Detection of a Novel Bovine Astrovirus in a Cow with Encephalitis

Abstract

Encephalitis can be caused by several infectious agents, including bacteria, fungi, parasites and viruses. In many cases, the causative agent cannot be identified, because the pathogens are unknown or detection methods are not routinely available. In our case, a 15-month-old cow developed central nervous disorders and died within 6 days after the onset of clinical signs. The histopathology revealed an acute encephalitis, predominantly in the brain stem, and a ganglionitis of the trigeminal ganglion with massive neuronal necroses in both the brain and the ganglion. However, a relevant panel of bacterial and viral infections of cattle could be routinely excluded. Therefore, a brain sample from the cow was analysed using a metagenomics approach with next-generation sequencing. A novel bovine astrovirus (BoAstV-BH89/14) could be identified using the analysis pipeline RIEMS, and the finding could be confirmed with a specific BoAstV RT-qPCR. The genome of the bovine astrovirus (BoAstV), belonging to the family Astroviridae in the genus Mamastrovirus, has a length of 6478 bp. Sequence identities between 71% to a sheep astrovirus and 69% to two recently described bovine astroviruses from the USA and Switzerland were ascertained. The latter were also connected to encephalitis cases in cattle. Like these, the new virus described here was detected in different brain sections using the specific BoAstV RT-qPCR and fluorescent in situ hybridization. In conclusion, while astroviruses so far were mainly found in relation to gastroenteritis in animals and humans, recently detected astrovirus infections were also related to encephalitis.

The Broad Host Range and Genetic Diversity of Mammalian and Avian Astroviruses

“…Similarly, astroviruses are not associated with a significant burden of diarrheal disease in bovine species. The first bovine astrovirus was detected in England in 1978 [66] and bovine astrovirus strains have been detection in association with neurological disease, including encephalitis (BoAstV-CH13/NeuroS1) [14,15,16,67,68,69] and diarrheal disease in calves in South Korea [70] and cattle and buffalo calves in China [71]. Two serotypes were previously recognized, BoAstV-1 and BoAstV-2 [72], however based on phylogenetic analysis there are multiple lineages of BoAstV strains circulating in farmed bovine populations, and the close clustering of bovine, porcine, and ovine strains in multiple lineages reflects the common interspecies transmission events that occur between farmed animals (Figure 1a,b).…”

“…Animal astroviurses, have been isolated from numerous mammalian and avian species. In animals, astrovirus infection may be asymptomatic or associated with enteric disease and a range of other symptoms indicative of the involvement of other organ systems including hepatitis and nephritis in avian species [12,13], and neurological symptoms in cattle [14,15,16] and mink [17]. …”

Propagation of Astrovirus VA1, a Neurotropic Human Astrovirus, in Cell Culture

“…In minks, an astrovirus genotype is the causative agent of shaking mink syndrome, a neurological disorder of minks characterized by tremors and seizures (40,41). Bovine astroviruses have been identified as a significant cause of encephalitis in cattle, as these viruses have been detected in 34% of previously unexplained cases of encephalitis (42)(43)(44)(45)(46)(47). An additional astrovirus genotype has also been identified as a cause of encephalitis in sheep (48).…”

Neurologic Clinical Signs in Cattle With Astrovirus‐Associated Encephalitis

“…By means of unbiased next‐generation sequencing, a neurotropic bovine astrovirus (BoAstV CH13/NeuroS1) has been found in brain tissue of cattle suffering from encephalitis of undetermined origin nearly simultaneously in Switzerland and the United States . In the meantime, these viruses have been found in additional bovine cases, and diagnostic tools such as in situ hybridization (ISH) or reverse transcriptase polymerase chain reaction (RT‐PCR) have been developed . Approximately 25% of the tested brain samples from cattle with nonsuppurative encephalitis of undetermined etiology were positive for BoAstV CH13/NeuroS1, and none of the control animals was positive for this viru s in case‐control studies, which supports the conclusion that the infection is likely associated with the disease …”