Marked host specificity and lack of phylogeographic population structure of Campylobacter jejuni in wild birds

Petra Griekspoor,Noel D Mccarthy,Chris Ashhurst‐Smith,Dennis Hasselquist,Jonas Waldenström,Philip M Hansbro,Martin C J Maiden,Frances M Colles,Björn Olsen

doi:10.1111/mec.12144

Abstract

Zoonotic pathogens often infect several animal species, and gene flow among populations infecting different host species may affect the biological traits of the pathogen including host specificity, transmissibility and virulence. The bacterium Campylobacter jejuni is a widespread zoonotic multihost pathogen, which frequently causes gastroenteritis in humans. Poultry products are important transmission vehicles to humans, but the bacterium is common in other domestic and wild animals, particularly birds, which are a potential infection source. Population genetic studies of C. jejuni have mainly investigated isolates from humans and domestic animals, so to assess C. jejuni population structure more broadly and investigate host adaptation, 928 wild bird isolates from Europe and Australia were genotyped by multilocus sequencing and compared to the genotypes recovered from 1366 domestic animal and human isolates. Campylobacter jejuni populations from different wild bird species were distinct from each other and from those from domestic animals and humans, and the host species of wild bird was the major determinant of C. jejuni genotype, while geographic origin was of little importance. By comparison, C. jejuni differentiation was restricted between more phylogenetically diverse farm animals, indicating that domesticated animals may represent a novel niche for C. jejuni and thereby driving the evolution of those bacteria as they exploit this niche. Human disease is dominated by isolates from this novel domesticated animal niche.

Highlights

Many pathogens that infect humans or domestic animals can inhabit multiple animal hosts and environmental reservoirs (Daszak et al 2000; Woolhouse et al 2001)
The most genetically distinct C. jejuni populations were isolated from different wild bird species, with farm animal isolates much more similar to each other (Fig. 1)
The genetic population structure was clearly associated with host taxonomy, with C. jejuni populations from taxonomically closely related bird species being most similar to each other (Fig. S2)

Summary

Introduction

Many pathogens that infect humans or domestic animals can inhabit multiple animal hosts and environmental reservoirs (Daszak et al 2000; Woolhouse et al 2001). Most studies have investigated C. jejuni isolates from domestic animals or human patients, the bacterium has a much broader host range. Disease manifestation in wild birds has not been extensively evaluated, but a recent study showed a slight reduction in body mass in European robins, Erithacus rubecula, challenged with a C. jejuni isolate from another songbird species (Waldenstro€m et al 2010). C. jejuni has been mainly studied in relation to its role as a human pathogen, its growth characteristics at different temperatures (i.e. able to grow at 37– 42 °C) and frequent isolation from domestic and wild birds suggest that it is primarily an avian bacterium and that wild avian species may function as natural reservoirs for C. jejuni (Luechtefeld et al 1980; Hermans et al 2011; Sheppard et al 2011)

Methods

Results

Conclusion