Anticipating the species jump: surveillance for emerging viral threats

Zoonotic disease surveillance is typically triggered after animal pathogens have already infected humans. Are there ways to identify high‐risk viruses before they emerge in humans? If so, then how and where can identifications be made and by what methods? These were the fundamental questions driving a workshop to examine the future of predictive surveillance for viruses that might jump from animals to infect humans. Virologists, ecologists and computational biologists from academia, federal government and non‐governmental organizations discussed opportunities as well as obstacles to the prediction of species jumps using genetic and ecological data from viruses and their hosts, vectors and reservoirs. This workshop marked an important first step towards envisioning both scientific and organizational frameworks for this future capability. Canine parvoviruses as well as seasonal H3N2 and pandemic H1N1 influenza viruses are discussed as exemplars that suggest what to look for in anticipating species jumps. To answer the question of where to look, prospects for discovering emerging viruses among wildlife, bats, rodents, arthropod vectors and occupationally exposed humans are discussed. Finally, opportunities and obstacles are identified and accompanied by suggestions for how to look for species jumps. Taken together, these findings constitute the beginnings of a conceptual framework for achieving a virus surveillance capability that could predict future species jumps.

Bovine leukaemia virus infection in New Zealand cattle

Bovine Leukaemia Virus (BLV) infection in New Zealand cattle was investigated. In a national survey of 5000 sera from 500 herds, BLV antibody was not detected. An additional 1062 sera from 140 herds were tested and 3 sera were positive. In the herd of origin of one of these 3 sera, 22.6% of cattle were serologically positive for BLV. Where cases of bovine lymphosarcoma had been diagnosed, 38 of 39 herds tested were negative for BLV antibody. Within the remaining herd, 36% of cows tested were serologically-positive. BLV was isolated from 2 serologically positive cows in this herd.

Gastroparesis and functional dyspepsia: excerpts from the AGA/ANMS meeting

BACKGROUND

Despite the relatively high prevalence of gastroparesis and functional dyspepsia, the aetiology and pathophysiology of these disorders remain incompletely understood. Similarly, the diagnostic and treatment options for these two disorders are relatively limited despite recent advances in our understanding of both disorders.

PURPOSE

This manuscript reviews the advances in the understanding of the epidemiology, pathophysiology, diagnosis, and treatment of gastroparesis and functional dyspepsia as discussed at a recent conference sponsored by the American Gastroenterological Association (AGA) and the American Neurogastroenterology and Motility Society (ANMS). Particular focus is placed on discussing unmet needs and areas for future research.

Treatment of gastroparesis: a multidisciplinary clinical review

This clinical review on the treatment of patients with gastroparesis is a consensus document developed by the American Motility Society Task Force on Gastroparesis. It is a multidisciplinary effort with input from gastroenterologists and other specialists who are involved in the care of patients with gastroparesis. To provide practical guidelines for treatment, this document covers results of published research studies in the literature and areas developed by consensus agreement where clinical research trials remain lacking in the field of gastroparesis.

Flow cytometric characterization of perfused human bone marrow cultures: identification of the major cell lineages and correlation with the CFU-GM assay

BACKGROUND

Prolific cultures of human bone marrow mononuclear cells (BM MNCs) were recently developed that include a full spectrum of hematopoietic and accessory cells, with the presence of autofluorescent cells indicating adequate cell expansion. However, phenotypic and functional clonogenic characterizations of the autofluorescent cells and the various other subpopulations present in these cultures have not been carried out.

METHODS

Cells from a continuously perfused bioreactor inoculated with BM MNCs and cultured for 12 days in serum-containing medium with PIXY321, erythropoietin, and with or without FLT3-L were evaluated by using flow cytometry.

RESULTS

Two antibodies, CD71 and CD13, allowed the separation of the autofluorescent cells into two distinct populations. The CD71+CD13++ autofluorescent population contained the colony-forming unit (CFU) fibroblast, and the CD71++CD13++ autofluorescent population contained macrophage/dendritic like cells. The CFU-granulocyte/macrophage (CFU-GM) could not be thoroughly evaluated with CD71 and CD13. However, the number of CD13+/++Lin- cells correlated with the number of CFU-GM (r = 0.83), with approximately 1 CFU-GM for every 30 CD13+/++Lin- cells.

CONCLUSIONS

The data showed that CD71 and CD13 antibodies separate the autofluorescent cells into two populations but do not separate hematopoietic cells into specific phenotypic populations. The data also showed that the number of CD13+/++Lin- cells correlated with the number of CFU-GM. These data present the initial step toward detailed phenotypic analysis of ex vivo expanded human BM MNC cultures.

