Patterns of Bird-Bacteria Associations

Abstract

Birds, with their broad geographic ranges and close association with humans, have historically played an important role as carriers of human disease and as reservoirs for drug-resistant bacteria. Here, we examine scientific literature over a 15-year timespan to identify reported avian-bacterial associations and factors that may impact zoonotic disease emergence by classifying traits of bird species and their bacteria. We find that the majority of wild birds studied were migratory, in temperate habitats, and in the order Passeriformes. The highest diversity of bacteria was found on birds in natural habitats. The most frequently reported bacteria were Escherichia coli, Salmonella enterica, and Campylobacter jejuni. Of the bacteria species reported, 54% have shown pathogenicity toward humans. Percentage-wise, more pathogens were found in tropical (vs. temperate) habitats and natural (vs. suburban, urban, or agricultural) habitats. Yet, only 22% were tested for antibiotic resistance, and of those tested, 75% of bacteria species were resistant to at least one antibiotic. There were no significant patterns of antibiotic resistance in migratory versus non-migratory birds, temperate versus tropical areas, or different habitats. We discuss biases in detection and representation, and suggest a need for increased sampling in non-temperate zones and in a wider range of avian species.

Keywords: Antibiotic resistance; Avian; Literature; Microbial; Pathogen.

Figure 1.

Screening process. PRISMA flowchart detailing the review and data selection process. Six hundred and eighty-three studies were ultimately used for analysis.

Figure 2.

Map of avian sampling locations. Each unique sampling location studied is represented by one plotted point on the map. Purple and orange dots are wild and domesticated species, respectively. Most of the sampling locations are in temperate locations (defined by areas that are above or below 23.4371 degrees latitude) compared with tropical locations. Inset pie charts show proportions of sampling locations by unique study (n = 683) and by unique species (n = 530).

Figure 3.

Distribution of bird orders in the bird-bacteria literature over a 15-year timespan. We grouped the 530 unique bird species studied by their orders. In parentheses, the number of bird species in each order is shown. The most common orders were Passeriformes (47%), Charadriiformes (12%), and Anseriformes (8%). This chart includes 15 domestic species: 8 Galliformes, 5 Anseriformes, 1 Struthioniformes, 1 Rheiformes.

Figure 4.

Bird migratory and habitat traits. Migration status of wild birds in different habitats, excluding 16 birds whose migration status was unknown (n = 499). A bird found only in one habitat in this literature-based analysis was listed under its respective habitat. Birds sampled in several different habitats were grouped into the “Multiple habitats” category.

Figure 5.

Distribution of bacteria phyla in the bird-bacteria literature over a 15-year timespan. We grouped 368 unique bacteria species studied by phyla. In parentheses, the number of bacteria species in each phylum is shown. The most common phyla were Proteobacteria (46%), Firmicutes (31%), and Actinobacteria (11%). There was one bacterium (Avispirillum sp.) that has not been classified yet (Waldenström 2006) and is in the phylum labeled, “N/A”.

Figure 6.

Pathogenicity of bacteria in relation to bird characteristics. a Bacteria pathogenicity and migratory status of wild birds. Domestic birds were excluded from migratory counts. b Pathogenicity in each of the habitats. Bacteria on domestic species were included in the “Industrial livestock: domestic” category. Note: For both a and b, if multiple bacteria species were found on a bird, each bacteria species was counted.