Detection of astroviruses in feces of a cat with diarrhea. Brief report

Genetic characterization of canine astrovirus in non-diarrhea dogs and diarrhea dogs in Vietnam and Thailand reveals the presence of a unique lineage

The role of canine astrovirus (CaAstV) in canine gastrointestinal disease (GID) is unknown. In this study, a total of 327 fecal swab (FS) samples were collected, including 113 FSs in Vietnam (46 samples from healthy dogs and 67 samples from GID dogs) and 214 FSs in Thailand (107 samples from healthy dogs and 107 samples from GID dogs). Overall, the prevalence of CaAstV in Vietnam and Thailand was 25.7% (29/113) and 8.9% (19/214), respectively. CaAstV was detected in both non-diarrhea dogs (21.7 and 7.5%) and diarrhea dogs (28.4% and 10.3%), respectively, in Vietnam and Thailand. In both countries, CaAstV was frequently detected in puppies under 6 months of age (23.3%) (p = 0.02). CaAstV-positive samples in Vietnam and Thailand were identified as co-infected with canine parvovirus, canine enteric coronavirus, canine distemper virus, and canine kobuvirus. The complete coding sequence of seven Vietnamese CaAstV and two Thai CaAstV strains were successfully characterized. Phylogenetic analyses showed that Vietnamese and Thai CaAstV strains were genetically close to each other and related to the Chinese strains. Furthermore, analysis of complete coding sequences indicated that the OR220030_G21/Thailand/2021 strain formed a unique lineage, whereas no recombination event was found in this study, suggesting that this strain might be an original lineage. In summary, this is the first study to report the presence of CaAstV in dogs with and without diarrhea in Vietnam and Thailand, and it was most often found in puppies with diarrhea. Our results highlight the importance of the CaAstV in dog populations and the need for continued surveillance of these emerging pathogens.

Genetic Diversity and Evolution of Viruses Infecting Felis catus: A Global Perspective

Cats harbor many important viral pathogens, and the knowledge of their diversity has been greatly expanded thanks to increasingly popular molecular sequencing techniques. While the diversity is mostly described in numerous regionally defined studies, there lacks a global overview of the diversity for the majority of cat viruses, and therefore our understanding of the evolution and epidemiology of these viruses was generally inadequate. In this study, we analyzed 12,377 genetic sequences from 25 cat virus species and conducted comprehensive phylodynamic analyses. It revealed, for the first time, the global diversity for all cat viruses known to date, taking into account highly virulent strains and vaccine strains. From there, we further characterized and compared the geographic expansion patterns, temporal dynamics and recombination frequencies of these viruses. While respiratory pathogens such as feline calicivirus showed some degree of geographical panmixes, the other viral species are more geographically defined. Furthermore, recombination rates were much higher in feline parvovirus, feline coronavirus, feline calicivirus and feline foamy virus than the other feline virus species. Collectively, our findings deepen the understanding of the evolutionary and epidemiological features of cat viruses, which in turn provide important insight into the prevention and control of cat pathogens.

A One-Year Retrospective Analysis of Viral and Parasitological Agents in Wildlife Animals Admitted to a First Aid Hospital

This study aimed to provide information on the presence and frequency of viral and parasitic agents in wildlife presented to a Veterinary Teaching Hospital in 2020-2021. Serum and faecal samples were collected from 50 rescued animals (roe deer, fallow deer, foxes, badgers, pine martens, and porcupines) and examined by serological, molecular, and parasitological techniques. Transtracheal wash (TTW) was also collected post-mortem from roe deer. Overall, the results of the different techniques showed infections with the following viral and parasitic agents: Bovine Viral Diarrhea Virus, Small Ruminant Lentiviruses, Kobuvirus, Astrovirus, Canine Adenovirus 1, Bopivirus, gastrointestinal strongyles, Capillaria, Ancylostomatidae, Toxocara canis, Trichuris vulpis, Hymenolepis, Strongyloides, Eimeria, Isospora, Dictyocaulus, Angiostrongylus vasorum, Crenosoma, Dirofilaria immitis, Neospora caninum, Giardia duodenalis, and Cryptosporidium. Sequencing (Tpi locus) identified G. duodenalis sub-assemblages AI and BIV in one roe deer and one porcupine, respectively. Adult lungworms collected from the TTW were identified as Dictyocaulus capreolus (COX1 gene). This is the first molecular identification of G. duodenalis sub-assemblage AI and D. capreolus in roe deer in Italy. These results show a wide presence of pathogens in wild populations and provide an overview of environmental health surveillance.

Two Multiplex PCR Methods for Detecting Several Pathogens Associated with Feline Respiratory and Intestinal Tracts

Respiratory tract and intestinal diseases are common threats to feline health. Coinfection with multiple pathogens is not rare among clinical infectious cases. Rapid diagnosis of these coinfections is of great significance for timely and effective clinical treatment. In this study, two novel multiplex polymerase chain reactions (mPCRs) were established for simultaneous detection of four pathogens associated with the feline intestinal tract (feline coronavirus (FCoV), feline astrovirus (FeAstV), feline panleukopenia virus (FPV) and feline kobuvirus (FeKoV)) and five pathogens associated with the respiratory tract (feline calicivirus (FCV), feline herpesvirus 1 (FHV-1), feline leukemia virus (FeLV), Chlamydia felis (C. felis) and influenza A virus (IAV)). The results of sensitivity analysis revealed that the detection limits for FeKoV, FPV, FeAstV, FCoV, IAV, C. felis, FeLV, FHV-1 and FCV were 10³, 10⁴, 10³, 10³, 10³, 10⁴, 10⁴, 10⁵ and 10⁵ copies/µL, respectively. Moreover, the specificity of the two mPCRs was high. When the two mPCRs were applied to clinical samples, the assay worked well. In conclusion, we established two mPCR methods that provide an excellent tool for the diagnosis and monitoring of pathogens associated with the feline respiratory and intestinal tracts.

