Anthropogenic factors and the risk of highly pathogenic avian influenza H5N1: prospects from a spatial-based model

Paul, Mathilde; Tavornpanich, Saraya; Abrial, David; Gasqui, Patrick; Charras-Garrido, Myriam; Thanapongtharm, Weerapong; Xiao, Xiangming; Gilbert, Marius; Roger, Francois; Ducrot, Christian

We focussed on the RR values and highlighted the variables with high or very low RR. The estimated effects of the environmental, poultry farming and anthropogenic risk factors are displayed in Tables Ia, Ib and Ic. The level of relative risk of HPAI for ducks was the main risk factor associated with the relative risk for chickens, and vice versa. Apart from this, the mean number of rice crops per year was the most relevant risk factor for the relative risk of HPAI for both chickens and ducks. A low average altitude in a subdistrict ( 50 m) was also found to be a risk factor of HPAI for chickens and ducks, while medium altitude was associated to RR below 1. A high density of free-grazing ducks appeared to be one of the main risk factors for HPAI. For chickens and ducks, the HPAI risk was connected more closely to animal density than to the density of farms or households with poultry. Areas with a high density of broiler and layer ducks were associated with a strong increase in the relative risk for both chickens and ducks (RR > 4 for subdistricts with more than 80 ducks per km 2 ). A high density of broiler and layer chickens (> 500 chickens per km 2 ) was found to be associated with a high risk of HPAI (RR > 3) only in the duck model. Our results demonstrated a relationship between a high density of native chickens and a low risk of HPAI H5N1 for both chickens and ducks. To a lesser extent, a high density of fighting cocks was found to be associated with an increase in the HPAI risk for both species. The role of several anthropogenic factors related to proximity to main transportation axes and major cities (Fig. 3 ) still remained strong after adjusting for the effects of the other variables. We found that a high HPAI risk was strongly associated with highly-populated areas, short distances to the highway junction (< 20 km), and a high density of roads in a subdistrict. Moreover, the HPAI risk decreased when the distance radius to major cities (with a human population of over 100 000) increased. To a lesser extent, a very short distance to the closest highway (< 5 km) was also associated significantly with a higher HPAI risk for chickens and ducks.