Recovirus NS1-2 Has Viroporin Activity That Induces Aberrant Cellular Calcium Signaling To Facilitate Virus Replication

Enteric viruses in the Caliciviridae family cause acute gastroenteritis in humans and animals, but the cellular processes needed for virus replication and disease remain unknown. A common strategy among enteric viruses, including rotaviruses and enteroviruses, is to encode a viral ion channel (i.e., viroporin) that is targeted to the endoplasmic reticulum (ER) and disrupts host calcium (Ca2+) homeostasis. Previous reports have demonstrated genetic and functional similarities between the nonstructural proteins of caliciviruses and enteroviruses, including the calicivirus NS1-2 protein and the 2B viroporin of enteroviruses. However, it is unknown whether caliciviruses alter Ca2+ homeostasis for virus replication or whether the NS1-2 protein has viroporin activity like its enterovirus counterpart. To address these questions, we used Tulane virus (TV), a rhesus enteric calicivirus, to examine Ca2+ signaling during infection and determine whether NS1-2 has viroporin activity that disrupts Ca2+ homeostasis. We found that TV increases Ca2+ signaling during infection and that increased cytoplasmic Ca2+ levels are important for efficient replication. Further, TV NS1-2 localizes to the endoplasmic reticulum, the predominant intracellular Ca2+ store, and the NS2 region has characteristics of a viroporin domain (VPD). NS1-2 had viroporin activity in a classic bacterial functional assay and caused aberrant Ca2+ signaling when expressed in mammalian cells, but truncation of the VPD abrogated these activities. Together, our data provide new mechanistic insights into the function of the NS2 region of NS1-2 and support the premise that enteric viruses, including those within Caliciviridae, exploit host Ca2+ signaling to facilitate their replication.IMPORTANCE Tulane virus is one of many enteric caliciviruses that cause acute gastroenteritis and diarrheal disease. Globally, enteric caliciviruses affect both humans and animals and amass >65 billion dollars per year in treatment and health care-associated costs, thus imposing an enormous economic burden. Recent progress has resulted in several cultivation systems (B cells, enteroids, and zebrafish larvae) to study human noroviruses, but mechanistic insights into the viral factors and host pathways important for enteric calicivirus replication and infection are still largely lacking. Here, we used Tulane virus, a calicivirus that is biologically similar to human noroviruses and can be cultivated by conventional cell culture, to identify and functionally validate NS1-2 as an enteric calicivirus viroporin. Viroporin-mediated calcium signaling may be a broadly utilized pathway for enteric virus replication, and its existence within caliciviruses provides a novel approach to developing antivirals and comprehensive therapeutics for enteric calicivirus diarrheal disease outbreaks.

Caliciviridae Other Than Noroviruses

Besides noroviruses, the Caliciviridae family comprises four other accepted genera: Sapovirus, Lagovirus, Vesivirus, and Nebovirus. There are six new genera proposed: Recovirus, Valovirus, Bavovirus, Nacovirus, Minovirus, and Salovirus. All Caliciviridae have closely related genome structures, but are genetically and antigenically highly diverse and infect a wide range of mammalian host species including humans. Recombination in nature is not infrequent for most of the Caliciviridae, contributing to their diversity. Sapovirus infections cause diarrhoea in pigs, humans and other mammalian hosts. Lagovirus infections cause systemic haemorrhagic disease in rabbits and hares, and vesivirus infections lead to lung disease in cats, vesicular disease in swine, and exanthema and diseases of the reproductive system in large sea mammals. Neboviruses are an enteric pathogen of cattle, differing from bovine norovirus. At present, only a few selected caliciviruses can be propagated in cell culture (permanent cell lines or enteroids), and for most of the cultivatable caliciviruses helper virus-free, plasmid only-based reverse genetics systems have been established. The replication cycles of the caliciviruses are similar as far as they have been explored: viruses interact with a multitude of cell surface attachment factors (glycans) and co-receptors (proteins) for adsorption and penetration, use cellular membranes for the formation of replication complexes and have developed mechanisms to circumvent innate immune responses. Vaccines have been developed against lagoviruses and vesiviruses, and are under development against human noroviruses.

