Molecular characterization and phylogenetic analysis of Murray Valley encephalitis virus and West Nile virus (Kunjin subtype) from an arbovirus disease outbreak in horses in Victoria, Australia, in 2011.

This research investigated a 2011 outbreak of an arbovirus disease in horses from Victoria, Australia, discovering that these horses were infected with either Murray Valley encephalitis virus (MVEV) or a subtype of the West Nile virus (WNV, Kunjin subtype). Genetic examination revealed that the viruses were mostly homogenous and belonged to specific lineages prevalent in northern Australia.

Disease Detection and Identification

• An outbreak of disease in horses in Victoria, Australia, in 2011 led to the investigation described in this study.
• The virus was found in the central nervous system tissue of 11 horses that had died showing neurological symptoms.
• Researchers identified that five of the horses were infected with Murray Valley encephalitis virus (MVEV) and six were infected with the West Nile virus subtype Kunjin (WNV(KUN)).

Genetic Analysis of the Viruses

• The team investigated the genetic information from two particular genes (NS5 and E) from the viruses.
• All MVEVs from the samples were found to be highly similar (homogenous) and belonged to lineage I, which is commonly found in the tropical regions of northern Australia.
• The West Nile virus subtypes (WNV(KUN)) within the samples were also highly similar to each other.
• The WNV samples clustered with WNV lineage 1, clade b, similar to other WNV(KUN) isolates.

Complete Genome Sequencing and Comparison

• The researchers sequenced and characterized the full genomes of one MVEV isolate and two WNV(KUN) isolates.
• They found that the genome sequences of the Victorian WNV(KUN) samples were almost identical to that of a recently sequenced WNV isolate named WNV(NSW2011), with only 3 amino acid differences.

Metagenome Sequencing

• Using metagenome sequencing directly from the central nervous system tissue, researchers confirmed the presence of WNV(KUN) and MVEV within the infected tissue.

In conclusion, the study brings to light the importance of virological surveillance in an outbreak and offers valuable genetic data about these viruses, which could potentially help develop treatments or preventive measures in the future.