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Application of laboratory tests to investigate flock notifiable avian influenza status - SE0533

Avian influenza is a highly contagious disease of poultry and other birds caused by influenza A viruses. The level of risk to animal and public health posed by different strains of avian influenza viruses is very variable and unpredictable due to the possibility of rapid mutation from low to high pathogenicity and possible re-assortment of genetic material among influenza A virus strains. Highly pathogenic avian influenza (HPAI) causes a substantial proportion of deaths in susceptible poultry species and can lead to considerable economic losses.

Confirmation of notifiable avian influenza (NAI) (i.e. H5 or H7 strains) infection in one flock leads to tracing exercises and a requirement to establish the infection status of putative contact flocks. In highly susceptible species (e.g. turkeys) infected with highly pathogenic notifiable avian influenza virus, observation of clinical signs may lead to a high index of clinical suspicion that prompts a report of suspected notifiable avian disease to the competent veterinary authority, with subsequent confirmation by approved laboratory testing methods. However, in other less susceptible species (e.g. ducks), or for H5 or H7 low pathogenicity avian influenza viruses (which can be a progenitor for a highly pathogenic strain if mutation to a virulent phenotype occurs), clinical signs of disease may not always be readily apparent, and targeted sampling and laboratory testing may be required to determine flock status.

This project will utilise existing data on test performance and mathematical models of the within-flock epidemiology of high and low pathogenicity NAI viruses in order to determine the optimum testing approach to a contact flock of unknown status following an initial NAI detection. The individual flock-level results will be complemented by building on an existing between-flock network transmission model for a sector of the GB poultry industry to investigate optimisation of testing to detect potential spread through a network. This will be particularly relevant for certain defined epidemiological criteria and circumstances such as: infection with an H5 or H7 low pathogenicity virus strain that may have disseminated relatively widely without apparent clinical disease; infection of less susceptible species (e.g. ducks) with a highly pathogenic avian influenza virus; identification of current or previous NAI infection in a flock through investigation of some other primary condition; or as part of a targeted surveillance activity such as the annual EU-mandated national poultry survey for notifiable avian influenza.

This project will use existing experimental data generated through the Defra- and EU FP6-funded Avian Influenza R&D project portfolio at VLA Weybridge, as well as use of peer-reviewed literature, as appropriate. The data sought will cover variation in virus pathotype, host species and production system and include:
• Clinical parameters and variables, including incubation periods, virus shedding data and within flock prevalence estimates.
• Distribution and relative semi-quantitative data for virus levels in host tissues and specified commodities.
• Environmental survival of virus.
• Within-flock transmission data.
• Diagnostic test characteristics and performance for antigen and antibody detection.
• Consideration of contact networks and network structures.

In addition, data from “real life” notifiable avian influenza outbreaks will be obtained and analysed from sources such as: epidemiological reports, Animal Health and laboratory outbreak data and national poultry survey data. Critical data variables may be identified and sensitivity and comparative analyses performed between mathematical models and actual field incursions and outbreaks, where appropriate.

The conduction of this work will investigate and develop a within-flock transmission model for notifiable avian influenza infections in domestic poultry to predict the course of infection within a poultry flock under different scenarios. The sensitivity and specificity of different testing protocols such as those laid out by the EU Diagnostic Manual for Avian Influenza for AI will then be investigated and an economic analysis of optimised sampling and testing scenarios conducted.

The within-flock model will be related to a poultry network model to examine how time to detection of infection affects disease transmission in different outbreak situations.
Outputs including those from the mathematical models will then be used to produce recommendations for the application of laboratory tests to investigate notifiable avian influenza infections in the National poultry population.
1 Acquire and collate data on within-flock NAI transmission covering variation in virus pathotype, host species and production system.

2 Generate within-flock NAI transmission model and investigate efficiency of different testing scenarios.

3 Acquire and collate data on parameters required for between-flock NAI transmission model for one or more poultry species and sectors.

4 Generate between-flock NAI transmission model and investigate the effect of time to detection on infection dynamics.

5 Develop recommendations for application of laboratory tests to investigate NAI in National poultry flock in the form of a manuscript for submission to a peer-reviewed journal.

Project Documents
• EVID4 - Final project report : SE0533 Final report SID5 3 08 11 FINAL   (844k)
Time-Scale and Cost
From: 2009

To: 2011

Cost: £85,754
Contractor / Funded Organisations
Veterinary Laboratories Agency
Animal Health              
Avian Diseases              
Avian Infectious Influenza              
Plants and Animals              
Fields of Study
Animal Health