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PRRSV control strategies in Germany

More than half of the pig population is housed in only one region with a very high pig density and it is very likely that elimination would only be possible with the help of a mandatory national program supported by the EU.

Within the 27 EU countries, Germany has, currently, the largest pig production, that has reached a size of approx. 27,5 million pigs. The majority of the pig production takes place in the federal states of Lower Saxony and North Rhine Westphalia, both located in the North-West of Germany, where the 55% of the total pig population is housed. In some of the rural counties in this region the pig density is higher than 1,000 pigs per 100 hectares.

Since the early 1990s the German pig, as well as the wild boar population, are endemically infected with the PRRSV EU wild type strain, and since 1994 vaccine-related PRRSV NA strains are also frequently found. The ratio of infected pig herds is estimated to be 80%, at least.

Control by means of vaccination

Vaccination against PRRS is the most popular method for controlling the clinical disease caused by the PRRSV infection. Approximately an 80% of the sow herds are vaccinated to prevent reproductive disorders. The most common protocol comprises the vaccination of the entire sow herd with a 4 month interval. In PRRS unstable sow herds (according to the definition by Holtkamp et al. 2011) a herd vaccination interval of 3 months is preferred. Other vaccination protocols like at the 5th day of lactation/50th day of gestation or 6th day of lactation/60th day of gestation are not very frequently performed. PRRS vaccination in piglets for fighting the associated respiratory disease is not commonly used. The ratio of herds in which piglets are vaccinated against the PRRS can be estimated as being 20 to 30%. In these herds piglets are usually vaccinated at 2 weeks of age. In Germany, two attenuated PRRS vaccines based on the EU and on the NA strain, respectively, are licensed for application in sows and piglets (status quo November 2012). Moreover, a killed NA strain vaccine is licensed to be used in sows. The market share of the attenuated vaccines can be estimated as being higher than 90%.

Control by means of biosecurity and management measures

The prevention of the transmission of the PRRSV into herds free from this infectious agent, as well as the introduction of “different” strains into the endemically infected herds has become a major concern for many pig farmers, especially the owners of sow herds. Consequently, there is an increasing interest in purchasing replacement gilts, as well as semen, only from sources that are free from PRRSV. In winter 2011/12, a re-infection of three PRRSV-free boar-studs and the transmission of the virus via semen to several sow herds encouraged the pig farmers' interest in a critical evaluation of the intensity of the particular monitoring protocols.

Elimination

The elimination of the PRRSV is discussed in Germany like it is done in other European countries. The elimination has successfully been carried out in single herds, especially in nucleus and multiplier herds of some breeding companies. On an overall low level, herds producing slaughter pigs have also successfully eliminated PRRSV. Currently, the PRRSV elimination in German pig herds is only recommended for single herds, that are located in regions with a low pig density and no PRRSV positive pig holdings within a radius of at least 1,000 m (2,000 m being better). Since these recommendations do not apply to the majority of the pig herds in Germany, at this moment the PRRSV elimination is not an option for most of the pig farms. Nonetheless, the opportunities for regional or national PRRSV elimination programs are intensively discussed. Taking into account that more than half of the pig population is housed in only one region with a very high pig density, it is very likely that the elimination is only possible with the help of a mandatory national program supported by the EU.

Moreover, the consequences of the elimination need to be discussed in advance. In case that the PRRSV was successfully eliminated from the German domestic pig population, there would be a high risk of re-introduction from the wild boar population or from pig populations of other countries. The PRRSV is highly contagious, shed for a long period and airborne transmission is a reasonable risk. Moreover, no vaccine that reduces significantly the spread of the virus is available. A conclusion based on these facts is that the “stamping-out” policy, well-known from the fighting against classical swine fever or foot and mouth disease, is, currently, the only known effective strategy to handle a re-introduction of the PRRSV into a pig population on a larger scale, i.e. at a national level. In the face of all the debate on the ethical and economic aspects of culling millions of pigs during an outbreak of a notifiable disease, we need to answer the question whether a new infectious agent controlled by “stamping-out” should be “created” or not, before we start a nationwide PRRSV elimination program.

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