Self-assembly of the recombinant capsid protein of a bovine norovirus (BoNV) into virus-like particles and evaluation of cross-reactivity of BoNV with human noroviruses

A Passion for Small Things and Staying Primed: My Career in Virology and Immunology

A love of science and animals, perseverance, and happenstance propelled my career in veterinary virology and immunology. I have focused on deadly enteric and respiratory viral infections in neonatal livestock and humans with an aim to understand their prevalence, pathogenesis, interspecies transmission, and immunity and develop vaccines. Research on animal coronaviruses (CoVs), including their broad interspecies transmission, provided a foundation to understand emerging zoonotic fatal human respiratory CoVs [severe acute respiratory syndrome, Middle East respiratory syndrome, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)] and reverse zoonosis of SARS-CoV-2 to animals. A highlight of my early research was the discovery of the gut-mammary gland-sIgA axis, documenting a common mucosal immune system. The latter remains pivotal to designing maternal vaccines for passive immunity in neonates. Our discovery and innovative cell propagation of fastidious human and animal rotaviruses and caliciviruses and their infectivity in germ-free animals has provided cell-adapted and animal disease models for ongoing virologic and immunologic investigations and vaccines. Nevertheless, besides the research discoveries, my lasting legacy remains the outstanding mentees who have enriched my science and my life.

Animals as Reservoir for Human Norovirus

Norovirus is the most common cause of non-bacterial gastroenteritis and is a burden worldwide. The increasing norovirus diversity is currently categorized into at least 10 genogroups which are further classified into more than 40 genotypes. In addition to humans, norovirus can infect a broad range of hosts including livestock, pets, and wild animals, e.g., marine mammals and bats. Little is known about norovirus infections in most non-human hosts, but the close genetic relatedness between some animal and human noroviruses coupled with lack of understanding where newly appearing human norovirus genotypes and variants are emerging from has led to the hypothesis that norovirus may not be host restricted and might be able to jump the species barrier. We have systematically reviewed the literature to describe the diversity, prevalence, and geographic distribution of noroviruses found in animals, and the pathology associated with infection. We further discuss the evidence that exists for or against interspecies transmission including surveillance data and data from in vitro and in vivo experiments.

Phosphatidylinositol 3-Kinase/Akt and MEK/ERK Signaling Pathways Facilitate Sapovirus Trafficking and Late Endosomal Acidification for Viral Uncoating in LLC-PK Cells

Sapovirus, an important cause of acute gastroenteritis in humans and animals, travels from the early to the late endosomes and requires late endosomal acidification for viral uncoating. However, the signaling pathways responsible for these viral entry processes remain unknown. Here we demonstrate the receptor-mediated early activation of phosphatidylinositol 3-kinase (PI3K)/Akt and mitogen-activated protein extracellular signal-regulated kinase/extracellular signal-regulated kinase (MEK/ERK) signaling pathways involved in sapovirus entry processes. Both signaling pathways were activated during the early stage of porcine sapovirus (PSaV) infection. However, depletion of the cell surface carbohydrate receptors by pretreatment with sodium periodate or neuraminidase reduced the PSaV-induced early activation of these signaling pathways, indicating that PSaV binding to the cell surface carbohydrate receptors triggered these cascades. Addition of bile acid, known to be essential for PSaV escape from late endosomes, was also found to exert a stiffening effect to stimulate both pathways. Inhibition of these signaling pathways by use of inhibitors specific for PI3K or MEK or small interfering RNAs (siRNAs) against PI3K or MEK resulted in entrapment of PSaV particles in early endosomes and prevented their trafficking to late endosomes. Moreover, phosphorylated PI3K and ERK coimmunoprecipitated subunit E of the V-ATPase proton pump that is important for endosomal acidification. Based on our data, we conclude that receptor binding of PSaV activates both PI3K/Akt and MEK/ERK signaling pathways, which in turn promote PSaV trafficking from early to late endosomes and acidification of late endosomes for PSaV uncoating. These signaling cascades may provide a target for potent therapeutics against infections by PSaV and other caliciviruses.IMPORTANCE Sapoviruses cause acute gastroenteritis in both humans and animals. However, the host signaling pathway(s) that facilitates host cell entry by sapoviruses remains largely unknown. Here we demonstrate that porcine sapovirus (PSaV) activates both PI3K/Akt and MEK/ERK cascades at an early stage of infection. Removal of cell surface receptors decreased PSaV-induced early activation of both cascades. Moreover, blocking of PI3K/Akt and MEK/ERK cascades entrapped PSaV particles in early endosomes and prevented their trafficking to the late endosomes. PSaV-induced early activation of PI3K and ERK molecules further mediated V-ATPase-dependent late endosomal acidification for PSaV uncoating. This work unravels a new mechanism by which receptor-mediated early activation of both cascades may facilitate PSaV trafficking from early to late endosomes and late endosomal acidification for PSaV uncoating, which in turn can be a new target for treatment of sapovirus infection.

