Infection dynamics, transmission, and evolution after an outbreak of porcine reproductive and respiratory syndrome virus

Abstract

The present study was aimed at describing the infection dynamics, transmission, and evolution of porcine reproductive and respiratory syndrome virus (PRRSV) after an outbreak in a 300-sow farrow-to-wean farm that was implementing a vaccination program. Three subsequent batches of piglets (9–11 litters/batch) were followed 1.5 (Batch 1), 8 (Batch 2), and 12 months after (Batch 3) from birth to 9 weeks of age. The RT-qPCR analysis showed that shortly after the outbreak (Batch 1), one third of sows were delivering infected piglets and the cumulative incidence reached 80% by 9 weeks of age. In contrast, in Batch 2, only 10% animals in total got infected in the same period. In Batch 3, 60% litters had born-infected animals and cumulative incidence rose to 78%. Higher viral genetic diversity was observed in Batch 1, with 4 viral clades circulating, of which 3 could be traced to vertical transmission events, suggesting the existence of founder viral variants. In Batch 3 though only one variant was found, distinguishable from those circulating previously, suggesting that a selection process had occurred. ELISA antibodies at 2 weeks of age were significantly higher in Batch 1 and 3 compared to Batch 2, while low levels of neutralizing antibodies were detected in either piglets or sows in all batches. In addition, some sows present in Batch 1 and 3 delivered infected piglets twice, and the offspring were devoid of neutralizing antibodies at 2 weeks of age. These results suggest that a high viral diversity was featured at the initial outbreak followed by a phase of limited circulation, but subsequently an escape variant emerged in the population causing a rebound of vertical transmission. The presence of unresponsive sows that had vertical transmission events could have contributed to the transmission. Moreover, the records of contacts between animals and the phylogenetic analyses allowed to trace back 87 and 47% of the transmission chains in Batch 1 and 3, respectively. Most animals transmitted the infection to 1–3 pen-mates, but super-spreaders were also identified. One animal that was born-viremic and persisted as viremic for the whole study period did not contribute to transmission.

Spatiotemporal Distribution of PRRSV-1 Clades in Hungary with a Focus on the Era of Disease Eradication

“…One crucial pillar of disease control is the genetic characterization of circulating virus strains in order to identify the origin of infection and determine the routes of transmission between pig farms, within a geographical region or an administrative area. Sequencing one of the most variable genomic regions, the ORF5, is still a gold-standard procedure for surveying these issues [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ]. The information obtained by means of molecular epidemiology further assists the improvement of external disease control measures of a given pig herd and provides the basis for reliable production of animal goods.…”

Epidemiological Investigation and Bioinformatics Analysis of PRRSV, PCV2, and PCV3 in Guangdong Province, China

“…Currently, the e cacy of PRRSV vaccines in China has signi cantly weakened, and new infection cases have been reported in multiple regions. The main reason for this lies in the fact that PRRSV, being an RNA virus, lacks proofreading mechanisms during its replication, making it highly prone to mutations, resulting in diverse and complex patterns of its prevalence [9,49]. Similarly, porcine circovirus, especially PCV2, exhibits a high genetic variability despite being a DNA virus, with nucleotide mutation rates comparable to RNA viruses.…”

Porcine Reproductive and Respiratory Syndrome (PRRSV2) Viral Diversity within a Farrow-to-Wean Farm Cohort Study

“…Because the response to infection might vary by individual, these results might not represent animals born to subsequent weekly batches. In fact, this could be illustrated by a recent study in which higher PRRSV1 diversity was found within batches 1.5 months after the outbreak onset than within batches 12 months after, possibly representing the emergence of an escape variant [ 38 ].…”