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Biological and genetic differences between lung- and brain-derived isolates of maedi-visna virus
V Andrésdóttir1, X Tang, G Agnarsdóttir
1Institute for Experimental Pathology, University of Iceland, Reykjavík, Iceland. valand@rhi.hi.is
Abstract:
During the epidemic caused by maedi-visna virus (MVV) of sheep in Iceland, the pulmonary affection, maedi, was the predominant clinical manifestation. In some flocks, however, a central nervous system (CNS) affection, visna, was the main cause of morbidity and mortality. As there is only one breed of sheep in the country, host factors did apparently not play an important role in the different clinical manifestations. To obtain some information on possible viral genetic determinants of neurotropism and neurovirulence we studied both phenotypic and genotypic properties of two maedi-visna virus strains; a strain that was originally isolated from the brain of sheep with encephalitis (visna), and another strain isolated from the lungs of a sheep suffering from pneumonia (maedi). The brain isolate was found to grow faster in sheep choroid plexus cells than the lung isolate, whereas the growth rate in macrophages was similar for the maedi and visna virus strains. Intracerebral inoculation indicated that the visna virus isolate induced more severe brain lesions than the maedi isolate. In addition, a pathogenic molecular clone derived from a visna strain (KV1772kv72/67) was tested for growth in sheep choroid plexus cells and macrophages. The molecularly cloned virus retained the fast growth rate in choroid plexus cells. The nucleotide sequence of the env gene and the U3 of the LTR was determined for the maedi strain and compared to that of the visna strains. There was an 11.7% difference in deduced amino acid sequence in the Env protein and a 6% difference in the LTR. The molecular clone KV1772kv72/67 will be a useful reagent for characterization of viral determinants of cell tropism in vitro and possibly neurovirulence in vivo.
Insights
Maedi-visna virus (MVV) strains show distinct neurotropism and virulence. Genetic differences in the env gene and LTR influence maedi-visna virus
Area of Science:
- Veterinary Virology
- Molecular Biology
- Sheep Pathology
Background:
- Maedi-visna virus (MVV) causes significant morbidity and mortality in sheep, with distinct pulmonary (maedi) and neurological (visna) manifestations.
- Host factors appear minimal in determining clinical outcomes in Icelandic sheep populations.
- Understanding viral genetic determinants is crucial for explaining differential disease tropism and virulence.
Purpose of the Study:
- To investigate phenotypic and genotypic properties of MVV strains with differing clinical manifestations.
- To identify viral genetic factors contributing to neurotropism and neurovirulence.
Main Methods:
- Comparative analysis of MVV strains isolated from brain (visna) and lung (maedi) tissues.
- In vitro growth rate assessment in sheep choroid plexus cells and macrophages.
- Intracerebral inoculation in sheep to evaluate neuropathogenicity.
- Genomic sequencing of the env gene and U3 region of the LTR.
Main Results:
- The visna (brain) isolate exhibited faster growth in choroid plexus cells compared to the maedi (lung) isolate; growth in macrophages was similar.
- Intracerebral inoculation revealed the visna isolate induced more severe brain lesions.
- A molecular clone (KV1772kv72/67) retained fast choroid plexus cell growth.
- Sequence analysis showed significant differences in the Env protein (11.7%) and LTR (6%) between maedi and visna strains.
Conclusions:
- Viral genetic factors, particularly within the env gene and LTR, likely determine MVV neurotropism and virulence.
- The characterized molecular clone serves as a valuable tool for future research into MVV pathogenesis.