Management – PRRSControl

How to immunize a sow herd during a PRRS outbreak?

Daniel Linhares — Tue, 19 Sep 2023 14:01:58 +0000

What is the ratio of serum acclimatization used in USA when PRRS break out? How long would be the interval to vaccinate with a MLV when the PRRS is unstable in the farm?

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PRRSv infection in a boar stud in Mexico, how to manage it in terms of management and diagnostic?

Enric Marco — Fri, 23 Apr 2021 09:30:39 +0000

Our boar stud broke with PRRS one month ago (PCR positive and ELISA positive with very high titers). We gave 2 doses of Inmuno PRRS and then took new samples and grouped them in 3 pools of 5 samples each depending on the titer (high, medium, or low). We are waiting for the results, but is this the right way to make pools? And to introduce new boars, do we have to wait for the current animals to be negative and for the titers to drop? ELISA positive results; How should they be interpreted? First, it should be noted that ELISA readings (S:P ratio, commonly called titers) are not directly related to protective immunity. Interpretation of ELISA serological test readings should not go beyond saying whether or not there has been contact with the virus (Christopher-Hennings J, et al. 2002). Therefore, grouping the animals to be tested by high, medium, or low values should have no impact on the PCR values to be obtained. How many samples can a pool contain? As for how many samples a pool can contain, it will depend on the expected viral concentration. Under commercial conditions usually pools of 5 samples are taken, […]

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PRRSV immunization of pigs in positive unstable fattening units: Is it better to vaccinate the pigs at the origin or at the arrival?

Lars Erik Larsen — Wed, 18 Nov 2020 10:06:10 +0000

If you are producing PRRSV negative piglets at weaning from PRRS vaccinated sow herd but they are transferred to a PRRS positive finishing site (with PRRS related respiratory symptoms) at 40kgs, would it be sensible to vaccinate these piglets at weaning? Based on Lars Erik Larsen opinion, there are two different options to approach this situation: 1. Vaccinate the pigs at weaning, prior to shipment A lot of Danish herds are selling piglets to Germany and other countries and several of these pigs are vaccinated prior to shipment so vaccination at weaning is indeed a feasible solution. However, some of the pigs may remain viraemic so there is a risk that they may transfer the virus on to the finisher site, but if this herd is PRRSV positive anyway this will not be a problem. 2. Vaccinate the pigs at arrival to the finisher site We have also tried another solution in a single herd where we vaccinated the pigs at arrival at the finisher site followed by strict sectioning. We did that until all the sections contained vaccinated pigs and then stopped vaccinating incoming pigs. Using this approach, we pushed the circulating field strain out […]

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How should the quarantine, acclimation, and monitoring of replacement gilts be carried out on PRRS-positive farms?

Enric Marco — Tue, 28 Jul 2020 12:53:26 +0000

Length of the quarantine: When we want to introduce negative replacements to a PRRS positive farm, the quarantine, or acclimation rather, must be long. “Long” meaning a period of not less than 2 months, because during this period our intention is to infect the new arrivals, giving them time to recover from the infection and lose their status as virus shedders before introducing them into the farm and starting to work with them. PRRS status of the gilts when entering the breeding herd: The aim is for the gilts to be introduced to acquire immunity to PRRS, and therefore become ELISA positive, but without shedding the virus; that is, they become PCR negative. How to perform the acclimatization? There are many techniques to achieve this status, although some work better than others, especially when it comes to the risk of producing disease. 1. Virus exposure with shedding animals: The most common method is to put the gilts in contact with animals on the farm that we know are shedding the virus. This contact should last about 15 days and should allow direct contact between the shedders and the gilts. 2. Live virus inoculation: Another more effective, but more […]

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What is the protocol for epidemiological surveillance of PRRS?

Enric Marco — Wed, 22 Jul 2020 13:21:49 +0000

Monitoring programs will differ depending on whether they are to be applied to a farm, an area, or a country, but I understand that in this case we are referring to a farm. The program will vary depending on the type of farm and its disease status. In the case of the PRRS, five possible statuses have been described: What sample and technique should we use to check the PRRS status in a NEGATIVE farm? To confirm a negative status, it would be enough to take 30 samples from breeding animals every quarter. This sample size would allow us to detect at least one positive with a 10% prevalence and 95% confidence. We are looking for the presence of antibodies, so an ELISA would be performed. What sample and technique should we use to check the PRRS status in a POSITIVE farm? With positive farms we are interested in getting them to the stable, inactive status, meaning that although they are positive, they produce negative piglets (PCR negative). Phase 1 farms: In this case, we would check the status of the breeding animals by taking 30 samples every quarter as in the previous case, but we are […]

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Can modified live PRRS vaccines be administered to pre-farrowing sows in order to pass the antibodies on to their piglets?

