Astroviruses in Rabbits

Vito Martella

, Paschalina Moschidou, Pierfrancesco Pinto, Cristiana Catella, Constantina Desario, Vittorio Larocca, Elena Circella, Krisztian Bànyai, Antonio Lavazza, Chiara Magistrali, Nicola Decaro, and Canio Buonavoglia

Author affiliations: University of Bari Aldo Moro, Valenzano, Italy (V. Martella, P. Moschidou, P. Pinto, C. Catella, C. Desario, V. Larocca, E. Circella, N. Decaro, C. Buonavoglia); Hungarian Academy of Sciences, Budapest, Hungary (K. Bànyai); Istituto Zooprofilattico Sperimentale di Lombardia ed Emilia Romagna, Brescia, Italy (A. Lavazza); Istituto Zooprofilattico Sperimentale di Marche ed Umbria, Perugia, Italy (C. Magistrali)

Abstract

By screening rabbits with enterocolitis or enteritis complex and asymptomatic rabbits, we identified a novel astrovirus. The virus was distantly related (19.3%–23.7% aa identity) in the capsid precursor to other mammalian astroviruses within the Mamastrovirus genus. By using real-time reverse transcription PCR, with specific primers and probes and targeting a conserved stretch in open reading frame 1b, we found rabbit astrovirus in 10 (43%) of 23 samples from animals with enteric disease and in 25 (18%) of 139 samples from asymptomatic animals in Italy during 2005–2008. The mean and median titers in the positive animals were 10²× and 10³× greater, respectively, in the symptomatic animals than in the asymptomatic animals. These findings support the idea that rabbit astroviruses should be included in the diagnostic algorithm of rabbit enteric disease and animal experiments to increase information obtained about their epidemiology and potential pathogenic role.

Astroviruses (AstVs) (family Astroviridae) are nonenveloped, and their genome is composed of a plus-sense single-stranded RNA of 6.4–7.3 kb, containing 3 open reading frames (ORFs) and a 3′ poly-A tail (1). Two ORFs, located at the 5′ end of the genome (ORF1a and ORF1b), encode nonstructural proteins, and ORF2, located at the 3′ end, encodes the capsid protein (1). AstVs were first identified by electron microscopy (EM) in 1975 in Scotland in fecal specimens of infants hospitalized with diarrhea (2). Subsequently, similar viruses were identified from several mammalian and avian species (3–12), including bats (13) and aquatic mammals (14). AstV infection is associated with gastroenteritis in most animal species and humans. AstVs are regarded as the second or third most common cause of viral diarrhea in children (1).

Avian AstVs have also been associated with extraintestinal diseases, such as nephritis in chickens (12) and hepatitis in ducks (11). Even more notably, recently AstVs have been detected in the nervous tissues of minks with shaking disease (15) and in the central nervous system of a child with encephalitis (16). Also, novel human AstVs (MLB1, MLB2, VA1, HMO-C, HMO-B, HMO-A, VA-2) have been identified that are genetically unrelated to classical human AstVs (17–19) and more closely related to animal AstVs.

Rabbit enteritis, also referred to as enteritis complex (EC) or rabbit enterocolitis (REC), is a multiform enteric disease, characterized by a variety of symptoms. The syndrome can be caused by bacteria, viruses, and parasites. Moreover, environmental factors can alter rabbit physiology and impair rabbit welfare, thus increasing the effects EC/REC syndrome would have on rabbit production. Several different viruses have been isolated from rabbits with diarrhea, such as rotavirus, coronavirus, parvovirus, adenovirus, and caliciviruses (20). Whether natural outbreaks of enteritis can be caused by these viral agents alone or in conjunction/synergism with other pathogens is not clear, and the mechanisms of persistence/transmission are also not known.

Although AstVs have a peculiar star shape when purified fractions are observed in EM, which distinguishes them from other small, rounded viruses (SRVs), such as enteroviruses and caliciviruses, identifying them can be difficult when examining biologic samples because their typical morphologic features tend to be altered easily. During 1997–2005 surveillance by the National (Italian) Reference Centre for Viral Diseases of Rabbits, SRVs were identified by EM in 18 (3.49%) of 515 fecal samples from rabbits with enteric disease (20,21). In this study, we report the detection and characterization of AstVs in the intestinal contents of rabbits affected by EC/REC.

Suggested citation for this article: Martella V, Moschidou P, Pinto P, Catella C, Desario C, Larocca V, et al. Astroviruses in rabbits. Emerg Infect Dis [serial on the Internet]. 2011 Dec [date cited]. http://dx.doi.org/10.3201/eid1712.110967