Bovine Nebovirus Interacts with a Wide Spectrum of Histo-Blood Group Antigens

Some viruses within the Caliciviridae family initiate their replication cycle by attachment to cell surface carbohydrate moieties, histo-blood group antigens (HBGAs), and/or terminal sialic acids (SAs). Although bovine nebovirus (BNeV), one of the enteric caliciviruses, is an important causative agent of acute gastroenteritis in cattle, its attachment factors and possibly other cellular receptors remain unknown. Using a comprehensive series of protein-ligand biochemical assays, we sought to determine whether BNeV recognizes cell surface HBGAs and/or SAs as attachment factors. It was found that BNeV virus-like particles (VLPs) bound to A type/H type 2/Le^y HBGAs expressed in the bovine digestive tract and are related to HBGAs expressed in humans and other host species, suggesting a wide spectrum of HBGA recognition by BNeV. BNeV VLPs also bound to a large variety of different bovine and human saliva samples of all ABH and Lewis types, supporting previously obtained results and suggesting a zoonotic potential of BNeV transmission. Removal of α1,2-linked fucose and α1,3/4-linked fucose epitopes of target HBGAs by confirmation-specific enzymes reduced the binding of BNeV VLPs to synthetic HBGAs, bovine and human saliva, cultured cell lines, and bovine small intestine mucosa, further supporting a wide HBGA binding spectrum of BNeV through recognition of α1,2-linked fucose and α1,3/4-linked fucose epitopes of targeted HBGAs. However, removal of terminal α2,3- and α2,6-linked SAs by their specific enzyme had no inhibitory effects on binding of BNeV VLPs, indicating that BNeV does not use terminal SAs as attachment factors. Further details of the binding specificity of BNeV remain to be explored.

IMPORTANCE Enteric caliciviruses such as noroviruses, sapoviruses, and recoviruses are the most important etiological agents of severe acute gastroenteritis in humans and many other mammalian host species. They initiate infection by attachment to cell surface carbohydrate moieties, HBGAs, and/or terminal SAs. However, the attachment factor(s) for BNeV, a recently classified enteric calicivirus genus/type species, remains unexplored. Here, we demonstrate that BNeV VLPs have a wide spectrum of binding to synthetic HBGAs, bovine and human saliva samples, and bovine duodenal sections. We further discovered that α1,2-linked fucose and α1,3/4-linked fucose epitopes are essential for binding of BNeV VLPs. However, BNeV VLPs do not bind to terminal SAs on cell carbohydrates. Continued investigation regarding the proteinaceous receptor(s) will be necessary for better understanding of the tropism, pathogenesis, and host range of this important viral genus.

Vesivirus 2117 capsids more closely resemble sapovirus and lagovirus particles than other known vesivirus structures

Vesivirus 2117 is an adventitious agent that, in 2009, was identified as a contaminant of Chinese hamster ovary cells propagated in bioreactors at a pharmaceutical manufacturing plant belonging to Genzyme. The consequent interruption in supply of Fabrazyme and Cerezyme (drugs used to treat Fabry and Gaucher diseases, respectively) caused significant economic losses. Vesivirus 2117 is a member of the Caliciviridae, a family of small icosahedral viruses encoding a positive-sense RNA genome. We have used cryo-electron microscopy and three-dimensional image reconstruction to calculate a structure of vesivirus 2117 virus-like particles as well as feline calicivirus and a chimeric sapovirus. We present a structural comparison of several members of the Caliciviridae, showing that the distal P domain of vesivirus 2117 is morphologically distinct from that seen in other known vesivirus structures. Furthermore, at intermediate resolutions, we found a high level of structural similarity between vesivirus 2117 and Caliciviridae from other genera: sapovirus and rabbit hemorrhagic disease virus. Phylogenetic analysis confirms vesivirus 2117 as a vesivirus closely related to canine vesiviruses. We postulate that morphological differences in virion structure seen between vesivirus clades may reflect differences in receptor usage.

