Caliciviruses. Brief review

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.

Vesivirus viremia and seroprevalence in humans

Pathogenic caliciviruses of the genus Vesivirus circulate in oceanic ecosystems and spread to and among terrestrial mammals. Isolation of Vesivirus from natural and laboratory infections in humans led to this investigation of Vesivirus seroprevalence and viremia. Sera from four groups were tested for antibodies to Vesivirus as follows: blood donors whose units were cleared for donation, blood donors whose units were not accepted for donation solely because of elevated blood liver alanine aminotransferase (ALT) concentrations, patients with clinical hepatitis of unknown but suspected infectious cause, and patients with clinical hepatitis of unknown cause but associated with blood transfusion or dialysis. Additionally, sera were tested for Vesivirus genome by three methods: dot‐blot and two reverse transcription‐polymerase chain reaction (RT‐PCR) methods. The calculated seroprevalence against Vesivirus virions within these groups (N = 765) was 12%, 21%, 29%, and 47%, respectively (P < 0.001 for group differences). Additionally, 11 (9.8%) of 112 sera tested yielded RT‐PCR amplicons that by nucleotide sequence were distinct from each other and related to known Vesivirus. These data indicate that some blood donors in the population tested have serologic evidence of previous Vesivirus infection and some also have Vesivirus viremia. These results justify further investigation of an association between Vesivirus infection and illness in humans. J. Med. Virol. 78:693–701, 2006. © 2006 Wiley‐Liss, Inc.

Identification of a calicivirus isolate of unknown origin

Chinese hamster ovary (CHO) cells manifesting striking cytopathogenic changes in culture were investigated to determine the causative agent. Electron microscopic analyses revealed viral particles of about 40 nm in diameter, displaying typical calicivirus morphology. To date, this virus, designated isolate 2117, exclusively replicates in CHO cells, achieving only moderate titres. After cloning, the coding region of 7928 nucleotides, the 3' non-coding region and the poly(A) tail were sequenced. The genome consists of three open reading frames (ORFs), with the first and second ORF having the same reading frame. The overall genomic organization as well as the nucleotide sequence of isolate 2117 is most similar to that of a recently described canine calicivirus, but also shows significant similarity to the sequences of mink calicivirus and other caliciviruses within the genus Vesivirus: In Western blots, using antibodies against the viral protease, a stable, unprocessed 3CD protein of 68 kDa was identified in homogenates of 2117-infected CHO cells. Furthermore, antibodies raised against ORF 3 reacted with the respective protein in 2117-virions, demonstrating that this predicted 9 kDa protein is a minor structural component of the virion. In addition, an RT-PCR assay was established to detect 2117 viral RNA in biological products such as foetal bovine serum, which will aid the discovery of the origin and host of the virus.

An isolated epizootic of hemorrhagic-like fever in cats caused by a novel and highly virulent strain of feline calicivirus

An isolated epizootic of a highly fatal feline calicivirus (FCV) infection, manifested in its severest form by a systemic hemorrhagic-like fever, occurred over a 1-month period among six cats owned by two different employees and a client of a private veterinary practice. The infection may have started with an unowned shelter kitten that was hospitalized during this same period for a severe atypical upper respiratory infection. The causative agent was isolated from blood and nasal swabs from two cats; the electron microscopic appearance was typical for FCV and capsid gene sequencing showed it to be genetically similar to other less pathogenic field strains. An identical disease syndrome was recreated in laboratory cats through oral inoculation with tissue culture grown virus. During the course of transmission studies in experimental cats, the agent was inadvertently spread by caretakers to an adjoining room containing a group of four normal adult cats. One of the four older cats was found dead and a second was moribund within 48-72h in spite of symptomatic treatment; lesions in these animals were similar to those of the field cats but with the added feature of severe pancreatitis. The mortality in field cats, deliberately infected laboratory cats, and inadvertently infected laboratory cats ranged from 33-50%. This new isolate of calicivirus, named FCV-Ari, was neutralized at negligible to low titer by antiserum against the universal FCV-F9 vaccine strain. Cats orally immunized with FCV-F9, and then challenge-exposed shortly thereafter with FCV-Ari, developed a milder self-limiting form of disease, indicating partial protection. However, all of the field cats, including the three that died, had been previously immunized with parenteral FCV-F9 vaccine. FCV-Ari caused a disease that was reminiscent of Rabbit Hemorrhagic Disease, a highly fatal calicivirus infection of older rabbits.

