski said. The poultry industry has a practice of vaccinating newly hatched chickens against the Marek's disease virus, Gallid alphaherpesvirus 2. "We're not only doing it for the benefit of the chickens in the poultry industry, but also because it's a very similar mechanism that the virus that causes chickenpox uses, where it enters through the respiratory route and infects the lymphocytes, and that gets it to the skin." "We've been trying to understand how the virus spreads from one host to another," said University of Illinois Urbana-Champaign pathobiology professor Keith Jarosinski, who led the research. The study focused on Marek's disease, a viral infection that spreads when one chicken inhales fragments of dead skin or feather tissue from an infected chicken. Reported in the journal Virulence, the study offers direct evidence that a vaccine and virus can infect the same cells in living animals and share molecular tools that allow the virus to infect other animals - in this case, chickens.
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