Tag Archives: PRRS

Doses in the administration of Animal Health vaccines

Vaccines are not dosed in the same way as antibiotics.

A vaccine dose does NOT depend on body weight: The mechanism of action of vaccines is different to that of antibiotics and, as a result, the dose does not depend on the body weight of the target animal. A vaccine does not have to be distributed throughout the body and the vaccine components (antigen and adjuvant) do not act directly on the pathogen. In general, the activity of vaccines starts at the inoculation site itself by means of a rapid and local innate response. As a result of this phase, antigen-presenting cells are activated (dendritic cells and/or macrophages) that are responsible for processing the antigen and carrying it to the closest lymph nodes where they activate specific T and B lymphocytes, thereby starting the acquired immune response. In a second phase, effector T cells and B plasma cells are generated that produce cytokines and antibodies respectively, ensuring a concentration in the blood and tissues that is independent of the age/weight of the animal for the same dose of vaccine.

Does the same thing happen with human vaccines?

In human medicine, the vaccines that are used in children (paediatric vaccines) and in adults are the same and are used in the same dose. It would not occur to anyone to reduce a vaccine dose for children because of the risk of inadequate protection that this would entail. There are examples of toxoids (tetanus), inactivated vaccines (rabies) and live vaccines (varicella) where the dose is the same for children as for adults.

How is a vaccine dose determined?

The dose that is indicated in the leaflet for each vaccine is the one that has been shown to be effective during the different research phases in the target animal species and with the minimum age that can be vaccinated. On the basis of these studies, the health authorities in each country recommend the specified dose for each product. For this reason, the dose should be administered irrespective of the age of the animal.

There are some older products that have different doses for different age groups, but this would not be allowed nowadays.

What harm can be done by a dose that is lower than the recommended one?

Administration of a vaccine dose that is lower than the recommended one can result in a lower immune response, compromising the protection of the individual against the pathogen.


Is it possible to administer a live PRRS vaccine to animals already infected to stop the piglet’s infection?


Vaccinating the infected sows with a PRRS live vaccine does not seem to help to reduce the clinical signs. It normally reduces the clinical signs in sows when the vaccination is administered before the infection with the field virus. The non-immunised gilts are animals that can help in the replication of the virus on unstable positive farms, and because of this, the vaccination and adaptation before their introduction on the farm is recommended to reduce the clinical signs in these animals and to lower the circulation of the virus on the farm.

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A PRRS outbreak is causing 40% of stillborn piglets. Is it possible to administer a live vaccine to animals already infected to stop the piglet’s infection? Could a vaccine of this kind reduce the number of dead piglets and stop the transmission to new litters?

In this case, an outbreak of stillborn piglets (around 40%) is described, and it is suspected that the cause is PRRS. When we ask for more information on the case, we are told:

Most of the affected litters belong to first parity sows.

No PCR diagnosis of PRSSV on deadborn piglets has been carried out.

Gilts come from another farm, their health status regarding PRRS is unknown, and they are not vaccinated.

The semen used for AI has an external origin.

Vaccinating a newly infected animal with the PRRS field virus does not have practical advantages for the animal, because the immune system already has a strong antigen to process the answer needed. The difficulty does not lie in the individual animal, but on an animal population, because not all the animals become infected at the same time. The PRRS virus is not very contagious, and because of this, the contamination of all the sows on the farm with the field virus will take a long time if we leave the virus to circulate naturally. In these cases, the clinical symptomatology will go on until the last sow becomes immunocompetent against the virus. This can take several months or even years, when negative subpopulations appear on positive farms.

PRRSV-naive gilts are another source of active virus replication when they enter an unstable farm with an active virus circulation. In this case, a situation like the one described can appear. Nevertheless, to be sure, we must diagnose if the PRRSV is the agent responsible for the mortality of the piglets.

