Lars Erik Larsen – PRRSControl

Should we make PRRS negative farm for better productivity compared to PRRS stable status?

Lars Erik Larsen — Mon, 18 Oct 2021 07:33:04 +0000

Is the PRRSv infection reducing the growth performance of pigs? If so, what is the mechanism of growth retardation due to PRRSv infection? Should we make PRRS negative farm for better productivity compared to PRRS stable status? First, I regarded this question to be very easy to answer, but when I started, I realized the opposite especially if the answer should be based on scientific evidence. The negative impact of PRRSV is clearly documented in a range of studies when dealing with acute outbreaks of PRRSV and also in “unstable” herds where the virus may circulate among sows and pre-weaned pigs resulting in reproductive problems and increased pre-weaning disease morbidity and mortality. In some production systems, however, with a stable, seropositive sow herd that wean PRRS virus free piglets, there are still PRRS virus circulating in the nursery and even among the finishers. The impact of PRRSV on productivity and health in the latter situation has not been investigated to the same extent as the acute outbreaks, and therefore it is difficult to give an evidence-based clear answer. Pigs that are infected after weaning may develop respiratory clinical signs due to the direct viral damage of mainly the lungs and […]

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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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Is it possible that PRRSv causes an increase in irregular returns to estrus in sows?

Lars Erik Larsen — Wed, 08 Jul 2020 09:21:57 +0000

PRRSv is infamous for inducing severe reproductive problems when introduced into naïve / susceptible herds. The main problems are seen in late-term gestating sows (after day 90 of gestation) when the virus crosses the placenta, infects the fetuses and replicates in various tissues, mainly in the lymphoid organs (thymus, etc). Pathogenesis and clinical signs of PRRSv in sows The reason why PRRSv infection could not occur before this is probably because the virus requires macrophages at a certain maturation stage to replicate and these are not available in the fetus before day 90 of gestation. Clinical presentation of the disease in naïve sows The infection of naïve sows at earlier stages of the pregnancy may also lead to an increase in return rates. These are difficult to quantify, but in many of the published trials there is a significant decrease in return rates in vaccinated sows compared to unvaccinated groups, further supporting the view that PRRSv infections also lead to reproductive problems in the earlier stages of pregnancy. If you want to know more about the lesions and the PRRS clinical disease, visit the section “PRRS: The disease” of this site. You can ask your […]

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Can using the same needle to vaccinate multiple sows be a cause of transmission of PRRS virus or other swine infectious diseases? How often would you recommend changing the needle?

Lars Erik Larsen — Mon, 17 Feb 2020 16:00:46 +0000

The iatrogenic transmission by contaminated needles can indeed be a source of PRRS virus and other diseases transmission – this has been proved in several controlled experimental studies. In the field, it is difficult to estimate how often this happens because there are several other potential routes of transmission. A review from Spain from 2016 (Pileri and Mateu Vet Res, 2016) provided a very illustrative calculation of how little blood volume is needed to transmit the PRRS virus. Here is a slightly revised quote from the paper: “In the peak of the viraemia, infected animals have a viral load of at least 103 to 104 TCID50/mL. Assuming a minimum infectious dose (MID) of 101-102 TCID50 for the percutaneous route, blood volumes of 1–10 µL could be sufficient to produce transmission”. The tip of the needle may easily be contaminated with 1–10 µL blood/exudate from the last pig injected. Changing needles frequently is important for many other reasons, but in relation to PRRS virus the needle must be changed at least between pens to avoid the needle becoming a vector and contributing to transmission within the herd. You can ask your own question! Visit Pig333.com and submit your question […]

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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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One month after vaccinating sows and piglets with PRRSv MLV (VR2332 strain), is it normal and safe to detect the vaccine strain in over 20% of the serum samples?

