PRRS stands for ‘Porcine Reproductive and Respiratory Syndrome’. The PRRS virus likes to multiply in a particular cell type of the pig called a macrophage. A macrophage is like a tiny Pac-Man which patrols the body looking for invaders (bacteria and viruses). When it finds an invader in the body, it gobbles it up, digests it, and then tells the rest of the immune system what it found so the pig can create antibodies and fight the disease. When PRRS infects a macrophage it will no longer be able to complete its Pac-Man function. The PRRS virus essentially wipes out the first line defences of the pigs immune system.
Reproduction is at risk
When PRRS first infects a gilt/sow and she has no immunity to the virus she will develop a fever, and this could lead to regular or irregular returns as she might not conceive, or might lose an early pregnancy, as she is sick. The more dramatic reproductive signs are seen when the PRRS virus infects a non-immune gilt/sow in her last third of pregnancy. In the first two thirds of pregnancy the PRRS virus can’t cross the placenta from the sow to infect the piglets. From around day 85 of pregnancy, PRRS can directly infect the piglets in utero. When this happens it can lead to early farrowing with litters containing a mixture of mummies, stillborn, weak or apparently healthy piglets.
The effects on the respiratory system
The PRRS virus particularly likes to infect and replicate in macrophages living in the lungs, so it is the immune defences of the lung which are seriously compromised by PRRS virus. This makes the pig vulnerable to other disease which infect the lungs e.g. Enzootic Pneumonia (EP), Actinobacillus pleuropneumoniae (APP), Influenza etc. Usually, when you see coughing problems in a herd with PRRS, they are most likely caused by PRRS making the pig more susceptible to other diseases, rather than the direct action of the PRRS virus itself.
More than two ‘RR’s?
So that explains the two ‘RR’s in PRRS. However, nothing with PRRS is simple. There are many other clinical signs and consequences of PRRS that are not directly respiratory or reproductive. However, a lot can be linked to our understanding of PRRS damaging the pig’s immune system:
Increased levels of endemic disease
Decreased growth rates
Increased mortality rates
So what can we do to protect our pigs from PRRS? You can find updates in our ongoing PRRS blogs.
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. AH860/17
Laura graduated from the Royal Veterinary College in 2009; after her veterinary degree she went to the University of Nottingham to undertake a PhD specialising in enteric disease of the young pig. After being awarded her PhD Laura spent a very enjoyable three years in a specialist pig practice in the South West of England. She then took the leap into Industry and joined the Zoetis pig team in September 2016.
She decided on specialising in pigs before qualifying as a vet and has not looked back since; she is very passionate about welfare and the success of British Pig Farming!
In her free time Laura is also passionate about good food and wine, fortunately the eating and drinking is balanced out by the love of walking, trips to the gym and Sunday morning runs.