If the PRRSV diagnosis is confirmed in the piglets and the gilts that come from an external source, the next step is to reduce the virus circulation on the farm, mainly in the gilts, that may be where the virus proliferates. In cases like this, we recommend vaccinating all the sows to induce some kind of immunisation against the PRRSV and to reduce the clinical symptoms in the sows NOT infected at the time of vaccination. We are not going to avoid the infection of new litters with the field virus, but we can reduce its negative impact and the clinical signs if there is an immunisation previous to the infection.

There is the risk of not achieving enough immunological protection against the field virus with some vaccines, but as of today there is not a technology that allows us to say, with confidence, which is the most effective vaccine for a certain farm. Even after sequencing the virus and choosing the vaccine with the highest homology degree, nothing guarantees us that it will be the most effective one on the farm.

The strategy that we use in clinical outbreaks like this (with a confirmed PRRS diagnosis) is:

The vaccination of all the sows and boars on the farm with a live vaccine on the same day (we will vaccinate the most immunodepressed sows the following week: on the insemination/mating week and the farrowing week). The goal is to obtain a quick immune response against the PRRSV in all the sows in the group, and we expect a certain degree of cross-protection between the vaccine and the field strains. Revaccinate 4 weeks later with the same protocol. 

The gilts that enter the pregnancy stage must be well immunised and non-viraemic (PCR-negative to PRRS and IgG-positive). The vaccination and adaptation of viraemic animals on the farm and allowing enough time in quarantine until they do not excrete the virus (12 weeks is normally enough) are recommended. This is very important for the future control of PRRS on the farm. 

Buying PRRS-negative semen to inseminate the sows. 

Knowing if the virus is circulating in the nurseries. If there is circulation, implement biosecurity rules to reduce the transmission of the virus to the sow herd. 

After the second vaccination of the sows, evaluate if there are still viraemic piglets at birth. If this improves, we can keep the vaccination and adaptation programme only in the gilts in quarantine. 

What is a correct way to choose a PRRS sow vaccination program? When PRRS vaccination of piglets is needed?

Answered by: Enric Marco

Piglet vaccination is usually done when we would like to reduce PRRS virus circulation on the growing phase. Vaccine will reduce the amount of PRRS virus shed by viremic animals and also will reduce duration of shedding. Those reductions are not spectacular but can help to control the PRRS virus circulation.
Sow PRRS vaccination is used in two ways. The first one is to bring back to normality the farm after an outbreak; the second one is to help the farm to maintain stability by avoiding PRRS virus recirculation among sows which will produce viremic piglets.
By vaccinating sows, immunity will be higher and more stable helping to reduce subpopulations of sows which we know are the responsible for on farm virus recirculation.

What we have learned about PRRS disease after 20 years?

The Porcine Reproductive and Respiratory Syndrome has been the disease that has changed many ideas in global pig production in the same way as HIV did in the human population. Listening to the testimonies of opinion leaders in this video, it is fair to say that we have learned a lot and that the video captures two visions: that of the scientists and that of the practitioners.

Conceptually, there are certain similarities between the PRRS and AIDS, the latter appearing in the 1980s, whilst PRRS appeared in the 1990s. In both cases, they are very serious diseases in the affected populations and despite the fact that there is still no cure, there has been much progress in our knowledge of the viruses that are responsible for them, and how to improve control strategies for them. Improved biosecurity in pig production is equivalent to the educational measures used to reduce the risk of sexual transmission. 
Fortunately, today the mortality associated with HIV, despite having been very high, has been dramatically reduced and is associated with concomitant diseases, sounds familiar? 
There are also major differences between the two syndromes – the acquired immunodeficiency syndrome remains a potential cause of death throughout the world, with an estimated 37 million affected individuals* and, making a rapid calculation on the basis of a population of some 7,000 million, this means about 0.5% of the world population, and this is where it differs radically from the PRRS virus, as only 5% of the world pig population is considered to be free of the Porcine Reproductive and Respiratory Syndrome. 
If we look back to the first cases of both diseases, a great deal of time and money has been invested in deepening our understanding of both syndromes and in both cases there has been a great deal of progress so that today it is possible to live with both viruses and lead a dignified life as an AIDS sufferer or achieve an acceptable level of production if you are a PRRS-positive producer. 
Indeed, it is one of the lessons that our opinion leaders (the practitioners) have learned, we have learned to live with the disease, although there is still a great deal to learn because, as Alberto Stephano says, just when you think you know everything there is to know about the PRRS virus, you get PRRS again. The approach by our colleague Carlo Lasagna using an (Italian style) football metaphor is also worthy of note, firstly defence (biosecurity) and then good attacking (optimization of control measures). 
As for the scientists, we have learned how to diagnose it, monitor it, sequence it and even how it interacts with the immune system or how it evades it, we have learned how it can mutate or vary genetically, and a key area in which there has been a great deal of research (especially by American universities) has been the main routes of transmission of the disease (as with HIV, the greatest efforts have been devoted to minimizing transmission). 
Key aspects on which work is being carried out in the sector are biosecurity, both external and internal, and immunization etc., which should be understood as a series of measures, because if they are taken separately, the probability of failure increases exponentially. 
Following a more modern approach, Darwin Reicks points to air filtration for the control of aerosols and also, more recently, the probability of working with animals that are genetically resistant to the Porcine Reproductive and Respiratory Syndrome virus.

