Improving detection and diagnosis of maedi-visna virus infection in sheep in Norway

There is an ongoing maedi outbreak in Norway. The outbreak poses the most serious threat to the Norwegian sheep industry in the last decade. The nature of the infection, with a slow seroconversion, fluctuating antibody response, and individual differences in the immune response of sheep to viral epitopes make diagnosis and control of maedi challenging. Moreover, the virus was last detected in Norway in 2005, but preliminary genetic analyses indicate that the virus has persisted at low levels in the sheep population since that time, evading detection despite continuous surveillance. It is therefore highly relevant to evaluate if we can improve the design of mapping and surveillance programs to optimize the detection of truly infected individual sheep at a manageable cost.

The overall aim of the project is improved national preparedness in the context of maedivirus infections. This project will:

• Improve the ability to detect infected sheep in herds with low prevalence, by (1) comparing the performance of 3 commercially available ELISA tests in the current Norwegian outbreak by using latent class analysis; and (2) performing the first large-scale mapping of the immune response to different viral epitopes to improve strategies for serological screening. A multiplex assay will be established and made available for diagnostic purposes.

• Characterize currently circulating Norwegian maedivirus isolates to identify the need for tailor-made diagnostic solutions and explore phylogenetic relationships

• Design more precise computational models to predict the implications of different sampling and test regimes and map in-herd infection dynamics, including identifying risk factors for infection.

• Design of outbreak investigation tools and of future control programmes

The project will contribute to a more precise serological maedi diagnosis and improved tools for control and surveillance