Mapping H5N1 highly pathogenic avian influenza risk in Southeast Asia

Abstract

The highly pathogenic avian influenza (HPAI) H5N1 virus that emerged in southern China in the mid-1990s has in recent years evolved into the first HPAI panzootic. In many countries where the virus was detected, the virus was successfully controlled, whereas other countries face periodic reoccurrence despite significant control efforts. A central question is to understand the factors favoring the continuing reoccurrence of the virus. The abundance of domestic ducks, in particular free-grazing ducks feeding in intensive rice cropping areas, has been identified as one such risk factor based on separate studies carried out in Thailand and Vietnam. In addition, recent extensive progress was made in the spatial prediction of rice cropping intensity obtained through satellite imagery processing. This article analyses the statistical association between the recorded HPAI H5N1 virus presence and a set of five key environmental variables comprising elevation, human population, chicken numbers, duck numbers, and rice cropping intensity for three synchronous epidemic waves in Thailand and Vietnam. A consistent pattern emerges suggesting risk to be associated with duck abundance, human population, and rice cropping intensity in contrast to a relatively low association with chicken numbers. A statistical risk model based on the second epidemic wave data in Thailand is found to maintain its predictive power when extrapolated to Vietnam, which supports its application to other countries with similar agro-ecological conditions such as Laos or Cambodia. The model's potential application to mapping HPAI H5N1 disease risk in Indonesia is discussed.animal husbandry ͉ epidemiology ͉ remote sensing ͉ spatial modeling

Landscape attributes driving avian influenza virus circulation in the Lake Alaotra region of Madagascar

“…In particular, the present study not only showed that neighbourhood landscapes with predominant rice production were associated with higher seroprevalence level, which is consistent with previous studies on eco-epidemiology of HPAI H5N1 in Southeast Asia (Gilbert et al, 2008), but was also the first to demonstrate this effect for LPAI in a non-Asian setting. It has been suggested that rice paddy fields may favour HPAI H5N1 persistence because they constitute an interface between wild birds feeding there, and domestic poultry.…”

“…The fre-quent flooding of rice fields would also allow a greater viral persistence in this environment compared to dry soils (Van Boeckel et al, 2012). Reports from Thailand, Vietnam and Indonesia (Gilbert et al, 2008;Loth et al, 2011) found that HPAI H5N1 outbreaks occurred mainly in areas where rice is cultivated through an intensive, multiple crop system. The authors suggested that this may be related to the fact that the highest numbers of free-grazing ducks are raised in these areas, where the irrigation network is the densest and flooding the most frequent.…”

“…The Lake Alaotra site is of primary interest regarding the ecoepidemiology of avian influenza. Indeed, lakesides have large waterfowl populations, including species from the Anatidae family, which are known to harbour the most diverse and also the highest prevalence rates of AIV (Gilbert et al, 2008). Recent reports from Lake Alaotra indicate that avian influenza circulates in Anas erythrorhyncha, Anas melleri and Anas hottentota (Miguel Pedrono, personal communication).…”

Highly pathogenic avian influenza H5N1 clade 2.3.2.1 and clade 2.3.4 viruses do not induce a clade-specific phenotype in mallard ducks

“…Research 30 A study is published describing the epidemiological association between the presence of H5N1 virus and duck populations, human populations, and rice production in Viet Nam and Thailand.…”

Corneal Opacity in Domestic Ducks Experimentally Infected With H5N1 Highly Pathogenic Avian Influenza Virus

“…11,12,23,38 In contrast to chickens, in which infection is usually fatal, clinical signs in domestic ducks infected with the H5N1 HPAI virus greatly vary, ranging from asymptomatic to a fatal infection. 29,30,40,54 The main epidemiologic problem is that asymptomatically infected ducks can shed the virus for a particular period.…”