Experimental inoculation of juvenile rhesus macaques with primate enteric caliciviruses

BACKGROUND

Tissue culture-adapted Tulane virus (TV), a GI.1 rhesus enteric calicivirus (ReCV), and a mixture of GII.2 and GII.4 human norovirus (NoV)-containing stool sample were used to intrastomacheally inoculate juvenile rhesus macaques (Macaca mulatta) in order to evaluate infection caused by these viruses. METHODOLOGY & FINDINGS: Two of the three TV-inoculated macaques developed diarrhea, fever, virus-shedding in stools, inflammation of duodenum and 16-fold increase of TV-neutralizing (VN) serum antibodies but no vomiting or viremia. No VN-antibody responses could be detected against a GI.2 ReCV strain FT285, suggesting that TV and FT285 represent different ReCV serotypes. Both NoV-inoculated macaques remained asymptomatic but with demonstrable virus shedding in one animal. Examination of duodenum biopsies of the TV-inoculated macaques showed lymphocytic infiltration of the lamina propria and villous blunting. TV antigen-positive (TV+) cells were detected in the lamina propria. In most of the TV+ cells TV co-localized perinuclearly with calnexin--an endoplasmic reticulum protein. A few CD20+TV+ double-positive B cells were also identified in duodenum. To corroborate the authenticity of CD20+TV+ B cells, in vitro cultures of peripheral blood mononuclear cells (PBMCs) from healthy macaques were inoculated with TV. Multicolor flow cytometry confirmed the presence of TV antigen-containing B cells of predominantly CD20+HLA-DR+ phenotype. A 2-log increase of viral RNA by 6 days post inoculation (p<0.05) suggested active TV replication in cultured lymphocytes.

CONCLUSIONS/SIGNIFICANCE

Taken together, our results show that ReCVs represent an alternative cell culture and animal model to study enteric calicivirus replication, pathogenesis and immunity.

Two outbreaks of virulent systemic feline calicivirus infection in cats in Germany

Over the last years, several outbreaks of virulent systemic feline calicivirus (VS-FCV) infection have been described in the USA and several European countries. The paper describes two outbreaks of VS-FCV infection in cats in Germany. Data concerning clinical, laboratory, and histopathological features ofVS-FCV infection were collected from two outbreaks affecting 55 and 4 cats, respectively. Presence of feline calicivirus was confirmed by PCR followed by sequencing of the PCR-products. Clinical signs were variable, including severe upper respiratory tract infection, dyspnoea, oral and footpad ulceration, facial oedema, enteritis, pneumonia, bleeding disorder, high fever, and icterus. Both outbreaks were characterized by a high mortality rate.The present report describes the first documented outbreaks of VS-FCV infection in cats in Germany. Clinical and histopathological features are comparable to outbreaks described in the USA and Europe. However, phylogenetic analysis of the virus genome suggests that virus strains involved in these outbreaks were different from each other and from virulent strains isolated before, confirming the known genetic variability of FCV.

The candidate caliciviruses

The Caliciviridae are a family of small (35-40 nm) RNA viruses with a characteristic cupped morphology. They are unique in possessing only a single major structural polypeptide, of Mr 60,000-71,000. The use of electron microscopy to investigate diarrhoeal diseases has revealed viral particles with the size and structure of the caliciviruses in the faeces of humans, domestic and farm animals, birds, reptiles and insects. In vivo experiments indicate that they are species specific and have confirmed that they replicate in the gut, which often results in the host developing diarrhoea and failing to thrive. Biochemical characterization of these agents has been hampered by a failure to produce sufficient yields of virus in vitro. However, fluorescence and radiolabelling experiments indicate that the human, canine and chicken viruses replicate in the cytoplasm and possess an RNA genome. A major structural polypeptide (Mr 60,000-71,000) has been identified in the human, canine and insect viruses. Diagnosis of the candidate caliciviruses is dependent on electron microscopy and fluorescence labelling, with the exception of the human agents, for which radioimmunoassays have been developed. There is little epidemiological information on these agents but there is increasing evidence that the human caliciviruses are a common cause of outbreaks of diarrhoea and vomiting in infants, adults and the elderly.

European brown hare syndrome in wild European brown hares from Greece

From 1999 to mid-2003, 97 European brown hares (Lepus europaeus) found dead throughout Greece were examined by necropsy, histopathology, and reverse-transcription polymerase chain reaction (RT-PCR) for the presence of European brown hare syndrome (EBHS) and EBHS virus (EBHSV), respectively. Hare losses were sporadic, starting in the cold season and lasting for many months (December to May). The most prominent gross lesions were observed in the liver and included swelling and discoloration; congestion and hemorrhages were present mainly in lungs and tracheal mucosa. Necropsy findings were suggestive of EBHS, which was confirmed by histopathology and RT-PCR. This study documents, for the first time, EBHS in Greece.

