Differential Features of Fusion Activation within the Paramyxoviridae

Paramyxovirus (PMV) entry requires the coordinated action of two envelope glycoproteins, the receptor binding protein (RBP) and fusion protein (F). The sequence of events that occurs during the PMV entry process is tightly regulated. This regulation ensures entry will only initiate when the virion is in the vicinity of a target cell membrane. Here, we review recent structural and mechanistic studies to delineate the entry features that are shared and distinct amongst the Paramyxoviridae. In general, we observe overarching distinctions between the protein-using RBPs and the sialic acid- (SA-) using RBPs, including how their stalk domains differentially trigger F. Moreover, through sequence comparisons, we identify greater structural and functional conservation amongst the PMV fusion proteins, as compared to the RBPs. When examining the relative contributions to sequence conservation of the globular head versus stalk domains of the RBP, we observe that, for the protein-using PMVs, the stalk domains exhibit higher conservation and find the opposite trend is true for SA-using PMVs. A better understanding of conserved and distinct features that govern the entry of protein-using versus SA-using PMVs will inform the rational design of broader spectrum therapeutics that impede this process.

Co-Circulation and Excretion Dynamics of Diverse Rubula- and Related Viruses in Egyptian Rousette Bats from South Africa

The Egyptian rousette bat (Rousettus aegyptiacus) has previously been implicated as the natural host of a zoonotic rubulavirus; however, its association with rubulaviruses has been studied to a limited extent. Urine, spleen, and other organs collected from the R. aegyptiacus population within South Africa were tested with a hemi-nested RT-PCR assay targeting a partial polymerase gene region of viruses from the Avula- and Rubulavirus genera. Urine was collected over a 14-month period to study the temporal dynamics of viral excretion. Diverse rubulaviruses, including viruses related to human mumps and parainfluenza virus 2, were detected. Active excretion was identified during two peak periods coinciding with the host reproductive cycle. Analysis of additional organs indicated co-infection of individual bats with a number of different putative rubulaviruses, highlighting the limitations of using a single sample type when determining viral presence and diversity. Our findings suggest that R. aegyptiacus can harbor a range of Rubula- and related viruses, some of which are related to known human pathogens. The observed peaks in viral excretion represents potential periods of a higher risk of virus transmission and zoonotic disease spill-over.

Paramyxoviruses of Animals

Paramyxoviruses (some of which are also called parainfluenza viruses) cause a wide variety of diseases in animals. Many paramyxoviruses cause primarily respiratory disease, while others cause serious systemic disease. Many diseases caused by animal paramyxoviruses also have a neurological component or a reproductive disease component. Several of the most devastating diseases of animals, such as rinderpest, Newcastle disease, and canine distemper, are caused by paramyxoviruses. Some of the animal paramyxoviruses, such as the Hendra and Nipah viruses, are emerging zoonotic pathogens of major public health concern. New paramyxoviruses are being isolated on a continuing basis from a wide variety of animals.

All animal paramyxoviruses belong to the family Paramyxoviridae. The members of this virus family are enveloped and have genomes consisting of a single segment of negative-sense RNA that contains 6–10 genes encoding up to 12 proteins. Although there are many animal paramyxoviruses, only a few effective vaccines are currently available. In the last decade, methods of producing many animal paramyxoviruses entirely from cDNA clones (reverse genetics) have been developed. This has not only greatly improved our understanding of the molecular biology and pathogenesis of these viruses, but has also made it possible to engineer improved vaccines for them.