Study highlights potential issue in poultry vaccine design

Live vaccines and viruses can infect the same cells in chickens, which can sometimes lead to new infections in flocks, revealed new research at the University of Illinois Urbana-Champaign.

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JurgaR | iStockPhoto.com
JurgaR | iStockPhoto.com

Live vaccines and viruses can infect the same cells in chickens, which can sometimes lead to new infections in flocks, revealed new research at the University of Illinois Urbana-Champaign.

The findings, published in the journal, Virulence, could help design a better vaccine against viral diseases, like Marek’s disease, in people and poultry.

“Marek’s disease is similar to varicella zoster virus (VZV) that causes chicken pox and shingles with how it replicates in the skin, is shed into the environment and enters the new host via the respiratory route,” explained University of Illinois Urbana-Champaign pathobiology professor Keith Jarosinski, who led the research.

“Both viruses have very similar genes and gene expression in the skin, so Marek’s disease in chickens is an excellent model for studying homologous VZV genes in the skin.”

Marek’s disease is a highly contagious viral disease in poultry that can cause tumors to develop in various parts of the body, eye cancer, wing and leg paralysis and eventually death. It is spread through bird feed, bedding material, bird droppings, feathers and dead skin. The disease costs the poultry industry an estimated $1 billion each year.

Undercovering interactions between viruses and vaccines Live vaccines are designed to actively replicate and stimulate the immune system. This type of vaccination is very good at training the immune system to recognize Marek’s disease, however, it does not lead to the complete eradication of the virus.

Previous research suggested that viruses can pick up genes from the vaccines that fight them, which allows the viruses to evolve in a way that boosts virulence. In addition, a process called “complementation” can result in vaccines producing a molecule that makes the virus more infectious.

To learn more about the interaction between viruses and vaccines, the researchers inoculated chickens with both the virus and the vaccine and housed the birds with animals that had not been exposed to either.

The virus was tagged with a green fluorescent molecule, while the vaccines were tagged with a red light. This gave the researchers an easy way to monitor and track the course of the infection in cells.

Surprisingly, the results showed that some cells in the inoculated birds contained both the vaccine and the virus.

“This co-infection can result in functional complementation so the major thing the poultry industry should know is that serious thought should be taken when designed ‘vectored’ vaccines or vaccines that should protect chickens against multiple pathogens,” Jarosinski said.

 

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