Vaccine is key to PRRS control

In response, the Teagasc Pig Development Department organised for PRRS (Porcine Reproductive & Respiratory Syndrome) expert, Anders Elvstroem, a veterinarian from Svinepraksis in Denmark, to meet producers and other industry representatives.

He works in a region which has 30% of herds positive for PRRS, down from a previous high of 90%. He gave a thorough overview of PRRS in Denmark and his experiences to date. This report contains the key messages he had for Irish pig producers and a summary of the Questions & Answers session held after his presentations.

Motivation for PRRS Control

Increased income: PRRS negative pigs (30kg weaners) have a value of €3 to €4 more than PRRS positive pigs.

Other diseases: being PRRS negative enables a unit to have better control over secondary diseases that may occur on the farm.

Reduction of antibiotic use.

PRRS can be eradicated without a stop in production. In terms of cost per sow place, he reported that on a breeding herd, the European strain of PRRS costs, on average, €28 per sow place compared with €95 per sow place for the US strain of the virus.

He stated that the biggest losses occur in finishers at about 55% (through higher mortality, lower average daily gain and higher FCE) whereas 45% of the losses are accounted for in breeding herds.

Vaccination of Gilts

All gilts are vaccinated with the live vaccine. The piglets born subsequently are negative for the virus and the virus can be eradicated by a strict all-in/all-out practice. Using the live vaccine gilts will shed the virus for four to six weeks.

This should always take place in quarantine, i.e. on another site and the quarantine period should last for a minimum of eight weeks, but 12 weeks ideally. It’s best if all-in/all-out practice is used.

Multi-Site Production

This is the key to successful eradication.

It is most important that finishers are moved to a separate site away from the sow herd.

This stops the virus spreading in the herd. Achieving eradication in Ireland would be difficult because of the integrated nature of the herds here, i.e. we don’t have too many multi-site production systems in place.

Conclusion

PRRS can be eliminated while in full production. The biggest challenge is to operate on an all-in/all-out basis.

It is possible to control other respiratory diseases on the farm.

It will see a reduction in medicine or antibiotic usage on farms.

Vaccination protocol:

(a) Negative herds: do nothing. Do not use the live vaccine, it may cause clinical signs and it is too risky to have the real virus circulating. Blood test these farms at least once a year for the PRRS virus and/or on suspicion of any symptoms occurring on the farm.

(b) Positive herds with clinical symptoms: Vaccinate gilts and sows and also piglets if there are symptoms in the finisher stage.

(c) Positive herd — no symptoms: Vaccinate gilts and sows now and continue on an ongoing basis by vaccinating gilts as they come into the herd. You may also need to use antibiotics for treatment of disease on this farm. Don’t wait for the symptoms, they will come, so vaccinate.

Q&A SESSION

The questions and answers session that followed Anders Elvstroem’s presentation is summarised under the following headings:

Vaccine type

Is there any role for the dead PRRS vaccine?

We don’t use it in Denmark. If the live virus comes in, it will cause problems in the unit whether it is vaccinated with the dead vaccine or not.

For a naïve herd at risk from a neighbouring farm, is there any role for the dead vaccine?

You may reduce the clinical symptoms but it is not good enough. It could be used as a precursor, i.e. will give some protection and may result in less clinical symptoms, but if you break with the actual virus, the problems could be significant.

After day 70 of pregnancy, the virus can cross the placenta which could result in six to seven weeks of poor piglets being born. Therefore, is there not a role for the dead vaccine to reduce the effects of this?

Maybe, but you need to consider the financial cost of this. In Denmark, we consider that there is no real role for the dead vaccine.

Should I vaccinate?

My herd is negative for PRRS. However, there is a positive farm within two miles of my farm — what should I do?

I wouldn’t vaccinate a negative herd. It is too risky.

Vaccination Protocol

Gilt vaccination: when and how often should the vaccine be given?

Just once before entry to the main herd.

What’s the best option for Irish herds with their integrated nature and the rearing of gilts on farm as opposed to purchasing them?

It is important never to introduce gilts into a herd that is positive without vaccinating them. They should be vaccinated in quarantine before entering the main herd. They should spend a minimum of eight weeks in quarantine but, ideally, 12 weeks. You can vaccinate them at all stages from 30kg weight upwards.

In the case of an acute outbreak, what procedure should be followed?

Vaccinate all pigs, i.e. sows, gilts and piglets/weaners. This will help speed up the process of elimination.

What are your vaccination recommendations for different types of pigs?

My herd is positive for PRRS but I have no clinical signs. I have vaccinated my sows. What strategy should I pursue?

Continue vaccinating the gilts at least. You may consider doing all piglets if other diseases are a problem, e.g. haemophilus pneumonia. As the unit is an integrated unit, the containment process is the best option, i.e. eradication would be very difficult.

With negative herds, there are mixed recommendations. If you take gilts off-site at 50kg to 70kg weight, vaccinate them with the live vaccine, let them shed the virus and then introduce them back into the herd. Does this mean that after two years you would have negative pigs and would never be exposed to the wild virus? Could this be done with a positive herd with no symptoms?

