The role of wild birds and the environment in the epidemiology of Yersiniae in New Zealand

Wildlife diseases in New Zealand: recent findings and future challenges

Our knowledge of diseases in New Zealand wildlife has expanded rapidly in the last two decades. Much of this is due to a greater awareness of disease as a cause of mortality in some of our highly threatened species or as a limiting factor to the successful captive rearing of intensely managed species such as hihi (Notiomystis cincta), kiwi (Apteryx spp.) and kakapo (Strigops habroptilus). An important factor contributing to the increase of our knowledge has been the development of new diagnostic techniques in the fields of molecular biology and immunohistochemistry, particularly for the diagnosis and epidemiology of viral and protozoan diseases. Although New Zealand remains free of serious exotic viruses there has been much work on understanding the taxonomy and epidemiology of local strains of avipox virus and circoviruses. Bacterial diseases such as salmonellosis, erysipelas and tuberculosis have also been closely investigated in wildlife and opportunist mycotic infections such as aspergillosis remain a major problem in many species. Nutritional diseases such as hyperplastic goitre due to iodine deficiency and metabolic bone disease due to Ca:P imbalance have made significant impacts on some captive reared birds, while lead poisoning is a problem in some localities. The increasing use of wildlife translocations to avoid the extinction of threatened species has highlighted the need for improved methods to assess the disease risks inherent in these operations and other intensive conservation management strategies such as creching young animals. We have also become more aware of the likelihood of inbreeding suppression as populations of many species decrease or pass through a genetic bottleneck. Climate change and habitat loss, however, remain the greatest threats to biodiversity and wildlife health worldwide. Temperature changes will affect our wildlife habitats, alter the distribution of disease vectors and wildlife predators, or directly harm threatened species in vulnerable localities.

Effects of urbanization on host-pathogen interactions, using Yersinia in house sparrows as a model

Urbanization strongly affects biodiversity, altering natural communities and often leading to a reduced species richness. Yet, despite its increasingly recognized importance, how urbanization impacts on the health of individual animals, wildlife populations and on disease ecology remains poorly understood. To test whether, and how, urbanization-driven ecosystem alterations influence pathogen dynamics and avian health, we use house sparrows (Passer domesticus) and Yersinia spp. (pathogenic for passerines) as a case study. Sparrows are granivorous urban exploiters, whose western European populations have declined over the past decades, especially in highly urbanized areas. We sampled 329 house sparrows originating from 36 populations along an urbanization gradient across Flanders (Belgium), and used isolation combined with 'matrix-assisted laser desorption ionization- time of flight mass spectrometry' (MALDI-TOF MS) and PCR methods for detecting the presence of different Yersinia species. Yersinia spp. were recovered from 57.43% of the sampled house sparrows, of which 4.06%, 53.30% and 69.54% were identified as Y. pseudotuberculosis, Y. enterocolitica and other Yersinia species, respectively. Presence of Yersinia was related to the degree of urbanization, average daily temperatures and the community of granivorous birds present at sparrow capture locations. Body condition of suburban house sparrows was found to be higher compared to urban and rural house sparrows, but no relationships between sparrows' body condition and presence of Yersinia spp. were found. We conclude that two determinants of pathogen infection dynamics, body condition and pathogen occurrence, vary along an urbanization gradient, potentially mediating the impact of urbanization on avian health.

