Free-grazing ducks in rice paddies are a critical factor in the spread and persistence of avian influenza.
Thailand has recently had 3 epidemic waves of highly pathogenic avian influenza (HPAI); virus was again detected in July 2005. Risk factors need to be identified to better understand disease ecology and assist HPAI surveillance and detection. This study analyzed the spatial distribution of HPAI outbreaks in relation to poultry, land use, and other anthropogenic variables from the start of the second epidemic wave (July 2004–May 2005). Results demonstrate a strong association between H5N1 virus in Thailand and abundance of free-grazing ducks and, to a lesser extent, native chickens, cocks, wetlands, and humans. Wetlands used for double-crop rice production, where free-grazing duck feed year round in rice paddies, appear to be a critical factor in HPAI persistence and spread. This finding could be important for other duck-producing regions in eastern and southeastern Asian countries affected by HPAI.
Avian influenza; epidemiology; spatial analysis; Thailand; animal husbandry; research
The highly pathogenic avian influenza (HPAI) H5N1 virus has spread across Eurasia and into Africa. Its persistence in a number of countries continues to disrupt poultry production, impairs smallholder livelihoods, and raises the risk a genotype adapted to human-to-human transmission may emerge. While previous studies identified domestic duck reservoirs as a primary risk factor associated with HPAI H5N1 persistence in poultry in Southeast Asia, little is known of such factors in countries with different agro-ecological conditions, and no study has investigated the impact of such conditions on HPAI H5N1 epidemiology at the global scale. This study explores the patterns of HPAI H5N1 persistence worldwide, and for China, Indonesia, and India includes individual provinces that have reported HPAI H5N1 presence during the 2004–2008 period. Multivariate analysis of a set of 14 agricultural, environmental, climatic, and socio-economic factors demonstrates in quantitative terms that a combination of six variables discriminates the areas with human cases and persistence: agricultural population density, duck density, duck by chicken density, chicken density, the product of agricultural population density and chicken output/input ratio, and purchasing power per capita. The analysis identifies five agro-ecological clusters, or niches, representing varying degrees of disease persistence. The agro-ecological distances of all study areas to the medoid of the niche with the greatest number of human cases are used to map HPAI H5N1 risk globally. The results indicate that few countries remain where HPAI H5N1 would likely persist should it be introduced.
Electronic supplementary material
The online version of this article (doi:10.1007/s10393-010-0324-z) contains supplementary material, which is available to authorized users.
global ecology; highly pathogenic avian influenza; agro-ecology; epidemiology
Highly pathogenic avian influenza (HPAI) H5N1 virus persists in Asia, posing a threat to poultry, wild birds, and humans. Previous work in Southeast Asia demonstrated that HPAI H5N1 risk is related to domestic ducks and people. Other studies discussed the role of migratory birds in the long distance spread of HPAI H5N1. However, the interplay between local persistence and long-distance dispersal has never been studied. We expand previous geospatial risk analysis to include South and Southeast Asia, and integrate the analysis with migration data of satellite-tracked wild waterfowl along the Central Asia flyway. We find that the population of domestic duck is the main factor delineating areas at risk of HPAI H5N1 spread in domestic poultry in South Asia, and that other risk factors, such as human population and chicken density, are associated with HPAI H5N1 risk within those areas. We also find that satellite tracked birds (Ruddy Shelduck and two Bar-headed Geese) reveal a direct spatio-temporal link between the HPAI H5N1 hot-spots identified in India and Bangladesh through our risk model, and the wild bird outbreaks in May–June–July 2009 in China (Qinghai Lake), Mongolia, and Russia. This suggests that the continental-scale dynamics of HPAI H5N1 are structured as a number of persistence areas delineated by domestic ducks, connected by rare transmission through migratory waterfowl.
Electronic supplementary material
The online version of this article (doi:10.1007/s10393-010-0672-8) contains supplementary material, which is available to authorized users.
avian influenza; epidemiology; disease ecology; migration
Highly pathogenic avian influenza virus (HPAIV) H5N1 continues to impact on smallholder livelihoods, to constrain development of the poultry production sector, and to cause occasional human fatalities. HPAI H5N1 outbreaks have occurred in a variety of ecological systems with economic, agricultural and environmental differences. This review aimed to identify common risk factors amongst spatial modelling studies conducted in these different agro-ecological systems, and to identify gaps in our understanding of the disease’s spatial epidemiology. Three types of variables with similar statistical association with HPAI H5N1 presence across studies and regions were identified: domestic waterfowl, several anthropogenic variables (human population density, distance to roads) and indicators of water presence. Variables on socio-economic conditions, poultry trade, wild bird distribution and movements were comparatively rarely considered. Few studies have analysed the HPAI H5N1 distribution in countries such as Egypt and Indonesia, where HPAIV H5N1 continues to circulate extensively.
