New insights to control PRRS virus

Porcine Reproductive and Respiratory Syndrome (PRRS) virus is one of the biggest threats for the global swine industry. The impact is not only caused by the virus itself but is also due to an increased prevalence of secondary infections. On “problem” farms, where farm management and biosecurity measures cannot fully control the disease, an immunomodulation strategy could help to control PRRS.

PRRS virus (PRRSv) belongs to the family of arteriviruses and is a small, enveloped, positive single-stranded RNA virus. Clinical signs of PRRS are highly variable. Substantial increases in abortions, stillbirths, pre-weaning mortality and respiratory diseases in weaners and growers are commonly reported clinical signs of PRRS. The susceptibility of PRRSv-infected pigs to secondary bacterial or viral infections increases dramatically. For instance, concurrent infections with Streptococcus suis are frequently reported. The prevalence of secondary infections together with the direct losses caused by PRRSv are the reason for the major economic impact of this viral syndrome.

Imbalance between cytokines

The production of pro-inflammatory cytokines has shown to be limited in PRRSv-infected animals. The absence of sufficient amounts of pro-inflammatory cytokines seems to allow PRRSv to escape from the host immune response. Hence, the immune system is not activated and viral clearance is not initiated, allowing PRRSv to multiply easily inside the host.

There is also evidence that neutralising antibodies and virus-specific interferon-gamma (IFN-γ­) responses are delayed. Interferon-gamma is involved in the inhibition of PRRSv replication but is downregulated in PRRSv-infected animals. Hence, controlling PRRSv is not simple. Adapting farm management and implementing biosecurity measures can help to control the disease to a certain level and can be supported by vaccination. However, on ‘problem’ farms, an immunomodulation strategy might be necessary to control PRRS.

FRA C12 seems to be a perfect fit in such immunomodulation strategy as the product based on glycerides of lauric acid (C12), including α-monolaurin, has already shown to increase infectious bronchitis (IB) antibody titer values as well as IFN-γ levels in IB vaccinated broilers. Next to these immunomodulating properties, in vitro studies have shown that alpha-monolaurin is able to destroy the viral envelope and to reduce host cell membrane fusion or entry.

Modulating the inflammatory response

The impact of PRRSv is also due to increased prevalence of secondary infections. At a farm suffering from a severe PRRSv outbreak in Belgium, one group of sows received FRA C12 before farrowing and during lactation. Their weaned piglets also received the product. Interestingly, these weaned piglets received fewer individual injections against locomotor problems compared to the other weaned piglets (1.9% versus 3.2% of the total amount of weaned piglets). Based on historical data, the causative agent of these locomotor problems was most likely S. suis. Hence, glycerides of C12 seemed to have suppressed the susceptibility to secondary infections with S. suis.

Glycerides and PRRSv shedding

The effect of FRA C12 on PRRSv shedding was studied in a recent trial where researchers collected oral fluids from weaned piglets. At seven days after weaning, 20% of the pens in the control group tested positive for PRRSv, whereas in the treatment group this was 10%. At 37 days after weaning, 70% of the pens in the control group tested positive and only 20% in the treatment group. Based on these results, it seemed that FRA C12 reduced PRRSv shedding in weaned piglets.

Want to learn more?

Complete the form below or login to Pig Progress to receive the full article in PDF.