PRRS (Pig Reproductive Respiratory Syndrome) is one of the most feared diseases by farmers for the economic impact that their entry into a farm can cause. Jordi Baliellas, the veterinarian of the GSP Lleida (Grup de Sanejament Porcí), tells us about the characteristics of this disease and about the tools we have to prevent its entry and/or spread on the farm.

Jordi Baliellas, veterinarian of the GSP Lleida. Photo: J. Baliellas. 

What is the affectation of PRRS in Spain?
The first detection of a PRRS case in Spain, which was made public in 1991, has come a long way in terms of scientific knowledge. However, it is a very complex disease, against which there is no single form of control. Different tools have been created that They help control the disease, but unfortunately, we still have a lot to discover.

What consequences does the disease have on animals?
When people think of PRRS, they usually think of a reproductive issue, whose primary manifestation is abortion, loss of sow gestation, which generally occurs in advanced stages, around the month before delivery. But we also have a respiratory issue that usually affects piglets, infants or transition. However, adult pigs tend to be more resistant to this respiratory issue, although some strains and situations can also generate this type of case in adult pigs.

What are the main symptoms that can indicate that we have this infection on the farm?
In the case of a sow farm, the most common are problems around childbirth, which are usually abortions at the end of pregnancy or problems of weak births and lactating piglet mortality. However, there are some strains whose first manifestations are respiratory problems very similar to the flu, also causing fever. Therefore, on a sow farm, the rancher or veterinarian should suspect that he has PRRS if he detects respiratory or reproductive problems at the end of pregnancy. On the other hand, in the transition and fattening phases, the issue is respiratory and is very similar to other viral problems, aggravated by the increase in secondary diseases. In this case, we find animals that stop eating, that have a fever, cough, pneumonia from these symptoms and from taking samples for PCR, which is determined if the farm has PRRS problems.

How is it transmitted?
The main transmission routes of the virus are replacement animals, semen, transport vehicles without proper cleaning or disinfecting, visits, and all the material that enters the farm. However, we can contemplate other risks such as corpse transport and inadequate slurry management. For all these reasons, biosecurity is the most crucial tool in PRRS control. Finally, there is the aerogenic transmission route, being usually the least frequent. Besides, there are few studies on how far the virus can be transmitted and under what climatic conditions.

What role does biosecurity play then in reducing the risk of PRRS entry into a farm and its dissemination?
It is crucial. If we want to prevent the virus from entering, we have to focus our efforts, first of all, on improving everything related to external biosecurity, everything from outside the farm that can help introduce the virus. In this sense, biosecurity measures must be applied to correctly control aspects such as replacement, semen, animal transport vehicles, visits and materials. When the external biosecurity measures fail, and the PRRS enters the farm, it is when the internal biosecurity measures must be efficient, that is, all those measures that are applied to prevent the spread of the virus between animals of different ages and different areas. About this point, much has been studied about the importance of pathways such as iatrogenic through needles, since a small drop of blood can contain a large number of viruses that can infect many animals. In this sense, among the internal biosecurity and adequate management measures that must be applied, the frequent change of needles, the use of clothing and footwear in phases, limiting adoptions, working with batches "all inside"/" all outside" to guarantee good cleaning and disinfection, etc. These measures are what will allow us to control the virus inside the farm and reduce the effects that its presence can cause.

"It is a very complex disease, against which there
is no single form of control."

Is there not, therefore, a single treatment to end PRRS?
The best treatment is prevention, that is, prophylaxis, based on good external and internal biosecurity. On the other hand, in Spain, we have vaccines registered with different strains. The combination of both can offer some protection. On the other hand, since PRRS often generates immunosuppression in animals, we find secondary diseases to the virus, many of them bacterial, such as streptococci, Glässer, colibacillosis... that we must monitor and manage the presence of secondary pathogens.

How long can it take to have a PRRS free farm?
Typically, three different stages are proposed: a first one, in which we detect the presence of the virus and which lasts for a few months; a second one that is stabilisation, which means that animals have antibodies, but we no longer detect the virus and the PCRs are negative; and a final phase, the eradication of the disease, in which measures such as stopping vaccinating, improving biosecurity measures to prevent the disease from entering again. Usually, between detecting a PRRS outbreak and finally getting a PRRS-free farm, it takes at least one to two years.

And what might the economic impact of the PRRS be?
This virus, which only affects the pig species, is typified as the virus that causes the most economic losses in the pig sector worldwide, and its impact is highly variable since it depends on many factors. Not all typified virus strains are just as virulent, which also influences economic losses. In this sense, we can go from having losses due to an outbreak of PRRS of about 30 euros per sow to 500-600 euros per sow. That is, on a farm of 1.000 sows, losses can go from 30.000 to 600.000 euros per outbreak.

What are the main future challenges to fight this disease?
At the genomics and sequencing level, the investigation of specific genes that code by pathogenicity, and control mechanisms based on the stimulation of the immune system, with the generation of new vaccination strategies, can be if sufficient economic resources are allocated, options that will help us in the control of the PRRS. However, I think what we have to do is apply what we already know works in the prevention and control of PRRS. Unfortunately, we still find farms that are not implementing specific measures that we know are effective. From there, we hope that in the future science will provide new measures that help us control the PRRS.