Ice as a reservoir for pathogenic human viruses: specifically, caliciviruses, influenza viruses, and enteroviruses

Hundreds of isolates of viable bacteria and fungi have been recovered from ancient ice and permafrost. Evidence supports the hypothesis that viral pathogens also are preserved in ice repositories, such as glaciers, ice sheets, and lake ice. Proof may depend upon narrowing the search by applying specific criteria, which would target candidate viruses. Such criteria include viral pathogens likely to occur in great abundance, likely to be readily transported into ice, and then participate in ongoing disease cycles suggestive of their having been deposited in and subsequently released from ice. Caliciviruses, influenza A, and some enteroviruses appear to satisfy all three criteria. Environmental ice appears to be an important abiotic reservoir for pathogenic microbes. World health and eradication of specific pathogens could be affected by this huge reservoir.

Viruses causing gastroenteritis

Acute gastroenteritis is one of the most common diseases in humans worldwide. Viruses are recognized as important causes of this disease, particularly in children. Since the Norwalk virus was identified as a cause of gastroenteritis, the number of viral agents associated with diarrheal disease in humans has steadily increased. Rotavirus is the most common cause of severe diarrhea in children under 5 years of age. Astrovirus, calicivirus and enteric adenovirus are also important etiologic agents of acute gastroenteritis. Other viruses, such as toroviruses, coronaviruses, picobirnaviruses and pestiviruses, are increasingly being identified as causative agents of diarrhea. In recent years, the availability of diagnostic tests, mainly immunoassays or molecular biology techniques, has increased our understanding of this group of viruses. The future development of a safe and highly effective vaccine against rotavirus could prevent, at least, cases of severe diarrhea and reduce mortality from this disease.

Comparative pathogenesis of tissue culture-adapted and wild-type Cowden porcine enteric calicivirus (PEC) in gnotobiotic pigs and induction of diarrhea by intravenous inoculation of wild-type PEC

Porcine enteric calicivirus (PEC/Cowden) causes diarrhea in pigs, grows in cell culture, and is morphologically and genetically similar to the Sapporo-like human caliciviruses. Genetic analysis revealed that the tissue culture-adapted (TC) Cowden PEC has one distant and three clustered amino acid substitutions in the capsid region and 2 amino acid changes in the RNA polymerase region compared to wild-type (WT) PEC (M. Guo, K.-O. Chang, M. E. Hardy, Q. Zhang, A. V. Parwani, and L. J. Saif, J. Virol. 73:9625-9631, 1999). In this study, the TC PEC, passaged in a porcine kidney cell line, and the WT PEC, passaged in gnotobiotic (Gn) pigs, were used to orally inoculate 13 4- to 6-day-old Gn pigs. No diarrhea developed in the TC-PEC-exposed pigs, whereas moderate diarrhea developed in the WT-PEC orally inoculated pigs, persisting for 2 to 5 days. Fecal virus shedding persisting for at least 7 days was detected by both reverse transcription (RT)-PCR and antigen-enzyme-linked immunosorbent assay (antigen-ELISA) in both TC-PEC and WT-PEC orally inoculated pigs but not in mock-inoculated pigs. The PEC particles were detected by immunoelectron microscopy (IEM) in intestinal contents from all the WT-PEC-inoculated pigs, but not from the TC-PEC-inoculated pigs. Mild (duodenum and jejunum) or no (ileum) villous atrophy was observed in histologic sections of the small intestines of TC-PEC-inoculated pigs, whereas WT PEC caused mild to severe (duodenum and jejunum) villous atrophy and fusion. Scanning electron microscopy confirmed mild shortening and blunting of villi in the duodenum and jejunum of the TC-PEC-inoculated pigs, in contrast to moderate to severe villous shortening and blunting in the duodenum and jejunum of WT-PEC-inoculated pigs. Higher numbers of PEC antigen-positive villous enterocytes were detected by immunofluorescent (IF) staining in the proximal small intestine of the WT-PEC-inoculated pigs, in contrast to low numbers of PEC antigen-positive enterocytes in only one of four TC-PEC-inoculated pigs. No PEC antigen-positive cells were observed in the colon or extraintestinal tissues of all inoculated pigs or in the small intestine of one mock-inoculated pig. Thus, the TC PEC was at least partially attenuated (no diarrhea, mild lesions) after serial passage in cell culture. In further experiments, three 4- to 6-day-old Gn pigs were intravenously (i.v.) inoculated with WT PEC, and all pigs developed diarrhea and villous atrophy in the small intestines resembling that observed in the orally inoculated pigs. Fecal viral shedding persisting for 8 days was detected by both RT-PCR and antigen-ELISA, and PEC was detected by IEM in feces or intestinal contents. The PEC RNA and antigens (at low titers) were detected in acute-phase sera from all the WT-PEC i.v.-inoculated pigs and also from seven of nine of the WT-PEC orally inoculated pigs. Oral or i.v. inoculation of four additional pigs with the PEC-positive acute-phase sera induced diarrhea, small intestinal lesions, PEC shedding in feces, and seroconversion to PEC, confirming the occurrence of viremia during PEC infection, with infectious PEC present in acute-phase sera. No diarrhea, histopathologic changes, or IF staining in the small intestine or fecal or serum detection of PEC was evident in two pigs i.v. mock-inoculated or a pig inoculated i.v. with inactivated WT PEC. To our knowledge, this is the first report of an attenuated enteric calicivirus, the induction of diarrhea, and intestinal lesions in Gn pigs caused by i.v. inoculation of WT PEC and the presence of viremia following PEC infection.

