Increasing incidence of viruses has had a major impact on modern pig production practices and more commonly than often realised
Production viruses cause extensive primary and secondary diseases
They are involved in multi-pathogen complexes which are difficult to treat and expensive to manage
Viral infections are ongoing and often sub-clinical
Antibiotics have almost no effect against viruses
Vaccination not always successful and can be expensive
Biosecurity programmes must include disinfectants with proven virucidal activity
Laboratory and field research highlight DuPont Animal Health Solutions Virkon® S for its proven, on-farm performance.
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In the late 1980’s and early 1990’s pig production throughout the world started to experience achange in disease patterns that has had a profound impact on the way we have kept pigs eversince. Prior to that time most diseases were bacterial or mycoplasmal. Viral disease occurredeither as discrete outbreaks or as emergency diseases such as Foot and Mouth Disease orClassical Swine Fever.
The change started with the emergence of Porcine Reproductive and Respiratory Syndrome(PRRS), and has been followed by diseases such as Swine Influenza and Porcine CircovirusDisease (PCVD) which includes PMWS. These diseases can produce major outbreaks if they areintroduced into a naïve herd, but are now more commonly seen as lower grade ongoing infections which have a daily impact on unit health and productivity. These “production” viruses can cause disease in their own right, but also tend to have an immunosuppressive impact allowing other pathogens to cause problems. Worse is when several of these viruses interact on a farm to cause multi-pathogen diseases such as a Porcine Respiratory Disease Complex (PRDC). This major respiratory problem usually involves PRRS, PCV2, Mycoplasma hyopneumoniae and bacteria such as Pasteurella multocida and Actinobacillus pleuropneumoniae (APP). The resultantcombination has devastating effects on farm and can be almost impossible to control without major changes in management.
Not just an emergency outbreak
Major outbreaks of viral disease have hit the headlines over recent years. Notifiable diseases such as Foot and Mouth Disease have had a major impact, mainly through the restrictions needed to control them. There have also been the initial outbreaks of these production viruses leading to major disease. Anyone who has experienced the trauma of abortions, stillbirths, weak pigs and mortality in a PRRS infection in a naïve unprotected herd will tell you how bad it was. So will a farmer experiencing the devastating losses of PMWS.
The trouble is that although the headline losses have gone away the impact of these production viruses goes on from day to day draining productivity and costing money. Herds that were achieving a wean-to-finish mortality of 2.5% before infection with PRRS now struggle to get below 5%. Herds with PCVD are the same and herds with both might have losses of 7% or more throughout this stage. The costs are not just in mortality, but also in lost performance, increased medication costs and the changes in management needed to control them. Just think, would so many people have gone to batch farrowing or very large units if we hadn’t had these diseases? What have the impacts of batching and large units been on reproduction?
These viruses are common
You only have to look around European pig production to know how common these viruses have become. Except for the high biosecurity units with good geographic location, most units have ongoing problems with at least one of the following: PRRS, PCV2, Swine Influenza or Porcine Respiratory Coronavirus (PRCV). They may not be causing major disease, but they are eroding potential profitability on a daily basis.
So why don’t we recognise the extent of these viruses on a day to day basis? One of the problems is that diagnostic tests cost money and are not done routinely. Even if they are carried out it is difficult to interpret the results, after all we know the virus is there, we just don’t know if it is active. The result is that the infections become under diagnosed and people tend to forget they are a problem and instead look at more obvious bacterial problems. A typical example would be where a Glassers Disease (Haemophilus parasuis) problem was leading to special medication and/orvaccination, but was being aggravated by PRRS. Also look at the way that PCV2 vaccination has led to performance on some farms becoming better than before PMWS started. PCV2 was obviously doing something before PMWS.
Their impact is high
The real issue is that these production viruses are on the farm causing problems everyday. These problems may not be headline makers, but by virtue of their ongoing nature they cost a lot of money. PCV2 infection leading to increased Salmonella and E.coli infections in newly weaned pigs will slow growth in crucial periods and lead to gut damage that will have an ongoing impact on the pig, and this might be without showing any of the other signs of PMWS. Not only that but they can interfere with other disease control measures as demonstrated by workers from Iowa State University who showed that high PCV2 challenge can interfere with PRRS vaccination and protection1.
So we have got to control them!
The impact of these viruses is ongoing and they are easily spread from pig to pig and farm to farm.As we have seen they are having a profound, often unseen, impact. So we have got to work atcontrolling them. How can we do this?
The first point may seem obvious, but is often forgotten. With one minor exception antibiotics have no effect on these viruses, so using antibiotics will only reduce the secondary bacterial effects, not the primary hidden virus.
