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Study of the factors influencing disease dynamics and emergence of LPAI from HPAI using UK H7N7/2008 . - SE0793

This proposal aims to study the complex dynamics of transmission and adaptation that occur in the emergence of highly pathogenic avian influenza (HPAI) from low pathogenic avian influenza (LPAI). We will capitalize on the collection of a unique set of clinical specimens obtained during detailed investigations on the single infected premises associated with the UK H7N7 outbreak in 2008. This presents an opportunity for the first time to study host-virus interaction from a natural setting leading to the emergence of HPAI from LPAI in the domestic poultry compartment. Understanding the key events and drivers that result in mutation to virulence are important in developing a strong evidence base for identifying risk pathways. This data in turn will inform risk assessments and appropriate prevention/intervention strategies. The outputs of the project will directly provide an evidence base for key policy decisions relating to control. In addition, improved knowledge of factors influencing such mutation (that is not always a direct natural consequence of infection of poultry with LPAI) will better inform industry stakeholders in practices that might mitigate or reduce risk for incursion.

Much attention has focused upon determining the best control strategies for dealing with outbreaks and new introductions of HPAI viruses in poultry. Successful control strategies must be tailored to the farming practices and cultures of affected countries but also depend upon knowledge about the infecting virus e.g. the host species affected, rates and mechanisms of transmission between animals of the same or different species and the molecular determinants for pathogenicity. It will be valuable to determine the extent to which pathological differences are a virus specific trait.

In this study we will investigate currently unknown dynamic infection parameters and determine whether molecular changes relate to pathological changes in the transmitted virus from LPAI infected birds to those with HPAI. Using the UK H7N7 outbreak in 2008, during which both LPAI and HPAI viruses were either detected or isolated, as a model we will be able to mimic the interactions between birds housed in different sheds and the acquisition and change of the virus when LPAI is introduced. The influence of partial and/or prior immunity on the infecting LPAI on virus evolution will be considered. Genetic analysis of a LPAI isolate from Sweden in 2008 showed a matching HA cleavage site to that found in the UK serving as a possible progenitor to the outbreak and providing us with a unique opportunity to investigate further.

It has been noted that the presence of a polybasic HA cleavage site is not the sole determinant for virulence in chickens and that additional pathogenicity determinants within the HA or other viral proteins have an influence (Stech et al, 2009). It is therefore essential to begin investigating and comparing the full genome sequence of the HPAI isolate from Banbury with the LPAI isolate on the same premises. A comparison will also be made with two LPAI viruses isolated from wild mallard ducks in Sweden which have been matched and hypothesised to be the precursor of the outbreak in England. This comparison will identify mutations in HA and other genes and can highlight the sequence of mutational events that occurred in Banbury, UK in June 2008.

If mutations are identified, there will be an opportunity to investigate further using reverse genetic approaches, in collaboration with Imperial College, to explore the functionality of each mutation and whether the change played a role in the virus establishing virulence. This can present insight into the prediction of when the virus entered the population and the pre-clinical window that is currently an area of uncertainty. Further collaboration with colleagues from Oxford University and Hong Kong can integrate mathematical modeling to predict transmission dynamics between birds to make assumptions on the origin of the virus and the extent of spread. This modeling could also serve as a method to suggest control planning in an outbreak. These in-vitro experiments can also be applied to in-vivo models where engineered viruses are experimentally infected into chickens, turkeys, ducks and 14 day embryonated eggs.

In vivo experiments will be used to simulate the outbreak conditions by infecting chickens with viruses deemed to have been present early in the Banbury outbreak, including a related LPAI virus isolated from a wild bird in Sweden. Buccal and cloacal swabs will be tested for virus load and shedding by real time RT-PCR and blood samples will be taken to test for seroconversion by haemagglutination inhibition (HAI) tests. Sequencing of the genes of the input virus and the reisolated virus will be compared for genetic traits and rates of mutation. The mutations observed over several passages will be used to establish the evolution of the virus through transmission. In-vivo studies offer the opportunity to explore the dissemination of the virus within a particular species by applying histopathology and immunohistochemistry techniques. These studies will also allow for specimens to be collected for innate immunity studies, in collaboration with Nottingham University and Roslin Institute thereby strategically strengthening interaction with academia.
Project Documents
• EVID4 - Final project report : SE0793 evid4 final report   (1024k)
Time-Scale and Cost
From: 2010

To: 2013

Cost: £463,388
Contractor / Funded Organisations
Veterinary Laboratories Agency
Animal Diseases              
Animal Health              
Avian Diseases              
Avian Infectious Influenza              
Plants and Animals              
Fields of Study
Animal Health