Porcine Reproductive and Respiratory Syndrome (PRRS) is an infection caused by the PRRS virus (PRRSV) and often compromises the health and profitability of pig herds. It causes respiratory problems in growing and finishing pigs plus reproductive failure in breeding herds.
The economic impact of PRRS in a finishing unit is substantial. In a breeding herd it is dramatic and generally lasts several months until the herd reaches a stable condition. However reproductive problems may reoccur if the breeding herd is destabilised due to recycling of the PRRSV from the finishing herd or excreting gilts. It is important to prevent the virus taking hold through good biosecurity, management practices and vaccination.
Signs of PRRS
The signs of PRRS vary depending on the age of the pig.
Neonatal piglets can display a variety of clinical signs. The most characteristic are heavy breathing, rapid breathing and death.
Growers and finishing pigs
PRRSV infection alone will not always show symptoms. However, it plays a major role in developing Porcine Respiratory Disease Complex. Because PRRS will weaken the immune system, weaned and finishing pigs will often pick up a secondary virus and develop pig respiratory disease.
If clinical signs are present, they are usually respiratory and include:
- Periocular oedema
- Oculonasal discharge
In breeding herds, PRRS causes porcine respiratory and reproductive disease symptoms.
Red/blue discolouration of the ears and vulva
Subcutaneous and hind limb oedema
Stillborn or mummified piglets
Weak PRRSV-positive piglets (50% die soon after birth)
Delayed return to service
Delayed return to oestrus after weaning
Diagnosis of PRRS
Confirming PRRS is complicated as symptoms are not exclusive to the PRRSV. Confirming the virus is present requires:
- Serology (blood testing)
- Virus isolation testing
- Reverse Transcriptase Polymerase Chain Reaction (RT-PCR)
- Nucleotide or amino acid sequencing
Treatment of PRRS
As the impact of PRRS is measured by a weakened immune system developing a secondary infection, you can not ‘treat’ it. The best approach is prevention through good biosecurity, management and vaccination. Gilts entering the breeding unit should be acclimatised. Strict adherence needs to be paid both to the all-in, all-out principle and to the unidirectional flow of animals during the nursery and growing phases.
A live vaccine for vaccinating the whole herd is available.
Understanding the virus
The PRRS virus is a single-strand RNA virus.
- Order: Nidovirales
- Family: Arteriviridae
- Genus: Arterivirus.
The PRRSV is transmitted through close contact and body fluids. The virus enters and replicates in macrophages (white blood cells of the immune system). The resulting porcine respiratory and reproductive disease is dependent on the age of the pigs affected.
The PRRSV also interacts with other viruses to cause severe pig respiratory disease. The mechanism is still under investigation; however, it has been demonstrated that:
- Mycoplasma hyopneumoniae enhances the pathological effects of PRRSV
- PRRSV enhances the pathological effects of Swine Influenza
- PRRSV predisposes pigs to infection and disease caused by Streptococcus suis bacteria
- PRRSV can cause a loss of the bactericidal (bacteria fighting) function of pulmonary intravascular macrophages in the lungs
It is still not possible to conclude which are the most important combinations of pathogens or to define the importance of PRRSV in the severity of pig respiratory disease. This is difficult to prove experimentally due to pathogenicity of virus strains used, timing of infections, serological status of pigs used and the lack of predisposing or stress factors due to housing and/or management. Clinical experience in the field has shown that the occurrence of new respiratory pathogens result in increasingly complex respiratory problems and improved performance has been observed in herds vaccinated for PRRSV.