Spatial epidemiology; avian influenza; H5N1
Highly pathogenic avian influenza (HPAI) H5N1 viruses are now endemic in many Asian countries, resulting in repeated outbreaks in poultry and increased cases of human infection. The immediate precursor of these HPAI viruses is believed to be A/goose/Guangdong/1/96 (Gs/GD)-like H5N1 HPAI viruses first detected in Guangdong, China, in 1996. From 2000 onwards, many novel reassortant H5N1 influenza viruses or genotypes have emerged in southern China. However, precursors of the Gs/GD-like viruses and their subsequent reassortants have not been fully determined. Here we characterize low-pathogenic avian influenza (LPAI) H5 subtype viruses isolated from poultry and migratory birds in southern China and Europe from the 1970s to the 2000s. Phylogenetic analyses revealed that Gs/GD-like virus was likely derived from an LPAI H5 virus in migratory birds. However, its variants arose from multiple reassortments between Gs/GD-like virus and viruses from migratory birds or with those Eurasian viruses isolated in the 1970s. It is of note that unlike HPAI H5N1 viruses, those recent LPAI H5 viruses have not become established in aquatic or terrestrial poultry. Phylogenetic analyses revealed the dynamic nature of the influenza virus gene pool in Eurasia with repeated transmissions between the eastern and western extremities of the continent. The data also show reassortment between influenza viruses from domestic and migratory birds in this region that has contributed to the expanded diversity of the influenza virus gene pool among poultry in Eurasia.
Highly pathogenic avian influenza (HPAI) virus H5N1 is now endemic in South-East Asia but HPAI control methods differ between countries. A widespread HPAI vaccination campaign that started at the end of 2005 in Viet Nam resulted in the cessation of poultry and human cases, but in 2006/2007 severe HPAI outbreaks re-emerged. In this study we investigated the pattern of this first post-vaccination epidemic in southern Viet Nam identifying a spatio-temporal cluster of outbreak occurrence and estimating spatially smoothed incidence rates of HPAI. Spatial risk factors associated with HPAI occurrence were identified. Medium-level poultry density resulted in an increased outbreak risk (Odds ratio (OR) = 5.4, 95% confidence interval (CI): 1.6–18.9) but also climate-vegetation factors played an important role: medium-level normalised difference vegetation indices during the rainy season from May to October were associated with higher risk of HPAI outbreaks (OR = 3.7, 95% CI: 1.7–8.1), probably because temporal flooding might have provided suitable conditions for the re-emergence of HPAI by expanding the virus distribution in the environment and by enlarging areas of possible contacts between domestic waterfowl and wild birds. On the other hand, several agricultural production factors, such as sweet potatoes yield, increased buffalo density, as well as increased electricity supply were associated with decreased risk of HPAI outbreaks. This illustrates that preventive control measures for HPAI should include a promotion of low-risk agricultural management practices as well as improvement of the infrastructure in village households. Improved HPAI vaccination efforts and coverage should focus on medium poultry density areas and on the pre-monsoon time period.
avian influenza; H5N1; poultry; risk factor; HPAI outbreak
The continued spread of highly pathogenic avian influenza (HPAI) viruses of H5 and H7 subtypes and low pathogenic avian influenza (LPAI) viruses of H5, H7 and H9 subtypes in birds and the subsequent infections in humans pose an ongoing pandemic threat. It has been proposed that poultry workers are at higher risk of exposure to HPAI or LPAI viruses and subsequently infection due to their repeated exposure to chickens or domestic waterfowl. The aim of this study was to examine the seroprevalence of antibodies against H5, H7 and H9 viruses amongst duck-related workers in Beijing, China and the risk factors associated with seropositivity. In March, 2011, 1741 participants were recruited from (1) commercial duck-breeding farms; (2) private duck-breeding farms; and (3) duck-slaughtering farms. Local villagers who bred ducks in their backyards were also recruited. A survey was administered by face-to-face interview, and blood samples were collected from subjects for antibody testing against H5, H7 and H9 viruses. We found that none of the subjects were seropositive for either H5 or H7 viruses, and only 0.7% (12/1741) had antibody against H9. A statistically significant difference in H9 antibody seroprevalence existed between the various categories of workers (P = 0.005), with the highest figures recorded amongst the villagers (1.7%). Independent risk factors associated with seropositivity toinfection with H9 virus included less frequent disinfection of worksite (OR, 5.13 [95% CI, 1.07–24.58]; P = 0.041; ≤ twice monthly versus>twice monthly) and handling ducks with wounds on hands (OR, 4.13 [95% CI, 1.26–13.57]; P = 0.019). Whilst the risk of infection with H5, H7 and H9 viruses appears to be low among duck-related workers in Beijing, China, ongoing monitoring of infection with the H9 virus is still warranted, especially amongst villagers who breed backyard ducks to monitor for any changes.
