Search

Wild dabbling ducks are the main reservoir for avian influenza (AI) viruses and pose an ongoing threat to commercial poultry flocks. Combining the (i) size of that population, (ii) their flight distances and (iii) their AI prevalence, the density of AI-infected dabbling ducks (DID) was calculated as a risk factor for the introduction of AI viruses into poultry holdings of Emilia-Romagna region, Northern Italy. Data on 747 poultry holdings and on 39 AI primary outbreaks notified in Emilia-Romagna between 2000 and 2017 were used to validate that risk factor. A multivariable Bayesian logistic regression was performed to assess whether DID could be associated with the occurrence of AI primary outbreaks. DID value, being an outdoor flock, hobby poultry trading, species reared, length of cycle and flock size were used as explanatory variables. Being an outdoor poultry flock was significantly associated with a higher risk of AI outbreak occurrence. The probability of DID to be a risk factor for AI virus introduction was estimated to be 90%. A DID cut-off of 0.23 was identified to define high-risk areas for AI virus introduction. Using this value, the high-risk area covers 43% of the region. Seventy-four per cent of the primary AI outbreaks have occurred in that area, containing 39% of the regional poultry holdings. Poultry holdings located in areas with a high DID value should be included in a risk-based surveillance programme aimed at AI early detection., (© 2018 Blackwell Verlag GmbH.)

Italy has experienced recurrent incursions of H5N2 avian influenza (AI) viruses in different geographical areas and varying sectors of the domestic poultry industry. Considering outbreak heterogeneity rather than treating all outbreaks of low pathogenicity AI (LPAI) viruses equally is important given their interactions with the environment and potential to spread, evolve and increase pathogenicity. This study aims at identifying potential environmental drivers of H5N2 LPAI outbreak occurrence in time, space and poultry populations. Thirty-four environmental variables were tested for association with the characteristics of 27 H5N2 LPAI outbreaks (i.e. time, place, flock type, number and species of birds affected) occurred among domestic poultry flocks in Italy in 2010-2012. This was done by applying a recently proposed analytical approach based on a combined non-metric multidimensional scaling, clustering and regression analysis. Results indicated that the pattern of (dis)similarities among the outbreaks entailed an underlying structure that may be the outcome of large-scale, environmental interactions in ecological dimension. Increased densities of poultry breeders, and increased land coverage by industrial, commercial and transport units were associated with increased heterogeneity in outbreak characteristics. In areas with high breeder densities and with many infrastructures, outbreaks affected mainly industrial turkey/layer flocks. Outbreaks affecting ornamental, commercial and rural multi-species flocks occurred mainly in lowly infrastructured areas of northern Italy. Outbreaks affecting rural layer flocks occurred mainly in areas with low breeder densities in south-central Italy. In savannah-like environments, outbreaks affected mainly commercial flocks of galliformes. Suggestive evidence that ecological ordination makes sense genetically was also provided, as virus strains showing high genetic similarity clustered into ecologically similar outbreaks. Findings were informed by hypotheses about how ecological interactions among poultry populations, viruses and their environments can be related to the observed patterns of H5N2 LPAI occurrence. This may prove useful in enhancing future interventions by developing site-specific, ecologically-grounded strategies.

Background: Infections of wild birds with highly pathogenic avian influenza (AI) subtype H5N1 virus were reported for the first time in the European Union in 2006., Objectives: To capture epidemiological information on H5N1 HPAI in wild bird populations through large-scale surveillance and extensive data collection., Methods: Records were analysed at bird level to explore the epidemiology of AI with regard to species of wild birds involved, timing and location of infections as well as the applicability of different surveillance types for the detection of infections., Results: In total, 120,706 records of birds were sent to the Community Reference Laboratory for analysis. Incidents of H5N1 HPAI in wild birds were detected in 14 EU Member States during 2006. All of these incidents occurred between February and May, with the exception of two single cases during the summer months in Germany and Spain., Conclusions: For the detection of H5N1 HPAI virus, passive surveillance of dead or diseased birds appeared the most effective approach, whilst active surveillance offered better detection of low pathogenic avian influenza (LPAI) viruses. No carrier species for H5N1 HPAI virus could be identified and almost all birds infected with H5N1 HPAI virus were either dead or showed clinical signs. A very large number of Mallards (Anas platyrhynchos) were tested in 2006 and while a high proportion of LPAI infections were found in this species, H5N1 HPAI virus was rarely identified in these birds. Orders of species that appeared to be very clinically susceptible to H5N1 HPAI virus were swans, diving ducks, mergansers and grebes, supporting experimental evidence. Surveillance results indicate that H5N1 HPAI virus did not establish itself successfully in the EU wild bird population in 2006.

Following the avian influenza epidemics that occurred in Italy between 1997 and 2003, the Italian Ministry of Health in collaboration with veterinary authorities promoted, funded and implemented a national surveillance programme. The main objectives of the surveillance effort were to identify avian influenza viruses circulating in wild birds and to investigate the role of backyard poultry flocks in the dynamics of infection in a densely populated poultry area. Over 2 years (2004 to 2006), 164 backyard flocks and 4083 wild birds (mainly migratory Anseriformes and Charadriiformes) were sampled in three regions in the North of Italy. Samples collected were screened by means of real-time reverse transcriptase-polymerase chain reaction and the positive samples were processed for attempted virus isolation in embryonated fowl's specific pathogen free eggs. At the end of the study period, 27 low-pathogenic avian influenza viruses had been isolated from backyard flocks and 49 strains obtained from wild birds. Of these, 26 belonged to the H5 or H7 subtype and were closely related to contemporary low-pathogenic strains of Eurasian lineage. The findings confirm that backyard free-range farming is at high risk for avian influenza virus introduction, and confirm the role of wild waterfowl in the introduction and perpetuation of low-pathogenic avian influenza viruses during the winter season in Southern Europe.

Anseriformes are the reservoir of low-pathogenicity avian influenza viruses (LPAIV). Studies have shown a high LPAIV prevalence associated with low antibody detection in a wild duck population in northern European countries, whereas in winter areas (Mediterranean basin), low viral detection and high seroprevalence were observed. In order to gain insight into the role played by both population recruitment and migration on AIV persistence, an epidemiological model was developed. A susceptible, infectious and removed (immune or dead)-individuals model coupling population and infection dynamics was developed to simulate LPAIV circulation in dabbling ducks throughout the entire year. The transmission coefficient (beta) was calculated using the original dataset of published works, whereas dabbling duck demographic parameters were obtained from the literature. The estimated host density threshold for virus persistence is 380 susceptible individuals per day whereas the critical community size needed for maintaining the virus throughout the winter has been estimated to be about 1200 individuals. The model showed peaks of viral prevalence after nesting and during the moult period because of population recruitment and high host density, respectively. During the winter and spring periods, the viruses reach the minimal endemic level and local extinction is highly probable because of stochastic phenomena, respectively 80% and 90% of probabilities. The most sensitive parameters of the model are the recruitment rate of young susceptible animals and the duration of virus shedding.