Biology and Cellular Tropism of a Unique Astrovirus Strain: Murine Astrovirus 2

Murine astrovirus 2 (MuAstV2) is a novel murine astrovirus recently identified in laboratory and wild mice. MuAstV2readily transmits between immunocompetent mice yet fails to transmit to highly immunocompromised mouse strains-a unique characteristic when contrasted with other murine viruses including other astroviruses. We characterized the viralshedding kinetics and tissue tropism of MuAstV2 in immunocompetent C57BL/6NCrl mice and evaluated the apparentresistance of highly immunocompromised NOD Prkdcem26Cd52Il2rgem26Cd22/NjuCrl mice to MuAstV2 after oral inoculation. Temporal patterns of viral shedding were determined by serially measuring fecal viral RNA. Tissue tropism and viral load were characterized and quantified by using in-situ hybridization (ISH) targeting viral RNA. Cellular tropism was characterized by evaluating fluorescent colocalization of viral ISH with various immunohistochemical markers. We found a rapidincrease of fecal viral RNA in B6 mice, which peaked at 5 d after inoculation (dpi) followed by cessation of shedding by 168dpi. The small intestine had the highest percentage of hybridization (3.09% of tissue area) of all tissues in which hybridization occurred at 5 dpi. The thymus displayed the next highest degree of hybridization (2.3%) at 7 dpi, indicating extraintestinal viral spread. MuAstV2 RNA hybridization was found to colocalize with only 3 of the markers evaluated: CD3 (T cells), Iba1 (macrophages), and cytokeratin (enterocytes). A higher percentage of CD3 cells and Iba1 cells hybridized with MuAstV2 as compared with cytokeratin at 2 dpi (CD3, 59%; Iba1, 46%; cytokeratin, 6%) and 35 dpi (CD3, 14%; Iba1, 55%; cytokeratin, 3%). Neither fecal viral RNA nor viral hybridization was noted in NCG mice at the time points examined. In addition, mice of mixed genetic background were inoculated, and only those with a functioning Il2rg gene shed MuAstV2. Results from this study suggest that infection of, or interaction with, the immune system is required for infection by or replication of MuAstV2.

Development of a TaqMan-based real-time assay for the specific detection of canine astrovirus

In this study, a TaqMan-based real-time polymerase chain reaction (PCR) method to detect canine astrovirus in clinical samples was developed. Primers and probes were designed to target conserved regions of the complete viral genome sequence. The results showed that the proposed method can detect a minimum of 10¹ copy numbers. No cross-reactivity with other canine and feline viruses was observed. The coefficient of variation was <5%. Evaluation of the clinical samples showed that quantitative PCR had a 5.26 % higher positive detection rate than conventional PCR. These results indicate that the method developed in this study is highly reliable and suitable for veterinary clinical diagnosis and epidemiological investigations.

Development and application of a TaqMan-based real-time PCR assay for specifically detecting feline astrovirus

Feline astrovirus (FeAstV), an enteric RNA virus of recent concern that is associated with diarrheal illness in cats, has been described in several countries throughout the world. However, no scientific and sensitive diagnostic method against FeAstV was reported up to now. Here, we developed a specific, sensitive and repeatable TaqMan fluorescence quantitative PCR (qPCR) assay to investigate the prevalence of FeAstV in domestic cats from China, especially low copy numbers in clinical sample. Specific assay showed that no cross-reactivity was observed with other non-FeAstV cat-derivied pathogens, suggesting this method was highly specific for FeAstV. The lowest detection limit of this assay was 3.52 copies/μl, and 1000-times more sensitive than conventional PCR. Intra- and inter-assay variability was less than 1.72%, means a high degree of repeatability. A total of 578 clinical fecal samples were collected from northeast China, and were tested for FeAstV using our developed qPCR assay. 105 samples were positive for FeAstV with an overall prevalence of 18.17%. Moreover, a higher positive rate was found in cats with diarrhea (32.26%, 80/248) than that in asymptomatic cats (7.58%, 25/330), further demonstrating that FeAstV infection was associated with diarrhea in cats. In brief, our developed assay showed high specificity, sensitivity, reproducibility for detecting FeAstV, and can be used for clinical diagnosis and epidemiological investigation of FeAstV.

Astrovirus Outbreak in an Animal Shelter Associated With Feline Vomiting

An outbreak of cat vomiting was observed in an animal shelter. Testing for known enteric feline pathogens did not identify a causative agent. Viral metagenomics on four mini pools of feces from cases and controls housed in the same area revealed the presence of feline astrovirus in all pools. Also found with fewer reads in one pool each were rotavirus I, carnivore bocaparvovirus 3, norovirus (NoV) GVI, and a novel dependovirus. The genome of the highly prevalent astrovirus was sequenced and classified into mamastrovirus species two, also known as feline astrovirus. Real-time RT-PCR on longitudinally acquired fecal samples from 11 sick cases showed 10 (91%) to be shedding astrovirus for as long as 19 days. Affected cats were sick for an average of 9.8 days, with a median of 2.5 days (range = 1–31 days). Unaffected control cats housed in the same areas during the outbreak showed five out of nine (56%) to also be shedding astrovirus. Feline fecal samples collected from the same animal shelter ~1 year before (n = 8) and after (n = 10) showed none to be shedding astrovirus, indicating that this virus was temporarily associated with the vomiting outbreak and is not part of the commensal virome for cats in this shelter. Together with the absence of highly prevalent known pathogens, our results support a role for feline astrovirus infection, as well as significant asymptomatic shedding, in an outbreak of contagious feline vomiting.

Identification of Novel Astroviruses in the Gastrointestinal Tract of Domestic Cats

Astroviruses, isolated from numerous avian and mammalian species including humans, are commonly associated with enteritis and encephalitis. Two astroviruses have previously been identified in cats, and while definitive evidence is lacking, an association with enteritis is suggested. Using metagenomic next-generation sequencing of viral nucleic acids from faecal samples, we identified two novel feline astroviruses termed Feline astrovirus 3 and 4. These viruses were isolated from healthy shelter-housed kittens (Feline astrovirus 3; 6448 bp) and from a kitten with diarrhoea that was co-infected with Feline parvovirus (Feline astrovirus 4, 6549 bp). Both novel astroviruses shared a genome arrangement of three open reading frames (ORFs) comparable to that of other astroviruses. Phylogenetic analysis of the concatenated ORFs, ORF1a, ORF1b and capsid protein revealed that both viruses were phylogenetically distinct from other feline astroviruses, although their precise evolutionary history could not be accurately determined due to a lack of resolution at key nodes. Large-scale molecular surveillance studies of healthy and diseased cats are needed to determine the pathogenicity of feline astroviruses as single virus infections or in co-infections with other enteric viruses.

Prevalence of astrovirus and parvovirus in Japanese domestic cats

Feces obtained from 204 domestic cats with gastrointestinal symptoms were genetically examined for feline astrovirus (FeAstV) and feline parvovirus (FPV), both of which are known feline gastroenteric viruses. FeAstV detection rates were significantly higher in winter (44.4%) than in other seasons, and in cats under a year old (27.8%) than in a year or older ones (12.4%) (P<0.05). In contrast, no significant seasonal and age differences were obtained in FPV detection rates. Upon FeAstV ORF2 sequence analysis, the 23 present isolates were classified into the same clade (Mamastrovirus 2) as the 18 reference strains from other countries. Our findings suggest that FeAstV is already circulating in Japan, and it is more prevalent in juvenile cats in winter, unlike FPV.