Sapporo virus: history and recent findings

Morphologically distinct caliciviruses of human origin were first found in stools of children with gastroenteritis in 1976. Sapporo virus, or human calicivirus Sapporo, with typical surface morphology was first detected during a gastroenteritis outbreak in a home for infants in Sapporo, Japan, in 1977. Since then, morphologically and antigenically identical virus has been detected frequently in the same institution in association with outbreaks of gastroenteritis. Sapporo virus is widely distributed worldwide, as evidenced by the appearance of antigenically or genetically similar viruses and seroepidemiologic findings. Sapporo virus plays an important role in outbreaks of infantile gastroenteritis and is less important in foodborne outbreaks. Sapporo virus has been approved as the type species of the genus "Sapporo-like viruses in the family Caliciviridae. The history of and recent findings, as obtained by newly developed techniques, about Sapporo viruses are presented.

Partial characterization of the genome of nine animal caliciviruses

Caliciviruses (CVs) include at least 42 distinct serotypes. Seventeen CV serotypes have been isolated from marine sources and are called San Miguel sea lion caliciviruses (SMSVs). CVs also have been isolated from reptiles, primates, and other terrestrial animals. Nucleotide sequences from portions of genome of prototype strains for six SMSV serotypes, the reptile CV, Cro-1, the cetacean CV, Tur-1, and the primate CV, Pan-1, are presented. cDNA products of the polymerase (all strains characterized) and capsid (SMSV-17) regions were produced by reverse transcription-polymerase chain reaction using Pan-1 primers. Comparisons of nucleotide and amino acid identity among these and published CV sequences indicated that the nine characterized CVs fall into a phylogenetic group that includes SMSV-1 and SMSV-4 and that is more closely related to other characterized animal CVs than to most human CVs. The phylogenetic analysis also indicated that distinct genera exist among the Caliciviridae. SMSV-17 and SMSV-4 are predicted to be closer to each other than other caliciviruses of known serotype; 574 (82%) of the 704 amino acids in the SMSV-17 and SMSV-4 capsid genes were identical.

Serological analysis of feline calicivirus isolates from the United States and United Kingdom

The antigenic relationship of 181 feline calicivirus (FCV) isolates from the United States (USA) and United Kingdom (UK) to 5 reference viruses, representing 2 vaccine strains (F9 VacNor, 2280) and 3 field strains (H, J, TN) was determined by a neutralization assay using two standardized dilutions of reference sera. A comparison between USA and UK isolates indicated that significantly fewer UK isolates could be neutralized by sera specific for each of the reference strains. Isolates from the USA were also analyzed based on the time period and geographical location from which they were derived. Analysis of the cross-neutralization results for isolates derived from the USA indicated that no single reference strain was predominant in all the geographical locations, however, antisera specific to strains 2280, H and J neutralized the highest number of isolates overall. Analysis of the neutralization patterns based on the time period from which the isolates were derived indicated that F9 VacNor was antigenically similar to 86% of feline caliciviruses isolated in 1958-1979. This number decreased to 43% for isolates derived in 1980-1995. By contrast, the J strain maintained its antigenic relatedness to approximately 75% of representative FCV isolates circulating during the last 40 years.

Identification of canine calicivirus capsid protein and its immunoreactivity in western blotting

A canine calicivirus (CaCV) isolated in Japan, designated as CaCV No. 48 strain, was propagated in MDCK cells and purified by CsCl equilibrium gradient centrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the purified samples revealed the presence of only one major species of viral protein of about 60 kilodaltons after Coomassie staining. The same band, presumably that of the capsid protein, was detected by western blotting using a mouse hyperimmune serum. This capsid protein was synthesized in MDCK cells as early as 2 hr post-inoculation. Experimental infection of dogs resulted in the production of anti-CaCV antibodies which were detected by microneutralization test and western blotting. Likewise, serosurvey revealed not only the presence of neutralizing antibodies but also reactivity of the field sera against the capsid protein of the purified virus. These results indicate that the capsid protein of CaCV No. 48 strain is immunogenic and could be detected by antibodies in western blotting.

