Presence of ducks, and in particular of free-grazing ducks, has consistently been shown to be one of the most important risk factors for highly pathogenic avian influenza outbreaks which has compromised poultry production in South-East Asia since the early 2000s and continues to threaten public health, farmers' livelihood and food security. Although free-grazing duck production has been practised for decades in South-East Asia, there are few published studies describing this production system, which is suspected to play an important role in the maintenance of avian influenza viruses. This study aimed at describing quantitatively the long-distance free-grazing duck production system in South Vietnam, characterising the movement and contact patterns of the duck flocks, and identifying potential associations between farming practices, movement and contact patterns and the circulation of avian influenza viruses. We conducted interviews among stakeholders involved in the free-grazing duck production system (duck farmers, transporters and rice paddy owners) in combination with a virological cross-sectional survey in South Vietnam. Results show that both direct and indirect contacts between free-grazing duck flocks were frequent and diverse. The flocks were transported extensively across district and province boundaries, mainly by boat but also by truck or on foot. A third of the investigated flocks had a positive influenza A virology test, indicating current circulation of avian influenza viruses, but none were positive for H5 subtypes. The age and size of the flock as well as its location at the time of sampling were associated with the risk of influenza A circulation in the flocks. These findings should be considered when developing risk assessment models of influenza virus spread aimed at informing the development of improved biosecurity practices leading to enhanced animal health, sustainable animal production and reliable income for farmers.
Species of Old World fruit-bats (family Pteropodidae) have been identified as the natural hosts of a number of novel and highly pathogenic viruses threatening livestock and human health. We used GPS data loggers to record the nocturnal foraging movements of Acerodon jubatus, the Golden-crowned flying fox in the Philippines to better understand the landscape utilisation of this iconic species, with the dual objectives of pre-empting disease emergence and supporting conservation management. Data loggers were deployed on eight of 54 A. jubatus (two males and six females) captured near Subic Bay on the Philippine island of Luzon between 22 November and 2 December 2010. Bodyweight ranged from 730 g to 1002 g, translating to a weight burden of 3–4% of bodyweight. Six of the eight loggers yielded useful data over 2–10 days, showing variability in the nature and range of individual bat movements. The majority of foraging locations were in closed forest and most were remote from evident human activity. Forty-six discrete foraging locations and five previously unrecorded roost locations were identified. Our findings indicate that foraging is not a random event, with the majority of bats exhibiting repetitious foraging movements night-to-night, that apparently intact forest provides the primary foraging resource, and that known roost locations substantially underestimate the true number (and location) of roosts. Our initial findings support policy and decision-making across perspectives including landscape management, species conservation, and potentially disease emergence.
In his article “Evidence points to migratory birds in H5N1 spread” (3 Mar., p. [1225][1]), D. Normile reports that “increasingly, scientists are attributing this remarkably fast spread [of H5N1] to migratory birds, but dissenters remain.” All agreed that wild birds have a role, but attributing the spread of HPAI H5N1 entirely to migratory birds overlooks evidence that is inconsistent with this conclusion.
One cannot ignore the apparent lack of previous outbreaks along migratory pathways. Birds have been migrating along these same routes annually since this genotype of HPAI H5N1 was first identified in Asia in 1997, yet there was no spread of disease to Eurasia or Europe in the interim years. Although fewer than 0.05% of more than 13,000 healthy waterfowl tested ([1][2]) were positive for HPAI H5N1, billions of birds have traveled to Eurasia and Europe for 8 years. It seems suspicious that none has managed to transmit this highly pathogenic virus until now. The introduction of HPAI H5N1 onto the continent of Africa, as well as the earlier outbreaks in poultry, notably in Russia and Turkey, could have been as easily accommodated by the movement of infected poultry, poultry products, or contaminated fomites as suggested for migratory bird routes. Meanwhile, Japan, with strong controls on poultry imports, has remained H5N1-free since early 2004, when infected poultry flocks were destroyed, despite the annual arrival of large migratory bird populations from areas with known H5N1 outbreaks.
Four pathways are most likely involved in the movement of HPAI H5N1: poultry shipments; the movement of contaminated equipment, materials, and waste products; migratory birds; and the wild bird trade. At most, the evidence suggests that wild birds may be responsible for short-distance, secondary movement of HPAI H5N1. Ornithologists, virologists, veterinarians, and others must work together, sharing their specialized knowledge to understand more thoroughly the movement of this virus.
1. 1.[↵][3]1. H. Chen 2. et al.
, Proc. Natl. Acad. Sci. U.S.A. 103, 2845 (2006).
[OpenUrl][4][Abstract/FREE Full Text][5]
[1]: /lookup/doi/10.1126/science.311.5765.1225
[2]: #ref-1
[3]: #xref-ref-1-1 View reference 1. in text
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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 ( r e ) 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 r e 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.
Species of Old World fruit-bats (family Pteropodidae) have been identified as the natural hosts of a number of novel and highly pathogenic viruses threatening livestock and human health.We used GPS data loggers to record the nocturnal foraging movements of Acerodon jubatus, the Golden-crowned flying fox in the Philippines to better understand the landscape utilisation of this iconic species, with the dual objectives of pre-empting disease emergence and supporting conservation management.Data loggers were deployed on eight of 54 A. jubatus (two males and six females) captured near Subic Bay on the Philippine island of Luzon between 22 November and 2 December 2010.Bodyweight ranged from 730 g to 1002 g, translating to a weight burden of 3-4% of bodyweight.Six of the eight loggers yielded useful data over 2-10 days, showing variability in the nature and range of individual bat movements.The majority of foraging locations were in closed forest and most were remote from evident human activity.Forty-six discrete foraging locations and five previously unrecorded roost locations were identified.Our findings indicate that foraging is not a random event, with the majority of bats exhibiting repetitious foraging movements night-tonight, that apparently intact forest provides the primary foraging resource, and that known roost locations substantially underestimate the true number (and location) of roosts.Our initial findings support policy and decision-making across perspectives including landscape management, species conservation, and potentially disease emergence.
Advanced satellite tracking technologies enable biologists to track animal movements at fine spatial and temporal scales. The resultant data present opportunities and challenges for understanding animal behavioral mechanisms. In this paper, we develop a new method to elucidate animal movement patterns from tracking data. Here, we propose the notion of continuous behavior patterns as a concise representation of popular migration routes and underlying sequential behaviors during migration. Each stage in the pattern is characterized in terms of space (i.e., the places traversed during movements) and time (i.e. the time spent in those places); that is, the behavioral state corresponding to a stage is inferred according to the spatiotemporal and sequential context. Hence, the pattern may be interpreted predictably. We develop a candidate generation and refinement framework to derive all continuous behavior patterns from raw trajectories. In the framework, we first define the representative spots to denote the underlying potential behavioral states that are extracted from individual trajectories according to the similarity of relaxed continuous locations in certain distinct time intervals. We determine the common behaviors of multiple individuals according to the spatiotemporal proximity of representative spots and apply a projection-based extension approach to generate candidate sequential behavior sequences as candidate patterns. Finally, the candidate generation procedure is combined with a refinement procedure to derive continuous behavior patterns. We apply an ordered processing strategy to accelerate candidate refinement. The proposed patterns and discovery framework are evaluated through conceptual experiments on both real GPS-tracking and large synthetic datasets.
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