This strategy would be too risky. They might not have finished shedding before re-introduction. Although the average might be four to six weeks, in terms of shedding, the length varies and it could be much longer. The gilt will have immunity after two years but it’s risky to take her off-site and re-introduce her to the main farm again.

How soon will the effects of the vaccine kick in after blanket vaccination of the herd?

For the last two thirds of pregnancy, i.e. sows that were in the last two thirds of pregnancy when vaccination programme took place. You will have poor pigs but after that things should be okay — approximately four months.

What are your recommendations for symptoms occurring in finishers?

Vaccinate piglets using half the normal dose. They can be vaccinated around weaning at 7kg weight. Financial judgement is required.

If the symptoms in the grower/finisher stage merit vaccination of the piglets, when should you vaccinate?

Vaccinate them at weaning. You can vaccinate for PCV and other diseases at the same time.

How long should you vaccinate piglets if there are clinical problems on-farm?

Continue vaccination until first piglets vaccinated are gone through to slaughter and see how symptoms look at that stage. Then you can re-evaluate your programme.

Is vaccinating gilts enough, i.e. should I also be vaccinating my sows on a regular basis?

Once the gilt is vaccinated, she should be okay as a sow until culled. There is no benefit in vaccinating sows every year. You need to look at the breeding herd and the finisher herd separately, even in an integrated situation. See what the problems are and then vaccinate accordingly.

Should I blanket treat all sows or wait until after farrowing?

If you are in no hurry, vaccinate up to day 70 and after farrowing, i.e. leave the sows in the last four weeks of pregnancy alone to farrow without vaccinating them. You need to get them all vaccinated so they will need to be vaccinated after farrowing.

What protocol should be used from gilts onwards for a de-stocked herd, i.e. what protocol should be used for the new herd?

Blood sample once per year and monitor. The gilts should also have been blood sampled on the supplier herd within the previous month of movement to your quarantine facility.

Use the Elisa test to sample 20 bloods from different sections of the herd and different ages of the pigs on a yearly basis. With regards to the introduction of gilts and the ongoing introduction of gilts, two samples should be negative — one at the supplier unit and one in the quarantine facility before they are moved into the main herd.

If I vaccinate sows just prior to farrowing, do I need to vaccinate their piglets at weaning?

No, there is no need to vaccinate piglets of sows just vaccinated before farrowing.

PRRS Transmission

Is there any risk of spreading disease through slurry spreading, i.e. can the virus be carried in the slurry and is it a risk factor in spreading the disease to other farms?

We don’t consider slurry a factor in carrying PRRS in Denmark. We do not have any limitations from where slurry on positive farms can be spread but, in Denmark, we mostly spread with a bandspreader or direct injection into the ground so there is minimal aerosol created when we are spreading slurry.

What is the most common method of spreading of the virus?

Apart from buying in gilts, aerosol spread (through the air) is the most common method of spread. It can travel up to 4km or 5km in the air. Spread is more common in winter as the virus is more suited to a cold climate. A small percentage can spread through semen.

If the sow is vaccinated, will it pass the virus onto piglets?

The virus will be carried into the growing herd through the piglets. It may or may not cause problems, i.e. symptoms may or may not be seen. In terms of vaccination, it’s a financial issue and to be safe you may need to vaccinate all animals, gilts, sows and piglets.

In addition to the vaccination programme, what additional biosecurity measures should be used?

You need to look at your farm in terms of overall biosecurity. Quarantine is very important. The biggest risk in Denmark is incoming stock onto a farm. Ideally, you should quarantine for 12 weeks but a minimum of eight weeks is necessary for incoming stock. Gilts and boars should be blood tested twice in quarantine before introduction to the main herd.

Is eradication of PRRS possible?

Yes, it is possible and we have gone from 90% positive down to 30% positive. Our advantage is that we have a multi-site production system. Ireland would be at a disadvantage on this basis in that it would be more difficult to eradicate the disease from integrated herds.

Are disinfectants effective against PRRS virus?

Yes, the virus is easily inactivated by phenol, formaldehyde, and most common disinfectants.

General/Danish Situation

Are there positive and negative boar studs in Denmark?

Yes, there are 10 AI studs in Denmark, with about 500 boars in each. Five of the 10 studs are positive. In these studs, boars are vaccinated with the live vaccine, just once, at 7kg weight. The five negative herds source their boars from negative nucleus farms at 22 weeks of age.

Is there a case for having a positive PRRS stud?

Yes, in Denmark, many farms will source their AI from one of the five positive studs. These studs would be vaccinating their boars as they come into the stud. They vaccinate (using the live vaccine) young boars at approximately 7kg weight before entering the AI stud. They are isolated for a period before they are transferred into the stud.

Semen from these boars is subsequently sold as negative for PRRS. Some negative herds are using this vaccinated semen source.