Enric Marco – PRRSControl

How to manage the vaccination against PRRSV in farms positive to highly pathogenic strains?

Enric Marco — Thu, 25 Apr 2024 07:29:51 +0000

In Spain we are having many problems with highly pathogenic PRRSV1 strains, and the vaccines do not seem to work at all. Would it be recommended to stop vaccinating sows and piglets in these cases?

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Can PRRSV be transmitted to pigs through the consumption of meat from positive animals?

Enric Marco — Mon, 04 Mar 2024 09:00:23 +0000

Regarding meat transmission of PRRS in the fresh meat market from PRRS positive farms: what protocol do countries follow when slaughtering PRRS positive pigs? And how many pigs that are positive still have the antigen within the glands at age of slaughter of 23 weeks?

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When to vaccinate piglets with a PRRS modified live vaccine?

Enric Marco — Mon, 28 Nov 2022 07:42:47 +0000

Is it necessary to vaccinate and revaccinate piglets with a PRRS modified live vaccine? When is the optimal time to do it? In a geographical area with a high incidence of PRRS. On a stable PRRS-positive farm, what do you think about piglets vaccination with a modified live vaccine (MLV) (negative at birth) at 7 days of age and then again at 3.5 weeks of age? Vaccination of piglets is designed to try to reduce the problems that may arise from PRRS circulation in the post-weaning or early finishing phase. The geographical area may influence the risk of introduction of a new variant of PRRS, but in the face of a new introduction, vaccines are not able to effectively contain the damage that this new strain may do. In fact, this is why they are usually recommended on farms that are already infected. With this characteristic in mind, I would not vaccinate piglets based on that objective alone. However, if piglets are vaccinated with a modified live virus vaccine (MLV), they would only need one dose of vaccine. The viral replication generated is enough to produce a complete immune response, without the need to revaccinate, which is so important when […]

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What do we expect to see in piglet’s antibody titres from sows vaccinated every 4 months?

Enric Marco — Mon, 25 Apr 2022 08:13:24 +0000

In a PRRS stable farm, whereby no recent outbreak of PRRS and that the sows are vaccinated every 4 months, what do we expect to see from the piglet’s titre? Will maternally derived antibodies (MDA) affect serology profile of the piglets and is it a good sign to see more seronegative or more seropositive piglets? Live attenuated vaccines applied to the entire population in regular periods of 4 months develop a serological response in most sows that is consolidated with repeated vaccinations (Pedersen, K. et al. 2021), but it must be said that the titres reached can be variable depending on whether have been exposed to wild virus or not and how long before. The antibodies detected in piglets up to 6-10 weeks of life are those derived from acquired maternal immunity and therefore if the sows have developed a response, it will pass to the piglets. If wild virus circulations are not produced again, the rate of antibodies in the mothers will go down and consequently also in the piglets, shortening the duration of maternal antibodies. But the rate of positive piglets should continue being initially high and decline faster with age (higher percentage of negative piglets). […]

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How to use ELISA and PCR for PRRS detection and monitoring?

Enric Marco — Wed, 06 Apr 2022 06:34:40 +0000

Verify seroconversion of all animals on a farm is a method used today on multiplication and commercial farms in Spain/Europe? If it is, in what proportion of these evaluations are PCR and ELISA used? Is the gold standard always used or are other commercial options available? At what ages should samples be taken and how often should this be done to get a clear picture of what is happening on the farm? Using ELISA to detect seroconversion is not the best method to verify if a farm has a homogeneous immune status that would prevent the PRRS virus from recirculating internally. After an infection, not all animals develop an immune response so, given a positive ELISA result and depending on the cases, there can always be a percentage of animals that do not have a response and remain negative, without this implying that they have not been infected. Also, the duration of detectable antibodies with the ELISA test has a high individual variability, with no correlation with the duration of actual protection, which can also increase the percentage of negatives when serological monitoring of a population is done. In general, ELISA is used to check the health status […]

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How to clean and disinfect the material before introducing it into a farm?

Enric Marco — Tue, 08 Mar 2022 09:00:13 +0000

Repair and maintenance workers can unintentionally bring PRRS virus onto farms. How can we prevent this when some of their equipment is hard to wash and disinfect? Farm maintenance is one of the ways a new PRRS virus strain can be introduced on a farm. Obviously, without maintenance there would not be this specific risk, but everyone knows that farms need maintenance. After reviewing some outbreaks due to this reason, we realized that the key is the proper management of the tools used. Very often maintenance teams working in farms are specialized in this type of facilities, and therefore they are moving between farms often, sometimes even in a matter of minutes or hours. PRRS virus is not very resistant in the environment, but it is resistant enough to infect a farm if the infected material is introduced and there is direct contact with pigs. The material to be used can be disinfected in the disinfection and drying room (D&D room). A specific room should be used as a D&D room for fomites. All incoming supplies should be placed in this room, disinfected on all sides, and allowed the minimum 2 hour contact time prior to entry. This […]

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What role do inactivated vaccines play in PRRS control?