Bovine noroviruses: A missing component of calf diarrhoea diagnosis

Noroviruses are RNA viruses that belong to the Genus Norovirus, Family Caliciviridae, and infect human beings and several animal species, including cattle. Bovine norovirus infections have been detected in cattle of a range of different ages throughout the world. Currently there is no suitable cell culture system for these viruses and information on their pathogenesis is limited. Molecular and serological tests have been developed, but are complicated by the high genetic and antigenic diversity of bovine noroviruses. Bovine noroviruses can be detected frequently in faecal samples of diarrhoeic calves, either alone or in association with other common enteric pathogens, suggesting a role for these viruses in the aetiology of calf enteritis.

Pathogenesis of GIII.2 bovine norovirus, CV186-OH/00/US strain in gnotobiotic calves

The pathogenesis of GIII.2 bovine norovirus (BoNoV) is not well understood. Our study demonstrated persisting diarrhea and prolonged fecal shedding, but with a lack of significant intestinal lesions in gnotobiotic (Gn) calves infected with GIII.2 BoNoV, CV186-OH/00/US strain. Nine 4 to 7-day-old Angus/Jersey crossbred Gn calves were orally inoculated with 10.0-11.9 log10 genomic equivalents (GE)/calf of CV186-OH (n=7) or mock (n=2). Calves were euthanized at post-inoculation day (PID) 1 (n=1) when moderate to severe lethargy was observed and at PIDs 2-6 (n=4) after lethargy had subsided. Two calves were kept longer term (until PID 30) for monitoring fecal shedding patterns by TaqMan real-time RT-PCR (qRT-PCR). Most infected calves exhibited two clinical signs: (i) acute but persisting diarrhea and (ii) acute moderate to severe lethargy. The two infected calves, followed longer-term, had prolonged fecal viral RNA shedding [peak average titer of 11.8 (± 0.2) log10GE/ml] at least until PID 20. By qRT-PCR, 5 infected calves had low viral RNA titers in serum, ranging from 4.0 to 5.8 log10GE/ml, at PIDs 1-5, but not (<2.7 log10GE/ml) at PIDs 6-30. The latter observation coincided with the presence of serum IgG antibody to BoNoV at PIDs 8-30. Collectively, the GIII.2 BoNoV strain CV186-OH induced only mild enteropathogenicity, evident by the lack of significant intestinal lesions, but it led to persisting mild diarrhea and prolonged fecal virus shedding in Gn calves. The prolonged fecal shedding of GIII.2 BoNoV might partially explain how this virus is maintained as endemic infections in cattle.

Retrospective serosurveillance of bovine norovirus (GIII.2) and nebovirus in cattle from selected feedlots and a veal calf farm in 1999 to 2001 in the United States

There is a dearth of information on the seroprevalence of bovine norovirus (BoNoV) and nebovirus in cattle of the US. In this retrospective study, serum IgG antibodies to two bovine enteric caliciviruses, GIII.2 BoNoV (Bo/CV186-OH/00/US) and genetically and antigenically distinct nebovirus (Bo/NB/80/US), were evaluated in feedlot and veal calves from different regions of the US during 1999-2001. Three groups of 6- to 7-month-old feedlot calves from New Mexico (NM) (n=103), Arkansas (AR) (n=100) and Ohio (OH) (n=140) and a group of 7- to 10-day-old Ohio veal calves (n=47) were studied. Serum samples were collected pre-arrival or at arrival to the farms for the NM, AR and OH calves and 35 days after arrival for all groups for monitoring seroconversion rates during the period. Virus-like particles of Bo/CV186-OH/00/US and Bo/NB/80/US were expressed using the baculovirus expression system and were used in ELISA to measure antibodies. A high seroprevalence of 94-100 % and 78-100 % was observed for antibodies to GIII.2 BoNoV and nebovirus, respectively, in the feedlot calves tested. In the Ohio veal farm, an antibody seroprevalence of 94-100 % and 40-66 % was found for GIII.2 BoNoV and nebovirus, respectively. Increased seropositive rates of 38-85 % for GIII.2 BoNoV and 26-83 % for nebovirus were observed at 35 days after arrival and commingling on farms for all groups. Infection of calves with either GIII.2 BoNoV or nebovirus, or both viruses, appeared to be common in the regions studied in the US during 1999-2001. These two viruses likely remain endemic because no commercial vaccines are available.