Rabbit hemorrhagic disease virus (RHDV): ultrastructure and biochemical studies of typical and core-like particles present in liver homogenates

Calicivirus particles isolated from rabbits suffering from acute RHD were compared with virions found in rabbits with chronic disease. Liver homogenates of rabbits with the protracted disease display no hemagglutinating activity and contain viral particles with diameters of 25-27 nm. These virions contain only one structural protein of 30 kDa and are distinctly smaller than intact rabbit hemorrhagic disease virus (RHDV) (32-40 nm). To prove the RHDV identity of the smaller virions, their reactivity with RHDV specific antibodies was investigated by immunoblots of the virion protein and by immunoelectron microscopy. Proteolytic digestion of RHDV particles with alpha-chymotrypsin did not transform RHDV into the smaller form. We assume that these core-like particles (CLPs) are not a result of proteolytic digestion but arise from a truncated RHDV genome or defective expression.

Viral infections of the feline urinary tract

The exact cause of hematuria, dysuria, and urethral obstruction remains unknown in a large percentage of naturally occurring cases of feline lower urinary tract disease (FLUTD). One attractive hypothesis implicates viruses as the cause of some idiopathic forms of FLUTD; supporting this hypothesis is the fact that a gamma herpesvirus, a calicivirus, and a retrovirus have been isolated from urine and tissues obtained from cats with this type of disease. Although the clinical course and laboratory findings of cats with idiopathic FLUTD are suggestive of an infectious cause, the question of whether viruses have a pathologic role in some forms of naturally acquired FLUTDs has not been completely answered.

Study on occurrence of human calicivirus (Mexico strain) as cause of sporadic cases and outbreaks of calicivirus-associated diarrhoea in the United Kingdom, 1983-1995

The use of a recently developed EIA using antisera raised against purified baculovirus expressed recombinant Mexico virus (rMx) capsid protein is described for screening for human calicivirus in stools. The results show that MX-like viruses have been circulating in the UK periodically since 1983 and were an occasional cause of sporadic cases of diarrhoea in infants and outbreaks of infection among elderly patients in hospitals and old people's homes. Further evidence is presented that some strains of caliciviruses with characteristic surface morphology (HuCVs) and some with an indistinct appearance, small round structured viruses (SRSVs) are antigenically related to MxV. Tests on SRSVs from four unrelated outbreaks typed as UK3 failed to react in the Mx EIA or recombinant Norwalk virus (rNV) EIA. A 2-month survey of 206 children treated in two London hospitals for diarrhoea showed that only one was positive for MxV, a child known to be infected with HIV-1. None of the samples reacted in the rNV EIA.

Mechanisms for persistence of acute and chronic feline calicivirus infections in the face of vaccination

The study was concerned with possible reasons for the persistence of both acute and chronic feline calicivirus (FCV)-induced disease and sustained oral carriage in the field in the face of routine FCV immunization. It was concluded from this study that: 1) the original FCV-F9 strain, which is the basis of most live vaccines, still generates cross-reactive antibodies against almost all field strains in California, 2) vaccine strains derived from FCV-F9 may not be as broadly cross-protective as the parent strain, 3) whole inactivated FCV-2280 vaccine evokes high virus neutralizing antibody titers with an equally broad spectrum of cross-reactivity as FCV-F9, 4) all vaccine strains of FCV cause acute disease signs and protracted oral shedding when administered orally, 5) strains isolated from the mouth five to ten weeks following oral inoculation can differ from parental virus, usually appearing more vaccine resistant, 6) cats previously infected with field or vaccine strains develop much less severe acute illness when subsequently infected with heterologous FCV strains but are not protected against the chronic carrier state. Therefore, the persistence of FCV in the field cannot be explained solely by the emergence of vaccine resistant strains and vaccine virus itself may contribute to both acute and chronic infection and disease.