An outbreak of calicivirus associated with consumption of frozen raspberries

In April 1988, an outbreak of gastroenteritis occurred among employees in a large company in Helsinki, Finland. A retrospective cohort study, using a self-administered questionnaire, was carried out to ascertain the cause and extent of the outbreak. To meet the case definition, employees had to have had diarrhoea and/or vomiting since 2 April, 1998. A subanalysis was made in the biggest office, consisting of 360 employees, of whom 204 (57%) completed the questionnaire. Of these 108 (53%) met the case definition. Employees who had eaten raspberry dressing were more likely to meet the case definition than those who had not (Attack Rate (AR) 65% versus AR 18% Relative Risk, (RR) 3.7, 95%, Confidence Intervals (CI) 2.0-6.7). Four stool specimens obtained from affected kitchen staff who had all eaten the raspberry dressing and who had all become ill simultaneously with the employees were positive by polymerase chain reaction (PCR) for calicivirus. The data suggest that the primary source of the outbreak was imported frozen raspberries contaminated by calicivirus.

Transmission of calicivirus by a foodhandler in the pre-symptomatic phase of illness

After a Christmas party in a restaurant, 48 (68%) of the 82 guests contracted calicivirus gastroenteritis. The epidemiological investigation showed that salad was strongly associated with the disease episode (RR = 2.43, P = 0.0005). Similar symptoms occurred among other customers who had had a meal at the same restaurant on the same evening. A foodhandler who had only prepared salad and appetizers became sick about 30 min after the end of his shift. He had been free of symptoms while preparing food. Few outbreak investigations have shown calicivirus transmission by foodhandlers some hours before becoming symptomatic.

A review of virus infections of cataceans and the potential impact of morbilliviruses, poxviruses and papillomaviruses on host population dynamics

Viruses belonging to 9 families have been detected in cetaceans. We critically review the clinical features, pathology and epidemiology of the diseases they cause. Cetacean morbillivirus (family Paramyxoviridae) induces a serious disease with a high mortality rate and persists in several populations. It may have long-term effects on the dynamics of cetacean populations either as enzootic infection or recurrent epizootics. The latter presumably have the more profound impact due to removal of sexually mature individuals. Members of the family Poxviridae infect several species of odontocetes, resulting in ring and tattoo skin lesions. Although poxviruses apparently do not induce a high mortality, circumstancial evidence suggests they may be lethal in young animals lacking protective immunity, and thus may negatively affect net recruitment. Papillomaviruses (family Papovaviridae) cause genital warts in at least 3 species of cetaceans. In 10% of male Burmeister's porpoises Phocoena spinipinnis from Peru, lesions were sufficiently severe to at least hamper, if not impede, copulation. Members of the families Herpesviridae, Orthomyxoviridae and Rhabdoviridae were demonstrated in cetaceans suffering serious illnesses, but with the exception of a 'porpoise herpesvirus' their causative role is still tentative. Herpes-like viruses and caliciviruses (Caliciviridae) give rise to cutaneous diseases in Monodontidae and Delphinidae. Antibodies to several serotypes of caliciviruses were found in odontocetes and mysticetes. An unrecognized Hepadnaviridae was detected by serology in a captive Pacific white-sided dolphin Lagenorhynchus obliquidens with chronic persistent hepatitis. Adenoviruses (Adenoviridae) were isolated from the intestinal tracts of mysticeti and a beluga Delphinapterus leucas but were not associated with any pathologies. We discuss the potential impact of Paramyxoviridae, Poxviridae and Papovaviridae on the dynamics of several odontocete populations.