Exposure to human and bovine noroviruses in a birth cohort in southern India from 2002 to 2006

Human and bovine norovirus virus-like particles were used to evaluate antibodies in Indian children at ages 6 and 36 months and their mothers. Antibodies to genogroup II viruses were acquired early and were more prevalent than antibodies to genogroup I. Low levels of IgG antibodies against bovine noroviruses indicate possible zoonotic transmission.

Characterization of emerging GII.g/GII.12 noroviruses from a gastroenteritis outbreak in the United States in 2010

Norovirus is a major cause of acute gastroenteritis in humans. A norovirus outbreak occurred in Ohio in January 2010. Stool and saliva samples were obtained from six infected individuals. The full-length genomes of two representative strains (HS206 and HS210) were characterized. They belonged to GII.12 in the capsid but GII.g in the RNA polymerase region. Interestingly, an immunocompetent 2-year-old male shed virus for up to 30 days, as detected by real-time reverse transcription (RT)-PCR. Histo-blood group antigen (HBGA) typing of saliva showed that the norovirus strains infected various types of secretor-positive individuals (types A, B, and O). The viruslike particles of strain HS206 did not bind substantially to A/B/O antigens by synthetic HBGA binding, hemagglutination, or saliva binding assays. These results suggest that infection by this strain may not be A/B/O antigen dependent or that in vitro binding patterns do not always accurately reflect in vivo HBGA usage. This is different from the HBGA binding pattern of the previously reported GII.12/Aichi76 strain. Structural analysis of the predicted capsid of these GII.12 strains revealed two amino acid mismatches located near the HBGA binding sites. Four gnotobiotic pigs were inoculated orally with HS206 (6 × 10(10) genomic equivalents [GE]/pig). Virus shedding began at postinoculation days (PID) 1 to 3 and continued up to PID 16 (1 × 10(5) to 2 × 10(7) GE/ml). Gastroenteritis cases caused by GII.12 noroviruses have been recently reported worldwide. We observed that this emerging GII.12 norovirus infected humans regardless of A/B/O blood type. The infection of pigs by strain HS206 suggests that interspecies transmission of this strain is possible under experimental conditions.

Alternative attachment factors and internalization pathways for GIII.2 bovine noroviruses

Bovine noroviruses belong to the family Caliciviridae, genus Norovirus. Two genotypes have been described and viruses genetically related to the Jena and Newbury2 strains have been classified into genotypes 1 and 2, respectively. In this study, virus-like particles (VLP) of the previously detected B309 Belgian strain, genetically related to genotype 2 bovine noroviruses, were used to investigate virus-host interactions in vitro. B309 VLP were shown to bind to several bovine cell lines. This binding was not affected by heparinase or chondroitinase treatment but was significantly inhibited by both sodium periodate, α-galactosidase, trypsin and phospholipase C treatment. Cell treatment by neuraminidase also moderately affected this binding. Taken together, these results show that, in addition to a galactosyl residue, sialic acid could also be involved in binding to susceptible cells. In addition, both the cholesterol-dependent pathway and macropinocytosis are used for B309 VLP internalization by Madin-Darby bovine kidney cells. The data increase the knowledge on bovine norovirus cell interactions.

Recombinant protein-based viral disease diagnostics in veterinary medicine

Identification of pathogens or antibody response to pathogens in human and animals modulates the treatment strategies for naive population and subsequent infections. Diseases can be controlled and even eradicated based on the epidemiology and effective prophylaxis, which often depends on development of efficient diagnostics. In addition, combating newly emerging diseases in human as well as animal healthcare is challenging and is dependent on developing safe and efficient diagnostics. Detection of antibodies directed against specific antigens has been the method of choice for documenting prior infection. Other than zoonosis, development of inexpensive vaccines and diagnostics is a unique problem in animal healthcare. The advent of recombinant DNA technology and its application in the biotechnology industry has revolutionized animal healthcare. The use of recombinant DNA technology in animal disease diagnosis has improved the rapidity, specificity and sensitivity of various diagnostic assays. This is because of the absence of host cellular proteins in the recombinant derived antigen preparations that dramatically decrease the rate of false-positive reactions. Various recombinant products are used for disease diagnosis in veterinary medicine and this article discusses recombinant-based viral disease diagnostics currently used for detection of pathogens in livestock and poultry.

