Improving detection of PRRS virus in aborted material

  

Abortion in the later stages of pregnancy is the clinical manifestation of PRRS virus infection that causes most concern to farmers. Although aborted material is sent to the lab in an attempt to detect the virus, the result is often frustrating.
Even though much research has been done, the pathogenesis of intrauterine PRRS virus infection remains largely unknown. Results from recent studies and judicious observation of the aborted material, however, can help to increase the success rate in detecting the PRRSV in the laboratory.
Determining the cause of late abortions in sows is a challenge, as they may be infectious or not depending largely on herd management, the overall health status, the region where the farm is located, the specific prevention measures against abortogenic pathogens, etc. Pregnancy itself is a risk status for the sow; if they are subjected to sudden changes in the environment, abortion can occur spontaneously. If the herd management and housing conditions are adequate, outbreaks of late abortions are usually attributed to an acute PRRS virus infection. In these cases the sample used to confirm the presence of the virus in the laboratory is the aborted material, usually accomplished by the polymerase chain reaction assay (PCR).
Although this is the standard procedure for PRRS virus identification in clinical material coming from abortion, a high proportion of PCR-negative results are the most common outcome from the diagnostic laboratory, as was reported in a large-scale study in Germany. The German3 researchers analyzed not only fetuses, but also samples collected from the affected sows. However, infection with the PRRS virus was confirmed in only 8.6% of the samples. These results contrast sharply with those reported from a similar field investigation of late-term abortions in sows in Thailand4, with up to 65.6% of the samples being PCR-positive. Taking into consideration the differences in the development of the pig industry in the two countries, in particular the difference in the rate of vaccination against PRRS, which is much higher in Germany, it seems plausible that the characteristics of the farm and overall health management greatly influence the success of PRRS virus detection in this kind of sample.
The selection of samples to confirm the presence of the PRRS virus in cases of abortion may also influence the outcome of the PCR, as can be deduced from the accumulated scientific evidence on the distribution of the PRRS virus in maternal and fetal tissues in cases of transplacental infection. A recent study1 suggests that meconium-stained fetuses, along with those decomposed but not autolytic, are the best samples for detection of the PRRS virus in the thymus, lungs and serum of fetuses using PCR. The results further indicate that fetuses in advanced autolysis and those of normal appearance are usually negative in the PCR, and therefore should not be used for diagnosis. Meconium staining was the most consistent gross abnormality observed in fetuses infected with the PRRS virus in another study2, suggesting that this is a reliable indicator of intrauterine infection.

  

Because aborted fetuses are by definition autolytic samples, since death occurs hours or days before they are delivered, it is likely that the autolysis has a negative impact on the PCR as a consequence of viral RNA degradation. However, there is little information about the stability of RNA virus in samples of pig origin in advanced autolysis. A recent study5 revealed an average half-life of viral RNA in pig tissues stored at room temperature for up to 21 days, ranging from 0.95 to 2.55 days. This indicates that there is a very short timeframe between detection of abortion on the farm, and sample submission for PCR analysis in the laboratory.
All in all, demonstration of PRRS virus infection in late-term aborted fetuses can be improved by sampling both meconium-stained and decomposed (non-autolytic) fetuses, umbilical cord and placenta on the farm. Sampling should be performed as soon as the abortion occurs, and should be delivered under refrigeration by express transport, when possible.
REFERENCES:
1. Ladinig A., et al., 2014. Variation in Fetal Outcome, Viral Load and ORF5 Sequence Mutations in a Large Scale Study of Phenotypic Responses to Late Gestation Exposure to Type 2 Porcine Reproductive and Respiratory Syndrome Virus. PLoS ONE, 9(4), e96104.

2. Lager K. M. and Halbur P.G., 1998. Gross and microscopic lesions in porcine fetuses infected with porcine reproductive and respiratory syndrome virus. J Vet Diagn Invest. 8(3):275-82.

3.Nathues H., et al., 2011. Infectious agent detection in reproductive disorders in swine herds. Retrospective evaluation of diagnostic laboratory examinations. Tierarztl Prax Ausg G Grosstiere Nutztiere. 39(3):155-61.

4.Olanratmanee E., et al., 2015. Prevalence of porcine reproductive and respiratory syndrome virus detection in aborted fetuses, mummified fetuses and stillborn piglets using quantitative polymerase chain reaction. J. Vet. Med. Sci. 77(9): 1071–1077.

5. Weesendorp, et al., 2008. The effect of tissue degradation on detection of infectious virus and viralRNAto diagnose classical swine fever virus, Vet Microbiol. 2009.09.028.