Vaccination of domestic poultry against avian influenza (AI) has been used on a large-scale in South East Asia since 2003 and in Egypt since 2006 to fight H5N1 highly-pathogenic avian influenza (HPAI) epidemics. The decision to use mass vaccination against HPAI in Egypt was taken as an emergency measure based on positive impact of such control measures in Vietnam and the People's Republic of China. However, three years on, the impact on disease control of AI vaccination in Egypt has been very limited. Despite the continuous vaccination of poultry against HPAI, poultry outbreaks and human cases are reported regularly. A recent assessment study highlighted substantial weaknesses in the current immunisation programme and its lack of positive impact on the spread of infection or the maintenance of public health safety. The shortcomings of the vaccination strategy may be attributed in part to a lack of sufficient support in terms of funding and communication, the absence of an efficient monitoring system, and inadequate training of field technicians. The difficulties of blanket vaccinations in semi-commercial farms and household poultry sectors are well known, however, improvements in the industrial sector should be possible though better government controls and greater collaboration with the private sector. AI vaccination should be regarded as just one control tool within a broader disease control program integrating surveillance, outbreak investigation, disease management systems, and the rigorous implementation of bio-security measures. If incorrectly implemented, AI vaccination has a limited impact as a disease control measure. Moreover, without strict bio-security precautions undertaken during its application, farm visits to vaccinate poultry could facilitate the spread of the virus and therefore become a risk factor with important implications on the maintenance of the virus and potential risk for human exposure.
Avian influenza; disease control; vaccination strategy; public health risk; Egypt
Highly pathogenic avian influenza H5N1 remains a serious concern for both poultry and human health. Wild waterfowl are considered to be the reservoir for low pathogenic avian influenza viruses; however, relatively little is known about their movement ecology in regions where HPAI H5N1 outbreaks regularly occur. We studied movements of the ruddy shelduck (Tadorna ferruginea), a wild migratory waterfowl species that was infected in the 2005 Qinghai Lake outbreak. We defined their migration with Brownian Bridge utilization distribution models and their breeding and wintering grounds with fixed kernel home ranges. We correlated their movements with HPAI H5N1 outbreaks, poultry density, land cover, and latitude in the Central Asian Flyway. Our Akaike Information Criterion analysis indicated that outbreaks were correlated with land cover, latitude, and poultry density. Although shelduck movements were included in the top two models, they were not a top parameter selected in AICc stepwise regression results. However, timing of outbreaks suggested that outbreaks in the flyway began during the winter in poultry with spillover to wild birds during the spring migration. Thus, studies of the movement ecology of wild birds in areas with persistent HPAI H5N1 outbreaks may contribute to understanding their role in transmission of this disease.
Brahminy duck; movement ecology; Tadorna ferruginea; avian influenza
The potential existence of a wild bird reservoir for highly pathogenic avian influenza (HPAI) has been recently questioned by the spread and the persisting circulation of H5N1 HPAI viruses, responsible for concurrent outbreaks in migratory and domestic birds over Asia, Europe, and Africa. During a large-scale surveillance programme over Eastern Europe, the Middle East, and Africa, we detected avian influenza viruses of H5N2 subtype with a highly pathogenic (HP) viral genotype in healthy birds of two wild waterfowl species sampled in Nigeria. We monitored the survival and regional movements of one of the infected birds through satellite telemetry, providing a rare evidence of a non-lethal natural infection by an HP viral genotype in wild birds. Phylogenetic analysis of the H5N2 viruses revealed close genetic relationships with H5 viruses of low pathogenicity circulating in Eurasian wild and domestic ducks. In addition, genetic analysis did not reveal known gallinaceous poultry adaptive mutations, suggesting that the emergence of HP strains could have taken place in either wild or domestic ducks or in non-gallinaceous species. The presence of coexisting but genetically distinguishable avian influenza viruses with an HP viral genotype in two cohabiting species of wild waterfowl, with evidence of non-lethal infection at least in one species and without evidence of prior extensive circulation of the virus in domestic poultry, suggest that some strains with a potential high pathogenicity for poultry could be maintained in a community of wild waterfowl.
