New approach to battling PRRS virus

By Robert Fieldhouse, Ontario Pork - A viral menace called the porcine reproductive and respiratory syndrome (PRRS) virus has plagued the hog industry for the past decade, causing major health problems for pregnant sows and piglets - and major economic woes for producers.
calendar icon 15 October 2004
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If it reaches a farrowing operation, it can induce abortions in pregnant sows and cause respiratory illness in piglets.

But University of Guelph pathobiology professor Dongwan Yoo has made a breakthrough. He's found that PRRS virus targets a different part of the cell to beat hog immune systems, and he's working on a second-generation vaccine against the virus.

"This porcine virus is the number-one economically important swine pathogen," says Yoo. "Despite the importance of the disease, no one knows how the virus works at the molecular level, and the response of the infected host needs to be better understood."

Viruses are simple and PRRS virus is no exception: it hijacks a host cell's energy and resources that it doesn't have itself, and uses them to produce virus copies. After enough copies of a virus are made, the host cell is split open and the process repeats as viruses spread to surrounding cells.

Yoo believes the solution to the PRRS virus lies in how the capsid (the virus's protein component) affects the pig's immune system. By following the capsid's movements inside the cell, he's found that - unlike most viral proteins that stay in the main body of the cell - the PRRS virus capsid is transported to an infected cell's nucleus, where all the cell's activities are controlled and regulated. There, the capsid interferes with the manufacture of immune system proteins, effectively crippling the immune system and leaving the cell vulnerable to all types of disease.

The current PRRS vaccine on the market has undesirable side effects, so Yoo is developing a vaccine that's safer and more effective.

First, he's trying to identify the parts of the virus that attack a host cell, and how the cell responds to infection. Then, he'll develop new genetic methods to modify the PRRS virus' DNA. His goal is to create a non-pathogenic PRRS virus that can be used in a vaccine, which will give animals immunity from the disease-causing PRRS virus.

"The vaccine will be safe to use and effective to prevent the infection," says Yoo. "The effective prevention of PRRS virus infection will be a significant benefit not only to Ontario pig farmers but also to the global swine industry."

He is also working on a method of stopping PRRS virus gene replication. This strategy attacks the problem from a different angle, before the PRRS virus capsid gene can even be produced.

Yoo collaborated with University of Guelph graduate students Changhee Lee, Gang Li and Sarah Wootton and Prof. Robert Rowland of Kansas State University. This research is sponsored by Ontario Pork, the Ontario Ministry of Agriculture and Food, the Natural Sciences and Engineering Research Council.

For more information, contact Jean Howden, Ontario Pork research coordinator, at 1-877-668-7675 or
[email protected]

Source: Ontario Pork, October 2004

Robert Fieldhouse is a writer with SPARK, the University of Guelph's student writing program.

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