Eradication-PRRS

GIS card

In connection with eradication, the first step is to have a GIS card made (Geographical Information System Card). The GIS card shows your farm in relation to other farms in a 5 km zone plus a calculation of the infection risk of PRRS (there is no distinguishing between the two types) in a radius of 5 km and the infection risk of Mycoplasma and Ap2 in a radius of 3 km.

The GIS card has been improved in respect of PRRS on several points:

• The farms’ own size is now included in the risk calculation as larger farms have a higher risk of infection due to increased air intake.
• Farms in a distance of 5 km are now included compared to 3 km before.
• The air direction is now included in the risk calculation as it is well-documented that PRRS spreads with the wind.
• The likelihood of staying free from PRRS after eradication is now calculated for 1, 2, 3, 4 and 5 years after eradication compared to previously only the first year after eradication.
• It has become possible to simulate changes on neighbouring farms so that potential expansions or eradications are included in the calculation.

Be critical of your GIS card

Is the information and locations of buildings correct and is their status correct?

Unknown status is included as being positive in the calculation, but you can do simulations if their status is known despite them being unknown within SPF.

Considerations of eradication should not be done based on old GIS cards where the information may be obsolete and the new PRRS calculation factors are not included.

A new GIS card can be ordered at sundhedsstyringen@lf.dk.

Alternatively, ask your veterinarian to order one.

Eradication or not?

There are several aspects worth considering before an eradication. In the first instance, the relative risk of reinfection (based on the GIS card) and then whether to do partial or total eradication. In case of partial eradiation, this could be for only one or more diseases at the same time. Finally, economy before and after eradication is a deciding factor. You can always discuss these considerations with your veterinarian who knows you and your herd best.

Eradication method

Here we distinguish between two types: Total eradication and partial eradication

Total eradication: Has the clear advantage that it will remove all SPF diseases in the herd. Furthermore, the infection pressure of other diseases in the herd will be reduced significantly including e.g. influenza, Brachyspira pilosicoli, Lawsonia and Streptococcus suis.

Total eradication is very close to 100% certain if empty periods, cleaning procedure etc. are followed. The disadvantage is of course that it is expensive, but during recessions it is worth considering it. Briefly, the entire system must be empty of pigs for minimum one week and each section for minimum 3 weeks.

Partial eradication: At present, it is possible to partially eradicate pig herds in operation against Mycoplasma hyopneumonia (medical), swine dysentery (medical) and PRRS (operations). Partial eradication against AC is dubious with the present, available types of antibiotic and is therefore not recommended. There are big overlaps in the eradication methods for PRRS and Mycoplasma hyopneumonia – i.e. if you wish to partially eradicate one, you might as well include the other one if the GIS card allows for this. At a partial eradication where Mycoplasma hyopneumonia is included, quite heavy medication in the sow herd is needed. This always has consequences. In the first instance, the positive consequence that partial eradication succeeds but unfortunately also some negative ones in the form of increased mortality during the eradication period (the medicine used has a low toxic dose), resistance development and any long-term effects before the herd is again “stable”.

Specifically, regarding partial eradication of PRRS:

Before a partial eradication of PRRS, it is extremely important to know the PRRS status in the herd. Is the herd stable (i.e. without virus circulation) or is virus circulating in one or more sections on the farm?

If a sow herd is weaning virus negative pigs, it is considered to be stable. If this is the case, the herd can often be partially eradicated by putting a stop to introduction of young gilts (must be planned so that the herd is “boosted” with young gilts for at least 6 months – preferable longer) and an emptying of the nursery.

If the sow herd is unstable i.e. PRRS virus is circulating in the farrowing unit, and pigs are therefore weaned with virus in their bodies, a PRRS partial eradication is typically done according to the following formula:

Load: Insert young gilts for minimum 200 days. This can be done at an external site.

Close: Then the ”sow herd is closed” for introduction of new animals for the next 200 days during which there is extra focus on internal and external biosecurity.

These golden rules are followed:

• When litter equalising, only the excess pigs are moved. As little moving as possible should be done
• Nurse sows must only be made the first 48 hours after farrowing
• Handling of pigs in the pen in order to avoid spreading of infection
• Replace syringes etc. between each litter.
• Sick pigs are euthanised – they must not be moved.
• Wean entire week batches – no weaned pigs in the farrowing unit.
• Strict batch production AI/AO
• No contact between different age groups of pigs

Homogenize: Achieve uniform immunity on all breeding animals by mass vaccinating all young gilts, gilts, sows and boars twice with a 1-month interval. This can be done with a live PRRS vaccine against the type(s) present in the herd. The nurseries are emptied, and the pigs weaned until we can be certain that virus negative pigs are weaned for an external site or a nursery that can be kept 100% separated from the sow herd.

Test strategy

12 weeks after the first mass vaccination, testing of newborn pigs for PRRS virus is started. Processing fluid samples are taken (testicles and tails) every two weeks. This is done from 10 random litters every time. Await 4 negative, consecutive test results (minimum 8 weeks).

Test of newly weaned pigs is started. This is done with pooled rope test samples every two weeks. To ease taking of samples, this can be done in the farrowing unit right before weaning (FOF = Family Oral Fluid. The sow is also allowed to chew on the rope to stimulate the pigs to do this). Await 4 negative, consecutive test results.

Young sentinel gilts are inserted (young, purchased PRRS-negative gilts). These are tested with blood tests 30 days after insertion and again 6 months after the first blood testing to achieve PRRS negative status within SPF.

If the above is followed, most herds will be free from PRRS after maximum 6 months and can be declared PRRS-free within SPF latest one year after start-up.

Partial eradication typically has a success rate of 80-85%.

Whether you choose one method or the other, the herd veterinarian will go through all further procedures with you including wash, disinfection etc.

Individual customisation

There are basically always special conditions on a farm which means that eradication must be customised. It is important to take into account individual conditions to ensure the best success and economy. In respect of PRRS, this might e.g. in some situations be appropriate to use a killed vaccine instead of a live vaccine.

MCREBEL/virus management

The MCREBEL principles are used to limit introduction and to limit spreading of possible virus in a herd.

1. Nurse sows are made with as few moves of piglets as possible.
2. Nurse sows are to the widest extent possible not made later than 48 hours after birth.
3. Let the pigs stay in the pens and avoid unnecessary handling.
4. Always replace syringe between the pens.
5. Do not move sick pigs.
6. Avoid weaned pigs in the farrowing unit (no pigs without a sow).
7. All in/all out at section level.
8. No mixing of age groups.
9. No contact between weaned pigs up to 6 months old and sows.
10. Introduction of young gilts via a quarantine and with prior vaccination.

To prevent spreading of virus, it is also important to ensure optimal ventilation on a farm, be aware of correct vaccination procedure, to vaccinate at the correct time and only vaccinate healthy pigs as they otherwise risk not responding to the vaccine.