There is a saying in the pig-farming community: “African swine fever can kill a pig farm, but PRRS can make life worse than death for one.” Many farms have probably been hit by PRRS, resulting in heavy losses. Today, let’s discuss how this disease develops.
PRRS virus primarily replicates and spreads by infecting macrophages, which are abundant in the lungs. This can then cause damage to immune organs, as well as systemic vasculitis. In the lungs, it causes diffuse interstitial pneumonia and extensive pulmonary consolidation. The alveolar walls thicken and lose their ability to exchange oxygen. The lung interstitium proliferates. This is why, once PRRS infection reaches the middle or late stages, the entire lung becomes a solid mass, with almost no gas-exchange function except in the trachea. This lesion is irreversible.
PRRS is also known as reproductive and respiratory syndrome. In other words, PRRS is closely associated with reproductive problems in sows and respiratory problems on pig farms. PRRS is also an immunosuppressive disease. Once PRRS occurs, pigs may also have reductions in antibodies to circovirus, pseudorabies, and swine fever, and many of the vaccines administered may fail to induce immunity.
Once PRRS breaks out on a pig farm, the losses can be severe: large numbers of sows miscarry, many pigs cough and gasp for breath, and piglets develop uncontrollable diarrhea in the farrowing room. There may be many stillborn and mummified fetuses, and sows may fail to conceive after mating or fail to come into heat. These reproductive problems are all caused by PRRS, which has a significant impact on the herd.
Many farmers also ask whether their pig farms should use a PRRS vaccine.
First, if your farm is PRRS-negative, substantial annual medication costs are needed to keep the herd PRRS-negative. PRRS-negative farms must strictly avoid using PRRS vaccines. Using a PRRS vaccine could cause the farm’s PRRS status to change from negative to positive, because vaccinating against PRRS is equivalent to the farm experiencing a mild case of PRRS. There is also a risk of sow miscarriage.
Next, many pig farms in China are PRRS-positive and stable. Stability can be achieved through medication and herd health management, or through vaccination. Farms that can keep their herds stable through medication should avoid using PRRS vaccines. For farms that achieve stability through vaccination, it is recommended to gradually reduce the number of vaccinations each year until vaccination is stopped completely. Long-term use of PRRS vaccines can readily lead to problems such as increased virulence. This is mainly because the PRRS virus can combine with other viruses to form new strains, increasing the risks to the farm.
Finally, there are PRRS-positive, unstable farms. These farms make up a large group that uses PRRS vaccines. However, the reality is that PRRS vaccines can only alleviate clinical signs after PRRS infection; they cannot prevent the herd from becoming infected. Therefore, PRRS vaccines are neither the only nor the best way to stabilize PRRS in a herd. Livestock farmers can choose medication-based elimination to stabilize PRRS in the herd as soon as possible, or combine elimination with vaccination.
In general, it is best to avoid PRRS vaccination. Vaccines are indeed not very effective at preventing PRRS in pigs. In clinical practice, many pig farmers have experienced infection or co-infection after immunizing against PRRS virus. Therefore, vaccination is not recommended as a way to prevent PRRS.
In summary, eliminating PRRS or keeping a pig farm PRRS-stable can help maximize the herd’s ability to resist ASF. For PRRS elimination, we recommend that producers use traditional Chinese antiviral preparations such as Beilijian and Zhongzhengkangsan on a regular basis. During a PRRS outbreak, in addition to using traditional Chinese antivirals, antibiotics such as tilmicosin (Zhujianzhuang) should also be used to prevent secondary infections.
If PRRS is completely eliminated, your pig farm will be very safe and will not suffer a high mortality rate. This PRRS elimination approach has also been developed through practical experience, and the results are very promising.