Abstract
In order to assess influenza D virus (IDV) infections in swine in France, reference reagents were produced in specific pathogen free pigs to ensure serological and virological analyses. Hemagglutination inhibition (HI) assays were carried out on 2090 domestic pig sera collected in 2012–2018 in 102 farms. Only 31 sera from breeding sows sampled in 2014–2015 in six farrow-to-finish herds with respiratory disorders contained IDV-specific antibodies. In two of them, within-herd percentage of positive samples (73.3% and 13.3%, respectively) and HI titers (20–160) suggested IDV infections, but virus persistence was not confirmed following new sampling in 2017. All growing pigs tested seronegative, whatever their age and the sampling year. Moreover, PB1-gene RT-qPCR performed on 452 nasal swabs taken in 2015–2018 on pigs with acute respiratory syndrome (137 farms) gave negative results. In Corse, a Mediterranean island where pigs are mainly bred free-range, 2.3% of sera (n = 177) sampled on adult pigs in 2013–2014 obtained low HI titers. Finally, 0.5% of sera from wild boars hunted in 2009–2016 (n = 644) tested positive with low HI titers. These results provide the first serological evidence that sows were exposed to IDV in France but with a limited spread within the swine population.
Highlights
Influenza D virus (IDV), the fourth genus of influenza virus among the Orthomyxoviridae family, is supposed to circulate mainly in cattle which seems to be the natural reservoir
The three specific pathogen free (SPF) pigs inoculated with D/Bovine/Nebraska/9-5/2012 exhibited specific anti-influenza D virus (IDV)
One hyper-immune serum was selected as a positive control for cross-Hemagglutination inhibition (HI) tests and further analyses of unknown swine sera
Summary
Influenza D virus (IDV), the fourth genus of influenza virus among the Orthomyxoviridae family, is supposed to circulate mainly in cattle which seems to be the natural reservoir. Little is still known about exact IDV host range. As suggested by virus detections, serological investigations and/or experimental infections, Viruses 2020, 12, 25; doi:10.3390/v12010025 www.mdpi.com/journal/viruses. Questions about IDV host range relate especially to the role pigs may play in IDV ecology. The virus was first isolated from a pig exhibiting a respiratory syndrome [1]; pigs were demonstrated to be sensitive to IDV infection experimentally [1,21], and to cattle, IDV was isolated or molecularly detected in pigs in different continents, i.e., America [1], Asia [11] and Europe [6,7,8,22]
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