Risk Assessment of the Introduction of Porcine Reproductive and Respiratory Syndrome Virus via Boar Semen into Switzerland as an Example of a PRRSV-Free Country

Abstract

Switzerland is currently porcine reproductive and respiratory syndrome virus (PRRSV) free, but semen imports from PRRSV-infected European countries are increasing. As the virus can be transmitted via semen, for example, when a free boar stud becomes infected, and the risk of its import in terms of PRRSV introduction is unknown, the annual probability to accidentally import the virus into Switzerland was estimated in a risk assessment. A quantitative stochastic model was set up with data comprised by import figures of 2010, interviews with boar stud owners and expert opinion. It resulted in an annual median number of 0.18 imported ejaculates (= imported semen doses from one collection from one donor) from PRRSV-infected boars. Hence, one infected ejaculate would be imported every 6 years and infect a mean of 10 sows. These results suggest that under current circumstances, there is a substantial risk of PRRSV introduction into Switzerland via imported boar semen and that measures to enhance safety of imports should be taken. The time from infection of a previously negative boar stud to its detection had the highest impact on the number of imported 'positive' ejaculates. Therefore, emphasis should be placed on PRRSV monitoring protocols in boar studs. Results indicated that a substantial increase in safety could only be achieved with much tighter sampling protocols than currently performed. Generally, the model could easily be customized for other applications like other countries or regions or even sow farms that want to estimate their risk when purchasing semen from a particular boar stud.

An Outbreak of Porcine Reproductive and Respiratory Syndrome Virus in Switzerland Following Import of Boar Semen

“…Even though a biweekly PRRSV monitoring was in place, it did not prevent introduction of infectious semen into Switzerland. This confirms findings of an earlier risk assessment (Nathues et al., ) that current monitoring protocols in many boar studs cannot be considered sufficient for a timely detection of an infection in the stud. Firstly, the examination interval of 2 weeks was too long.…”

Population structure, genetic diversity and pathotypes of Streptococcus suis isolated during the last 13 years from diseased pigs in Switzerland

“…The physiological behavior in nesting is impaired due to the narrowing conditions in farrowing crates and consequently, a more natural environment helps to avoid complications during birth of piglets thereby strengthening their immune status. In addition, Switzerland is considered to be free of porcine reproductive and respiratory syndrome virus (PRRSV) [49] and Mycoplasma hyopneumoniae [50]. Moreover, a majority of farms vaccinate piglets against porcine circovirus (PCV) [51].…”

Diagnosis of the Lelystad strain of Porcine reproductive and respiratory syndrome virus infection in individually housed pigs: comparison between serum and oral fluid samples for viral nucleic acid and antibody detection

“…8 In Europe, PRRSV is endemic in nearly all countries with major pig production, whereas countries with smaller swine stocks such as Finland, Norway, Sweden, and Switzerland are considered PRRSV free. 18 PRRSV is differentiated into 2 genetically distinct genotypes: type 1, or European genotype, and type 2, or North American genotype. Based on DNA sequencing of open reading frame (ORF)5 and ORF7, 3 genetic subtypes are recognized in type 1 PRRSV, and the presence of a fourth subtype has been proposed.…”