Genomic mapping of a calicivirus VPg

We identified a primate calicivirus (Pan-1) VPg in Pan-1-infected cells. The Pan-1 VPg was associated with both genomic and subgenomic RNAs. RNase digestion of Pan-1 RNA yielded a residual protein of 16 kDa. The N-terminal sequence of Pan-1 VPg was determined by direct amino acid sequencing and mapped to a region of the genome equivalent to picornavirus VPgs. Alignment of this protein sequence with similar regions of other calicivirus genomes allowed identification of conserved amino acid motifs and potential boundaries of the calicivirus VPg genes. Proteinase K treatment abolished the infectivity of Pan-1 RNA, suggesting that Pan-1 VPg is required for RNA infectivity.

Detection and preliminary characterization of a new rabbit calicivirus related to rabbit hemorrhagic disease virus but nonpathogenic

A new rabbit calicivirus related to the rabbit hemorrhagic disease virus (RHDV) was identified. The new virus contains significant differences from the previously characterized RHDV isolates in terms of pathogenicity, viral titer, tropism, and primary sequence of the structural protein. Cross-protection experiments, antigenic data, and sequence comparisons demonstrate that the new virus is more closely related to RHDV than to the European brown hare syndrome virus, another member of the caliciviruses of the lagomorph group. The existence of a nonpathogenic calicivirus, which we propose to name rabbit calicivirus (RCV), provides an explanation for the early discrepancies found in the course of serological surveys of the rabbit population in European countries.

Viral gastroenteritis: small round structured viruses, caliciviruses and astroviruses. Part I. The clinical and diagnostic perspective

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A university outbreak of gastroenteritis due to a small round-structured virus. Application of molecular diagnostics to identify the etiologic agent and patterns of transmission

An epidemiologic investigation of a gastroenteritis outbreak in December 1994 indicated that salad consumption during lunch was linked with illness on 2 days (5 December: odds ratio [OR]=3.1, 95% confidence interval [CI]=2.0-5.0; 6 December: OR=3.1, 95% CI=1.9-4.9). Single stool or vomitus specimens from ill students and staff (case-patients) were examined for bacterial and viral pathogens. Small round-structured viruses (SRSVs) were detected by electron microscopy in stool specimens from 9 of 19 case-patients and in vomitus specimens from 3 of 5 case-patients. By reverse transcription-polymerase chain reaction (RT-PCR), the SRSVs were shown to be G-2/P2-B type strain. The nucleotide sequences of RT-PCR products from vomitus and stool specimens of ill students were identical to stool specimens from the ill salad chef. These findings suggest that a single SRSV strain was the etiologic agent in the outbreak that was possibly transmitted to students through consumption of contaminated salad. Epidemiologic investigation in conjunction with molecular diagnostics may enable early identification of sources of infection and improve outbreak control.

[Regenerative activity in experimental hepatitis in rabbits with viral hemorrhagic disease (VHD)]

Liver regeneration has been studied in necrotic hepatitis of 21 rabbits infected with the haemorrhagic disease virus (VHD). Formalin fixed and paraffin embedded liver sections have been immunostained for the proliferation associated antigen PCNA (Proliferating Cell Nuclear Antigen-clone PC10) and counterstained with toluidine blue that enhances histologic recognition of mitoses. Hepatocyte and bile duct proliferative activity has been quantified, by means of image analysis, both as PCNA reactivity and mitotic activity. The results, compared with a semiquantitative estimation of liver necrosis, showed a positive correlation between hepatocyte proliferative activity and liver necrosis, both in acute and subacute hepatitis. In the chronic phase a residual proliferative activity appeared in bile duct cells.