Enric Marco — Tue, 26 Nov 2019 07:26:46 +0000

Attenuated PRRS vaccines (Modified Live Vaccines) are not designed to pass immunity to the piglets, although they will. How do naïve animals response to PRRS vaccines? PRRS live attenuated vaccines do not produce high levels of circulating antibodies (IgG), which we want to find present in the colostrum (humoral immunity). In PRRS-negative animals the PRRS vaccines produce a weak serological reaction, although it allows cellular immunity development sufficient to protect against homologous challenges and partially against heterologous ones. How do PRRS ELISA positive animals response to PRRS vaccines? When the vaccine is administered to already PRRS-positive animals (animals with previous exposure to wild virus), as is most often the case, an increase in humoral immunity is triggered, which will naturally pass to the piglets. What do we look for when using MLV PRRS vaccines? Modified Live PRRS vaccines are used to stabilize the virus among the breeding herd and not so used to prolong the immunity passed to their piglets. For that reason, the recommended vaccination plan is a blanket vaccination plan instead of vaccinating few days before farrowing, as is recommended for other vaccines designed to protect the piglet during the first weeks of life […]

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In a sow farm positive for PRRS should vaccines be done blanket or weekly at 60 days pregnant?

Lars Erik Larsen — Thu, 31 Oct 2019 07:42:38 +0000

This is quite a difficult question to answer, as it depends of a wide range of factors, such as: Herd structure, herd size, herd organization, PRRS virus gilt acclimation strategies and the number of herds situated in the area (i.e. how high the PRRSV infection risk is). Sow vaccination programmes against PRRS virus In a previous question answered by Enric Marco on this site, the different possibilities of sow vaccination were described: from PRRSV blanket vaccination 4 times a year, to the 6/60 program. Enric Marco also analyzed the pros and cons of each strategy, so reading this previous entry is highly recommended. PRRS virus status of the herd Another important issue is the PRRSV status. For instance, we’d need to know the following information of the herd: Is the sow herd stable -antibody positive and virus negative- and weans PRRSV negative piglets? Is the PRRS virus circulating in the farrowing unit? Are there clinical signs of PRRSV in the nursery? PRRSV blanket vaccination Let’s do a brief review of this vaccination programme: Objectives: As I understand it, then the rational for the use of blanket vaccinations 2-4 times a year is partly to avoid that some […]

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PRRSv MLV vaccine: Abortion or stillborn in sows less than 3 weeks before farrowing?

Enric Mateu — Fri, 25 Oct 2019 13:16:19 +0000

Could abortion or stillborn happen in sows less than three weeks before farrowing if they are given a PRRSv MLV vaccine? And what can be the consequences of vaccinating for PRRSv during late pregnancy (2-3 weeks before farrowing)? Because when blanket vaccination is applied in the farm, it sometimes falls three to two weeks before farrowing in some sows. To answer this question, a previous explanation of the pathogenesis of PRRSv-induced abortion is required. PRRSv vertical Transmission Abortion in PRRSv infection happens as a result of fetal infection (mainly) and damage to the placenta. The virus reaches the placenta during the viremic phase of the infection. To cross the placenta and to reach the fetuses it is needed that susceptible macrophages are present in there. Fig 1. PRRSv vertical transmission and its implications. Susceptible macrophages are not significantly present until the late gestation (around 80-90 days of gestation) and therefore, the PRRS virus is thought not being able to cross the placenta at least until day 86. Usually the PRRSv infects one of the fetuses in one uterine horn spreading afterwards fetus-to-fetus. Abortion happens on average between 10-14 days from the onset of the infection. This explains why […]

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What do you think about inoculation with live virus from the same farm to acclimatize the replacement gilts for PRRS control?

Enric Marco — Thu, 19 Sep 2019 12:46:44 +0000

The inoculation of PRRS live virus from the farm as a method to acclimatise the gilts has been used extensively with positive results provided that: It can be done on isolation as not to disturb the stability of the farm. It can be done early enough to have at least some 6 weeks so the PRRS infection produced has the time to cool down. But keep in mind that it carries certain risks. What’s the potential risk of PRRS live virus inoculation? PRRS field strains vary in virulence and very virulent strains can lead to animal losses. The infective dose is not known and therefore we do not know if we are always using the same amount of PRRS virus. The storage conditions on a farm are not those of a lab, so the PRRS virus may end up becoming inactivated if the infected serum is kept on farm. When immunization works properly it must be considered that the PRRS virus will not circulate among the breeding animals, however any mistake can lead to a new clinical outbreak. Figure 1: Risks of the PRRS live wild virus inoculation compared with the advantages of the immunisation of the replacement animals […]

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Can a PRRSv positive boar that has been vaccinated be used for artificial insemination?

Enric Mateu — Tue, 09 Jul 2019 08:22:25 +0000

To answer this question, the first thing to be considered, it´s that it is not possible to differentiate, by a serum antibody test, an animal infected with PRRSv from a vaccinated one. Secondly, the pathogenesis of infection should be considered. Pathogenesis of PRRSv infection in boars An infected boar usually develops viremia (the presence of virus in blood) that normally lasts for a week or two. During this viremia period, the semen also contains the PRRS virus. From the second week, the shedding of the virus in semen can last several weeks. However, at this stage the presence of the virus in semen is intermittent, so an animal can be negative by PCR in semen one day but be positive at a later date. In addition, if a boar is vaccinated, the vaccine virus can also be shed in semen and reach females without immunity. Finally, it must be considered that a vaccinated animal could eventually become infected, although the probability is much lower than it would be if it had not been vaccinated. As a summary, PRRSv positive animals should not be used on a PRRS-free farm, even if they were vaccinated. If you want to learn […]

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