Porcine reproductive respiratory syndrome virus (PRRSV) is the most economically impactful disease in pig production in the UK. The first ‘R’ is due to the reproductive signs you see when PRRSV infects ‘non-immune’ sows; you may see increased regular or irregular returns to service, and late abortions/early farrowing with litters containing mummies, stillborn, weak and/or apparently healthy piglets. The sows may also appear sick, have a fever, and may get purple/blue extremities (hence the traditional name of ‘blue ear’). During acute PRRSV outbreaks you may also see sick pigs with fevers in the feeding herd. You should always consider the notifiable diseases, particularly Classical/African Swine Fever, as a differential when you see pigs with high temperatures (≥40°C). In herds with endemic PRRSV, flare ups of reproductive signs may occur, but the biggest economic impact is via its affect on respiratory health, hence the second ‘R’ of PRRS. PRRSV particularly targets pulmonary alveolar macrophages, so it is the immune defences of the lung that are seriously compromised. This amplifies other diseases such as Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, Streptococcus suis, Haemophilus parasuis (Glässers) and influenza, resulting in increased coughing and mortality.
You may decide to either eliminate PRRSV or manage it within a herd. To eliminate you can either do a total farm depopulation followed by cleaning and disinfection, a break from production and restocking with high health animals, or a partial depopulation (weaning onwards) and vaccination-based virus elimination of the breeding herd. Both of these approaches have significant costs, but both can be very effective.
PRRSV can be well controlled long term within a herd, but this requires vaccination, good management, good biosecurity, and veterinary input with diagnostics and monitoring:
- Vaccination — control must involve the use of modified live PRRS vaccines. Only one brand of PRRS vaccine should be used within a herd
- Good management — gilt management is critical for PRRS stability. Ensure gilts are well isolated, vaccinated and acclimatised before being introduced to the breeding herd. The herd should be managed in a way which prevents spread of the virus, mostly through implementing good vaccination and biosecurity
- Biosecurity — implementation of external biosecurity is vital to stop PRRSV entering the herd. Even if a herd is PRRSV positive, a new strain can enter and cause severe disease. Internal biosecurity is vital to stop PRRSV spreading within the herd. Ideally all stages of production should be ‘all-in-all out’ by air space. Staff should be organised so they are dedicated to one stage of production each day. If this is not possible the day should be organised so that people are working from the most vulnerable animals to the least, change clothing, boots and washing hands between, and not going back if at all possible
- Diagnostics and monitoring — PRRS diagnostics can be tricky, and sometimes expensive, but they are very important to understand the PRRS situation in the herd, which must first be understood before it can be properly managed. Beware that live vaccines can cause positive results on PCR testing and immunohistochemistry.
A study demonstrated that a mild outbreak of PRRS on a finishing unit costs €3.77 per pig, and a mild PRRS reproductive disease costs €126.79 per sow per year (Nathues et al, 2017). The economic impact of PRRS can be limited by stabilising PRRS within the herd. Suvaxyn PRRS MLV is a modified live PRRS vaccine that can be administered from 1 day of age giving the earliest protection possible with immunity by weaning. The vaccine has a 26-week duration of immunity, meaning pigs have protection until slaughter, and giving the longest efficacy in gilts and sows.