Risk factors for sporadicYersinia enterocoliticainfections, Germany 2009–2010

Yersinia enterocoliticais an important cause of acute gastrointestinal disease and post-infectious complications. In Germany, incidence of reported yersiniosis is relatively high compared with other countries of the European Union. Children aged <5 years are most frequently affected. The aim of our study was to identify risk factors for sporadic yersiniosis in Germany. A population-based case-control study was conducted in five federal states of Germany from April 2009 to June 2010. Cases exhibiting gastrointestinal symptoms were notified to the local health department with aYersinia enterocoliticainfection culture-confirmed from stool. Controls were selected from population registries and frequency-matched on age group and state of residency. Cases and controls received a questionnaire on possible risk factors by mail. Multivariable logistic regression modelling was used to identify risk factors and to calculate adjusted odds ratios (aORs). Population attributable fractions (PAFs) were estimated for exposures associated with yersiniosis. We analysed data on 571 case patients and 1798 controls. Consumption of raw minced pork, a dish frequently consumed even by young children in Germany, was the main risk factor for disease (aOR 4·7, 95% confidence interval (CI) 3·5–6·3, PAF 30%). This association varied by age group and, unexpectedly, was strongest for children aged <2 years (aOR 17·5, 95% CI 6·0–51·2). Other independent risk factors included recent preparation of minced pork in the household (aOR 1·4, 95% CI 1·1–1·9, PAF 21%), playing in a sandbox (aOR 1·7, 95% CI 1·3–2·4, PAF 17%), and contact with birds (aOR 1·7, 95% CI 1·1–2·6, PAF 4%). Prevention efforts should specifically target parents and caregivers of young children and focus on the high infection risk associated with consumption of raw minced pork.

Yersinia enterocolitica: Epidemiological Studies and Outbreaks

Yersinia enterocolitica is the most common bacteriological cause of gastrointestinal disease in many developed and developing countries. Although contaminated food is the main source of human infection due to Y. enterocolitica, animal reservoir and contaminated environment are also considered as other possible infection sources for human in epidemiological studies. Molecular based epidemiological studies are found to be more efficient in investigating the occurrence of human pathogenic Y. enterocolitica in natural samples, in addition to conventional culture based studies.

virF-positive Yersinia pseudotuberculosis and Yersinia enterocolitica found in migratory birds in Sweden

During spring and autumn migrations, 468 fecal samples from 57 different species of migratory birds were collected in Sweden. In total, Yersinia spp. were isolated from 12.8% of collected samples. The most commonly found species was Yersinia enterocolitica, which was isolated from 5.6% of all collected samples, followed by Y. intermedia (3.8%), Y. frederiksenii (3.0%), Y. kristensenii (0.9%), Y. pseudotuberculosis (0.6%), and Y. rohdei (0.4%). The pathogenic, virF-positive Y. pseudotuberculosis strains were recovered from three thrushes. These strains belonged to the same bioserotype, 1/O:2, but had two different profiles as determined by pulsed-field gel electrophoresis with NotI and SpeI enzymes. In addition, 10 Y. enterocolitica strains, all from barnacle geese, belonged to bioserotype 3/O:3, which is associated with human disease. Two of the strains were pathogenic, carrying the virF gene on their plasmids. All pathogenic Y. pseudotuberculosis and Y. enterocolitica strains were recovered during the spring, and as the birds were caught during active migration they likely became infected at an earlier stage of the migration, thus potentially transporting these bacterial pathogens over long geographical distances.

Low occurrence of pathogenic Yersinia enterocolitica in clinical, food, and environmental samples: a methodological problem

While Yersinia enterocolitica is an important pathogen, which can cause yersiniosis in humans and animals, its epidemiology remains obscure. The pig is the major reservoir of pathogenic Y. enterocolitica of bioserotype 4/O:3, the most common type found in humans. Y. enterocolitica is thought to be a significant food-borne pathogen, although pathogenic isolates have seldom been recovered from foods. The low isolation rate of this pathogenic bacterium in natural samples, including clinical, food, and environmental samples, may be due to the limited sensitivity of culture methods. During the last decade, numerous DNA-based methods, such as PCR and colony hybridization assays, have been designed to detect pathogenic Y. enterocolitica in natural samples more rapidly and with better sensitivity than can be achieved by culture methods. In addition, the occurrence of pathogenic Y. enterocolitica in natural samples is clearly higher with PCR than with culture methods. The methods available for detection of pathogenic Y. enterocolitica in natural samples are reviewed in this article.