Until recently, the highly pathogenic avian influenza (HPAI) viruses responsible for high mortality in some domestic poultry were considered not to have a wild bird reservoir, but to emerge in domestic poultry populations from low pathogenic viruses perpetuated in wild waterbirds. The rapid spread of H5N1 HPAI virus in 2005–2006, with concurrent outbreaks reported in both domestic and wild birds over Asia, Europe, and Africa, has raised concerns about the potential role of migratory birds in the epidemiology of the HPAI infection. Wild birds were sampled in Africa and tested by molecular and virological methods in an attempt to trace the circulation of HPAI viruses. In addition, some of these wild birds were equipped with satellite transmitters to track their local and migratory movements in relation to the potential spread of avian diseases. Avian influenza viruses (H5N2) were detected in wild waterfowl in Nigeria, and were subsequently characterized as highly pathogenic by molecular sequencing (HPAI viral genotype). Movements of one infected bird tracked by satellite telemetry revealed that it survived infection by an HP viral genotype. This result constitutes a rare finding of infection by an AIV with an HPAI viral genotype in healthy wild birds.
TOC Summary: Migratory birds are unlikely introductory hosts for this highly pathogenic virus in its present form into North America.
Highly pathogenic avian influenza (HPAI) H5N1 expanded considerably during 2005 and early 2006 in both avian host species and geographic distribution. Domestic waterfowl and migratory birds are reservoirs, but lethality of this subtype appeared to initially limit migrant effectiveness as introductory hosts. This situation may have changed, as HPAI H5N1 has recently expanded across Eurasia and into Europe and Africa. Birds could introduce HPAI H5N1 to the Western Hemisphere through migration, vagrancy, and importation by people. Vagrants and migratory birds are not likely interhemispheric introductory hosts; import of infected domestic or pet birds is more probable. If reassortment or mutation were to produce a virus adapted for rapid transmission among humans, birds would be unlikely introductory hosts because of differences in viral transmission mechanisms among major host groups (i.e., gastrointestinal for birds, respiratory for humans). Another possible result of reassortment would be a less lethal form of avian influenza, more readily spread by birds.
Avian Influenza A; Orthomyxovirus; Migration; Birds; HPAI; H5N1; Movement; Western Hemisphere; Perspective
Highly pathogenic avian influenza (HPAI) viruses have had devastating effects on poultry industries worldwide, and there is concern about the potential for HPAI outbreaks in the poultry industry in Great Britain (GB). Critical to the potential for HPAI to spread between poultry premises are the connections made between farms by movements related to human activity. Movement records of catching teams and slaughterhouse vehicles were obtained from a large catching company, and these data were used in a simulation model of HPAI spread between farms serviced by the catching company, and surrounding (geographic) areas. The spread of HPAI through real-time movements was modelled, with the addition of spread via company personnel and local transmission.
The model predicted that although large outbreaks are rare, they may occur, with long distances between infected premises. Final outbreak size was most sensitive to the probability of spread via slaughterhouse-linked movements whereas the probability of onward spread beyond an index premises was most sensitive to the frequency of company personnel movements.
Results obtained from this study show that, whilst there is the possibility that HPAI virus will jump from one cluster of farms to another, movements made by catching teams connected fewer poultry premises in an outbreak situation than slaughterhouses and company personnel. The potential connection of a large number of infected farms, however, highlights the importance of retaining up-to-date data on poultry premises so that control measures can be effectively prioritised in an outbreak situation.
