Campylobacter jejuni and wild birds

Broman, Tina (1,2), Waldenström, Jonas (3,6); Dahlgren Daniel (4,5); Carlsson Inger (4); Eliasson, Ingvar (4); Olsen, Björn (2,5,6)

(1) Dept Molecular Biology, Univ Umeå, Sweden;
(2) Dept Infectious Diseases, Univ Umeå, Sweden;
(3) Dept Animal Ecology, Univ Lund, Sweden;
(4) Dept Clinical Microbiology, Kalmar County Hospital; Sweden;
(5) Research Institute for Zoonotic Ecology and Epidemiology, Öland, Sweden;
(6) Ottenby Bird Observatory, Öland, Sweden

The zoonotic bacterium Campylobacter jejuni is one of the most common causes of human bacterial enteritis in many parts of the world. Out-breaks of C. jejuni infections occur, but the vast majority of cases are sporadic which hampers identification of risk factors for infection. Case-control studies have shown that known risk factors only explain a portion of human cases, and there are still obscurities in the epidemiology of the organism. C.jejuni occurs among both mammals and birds, and wild birds are frequently suggested to be the natural reservoir. Little has, however, been known about the distribution of the organism among different types of wild birds, and about what sub-types of the organism that occur among wild living avians.

We have investigated the prevalence of C. jejuni in different types of bird populations, with varying levels of contact with human activities, and compared the prevalence to several ecological factors. We also sub-typed and compared strains from wild birds and humans using macrorestriction profiling by pulsed-field gel electrophoresis. Results showed that C. jejuni was unevenly distributed between groups of birds, such that birds with certain feeding behaviours more frequently were colonised than other birds. Also, we found that between some species with similar foraging habits differences existed both in prevalence and sub-type distribution. The genetic sub-typing of strains from birds and humans showed that sub-types most common among birds were not the same as those found among human clinical cases. Only a few of the bird strains had sub-types that were also found among strains from a few humans. The bird hosts from which these strains originated were of species that normally occur in close contact with human activities.

The results of our investigations indicate that ecological factors, and possibly also host genetic factors, can influence C. jejuni occurrence among wild birds. The birds investigated appeared to have little influence on human C. jejuni infections in the respective study regions. If the few cases of sub-type similarities that were observed between human and bird strains reflect a sharing of C. jejuni strains between the two hosts, the direction of transmission is unknown.

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Keynote speaker -Stervander M: Research activities and possibilities at Ottenby Bird Observatory

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