Parvovirus infections in wild carnivores

Various parvoviruses infect carnivores and can cause disease. In this review article the knowledge about infections of free-ranging or captive carnivores with the feline parvoviruses, feline panleukopenia virus, and canine parvovirus, including the antigenic types CPV-2a and -2b, as well as Aleutian disease of mink virus and minute virus of canines are summarized. Particular emphasis is placed on description of the evolution of canine parvovirus which apparently involved wild carnivore hosts.

Canine and feline parvoviruses can use human or feline transferrin receptors to bind, enter, and infect cells

Canine parvovirus (CPV) enters and infects cells by a dynamin-dependent, clathrin-mediated endocytic pathway, and viral capsids colocalize with transferrin in perinuclear vesicles of cells shortly after entry (J. S. L. Parker and C. R. Parrish, J. Virol. 74:1919-1930, 2000). Here we report that CPV and feline panleukopenia virus (FPV), a closely related parvovirus, bind to the human and feline transferrin receptors (TfRs) and use these receptors to enter and infect cells. Capsids did not detectably bind or enter quail QT35 cells or a Chinese hamster ovary (CHO) cell-derived cell line that lacks any TfR (TRVb cells). However, capsids bound and were endocytosed into QT35 cells and CHO-derived TRVb-1 cells that expressed the human TfR. TRVb-1 cells or TRVb cells transiently expressing the feline TfR were susceptible to infection by CPV and FPV, but the parental TRVb cells were not. We screened a panel of feline-mouse hybrid cells for susceptibility to FPV infection and found that only those cells that possessed feline chromosome C2 were susceptible. The feline TfR gene (TRFC) also mapped to feline chromosome C2. These data indicate that cell susceptibility for these viruses is determined by the TfR.

Canine parvovirus capsid assembly and differences in mammalian and insect cells

We examined the assembly processes of the capsid proteins of canine parvovirus (CPV) in mammalian and insect cells. In CPV-infected cells empty capsids assembled within 15 min, and then continued to form over the following 1 h, while full (DNA-containing) capsids were detected only after 60 min, and those accumulated slowly over several hours. In cells expressing VP1 and VP2 or only VP2, empty capsid formation was also efficient, but was slightly slower than that in infected cells. Small amounts of trimer forms of VP2 were detected in cells expressing wild type capsid proteins, but were not seen for mutants containing changes that prevented capsid assembly. CPV capsids accumulated in the cell nucleus, but mutant VP1 and VP2 proteins that did not assemble became distributed throughout the nucleus and the cytoplasm, irrespective of whether they were expressed as VP1 and VP2, or as VP2 only. Urea or pH treatment of empty capsids released dimer, trimer, or pentamer capsid protein combinations, while treatment of full capsids consistently released trimer and, in some cases, pentamer forms. When wild type or assembly-defective VP2 genes were expressed from recombinant baculoviruses in insect cells, most of the protein was recovered as noncapsid aggregates, and only a small proportion assembled into capsids. Both the assembled capsids and the noncapsid aggregates were seen primarily in the cytoplasm of the insect cells. The VP2 expressed in insect cells that was recovered in aggregates had an isoelectric point of about pH 6.3, while that recovered from assembled capsids had a pI of about 5.2, similar to that seen for the VP2 of capsids recovered from mammalian cells.

Host range and variability of calcium binding by surface loops in the capsids of canine and feline parvoviruses

Canine parvovirus (CPV) emerged in 1978 as a host range variant of feline panleukopenia virus (FPV). This change of host was mediated by the mutation of five residues on the surface of the capsid. CPV and FPV enter cells by endocytosis and can be taken up by many non-permissive cell lines, showing that their host range and tissue specificity are largely determined by events occurring after cell entry. We have determined the structures of a variety of strains of CPV and FPV at various pH values and in the presence or absence of Ca(2+). The largest structural difference was found to occur in a flexible surface loop, consisting of residues 359 to 375 of the capsid protein. This loop binds a divalent calcium ion in FPV and is adjacent to a double Ca(2+)-binding site, both in CPV and FPV. Residues within the loop and those associated with the double Ca(2+)-binding site were found to be essential for virus infectivity. The residues involved in the double Ca(2+)-binding site are conserved only in FPV and CPV. Our results show that the loop conformation and the associated Ca(2+)-binding are influenced by the Ca(2+) concentration, as well as pH. These changes are correlated with the ability of the virus to hemagglutinate erythrocytes. The co-localization of hemagglutinating activity and host range determinants on the virus surface implies that these properties may be functionally linked. We speculate that the flexible loop and surrounding regions are involved in binding an as yet unidentified host molecule and that this interaction influences host range.

