Climate Change Migratory Birds and Infectious Diseases

Several species of wild birds can act as biological or mechanical carriers of human pathogens as well as of vectors of infectious agents (Olsen et al., 1995; Klich et al., 1996; Gylfe et al., 2000; Friend et al., 2001; Niskanen et al., 2003; Rappole and Hubalek, 2003; Reed et al., 2003; Hubalek, 2004; Krauss et al., 2004). Many of these birds are migratory species that seasonally fly long distances through different continents (de Graaf and Rappole, 1995). Climate change has been implicated in changes in the migratory and reproductive phenology (advancement in breeding and migration dates) of several bird species, their abundance and population dynamics, as well as a northward expansion of their geographical range in Europe (Sillett et al., 2000; Parmesan and Yohe, 2003; Brommer, 2004; Both and Visser, 2005). Two possible consequences of these phenological changes in birds to the dispersion of pathogens and their vectors as follows:

1. Shifts in the geographical distribution of the vectors and pathogens due to altered distributions or changed migratory patterns of bird populations,

2. Changes in the life cycles of bird-associated pathogens due to the mistiming between bird breeding and the breeding of vectors, such as mosquitoes. One example is the transmission of St. Louis encephalitis virus, which depends on meteorological triggers (e.g., precipitation) to bring the pathogen, vector, and host (nestlings) cycles into synchrony, allowing an overlap that initiates and facilitates the cycling necessary for virus amplification between mosquitoes and wild birds (Day, 2001).

Wild water birds play an important role in the occurrence of both animal and human disease. They have been implicated as important carriers of poultry pathogens including Newcastle, paramyxo, and avian influenza viruses (Pederson et al., 2004; Jorgensen et al., 2004; Soares et al., 2005). These diseases are often sub clinical in wild water birds but can cause devastating infections with high mortality and huge economic loss in domestic poultry. These viruses readily infect migratory water birds that disseminate them along migratory pathways.

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