Porcine Reproductive Respiratory Sydrome
Porcine Reproductive and Respiratory Syndrome (PRRS) is endemic in large areas of the world and has a significant impact on the global pig industry. It is viewed by many pig veterinarians as one of the most economically important diseases affecting the global swine production industry.
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.