American PRRSv outbreaks in a traditional European strain PRRSv country. Case report.

Portugal is a country in south-west Europe where PRRSv strains affecting swine are mainly from the European type. Most of PRRS vaccines used have European strains. During late 2014 and 2015, we recorded 18 new cases of confirmed American type PRRSv (AS-PRRS), in farms previously positive for European type PRRSv (EU-PRRS) and vaccinated against European strains. All affected farms showed reproductive symptoms in sows and respiratory symptoms in nursery and fattening pigs. The purpose of this paper is to report this occurrence and to identify possible sources of infection for this new strain of PRRSv in our country.

We collected data from 20 farms from 4 Districts that had a confirmed PRRS outbreak (that means PRRS clinical signs and ELISA/ RT-PCR positive for PRRSv).

All farms belong to 4 different companies. Most farms (15/20) produce nursery piglets and 5 are farrow-to-finish. Clinical signs: 18/20 farms had mainly reproductive problems, including late and mid-term abortions, low fertility and higher number of stillbirths, as well as lower vitality of piglets born with higher mortality during lactation stage (up to 25%). 8 farms had respiratory problems in nursery piglets and only 2 in fattening pigs. These farms were previously stable for ES-PRRSv, and were vaccinated with live vaccines. Materials collected for diagnosis included blood samples from affected sows, piglets and fatteners, lungs and abortions. Results for ELISA and/or RT-PCR confirmed AS-PRRSv strain in 18/20 farms. One strain was sequenced, showing 99% homology with the US reference strain. Possible sources of the new virus: a) Live animals: All farms received negative AS-PRRSv gilts before; b) AI Semen: All farms received AI Semen from 3 external AI Centers, receiving boars from central Europe. PRRS control in the boars was done only by Elisa kits that may fail to detect AB from all PRRSv strains; c) Personnel working in several farms: Some maintenance workers did not follow strict biosecurity rules between farms, specially concerning tools and equipment; d) Lack of proper biosecurity of transport trucks: possible, but not different than before, one of the companies had high biosecurity protocols; e) lack of proper diagnostic tools in previous outbreaks: possible.

The origin of the AS-PRRSv that affects these farms could not be accurately identified. AI Semen is the most probable cause in at least 6 of the affected farms. Biosecurity failure from personnel and transport trucks are the 2nd and 3rd possible causes. Diagnostic failure to detect AS-PRRSv in the past is the 4th cause. Further sequencing of these PRRSv will enable us to understand the epidemiology of this outbreak.

Disclosure of Interest: None Declared.