Porcine Reproductive and Respiratory Syndrome (PRRS) affects the reproductive performance of breeding sows, slows growth rates among grower pigs and is considered the most costly disease facing North American pork producers.

Several strategies have been used to address PRRS including the establishment of more than two dozen regional PRRS elimination projects across the US.

Dr Lisa Becton, director of swine health information and research with the National Pork Board, acknowledges it is hard to know exact numbers but a lot of US farms are still seeing recurring issues with PRRS both in terms of new outbreaks as well recurring outbreaks in farms that have already been affected.

Dr Lisa Becton - National Pork Board:

We don't really have a uniform way of being able to categorize or at least understand how many infections occur on a monthly or quarterly basis.

What we're trying to focus on is understand some of the basic questions still regarding PRRS immunology and even virology.

We know there's a mechanism in that virus that it can evade the immune system and it has different ways to evade how normal cells get rid of the virus.

That causes problems for us because even though we may vaccinate with one strain it does not confer complete or absolute protection against any other strain.

There's some things that we still really need to understand with this virus and even how does the virus persist in an animal, can it persist and for how long, so there's quite a few questions that we have out there.

Dr Becton says that any time you have a PRRS outbreak, it shakes your confidence in what you're doing.

She says even though there have been some re-breaks and people aren't sure why, there's still a lot of support for keeping these regional PRRS projects going.