Development of epidemiological models to analyse the risk of entry of highly pathogenic avian influenza virus and Newcastle disease virus into Spain
PhD Thesis defense by Fernando Sánchez-Vizcaíno Buendía at the Faculty of Veterinary Medicine of the Complutense University of Madrid
December 10th, 2010
The Spanish poultry sector is considered the third most important of the European Union (EU). This sector results in an estimated income of 2.73 billion of Euros to the country’s economy. Therefore, it is a necessity to keep it free of diseases that may weaken it. Highly pathogenic avian influenza (HPAI) and Newcastle disease (ND) are considered the two most devastating infectious diseases of poultry that a country may suffer. Spain reported an outbreak of HPAI and other of ND in poultry farms in 2009. The HPAI outbreak occurred in a laying hens flock of Almoguera (Guadalajara) and resulted in the destruction of 308640 hens. The ND outbreak affected a cynegetic farm in Zumaia (Guipuzcoa) and resulted in the depopulation of 11000 pheasants. These outbreaks, along with the recent epidemics of HPAI and ND reported in poultry farms of several countries of the EU, with the large volume of risk material (animals, animal products, fomits) that annually is imported into our country, the high number of water birds wintering in Spain from countries that have recently reported outbreaks of HPAI and, the enormous Spanish census of susceptible poultry, make that both diseases are considered a serious threat for the Spanish poultry industry. Risk analysis is the methodological approach recommended by the World Organisation for Animal Health (OIE) for assessing the risk of entry of a disease in a free country. Presently, no risk analysis model adapted to the Spanish characteristics to estimate the risk for HPAI virus (HPAIV) and ND virus (NDV) introduction into Spain has been published in the peer-reviewed literature. Thus, in this study was developed the first qualitative analysis of the risk for HPAIV and NDV introduction into Spain, with the aim of identifying the entry routes and countries that impose a significant risk for HPAIV and NDV introduction, the Spanish regions with highest risk for the entrance of HPAIV and NDV, and the consequences of a potential HPAI and ND epidemic in Spain. Specifically, from each potential entry route, the risk assessment was carried out after a release assessment, exposure assessment and a consequence assessment of HPAIV and NDV in Spain. In the first two stages a qualitative estimation of risk for HPAIV and NDV introduction into Spain and their subsequent contact with a susceptible poultry was executed. Consequence assessment in the context of this study determines the qualitative risk of transmission of HPAIV and NDV between commercial poultry farms of the Valencia’s Region (RV) following the exposure of this sector to both disease. Since data needs were not available for all Spanish regions, this stage of risk assessment was illustrated by using RV because it is one of the most important Spanish regions in terms of poultry production and data needs were available for this region. Once identified the entry routes that impose highest relative risk for HPAIV and NDV introduction into Spain, the first quantitative risk assessment was developed to estimate the likelihood of introduction of both viruses into Spain through those routes with the highest relative risk associated and sufficient data. Specifically, it was quantified the annual probability of introduction of the HPAIV and the NDV into Spain through legal trade of live poultry, discriminated by susceptible species imported, country of origin of the export, and province of destination.
Results of the qualitative risk analysis indicated that the entry routes that imposed highest relative risk for HPAIV introduction into Spain were the legal trade of live poultry and the migration of wintering wild water birds, whereas for NDV introduction was the legal trade of live poultry. Countries that imposed a high relative risk for HPAIV and NDV introduction into Spain through legal trade of live poultry were France, the United Kingdom, and Germany, and the provinces where this entry route imposed a high relative risk were Barcelona, Gerona, Lerida, Tarragona, and Orense. Countries that imposed highest relative risk for HPAIV introduction into Spain via migration of wintering wild water birds were France, the United Kingdom, Germany, Switzerland and Denmark, and the provinces where this entry route imposed a high relative risk were Pontevedra, La Coruña, Alicante, Zamora, Asturias, and Gerona. Results of the qualitative consequence assessment indicated that if a HPAI and ND epidemic occurs in commercial poultry farms of Valencia’s Region, then it would be expected that the risk of spread of this epidemic be higher between broiler farms than between laying hen farms and it would most likely be associated with vehicles movement, specially throughout the thinning. Results of quantitative risk analysis suggest that if the conditions and parameters assumed in the model persist, then it would be expected that HPAIV and NDV outbreaks caused by legal trade of live poultry will occur, respectively, once every 735 and 196 years in Spain. These results suggest that the source of the recent HPAIV and ND outbreaks reported in Spain in 2009 were likely unrelated to the legal trade of live poultry. Nevertheless, it would expect that if a HPAIV and NDV epidemic associated with such route of introduction takes place in Spain, then it would most likely be caused by the introduction of ducks from France into Catalonia. These results suggest that a change in the structure of legal trade of Spain would not be necessary because it would not have any impact on the risk for HPAIV and NDV introduction into the country. However, the simulations included in the study identified that decrease the number of poultry shipments to Spain is a measure much more effective to reduce the risk of entry of HPAIV and NDV than decrease the number of poultry per shipment.
Finally, it may be conclude that the risk analysis models and results presented in this thesis are a new tool to support decision making in the development of contingency and control programs of HPAI and ND in our country
