How widespread is PRRSV in my country and which strain is dominant?

These can be difficult questions to answer.

1. Seroprevalence studies are often only carried out when there is a disease problem in a particular herd. This gives no real indication of the disease picture over the country as a whole.
   In a number of countries seroprevalence data are available from the National Veterinary Laboratory or a similar organisation. Some studies have shown the PRRSV infection has become endemic in nearly all the main important swine producing areas of the world.
   
2. The two main genotypes of PRRSV are the European and the North American (EU and NA). In North America only the NA type is found, even if isolations of European-like genotype have been reported (Ropp at al. 2004). In Europe, the EU type predominates. To date no field strains of the NA type have been isolated in Western Europe . In those countries where the NA type is also present, it was probably introduced through the use of a live attenuated PRRSV vaccine since 1996 (Madsen et al, 1998; Oleksiewicz et al, 1998). Both genotypes exist in Asia and South America. On individual sow farm level, the "PRRSV sequence monitor" can identify newly introduced strains and so verify the efficacy of a biosecurity program.

There was a positive PRRSV-antibody result in one adult sow recently. Does this mean that PRRSV is active in my herd?

My herd is PRRSV-free at the moment. What are my chances of becoming PRRSV-positive?

You can take steps to reduce the chances by implementing different biosecurity measures and procedures. You should only purchase replacements which are PRRSV-negative, because the most likely way to introduce infection is by buying in infected animals. If semen is purchased, this should be from a known PRRSV free source. Furthermore other means in which PRRSV is spread: infected needles, local airborne spread etc, should be taken into account.

If PRRS is widespread in my herd won't all my pigs be immune?

No, for the following reasons:

1. Immunity in sows and boars is not life-long.
2. A herd is a dynamic population, frequently taking in new animals. And because virus excretion does not continue indefinitely, a susceptible sub-population may emerge, even on an infected farm.

In grower and finisher units the situation is different. As the level of immunity passed on from sows has worn off by 4-6 weeks of age, the offspring of infected or vaccinated sows then become susceptible to PRRSV infections. Field studies have shown that, at the end of the finishing period, most pigs have seroconverted, indicating that they have contracted PRRS.

My herd is PRRS-positive but my finishers perform pretty well. Will vaccination give me even better results?

It depends what you mean by 'perform pretty well', and how much you spend on antibiotics or other medication to maintain this performance. If PRRSV is the only respiratory pathogen in your finishers, vaccination against PRRSV is not very likely to have much effect on production parameters; but that would be a very rare situation. It's far more common for finishers to harbour a variety of pathogens, in which case PRRSV vaccination will be very likely to improve their performance. It should also reduce the need for antibiotics to treat respiratory disease, resulting in reduced costs.

After a recent outbreak of pneumonia in my finishing pigs, antibody to PRRSV was detected. Will vaccination of finishing pigs prevent pneumonia in the future?

Vaccination with Porcilis PRRS will reduce the effects of a PRRS virus infection in finishers, including pneumonia. But the vaccine needs to be given before they become infected. You must remember that PRRSV is not the only cause of respiratory disease; many other pathogens are usually involved as well. So you may get some pneumonia in spite of vaccinating with Porcilis PRRS, but you should see improvements in ADG, FCR and mortality rates, and a reduced need for treatment of respiratory disease.

Having been free of PRRS until recently, I am now seeing much more respiratory disease in pigs. Antibodies against PRRSV have been detected in samples. Do I need to vaccinate all my finishing pigs or just the young ones?

If you've had a recent outbreak of PRRS, it is likely that all the present finishing pigs will already have been infected. In general terms, vaccinating older pigs is worthwhile if infection is spreading only slowly through the herd. It also helps to reduce the excretion of virus, or even stop it altogether. But vaccinating young animals 4 weeks before infection should protect them during the finishing period.

I have had PRRS in the finishing herd for years which animals should I vaccinate and when?

It is always helpful to known when the infection takes place and to vaccinate the pigs 3 -4 weeks prior to it.

I have been using Porcilis PRRS for several years and I have seen no sign of any problems in either the breeding herd or the finishing pigs. I am considering stopping vaccination. How can I tell if the virus is still present?