Since 1996 when Highly Pathogenic Avian Influenza type H5N1 first emerged in southern China, numerous studies sought risk factors and produced risk maps based on environmental and anthropogenic predictors. However little attention has been paid to the link between the level of intensification of poultry production and the risk of outbreak. This study revised H5N1 risk mapping in Central and Western Thailand during the second wave of the 2004 epidemic. Production structure was quantified using a disaggregation methodology based on the number of poultry per holding. Population densities of extensively- and intensively-raised ducks and chickens were derived both at the sub-district and at the village levels. LandSat images were used to derive another previously neglected potential predictor of HPAI H5N1 risk: the proportion of water in the landscape resulting from floods. We used Monte Carlo simulation of Boosted Regression Trees models of predictor variables to characterize the risk of HPAI H5N1. Maps of mean risk and uncertainty were derived both at the sub-district and the village levels. The overall accuracy of Boosted Regression Trees models was comparable to that of logistic regression approaches. The proportion of area flooded made the highest contribution to predicting the risk of outbreak, followed by the densities of intensively-raised ducks, extensively-raised ducks and human population. Our results showed that as little as 15% of flooded land in villages is sufficient to reach the maximum level of risk associated with this variable. The spatial pattern of predicted risk is similar to previous work: areas at risk are mainly located along the flood plain of the Chao Phraya river and to the south-east of Bangkok. Using high-resolution village-level poultry census data, rather than sub-district data, the spatial accuracy of predictions was enhanced to highlight local variations in risk. Such maps provide useful information to guide intervention.
In Laos, small backyard poultry systems predominate (90%). The first lethal human cases of highly pathogenic avian influenza (HPAI) occurred in 2007. Few studies have addressed the impact of outbreaks and education campaigns on a smallholder producer system. We evaluated awareness and behaviours related to educational campaigns and the 2007 HPAI outbreaks.
During a national 2-stage cross-sectional randomised survey we interviewed 1098 households using a pre-tested questionnaire in five provinces representative of the Southern to Northern strata of Laos. We used multivariate analysis (Stata, version 8; Stata Corporation, College Station, TX, USA) to analyse factors affecting recollection of HPAI educational messages, awareness of HPAI, and behaviour change.
Of the 1098 participants, 303 (27.6%) received training on HPAI. The level of awareness was similar to that in 2006. The urban population considered risk to be decreased, yet unsafe behaviours persisted or increased. This contrasted with an increase in awareness and safe behaviour practices in rural areas.
Reported behaviour changes in rural areas included higher rates of cessation of poultry consumption and dead poultry burial when compared to 2006. No participants reported poultry deaths to the authorities. Overall, 70% could recall an educational message but the content and accuracy differed widely depending on training exposure. Washing hands and other hygiene advice, messages given during the HPAI educational campaign, were not recalled. Trained persons were able to recall only one message while untrained participants recalled a broader range of messages. Factors associated with an awareness of a threat of AI in Laos were: having received HPAI training, literacy level, access to TV, recent information, living in rural areas.
We report a paradoxical relationship between unsafe behaviours and risk perception in urban areas, as well as exposure to HPAI training and message misinterpretation. Future educational campaigns need to be tailored to specific target populations and farming styles, for example, small holder farms as compared to commercial farms. Special attention must be given to varying risk perceptions and the risk of misinterpretation of key messages, economic hardship, and real life consequences of reporting.
Highly pathogenic avian influenza (HPAI) caused by H5N1 viruses has become a global scale problem which first emerged in southern China and from there spread to other countries in Southeast and East Asia, where it was first confirmed in end 2003. In previous work, geospatial analyses demonstrated that free grazing ducks played critical role in the epidemiology of the disease in Thailand in the winter 2004/2005, both in terms of HPAI emergence and spread. This study explored the geographic association between free grazing duck census counts and current statistics on the spatial distribution of rice crops in Thailand, in particular the crop calendar of rice production. The analysis was carried out using both district level rice statistics and rice distribution data predicted with the aid of remote sensing, using a rice-detection algorithm. The results indicated a strong association between the number of free grazing ducks and the number of months during which second-crop rice harvest takes place, as well as with the rice crop intensity as predicted by remote sensing. These results confirmed that free grazing duck husbandry was strongly driven by agricultural land use and rice crop intensity, and that this later variable can be readily predicted using remote sensing. Analysis of rice cropping patterns may provide an indication of the location of populations of free grazing ducks in other countries with similar mixed duck and rice production systems and less detailed duck census data. Apart from free ranging ducks and rice cropping, the role of hydrology and seasonality of wetlands and water bodies in the HPAI risk analysis is also discussed in relation to the presumed dry season aggregation of wild waterfowl and aquatic poultry offering much scope for virus transmission.
