Pedro Lopes – PRRSControl

How can we evaluate the safety of a PRRS live vaccine after mass vaccination?

Pedro Lopes — Wed, 30 Sep 2020 08:49:08 +0000

Recently we switched to another commercial PRRS live vaccine for mass vaccination on our farm. Which points should we carefully check to compare the safety of PRRS vaccines? In regards to the safety of PRRS vaccines, there are two major issues that we should monitor after vaccination. 1. Adverse reactions after PRRS vaccination Safety concerning local and systemic reactions after using PRRS vaccines, such as fever or a local reaction (inflammation, swelling). Most PRRS live vaccines cause almost no reactions because they have a diluent and not an adjuvant, so they cause minor reactions after inoculation. 2. Safety related the use of a PRRS live vaccine different from the field virus The PRRS vaccine virus is live but attenuated, which means that in terms of safety we should look at 3 issues: · Duration of viral excretion · Possible recombination with existing virus circulating on the farm · Possible (but very unlikely) reversion to virulence of the vaccine virus 2.1 Virus excretion in PRRS live vaccines Concerning the duration of viral excretion, usually attenuated vaccines have a much lower excretion time than the field virus, so we can expect less than 12 weeks of excretion after […]

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PRRS vaccination with different PRRSv2 MLV consecutively: Can this cause clinical outbreaks?

Pedro Lopes — Thu, 04 Jul 2019 11:17:16 +0000

To control an unstable PRRS situation, a farm did more than 4 times a PRRS mass vaccination with 2 different commercial NA type MLV (one commercial vaccine in one week, and the second vaccine the following week, by turns). After 8 weeks from first mass vaccination, they found high fever and stillborn (confirmed PRRSv positive by PCR). This kind of excessive PRRS vaccination to sows in less than 8 weeks before farrowing, could it be the main cause of stillborn and high fever? Symptoms of fever and stillborn with PCR positive to PRRSv are a strong evidence of probable PRRSV viremia, in late gestation. If there were 4 PRRS vaccinations with 2 different live PRRSv vaccines, in 4 consecutive weeks, this is a massive immune challenge to the pregnant sow and for the unborn piglets. The viremia after one PRRS vaccination with a live vaccine in late gestation is not enough to cause abortions or significant stillborn. But such a huge viral load after 4 weeks of repeated PRRS vaccinations, in my understanding, can cause these symptoms. I do not see the benefits of such a PRRS vaccination scheme because there is not enough time to allow the […]

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Externally purchased gilts were PCR PRRS virus positive at destination farm however previous test in the source herd were negative. Could the transport stress induce viremia in latent infection? What about the possibility of infection during transport (3 hours driving and the car was disinfected)?

Pedro Lopes — Thu, 02 May 2019 14:02:13 +0000

The PCR technique is usually very sensitive and it detects very small amounts of PRRS virus in blood or other samples, but there are some limitations to the interpretation of the results. PCR technique limitations Firstly, I would want to make sure that the gilts are confirmed PRRS virus negative in the source herd before being transported. To detect a 10% prevalence level with a 95% confidence you need to test 29 gilts. Depending on the PCR test you can pool 3 to 5 blood samples per test, but individual testing of 100% of the gilts will give you 100% assurance about the final result (take into consideration that negative sub-populations to PRRS virus are common in positive farms). If all gilts are confirmed PCR negative at the source herd, latent infection can be excluded. Stress / contamination during transport as a risk of PRRS virus infection Transport is a stressor and induces some degree of immunosuppression so it can induce viremia in a latent infection. Contamination during transport is also possible but it will take some days after contamination before you can detect PRRS virus in the blood by most PCR kits. I would like […]

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How to interpret the results from PRRS serum samples where the ELISA was positive and the PCR negative?

Pedro Lopes — Tue, 15 Jan 2019 13:54:30 +0000

Diagnostic tests are absolutely necessary to confirm PRRS. The most common used techniques are ELISA and PCR. PRRS Diagnostic tools The ELISA technique detects antibodies produced against the infectious agent, and the PCR technique detects the presence of genetic genetic material of the infectious agent. The first technique, in this case the ELISA for PRRS, detects the antibodies in blood for a long period of time, usually for several months in the case of IgG for PRRS. The viraemia of the virus (its presence in the blood that is detected by PCR) usually lasts much less time than the antibodies that are detected by ELISA. Interpretation of the results The interpretation in this case is the following: the animals have been in contact at some point with the PRRS virus, they have produced antibodies detectable by ELISA, but at the time of sampling (and analytics) there were no virus in the blood of the animals. This situation is ideal, for example, in an adaptation program of negative gilts before entering in a PRRS positive farm. Positive ELISA and negative PCR gilts are protected with antibodies but they are not viraemic and do not shed the virus. For more information regarding […]

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What is the recommended age for vaccinating the piglets on a farm with a moderate PRRS virus outbreak?

Pedro Lopes — Thu, 10 Jan 2019 11:15:17 +0000

Disease outbreaks due to PRRS virus in piglets and fattening pigs can be controlled with vaccination strategies, with a very important basic rule: never vaccinate viraemic animals. Animals are vaccinated before viral circulation, at least 2-3 weeks before the age at which we anticipate the circulation of the virus begins. The veterinarian will need to collect blood samples for a PRRS-PCR and a serosurvey in post-weaning pigs and fattening pigs to identify when the PRRS virus circulation is detected. In the case of very early viral circulation in weaned piglets, PCR is also done in lactating piglets to determine if the viraemia is present in the first days of life. In the latter case, PRRS virus circulation in sows must be stabilized before initiating a vaccination program in piglets. In a “moderate PRRS virus outbreak” without knowing more information about the case, we lack information to be able to further detail our recommendation, but in any case we can comment on 2 more frequent field situations in our clinical practice: The clinical signs of PRRS occur more in fattening pigs, with viral detection 2-3 weeks after entry, and the post-weaning is PRRS virus negative: it is recommended to vaccinate 2 […]

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

Pedro Lopes — Thu, 06 Oct 2016 08:00:18 +0000

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 PRRSV 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 […]

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