Astrovirus evolution and emergence

Abstract

Astroviruses are small, non-enveloped, positive-sense, single-stranded RNA viruses that belong to the Astroviridae family. Astroviruses infect diverse hosts and are typically associated with gastrointestinal illness; although disease can range from asymptomatic to encephalitis depending on the host and viral genotype. Astroviruses have high genetic variability due to an error prone polymerase and frequent recombination events between strains. Once thought to be species specific, recent evidence suggests astroviruses can spread between different host species, although the frequency with which this occurs and the restrictions that regulate the process are unknown. Recombination events can lead to drastic evolutionary changes and contribute to cross-species transmission events. This work reviews the current state of research on astrovirus evolution and emergence, especially as it relates to cross-species transmission and recombination of astroviruses.

Keywords: Astrovirus; Cross-species transmission; Emergence; Recombination.

Fig. 1

Astrovirus genomic architecture. Individual protein coding regions with known identity are designated by inset boxes. In ORF2, the darker regions indicate the hypervariable region of the capsid protein. The frameshift signal between ORF1a and ORF1b consists of a slippery sequence followed by a hairpin. There is a highly conserved hairpin at the 3′ end of the genome.

Fig. 2

Astrovirus phylogenetic tree. Astroviridae is divided into two genera which are further divided into genogroups, species, and genotypes. Tree generated using ORF2 amino acid sequences. Classification proposed in Bosch et al., 2012. Viruses names are abbreviated as follows: avian nephritis virus (ANV), turkey astrovirus (TAstV), duck astrovirus (DAstV), human astrovirus (HAstV), feline astrovirus (FAstV), porcine astrovirus (PAstV), California sea lion astrovirus (CslAstV), canine astrovirus (CaAstV), bottlenose dolphin astrovirus (BdAstV), human astrovirus-Melbourne (HAstV-MLB), Capreolus capreolus astrovirus (CcAstV), rat astrovirus (RaAstV), bat astrovirus (BatAstV), human astrovirus-Virginia (HAstV-VA), human mink ovine astrovirus (HMOAstV), ovine astrovirus (OAstV), and mink astrovirus (MAstV).

Fig. 3

Potential routes of interspecies transmission and recombination of astroviruses. Humans, wild animals such as turkeys, water fowl, and bats, and agricultural animals such as pigs and cows all have been shown to be infected with astroviruses. Humans and animals often live close together in agricultural and rural settings. Given the high stability of astroviruses under environmental conditions, water contaminated with fecal waste from any of these sources could be consumed as improperly treated drinking water or accidentally ingested during water sports, resulting in a cross-species transmission event. If a water source is contaminated with two different astrovirus strains from two different sources (for example: pigs and humans), then, humans or other permissive animals exposed to both viruses could become infected. If a cell in the host becomes infected with both strains, then recombination can occur.