Genetic characterization and phylogenetic analysis of feline astrovirus from Anhui province in eastern China

This study aimed to explore the phylogenetic and molecular characteristics of feline astrovirus. A total of 33 fecal samples of domestic cats with or without diarrhea were collected from the Anhui province, and two positive samples were detected. The complete genome and ORF2 of the two strains were sequenced and phylogenetically analyzed. AH-1-2020 and AH-2-2020 displayed 83.4% homology, and their homologies with other reference strains were 75.3%-83.4% and 83.4%-95.0%, respectively. Phylogenetic tree analysis revealed that all strains could be classified into three different clusters; therefore, the mean amino acid genetic distances (p-dist) among the three clusters were estimated. The results suggested that the two strains and other FeAstV strains were grouped into three genotypes, with AH-1-2020 belonging to a novel genotype. High similarity was observed (65.9%-66.5% nucleotide identity and 63.8%-64.8% amino acid identity) in ORF2 between porcine astrovirus type 1 and AH-1-2020. Furthermore, inter-specific recombination between porcine astrovirus type 1 and FeAstV was observed. We, therefore, inferred that inter-specific transmission may exist between pigs and cats; however, further studies are required to verify this. This is the first report on the genetic characterization and phylogenetic analysis of FeAstVs in the Anhui province and would further the current understanding of the genetic diversity and epidemiology of FeAstVs.

Epidemiology, genetic diversity and evolution of canine astrovirus

Astroviruses (AstVs) are major causative agents of gastroenteritis in children and have been reported in many species. Canine astrovirus (CaAstV), as an enteric pathogen, has been widely detected worldwide, but little is known about their genetic diversity and evolution, partly owing to a lack of genomic data. Here, we sequenced 12 nearly full-length CaAstV genomes to address the gap in knowledge. We found 14 (13.2%) and 7 (3.35%) CaAstV-positive samples from pet dogs with and without diarrhoea, respectively. Co-infections were with co-infection with Torque teno canis virus (TTCaV) reported for the first time. Phylogenetic analysis of the ORF2 gene revealed four major lineages. In particular, lineage 4 might have evolved from a recombinant virus from lineage 2 and lineage 3. The strains sequenced here clustered with lineages 2, 3 and 4 in contrast with other Chinese strains identified previously that clustered with lineages 2 and 4. Amino acid sequence alignment within lineage revealed intralineage amino acid diversity and that the type of epidemic strains within lineages changes over time. Three amino acids substitutions located in predicted B-cell epitopes, which might be involved escape of host immunity. Moreover, frequent inter-clade ORF2 gene recombinants were identified. The identification of individual recombination events and a recombinant lineage indicated that recombination plays a crucial role in CaAstV genetic evolution and diversity by generating divergent viruses. Moreover, phylogenetic analysis of ORF1b, the most conserved gene of astrovirus, revealed a close relationship between CaAstV and California sea lion astroviruses. Overall, we report detailed information on the genetic evolution and diversity of CaAstV, which indicates that CaAstV may pose challenges for diagnostics and future control strategies.

A molecular survey, whole genome sequencing and phylogenetic analysis of astroviruses from roe deer

BACKGROUND

Although astroviruses (AstV) have been detected in a variety of host species, there are only limited records of their occurrence in deer. One of the most important game species in Europe, due to its meat and antlers, is roe deer. Infected game animals can pose a threat to the health of other animals and of humans, so more attention needs to be focused on understanding the diversity of viruses in wildlife. The complete genome and organization of the roe deer AstV genome have not so far been described.

RESULTS

In our study, 111 game animals were screened for the presence of AstV. While no AstVs were detected in red deer, wild boar, chamois and mouflon, AstV RNA was present in three samples of roe deer. They were further subjected to whole genome sequencing with next generation sequencing. In this study, two AstV genomes were assembled; one in sample D5-14 and one in sample D12-14, while, in sample D45-14, no AstV sequences were identified. The complete coding sequences of the AstV SLO/D5-14 strain genome and of the almost complete genome of the AstV SLO/D12-14 strain were determined. They showed a typical Mamastrovirus organization. Phylogenetic analyses and amino acid pairwise distance analysis revealed that Slovenian roe deer AstV strains are closely related to each other and, also, related to other deer, bovine, water buffalo, yak, Sichuan takin, dromedary, porcine and porcupine AstV strains - thus forming a highly supported group of currently unassigned sequences.

CONCLUSIONS

Our findings suggest the existence of a new Mamastrovirus genogroup might be constituted while this aforementioned group is distantly related to Mamastrovirus genogroups I and II. In this study, additional data supporting a novel taxonomic classification are presented.

Genomic characterization of a novel astrovirus identified in Amur tigers from a zoo in China

Astroviruses (AstVs) have a very wide range of hosts and are associated with enteric and extra-enteric disease in mammals and birds. Cross-species transmission of AstVs has been observed frequently. In the present study, the genome of a novel astrovirus from Amur tigers (Panthera tigris) from a zoo in China was characterized and was found to have the typical genomic features of other mammal AstVs. It showed the highest nucleotide sequence similarity (46.1-87.3% identity) to AstVs from cats, indicating a close phylogenetic relationship and possible cross-species transmission between them. To our knowledge, this is the first identification and characterization of AstV from tigers, and this virus is the third astrovirus identified in hosts of the family Felidae. The results of this study will be helpful for understanding the origin, genetic diversity, and cross-species transmission of AstV.

Feline Virome-A Review of Novel Enteric Viruses Detected in Cats

Recent advances in the diagnostic and metagenomic investigations of the feline enteric environment have allowed the identification of several novel viruses that have been associated with gastroenteritis in cats. In the last few years, noroviruses, kobuviruses, and novel parvoviruses have been repetitively detected in diarrheic cats as alone or in mixed infections with other pathogens, raising a number of questions, with particular regards to their pathogenic attitude and clinical impact. In the present article, the current available literature on novel potential feline enteric viruses is reviewed, providing a meaningful update on the etiology, epidemiologic, pathogenetic, clinical, and diagnostic aspects of the infections caused by these pathogens.