Self-assembly, antigenicity, and immunogenicity of the rabbit haemorrhagic disease virus (Czechoslovakian strain V-351) capsid protein expressed in baculovirus

Rabbit haemorrhagic disease virus (RHDV) capsid protein was expressed in a baculovirus system. Analysis of the expressed product showed that the recombinant protein, which is 60 kDa in size, was antigenic as revealed by its reactions in ELISA and Western blot with the antibodies raised against RHDV. Direct electron microscopy of the cell culture supernatant and the purified protein demonstrated that the capsid protein expressed in insect cells self-assembled to form empty virus-like particles (VLP) which are similar in size and morphology to that of native virus. These particles were immunoreactive with polyclonal anti-RHDV antibodies and with four monoclonal antibodies which recognise conformational epitopes of the virus. The results indicated that the VLPs were morphologically and antigenically indistinguishable from native virus. The recombinant VLPs induced high levels of RHDV-specific antibodies in rabbits and mice following immunisation. The immune response to the VLPs protected the rabbits following challenge with the virulent RHDV. In haemagglutination assays, the VLPs bound to human red blood cells similar to the native virus particles. The recombinant protein and or VLPs is suitable for the development of a rapid, sensitive and reliable test for detection of antibodies to RHDV and for use as a vaccine for domestic rabbits.

Carrier-state infection of feline T-lymphoblastoid cells with feline calicivirus

The susceptibility of feline T lymphocytes to feline calicivirus (FCV) in vitro was investigated using feline T-lymphoblastoid cell lines, namely MYA-1 and FL74 cells. The virus titers of supernatants in FCV-infected MYA-1 and FL74 cell cultures increased rapidly, and FCV antigens were also detected in the FCV-infected cells. There were slight differences in the molecular weights of capsid proteins expressed in FCV-infected MYA-1, FL74 and Crandell feline kidney cells. MYA-1 and FL74 cells were productively and persistently infected with FCV, and FCV antigens were observed in the FCV-infected cells for more than one month. At 3 months post infection, FCV-infected FL74 cells that stopped producing infectious FCV could be reinfected with FCV. However, no cytopathic effects were observed.

The role of uropathogens in feline lower urinary tract disease. Clinical implications

Bacterial, fungal, and parasitic uropathogens have small but significant roles as causative agents in naturally occurring feline lower urinary tract disease. However, the exact cause of hematuria, dysuria, and/or urethral obstruction remains unknown in a large percentage of cats. Feline calicivirus, feline syncytia-forming virus, bovine herpesvirus-4, mycoplasmas, and ureaplasmas are potential uropathogens whose etiopathogenic roles in idiopathic feline lower urinary tract disease remain, as of yet, unresolved.

Detection of rabbit haemorrhagic disease virus particles in the rabbit liver tissues

Liver tissues from rabbits experimentally infected with rabbit haemorrhagic disease virus (RHDV) were studied electron microscopically. The earliest change in hepatocytes of the rabbits infected with RHDV was hydropic degeneration. Rough endoplasmic reticulum was dilated with a mild increase in polysomes and cytoplasmic cisternae in degenerated hepatocytes. Characteristic cytopathological changes of necrotic hepatocytes included shrinkage of the cell body, formation of cytoplasmic vesicles, vacuoles or cisternae and karyolysis. A large number of viral particles resembling a calicivirus in size and morphology was demonstrated in the cytoplasm of many necrotic hepatocytes. The particles had accumulated mainly in the membrane-bound cisternae or scattered around the membrane-bound vacuoles of the necrotic hepatocytes. Western blot analysis demonstrated that RHDV antigen was present in the infected hepatocytes. RHDV particles were also detected by immunoelectron microscopy. Replicating patterns of RHDV particles and subsequent cytopathology resembled those in other calicivirus infections.

Some physicochemical properties of the virus of rabbit haemorrhagic disease

Purified and concentrated preparations of virus from liver extracts of infected rabbits contain virus specific components with sedimentation coefficients of about 175, 110 and sometimes 133S and more slow units. Full and empty virus particles with a diameter of about 34 nm were shown electron microscopically in the corresponding 175 and 110S fractions of the sucrose density gradient. The average of buoyant density of the 175, 133, 110S and more slow units are 1.36, 1.32 and 1.31 g/ml respectively. The extinction coefficient E260 nm is 4.3 +/- 0.7 cm2/mg. The RNA content is 17 +/- 4%. SDS-PAGE shows a "65" kD protein as a single or major component. Beside smaller polypeptides with lower intensities, the 67 kD polypeptide reacts positively in the Western blot with polyclonal antibodies of rabbits. The molecular weight of the virus is 15 +/- 4 x 10(6)D. The pH stability of the 175S unit was also tested.