Does vaccination of 8 weeks old pigs protect them against PRRS until slaughter?

Answered by: Tomasz StadejekPublished on: July 21
Vaccination of 8 weeks old pigs can protect them against PRRS until slaughter. However it is very important to remember that the protective immunity against PRRSV develops slowly and it takes at least 4 weeks, or longer.

So, pigs vaccinated at 8 weeks of age should be protected against the challenge at least until 12 weeks of age. Even then vaccinated pigs can get infected. The level of cross protection of a given vaccine and a given wild type strain can be different. The same vaccine can have different efficacy in different farms.
However, even if the cross protection against the infection with filed PRRSV is not ideal, it is usually sufficient to protect against clinical disease caused by the infection and limits virus shedding.

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Why in 5 weeks old piglets respiratory disease due to PRRSV appears despite vaccination of sows with a MLV PRRS vaccine every 4 months, and which have high level of antibodies?

Answered by: Tomasz Stadejek
Respiratory symptoms in piglets can be caused by a number of pathogens. In order to identify a causing factor it is necessary to conduct laboratory diagnosis.
Confirmation of PRRSV role can be performed through PCR analysis of lungs from sick animals. If such material is not available, serum obtained from pigs from different age groups can be tested by PCR or ELISA. Detection of PRRSV in serum of sick animals indicates viremia and can be considered as a proof of the virus’ role in respiratory disease in a given age group.
Appearance of antibodies against PRRSV in pigs at about 2 weeks from the start of the symptoms also supports such diagnosis. However, analysis of serological results is complex and we have to keep in mind that maternal antibodies can be detected in pigs for several weeks. This is why it is so important to test sera from groups of pigs of different age (e.g. 4, 6, 8 weeks of age etc.) and to assess the dynamics of seroconversion (compare the levels of antibodies in different age groups).
If diagnostic results confirm the role of PRRSV in the clinical disease in piglets, it may suggest that the vaccination program in sows is inefficient. It can be caused by insufficient cross protection against the local strain, poor colostrum management as well as vaccination errors.
The impact of limited cross protection can be diminished with the increase of frequency of mass vaccination in sows, from 3 to 4 per year. Vaccination every 3 months will likely increase the level of passive immunity.
The level of antibodies in vaccinated sows is difficult to correlate with the level of immunity. Antibodies detected in ELISA are directed against capsid protein and they are not protective. Moreover, sows from stable farms, where PRRSV does not circulate, and which were vaccinated with modified live vaccine multiple times, can have low or undetectable in ELISA levels of antibodies, and still be immune

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Which few words come to mind when you hear PRRS?