Development and application of a multiplex PCR method for the simultaneous detection and differentiation of feline panleukopenia virus, feline bocavirus, and feline astrovirus

A multiplex polymerase chain reaction (mPCR) assay was developed to detect and distinguish feline panleukopenia virus (FPV), feline bocavirus (FBoV) and feline astrovirus (FeAstV). Three pairs of primers were designed based on conserved regions in the genomic sequences of the three viruses and were used to specifically amplify targeted fragments of 237 bp from the VP2 gene of FPV, 465 bp from the NP1 gene of FBoV and 645 bp from the RdRp gene of FeAstV. The results showed that this mPCR assay was effective, because it could detect at least 2.25-4.04 × 10⁴ copies of genomic DNA of the three viruses per μl, was highly specific, and had a good broad-spectrum ability to detect different genotypes of the targeted viruses. A total of 197 faecal samples that had been screened previously for FeAstV and FBoV were collected from domestic cats in northeast China and were tested for the three viruses using the newly developed mPCR assay. The total positive rate for these three viruses was 59.89% (118/197). From these samples, DNA from FPV, FBoV and FeAstV was detected in 73, 51 and 46 faecal samples, respectively. The mPCR testing results agreed with the routine PCR results with a coincidence rate of 100%. The results of this study show that this mPCR assay can simultaneously detect and differentiate FPV, FBoV and FeAstV and can be used as an easy, specific and efficient detection tool for clinical diagnosis and epidemiological investigation of these three viruses.

Immunogenicity and Efficacy Evaluation of Subunit Astrovirus Vaccines

A full understanding of the immune response to astrovirus (AstV) infection is required to treat and control AstV-induced gastroenteritis. Relative contributions of each arm of the immune system in restricting AstV infection remain unknown. In this study, two novel subunit AstV vaccines derived from capsid protein (CP) of mink AstV (MAstV) such as CPΔN (spanning amino acids 161–775) and CPΔC (spanning amino acids 1–621) were evaluated. Their immunogenicity and cytokine production in mice, as well as protective efficacy in mink litters via maternal immunization, were studied. Truncated CPs induced higher levels of serum anti-CP antibodies than CP, with the highest level for CPΔN. No seronegativity was detected after booster immunization with either AstV CP truncates in both mice and mink. All mink moms stayed seropositive during the entire 104-day study. Furthermore, lymphoproliferation responses and Th1/Th2 cytokine induction of mice splenocytes ex vivo re-stimulated by truncated CPs were significantly higher than those by CP, with the highest level for CPΔN. Immunization of mink moms with truncated CPs could suppress virus shedding and clinical signs in their litters during a 51-day study after challenge with a heterogeneous MAstV strain. Collectively, AstV truncated CPs exhibit better parameters for protection than full-length CP.

Discovery of novel astrovirus genotype species in small ruminants

Astroviruses (AstV) are single-stranded, positive-sense RNA viruses, best known for causing diarrhea in humans and are also found in many other mammals; in those, the relevance in gastroenteritis remains unclear. Recently described neurotropic AstV showed associations with encephalitis in humans as well as in other mammals. In Switzerland, two different neurotropic AstV were identified in cattle, as well as one in a sheep. The high genetic similarity between the ovine and one of the bovine AstV strengthens the hypothesis of an interspecies transmission. In humans, AstV associated with encephalitis were found also in human stool samples, suggesting that in these patients the infection spreads from the gastrointestinal tract to the brain under certain conditions, such as immunosuppression. Whether a similar pathogenesis occurs in ruminants remains unknown. The aims of this study were (1) the investigation of the potential occurrence of neurotropic AstV in feces samples, (2) the discovery and analysis of so far unknown AstV in small ruminants and other ruminant species’ fecal samples and (3) the examination of a potential interspecies transmission of AstV. To achieve these aims, RNA extraction out of 164 fecal samples from different ruminant species was performed and all samples were screened for known neurotropic AstV occurring in Switzerland, as well as for various AstV using RT-PCR. Positive tested samples were submitted to next generation sequencing. The generated sequences were compared to nucleotide- and amino acid databases, virus properties were identified, and phylogenetic analyses as well as recombination analysis were performed. The excretion of neurotropic AstV in small ruminants’ feces could not be demonstrated, but this work suggests the first identification of AstV in goats as well as the discovery of multiple and highly diverse new genetic variants in small ruminants, which lead to a classification into novel genotype-species. Additionally, the prediction of multiple recombination events in four of five newly discovered full or almost full-length genome sequences suggests a plausible interspecies transmission. The findings point out the occurrence and fecal shedding of previously unknown AstV in sheep and goats and pave the way towards a better understanding of the diversity and transmission of AstV in small ruminants.

First report and genetic characterization of porcine astroviruses of lineage 4 and 2 in diarrhoeic pigs in India

Porcine astroviruses (PAstVs) have extended their distribution globally and have a high prevalence; however, their clinical significance is still under investigation. Thus far, information about their prevalence and diversity in the Indian pig population is unknown. This study is the first report on the prevalence and genetic characterization of PAstVs in diarrhoeic piglets in India. From January 2013 to December 2017, 757 samples were screened using an RT-PCR assay and PAstV infection was detected in 17.6% (133/757) pigs. Of the 133 positive samples, 79 (59.4%) were positive for PAstV alone, whereas 54 (40.6%) were found to be co-infected with porcine rotavirus A (PoRVA). Phylogenetic analysis of RdRp/capsid gene region revealed high genetic heterogeneity among PAstV sequences, with a predominance of PAstV lineage 4 and detection of lineage 2. The lineage 4 PAstVs exhibited 61.2%-94.5% sequence similarity at the nucleotide level to other reported sequences, whereas lineage 2 strain shared 66.0%-71.6% sequence identity with cognate sequences of the same lineage. This is the first report on PAstV and circulation of lineages 4 and 2 in India. Further, phylogenetic analysis indicates a multiphyletic origin of PAstV strains and suggests cross-border circulation of PAstVs with a similar genetic configuration in Asian countries.

Molecular characterization of feline astrovirus in domestic cats from Northeast China

Feline astrovirus (FeAstV) which belonged to the genus Mamastrovirus was first identified in the feces of kittens with diarrhea in the USA in 1981 by electron microscopy, and had been reported in many countries. Presently, there are no any reports of the circulation of FeAstV in mainland China. We performed this study to investigate the apparent prevalence and genetic variability of FeAstV infected in cats in mainland China for the first time. We tested fecal samples of 105 cats with diarrhea and 92 asymptomatic cats in five cities in northeast China by RT-PCR targeting RNA-dependent RNA polymerase (RdRp) gene of FeAstV, and analyzed sequences variability and phylogenetic evolution based on the complete capsid gene of FeAstV strains obtained from positive samples. The overall prevalence of FeAstV was 23.4% (46/197) of which 38 were tested in cats with diarrhea (36.2%, 38/105) and 8 were in asymptomatic cats (8.7%, 8/92). Mixed infection with other enteroviruses including feline parvovirus (FPV), feline bocavirus (FBoV) and feline kobuvirus (FeKoV) was found in 38 FeAstV-positive samples. Phylogenetic analysis based on the complete capsid gene revealed all FeAstV strains were divided into two different groups with a 0.454±0.016 of mean amino acid genetic distance between two groups, suggesting that FeAstVs should be classified into two different genotype species. This study provided the first molecular evidence that FeAstV with considerable genetic diversity was circulating in northeast China, and analyzed genetic variability and classification of FeAstVs for the first time.