Lars Erik Larsen — Mon, 29 Apr 2019 13:36:57 +0000

Published controlled studies have estimated the length of viremia after PRRSv vaccination with MLV vaccines to be 29 days on average (range 10–42 days). However, PRRSv viral RNA has been detected in tonsil scrapings up to 90 days post vaccination. We recently performed a challenge study where we followed the pigs for 62 days after vaccination also with the VR2332 strain and found positive pigs up to 42-62 days after PRRSv vaccination (Kristensen et al., 2018). So, the answer is YES. Extended viremia after vaccination It’s not unusual to see extended viremia after vaccination in 20% of the animals. In the same study, we found viral shedding (by PCR) up to 14 days after vaccination. Thus, even though some animals are PRRSv positive beyond 2 weeks after vaccination, the risk that these animals will transmit the virus horizontally to other vaccinated animals is probably low, but the persistence of vaccine virus for two-three months after vaccination emphasize the importance of keeping vaccinated animals isolated from non-vaccinated animals for a sustained time period prior to mingling. Which is the risk of having over 20% PRRSv positive serum samples 1 month after vaccination? In respect to risks […]

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Does intradermal injection of attenuated live PRRSV vaccines offer an immune response as good as intramuscular ones in sows?

Lars Erik Larsen — Thu, 24 May 2018 17:11:50 +0000

Intradermal vaccination have been approved for a number of vaccines including PRRSV MLV. In order for a company to get such a vaccine approved they need to provide detailed information on safety and efficacy. To the best of my knowledge the intradermal vaccination route induce immunity comparable to the intramuscular route. The intradermal route have some positive aspects: no need for needles and by that decrease the risk of transfer of pathogens from pig to pig, less harm to the pig, easier and faster vaccination. My major concern is that it require that the vaccination is performed according to the guideline for the device – i.e. it is important that the device is in close horizontal contact with the skin of the pig at the time of vaccination. The dose volume is typically 10 times less than for the intramuscular vaccination and therefore it is important that the full dose is deposited correct. Thus, you need to give very detailed instructions to the persons that perform the vaccination – when a lot of pigs are to be vaccinated things may go too fast! An idea would be to take blood samples of 10-20 pigs 3 weeks after vaccination and test […]

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How many animals should be sampled to get reliable results about the presence of PRRSV in a 1200 sow herd?

Lars Erik Larsen — Fri, 01 Sep 2017 10:27:39 +0000

The sampling strategy very much depend on the purpose of the test, the status of the herd and also what kind of analysis to be performed and of course also on the sensitivity of the applied test. In larger herds it’s important to test all sections or so-called epidemiological units (i.e. batches and age groups that are kept separated). The number of samples per section again depend on the purpose and the status of the herd or – by the end of the day – the expected prevalence and the required confident level (95 or 99 % is normally required). To confirm negative status in a herd/section/epidemiological unit (i.e. in a PRRSV free herd): In the Danish SPF system, 20 serum samples are taken and tested for antibodies by ELISA – in a population of 1000 animals this will identify minimum 1 positive animal (95% confidence level) if the prevalence is above approximately 15 % which will be the case if a naïve herd is infected. To find virus positive animals in a PRRSV positive population (i.e. where all or a subset of animals have antibodies): You need to perform PCR on serum or oral fluid – again 20 samples […]

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After controlling a PRRS outbreak in a farm, can we produce own replacement animals in the same farm?

Lars Erik Larsen — Fri, 30 Jun 2017 08:00:05 +0000

According to experimental data and also some field tests most pigs would have cleared the infection after 8 weeks, however, it cannot be 100 % excluded that very few pigs can harbor the virus for a longer time period. Thus, if the outbreak has been controlled in the sense that there is no virus circulation in any sections (PCR negative and ELISA positive) and the female pigs were not pregnant at the time of the outbreak the use of these pigs as future breeding animals should be quite safe. I would recommend, however, to put them in quarantine for 8-12 weeks and test them for antibody and virus at the end of the quarantine period – prior to the introduction into the sow herd. It would be optimal also to test them prior to the quarantine period. At the end of the quarantine period all pigs should be PCR negative, but its ok that they are antibody positive – providing that they were antibody positive also at the start of the quarantine. You can ask your own question! Visit Pig333.com and submit your question to our experts. En el caso de una granja que haya pasado un brote de PRRS […]

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