Bergervoet SA, et al. Genetic analysis identifies potential transmission of low pathogenic avian influenza viruses between poultry farms. Transbound Emerg Dis. 2019 Apr 9.
Poultry can become infected with low pathogenic avian influenza (LPAI) viruses via (in)direct contact with infected wild birds, or by transmission of the virus between farms. This study combines routinely collected surveillance data with genetic analysis to assess the contribution of between-farm transmission to the overall incidence of LPAI virus infections in poultry. Over a ten-year surveillance period, we identified 35 potential cases of between-farm transmission in the Netherlands, of which ten formed geographical clusters. A total of 21 LPAI viruses was isolated from nine potential between-farm transmission cases, which were further studied by genetic and epidemiological analysis. Whole genome sequence analysis identified close genetic links between infected farms in seven cases. The presence of identical deletions in the neuraminidase stalk region and minority variants provided additional indications of between-farm transmission. Spatiotemporal analysis demonstrated that genetically closely related viruses were detected within a median time interval of eight days, and the median distance between the infected farms was significantly shorter compared to farms infected with genetically distinct viruses (6.3 vs. 69.0 km; p<0.05). The results further suggest that between-farm transmission was not restricted to holdings of the same poultry type. Although separate introductions from the wild bird reservoir cannot be excluded, our study indicates that between-farm transmission occurred in seven out of nine virologically analysed cases. Based on these findings, it is likely that between-farm transmission contributes considerably to the incidence of LPAI virus infections in poultry.
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