The Expanding Field of Mammalian Astroviruses: Opportunities and Challenges in Clinical Virology

Astroviruses are best known as being one of the leading causes of diarrhea in infants and were first described in this context in 1975. In its first years, astrovirus research was mainly restricted to electron microscopy and serology studies. The ability to culture some of these viruses in vitro allowed a first consequent step forward, especially at the molecular level. Since the emergence of more powerful genetic methods, though, the face of this research field has dramatically changed and evolved. From the exponential number of discoveries of new astrovirus strains in the most varied of animal species to their association with atypical diseases, these viruses revealed a lot of surprises, and many more are probably still waiting to be uncovered. This chapter summarizes the most important knowledge about astroviruses and discusses the implication of the latest findings in this area of research.

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

Astroviruses are a diverse family of viruses that infect a wide range of mammalian and avian hosts. Here we describe the phylogenetic diversity and current classification methodology of astroviruses based on the ORF1b and ORF2 genes, highlighting the propensity of astroviruses to undergo interspecies transmission and genetic recombination which greatly increase diversity and complicate attempts at a unified and comprehensive classification strategy.

Astrovirus Pathogenesis

Astroviruses are a major cause of diarrhea in the young, elderly, and the immunocompromised. Since the discovery of human astrovirus type 1 (HAstV-1) in 1975, the family Astroviridae has expanded to include two more human clades and numerous mammalian and avian-specific genotypes. Despite this, there is still little known about pathogenesis. The following review highlights the current knowledge of astrovirus pathogenesis, and outlines the critical steps needed to further astrovirus research, including the development of animal models of cell culture systems.

Antiviral Probiotics: A New Concept in Medical Sciences

In recent decades, probiotics have shown beneficial effects on animal and human health. Probiotics can protect the host against several health threats, including infectious diseases. Before 1995, researchers believed that the effect of probiotics was only on gut microbiota which can restore the gut flora and thus prevent pathogenic bacteria from triggering gastroenteritis. Recent studies have shown that the immunomodulatory activity is the most important mechanism of action of probiotics. From this information, researchers started to evaluate the effect of some immunobiotics, not only on pathogenic bacteria but also on viruses, including enteric and respiratory viruses. Several studies have confirmed the potential antiviral activity of some probiotics due to the immunomodulatory effect. These studies were conducted on humans (clinical trials) and in animal models. In this chapter, probiotics with antiviral effect against respiratory and enteric viruses will be presented and discussed, as well as their mechanisms of action.

Complete genome sequence analysis of chicken astrovirus isolate from India

Objective

Chicken astroviruses have been known to cause severe disease in chickens leading to increased mortality and “white chicks” condition. Here we aim to characterize the causative agent of visceral gout suspected for astrovirus infection in broiler breeder chickens.

Methods

Total RNA isolated from allantoic fluid of SPF embryo passaged with infected chicken sample was sequenced by whole genome shotgun sequencing using ion-torrent PGM platform. The sequence was analysed for the presence of coding and non-coding features, its similarity with reported isolates and epitope analysis of capsid structural protein.

Results

The consensus length of 7513 bp genome sequence of Indian isolate of chicken astrovirus was obtained after assembly of 14,121 high quality reads. The genome was comprised of 13 bp 5′-UTR, three open reading frames (ORFs) including ORF1a encoding serine protease, ORF1b encoding RNA dependent RNA polymerase (RdRp) and ORF2 encoding capsid protein, and 298 bp of 3′-UTR which harboured two corona virus stem loop II like “s2m” motifs and a poly A stretch of 19 nucleotides. The genetic analysis of CAstV/INDIA/ANAND/2016 suggested highest sequence similarity of 86.94% with the chicken astrovirus isolate CAstV/GA2011 followed by 84.76% with CAstV/4175 and 74.48%% with CAstV/Poland/G059/2014 isolates. The capsid structural protein of CAstV/INDIA/ANAND/2016 showed 84.67% similarity with chicken astrovirus isolate CAstV/GA2011, 81.06% with CAstV/4175 and 41.18% with CAstV/Poland/G059/2014 isolates. However, the capsid protein sequence showed high degree of sequence identity at nucleotide level (98.64-99.32%) and at amino acids level (97.74–98.69%) with reported sequences of Indian isolates suggesting their common origin and limited sequence divergence. The epitope analysis by SVMTriP identified two unique epitopes in our isolate, seven shared epitopes among Indian isolates and two shared epitopes among all isolates except Poland isolate which carried all distinct epitopes.

Electronic supplementary material

The online version of this article (doi:10.1007/s11259-016-9673-6) contains supplementary material, which is available to authorized users.

Human astroviruses

Human astroviruses (HAtVs) are positive-sense single-stranded RNA viruses that were discovered in 1975. Astroviruses infecting other species, particularly mammalian and avian, were identified and classified into the genera Mamastrovirus and Avastrovirus. Through next-generation sequencing, many new astroviruses infecting different species, including humans, have been described, and the Astroviridae family shows a high diversity and zoonotic potential. Three divergent groups of HAstVs are recognized: the classic (MAstV 1), HAstV-MLB (MAstV 6), and HAstV-VA/HMO (MAstV 8 and MAstV 9) groups. Classic HAstVs contain 8 serotypes and account for 2 to 9% of all acute nonbacterial gastroenteritis in children worldwide. Infections are usually self-limiting but can also spread systemically and cause severe infections in immunocompromised patients. The other groups have also been identified in children with gastroenteritis, but extraintestinal pathologies have been suggested for them as well. Classic HAstVs may be grown in cells, allowing the study of their cell cycle, which is similar to that of caliciviruses. The continuous emergence of new astroviruses with a potential zoonotic transmission highlights the need to gain insights on their biology in order to prevent future health threats. This review focuses on the basic virology, pathogenesis, host response, epidemiology, diagnostic assays, and prevention strategies for HAstVs.

