The emergence of porcine epidemic diarrhoea in Croatia: molecular characterization and serology

Abstract

Background: Porcine epidemic diarrhoea (PED) is an emergent/re-emergent viral pig disease (caused by the virus belonging to the Coronaviridae family, in specific the Alphacoronavirus genus) of global importance. Clinical presentation is characterized with acute diarrhoea, vomiting and dehydration in pigs of all ages, with a possible high mortality in suckling piglets. The disease emerged in the USA in 2013 causing heavy losses, and re-emerged in Europe in 2014, but with milder consequences.

Results: In the spring 2016, PED-like symptoms were reported to be seen on an agricultural holding in Eastern Croatia; laboratory workup confirmed the Croatia's first PED outbreak ever. Porcine epidemic diarrhoea virus (PEDV) strain responsible for the outbreak was of the S-INDEL genotype, much the same as other European PEDV strains. In 2017, a post-outbreak serology was carried out in three counties in Eastern Croatia, revealing seropositivity in pigs bred on four large industrial holdings (9.09%). The seroprevalence across PEDV-positive holdings was up to 82.8%. The latter holdings were unanimously managed by an enterprise that had never reported PED before.

Conclusions: PED has emerged in Croatian pig population causing potentially considerable losses. The circulating strain was of the S-INDEL genotype. Serological workup proved PEDV spread to another four agricultural holdings, demonstrating the importance of not only external, but also internal biosecurity measures.

Keywords: Croatia; Domestic pig; ELISA; Outbreak; Porcine epidemic diarrhoea virus; S-INDEL.

Fig. 1

Geographical location of PEDV-positive holdings. The map shows the counties included into serological workup (light grey); 1 Osijek-Baranja County; 2 Vukovar-Srijem County; 3 Brod-Posavina County. The agricultural holdings hosting PEDV antibodies-positive animals are marked with dark blue dots, while the holding hosting the primary PEDV outbreak is tagged with a red rhombus. The map source is available at: https://commons.wikimedia.org/wiki/File:Croatia_location_map.svg (NordNordWest; CC BY-SA 3.0; https://creativecommons.org/licenses/by-sa/3.0)

Fig. 2

Phylogenetic relationship between the Croatian PEDV strain detected in 2016 and the selected reference strains (S gene segment-based). The phylogenetic tree was constructed from an almost complete PEDV S gene and a partial ORF 3 gene (4,173 nt in total) using a neighbour-joining method and the MEGA7 software with p-distances and 1000 bootstrap replicates (indicated adjacent to the nodes when > 70%). The first Croatian PEDV strain (CRO/OB-15343/2016) is tagged with a red rhombus. The GenBank accession numbers for the selected PEDV reference strains are designated within taxa. The scale bar represents the number of nucleotide substitutions per site

Fig. 3

Phylogenetic relationship between the Croatian PEDV strain detected in 2016 and the selected reference strains (RdRp and M gene segments-based). The phylogenetic tree was constructed from partial RdRp gene (a) and partial M gene (b) segments using a neighbour-joining method and the MEGA7 software with p-distances and 1000 bootstrap replicates (indicated adjacent to the nodes when > 70%). The first Croatian PEDV strain (CRO/OB-15343/2016) is tagged with a red rhombus. The GenBank accession numbers for the selected PEDV reference strains are designated within taxa. The scale bar represents the number of nucleotide substitutions per site