Detection of Antibodies Against Influenza D Virus in Swine Veterinarians in Italy in 2004

Influenza D virus was firstly isolated from a swine with respiratory disease symptoms in 2011 in USA. Epidemiological and serological studies support the hypothesis that cattle represent the natural reservoir of influenza D virus with periodical spillover events to other animal hosts. Little is known about the seroprevalence in humans and in specific target groups such as veterinarians in Italy. This study was designed to assess the prevalence of antibodies against two influenza D lineages (D/660 and D/OK) in Italy in archived serum samples from veterinarians working with swine collected in 2004. Serum samples were tested by haemagglutination inhibition and virus neutralization assays. Results showed that 4.88% (4/82) of tested samples were positive for D/660 and 2.44% (2/82) for D/OK by haemagglutination inhibition assay. Three out of 4 samples showed positivity when tested by virus neutralization assay. Our data suggest undetected influenza D viruses might have circulated and/or introduced in Italy as early as 2004 at least in some animal species such as swine. In addition, it seems that the virus was circulating among veterinarians before the first isolation in 2011. This finding highlights the importance to continue monitoring influenza D virus spread in animals and humans for a more detailed surveillance. This article is protected by copyright. All rights reserved.