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Freie Universität Berlin (2011)

Studies on potential risk factors for introduction and spread of avian influenza in domestic poultry of Pakistan

Abbas, Tariq

Titre : Studies on potential risk factors for introduction and spread of avian influenza in domestic poultry of Pakistan

Studien zu potentiellen Risikofaktoren für die Einschleppung und Verbreitung von aviärer Influenza beim Hausgeflügel in Pakistan

Auteur : Abbas, Tariq

Université de soutenance : Freie Universität Berlin

Grade : Doktors der Veterinärmedizin 2011

Since 1994, the domestic poultry in Pakistan has experienced several outbreaks due to avian influenza viruses (AIVs) of subtypes H7N3, H5N1, and H9N2. Many aspects of the epidemiology of the disease are unknown. Assessment of the risk factors for introduction, spread and persistence of AIVs is necessary so that informed decisions can be made by the government and the industry to manage outbreaks. In this thesis, available country-specific information on poultry production, avian influenza situation (and its evolution) and institutional responses was collated for epidemiological analyses and to assist in the design of control strategies. In addition, studies were carried out to provide insight into risk factors of the disease. One possible route by which AIVs may be introduced into domestic poultry is through migratory wild birds. Pakistan is situated within the Central Asian flyway of migrating birds and contains more than 225 wetlands. The wetland areas provide wintering and staging grounds for a large number of migratory birds coming from Siberia and Central Asian states. The migratory season ranges from September until March. A retrospective case-series analysis of previous H5N1 outbreaks (2006-2008) was performed which revealed that 64% of outbreaks reported to the Office International des Epizooties (OIE) occurred during the migratory period. To answer the question, which areas should be given priority in surveillance and prevention of AIVs transmission during the migratory season, a subset of Asian waterbird census (AWC) data was reviewed and mapped. The data contained local names of 535 sites and annual mid-winter counts of waterbirds from 1987 to 2007. The majority of the sites were not counted regularly leading to gaps in sites-by-years data matrix, (here called missing values). The location of AWC sites provided a crude approximation of spatial distribution of waterbirds during the migratory period. It was also possible to map the maximum reported count per site and find out clusters of undersampled sites (i. e. those with high number of missing values). With improved data on the distribution of migratory/waterbirds, the established geographic information system may help to assess the risk of transmission of avian influenza viruses between migratory birds and domestic poultry. A list of wild bird species was generated that occur in Pakistan and were known to be infected with H5N1. Another focus of this project was the investigation of the contact structure and possible transmission pathways among traditional open-sided chicken farms, a sub-sector of commercial poultry. Between April and June 2009, a cross-sectional survey was conducted in Kamalia, which is a part of the district Toba Tek Singh in central Punjab. Data were collected from 78 growers in interviews based on a standard questionnaire. Important findings of the survey regarding the transmission of AIVs were : short buffer distances among the farms, inappropriate methods for disposal of carcasses of dead birds, entry of bridge species into poultry sheds, incomplete biosecurity on high-risk visitors and essential vehicles, sharing of equipment (e. g. reuse of egg trays), and visits of farmers to potential cross-contamination points. Considering flock size and structure of the farms and conventional meteorological assumptions (very stable boundary layers, very low and constant wind velocity as 1 m/s over 24 h and a wind direction straight towards the next adjacent settlement), the extent of the dispersion of smallsized particulate matter (PM10) was simulated using a Lagrangian dispersion approach. For a velocity of 1 m/s, stable conditions and higher emissions (meat producing birds) concentrations of more than 0,01 μg/m³ were simulated at a distance of 3 km. Compared to velocities of 3 m/s and indifferent conditions, the same concentration was detected up to a distance of 2.5 km. Finally, a pilot study was conducted to elicit the opinion of poultry veterinarians regarding potential risk factors for HPAI outbreaks in Pakistan. For this purpose, the technique of adaptive conjoint analysis (ACA) was used which involves computer-mediated interactive interviewing optionally over the internet. A total of 21 risk factors “attributes” were divided into four categories namely area, pests, people, organic (and inorganic) items. The ACA interview was emailed to 33 local veterinarians in Pakistan. The response rate was 39%. Potential risk factors with the highest mean relative importance were : short buffer distance between the farms, entry of wild birds into poultry sheds, visits of intermediaries and service providers, and sharing high-risk equipment with other farms

Mots clés  : avian influenza ; transmission ; Pakistan ; epidemiology ; poultry ; risk factors ; wild birds ; wetlands ; surveys ; mapping ; geographic


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