Different stabilities to bile among feline calicivirus strains of respiratory and enteric origin

Feline calicivirus (FCV) strains isolated from feces (E-FCV) were compared with FCV strains of respiratory origin (R-FCV). All strains were shown to be labile at pH 3.0. All strains except one strain of E-FCV were found to be sensitive to the action of trypsin. When exposed to bile salt (deoxycholic acid sodium salt), all R-FCV strains were markedly inactivated, but none of the E-FCV strains was inactivated. It was possible to select bile-resistant substrains from a bile-sensitive strain.

Detection of rabbit haemorrhagic disease virus antigen in tissues by immunohistochemistry

Formalin fixed liver, spleen, kidney, heart, lung, duodenum and appendix tissues from nine rabbits, experimentally infected with rabbit haemorrhagic disease virus (RHDV), were investigated for evidence of RHDV antigen by the direct avidin-biotin peroxidase complex immunohistochemical method. In all the rabbits examined, RHDV antigen was detected in degenerative and necrotic hepatocytes of the liver tissues. The area involved coincided with histopathological lesions on serial liver sections. The RHDV antigen was expressed in the cytoplasm of the hepatocytes, suggesting that RHDV replicated in these cells. RHDV antigen was also detected in the spleen. The results of immunohistochemistry were supported by the demonstration of RHDV protein by Western blot analysis and of RHDV particles by protein A-gold immunoelectron microscopy in the liver homogenate from all the rabbits that were examined.

Serial propagation of porcine enteric calicivirus in a continuous cell line. Effect of medium supplementation with intestinal contents or enzymes

A porcine enteric calicivirus (PEC) was adapted to serial propagation in a continuous porcine kidney cell line (LLC-PK) by inclusion of an intestinal contents preparation (ICP), derived from uninfected gnotobiotic pigs, in the maintenance medium. Infected cells were detected by immunofluorescent staining of cell monolayers. Attempts to propagate PEC in the presence of various intestinal enzymes of porcine origin, bacterial protease, bovine ICP, avian ICP or without medium supplementation were unsuccessful.

Electron and immunoelectron microscopy of rabbit haemorrhagic disease virus (RHDV)

Rabbit haemorrhagic disease virus (RHDV) had a calicivirus-like structure and a diameter of 31.5-33.0 nm. Antigenic relationship between the investigated RHDV strain and the causal agent of RHD in China was demonstrated by immunoelectron microscopy.

Purification and characterization of a calicivirus as the causative agent of a lethal hemorrhagic disease in rabbits

The causative viral agent of a lethal rabbit hemorrhagic disease has been purified and characterized. In negative-stained preparations, the virions were icosahedral, measured 27 to 35 nm in diameter, were without an envelope, and showed 10 peripheral cup-shaped depressions. The major structural protein was 60 kilodaltons, which constitutes a unique characteristic of the Caliciviridae.

Biochemical characterization of porcine enteric calicivirus: analysis of structural and nonstructural viral proteins

In this report, the molecular weight and antigenicity of the proteins of a porcine enteric calicivirus (PEC) were characterized. The PEC virions were purified from intestinal contents of infected pigs and from infected cell culture lysates. The average buoyant density of the purified virus was 1.37 gm/cm3 in cesium chloride. One major structural protein with a molecular weight of approximately 58 k was found in the gut and cell culture-passaged PEC using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Using immunoblotting techniques only one immunoreactive protein (58 k) ws identified. The PEC and a prototype calicivirus, feline calicivirus (FCV) were propagated in pig kidney and feline kidney (Crandell) cell lines, respectively and intrinsically labeled using [35S]methionine at various times post-inoculation (PI). SDS-PAGE of the radiolabeled proteins indicated the presence of the major structural protein (58 k) and one probable nonstructural protein (28 k) synthesized in the PEC-infected cell lysates by 12 h PI. Other minor protein bands were also evident by 24 h PI (32 k and 82 k). Only the 58 k major protein was detected by radioimmunoprecipitation (RIP) analysis using hyperimmune anti-PEC serum. SDS-PAGE and RIP analysis of FCV-infected cell lysates using hyperimmune anti-FCV serum identified a single major protein of approximately 64 k. No antigenic relationship between PEC and FCV proteins was detected by RIP analysis. The single major structural protein of PEC, the morphological appearance and size of the virus, and its average density of 1.37 gm/cm3 in cesium chloride are consistent with properties of other members of the family Caliciviridae.

