Porcine Reproductive Respiratory Sydrome
Prevention & Control
If a pig production site becomes infected with the disease, the PRRS virus spreads rapidly through the herd within 7-10 days, resulting in high morbidity and mortality rates.
Whilst vaccines for PRRS are commercially available in many countries, each type of vaccine possesses its own strengths and limitations against the virus. In general, vaccination of pigs against PRRS does not prevent infection but only helps to reduce transmission of the virus and subsequent clinical disease.
Therefore, advanced biosecurity best practice procedures, using proven effective heavy-duty detergents and broad spectrum virucidal disinfectants is essential for effective prevention, control and eradication of PRRS.
WHAT TO LOOK FOR? THE CLINICAL SIGNS OF PRRS
The clinical signs of PRRS vary with each strain of the virus, the immune status of the pig herd and the flow management procedures on individual production sites. The following table outlines the signs and symptoms of PRRS which should be monitored:
| In adult pigs | In affected litters | In weaned pigs |
| Reduced appetite | Stillborn pigs | Loss of appetite & lethargy |
| Fever | High pre-weaning mortality | Obvious failure to thrive |
| Premature farrowing & abortion | Mummified pigs | Laboured or rapid breathing and/or respiratory distress |
| Death in up to 10% or more of sows | Variably sized weak-born pigs |
Blotchy reddening of the skin |
| Loss of balance, circling and falling to one side | Excess oedema (watery fluid) around the eyes | Rough hair coats |
Contact your swine veterinarian immediately for advice if you identify any of the above symptoms in your herd.
Some infected pigs may fail to show any noticeable symptoms or signs of having PRRS. This is extremely concerning as these animals can often become the mobile vector through which the disease is spread internally, around the farm, or externally to other production sites, even though they don’t appear to be sick.
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.
Thoroughly review your biosecurity plans at all levels using a risk based approach involving your veterinarian, management team and farm staff.
Starting with transport, scheduling is vital; breeding herds should preferably have dedicated transport being at the top of the biosecurity pyramid. Have different transport for infected and free farms and ensure pig delivery and collection procedures adhere to strict biosecurity protocols.
Personnel movement is another target area, with staff sharing avoided and movement only down the pyramid. Advisers, management and field staff are all increased risks as they move more between units.
Delivery and entry of equipment needs planning, as do removal of dead pigs, manure and any other waste. Control of wild animals, rodents and birds should be reviewed as they could possibly transmit the disease mechanically . Ensure a secured perimeter barrier/fence is in place to stop large animals from entering the site.
Review your insect control measures as flies and mosquitoes have been demonstrated to carry the PPRS virus and may have a role to play in the transmission of the disease.
Finally, in planning, there is another good rule that should be adhered to at all times; never share anything between positive or negative units, be it via transport, personnel or equipment.
One of the most important aspects of biosecurity is the understanding and use of lines of separation between “clean” and “dirty” areas. This has to happen throughout the production system, for example, between the loadingbay and ramp and pig transporter between the “dirty” and “clean” sides in a Danish entry system or between the ground and the cab of a feed delivery vehicle. All the relevant lines of separation have to be identified and correct procedures for achieving separation established and used.
There are many other procedures that need complying with. These include such things as correct use of shower facilities, correct procedures for leaving and re-entering the farm, disinfection of equipment arriving at the farm, disinfection after risk vehicles have been near the farm, and contractor and staff behaviour during manure hauling.
In an infected farm, where bio-containment is being practised, examples of procedures are: control of staff movement around the farm, cleaning and disinfection of walkways after pig movement, correct local manure removal and flushing, and high level terminal cleaning and disinfection between batches.
Buy-in and training is an integral part of any biosecurity program. This must include management, farm staff, drivers, service personnel and visitors. They need to understand why biosecurity against horizontal PRRS transmission is important, that it is still important, and how easily the virus spreads so they can understand what they need to do.
Biosecurity coordinators must make it a prime task to train, review and retrain as needed. One challenge is high staff turnover and the need to keep up to date.
Compliance is everything, and failure to comply will lead to a biosecurity breach sooner or later.
Without the right tools, biosecurity will fail
The vehicle washes must allow manure removal, provide good cleaning and subsequent disinfection, and vitally prevent cross contamination. The provision of drying and heating for trucks after cleaning and disinfection is an advantage, but does not replace it. Other examples of good biosecurity tools are disinfectant arc sprays made available on approach to farms, dedicated feed and equipment delivery bays to keep trucks away from pig sheds and becoming a possible vector of transmission, external washes to disinfect where trucks have been, remote dead pig collection, and good entry facilities such as showers or a Danish entry system.
Evaporator cooling cell pad biosecurity disinfection should be another key factor for consideration. Adding disinfectant solution to the water reservoir recirculation tanks provides a constant flow of disinfectant solution over the pads. This helps to reduce the possibility of infection being introduced into a building via aerial transmission on dust particles.
