Tomasz Stadejek – PRRSControl

Can be verified with laboratory methods if the purchased piglets were vaccinated against PRRSV?

Tomasz Stadejek — Wed, 23 Aug 2017 08:00:20 +0000

An outsourced fattening farm receives piglets claimed to be vaccinated with a MLV PRRSV vaccine. Several weeks after arrival pigs start to exhibit respiratory symptoms compatible with PRRS. Can be verified with laboratory methods if the purchased piglets were vaccinated against PRRSV? Does it make sense to vaccinate them upon arrival? Serological response of animals vaccinated against PRRSV can differ between individuals. Some pigs may not show any response, or very low level of ELISA antibodies. Positive results of ELISA prove contact of a population with PRRSV (wild type or modified live vaccine). The larger the number of pigs tested, the more accurate is the diagnosis. PRRS ELISA can detect antibodies starting from 10-14 days after the contact with the virus. Some pigs can seroconvert later than others. ELISA results are very difficult to interpret in individual pigs. The antibodies detected in ELISA are usually targeted against nucleocapsid protein. These antibodies play no role in immunity against PRRSV. There are no commercially available ELISA kits (or experimental ones) to verify the level of immunity. Pigs negative in ELISA can still be immune. Vaccines against PRRS usually don’t protect pigs against infection for entire life. They are intended to limit virus shedding […]

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Is it important for large farms to perform sequencing of a local PRRSV strain before starting the vaccination program?

Tomasz Stadejek — Wed, 27 Jul 2016 13:59:38 +0000

Were there identified field strains heterologous to a MLV PRRS vaccine and where the vaccine lacked efficacy? Is there any risk for a farm to change the vaccine against PRRS? Is it important for large farms to perform sequencing of a local PRRSV strain before starting the vaccination program? The level of cross protective immunity following natural infection, or following vaccination with modified live vaccine depends on the antigenic relationship of an immunizing and a challenge strains. Complete protection (sterile) is possible if the immunizing and challenging strain is the same. Only in case of highly virulent strains the immunity against challenge with the same strain not complete immunity has been described, still, it was protective against clinical disease. It could be assumed that always the vaccine strain is heterologous to the field strain of a farm, and in effect the protection of vaccinated pigs against the challenge is only partial. The level of cross protection will depend on the antigenic relationship of the vaccine and the wild type strain. In extreme cases the level of cross protection may be seen as not satisfactory. It has to be remembered that environmental conditions and other infectious factors can impact the level […]

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

Tomasz Stadejek — Thu, 21 Jul 2016 08:00:34 +0000

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. You can ask your own question! Visit Pig333.com and submit your question to our experts. Czy szczepienie 8 tygodniowych prosiąt daje odporność na PRRS do końca tuczu? Szczepienie szczepionką żywą 8 tygodniowych świń może zabezpieczać je przed PRRS do końca tuczu. Należy jednak pamiętać, że odporność poszczepienna narasta stopniowo i trwa to co najmniej 4 tygodnie. W związku z tym świnie szczepione w 8 tygodniu życia nie powinny być narażone na kontakt z wirusem do […]

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Which of vaccination protocols (mass vaccination or 6/60, or others) will be more effective in PRRS elimination from a herd? Can we introduce naïve replacement gilts, or rather vaccinated?

Tomasz Stadejek — Thu, 14 Jul 2016 08:00:19 +0000

Having in mind that PRRSV can persist in tonsils for a year, and that following elimination procedure, after 8 months the diagnostic results are negative, can we introduce naïve replacement gilts, or rather vaccinated? If vaccinated, with what vaccine, modified live or inactivated? The question should be more specific, are we talking about elimination of PRRSV circulation in sows and production of PRRSV free piglets (stable herd), or the plan is to obtain complete elimination of PRRSV and specific antibodies (negative herd)? At present the most often used criteria are those developed by Holtkamp and co-workers. Sow farms with animals reacting positive in ELISA and PCR, and showing clinical symptoms of PRRS are termed positive unstable (category I). Sow farms positive stable (category II) are ELISA positive but in piglets at weaning PRRSV was not detected in the last 90 days, in at least 4 consecutive tests, and no clinical symptoms of PRRS are observed. In provisionally negative farms (category III) naïve replacement gilts remain seronegative after 60 days from introduction to a seropositive herd. Lack of seroconversion after direct contact with seropositive sows proves that older sows do not shed PRRSV. Negative sow farms (category IV) are PCR and […]

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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?