Serial propagation of porcine enteric calicivirus-like virus in primary porcine kidney cell cultures

A porcine enteric calicivirus-like virus was adapted to serial propagation in primary porcine kidney cell cultures. Attempts to propagate this virus in primary porcine kidney cells in the presence of trypsin or pancreatin or without medium supplementation were unsuccessful. A low-pH medium (pH 6.8) was also ineffective in virus propagation. Successful serial propagation of the virus required the presence of an intestinal-content preparation, derived from uninfected gnotobiotic pigs, in the cell culture medium. The best results were obtained with six-well plate cultures which were centrifuged after virus inoculation. Infected cells were detected by immunofluorescent staining of cell monolayers or detached cells which were harvested by centrifugation. Infected cells were first detected at passage 4 (1% infected cells), and infectivity increased with successive passages, with as many as 80% of the cells infected by passage 16. Extensive cytopathic effects were observed in inoculated cell cultures, but not in uninoculated control cell cultures, at each passage level after passage 13. The infected cells became separated, rounded, and detached, forming holes in the cell monolayer. Only virus particles exhibiting the six-pointed star appearance or stain-filled, cup-shaped depressions characteristic of caliciviruses were detected in inoculated cell culture supernatants by immune electron microscopy. Attempts to determine the titer of the virus by a cell culture immunofluorescence assay or plaque assay were unsuccessful.

Virus and virus-like particles in the faeces of cats with and without diarrhoea

Negative staining electron microscopy was used to identify viruses in 166 normal and 62 diarrhoeal faecal samples from 208 cats admitted to an animal shelter during a 16-month period (March 1984 to June 1985). On the basis of size and shape 7 distinct viral types were detected: 24 nm parvovirus-like particles, 30 nm astrovirus, 30 nm picornavirus-like particles, reovirus, rotavirus, coronavirus and a 75 nm "togavirus-like" particle. The incidence of these particles in the 208 cats was 11%, 7%, 6%, 0.4%, 5%, 1% and 1% respectively. Virus isolation studies using 40 of the faecal samples succeeded in isolating reovirus 1 in 2 cases. Immune electron microscope studies demonstrated the presence of antibody in a human serum to cat astrovirus, but failed to clarify the identity of the parvovirus-like particles and picornavirus-like particles, other than showing that some of the parvovirus-like particles were not related to feline panleukopenia virus. It was found that parvovirus-like particles, astrovirus, picornavirus-like particles, reovirus and rotavirus could be excreted by cats with normal faeces as well as cats with diarrhoeal faeces. Parvovirus-like particles, astrovirus, picornavirus-like particles and rotavirus could be excreted in high concentration in normal faeces. There was no simple relationship between age and diarrhoea in the population of cats studied. Age was not a critical factor in the excretion of parvovirus-like particles, astrovirus, picornavirus-like particles and rotavirus. The incidence of diarrhoea was not clearly associated with the seasons.

Variable sensitivity of a feline embryo cell line and of three kitten kidney cell cultures to feline herpes- and caliciviruses

The number of plaques produced in a feline embryo (FEmb) cell line and in three independently derived kitten kidney (KK) cell cultures varied in a consistent and reproducible manner when each was inoculated with the same number of feline herpesvirus 1 (FHV1) plaque forming units (PFU); the three KK cells produced 2-9 times more plaques than FEmb cells. One of the three KK cells produced FHV1 plaques that were smaller in diameter than those FEmb cells. Each of the three KK cell cultures inoculated with the same number of FEmb cell PFU of a strain of feline calicivirus (FCV) produced different numbers of plaques; two of the three KK cell cultures produced 2-3 times more plaques than FEmb cells. The plaque diameter of FCV in the three KK cells was 30-50% smaller than the plaque diameter in FEmb cells.

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?

An outbreak of calicivirus associated gastroenteritis in an elderly persons home. A possible zoonosis?

An outbreak of gastroenteritis caused by calicivirus began amongst residents and staff of an old persons home 24 hours after the proprietor's dog had been sick. Serological evidence suggests that the calicivirus isolated from one of the cases may be capable of infecting dogs as well as man. The virus strain responsible for this outbreak differs antigenically from those associated with two other outbreaks in the U.K. and one in Japan. The characteristic morphology of calicivirus is lost if stool is stored at -70 degrees C.

