Astrovirus infections are among the main causes of diarrhea in children, but their significance for animal health has remained underestimated and largely unknown. This is changing due to the increasing amount of newly identified neurotropic astroviruses in cases of nonsuppurative encephalitis and neurological disease in humans, pigs, ruminant species and minks. Neurological cases in ruminants and humans usually occur sporadically and as isolated cases. This contrasts with the situation in pigs and minks, in which diseases associated with neurotropic astroviruses are endemic and occur on the herd level. Affected animals show neurological signs such as mild ataxia to tetraplegia, loss of orientation or trembling, and the outcome is often fatal. Non-suppurative inflammation with perivascular cuffing, gliosis and neuronal necrosis are typical histological lesions of astrovirus encephalitis. Since astroviruses primarily target the gastrointestinal tract, it is assumed that they infect the brain through the circulatory system or retrograde following the nerves. The phylogenetic analysis of neurotropic astroviruses has revealed that they are genetically closely related, suggesting the presence of viral determinants for tissue tropism and neuroinvasion. In this review, we summarize the current knowledge on neurotropic astrovirus infections in animals and propose future research activities.

Interdigital hyperplasia (IH) is a fold of fibrous tissue protruding into the interdigital space that rarely occurs in sheep. Interdigital hyperplasia secondary infected with bovine digital dermatitis (BDD) treponemes has been reported in cattle in the course of the increasing spread of classical BDD lesions. In this report, we describe proliferative/ulcerative interdigital lesions associated with contagious ovine digital dermatitis (CODD) treponemes and clinically scored as (IH+CODD), occurring in both hind limbs of a ram and the left hindlimb of a ewe. Both cases exhibited epidermal hyperplasia, parakeratosis and focal-extensive areas of epidermal necrosis with numerous infiltrating neutrophils. Treponema PCR and fluorescence in situ hybridization (FISH) were positive for Treponema phylotype 1 (PT1). In addition, Dichelobacter (D.) nodosus and Porphyromonas (P.) levii were detected in the biopsy by PCR. In three slaughter sheep, without claw lesions, which were kept together with both affected sheep, Treponema spp. were detected neither with PCR nor FISH; the PCRs for D. nodosus and P. levii were also negative. Complete clinical healing occurred in the ewe within 6 weeks after three local applications of a chlortetracycline spray in 2 weeks intervals. This report is the first description of IH+CODD in sheep as demonstrated by a combination of histopathological and molecular analyses.

Astroviruses are small nonenveloped single-stranded RNA viruses with a positive sense genome. They are known to cause gastrointestinal disease in a broad spectrum of species. Although astroviruses are distributed worldwide, a gap in knowledge of their biology and disease pathogenesis persists. Many positive-sense single-stranded RNA viruses show conserved and functionally important structures in their 5′ and 3′ untranslated regions (UTRs). However, not much is known about the role of the 5′ and 3′ UTRs in the viral replication of HAstV-1. We analyzed the UTRs of HAstV-1 for secondary RNA structures and mutated them, resulting in partial or total UTR deletion. We used a reverse genetic system to study the production of infectious viral particles and to quantify protein expression in the 5′ and 3′ UTR mutants, and we established an HAstV-1 replicon system containing two reporter cassettes in open reading frames 1a and 2, respectively. Our data show that 3′ UTR deletions almost completely abolished viral protein expression and that 5′ UTR deletions led to a reduction in infectious virus particles in infection experiments. This indicates that the presence of the UTRs is essential for the life cycle of HAstV-1 and opens avenues for further research.

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