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Hog Production Viruses:
« on: April 12, 2008, 09:48:42 AM »
Production Viruses - A Global Challenge That's Costing a Fortune
By Jake Waddilove, MA, VetMB, MRCVS. In the late 1980's and early 1990's pig production throughout the world started to experience a change in disease patterns that has had a profound impact on the way we have kept pigs ever since. Before that time most diseases were bacterial or mycoplasmal. Viral disease occurred either as discrete outbreaks or as emergency diseases such as Foot and Mouth Disease or Classical Swine Fever.

Jake Waddilove MRCVS

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 Circovirus Disease (PCVD) which includes PMWS. These diseases can produce major outbreaks if they are introduced into a naive 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 resultant combination 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 naive 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 per cent before infection with PRRS now struggle to get below 5%. Herds with PCVD are the same and herds with both might have losses of  per cent 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?

Very 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/or vaccination, 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.

High Impact
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.

Control Options
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 at controlling 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 Global 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 flows 5,6. 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.

Toughen-up Tactics
In summary, the increasing incidence of viruses has had a major impact on modern pig production practices and more commonly than often realised.
These production viruses cause extensive primary and secondary diseases and are also involved in multi-pathogen complexes that are difficult to treat and expensive to manage.

Viral infections are ongoing, often sub-clinical and do not respond to antibiotic treatments. Vaccination is not always successful either.

Tough biosecurity becomes is vitally important when aiming to control viral pathogens, but programmes must include the use of rigourous disinfectants with a proven virucidal activity. Laboratory and field research highlights that Virkon® S, from DuPont Animal Health Solutions, offers proven, on-farm performance.


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