The most common method of control is vaccination. The development of PRRS and then PCV2 vaccines were eagerly awaited. They have been of major help in reducing losses and will undoubtedly be a long term part of viral control. The problem is that they can cost a lot of money and often are laborious to give. Importantly the protection they offer is not always perfect. This can be due to faulty administration, changes in the virus (e.g. differing PRRS strains) or just too much challenge2,3 on the farm.
Too much challenge
It’s this phrase that gives a hint to the other major method of controlling production viruses apart from vaccination. The way we can control these viruses is by reducing their levels on the farm, especially at times when infection is potentially critical. It was this concept that lead to the development of multiple site production systems that now dominate major pig production. By separating pigs of different ages onto different sites we have not only reduced these diseases, but also many of the more traditional diseases, and it’s all down to reduced challenge. Smaller enterprises can still get many of the same benefits by improving pig flow and segregation throughout the unit. Separate different age groups into different areas on the farm and make sure rooms and possibly buildings are operated on a strictly all-in, all-out basis.
For segregation to work properly, be it on a large scale or smaller farm, we have got to prevent infection spreading from group to group of pigs, and this is where we must use a specialist biosecurity programme, for example the Pig Biosecurity Programme from DuPont Animal Health Solutions. This works at two levels. First pigs must move into accommodation that has been thoroughly cleaned and disinfected after the last batch. Secondly once a group is in its housing we must prevent the spread of infection from other groups. This includes such things as controlling personnel movements, foot dips, vehicle biosecurity, use of separate equipment and the many other areas of continuous biosecurity.
There is however another major fundamental biosecurity pitfall that many farmers fail to appreciate and which leads to production viruses remaining an issue on their farms. The problem is that we are talking about viruses and in the case of some (e.g. PCV2) these are highly resistant viruses. This is demonstrated by US research which shows that Virkon® S was the only disinfectant which achieved internationally acceptable kill levels against PCV24.
Real world virus control
Field experience and a series of studies have implicated live pig transport as an important method of spread of PRRS into farms and within pig flows5,6. Dr Scott Dee and colleagues from the Swine Disease Eradication Center, University of Minnesota recently published important results aimed at helping producers reduce the risk of spread of highly infective PRRS virus by live animal transport7 .
Scott Dee’s study was performed on a full size pig trailer under practical constraints to match field conditions. The researchers selected Virkon® S as the study disinfectant due to its proven broad spectrum virucidal activity including against PRRSV. Their results were excellent, producing “good inactivation of PRRSV within the target time when cold water was used and disinfection applied by foaming”. This work coupled with the known broad spectrum of activity of Virkon® S confirmed that this is the disinfectant of choice for transport biosecurity.
To conclude, it is essential to choose a disinfectant that has a broad proven efficacy against viruses and bacteria. Virkon® S (DuPont Animal Health Solutions) has been proven to meet this requirement better than any of its competitors4,7 and must be the final piece in the jigsaw that is recognising and combating the effects of production viruses in pig production. The use of Virkon® S as part of a control strategy for ongoing production virus infections has been widely reported in the scientific and industry literature8,9,10,11 . Without effective biosecurity using Virkon® S these viruses will continue to cost the pig producer huge amounts of money every day.
1 Opriessnig, T, McKeown, NE, Harmon, KL, Meng XJ, Halbur PG. 2006a. Porcine circovirus type 2 infection decreases the efficacy of a modified live porcine reproductive and respiratory syndrome virus vaccine. Clin Vaccine Immunol. 13:923-929.
2 Yoon K-J. et al. Effect of challenge dose and route on PRRS virus infection in young swine. Vet Rec (1999) 30: 629-638
3 McKintosh K et al (2007) 5th International Symposium on Emerging and Re-emerging Pig Diseases – Krakow Poland 2007 - p131
4 Royer, R.L. (2001) Susceptibility of Porcine Circovirus type 2 to commercial and laboratory disinfectants. J. Swine Health Prod. 9 (6) 281-284
5 Dee S. et al. Mechanical transmission of PRRS virus through a co-ordinated sequence of events during cold weather. Can. J Vet Res (2002) 232-239.
6 Poumain, E Disinfection of trucks and trailers. Rev Sci Tech Off Int Epiz (1995) 14: 171-176
7 Dee SA, Deen J, Pijoan C. Evaluation of an industry-based sanitation protocol for full-size transport vehicles contaminated with porcine reproductive and respiratory syndrome virus. J Swine Health Prod. 2006;14(6):307–311.
8 Desrosiers, R. (2007) Advances in Pork Production Volume 18, pg. 35
10 John Gadd article in Alberta Pork, Thoughts from Europe, Summer 2001.
11 Jim McKean, ISU Veterinarian & Assistant Director, Iowa Pork Industry Centre, presentation at Iowa Pork Regional Conference 2006.