The key points that make oral fluid an alternative to serum for PRRSv serological monitoring

The advantages of oral fluid (OF) compared with serum for the serological diagnosis of PRRSv infection are diverse. The practicality, the non-invasiveness, and more importantly, the almost absolute correlation in the content of anti-PRRSv antibodies, make oral fluid a real alternative to bleeding and testing on serum.

Even more, several written and interactive interactive tutorials available online can help nearly any farm to implement the process of oral fluid sampling without major inconvenience.

A recent study published by researchers at CODA-CERVA in Belgium, has provided new data on the detection of various types of antibodies to PRRSv in the oral fluid of pigs, generated after experimental infection or vaccination. It was known that the pig oral fluid contains large quantities of IgA antibodies, in addition to IgGs and IgMs. But this study showed that although the concentrations of antibodies are similar, both after vaccination and infection, what is really critical is the system used to measure these antibodies in a reliable and robust way.

Researchers at Iowa State University in the US, recently released the analytical characteristics of some ELISA kits routinely used for serological diagnosis of PRRS (IDEXX-SO, IDEXX-OF and CIVTEST® SUIS PRRS E/S PLUS by HIPRA). The kits showed similar characteristics in terms of sensitivity and specificity in the detection of IgGs against PRRSv in oral fluid. In fact, these kits are available in the market, and offer excellent performance for serological monitoring of PRRSv infection.

The fact that the IgGs are the antibodies of choice for indirect detection (serology) of PRRSv infection, is mainly due to the reliability offered by the ELISA kits available, which are based on the detection of anti-PRRSv IgGs. Moreover the study from CODA-CERVA indicates that the material of the rope used to collect the oral fluid determines the concentration of IgA present in the sample, but not that of the IgGs. The use of natural cotton ropes allows collection of consistent volumes oral fluid, and the detection of anti-PRRSv IgGs in a predictable kinetic in various scenarios.

The oral fluid has proved superior to directly detect the presence of PRRSv by PCR.

study combining the use of PCR and the detection of various types of anti-PRRSv antibodies in piglets sampled the day before weaning, showed that it is possible to increase the detection of PRRSv by PCR in endemically infected and vaccinated farms, and also that the levels of the studied antibody isotypes (IgGs, IgMs, and IgAs) correlate with the infectious status (PCR positive or negative) in the same groups of animals. The general conclusion from this study was that the oral fluid of piglets before weaning is a sample that allows monitoring endemically infected farms in an efficient and sensitive manner, and even predict the circulation of PRRSV in subpopulations of sows, that could perpetuate the circulation of PRRSv on the farm.

While standard ELISA systems allow monitoring PRRSV infection in pig populations using oral fluid, they do not determine whether the detected antibodies are neutralizing (NA) or not. NA against PRRSV are important in eliminating the virus in the viremic animal, and consequently in solving the clinical symptoms of the disease. The question of whether the oral fluid can be used to detect NA specific against PRRSv has been answered in a recent study. Researchers managed to standardize a serum neutralization system using collective and individual oral fluids from infected or vaccinated animals. The results were comparable to those obtained in serum in similar circumstances, which gives an added value to the oral fluid samples for monitoring PRRSv infection.

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