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. 2020 May 21;10(1):8432.
doi: 10.1038/s41598-020-65413-2.

Transmission of Highly Pathogenic Avian Influenza in the Nomadic Free-Grazing Duck Production System in Viet Nam

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Free PMC article

Transmission of Highly Pathogenic Avian Influenza in the Nomadic Free-Grazing Duck Production System in Viet Nam

Katriina Willgert et al. Sci Rep. .
Free PMC article

Abstract

The presence of free-grazing ducks (FGD) has consistently been shown to be associated with highly pathogenic avian influenza virus (HPAIV) H5N1 outbreaks in South-East Asia. However, the lack of knowledge about the transmission pathways limits the effectiveness of control efforts. To address this gap, we developed a probabilistic transmission model of HPAIV H5N1 in the nomadic FGD production system in Viet Nam, assuming different scenarios to address parameter uncertainty. Results suggested that HPAIV H5N1 could spread within the nomadic FGD production system, with an estimated flock-level effective reproduction number (re) ranging from 2.16 (95% confidence interval (CI): 1.39-3.49) to 6.10 (95%CI: 3.93-9.85) depending on the scenario. Indirect transmission via boats and trucks was shown to be the main transmission route in all scenarios. Results suggest that re could be reduced below one with 95% confidence if 86% of FGD flocks were vaccinated in the best-case scenario or 95% in the worst-case scenario. If vaccination was combined with cleaning and disinfection of transport vehicles twice a week, vaccination coverage could be lowered to 60% in the best-case scenario. These findings are of particular relevance for prioritising interventions for effective control of HPAIV in nomadic free-grazing duck production systems.

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Distributions of the average number of susceptible nomadic FGD flocks that would be infected by one HPAIV H5N1 infectious nomadic FGD flock over the course of its infection through each of the six most likely transmission routes and different probabilities of transmission given exposure.
Figure 2
Figure 2
Impact of an increase in vaccination coverage on the average number of susceptible nomadic FGD flocks that would be infected by a HPAIV H5N1 infectious nomadic FGD flock over the course of its infection by direct transmission in the field (left), indirect transmission on boats (middle) and trucks (right). Lines represent medians and coloured polygons represent the 95% confidence regions.
Figure 3
Figure 3
Impact of variations in the length of time between successive cleaning and disinfection (C&D) of transport vehicles on the average number of susceptible nomadic FGD flocks that would be infected by a HPAIV H5N1 infectious nomadic FGD flock over the course of its infection by indirect transmission in boats (left) and trucks (right). Lines represent medians and coloured polygons represent the 95% confidence regions.
Figure 4
Figure 4
Impact of different combinations of vaccination coverage and length of time between successive cleaning and disinfection (C&D) of transport vehicles on the average number of susceptible nomadic FGD flocks that would be infected by a HPAIV H5N1 infectious nomadic FGD flock over the course of its infection (re) in the best-case scenario. The colour scale illustrates the 95th percentile of the distribution of re. The white line represents the limit of the 95% confidence that re < 1.

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