The biological background of a recurrently emerging infectious disease: prevalence, diversity and host specificity of Avipoxvirus in wild Neotropical birds

Abstract

Understanding which factors promote disease emergence and transmission remains a major challenge of epidemiology. A problem with research on emerging diseases is that we seldom know to what extent pathogens circulate in natural popula-tions before emergence is already occurring. Moreover, it is critical to determine which pathogen characteristics are key to predict their emergence and invasion potential. We examined the prevalence, host specificity and evolutionary relationships of Avipoxvirus causing skin lesions in birds in two megadiverse and unexplored geographical regions of South America: an elevational gradient in the south Ecuadorian Andes, and a lowland Amazon rainforest in French Guiana. Next, we analyzed the host specificity and distribution of the worldwide Avipoxvirus diversity in order to understand their invasion potential. In French Guiana Avipoxvirus prevalence was 0% (n  889, 94 bird species). In Ecuador, prevalence was 0.3% (n  941, 132 bird species), with cases spanning the range of elevations between 1500 and 2500 m. ese were caused by two newly described strains, one of which belonged to an American clade of Avipoxvirus shared by different bird families, and another one closely related to a strain recovered from a different family of birds in Madeira. An analysis of the host specificity and geographic distribution of all Avipoxvirus strains known worldwide finds that these viruses are usually host generalists (particularly those in the fowlpox clade), and that many closely related strains are found on multiple continents. Our study at the community level suggests that distantly related Avipoxvirus strains circulate at very low prevalence in continental tropical South America. Avipoxvirus assemblages are composed of generalist strains with different ancestry and widespread distribution, a combination of characteristics which may make these typically scarce viruses perfect candidates to emerge under favorable ecological conditions.