Marek’s disease can be pervasive in chicken houses. Chickens infected by this highly contagious viral disease often develop tumors, become paralyzed and die. They can shed the virus through their skin, enabling it to linger in the environment for years, even decades.
Vaccination controls the losses caused by Marek’s disease virus. In the United States, poultry producers have used a herpesvirus of turkeys (HVT) vaccine to combat Marek’s disease in chickens since the 1970s.
“It worked incredibly well, but the viruses that broke through replicated much faster and caused tumors more quickly,” said Mark Parcells, a University of Delaware professor of molecular virology.
By the mid-1980s, the U.S. implemented a combination of HVT with another vaccine. Then a different vaccine, commonly used in Europe, was licensed in the U.S. by the mid-1990s.
Circumstances are different in Nigeria, where the virus has been circulating since the 1960s. It has cropped up frequently since the country’s poultry industry expanded in the 1980s. Rates continue to increase today, sending economic shockwaves through the country’s agricultural system.
Parcells along with several researchers, including Joseph Patria, a doctoral student in Parcells’ lab who graduated in August 2024, worry the virus will continue to get smarter and be able to mutate to resist vaccine efforts.
“It’s important to continue vaccine research because you never know when you’re going to need a more effective vaccine,” Patria said.
In new research published in the journal Viruses, Parcells and colleagues at UD and in Nigeria and Germany suggest that outbreaks of Marek’s disease virus in Nigeria were caused by genetic variation in the viral oncogene, a gene called meq, that also apparently mediates resistance to vaccines. The findings give insight into how the virus could continue to evolve, not just in Nigeria, but along the Delmarva Peninsula, where the poultry industry is essential for the region’s economy.
Reading virus DNA
In 2012, Parcells attended an international Marek’s disease conference in France, where he met Luka Jwander, a state poultry veterinarian from Nigeria who told him the country was losing many laying hens to Marek’s disease.
Parcells, who