First report on the phylogeny of bovine norovirus in Turkey

Bovine norovirus (BoNoV) is an important cause of diarrhea in calves and has been reported in several countries. The aims of this study were to investigate for the first time the presence of norovirus in Turkish calves by real-time reverse transcription-polymerase chain reaction (qRT-PCR) and to determine the phylogeny of any circulating strains. Fecal samples from 70 diarrheic calves were collected and analysed by SYBR Green qRT-PCR. BoNoV was detected in fecal samples from six calves. The capsid gene was partially sequenced, and phylogenetic analysis was performed. This showed that the six Turkish BoNoVs clustered with the GIII-2 prototype.

Bovine norovirus: carbohydrate ligand, environmental contamination, and potential cross-species transmission via oysters

Noroviruses (NoV) are major agents of acute gastroenteritis in humans and the primary pathogens of shellfish-related outbreaks. Previous studies showed that some human strains bind to oyster tissues through carbohydrate ligands that are similar to their human receptors. Thus, based on presentation of shared norovirus carbohydrate ligands, oysters could selectively concentrate animal strains with increased ability to overcome species barriers. In comparison with human GI and GII strains, bovine GIII NoV strains, although frequently detected in bovine feces and waters of two estuaries of Brittany, were seldom detected in oysters grown in these estuaries. Characterization of the carbohydrate ligand from a new GIII strain indicated recognition of the alpha-galactosidase (α-Gal) epitope not expressed by humans, similar to the GIII.2 Newbury2 strain. This ligand was not detectable on oyster tissues, suggesting that oysters may not be able to accumulate substantial amounts of GIII strains due to the lack of shared carbohydrate ligand and that they should be unable to contribute to select GIII strains with an increased ability to recognize humans.

Human antibody responses to bovine (Newbury-2) norovirus (GIII.2) and association to histo-blood group antigens

Serum antibodies to bovine norovirus have been found recently in about 22% of humans. Whether this prevalence reflects limited virulence properties of the virus or that inherited host factors provide protection against bovine norovirus infection in humans remains to be established. To investigate whether histo-blood group antigens correlate with the presence of bovine norovirus (GIII.2) antibody, plasma (n = 105) from Swedish blood donors, genotyped and phenotyped for secretor, Lewis and ABO, were tested and compared for the frequency of IgG antibody and antibody titer to Bo/Newbury2/76/UK. In total, 26.7% (28/105) of Swedish blood donors were antibody-positive. Two non-secretors (2/21, 9.5%) were antibody-positive compared with 26/84 (31%) secretors (P = 0.047). While no statistically significant correlation was found between the frequency of antibodies to bovine norovirus and different ABO blood groups, individuals with blood type B presented the highest frequency of antibodies (37.5%) compared with 0-30% among other blood groups. Individuals with Le(a-b+) had not only higher frequency of antibodies (31.3%) compared with Le(a+b-) (11%) (P = 0.068) but also higher antibody titer (P = 0.085) although this was not significant statistically. No detectable cross-reaction between bovine GIII.2 and human GII.3 NoV VLP was found with human and animal sera. The results of this study suggest that bovine norovirus infections occur in Sweden and that secretor status but not ABO blood groups is a possible risk factor for infection.

Molecular detection of norovirus in sheep and pigs in New Zealand farms

Human norovirus (NoV) is reportedly the major cause of non-bacterial gastroenteritis outbreaks worldwide and is commonly associated with water- and food-borne transmission via the faecal-oral route. Aside from humans, norovirus has been detected in pigs, cattle and mice. The close relatedness of some human and animal noroviruses has raised concerns about potential zoonotic transmission. Our laboratory recently reported the development of a multiplex real-time RT-PCR for the detection and genotyping of norovirus of genogroups I-III. Here we report a study of 56 faecal specimens from pigs and sheep that were collected and screened for noroviruses using this assay. Norovirus was found in 2/23 (9%) of porcine specimens (all were genogroup II) and in 8/33 (24%) of ovine specimens (all were genogroup III). Samples tested positive for norovirus were verified by conventional RT-PCR with different primer sets. Genomes of representative porcine and ovine norovirus strains underwent partial sequence analysis (343 and 2045 bases, respectively). This is the first report describing norovirus in sheep.