This is a very satisfactory situation, so any change should be considered very carefully indeed. Just because the disease situation is under control at the moment does not guarantee that there is no infection pressure. Having checked that you have covered all the possible means by which PRRS virus could be introduced into the herd, you might consider using a group of growers as sentinels to check whether virus is still circulating, by not vaccinating them. If this group remains sero-negative, it will give some weight to the argument in favour of ceasing to vaccinate the herd.

I sell some gilts and some of my customers ask for PRRSV-negative animals. If I vaccinate all my young pigs will this affect the market for my stock?

Yes, it probably would. If the market requires PRRSV-negative gilts, then sero-positive gilts are likely to be refused. The antibodies induced by vaccination cannot be distinguished from those induced by a field virus infection.

I want to make sure that all breeding stock joining the herd will not suffer PRRS disease. Can I vaccinate them and at what age should I do it?

Ideally, gilts should be vaccinated before they join the breeding herd. Porcilis PRRS can be given from 2 weeks of age. There should be at least 4 weeks between vaccination and joining the herd. However gilts coming from a PRRSV negative farm should not be vaccinated at the farm of origin. Vaccination in a quarantine facility before entering the breeding farm would be a good option.

My gilt supplier is PRRS-positive. They deliver them at 90 kg. Can I still vaccinate gilts on arrival?

If you are PRRSV-negative, then these PRRSV-positive gilts should not be allowed on the farm. You should only buy PRRSV-free stock. If you are PRRSV-positive it is advised to vaccinate gilts on arrival before entering the breeding farm.

I intend to purchase vaccinated gilts, when will I need to revaccinate these animals?

For gilts revaccination during quarantine the latest 2-4 weeks before mating is recommended.

I am going to use Porcilis PRRS in my breeding herd because we have just detected PRRS for the first time and it is affecting litter size and viability. I have heard that it is OK to vaccinate lactating sows. Can I vaccinate any pregnant animals?

Mass vaccination is one of the vaccination schedules advised in the breeding herd. If you choose this approach, revaccination is recommended at 4 month intervals. However, in herds with an unknown or mostly negative PRRS-status a tiered approach to vaccination might be useful. Only sows up to day 60 of pregnancy are vaccinated in the first round, all other sows are vaccinated after farrowing (grosse Beilage u. grosse Beilage 2004). This tiered approach ensures maximum safety. However, it takes 12 weeks before basic immunisation of the herd is finalized

I am going to use Porcilis PRRS in my breeding herd because we have just detected PRRS for the first time and it is affecting litter size and viability. How soon after vaccination should I see an improvement?

A recently infected farm is always a difficult scenario to give advice on, it depends largely on management. Normally PRRS virus spreads rapidly, so all sows will have seroconverted within a few weeks. It is therefore best to concentrate on protecting replacement stock and growers or finishers. But if there are many separate units and some of them are not yet infected with PRRSV, vaccination may be worthwhile. If only lactating sows are vaccinated, it will take until the following farrowing before seeing the benefits of vaccination. During an acute outbreak of abortions, when we vaccinate pregnant sows too, some of them could have reproductive disorders already in progress. So we should be aware of the fact that even abortion due to field virus can be seen for some time after PRRS vaccination.

Once I have injected a sow when should I consider revaccination?

To maintain a high homologous level of immunity, revaccination at regular intervals is recommended, either before each gestation or at random at 4 month intervals.

It would be less stressful to my pigs if I could vaccinate with Porcilis PRRS at weaning (3 - 4 weeks of age), can I do this?

It is absolutely essential to vaccinate piglets at least 2-3 weeks before field infection takes place. In some instances this can be as early as two weeks of age. Some farmers are already using this schedule without any evidence of reduced efficacy. Porcilis PRRS is licensed in piglets from 2 weeks of age onwards and according to registration data we have produced, the vaccination of young piglets is able to induce protection, even if they are MDA-positive.
However, you should keep in mind that there might be some interference with maternal immunity, especially if it comes to seroconversion after vaccination.

My pigs are vaccinated against Mycoplasma at weaning, can I also use the Porcilis PRRS vaccine at weaning?

Porcilis PRRS is licensed for use from 2 weeks of age onwards, we can administer it at weaning. Preliminary data about the combined use of Porcilis PRRS with Porcilis M Hyo show no interference with the vaccine efficacy of Porcilis M Hyo (Drexler, 2006; Witvliet, 2006).