Enric Marco — Mon, 28 Feb 2022 12:39:21 +0000

Inactivated vaccines against PRRS have been used as a complement in vaccine plans with live attenuated vaccines. We already know that inactivated vaccines do not produce good protection when used in animals that have not had contact with an active PRRS virus; they do not generate seroconversion in this case. However, when these vaccines are used in animals previously infected or vaccinated with attenuated vaccines, they generate a marked and easily detectable serological response. Unfortunately, an excellent serological response does not always correspond to a better response against wild PRRS virus, which is one of the weak points we have when we want to establish effective prophylactic plans. Inactivated vaccines are commonly used in prophylactic plans for replacement gilts in combination with administering of one or two live attenuated vaccines and always applied afterwards. Inactivated vaccines reinforcing the serological response make it easier to verify that animals have been correctly vaccinated (especially in those cases when they come from PRRS negative origins), increasing our confidence in them. Some producers have used them in cycle too. Again, in combination with live attenuated vaccines applied in blanket vaccination. The objective of this kind of vaccine plan is to obtain better results in […]

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What can we do when a “false positive” is suspected in a serology test?

Enric Marco — Tue, 08 Feb 2022 14:59:14 +0000

On a farrow to nursery farm with 200 sows, 20 blood samples were taken from sows, gilts, and piglets. All samples were negative for PRRS by ELISA except one, which was from a 5th parity sow. No pathology associated with PRRS was observed, and no vaccination against this disease was done. The farm has good performance, 90% fertility and 14 piglets weaned per sow. How should we interpret these analytical results? No ELISA test is 100% specific. Specificity is the test’s probability of correctly detecting negative animals. When referring specifically to the PRRS virus, the best ELISA tests on the market are capable of correctly detecting 94-99% of negative animals, but there is always a small percentage that can give a positive ELISA reaction without actually having been infected by the virus: these are known as false positives. The causes can be multiple and in many cases, it is related to the presence of proteins in the blood of the animal detected positive that can be identified as antibodies against PRRS. If the farm has not had clinical signs suggestive of the disease, the positive is most likely a “false positive“. The way to confirm this would be to retest […]

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After a recent outbreak, when should piglet vaccination start?

Enric Marco — Mon, 24 Jan 2022 07:38:29 +0000

Once a sow vaccination program has been initiated on a farm that was previously negative for PRRS but has recently had an outbreak, when should piglet vaccination start? When a negative farm becomes infected with PRRS virus it will continue to produce piglets that have been infected during gestation and are therefore viremic for at least a 4-month period. When these piglets are vaccinated, they tend not to handle the vaccine virus well as their immune response will not be entirely adequate, having lived with the virus while their immune system was developing during late gestation. Vaccination of piglets will only make sense when there is a low percentage of piglets born viremic. The percentage of piglets born viremic will be very high during the first 2 months after infection of the farm and will progressively decrease over time. Ideally, vaccination of piglets should be initiated once all piglets are negative, but reaching this point may take many months, depending on the farm, so vaccination is generally initiated when there is a reduced percentage of viremic piglets. Since not all piglets can be tested individually, this can be done by quantifying the virus present in testicular fluids by following […]

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Is there any interference when administering PRRS and Mycoplasma vaccines simultaneously?

Enric Marco — Tue, 09 Nov 2021 09:11:40 +0000

Is there any interference when administering PRRS and mycoplasma vaccines simultaneously? If yes, how long should I wait between administering? Based on the data we have, there is no interference between simultaneously administering the PRRS and M. hyo vaccines as long as they are injected at independent points. The simultaneous administration of modified live vaccines (MLV) and inactivated vaccines is a common practice in human medicine, and there is a multitude of literature that supports this evidence (1). In human medicine, very few cases are described in which the simultaneous administration of two vaccines is not indicated, one of which would be in immunosuppressed people, such as in AIDS patients (infected by the HIV virus). Mycoplama vaccine efficacy has been investigated in pigs previously infected with PRRS virus using a field strain; even in that case the vaccinated pigs developed a complete response to the vaccine (2). However, I think it is important to specify that in cases in which the two vaccines are to be administered simultaneously using a single inoculation point, a commercial product designed for this particular purpose should be used, since it could happen that the adjuvant used in the M. hyo vaccine could […]

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