Biomolecular and virological tests

Recent studies have identified a novel influenza virus circulating in swine and cattle. The virus, distantly related to human influenza C virus, has been provisionally designated as influenza D virus (IDV) and a new genus of the Orthomyxoviridae family was proposed. This novel virus was identified for the first time in pigs with influenza-like illness, but subsequent serologic and virological studies conducted in USA and in France have suggested cattle as a possible reservoir.

To investigate the circulation of IDVs among pigs in Italy, we performed biomolecular and virological tests on clinical samples collected from herds affected by respiratory distress located in Po Valley, the area in Italy with the highest density of swine and cattle farms. During a 5- month period spanning August 2015-December 2015, 530 samples of nasal swabs (n. 219), lungs (n. 211) and oral fluids (n. 100) were collected from 273 pig farms.

We screened clinical specimens by reverse transcription quantitative PCR. All positive samples were confirmed by partial polymerase basic 1 gene sequencing and submitted to viral isolation in CACO-2, HRT18 and ST cell cultures. RNA was isolated from IDV positive clinical samples or positive supernatants and full-genome amplification and sequencing were performed. Phylogenetic analysis of viral gene segments was carried out.

Screening of samples by biomolecular test (PCR) found that 17 samples (3.2%) from 4 different farms (1.4%) were positive for IDV. Among the 17 positive specimens 14 were nasal swabs, 2 were oral fluids and only one was a lung tissue.

IDV was isolated on CACO-2, HRT18 and ST cell cultures from 3 nasal swabs collected in two positive farms. Genetic analysis highlighted that Italian IDVs are very closely related belonging to the D/swine/Oklahoma/1334/2011 cluster.

Our findings show that one cluster of IDV circulate among swine affected by respiratory disease in Italy. In all the considered clinical cases other viral and / or bacterial pathogens were detected in IDV positive specimens but in samples from one farm where mild symptoms were observed. These findings confirm the presence of IDV in Italian herds. Nevertheless it is difficult to outline the pathogenic role of IDV in swine respiratory distress complex.

Considering the higher percentage of positive nasal swabs it seems that upper respiratory tract is a preferred location. Further studies are ongoing to better understand epidemiology, virology, pathobiology and zoonotic aspects of IDV, especially concerning the evidence that Koch’s postulates are fulfilled for this agent.

Disclosure of Interest: None Declared.