Characterization of a calici-like virus (Newbury agent) found in association with astrovirus in bovine diarrhea

A bovine calici-like virus and astrovirus, present in the same fecal sample from an outbreak of diarrhea, were separated from each other by calf passage. The calici-like virus (Newbury agent SRV-1) caused anorexia, diarrhea, and xylose malabsorption in gnotobiotic calves aged 17 to 60 days, whereas the bovine astrovirus was nonpathogenic in similar calves. The calici-like virus was shown to be antigenically distinct from a previously described isolate (Newbury agent SRV-2) by two-way cross-protection experiments in calves; calves immune to homologous challenge became clinically ill and excreted virus when challenged with the heterologous virus.

Ultrastructure of newly recognized caliciviruses of the dog and mink

Two recently recognized viruses obtained from a dog with glossitis and from mink with hemorrhagic pneumonia were characterized by electron microscopy. The results of the negative-stained preparations indicated that the viruses were structurally compatible with the calicivirus group.

The pathogenesis of vesicular exanthema of swine virus and San Miguel sea lion virus in swine

Vesicular exanthema of swine virus type A48 or San Miguel sea lion virus type 2, when inoculated intradermally into swine, resulted in fluid-filled vesicles at the sites of inoculation in the snout, coronary band, and tongue. Pigs that developed vesicles also had fevers. Secondary vesicle formation varied, depending on virus serotype. Viremia was found in one pig infected with San Miguel sea lion virus five days after infection. Virus was recovered from nasal-oral passages for up to five days after infection in both groups of pigs and from the gastrointestinal and urinary tracts of pigs infected with San Miguel sea lion virus. Neutralizing antibodies began to increase three days after inoculation and reached peak titers in seven to ten days. In the absence of secondary bacterial infection, healing was well advanced by ten days after inoculation. Lesions usually were limited to nonhaired portions of the integument and tongue. Individual epithelial cells became infected when a break in the skin allowed virus access to susceptible epithelial cells from either exogenous or endogenous sources. Individual infected cells ruptured and adjacent cells were infected, resulting in the formation of multiple microvesicles. Centrifugal coalescence of microvesicles led to formation of grossly visible macrovesicles. Lesions rarely developed from viral contamination of intact hair follicles. A mild virus-induced encephalitis was seen in pigs infected with vesicular exanthema of swine virus, and virus was recovered from brain tissue of pigs infected with San Miguel sea lion virus.

Prevalence of antibody to human calicivirus in general population of northern Japan

Serum specimens from children and adults living in Saporo, Japan, were tested for antibody against human calicivirus by immune electron microscopy (IEM), using virus-rich faecal extracts as the source of antigen. Of 83 serum specimens tested, 49 (59%) were positive for calicivirus antibody. Age-related prevalence of antibody to calicivirus was as follows: 23% (3/13) in the 0-5-month-old group, 30% (6/20) in the 6-23-month-old group, 65% (13/20) in the 2-5-year-old group, and 90% in school children (18/20) and adults (9/10). As for IEM antibody ratings scored from 0 to 4, almost all positive sera from older infants and preschool children scored 3 to 4. Antibody scores were rather more scattered in school children. The results indicated that caliciviral infection is prevalent in younger children in this part of Japan.

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.

An outbreak of gastroenteritis associated with calicivirus in an infant home

In October 1977 an outbreak of acute infectious diarrhea occurred in an infant home in the city of Sapporo, Japan. Of 34 residents aged two to 20 months, 26 (77%) suffered from diarrhea. In ten of these patients the diarrhea was accompanied by vomiting. Electron microscopic examinations revealed typical calicivirus particles in eight faecal specimens, seven of which were from the group of 26 affected patients (28%) and one of which was from the group of eight infants without symptoms (13%). Immune electron microscopy tests for antibody responses against one of the isolated strains of calicivirus were carried out on 27 paired pre- and post-outbreak sera. Seroconversions were demonstrated in 18 of 19 (95%) affected infants and in six of eight (75%) unaffected infants. One patient with lack of antibody response was the youngest child--two months old. Periodic surveys on enteric viruses circulating in the home revealed that calicivirus was specifically associated with the outbreak of gastroenteritis. These observations provide further evidence for the causative role of calicivirus in acute gastroenteritis in children.