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Genomic sequencing could aid ILT control efforts in poultry

by 5m Editor
18 March 2019, at 12:00a.m.

Molecular virology is already leading to discoveries that will improve management of infectious laryngotracheitis (ILT), according to Stephen Spatz, PhD, molecular virologist with USDA’s Southeast Poultry Research Laboratory, Athens, Georgia.

With genomic sequencing, it is now possible to differentiate vaccinal from wild-type ILT strains, Spatz told Poultry Health Today.

He’s been testing a portable device called MinION to identify ILT type. The turnaround time would be just a couple of days and the assay would be relatively inexpensive, he said.

The device utilises nanopore sequencing, a technology that makes it possible to sequence a single molecule of DNA or RNA. A nanometer is one-billionth of a meter. Sequencing simply means determining the DNA’s or RNA’s structure.

‘It’s phenomenal’

“A piece of DNA is threaded through a nanopore, and it reads the sequence based on electrical resistance. It’s phenomenol,” Spatz said, and noted that the technology is already in use for rapid identification of viruses such as Ebola.

The ability to differentiate between vaccinal and wild-type ILT will help producers make better vaccine choices, Spatz continued.

The scientist explained that modified-live chicken-embryo ILT vaccines and tissue-culture origin vaccines protect well, but the ILT herpesvirus they contain can reactivate. Spatz compared the situation to herpesvirus and cold sores in people. The sore may go away, but the virus hides out and can reactivate in a more virulent form.

The recombinant vectored ILT vaccines don’t revert to virulence, but they also don’t protect as well, he said.

Wild-type strain

The majority of isolates he tests from commercial flocks with ILT are vaccinal revertants. Backyard flocks with ILT are most often affected by a wild-type strain, though not always, Spatz continued.

“If you have wild-type [ILT] you really need to vaccinate,” he said.

If flocks have ILT of vaccinal origin, producers need to change to a recombinant vectored ILT vaccine. Likewise, if the vectored vaccines are not providing adequate immunity, producers can replace or supplement them with one of the modified-live ILT vaccines.

Some producers are using a vectored vaccine in ovo then boost with a modified-live ILT vaccine, and “that seems to be the best combination,” but using two vaccines can be expensive, he noted.

Looking to the future, Spatz said one goal is the development of a vaccine that protects well but doesn’t revert to virulence. He predicted that, eventually, it will be possible to develop breeds of chickens resistant to viral disease. “It’s going to happen before you know it,” he said.