Emerging orthobunyaviruses associated with CNS disease

Abstract

The Orthobunyavirus genus comprises a wide range of arthropod-borne viruses which are prevalent worldwide and commonly associated with central nervous system (CNS) disease in humans and other vertebrates. Several orthobunyaviruses have recently emerged and increasingly more will likely do so in the future. Despite this large number, an overview of these viruses is currently lacking, making it challenging to determine importance from a One Health perspective. Causality is a key feature of determining importance, yet classical tools are unfit to evaluate the causality of orthobunyaviral CNS disease. Therefore, we aimed to provide an overview of orthobunyaviral CNS disease in vertebrates and objectify the causality strength of each virus. In total, we identified 27 orthobunyaviruses described in literature to be associated with CNS disease. Ten were associated with disease in multiple host species of which seven included humans. Seven viruses were associated with both congenital and postnatal CNS disease. CNS disease-associated orthobunyaviruses were spread across all known Orthobunyavirus serogroups by phylogenetic analyses. Taken together, these results indicate that orthobunyaviruses may have a common tendency to infect the CNS of vertebrates. Next, we developed six tailor-made causality indicators and evaluated the causality strength of each of the identified orthobunyaviruses. Nine viruses had a 'strong' causality score and were deemed causal. Eight had a 'moderate' and ten a 'weak' causality score. Notably, there was a lack of case-control studies, which was only available for one virus. We, therefore, stress the importance of proper case-control studies as a fundamental aspect of proving causality. This comprehensible overview can be used to identify orthobunyaviruses which may be considered causal, reveal research gaps for viruses with moderate to low causality scores, and provide a framework to evaluate the causality of orthobunyaviruses that may newly emerge in the future.

Fig 1. Phylogeny of 27 orthobunyaviruses linked to CNS disease in vertebrates.

The tree is rooted by an outgroup of Herbeviruses (Tai virus, Herbert virus and Kibale virus), based on a recent phylogeny by Shchetinin et al. [64]. Nucleocapsid (S-segment) protein sequences were retrieved from reference phylogeny, and if not available, from GenBank (preferably RefSeq or Swiss-Prot). Protein sequences were aligned using M-Coffee and only columns with scores of 5 or higher were retained. A Maximum-Likelihood model with LG + G + I, complete deletion and a bootstrap of 1000 was used to infer the phylogeny in Mega v10. The phylogeny contains at least one virus from each of the known orthobunyavirus serogroups, in grey are representative viruses from serogroups without any virus linked to CNS disease. Between brackets: number of viruses associated with CNS infection in each specific serogroup. Coloured branches correspond to specific serogroups. Only Maximum Likelihood bootstrap values >50% are displayed. Pictograms indicate hosts associated with CNS disease, orange: postnatal disease, blue: congenital disease. Abbreviations describe the known host range (not per se requiring association with CNS disease), obtained from ArboCat [65] and other sources [,–68].