Genetic characterization of a new astrovirus detected in dogs suffering from diarrhoea

Abstract

Astroviruses have been described in several animals species frequently associated with diarrhoea, especially in young animals. In dogs, astrovirus-like particles have been observed sporadically and very little is known about their epidemiology and characteristics. In this paper, we describe the detection of astrovirus-like particles in symptomatic puppies. Furthermore, for the first time in this species, the presumptive identification made by electron microscopy was confirmed by genetic analysis of the viral RNA conducted directly on the clinical specimens. Genetic sequences of ORF2 (2443 nt), encoding for the capsid protein, and partial sequence of ORF1b (346 nt), encoding for the viral polymerase, identified the viruses as member of the family Astroviridae. The phylogenetic analysis clearly clustered canine astroviruses in the genus Mamastrovirus. Relative closest similarities were revealed with a cluster comprising human, porcine and feline astroviruses, based on the ORF2 sequences available. Based on the species definition for astroviruses and on the data obtained in this study, we suggest a new species of astrovirus - canine astrovirus, CaAstV - to be included in the genus Mamastrovirus.

Fig. 1

Electron microscopy picture of astrovirus (larger particles of 18–20 nm) and parvovirus (smaller particles of 27–30 nm) observed directly in faecal sample of puppy no. 6 (36,000 Kx). The characteristic “star-like appearance” of astrovirus particles is evident compared to the round shaped morphology of parvovirus. Negative staining was obtained with 2% sodium phosphotungstate solution.

Fig. 2

Phylogenetic tree constructed by Bayesian analysis of the nucleotide sequences of ORF2. Posterior probabilities of the clades are indicated at the nodes. In this figure, bat astrovirus sequence is identified as BAstV; sheep astrovirus as SAstV; mink astrovirus as MAstV; feline astrovirus as FAstV; human astroviruses as HAstV; porcine astrovirus as PAstV; canine astroviruses as CaAstV; turkey astrovirus type I and II as TAstV1 and TAstV2, respectively. GenBank accession numbers are indicated.

Fig. 3

Part of the CaAstV sequence in the junction between the ORF1b and ORF2 genes. Both nucleotide sequences and the amino acid sequences for the C-terminal part of the ORF1b (with grey shade), and for the putative capsid precursor protein (in bold) are shown, displaying the two possible start codons for the putative capsid precursor in bold italics. The start of the ORF2 protein homologous to other Mamastroviruses is underlined. The stop codon of the ORF1b is shaded grey.