Porcine Reproductive Respiratory Sydrome
Clinical Signs of PRRS:
- Adult Pigs: Reduced appetite, fever, premature farrowing, sow mortality
- Affected Litters: Stillborn pigs, high pre-weaning mortality, mummified pigs
- Weaned Pigs: Loss of appetite, failure to thrive, respiratory distress
Transmission:
PRRS virus spreads through both vertical (from sow to offspring) and horizontal (pig-to-pig) transmission, via direct contact, contaminated equipment, clothing, and vehicles. It can also be transmitted by air over distances up to 5.5 miles (9 km).
Prevention & Control:
Biosecurity is key to controlling and prevent PRRS spread, especially through pig transportation and contaminated equipment. Producers must maintain high biosecurity standards with support from management, staff, and suppliers. The virus can also spread through wild boars and invasive equipment like tattooers and castration knives.
A comprehensive biosecurity plan, combined with consistent training and compliance, is essential to minimize the risk of PRRS outbreaks and maintain herd health.
To establish an effective biosecurity program for PRRS prevention and control it is essential to understand how the virus is transmitted.
Transmission of the disease can occur via a variety of routes; vertically, horizontally, direct, indirect and by air.
Vertical transmission is from one generation to the next, by infection of the embryo or foetus in the uterus (womb).
This can produce symptomless long-term carriers e.g. the next generation of pigs (contact your veterinarian for further advice addressing this endemic form of transmission). This can have long-term implications
in the control of the disease in endemically infected herds and is considered a serious breach of biosecurity.
Horizontal infection occurs most frequently from pig to pig, direct contact. Infected pigs can secrete high levels of virus in nasal secretions, saliva, urine, semen, milk, blood and faeces, which subsequently exposes previously non-infected pigs to the disease.
Additionally, indirect transmission of the disease can occur via coughing & sneezing, and contaminated equipment, clothing, footwear, farm personnel and, most importantly, vehicles. Temperature also plays an important role in transmission, with the PRRS virus surviving much better in cold conditions rather than warm.
Aerial transmission of the PRRS virus, via the wind, has been recorded at up to 5.5 miles (9km) making the proximity of neighbouring production sites possible vectors of transmission, if they are PRRS positive.
So how can the horizontal spread of this highly contagious and devastating pig disease be prevented and controlled?
Biosecurity is the only real way. It will reduce the impact on affected farms and will be a key to clinical recovery and virus elimination, especially on larger farms.
Producers need to achieve the highest possible levels of biosecurity, leveraged by good buy-in and compliance from management, their staff and their suppliers.
PRRS is very good at ‘Hitching a ride’ so it spreads easily. A high proportion of spread will be by pig transportation, and so is the first target of biosecurity.
However, there are many other means of spread. All other transport is a risk, from feed to dead-haul, to service vehicles, to manure removal. People can also be vectors, via their clothes, on their boots and large equipment, or any inanimate objects they may bring onto, or move around the unit. Wild boars are also a potential source of the infection.
Additionally, invasive equipment which enters the body such as, tattooers, castration knives, and tail dockers should be considered important vectors through which the transfer of infection from one pig to another is made possible.
Vehicle washes must remove manure, clean, disinfect, and prevent cross-contamination. Drying and heating trucks post-cleaning is helpful but not a replacement. Additional tools include disinfectant sprays, dedicated feed and equipment bays, external washes, remote dead pig collection, and entry facilities like showers or Danish entry systems.
Special attention should also be given to evaporative cooling systems, particularly cooling cell pads. Adding disinfectant to water tanks used in these systems helps reduce the risk of aerial transmission via contaminated dust particles, further strengthening airborne disease control measures.
Key Tools:
Virkon® S and Virkon® LSP are vital for an advanced biosecurity cleaning and disinfection program. Water alone reduces contamination by 60%, while a heavy-duty detergent cuts the organic load by 99%.
Virkon® Sand Virkon® LSP have been independently tested and proven effective against PRRS virus.
| Disease |
LANXESS |
Method | Dilution rate |
Contact time |
Temperature |
| PRRS | Virkon®S | US EPA | 0.5% | 1 min | 5 °C |
| 0.17% | 10 min |
5 °C |
|||
| PRRS | Virkon®LSP |
US EPA | 0.16% | 10 min | 20 °C |
The disinfectant must be effective against PRRS and other pig pathogens. Virkon® S has proven broad-spectrum activity, demonstrated by independent lab tests, inactivating PRRS virus at various dilution rates even in cold conditions. Adding Propylene Glycol to Virkon® S solutions can lower the freezing point to -10˚C without affecting efficacy.
Virkon® S can be sprayed around animals at a 1:200 dilution, offering continuous disinfection during periods of heightened disease risks, making it ideal and suitable for all stages of production, from nursery to slaughter plant.
Review your biosecurity plans at all levels using a risk-based approach with your veterinarian, management team, and staff.
Key areas:
- Transport: Use dedicated transport for breeding herds, separate for infected and clean farms, with strict delivery and collection protocols.
- Personnel movement: Limit staff sharing and movement between units.
- Equipment, waste, and dead pig removal: Ensure proper planning for delivery and removal.
- Wildlife control: Prevent entry of large animals with a secure perimeter; review control of rodents, birds, and insects, as they may transmit PRRS.
- General rule: Never share resources between positive and negative units.
Effective biosecurity relies on maintaining strict separation between clean and dirty areas, such as between loading bays, pig transporters, and the clean/dirty sides in a Danish entry system. Proper procedures must be in place to maintain these separations.
Other essential procedures include:
- Correct use of shower facilities
- Disinfection of all incoming equipment and supplies
- Disinfection after risk vehicles approach the farm
- Proper behavior during manure handling and hauling
When dealing with infected farms practicing bio-containment, procedures are essential to prevent further spread, including controlling staff movement, cleaning walkways after pig movement, and thorough cleaning and disinfection between batches.
Biosecurity coordinators should prioritize training, reviewing, and retraining. High staff turnover is a challenge, and keeping up to date is essential.
Compliance is critical—failure to comply will lead to biosecurity breaches.