The Porcine Reproductive and Respiratory Syndrome is at the centre of every conversation between farmers and swine veterinarians in the most important pig producing countries worldwide, with the exception of Australia, Brazil, Argentina and some Scandinavian countries.
If you are working in an environment that is positive for the porcine respiratory and reproductive syndrome, control of the disease is the key element in all discussions. The vets in this video reflect perfectly what PRRS means when someone mentions this BIG WORD.
PRRS means problems, regardless of whether it is the respiratory or the reproductive form of the disease, everything gets worse when PRRS is around, says Albert Rovira in his contribution, and this is really relevant because working in diagnostics as he does, there are few cases where the porcine respiratory and reproductive syndrome is not involved. It´s pretty well known that this disease is normally at the centre of any respiratory coinfection in piglets and fatteners.

However, for Alberto Stephano the key word is frustration and it certainly is, he is absolutely right because, in the past or even today, a great deal of effort has gone into to controlling this syndrome and yet there have been many failures. Moreover, another of our speakers, Darwin Reicks from the Swine Vet center in Minnesota, agrees on that statement and I loved one of the quotes when he says: It seems the virus is often one step ahead of us . 
Coming back to Europe and from Barcelona University, one of the most highly regarded European researchers in the porcine respiratory and reproductive syndrome, Enric Mateu, introduces a new word to us: challenges, because of the difficulty of control in the long term, and this is also a key point we would like to mention. We have enough knowledge for this disease to be controlled, but the question here is for how long? It´s clear and even though it is a parameter, some vets are using it as an indicator, reinfections do exist, and the question that many producers are asking is… When will the next PRRS outbreak occur on my farm?
Quim Segales and Luc Dufresne concur on another shocking word, devastation and devastating disease, but not only when the disease affects a negative farm for the first time, but with the persistence of the virus circulating with a heterologous pattern around the multiple buildings of the farms.
However, for practitioners like Albert Finestra and Alberto Morillo, the disease symptoms are at the top of the list of words that come to mind, and as well as that, Albert adds that more than words you´ll have mixed feelings, such as panic amongst others. Carlo Lasagna from Italy agrees on panic and he adds a crucial term, not mentioned so far….disappointment for the farm´s employees.
Last but not least, and as usual, from the American point of view and with a tremendously practical vision, Scott Dee reflects on what the porcine respiratory and reproductive syndrome really means for producers and veterinarians…and it means ECONOMIC LOSSES.
We believe that the highlighted words (in bold) in the text provide a true summary of what this disease means for everyone involved in this industry. Let´s not lose hope!!!!!!


Busquet*, M.; Blanch, M.; Torrents, D.; Verdaguer, J.; Sánchez-Matamoros, A. *Corresponding author (marta.busquet@hipra.com)
HIPRA, Amer (Girona), Spain

Hipradermic®, a needle-free injection device, has been designed as a new option for the intradermal (ID) vaccination of the MLV UNISTRAIN® PRRS on swine farms. Intradermal and needle-free vaccination in pigs has been reported to improve animal welfare, to generate an effective immune response and to be easy to administer, amongst other benefits (Chase et al., 2008). The aim of this study was to demonstrate that UNISTRAIN® PRRS administered using Hipradermic® was as safe and efficacious as when administered via the conventional intramuscular (IM) and intradermal (ID) route in a mass vaccination in sows.

Click here to read the article.


Miranda*1, J.; Torrents1, D.; Busquet1, M.; Fenech1, M.; Mateu2, E.; Díaz2, I. *Corresponding author (joel.miranda@hipra.com)
1HIPRA, Amer (Girona), Spain. / 2CReSA (Centre de Recerca en Sanitat Animal), Barcelona, Spain.
Current knowledge on PRRS virus immunology is still limited but it seems clear that modi ed live vaccines (MLV) are a reasonable choice for the immunisation of pigs (1). Cell-mediated responses after MLV vaccination could be responsible for limiting the duration of viraemia, and consequently the spread of the virus (2). Recently, interest in intradermal vaccination has increased due to research on the skin and subcutaneous tissues immunology. Although the intradermal PRRSV vaccination has been investigated (3), the high variability between different virus isolates makes it advisable to assess the intradermal response for each vaccine strain. The aim of this study was to compare the cell-mediated immune response developed in gilts vaccinated intramuscularly and intradermally with UNISTRAIN® PRRS.

Click here to read the full article.