Cytoplasmic trafficking of the canine parvovirus capsid and its role in infection and nuclear transport

To begin a successful infection, viruses must first cross the host cell plasma membrane, either by direct fusion with the membrane or by receptor-mediated endocytosis. After release into the cytoplasm those viruses that replicate in the nucleus must target their genome to that location. We examined the role of cytoplasmic transport of the canine parvovirus (CPV) capsid in productive infection by microinjecting two antibodies that recognize the intact CPV capsid into the cytoplasm of cells and also by using intracellular expression of variable domains of a neutralizing antibody fused to green fluorescence protein. The two antibodies tested and the expressed scFv all efficiently blocked virus infection, probably by binding to virus particles while they were in the cytoplasm and before entering the nucleus. The injected antibodies were able to block most infections even when injected 8 h after virus inoculation. In control studies, microinjected capsid antibodies did not interfere with CPV replication when they were coinjected with an infectious plasmid clone of CPV. Cytoplasmically injected full and empty capsids were able to move through the cytosol towards the nuclear membrane in a process that could be blocked by nocodazole treatment of the cells. Nuclear transport of the capsids was slow, with significant amounts being found in the nucleus only 3 to 6 h after injection.

Comparison of two single-chain antibodies that neutralize canine parvovirus: analysis of an antibody-combining site and mechanisms of neutralization

We cloned the heavy- and light-chain variable domains of two monoclonal antibodies that recognize each of the two major neutralizing antigenic sites of the canine parvovirus (CPV) capsid. After expression in Escherichia coli as single-chain variable domains (scFv) with glycine-serine linker sequences, both scFv bound CPV capsids with the same specificity as the intact IgG, but with 10- to 20-fold lower avidity. Both scFvs neutralized CPV infectivity with efficiency similar to that of the IgG. Although both IgGs inhibited hemagglutination by CPV, only one scFv was inhibiting. The binding of one of the antibodies has previously been analyzed by cryoelectron microscopic reconstruction and the epitope-binding residues predicted. Mutagenesis of predicted contact residues in three heavy-chain complementarity-determining regions (CDR) showed that mutants of CDR1 or CDR3 reduced the binding of the scFv by about 10-fold compared with the wild-type scFv, while no effect was seen for one mutant of CDR2. The levels of neutralization of CPV and of hemagglutination inhibition by the scFv mutants were proportional to their reduction in binding affinity compared with the wild type. Neither scFv blocked virus binding to host cells, but they both caused aggregation of the capsids and appeared to affect the process of infection after virus uptake into the cells.

Cellular uptake and infection by canine parvovirus involves rapid dynamin-regulated clathrin-mediated endocytosis, followed by slower intracellular trafficking

Canine parvovirus (CPV) is a small, nonenveloped virus that is a host range variant of a virus which infected cats and changes in the capsid protein control the ability of the virus to infect canine cells. We used a variety of approaches to define the early stages of cell entry by CPV. Electron microscopy showed that virus particles concentrated within clathrin-coated pits and vesicles early in the uptake process and that the infecting particles were rapidly removed from the cell surface. Overexpression of a dominant interfering mutant of dynamin in the cells altered the trafficking of capsid-containing vesicles. There was a 40% decrease in the number of CPV-infected cells in mutant dynamin-expressing cells, as well as a approximately 40% decrease in the number of cells in S phase of the cell cycle, which is required for virus replication. However, there was also up to 10-fold more binding of CPV to the surface of mutant dynamin-expressing cells than there was to uninduced cells, suggesting an increased receptor retention on the cell surface. In contrast, there was little difference in virus binding, virus infection rate, or cell cycle distribution between induced and uninduced cells expressing wild-type dynamin. CPV particles colocalized with transferrin in perinuclear endosomes but not with fluorescein isothiocyanate-dextran, a marker for fluid-phase endocytosis. Cells treated with nanomolar concentrations of bafilomycin A1 were largely resistant to infection when the drug was added either 30 min before or 90 min after inoculation, suggesting that there was a lag between virus entering the cell by clathrin-mediated endocytosis and escape of the virus from the endosome. High concentrations of CPV particles did not permeabilize canine A72 or mink lung cells to alpha-sarcin, but canine adenovirus type 1 particles permeabilized both cell lines. These data suggest that the CPV entry and infection pathway is complex and involves multiple vesicular components.

