Role of migrating birds in the movement of zoonotic pathogens

Background/Question/Methods

Birds are the natural reservoir for several pathogens of economic and public health importance, including West Nile virus (WNV), highly pathogenic avian influenza viruses including H5N1, Japanese encephalitis, and Lyme disease. The spread of these pathogens has often been attributed to the movements of migratory birds. Yet, the potential of migrating birds in the long-range movement of pathogens has not been confirmed and is far from being understood. The question of whether migratory birds are responsible for the spread of disease, and to what extent is a major gap in the understanding of the ecology of these disease agents and their avian hosts. We simply do not know whether these pathogens or others negatively impact the migratory performance of the infected host or, how the infection subsequently influences the pattern of spread of these pathogens by migrating birds. To gain a better understanding of how these bird-borne pathogens are maintained and spread in nature, more detailed knowledge about the interaction between the wild avian host, including migratory behavior, and the virus is essential. Our research has addressed the following questions: (1) Does a bird’s infection status affect its migratory behavior? (2) Do the energetic challenges associated with migration influence a bird’s susceptibility to infection and/or disease? (3) Do migratory birds differ in their resistance or tolerance relative to non-migratory species? To address these and related questions we conducted primarily captive-based experiments with several species of migratory birds and two zoonotic pathogens, WNV and avian influenza virus (AIV).

Results/Conclusions

Our findings show that there are inter- and intraspecific differences in a bird’s capacity to maintain and move WNV. Furthermore, a bird’s energetic condition affects its susceptibility to infection with AIV. On average migratory species are less susceptible to WNV than resident species. These and other results are discussed as well as the remaining knowledge gaps that warrant further investigation. This knowledge is a prerequisite to the effective evaluation of the role of migratory birds in the intra- and inter-continental spread of bird-borne pathogens. Without this information our ability to make accurate predictions about spatial and temporal patterns of disease occurrence is limited, compromising efforts to control outbreaks in both human and animal populations.