Different Environmental Drivers of Highly Pathogenic Avian Influenza H5N1 Outbreaks in Poultry and Wild Birds

Abstract

A large number of highly pathogenic avian influenza (HPAI) H5N1 outbreaks in poultry and wild birds have been reported in Europe since 2005. Distinct spatial patterns in poultry and wild birds suggest that different environmental drivers and potentially different spread mechanisms are operating. However, previous studies found no difference between these two outbreak types when only the effect of physical environmental factors was analysed. The influence of physical and anthropogenic environmental variables and interactions between the two has only been investigated for wild bird outbreaks. We therefore tested the effect of these environmental factors on HPAI H5N1 outbreaks in poultry, and the potential spread mechanism, and discussed how these differ from those observed in wild birds. Logistic regression analyses were used to quantify the relationship between HPAI H5N1 outbreaks in poultry and environmental factors. Poultry outbreaks increased with an increasing human population density combined with close proximity to lakes or wetlands, increased temperatures and reduced precipitation during the cold season. A risk map was generated based on the identified key factors. In wild birds, outbreaks were strongly associated with an increased Normalized Difference Vegetation Index (NDVI) and lower elevation, though they were similarly affected by climatic conditions as poultry outbreaks. This is the first study that analyses the differences in environmental drivers and spread mechanisms between poultry and wild bird outbreaks. Outbreaks in poultry mostly occurred in areas where the location of farms or trade areas overlapped with habitats for wild birds, whereas outbreaks in wild birds were mainly found in areas where food and shelters are available. The different environmental drivers suggest that different spread mechanisms might be involved: HPAI H5N1 spread to poultry via both poultry and wild birds, whereas contact with wild birds alone seems to drive the outbreaks in wild birds.

Risk for Low Pathogenicity Avian Influenza Virus on Poultry Farms, the Netherlands, 2007–2013

“…The presence of avian influenza in wild water birds and the frequency of direct or indirect contact between reservoir birds and poultry are risk components that enable transmission from wild birds to poultry. However, in addition to the higher introduction rate on outdoor-layer farms (this study) and the genetic relationship of wild bird strains and avian influenza outbreak viruses ( 17 ), no scientific data have been available that could support this assumption, although physical environmental factors, such as surface water availability and proximity to lakes and wetlands, have been suggested as drivers of HPAIV H5N1 outbreaks in poultry and wild birds ( 18 , 19 ). …”

Quantifying predictors for the spatial diffusion of avian influenza virus in China

“…In addition, H7 viruses with multiple NA subtypes were found in ducks in Jiangxi province (in South Central), suggesting an epidemiological bridge from migratory birds to sentinel farm ducks and then to market birds. Epidemiological studies also suggested that HPAI H5N1 outbreaks in poultry mostly occurred in areas which overlapped with habitats for wild birds, whereas outbreaks in wild birds were mainly found in areas where food and shelter are available [48]. Bidirectional movement of wild birds among the provinces along the flyway route in south central areas were identified in studies tracking the movements of migrating wild birds, and the transmission of HPAI H5N1 to Qinghai lake (Northwest) have also been identified [15, 49, 50].…”

Mesenchymal stromal cell treatment prevents H9N2 avian influenza virus-induced acute lung injury in mice

“…Infections with avian influenza virus (AIV) strains have become highly prevalent in poultry worldwide [1–4]. Avian influenza (AI) is a leading cause of morbidity, mortality, and economic loss in many countries.…”