Susceptibility of hares and rabbits to a Belgian isolate of European brown hare syndrome virus

Signs and pathologic changes of European brown hare syndrome (EBHS) were reproduced in four hares (Lepus europaeus) after experimental inoculation of a liver suspension from hares from Belgium, which naturally died of EBHS. Virus particles were demonstrated by electron microscopy in the liver of an experimentally infected hare. They were spherical with a diameter of 28 to 30 nm. After density gradient centrifugation, virus particles were detected in the density zone of 1.34 g/ml. Based on immunoelectron microscopy with a convalescent serum, we identified the virus as the cause of EBHS. Clinical signs were not produced in three seronegative domestic rabbits after subcutaneous inoculation of the EBHS virus. Although low levels of antibodies against EBHS virus were found in the serum of these three rabbits 4 weeks after the inoculation of EBHS virus, the rabbits were not protected when challenged with viral hemorrhagic disease (VHD) virus. The different pathogenicity of the Belgian EBHS and VHD virus isolates in rabbits and the lack of protection in rabbits with circulating EBHS virus antibodies against a challenge with VHD virus indicates that both Belgian virus isolates form two different virus populations.

Astroviruses and caliciviruses: emerging enteric pathogens

Acute, infectious gastroenteritis is an extremely common disease that contributes significantly to morbidity and mortality worldwide. In the United States, it is the second most frequent illness encountered in families. While this illness generally runs a self-limited course, it may be temporarily incapacitating and impact substantially on numbers of days lost from work or school. At present, 30-40% of infectious gastroenteritis cases in the United States are attributable to viral agents, while 20-30% are due to bacteria and parasites. These estimates are almost certainly low, since the cause of gastroenteritis is not discernible in approximately 40% of the cases, and gastroenteritis may be caused by viruses or other pathogens that cannot be identified at this time. Rotavirus and enteric adenovirus are two of the most prevalent and well-studied of the viral agents and have been reviewed extensively elsewhere. This review focuses on two broad groups of small round structured viruses (SRSV), astroviruses and caliciviruses (classic, Norwalk, and Norwalk-like). Although recognized in association with acute, nonbacterial gastroenteritis since the early 1970s, the study of these viruses has been hampered by the relatively low levels of viral shedding in feces, difficulty in propagating the virus in cell or organ culture, and the lack of widely available, well-standardized reagents for their detection. In spite of these obstacles, much has been learned about these viruses using standard virologic (electron microscopy, biophysical characterization, immunoassays) and epidemiologic methods. More recently, substantial progress has been made in studying astroviruses and caliciviruses at the molecular level. Molecular techniques are now being used as diagnostic aids to characterize the epidemiology of these agents in greater detail.

New marine calicivirus serotype infective for swine

A new serotype of calicivirus was isolated from California sea lions (Zalophus californianus) with severe vesicular disease. Neutralizing antibodies were found in 27 of 82 (32.9%) serum samples from California sea lions and in 15 of 146 (10.3%) serum samples from Steller sea lions (Eumetopias jubatus) tested. The seropositive animals were widely dispersed along the margins of the eastern Pacific basin, from the Bering Sea to the Santa Barbara Channel. Seropositive samples were found from as early as 1976 through the present time. This new calicivirus serotype, San Miguel sea lion virus type 13, was inoculated into weaned pigs, resulting in induction of severe vesicular disease, which spread to all pigs, including uninoculated pen contacts. Virus was continually shed by most of the pigs throughout the 2-week duration of the experiment.

Feline viral respiratory disease. The carrier state, vaccination, and control

A thorough understanding of the epizootiology of FCV and FRTV is critical when implementing control measures in premises with enzootic URD. Failure to properly segregate cats, reduce fomite contamination, or implement a vaccination schedule most suited to that population will undoubtedly allow perpetuation of disease. Several questions remain unanswered about URD in cats. Following several years of widespread routine vaccination, what is the prevalence of the carrier state in vaccinated cats? What are the immunologic mechanisms responsible for the development of the latent FRTV carrier state and the variable level of virus excretion in FCV carriers? Why do some cats terminate primary infections with these viruses without entering a chronic carrier phase? Could immunomodulating agents be used to terminate the carrier state in persistently infected animals?

Calicivirus-induced vesicular disease in cetaceans and probable interspecies transmission

A calicivirus isolated from cetaceans is a new serotype designated cetacean calicivirus Tursiops-1 (CCV-Tur-1). It appears to have spread from an initially infected Atlantic bottlenose dolphin to a California sea lion, and was then carried by the sea lion to a second facility several miles away, where a second dolphin became infected and developed vesicular skin lesions that eroded, leaving shallow ulcers. Cetaceans and pinnipeds belong to separate orders, so this finding of interspecies transmission demonstrates the potentially broad host spectrum for yet another calicivirus.

