Prevention and Control of PRRS

July 8, 2022, 4:23 pm

A viral disease, Porcine Reproductive and Respiratory Syndrome (PRRS) is the most economically significant disease to affect swine industry (along with the African Swine Fever in the past years). Estimates in Europe show that it costs the industry almost €2 billion every year.

It is estimated that in a 1,000 sow farm a PRRS outbreak can cost up to €400,000. PRRS spreads every way possible: air – up to 9-10 km; faeces, urine, saliva, semen, blood, intrauterine, milk and colostrum. The virus is immunosuppressive and can survive for a long time in cold wet conditions. It is a highly infectious virus – only the smallest amount of the virus can infect a herd. Commercial vaccines are inconsistent efficient because the virus mutates easily.

The main issues caused by PRRS are:

  • Abortions
  • Slow growth
  • Sick pigs
  • Respiratory disease
  • Mortality.

Eradication of PRRSV may be achieved through herd depopulation and repopulation but is costly and may only be justifiable if the elimination of other concurrent diseases is desired. Until now, this is the only feasible alternative for farrow-to-finish herds, where replication of the PRRS virus in the growing population does not allow for other methods to be used. Implementation of strict biosecurity measures to prevent the herds from becoming re-infected is also crucial. To eliminate the PRRS virus in a herd, a herd closure of minimum 200 days is recommended.

Prevention

Prevention’s role is to stop the entry of PRRS onto farms into negative herds and the introduction of new viral variants into PRRS-infected herds.

Best practices include:

  • Quarantine facilities and testing protocols for incoming breeding stock
  • Transport vehicles sanitation and drying
  • Entry protocols and sanitation for incoming supplies
  • Entry protocols for personnel entry protocols
  • Insect control programmes
  • PRRS prevention may include the use of air filtration or air treatment systems. Filtration has been shown to effectively reduce the risk of the introduction of PRRS and other airborne agents

Control

There are no available specific treatments for PRRS. The objective of PRRS control is to limit the adverse effects of the virus in all stages of pig production.

In breeding herds, the control of virus circulation is based on the use of replacement animals that have developed immunity to PRRS prior to their introduction into the herd.

Gilt acclimatisation relies on:

  • Contact with PRRS infected animals
  • Intentional exposure to PRRS
  • Vaccination

These animals are introduced into the herd when they are less likely to transmit the virus. Exposure of replacement gilts starting at two months of age, provides time for the development of immunity before they are introduced into the herd. All exposure methods utilise PRRS-negative gilts as the starting point. Herd stability is improved with a temporal stop in introducing of replacement animals. The herd is temporally closed. This may minimise the effects of PRRS in the face of a recent infection and/or accelerate negative weaned pig production. 60-120 days may be sufficient time to minimise the effects of the virus, but not to eliminate it.

In the maternity, regarding piglets, control of PRRS aims to limit the spread of virus among litters:

  • Restrict cross-fostering to the first day of life
  • Eliminate severely affected piglets
  • All-in/all-out animal flow of the nursery

Control of chronic PRRS in the weaned pig population is challenging. Transmission of the virus is maintained from older, infected pigs to recently weaned piglets.

Depopulation is a strategy that consists of an adjustment in the pig flow to prevent the spread of PRRS within chronically infected populations. Partial depopulation can produce significant improvements in the overall economic performance of the nursery, average daily gain and mortality. Without depopulation, we can apply MLV vaccination and unidirectional pig flow to eliminate the virus from growing pigs.

Alternative measures for support should also be taken into consideration. A study in the US, in a 14,000 sow PRRS positive farrowing only unit, showed that pre-weaning and post-weaning supplementation with Tonisity Px to PRRS exposed pigs reduced overall mortality by 50%, compared with a control group where only an electrolyte supplement was administered. By helping to reduce death losses, strategic Tonisity Px supplementation allowed producers to preserve productivity and recoup profit potential under challenging conditions involving PRRS infection.

Vaccines

Multiple studies have showed that vaccination against PRRS can result in protective immunity and mild clinical signs. A variety of MLV and inactivated products are available, depending on the geographical region. MLV vaccines are considered to induce a more efficacious immune response than inactivated vaccines, although there are concerns regarding the safety and efficiency of some products.

References

Albina E, Mesplede A, Chenut G, et al. 2000. Vet Microbiol 77:43–57.

Alfonso P, Frías-Lepoureau MT. 2003. PRRS in Central America and the Caribbean region. In J

Zimmerman, K-J Yoon, eds. The PRRS Compendium, 2nd ed. Des Moines, IA: National Pork Board, pp. 217–220.

Allan G, McNeilly F, Ellis J, et al. 2000. Arch Virol 145: 2421–2429.

Batista L, Pijoan C, Torremorell M. 2002. J Swine Health Prod 10(4):147–150.

Bautista EM, Goyal SM, Yoon I-J, et al. 1993. J Vet Diagn Invest 5:163–165.

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