Mapping H5N1 highly pathogenic avian influenza risk in Southeast Asia

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 con-
trol efforts. A central question is to understand the factors favoring
the continuing reoccurrence of the virus. The abundance of do-
mestic 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 pre-
diction of rice cropping intensity obtained through satellite imag-
ery 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 popu-
lation, 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 extrap-
olated to Vietnam, which supports its application to other coun-
tries with similar agro-ecological conditions such as Laos or Cam-
bodia. The model’s potential application to mapping HPAI H5N1
disease risk in Indonesia is discussed.