Molecular characterisation and phylogenetic analysis of feline astrovirus in Korean cats

Astroviruses (AstVs) are important pathogens associated with enteric diseases in humans and other animals. However, most animal AstVs, including feline astrovirus (FAstV), are poorly understood. The aim of the present study was to investigate the prevalence and association of FAstV with enteric diseases in cats, and to conduct a molecular analysis of FAstVs, in Korea. Eleven faecal samples from 62 hospitalised cats at animal hospitals in the Moran market in South Korea tested positive for FAstV. The prevalence of FAstV was higher in cats <2 months old (25%) than in cats >2 months old (14.3%) (P = 0.31). Diarrhoea and normal faeces were observed in 19% (8/42) and 15% (3/20) of cats with FAstV, respectively (P = 1.00). Amino acid sequences alignment and phylogenetic tree analysis showed that FAstVs, including Korean strains, formed a single clade within the mamastroviruses.

Feline fecal virome reveals novel and prevalent enteric viruses

Humans keep more than 80 million cats worldwide, ensuring frequent exposure to their viruses. Despite such interactions the enteric virome of cats remains poorly understood. We analyzed a fecal sample from a single healthy cat from Portugal using viral metagenomics and detected five eukaryotic viral genomes. These viruses included a novel picornavirus (proposed genus "Sakobuvirus") and bocavirus (feline bocavirus 2), a variant of feline astrovirus 2 and sequence fragments of a highly divergent feline rotavirus and picobirnavirus. Feline sakobuvirus A represents the prototype species of a proposed new genus in the Picornaviridae family, distantly related to human salivirus and kobuvirus. Feline astroviruses (mamastrovirus 2) are the closest known relatives of the classic human astroviruses (mamastrovirus 1), suggestive of past cross-species transmission. Presence of these viruses by PCR among Portuguese cats was detected in 13% (rotavirus), 7% (astrovirus), 6% (bocavirus), 4% (sakobuvirus), and 4% (picobirnavirus) of 55 feline fecal samples. Co-infections were frequent with 40% (4/10) of infected cats shedding more than one of these five viruses. Our study provides an initial description of the feline fecal virome indicating a high level of asymptomatic infections. Availability of the genome sequences of these viruses will facilitate future tropism and feline disease association studies.

Phylogenetic analysis of bovine astrovirus in Korean cattle

Bovine astrovirus (BAstV) belongs to a genetically divergent lineage within the genus Mamastrovirus. The present study showed that BAstV was associated with the gastroenteric tracts of cattle in nine positive fecal samples from 115 cattle, whereas no positive samples were found in the brain tissues of 14 downer cattle. Interestingly, the positive diarrheal samples were obtained mainly from calves aged 14 days–3 months. Bayesian inference tree analysis of the partial ORF1ab and capsid (ORF2) gene sequences of BAstVs identified four divergent groups. Eleven BAstVs, four porcine astroviruses, and two deer astroviruses (DAstVs; CcAstV-1 and -2) belonged to group 1; group 2 contained two BAstVs (BAstK08–51 and BAstK10–96) with another two in group 3 (BAstK08–2 and BAstK08–53); and group 4 comprised the BAstV-NeuroS1 strain derived from a cattle brain tissue sample and an ovine astrovirus. The same divergent groups were obtained when the pairwise alignments were produced using both amino acid and nucleotide sequences. The Korean BAstVs isolated from infected cattle had a nationwide distribution and they belonged to groups 1, 2, and 3.

Gastrointestinal Disease in Exotic Small Mammals

Exotic small mammal medicine is a relatively new specialty area within veterinary medicine. Ferrets, rabbits, and rodents have long been used as animal models in human medical research investigations, resulting in a body of basic anatomic and physiologic information that can be used by veterinarians treating these species. Unfortunately, there is a paucity of veterinary articles that describe clinical presentation, diagnosis, and treatment options of gastrointestinal (GI) disease as it affects exotic small mammals. Although there is little reference material relating to exotic small mammal GI disease, patients are commonly presented to veterinary hospitals with digestive tract disorders. This article provides the latest information available for GI disease in ferrets (Helicobacter mustelae gastritis, inflammatory bowel disease [IBD], GI lymphoma, systemic coronavirus, coccidiosis, and liver disease), rabbits (GI motility disorders, liver lobe torsion, astrovirus, and coccidiosis), guinea pigs (gastric dilatation volvulus [GDV]), rats (Taenia taeniaeformis), and hamsters (Clostridium difficile). Both noninfectious diseases and emerging infectious diseases are reviewed as well as the most up-to-date diagnostics and treatment options.

Phylogenetic analysis of porcine astrovirus in domestic pigs and wild boars in South Korea

Porcine astrovirus (PAstV) belongs to genetically divergent lineages within the genus Mamastrovirus. In this study, 25/129 (19.4 %) domestic pig and 1/146 (0.7 %) wild boar fecal samples tested in South Korea were positive for PAstV. Positive samples were mainly from pigs under 6 weeks old. Bayesian inference (BI) tree analysis for RNA-dependent RNA polymerase (RdRp) and capsid (ORF2) gene sequences, including Mamastrovirus and Avastrovirus, revealed a relatively geographically divergent lineage. The PAstVs of Hungary and America belong to lineage PAstV 4; those of Japan belong to PAstV 1; and those of Canada belong to PAstV 1, 2, 3, and 5, but not to 4. This study revealed that the PAstVs of Korea belong predominantly to lineage PAstV 4 and secondarily to PAstV 2. It was also observed that PAstV infections are widespread in South Korea regardless of the disease state in domestic pigs and in wild boars as well.

Astroviruses in rabbits

A novel astrovirus was found more frequently in rabbits with enteric disease than in asymptomatic animals.

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.

Mixed infection by Feline astrovirus and Feline panleukopenia virus in a domestic cat with gastroenteritis and panleukopenia

Astroviruses are important pathogens of human beings and animals. Feline astroviruses have been identified by electron microscopy in the feces of either asymptomatic or symptomatic cats, and experimental infection with one isolate was shown to induce enteric clinical signs and virus excretion, thus suggesting a possible role as enteric pathogen. However, due to the lack of specific diagnostic assays, feline astroviruses are not included in the diagnostic algorithms of feline infectious diseases, and their role as feline pathogens remains unclear. The present report describes a dual infection by Feline astrovirus and Feline panleukopenia virus in a 4-month-old cat with severe gastroenteritis and panleukopenia. Upon sequence analysis, the Feline astrovirus strain was found to be genetically related to astroviruses identified in human beings and felids.