Isolation and partial characterization of a calicivirus from calves

A calicivirus was isolated from 3 dairy calves in a herd with persistent calf respiratory tract problems. This virus, named Tillamook calicivirus, was not neutralized by 18 different calicivirus-typing serums available. The agent caused only minimal lesions in 2 experimentally exposed calves, but did establish a persistent infection with virus shedding for 45 days, after which time the experiment was terminated. Experimentally exposed swine developed clinical vesicular lesions. The possible origins, disease potential, and relationships to the exotic animal disease agent, vesicular exanthema of swine are discussed for this first calicivirus isolate of bovine origin.

Rotavirus-like, calicivirus-like, and 23-nm virus-like particles associated with diarrhea in young pigs

Virus particles morphologically similar to caliciviruses and rotaviruses were detected by electron microscopy (EM) in the intestinal contents of a 27-day-old diarrheic nursing pig. A third small spherical 23-nm virus-like particle was also observed. Calicivirus-like particles averaged 33 nm in diameter. Similar to rotaviruses, rotavirus-like particles were present as single-capsid 55-nm forms or double-capsid 70-nm particles. Most gnotobiotic pigs orally exposed to samples containing these three viruses developed diarrhea and villous atrophy of the small intestine, and all shed the three viruses in their intestinal contents. Attempts to propagate these viruses in cell culture were unsuccessful. The antigenic relationship of the rotavirus-like particles to known rotaviruses was explored by immune EM and immunofluorescent staining. By these techniques, the rotavirus-like particles did not cross-react with antisera to porcine, bovine, or human rotaviruses or to reovirus type 3. Antisera from gnotobiotic pigs exposed to all three viruses had enzyme-linked immunosorbent assay and virus neutralization titers of <4 against porcine rotavirus. Previous infection of gnotobiotic pigs with the mixture containing rotavirus-like particles failed to protect them against a subsequent challenge with porcine rotavirus. The antigenic relationship of the calicivirus-like particles to known caliciviruses was investigated by immune EM and virus neutralization. By these tests, the calicivirus-like particles did not react with antisera against feline calicivirus strain 255 or M-8. In a study conducted at Plum Island Animal Disease Center, antiserum against the three combined agents did not specifically neutralize any serotype of swine vesicular exanthema virus.

Isolation of small viruses resembling astroviruses and caliciviruses from acute enteritis of calves

Small round viruses (SRV) were isolated from the faeces of diarrhoeic calves from three farms. All three SRV preparations caused diarrhoea experimentally in gnotobiotic calves. Each preparation contained viral particles of two morphological types, "astrovirus-like" and "calicivirus-like", and from one preparation the two particle types were separated from each other. The calicivirus-like agent ("Newbury agent") was 33 nm in diameter, and caused diarrhoea in gnotobiotic calves with villous atrophy and D-xylose malabsorption. This virus did not infect cell cultures. The astrovirus-like agent did not cause diarrhoea in two gnotobiotic calves; however, it infected cell cultures (primary calf kidney) and the infected cells immunofluoresced with convalescent gnotobiotic-calf antiserum. The astrovirus-like agents in the three preparations were antigenically related. Experiments in calves showed that there was a degree of cross-protection between the three SRV preparations, as judged by the presence or absence of diarrhoea, but that at least three unrelated pathogens were present.

Pathogenicity of a strain of feline calicivirus for domestic kittens

A strain of feline calicivirus, isolated from a cheetah exhibiting ulcerative glossitis and conjunctivitis, was administered by aerosol to 4 domestic cats and by contact to a fifth cat. Despite the limited number of animals available for the experiment, the pathogenicity of the virus strain for domestic cats was established. In aerosol-infected animals, clinical signs were referable to infection of both upper and lower respiratory tracts. The virus produced an interstitial pneumonia which, early in infection, was uncomplicated by secondary bronchopneumonia. The in-contact cat exhibited clinical signs referable to infection of the oral cavity only and no lesions were noted in the lower respiratory tract at autopsy. Ulcerative glossitis was a feature of the disease in aerosol-infected and in-contact cats. The virus was isolated from the pharynx of all cats for up to 21 days after infection and from the tonsils at autopsy. The tonsils were considered to be a probable site of multiplication of virus in "carrier" cats.