PRRS: Four Small Letters, One Big Problem!
There are four pillars of PRRS control and to successfully control PRRS – you must apply all of them!
Pillar Number One: Biosecurity.
Please don’t fall asleep just because I said the ‘B’ word! In the pig industry we talk about biosecurity until we’re blue in the face. We are an industry of experts in biosecurity, but most of us are not putting it into practice. If we were, diseases wouldn’t spread between or around herds and unfortunately that is obviously not the case!
I’m not going to go through a step by step guide to biosecurity (or you would fall asleep!), but let’s think about how PRRS virus transfers between pigs.
A pig that is recently infected with PRRS will be excreting lots of virus in its bodily fluid:
|Fluid Type||Number of PRRS Virus per ml of fluid|
Now if we compare that to the amount of virus that is needed to infect a pig by each possible route:
|Entry Route||Number of PRRS Virus|
|In the Mouth||100,000|
|Breathed up the Nose||10,000|
From this we can work out the highest risk routes; for example a PRRS infected boar will be shedding 1,000,000 PRRS viruses per millilitre of semen, and all it takes is 1000 viruses to infect the sow by mating or AI. Therefore it only takes 0.001ml of raw semen to infect a sow; so basically any sexual activity will result in PRRS transmission from an infected boar to a sow/gilt. The other very interesting case is that through skin penetration it only takes 100 viruses. That means only 0.01ml of blood or saliva needs to get through the skin of another pig to infect it with PRRS. Think of the amount of saliva and blood contact that happens between individuals when it comes to riding, fighting or tail biting; or how the tiniest drop of blood on your needle as you’re vaccinating might pass PRRS from one pig to another. Most of us know what we should be doing, but thinking about the subject like this should emphasis to us how important it is, for example, for us to change our needles regularly: as often as possible, always between litters, always between different pens, and always between different groups. You might think you’re saving a bit of money getting more use out of a needle, but needles cost pence and take seconds to change. PRRS will cost you thousands of pounds!
One thing that is on our side when it comes to PRRS management is that the PRRS virus can only multiply in a pig (it can’t spread to other animals or humans), and it is very poor at surviving in the environment e.g. outside of the pig it will die pretty quickly, even quicker when you are applying good cleaning and disinfection! This environmental instability also means live virus spreading over any distance in aerosol is quite unlikely. There have been a lot of neighbouring farms blamed for spreading PRRS on the wind, when realistically it is much more likely to be the fault of a person failing to apply appropriate biosecurity.
Essentially the virus needs a non-immune susceptible pig to survive, multiply and spread, if it doesn’t have any pigs to live in, and it can’t live in the environment, it should disappear! This has been shown to occur naturally in closed herds where all animals became immune, and it can be achieved via vaccination and management.
For further information please contact Zoetis UK Limited, Walton Oaks, Dorking Road, Tadworth, Surrey KT20 7NS. www.zoetis.co.uk Customer Support: 0845 300 8034. Use medicines responsibly (www.noah.co.uk/responsible). Date of preparation: December 2017. AH861/17