Astrovirus Infections in Animal Mammalian Species

The first reports of astroviruses in animals date back to the end of the 1970s, when infections in mammals such as lambs and calves suffering from diarrhea were reported for the first time. Since then, several mammalian species have been shown to be susceptible to astroviruses which appear to be genetically diverse and to have acquired host-specificity. To date, astroviruses have been detected in 16 different orders or species of mammals in addition to humans, and signs of infection range from unapparent infection or very mild disease to diarrhea, lethargy, and anorexia, mainly observed in young individuals. This chapter describes those astroviruses detected in nonhuman mammalian species worldwide, as well as their molecular and phenotypic characteristics and their role in diseases. The capacity of these viruses to cross-species barriers and their subsequent adaptation to novel hosts is also highlighted.

Astrovirus infections in humans and animals - molecular biology, genetic diversity, and interspecies transmissions

Astroviruses are small, non-enveloped, positive sense, single-stranded RNA viruses first identified in 1975 in children suffering from diarrhea and then described in a wide variety of animals. To date, the list of animal species susceptible to astrovirus infection has expanded to 22 animal species or families, including domestic, synantropic and wild animals, avian, and mammalian species in the terrestrial and aquatic environments. Astrovirus infections are considered among the most common cause of gastroenteritis in children, second only to rotavirus infections, but in animals their association with enteric diseases is not well documented, with the exception of turkey and mink astrovirus infection. Genetic variability has been described in almost all astrovirus species sufficiently examined infecting mammals and birds; however, antigenic variability has been demonstrated for human astroviruses but is far less investigated in animal viruses. Interestingly, there is an increasing evidence of recombination events occurring in astroviruses, which contributes to increase the genetic variability of this group of viruses. A wide variety of species infected, the evident virus genetic diversity and the occurrence of recombination events indicate or imply either cross-species transmission and subsequent virus adaptation to new hosts or the co-infection of the same host with different astroviruses. This can also favor the emergence of novel astroviruses infecting animals or with a zoonotic potential. After more than 30 years from their first description in humans, there are many exciting streams of research to be explored and intriguing questions that remain to be answered about the relatively under-studied Astroviridae family. In the present work, we will review the existing knowledge concerning astrovirus infections in humans and animals, with particular focus on the molecular biology, interspecies transmission and zoonotic potential of this group of viruses.

Detection and characterization of canine astroviruses

Astroviruses (AstVs) have been identified only occasionally in dogs. A canine AstV, strain Bari/08/ITA, was detected from a pup with gastroenteric signs and the virus was isolated in cell culture and characterized molecularly. In the full-length capsid protein, the virus displayed genetic similarities (83.5 % aa identity) to another canine AstV strain, although a high rate of variation occurred in the hypervariable domain, which is related to AstV antigenic specificity. Specific antibodies were detected in the convalescent dog, indicating seroconversion, and in 59 % of a collection of dog serum samples. Using primers specific for canine AstV, designed to detect a conserved region of ORF1b, canine AstVs were detected in 24.5 % of young pups with gastroenteritis, either alone or in mixed infections with other canine pathogens. In contrast, AstVs were detected in only 9.3 % of asymptomatic pups. These findings indicate that canine AstVs are common in dogs and may suggest a possible role as canine enteric pathogens.

Comparison of capsid gene sequences of turkey astrovirus-2 from poult-enteritis-syndrome-affected and apparently healthy turkeys

This study was conducted to determine genetic variations in the capsid gene of turkey astrovirus-2 (TAstV-2) detected in apparently healthy and poult enteritis syndrome (PES)-affected turkeys. Capsid genes of astroviruses obtained from 30 PES-affected and 45 apparently healthy turkey flocks had sequence homologies of 73.4-100% and 72.4-100% at the nucleotide levels, respectively. The analysis of deduced amino acid sequences revealed one amino acid deletion at position 552 in 28 (93.3%) of 30 PES-affected cases. However, there were two deletions (at positions 551 and 552) in 31 (68.9%) of 45 TAstV-2 from apparently healthy flocks. The TAstV-2 (6.7%) from two PES-affected cases had two amino acid insertions each between positions 552 and 553, while TAstV-2 from 14 (31.1%) of 45 healthy flocks had two insertions at the same position. Phylogenetic analysis based on nucleotide sequences revealed that the astroviruses in this study were closely related to most of the previously published TAstV-2 isolates. The sequence homology of TAstV-2 in this study ranged from 70.4% to 99.4% at the nucleotide level with those of previously published TAstV-2 isolates. The variations at the amino acid level in the capsid gene suggest the possibility of the existence of different serotypes of turkey astrovirus. The close relationship of turkey astroviruses from apparently healthy flocks to those from PES-affected cases in capsid gene phylogeny necessitates further studies to compare complete capsid gene sequences from both types of flocks from different geographic areas for better understanding of TAstV circulating in turkeys.

Characterization of an outbreak of astroviral diarrhea in a group of cheetahs (Acinonyx jubatus)

A Mamastrovirus was identified in an outbreak of diarrhea in cheetahs (Acinonyx jubatus). Five young adult and two adult cheetahs presented with lethargy, anorexia, watery diarrhea and regurgitation over an 11-day period. Fecal samples were submitted for electron microscopy and culture. Electron microscopy results revealed particles morphologically consistent with an astrovirus, and no other viral pathogens or significant bacterial pathogens were identified. The astrovirus was confirmed and sequenced using consensus astroviral PCR, resulting in a 367 base pair partial RNA-dependent-RNA polymerase (RdRp) product and a 628 base pair partial capsid product. Bayesian and maximum likelihood phylogenetic analyses were performed on both the RdRp and the capsid protein segments. All animals were monitored and treated with bismuth subsalicylate tablets (524mg PO BID for 5 days), and recovered without additional intervention. This is the first report we are aware of documenting an astrovirus outbreak in cheetah.

Astroviruses: human and animal

The name astrovirus was used by Madeley and Cosgrove in 1975 to describe a small round virus (approximately 28 nm diameter) with star-like appearance on electron microscopy. It was first seen in faeces from a few children with gastroenteritis. An aetiological role in gastroenteritis has since been confirmed. The virus causes a mild illness after an incubation period of 3-4 days. Antibody studies indicate that infection is widespread and, in Britain, mainly occurs in the 2-5 year age group. Outbreaks occur in, for example, institutions and paediatric wards. The virus usually spreads by the faecal-oral route but food- or water-borne outbreaks have occurred. Strains of astrovirus have been isolated from many animals including calf, lamb, pig, cat, dog, duck and turkey. The lamb strain can cause gastroenteritis but the bovine strain did not cause diarrhoea in gnotobiotic calves. Infected turkeys have scours, and infection in ducklings causes haemorrhagic hepatitis with a mortality up to 25%. Five human serotypes have been described, all antigenically distinct from the bovine and ovine strains. The human astrovirus does not replicate in conventional tissue cultures but undergoes a non-productive cycle in human embryo kidney cells, and productive replication in the presence of trypsin. It is a positive-strand RNA virus, which is acid stable (pH3), survives at 60 degrees C for five but not 10 minutes and, like the enteroviruses, resists inactivation by alcohols. It has a density of 1.35-1.37 g/ml in caesium chloride.

