Assessing the evidence for intercontinental redistribution of infectious agents by migratory birds
Ramey, Andrew Mark
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In order to assess risk associated with the introduction of foreign origin pathogens by wild birds and to develop effective surveillance programs for infectious agents that may affect human, avian, and ecosystem health, additional information is needed regarding the spread of infectious agents within and between migratory flyways. The intercontinental redistribution of avian paramyxovirus serotype 1 (APMV-1), blood parasites, and influenza A virus (IAV) was therefore assessed in migratory birds at locations along the continental margins of North America in the United States (USA) through a series of three investigations. The first assessed the redistribution of APMV-1 between East Asia and North America through genetic characterization of isolates from Japan, Russia, and Alaska (USA). Evidence supported the intercontinental redistribution of Class II genotype I viruses by wild birds and samples providing support for this conclusion originated from species with transhemispheric migratory tendencies. A second investigation assessed the redistribution of blood parasites between East Asia and North America using samples collected from the northern pintail (Anas acuta) in Alaska (USA), California (USA), and Japan. Genetic characterization of Haemoproteus, Leucocytozoon, and Plasmodium parasites supported gene flow among sampling areas on two continents which suggests intercontinental parasite exchange. A third study assessed the genetic exchange of IAV between North America and South America in migratory birds through the genomic characterization of isolates obtained from blue-winged teal (Anas discors). No evidence of viral gene flow was found between North America and southern South America (e.g. Argentina); however, results of this study and recent parallel investigations suggest that genetic exchange of IAV may be extensive between North America and the northern Neotropics. Collectively, these three projects provide new evidence supporting the role of migratory birds in redistributing viral and parasitic agents between continents. Furthermore, results from these projects are useful for identifying research priorities for clarifying the extent of intercontinental virus and parasite exchange.