Human-wildlife interface: Starling movements linked to E. coli carriage

By Dr. Liji Thomas, MDApr 10 2024Reviewed by Benedette Cuffari, M.Sc.

A recent study published in the journal Science of the Total Environment monitors spotless starlings and their potential role in spreading Escherichia coli (E. coli).

Study: Connectivity at the human-wildlife interface: starling movements relate to carriage of E. coli. Image Credit: smutan / Shutterstock.com

How birds bridge the gap

Birds can spread dangerous pathogens between domestic and wild animals. The avian influenza virus (AIV), for example, prefers to live in waterbirds, often as variants of low pathogenicity. However, once it is introduced into poultry on a farm, AIV undergoes various mutations to evolve into highly pathogenic agents.

The transmission of these pathogens to animals is often achieved through synanthropic birds, which refers to birds that live in close proximity to humans. Synanthropic birds, such as Eurasian tree sparrows (Passer montanus) and European starlings (Sturnus vulgaris), may be infected with pathogenic variants from poultry and subsequently transmit these agents to wild species that serve as natural reservoirs.

Enteric bacteria like E. coli are notoriously hard to manage on farms and are important human pathogens. These bacteria often carry antimicrobial resistance (AMR) genes, which increases the risk that infected birds may spread antimicrobial-resistant bacteria (ARB) from one farm to another and from farms to the city or forest.

About the study

Passerine birds are responsible for most avian diversity and abundance. The current study used miniaturized global positioning satellite (GPS) devices to monitor the movements of these birds, which were then linked into spatial networks. Each node represented one habitat patch, whereas each link between nodes represented the number of paths between them.

The aim was to identify associations between spotless starling movements and their infection status for E. coli. Birds were sampled for both obligate and opportunistic pathogens and tagged thereafter.

The study area comprised a partridge farm where most starlings fed, cottages with gardens or barns, a garlic factory used as a daylight roost, El Bonillo village with multiple roosts, an open pine forest, a horse stable, as well as poultry, pig, and egg farms.

Using the movement information, the investigators built E. coli-positive and -negative networks to represent changes in infection status or pathogen prevalence with movement between nodes. Exponential Random Graph Models (ERGMs) were employed to produce quantitative data showing how farms, urban surroundings, or natural habitats served as either sources or sinks of starling movements.

What did the study show?

All tagged starlings were free of any of the tested microbes at baseline. However, 17 of the 28 starlings carried E. coli, with 13 isolates resistant to at least one antibiotic. E. coli-positive and -negative starling networks had 47 and 49 links, respectively.

The cottage was a key node for the starling movements, as it ranked highest for strength and betweenness. Movements from the horse farm to any other node were markedly higher than expected for both networks. The horse farm was both a source and sink of trajectories, or starling movements, in all models.

The partridge farm also served as a source and sink in all models. Comparatively, pig farms, poultry yards, and sheep farms were associated with adverse effects. The village was a sink in the E. coli-positive network, whereas the open pine forest served as an E. coli-negative sink.

Spotless starlings using natural sites are less likely to carry bacteria of health importance to humans and livestock than those more linked to urban sites.”

Conclusions

The researchers utilized GPS to quantitatively track starling movements and construct spatial networks that elucidated the extent of connections between farms, natural habitats, and nearby cities.

The patterns of connection differed with E. coli carriage and the degree of antibiotic resistance. However, the risk of carriage was lower with forest starlings than urban starlings, where some birds roost but also forage. Birds that mostly visit the village may forage in the partridge farm or human foods.

E. coli-negative starlings may have a narrower habitat range, as shown by their mapped network, compared to E. coli-positive starlings. As a result, these groups may infrequently share habitats.  

The current study also demonstrates the utility of EGRMs for epidemiologic research in movement and interaction tracking and how these models could be used to monitor animals and restrict zoonotic pathogens. The distances between feeding and watering spots and roosting places affect the choice of habitat, which, in the current study, appeared to be optimal at the horse farm.

The connections we have identified could lead to transmission of agents that could impact animal production or survival.”