Highly pathogenic avian influenza; Domestic ducks; Remote sensing; Agriculture intensification; Rice paddy production
Highly pathogenic avian influenza (HPAI) is a striking disease in susceptible poultry, which leads to severe economic losses. Inactivated vaccines are the most widely used vaccines in avian influenza virus (AIV) vaccination programs. However, these vaccines interfere with the serological detection of wild-type AIV infections in immunized populations. The use of vaccines that allow differentiation between infected and vaccinated animals (DIVA strategy) would stop current stamping-out policies. Therefore, novel vaccination strategies are needed to allow improved protection of animals and humans against HPAI virus (HPAIV) infection. The presented study analyzed for the first time the immunogenic capacity of plant-expressed full-length hemagglutinin (rHA0) of HPAIV H5N1 in several vaccine formulations within the highly relevant host species chicken. We were able to express plant-expressed rHA0 at high levels and could show that, when administered with potent adjuvants, it is highly immunogenic and can fully protect chicken against lethal challenge infection. Real-time reverse transcription (RT)-PCR and serological tests demonstrated only marginally increased virus replication in animals vaccinated with plant-derived rHA0 compared to animals immunized with an inactivated reference vaccine. In addition, the use of plant-expressed rHA0 also allowed an easy serological differentiation of vaccinated from AIV-infected animals based on antibodies against the influenza virus NP protein.
Highly pathogenic avian influenza virus (HPAI) strain H5N1 has had direct and indirect economic impacts arising from direct mortality and control programmes in over 50 countries reporting poultry outbreaks. HPAI H5N1 is now reported as the most widespread and expensive zoonotic disease recorded and continues to pose a global health threat. The aim of this research was to assess the potential of utilising Hazard Analysis of Critical Control Points (HACCP) assessments in providing a framework for a rapid response to emerging infectious disease outbreaks. This novel approach applies a scientific process, widely used in food production systems, to assess risks related to a specific emerging health threat within a known zoonotic disease hotspot. We conducted a HACCP assessment for HPAI viruses within Vietnam’s domestic poultry trade and relate our findings to the existing literature. Our HACCP assessment identified poultry flock isolation, transportation, slaughter, preparation and consumption as critical control points for Vietnam’s domestic poultry trade. Introduction of the preventative measures highlighted through this HACCP evaluation would reduce the risks posed by HPAI viruses and pressure on the national economy. We conclude that this HACCP assessment provides compelling evidence for the future potential that HACCP analyses could play in initiating a rapid response to emerging infectious diseases.
A unique pattern of highly pathogenic avian influenza (HPAI) H5N1 outbreaks has emerged along the Central Asia Flyway, where infection of wild birds has been reported with steady frequency since 2005. We assessed the potential for two hosts of HPAI H5N1, the bar-headed goose (Anser indicus) and ruddy shelduck (Tadorna tadorna), to act as agents for virus dispersal along this ‘thoroughfare’. We used an eco-virological approach to compare the migration of 141 birds marked with GPS satellite transmitters during 2005–2010 with: 1) the spatio-temporal patterns of poultry and wild bird outbreaks of HPAI H5N1, and 2) the trajectory of the virus in the outbreak region based on phylogeographic mapping. We found that biweekly utilization distributions (UDs) for 19.2% of bar-headed geese and 46.2% of ruddy shelduck were significantly associated with outbreaks. Ruddy shelduck showed highest correlation with poultry outbreaks owing to their wintering distribution in South Asia, where there is considerable opportunity for HPAI H5N1 spillover from poultry. Both species showed correlation with wild bird outbreaks during the spring migration, suggesting they may be involved in the northward movement of the virus. However, phylogeographic mapping of HPAI H5N1 clades 2.2 and 2.3 did not support dissemination of the virus in a northern direction along the migration corridor. In particular, two subclades (2.2.1 and 2.3.2) moved in a strictly southern direction in contrast to our spatio-temporal analysis of bird migration. Our attempt to reconcile the disciplines of wild bird ecology and HPAI H5N1 virology highlights prospects offered by both approaches as well as their limitations.
Starting in late November 2010, the H5N1 highly pathogenic avian influenza (HPAI) virus was isolated from many types of wild ducks and raptors and was subsequently isolated from poultry in Korea. We assessed the genetic and pathogenic properties of the HPAI viruses isolated from a fecal sample from a mandarin duck and a dead Eurasian eagle owl, the most affected wild bird species during the 2010/2011 HPAI outbreak in Korea. These viruses have similar genetic backgrounds and exhibited the highest genetic similarity with recent Eurasian clade 18.104.22.168 HPAI viruses. In animal inoculation experiments, regardless of their originating hosts, the two Korean isolates produced highly pathogenic characteristics in chickens, ducks and mice without pre-adaptation. These results raise concerns about veterinary and public health. Surveillance of wild birds could provide a good early warning signal for possible HPAI infection in poultry as well as in humans.