Isolation and partial characterization of a novel porcine astrovirus

Astroviral infection has been described as one of the causes of porcine diarrhoeal disease. Here we describe the detection of astrovirus-like particles by electron microscopy in a diarrhoeal specimen. Furthermore, a cytopathic virus was isolated and propagated in an established porcine kidney cell line, PK-15. Reverse transcription and PCR performed with astrovirus-specific primers amplified a product with the expected size. Sequencing of the PCR product revealed that the virus observed by electron microscopy and propagated in the porcine cell line is an astrovirus, showing 86% identity at the nucleotide level with the only known porcine astrovirus, PAstV. Phylogenetic analysis clustered the novel isolate, Sb4685, together with PAstV in a broad clade comprising mammalian astroviruses.

Detection of astrovirus in the faeces of cats with diarrhoea

Examination by electron microscopy of faeces from two separate cases of young cats with diarrhoea revealed the presence of 28 nm viral particles morphologically consistent with an astrovirus. No visible cytopathic effect was observed when the virus was inoculated into a feline kidney cell culture.

Identification of structural domains involved in astrovirus capsid biology

Coat proteins of non-enveloped, icosahedral viruses must perform a variety of functions during their life cycle such as assembly of the coat protein subunits into a closed shell, specific encapsidation of the viral nucleic acid, maturation of the capsid, interaction with host receptors, and disassembly to deliver the genetic information into the newly infected cell. A thorough understanding of the multiple capsid properties at the molecular level is required in order to identify potential targets for antiviral therapy and the prevention of viral disease. The system we have chosen for study is the astrovirus, a family of icosahedral, single-stranded RNA viruses that cause disease in mammals and birds. Very little is known about what regions of the coat protein contribute to the diverse capsid functions. This review will present novel structural predictions for the coat protein sequence of different astrovirus family members. Based on these predictions, we hypothesize that the assembly and RNA packaging functions of the astrovirus coat protein constitutes an individual domain distinct from the determinants required for receptor binding and internalization. Information derived from these structural predictions will serve as an important tool in designing experiments to understand astrovirus biology.

Astrovirus induces diarrhea in the absence of inflammation and cell death

Astroviruses are a leading cause of infantile viral gastroenteritis worldwide. Very little is known about the mechanisms of astrovirus-induced diarrhea. One reason for this is the lack of a small-animal model. Recently, we isolated a novel strain of astrovirus (TAstV-2) from turkeys with the emerging infectious disease poult enteritis mortality syndrome. In the present studies, we demonstrate that TAstV-2 causes growth depression, decreased thymus size, and enteric infection in infected turkeys. Infectious TAstV-2 can be recovered from multiple tissues, including the blood, suggesting that there is a viremic stage during infection. In spite of the severe diarrhea, histopathologic changes in the intestine were mild and there was a surprising lack of inflammation. This may be due to the increased activation of the potent immunosuppressive cytokine transforming growth factor beta during astrovirus infection. These studies suggest that the turkey will be a useful small-animal model with which to study astrovirus pathogenesis and immunity.

Molecular characterization of a novel astrovirus associated with disease in mink

Pre-weaning diarrhoea is a well-known problem in mink farming in Europe, causing morbidity that varies between farms, regions and season. Different causalities for the disease have been proposed, but only most recently has a novel astrovirus been identified as an important risk factor. In this report, the molecular characterization, origin and evolution of this novel astrovirus of mink are discussed. The polyadenylated, positive-stranded RNA genome was sequenced and found to contain 6610 nt, organized into three ORFs and two short UTRs. A ribosomal frameshift sequence links the 5' two ORFs, containing sequence motifs for a serine protease (ORF1a) and an RNA-dependent RNA polymerase (ORF1b). The structural proteins are encoded by ORF2 and, presumably, are expressed as a polyprotein precursor to be cleaved into the mature capsid proteins. These results indicate that mink astrovirus (MiAstV) has all of the features typical of members of the Astroviridae. Phylogenetic analyses revealed that MiAstV is distantly related to established astroviruses, showing less than 67 % similarity at the nucleotide level with its closest relative, ovine astrovirus, and even lower identities at the predicted amino acid level. Nevertheless, sequence analysis of MiAstV isolates from geographically distinct Swedish and Danish farms showed much less diversity. This suggests either the spread in the mink population of a virus that has evolved a long time ago or the recent introduction of an ancient virus into a new host species.

Complete genomic sequences of astroviruses from sheep and turkey: comparison with related viruses

The genomes of astroviruses infecting sheep and turkey were sequenced. Detailed analyses of these sequences were performed, including comparison with the other complete astrovirus sequences available as well as with other RNA virus sequences, with focus on the non-structural proteins and RNA sequences. Earlier postulated functional astrovirus RNA motifs and protein domains could in most cases be recognised in the sheep and turkey astrovirus sequences. In addition, analyses of the available astrovirus sequences revealed: two protein regions with the potential for forming coiled coils, differences in the postulated transmembrane region, a similarity between the putative astrovirus nuclear localisation signal and calicivirus genome-linked proteins, and a stretch of a highly conserved RNA sequence with a possible role in the astrovirus capsid gene expression. The present analyses contribute to the deciphering of pertinent functions of the astrovirus genomes.

Comparison of capsid sequences from human and animal astroviruses

We have sequenced the genomic 3'-end, including the structural gene, of human astrovirus (HAstV) serotype 7 and morphologically related viruses infecting pig (PAstV), sheep (OAstV) and turkey (TAstV-1). These sequences were compared with corresponding astrovirus sequences available in the nucleic acid databases, including sequences of the seven other HAstV serotypes, two other avian astroviruses (TAstV-2 and avian nephritis virus) and astrovirus from cat (FAstV). A 35 nt stem-loop motif near the 3'-end of the genome, previously described as being highly conserved, was present in all of the astroviruses except TAstV-2. In the N-terminal half of the capsid precursor protein, there were several short conserved peptide motifs. Otherwise the capsid proteins of astroviruses infecting different hosts were highly divergent. Calculation of genetic distances revealed that the distance between FAstV and HAstV is comparable to the largest distances between different HAstV serotypes. Higher similarities between the HAstV, FAstV and PAstV capsid sequences suggest interspecies transmissions involving humans, cats and pigs relatively recently in the evolutionary history of astroviruses.