Tomasz Stadejek — Thu, 07 Jul 2016 08:00:25 +0000

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 […]

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Can we observe acute clinical symptoms of PRRS in sows with low titers of antibodies against PRRSV?

Tomasz Stadejek — Thu, 12 May 2016 08:00:21 +0000

Most serological analyses for PRRSV sare made with ELISA. There are several ELISA kits on the market but most of them detect antibodies against nucleocapsid protein. This protein is being produced in large quantities in infected cells and stimulates strong seroconversion. However, these antibodies have no impact on protection against reinfection. So, we can only interpret the seroconversion detected in ELISA as a proof of contact of a pig with PRRSV. Not as a proof of immunity against infection or clinical symptoms. The problem with serological assessment of sows using ELISA is that most of kits give some percent of false positive results. The phenomenon has been known for many years but the problem was not fully solved with new generations of ELISA kits. Another aspect of interpreting ELISA results is that the method can be used for assessment of populations and not for individuals. After infection or vaccination antibodies start to appear at 10-14 days, the level grows for several weeks and then decreases. Some animals can become seronegative at 4-6 months post exposure. It is dependent of the immunizing strain and also of the dose. In a stable sow herd (no virus circulation, no vertical transmission) gilts can be […]

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Would you recommend the vaccination of a PRRS seropositive herd, even there are no clear reproductive and respiratory signs, or would you recommend specific management measures?

Tomasz Stadejek — Thu, 05 May 2016 06:01:48 +0000

Not always we can observe clear clinical symptoms of PRRS. More often, in endemically infected farms, the disease affects the production parameters and its diagnosis can be made based on detailed analysis of those. If precise figures are not known or the losses are not evident it is good to evaluate the virus circulation, either with serological methods (ELISA) or PCR. If PRRSV starts to circulate pre-weaning or early post weaning it is indicative for unstable reproductive herd. It means that there is vertical transmission from sows to piglets. Even if the losses in the reproduction are minimal (only gilts maybe affected) the price is paid in piglets. Not necessarily directly due to PRRSV but more often due to multifactorial infections as PRRSV modulates immune system. It would be strongly recommended to vaccinate replacement gilts at quarantine, and the reproductive herd, in order to eliminate vertical transmission and increase maternal immunity in piglets. If the virus starts to circulate later in nursery, vaccination of piglets could be considered. It has to be kept in mind that the immunity against PRRSV is slow to develop. Piglets should be vaccinated at least 4 weeks before the infection is expected to occur. The […]

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What are the differences between type 1 and type 2 PRRSV vaccines currently available with regards to immunogenecity in sow herds?

Tomasz Stadejek — Thu, 28 Apr 2016 09:25:37 +0000

We should remember that the protection means different things for virologists and practitioners and producers. The best is when immunization protects completely against the infection. This is rarely achieved in the field conditions.What we are aiming at, using immunization protocols, is to protect against the clinical symptoms, and restricting virus shedding and transmission. In other words we are aiming at clinical protection and limiting the virus presence in the farm environment. The cross protection is best if induced by the strain that is used to challenge the pigs. Some scientific reports show that it can be lifelong, not only in terms of clinical symptoms but also can protect against the infection. The further away antigenically is the challenging virus from the immunizing virus, the lower is the cross protection. The problem is that we don’t know how to measure antigenic relationship between strains that would allow us to predict the level of cross protection (also vaccine induced). Today there are modified live virus vaccines produced from multiple genetic lineages of either Type 1 or Type 2. In theory better protection is provided by the vaccine of the same genotype as the wild type virus. Genetic classification of the vaccine strain […]

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