Pathogenesis of a genogroup II human norovirus in gnotobiotic pigs

We evaluated the gnotobiotic (Gn) pig as a model to study the pathogenesis of human norovirus (HuNoV) and to determine the target cells for viral replication. Sixty-five Gn pigs were inoculated with fecal filtrates of the NoV/GII/4/HS66/2001/US strain or with pig-passaged intestinal contents (IC) and euthanized acutely (n = 43) or after convalescence (n = 22). Age-matched Gn piglets (n = 14) served as mock-inoculated controls. Seventy-four percent (48/65) of the inoculated animals developed mild diarrhea compared to 0 of 14 controls. Pigs from postinoculation days (PID) 1 to 4 tested positive for HuNoV by reverse transcription-PCR of rectal swab fluids (29/65) and IC (9/43) and by antigen (Ag) enzyme-linked immunosorbent assay (ELISA) using antiserum to virus-like particles of HuNoV GII/4. No control pigs were positive. Histopathologic examination showed mild lesions in the proximal small intestine of only one pig (1/7). Seroconversion after PID 21 was detected by antibody ELISA in 13 of 22 virus-inoculated pigs (titers, 1:20 to 1:200) but not in controls. Immunofluorescent microscopy using a monoclonal antibody to HuNoV GII capsid revealed patchy infection of duodenal and jejunal enterocytes of 18 of 31 HuNoV-inoculated pigs with a few stained cells in the ileum and no immunofluorescence (IF) in mock-inoculated controls. Immunofluorescent detection of the viral nonstructural N-terminal protein antigen in enterocytes confirmed translation. Transmission electron microscopy of intestines from HuNoV-inoculated pigs showed disrupted enterocytes, with cytoplasmic membrane vesicles containing calicivirus-like particles of 25 to 40 nm in diameter. In summary, serial passage of HuNoV in pigs, with occurrence of mild diarrhea and shedding, and immunofluorescent detection of the HuNoV structural and nonstructural proteins in enterocytes confirm HuNoV replication in Gn pigs.

Complete genomic characterization and antigenic relatedness of genogroup III, genotype 2 bovine noroviruses

Bovine enteric noroviruses form a genogroup, III, distinct from the 2 human norovirus genogroups, I and II. Two genogroup III genotypes were suggested by partial genomic analyses. In the present study, analysis of the full-length genome sequence of Bo/Newbury2/76/UK and the more contemporary Newbury2-like virus, Bo/Dumfries/1994/UK, showed that both were 7311 nucleotides in length and had three open reading frames (ORFs), amino acids motifs typical of noroviruses, and 95% or greater amino acid identities to each other in all regions of their genome. Apart from the ORF1 NTPase region, their ORF1 regions had less than 90% identity to the genogroup III genotype 1 Bo/Jena/80/DE virus, confirming two genogroup III genotypes. A close antigenic relationship was demonstrated by ELISA between the genotype 2 viruses, which will allow their serological diagnosis.

Porcine noroviruses related to human noroviruses

Detection of genogroup II (GII) norovirus (NoV) RNA from adult pigs in Japan and Europe and GII NoV antibodies in US swine raises public health concerns about zoonotic transmission of porcine NoVs to humans, although no NoVs have been detected in US swine. To detect porcine NoVs and to investigate their genetic diversity and relatedness to human NoVs, 275 fecal samples from normal US adult swine were screened by reverse transcription-polymerase chain reaction with calicivirus universal primers. Six samples were positive for NoV. Based on sequence analysis of 3 kb on the 3' end of 5 porcine NoVs, 3 genotypes in GII and a potential recombinant were identified. One genotype of porcine NoVs was genetically and antigenically related to human NoVs and replicated in gnotobiotic pigs. These results raise concerns of whether subclinically infected adult swine may be reservoirs of new human NoVs or if porcine/human GII recombinants could emerge.

Immune responses to bovine norovirus-like particles with various adjuvants and analysis of protection in gnotobiotic calves

We evaluated serum and fecal antibody responses to bovine norovirus (BoNoV) virus-like particles (VLP) and protection against virulent BoNoV in gnotobiotic calves. Calves were vaccinated with two or three doses of VLPs (250 microg/dose) coadministered with oil, mutant E. coli heat-labile toxin (R192G) (mLT) or immunostimulating complexes (ISCOM). Fecal IgA antibody was detected only in calves vaccinated intranasally with VLP+mLT and after challenge, partial protection with delayed, shortened diarrhea (1-2 days) was observed only in these calves. Diarrhea presented from 2 to 6 days in calves vaccinated with VLP with oil or ISCOM and 8 to 9 days in controls. Virus shedding was detected post-challenge by ELISA in all vaccinated calves. All calves recovered from BoNoV infection had high titers of fecal IgA antibodies and were completed protection against challenge. We conclude that only BoNoV VLP+mLT given intranasally stimulated both serum and fecal IgA antibodies and partial protection.