Influenza Aviar Altamente Patogénica en la Gran Región del Mekong: Seis Años Después
26 de febrero de 2010 – The Greater Mekong Region (GMR) includes Cambodia, Lao PDR, Myanmar, Thailand, Viet Nam and the southern provinces of China. In the GMR, the emergence of Highly Pathogenic Avian Influenza (HPAI) from 2004 to 2010 has affected animal and human health through mortality and morbidity. Poultry production in the region is heterogeneous with a majority of households keeping small flocks of indigenous, dual-purpose birds raised in low-input systems. In rural settings, traditional and small-volume poultry supply chains support livelihoods across extended networks of people associated with production, distribution, processing and marketing. Thailand has a large-scale industrial poultry industry: an important source of export revenues, food, employment and income. In Cambodia, Lao PDR, and Myanmar, the bulk of poultry originates in rural smallholding farms and is consumed domestically; with little industrial poultry production taking place. Viet Nam is an intermediate between traditional backyard and industrial poultry.
In the initial HPAI waves in the GMR, duck abundance, human population and rice cropping intensity were associated with disease emergence. Furthermore, in the Red and Mekong River Deltas of Viet Nam, HPAI risk areas were linked to irrigated rice fields in the lowlands, areas with good market access and high poultry transaction frequencies. Further epidemic waves revealed spatial and temporal patterns that define ‘hot’ periods during which increased virus circulation can be expected; however, these periods are not synchronised across the GMR. Viral clade changes over time suggest that there are diverse virus introduction and maintenance mechanisms between and within countries.
In general, disease control measures in the GMR have focused on culling, movement controls, cleaning and disinfection of bird markets, biosecurity enhancements, grazing duck production prohibitions, cock fighter passports, nationwide disease detection surveys, awareness-raising programmes, and information campaigns. Mass vaccination was implemented in Viet Nam and southern China. These measures have had mixed results in halting disease transmission and outbreak occurrence, with oftentimes detrimental consequences to rural backyard poultry keepers and market networks. For instance, nowadays there are pockets of endemicity in Viet Nam and southern Cambodia; in these countries virus load reductions could be long-term endeavours. Shortcomings in HPAI control may arise from information and incentive failures, such as minimal communication, inadequate compensation and extensive preventive culling.
As for vaccination, it is now evident that it contributed significantly to reduce HPAI spread and human exposure, but it did not eliminate virus circulation in countries where it was implemented. Clearly, vaccination against avian influenza should be considered as one of the many tools within a broad portfolio of control measures. In fact, commentators ascertain that live mixed bird market hygiene and disinfection might be more cost-effective when compared against sustained fiscal obligations of vaccination campaigns.
The continued occurrence of outbreaks across much of the GMR is likely to be caused by active cross border bird trade, and the increasing phylogenetic variation of virus isolates suggests relatively frequent virus hosts introduction from southern China. In the GMR, domestic duck-rice production has been identified as a key factor affecting virus maintenance and establishment, therefore it seems warranted to focus surveillance and disease control efforts on high duck density areas.
Lastly, owing to diverse multi-country ecological landscapes and high transboundary disease transmission risks, there is urgent need for more determined multilateral policy coordination. Moreover, as HPAI remains endemic in certain locations it is increasingly difficult to justify and sustain public monies for conventional control measures, thus warranting more effective and sustainable long-term risk reduction strategies such as, for example, ‘unconventional’ privately-financed animal health mechanisms that align incentives with farmers’ motivations.
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The Pro-Poor HPAI Risk Reduction project is spearheading this research.