In vitro viability of the PRRSv vaccine when mixed with an inactivated Swine Influenza vaccine

Nowadays, the possibility of reducing or administering vaccines simultaneously clearly means both an improvement in animal welfare and in labor efficiency. Due to this tendency, the possibility of mixing UNISTRAIN® PRRS with other vaccines led HIPRA to assess the viability of PRRSv in combination with an inactivated Swine Influenza vaccine (GRIPORK®).
Nowadays, many vaccination protocols have to be implemented in sows during the gestation and lactation periods. The possibility of simultaneous vaccine administration protocols can potentially improve both animal welfare and the efficiency of farm employees.
Many PRRSv vaccine combinations has been evaluated, but only some of them have shown their safety and efficacy, such as the combination of UNISTRAIN® PRRS with PPV and SE vaccine ERYSENG® PARVO. As a first step in this combination strategy, an in vitro trial was carried out to asses UNISTRAIN® PRRSv viability, when reconstituted in an inactivated Swine Influenza vaccine- GRIPORK® and also in a commercial solvent.
One 50-dose freeze dried tablet of UNISTRAIN® PRRS (strain VP-046 BIS.) was reconstituted in a 50 dose bottle (100 ml) of s GRIPORK®. Another 50-dose freeze dried tablet of UNISTRAIN® PRRS was reconstituted in 100 ml of an aqueous commercial solvent. Just after reconstitution and at 1, 2, 3 and 4 hours post reconstitution at 25° C, virus titers were measure by cytopathic effect in the CLON 8 cell line.
The following table includes PRRSv titers at a specific time after reconstitution with both GRIPORK® and the commercial solvent:

  
The PRRSv vaccine, when mixed with GRIPORK®, maintained its in vitro viability for four hours after reconstitution. The virus titer values over the whole study (4 hours) were equivalent or higher than the Minimum Effective Concentration (MEC) of the product (103.5 – 105.5 CCID50). The same results, namely that the MEC remained constant, were obtained when UNISTRAIN® PRRS was diluted in the commercial solvent.
These In vitro results confirm that the inactivated swine influenza virus vaccine- GRIPORK® does not interfere with PRRSv- UNISTRAIN® PRRS-viability. Moreover, PRRSv titers keep their MEC for 4 hours after reconstitution. Subject to further in vivo studies to ensure safety and the immunogenic response after vaccine mixing, UNISTRAIN® PRRS and GRIPORK® could be considered as a potential vaccine combination on commercial farms.

UNISTRAIN® PRRS a polyvalent vaccine for controlling Porcine Reproductive and Respiratory Syndrome in all markets, farms and situations

Today, the Porcine Reproductive and Respiratory Syndrome is the most important technical disease in the swine industry for clinical veterinarians and producers alike, and the one which causes the biggest headaches.
There are other political or commercial diseases that can doubtless affect the agricultural economy or can hinder the sale of pork, but the production complications that this syndrome causes are many and are difficult to diagnose. However, sometimes a desperate clinical measure brings an excellent response.
All of us who have had contact with the swine industry at farm level have suffered problems since the appearance of the Porcine Reproductive and Respiratory Syndrome. Very often, it has surprised us, it has misled us and it has caused us to lose sleep. Its variability, its involvement in other syndromes, its ability to trigger or stimulate other pathogens or simply the fact that it can affect different categories of animals or have tropism for different systems (respiratory or reproductive) make it the most unpredictable and most complicated of diseases.
Sometimes, the Porcine Reproductive and Respiratory Syndrome has been the catch-all term behind which we have taken refuge when we have not been given a precise diagnosis or simply when this diagnosis has been multifactorial, multi-age or, as in the present case, at farm level causes an overall reduction in productivity at every level. On this occasion, a group of underperforming farms belonging to an Italian company were vaccinated with a PRRS vaccine without achieving the anticipated results.
The company’s veterinarian took two correct decisions, one was to change the vaccine and the other was to intensify the vaccination programme, not only in the case of pregnant and lactating sows and gilts (the latter being given 3 doses of UNISTRAIN® PRRS before mating). The results after the new programme and the new vaccine had been in use for 9 months were:

   
 
In the case of the sows:
9 % increased fertility.

1.8 % reduction in the rate of abortions.

1.7 more piglets weaned per sow and per year.

In the case of the piglets:
1.5 % less mortality during lactation.

250 g more per piglet at weaning.

2 more piglets per sow and per year.

1 % less mortality.

10 grams more average daily gain in the fattening period.

If we analyze the profitability of these decisions from an

economic perspective

, it is undeniable that the return on investment of this operation has enabled the company to grow and for a relationship of trust between the parties to be strengthened.