H5N1; highly pathogenic avian influenza; clade 22.214.171.124
The agro-ecology and poultry husbandry of the south Asian and south-east Asian countries share common features, however, with noticeable differences. Hence, the ecological determinants associated with risk of highly pathogenic avian influenza (HPAI-H5N1) outbreaks are expected to differ between Bangladesh and e.g., Thailand and Vietnam. The primary aim of the current study was to establish ecological determinants associated with the risk of HPAI-H5N1 outbreaks at subdistrict level in Bangladesh. The secondary aim was to explore the performance of two different statistical modeling approaches for unmeasured spatially correlated variation.
An ecological study at subdistrict level in Bangladesh was performed with 138 subdistricts with HPAI-H5N1 outbreaks during 2007–2008, and 326 subdistricts with no outbreaks. The association between ecological determinants and HPAI-H5N1 outbreaks was examined using a generalized linear mixed model. Spatial clustering of the ecological data was modeled using 1) an intrinsic conditional autoregressive (ICAR) model at subdistrict level considering their first order neighbors, and 2) a multilevel (ML) model with subdistricts nested within districts. Ecological determinants significantly associated with risk of HPAI-H5N1 outbreaks at subdistrict level were migratory birds' staging areas, river network, household density, literacy rate, poultry density, live bird markets, and highway network. Predictive risk maps were derived based on the resulting models. The resulting models indicate that the ML model absorbed some of the covariate effect of the ICAR model because of the neighbor structure implied in the two different models.
The study identified a new set of ecological determinants related to river networks, migratory birds' staging areas and literacy rate in addition to already known risk factors, and clarified that the generalized concept of free grazing duck and duck-rice cultivation interacted ecology are not significant determinants for Bangladesh. These findings will refine current understanding of the HPAI-H5N1 epidemiology in Bangladesh.
Avian influenza or “bird flu” is causing increasing concern across the world as experts prepare for the possible occurrence of the next human influenza pandemic. Only influenza A has ever been shown to have the capacity to cause pandemics. Currently A/H5N1, a highly pathogenic avian influenza virus, is of particular concern. Outbreaks of this disease in birds, especially domestic poultry, have been detected across Southeast Asia at regular intervals since 2003, and have now affected parts of Africa and Europe. Many unaffected countries across the world are preparing for the possible arrival of HPAI A/H5N1 in wild birds and poultry within their territories. All such countries need to prepare for the rare possibility of a small number of human cases of HPAI A/H5N1, imported through foreign travel. Although it is by no means certain that HPAI A/H5N1 will be the source of the next pandemic, many countries are also preparing for the inevitable occurrence of human pandemic influenza.
Domestic ducks are considered to be an important reservoir of highly pathogenic avian influenza (HPAI), as shown by a number of geospatial studies in which they have been identified as a significant risk factor associated with disease presence. Despite their importance in HPAI epidemiology, their large-scale distribution in monsoon Asia is poorly understood. In this study, we created a spatial database of domestic duck census data in Asia and used it to train statistical distribution models for domestic duck distributions at a spatial resolution of 1 km. The method was based on a modelling framework used by the Food and Agriculture Organisation to produce the Gridded Livestock of the World (GLW) database, and relies on stratified regression models between domestic duck densities and a set of agro-ecological explanatory variables. We evaluated different ways of stratifying the analysis and of combining the prediction to optimize the goodness of fit of the predictions. We found that domestic duck density could be predicted with reasonable accuracy (mean RMSE and correlation coefficient between log-transformed observed and predicted densities being 0.58 and 0.80, respectively), using a stratification based on livestock production systems. We tested the use of artificially degraded data on duck distributions in Thailand and Vietnam as training data, and compared the modelled outputs with the original high-resolution data. This showed, for these two countries at least, that these approaches could be used to accurately disaggregate provincial level (administrative level 1) statistical data to provide high resolution model distributions.
