Ecology and epidemiology of bird-borne Campylobacter and Helicobacter species

Aims and objectives

The Campylobacter and Helicobacter genera comprise a large variety of species and subspecies, many of which have profound clinical importance. Two taxa, Campylobacter jejuni, which is the leading cause of bacterial gastroenteritis worldwide, and Helicobacter pylori, the causative agent of acute gastritis, are particularly renowned. There are, however, several other species with confirmed, or suspected, clinical importance. Several of the Campylobacter and Helicobacter species are zoonotic, which warrants a multidisciplinary approach to understand their ecology and epidemiology.

In our studies, we aim for a better understanding on the occurrence of Campylobacter and Helicobacter species in wild avian hosts. Specifically, we are interested in how common these microorganisms are among wild bird populations and how the birds are affected by the infections. Furthermore, with the use of modern molecular techniques, we want to investigate if these bird bacteria are of the same genetic pool that inflicts disease in humans or domesticated animals or both.

Brief background

We primarily focus our studies to the human enteropathogen Campylobacter jejuni, and the occurrence of this bacterium in the wild bird population, but we also study several other less well known species of Campylobacter and Helicobacter, i.e. C. lari, C. coli, C. hyointestinalis and H. canadensis. C. jejuni is recognized as a major health problem worldwide, and many countries have an increasing trend in the incidence of C. jejuni enteritis. Certain risk factors have been identified: consuming undercooked chicken poultry meat or cross-contamination from raw poultry to other food products, drinking contaminated water, traveling to foreign countries or having a pet in the household. There are, however, reasons to believe that other sources can be important in the epidemiology of C. jejuni. The organism is known to occur naturally in mammals and birds, both domesticated and wild, and there seems to be an especially strong association between C. jejuni and birds. Several investigations have been performed to clarify the occurrence of this bacterium in wild birds, few however have addressed whether the bacterial isolates found among birds are related to those commonly isolated from humans with clinical disease. Our aim is to study the occurrence of C. jejuni and other enteropathogens in different bird species from an ecological and epidemiological perspective, i.e. to incorporate aspects of host ecology into the epidemiology of Campylobacter-associated disease.

Preliminary results

Large scale screening for Campylobacter and Helicobacter in wild migratory birds
Using the platform provided by Ottenby Bird Observatory we have been able to screen large numbers of birds of many different species for the occurrence of bacterial pathogens. Campylobacter spp. have hitherto attained largest focus, with more than 4000 samples from wild birds analysed up to date. We have shown (Waldenström et al 2002 see pdf) that the prevalence of C. jejuni, C. lari and C. coli differ markedly between different species of birds. Some bird species show high prevalence rates, others medium or low, while yet others lack colonisation altogether. This very heterogeneous pattern could in part be explained through a thorough analysis of the host ecology. Specifically, prevalence was highly influenced by host feeding guild, giving a strong link to host diet. Other relevant factors were host taxonomy, migration length and body mass of the host.

Genetic analysis of C. jejuni isolated from different sources
Modern molecular techniques, as PFGE (Pulsed-field Gel Electrophoresis) and AFLP (Amplified Fragment Length Polymorphism), enable epidemiological comparisons of related bacterial lineages. We are currently using these methods to address various topics in the ecology and epidemiology of different Campylobacter species.

Two studies, one published (Broman et al 2002, see pdf) and one coming, have identified genetic relationships of C. jejuni isolates from similar geographical areas but from different sources, e.g. wild birds, humans and poultry flocks. In the resulting genetic trees, wild bird isolates mainly cluster together, forming branches distinctly different from human or broiler strains, indicating minor rôle of wild birds in the transmission of human campylobacteriosis. There are, however, a few cases of wild bird isolates with genetic fingerprints highly similar to those commonly found in humans. Further work is needed to establish the epidemiological importance of these findings, and to infer in what direction transmission is likely to occur.