PARTNER FEATURE ▶▶▶
New insights to control PRRS virus
Porcine Reproductive and Respiratory Syndrome (PRRS) virus is one of the most important pathogens the swine industry is currently dealing with. The impact of the virus is not only caused by the disease itself, but is also due to increased prevalence of secondary infections. On “problem” farms, where farm- management and biosecurity measures cannot fully control the disease, an immunomodulation strategy could help control PRRS.
BY OLGA DANSEN, MSC, HEAD OF R&D, FRAMELCO P 80%
70% 60% 50% 40% 30% 20% 10% 0%
Control Glycerides of lauric acid*
70%
RRS virus (PRRSv) belongs to the family of arterivirus- es 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 bacte- rial 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. One of the main target cells for PRRSv replication are porcine alveolar macrophages (PAMs). These cells serve as the first
Figure 1 - Percentage of PRRSv positive pens at seven and 37 days after weaning.
line of defence against inhaled microbial particles by means of phagocytosis, antigen presentation and production of cytokines. These basic functions are directly impaired when PRRSv replicates in PAMs.
Imbalance between cytokines More specifically, the production of pro-inflammatory cytokines has shown to be limited in PRRSv-infected ani- mals. The absence of sufficient amounts of pro-inflammato- ry cytokines seems to allow PRRSv to escape from the host immune response. Hence, the immune system is not acti- vated and viral clearance is not initiated, allowing PRRSv to multiply easily inside the host. The immunosuppressive effect of PRRSv may also contribute to the increased risk of secondary infections. Apart from the insufficient response of the innate immune system upon PRRSv infection and the creation of an imbalance between pro- and anti-inflammatory cytokines, there is also evidence that neutralising antibodies and virus-specific inter- feron-gamma (IFN-γ) responses are delayed. Interferon-gam- ma is involved in the inhibition of PRRSv replication but is downregulated in PRRSv-infected animals. Together with an upregulation of interleukin-10 (IL-10), this might cause an increase of CD163 in macrophages, which is a component of a complex of receptors required for PRRSv entry. An increase of CD163 actually promotes PRRSv entry and replication. As PRRSv is susceptible to the direct antiviral effect of IFN-γ, it seems an interesting target for immunomodulation strategies to overcome PRRS.
20% 10% Day 7 * FRA C12, Framelco 22 ▶ PIG PROGRESS | Volume 37, No. 4, 2021 Day 37 20%
Modulating the inflammatory response Lately, alpha-monolaurin has been gaining more attention because of its ability to modulate the inflammatory response. Most research presents the reduction of pro-inflammatory cytokines. With respect to PRRSv, downregulation of IL-10 is desired. On the other hand, IFN-γ should be upregulated during PRRSv infection. Interestingly, Framelco and Belgian research facility Poul- pharm discovered a significant increase of IFN-γ in broilers vaccinated against infectious bronchitis (IB) receiving FRA C12 Dry, a product based on glycerides of lauric acid, includ- ing alpha-monolaurin. Moreover, a significant increase in anti-IBV antibody titres was observed in broilers receiving
PHOTO: BERT JANSEN
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