Surveillance for avian influenza in catalonia and development of new models to improve its sensitivity

Resumen

Since 2005, with the wide spread of H5N1 highly pathogenic avian influenza viruses, many surveillance programmes have been initiated in poultry and wild birds worldwide, including the surveillance programme for AI in Spain. The first study of this thesis provides information as baseline surveillance of the current strains of Low Pathogenicity Avian Influenza viruses (LPAIV) circulating in Catalonia (North-Eastern Spain). It describes for the first time the detection in this region of different subtypes of avian influenza viruses (AIV) in wild birds. During a 3 year-period (from Jul-2006 to Jun- 2009) 1,374 birds from 16 different families were examined, and a total of 62 AIV were detected by means of a real-time reverse transcriptase PCR assay. AIV were more frequently detected in Anatidae, Phoenicopteridae, Rallidae and Laridae families. Of the 62 positive samples, 28 AIV could be isolated in embryonated eggs. All isolates were subtyped by haemagglutinin and neuraminidase inhibition techniques and 10 different haemagglutinins (HA) and 7 neuraminidases (NA) were found in 13 different combinations of subtypes. The second study presents a stochastic model to simulate the possible spread of AIV inwild birds given different scenarios. This work provides a tool to identify the species and zones in a specific area that should be targeted in a risk-based avian influenza (AI) surveillance system. This model combines the available information related to the reference population, parameters related to the behaviour of the wild avian species, previous data obtained by the surveillance programmes in Europe, and diverse parameters of the epidemiology of AIV in wildlife. The model represents the spatiotemporal dynamics of AIV among wild birds based on an individual susceptible-infectious-susceptible approach. It has been focused on the Natural Park of Ebro Delta, which is one of the most important reserves of aquatic waterfowl in the Western Mediterranean Basin on the basis of abundance and variety of species. The model has as inputs: the onset date of introduction, the different areas according to ecological and ornithological criteria that composed the Natural Park of Delta Ebre, a list of frequent bird species divided into high-risk species and intermediate species, the census of each one of these bird species by area and period, their patterns of dispersion, the degree of affinity among bird species, the duration of infectiousness, and different transmission probabilities assigned by the modeller. This type of model can provide useful information for the decision makers to support the design and the implementation of future activities of surveillance for AIV in wild birds in specific areas. The third study is related to the surveillance for Avian Influenza in domestic poultry. In this work the sensitivities of different sampling designs for the commercial poultry population of Catalonia proposed by the Spanish authorities were assessed. This assessment was done using the methodology of the scenario tree model. The probabilities of detecting infection considering different design prevalences at individual and flock level were estimated. Furthermore, those subpopulations that contributed the most to the sensitivity of the system were identified. The model demonstrated that all the designs met the requirements of the European Commission. The probability of detecting AI circulating in Catalonian poultry did not change significantly when the within-flock design prevalence varied from 30% to 10%. In contrast, when the among-flock design prevalence decreased from 5% to 1%, the probability of detecting AI was drastically reduced. The sampling of duck and goose holdings, and to a lesser extent the sampling of turkey and game bird holdings, increased the sensitivity substantially. The sensitivity of passive surveillance in chickens for Highly Pathogenic Avian Influenza (HPAI) and Low Pathogenicity Avian Influenza (LPAI) was also assessed. For HPAI, the passive would be the most appropriate system to detect an early incursion, but its efficiency strongly depends on the probability of the manifestation of clinical signs in poultry holdings and the awareness of veterinarians and farmers on the risk of suffering the AI.