Livestock Mapping; Domestic ducks; Monsoon Asia; Regression models; Highly pathogenic avian influenza
Beginning in 2003, highly pathogenic avian influenza (HPAI) H5N1 virus spread across Southeast Asia, causing unprecedented epidemics. Thailand was massively infected in 2004 and 2005 and continues today to experience sporadic outbreaks. While research findings suggest that the spread of HPAI H5N1 is influenced primarily by trade patterns, identifying the anthropogenic risk factors involved remains a challenge. In this study, we investigated which anthropogenic factors played a role in the risk of HPAI in Thailand using outbreak data from the “second wave” of the epidemic (3 July 2004 to 5 May 2005) in the country. We first performed a spatial analysis of the relative risk of HPAI H5N1 at the subdistrict level based on a hierarchical Bayesian model. We observed a strong spatial heterogeneity of the relative risk. We then tested a set of potential risk factors in a multivariable linear model. The results confirmed the role of free-grazing ducks and rice-cropping intensity but showed a weak association with fighting cock density. The results also revealed a set of anthropogenic factors significantly linked with the risk of HPAI. High risk was associated strongly with densely populated areas, short distances to a highway junction, and short distances to large cities. These findings highlight a new explanatory pattern for the risk of HPAI and indicate that, in addition to agro-environmental factors, anthropogenic factors play an important role in the spread of H5N1. To limit the spread of future outbreaks, efforts to control the movement of poultry products must be sustained.
avian influenza; epidemiology; poultry farming; spatial analysis; Thailand
Global influenza surveillance is one of the most effective strategies for containing outbreaks and preparing for a possible pandemic influenza. Since the end of 2003, highly pathogenic avian influenza viruses (HPAI) H5N1 have caused many outbreaks in poultries and wild birds from East Asia and have spread to at least 48 countries. For such a fast and wide-spreading virulent pathogen, prediction based on changes of micro- and macro-environment has rarely been evaluated. In this study, we are developing a new climatic approach by investigating the conditions that occurred before the H5N1 avian influenza outbreaks for early predicting future HPAI outbreaks and preventing pandemic disasters. The results show a temperature drop shortly before these outbreaks in birds in each of the Eurasian regions stricken in 2005 and 2006. Dust storms, like those that struck near China's Lake Qinghai around May 4, 2005, exacerbated the spread of this HPAI H5N1 virus, causing the deaths of a record number of wild birds and triggering the subsequent spread of H5N1. Weather monitoring could play an important role in the early warning of outbreaks of this potentially dangerous virus.
More than 70 outbreaks of the highly pathogenic avian influenza (HPAI) H5N1 have been reported in poultry in the western and north-eastern parts of India. Therefore, in view of the recent HPAI H5N1 outbreaks in poultry, active AI surveillance encompassing wild, resident, migratory birds and poultry was undertaken during 2009–2011 in the State of West Bengal.
A total of 5722 samples were collected from West Bengal; 3522 samples (2906 fecal droppings + 616 other environmental samples) were from migratory birds and 2200 samples [1604 tracheal, cloacal swabs, environmental samples, tissue samples + 596 blood (serum)] were from domestic ducks and poultry. All tracheal, cloacal and environmental samples were processed for virus isolation. Virus isolates were detected using hemagglutination assay and identified using hemagglutination inhibition (HI) and reverse transcriptase polymerase chain reaction (RT-PCR) assays. Sequencing and phylogenetic analysis of partial region of the hemagglutinin and neuraminidase genes was done. Intravenous pathogenicity index assays were performed in chickens to assess pathogenicity of AI virus isolates. Serum samples were tested for detection of antibodies against AI viruses using HI assay.
A total of 57 AI H9N2, 15 AI H4N6 and 15 Newcastle Disease (NDV) viruses were isolated from chickens, from both backyard and wet poultry markets; AI H4N6 viruses were isolated from backyard chickens and domestic ducks. Characterization of AI H9N2 and H4N6 viruses revealed that they were of low pathogenicity. Domestic ducks were positive for antibodies against H5 and H7 viruses while chickens were positive for presence of antibodies against AI H9N2 and NDV.
In the current scenario of HPAI H5N1 outbreaks in West Bengal, this report shows presence of low pathogenic AI H9N2 and H4N6 viruses in chickens and domestic ducks during the period 2009–2011. This is the first report of isolation of H4N6 from India. Antibodies against AI H5 and H7 in ducks highlight the probable role of domestic ducks in the transmission of AI viruses. Human infections of H9N2 have been reported from China and Hong Kong. This necessitates implementation of prevention and control measures to limit the spread of AI viruses.
Avian influenza surveillance; H9N2 virus; H4N6 virus; NDV; Poultry; India