Early stages of influenza virus entry into Mv-1 lung cells: involvement of dynamin

Viruses generally have one of two mechanisms for entry and uncoating. They can enter the cell either by endocytosis or by direct fusion at the plasma membrane. We have established a novel mink lung (Mv-1) cell line that expresses a dominant-interfering form of dynamin-1 (K44A) under the control of a tetracycline-responsive element and studied the early events in influenza infection using these cells. We found that influenza virus binds equally to both induced and uninduced cells, but in K44A-expressing cells, electron microscopy showed viruses trapped in deep coated pits and irregular-shaped tubular structures that contain discrete coated regions. We also show by immunofluorescence and confocal microscopy that entry of incoming virus into the nucleus is blocked in K44A-expressing cells. Virus replication was assayed by immunofluorescence microscopy and was strongly inhibited at both early and late times postinfection in K44A-expressing cells. Virus infectivity was inhibited by approximately 2 log units in cells expressing K44A dynamin when analyzed by influenza plaque assay. Overall these data show that dynamin is required for efficient influenza virus entry, presumably due to its function in release of vesicles from coated pits.

Feline calicivirus capsid protein expression and self-assembly in cultured feline cells

Feline calicivirus (FCV) capsid protein was expressed in feline cells employing the vaccinia virus MVA/T7 RNA polymerase system. The precursor protein was processed to a mature size protein that assembled to virus like particles (VLPs).

A heterogeneous nuclear ribonucleoprotein A/B-related protein binds to single-stranded DNA near the 5' end or within the genome of feline parvovirus and can modify virus replication

Phage display of cDNA clones prepared from feline cells was used to identify host cell proteins that bound to DNA-containing feline panleukopenia virus (FPV) capsids but not to empty capsids. One gene found in several clones encoded a heterogeneous nuclear ribonucleoprotein (hnRNP)-related protein (DBP40) that was very similar in sequence to the A/B-type hnRNP proteins. DBP40 bound specifically to oligonucleotides representing a sequence near the 5' end of the genome which is exposed on the outside of the full capsid but did not bind most other terminal sequences. Adding purified DBP40 to an in vitro fill-in reaction using viral DNA as a template inhibited the production of the second strand after nucleotide (nt) 289 but prior to nt 469. DBP40 bound to various regions of the viral genome, including a region between nt 295 and 330 of the viral genome which has been associated with transcriptional attenuation of the parvovirus minute virus of mice, which is mediated by a stem-loop structure of the DNA and cellular proteins. Overexpression of the protein in feline cells from a plasmid vector made them largely resistant to FPV infection. Mutagenesis of the protein binding site within the 5' end viral genome did not affect replication of the virus.

Host range relationships and the evolution of canine parvovirus

Canine parvovirus (CPV) is an example of an unusual class of emerging virus-those that gain an altered host range through genetic variation and subsequently become widespread pathogens of their new and previously resistant host species. CPV was first detected in 1978 as the cause of new diseases in dogs throughout the world, when it rapidly spread throughout domestic populations, as well as becoming widespread in wild dogs. CPV was soon shown to be a variant of the long recognized feline panleukopenia virus (FPV), from which it differed in less than 1% at the nucleotide sequence level. Genetic analysis showed that virtually all of the biological differences between CPV and FPV, including the canine host range, were determined by three or four sequence differences in the viral capsid protein gene. Analysis of the atomic structures of the CPV and FPV capsids showed that the differences controlling host range were located within two different structural regions and were exposed on the capsid surface. The CPV which first emerged in 1978 appeared to be derived from a single ancestral sequence, which has allowed the ready analysis of the subsequent evolution of the virus in nature. Sequence analysis has also revealed that CPV strains have undergone a series of evolutionary selections in nature which have resulted in the global distribution of new virus variants. This was first seen in the global replacement between 1979 and 1981 of the original (1978) strain of the virus by a genetically and antigenically variant strain, and the subsequent widespread selection of other variants which have also become globally distributed. The genetic and antigenic variation in the virus strains was also correlated with changes in the host range of the virus, in particular in the ability to replicate in cats, and in canine host range differences seen in tissue culture cells.

Nutrition support for the mechanically ventilated patient

Nutrition support is a hotly debated topic in most intensive care units. Is enteral nutrition or TPN best? Is gastric or small-bowel feeding safer? Are specialized formulas needed? These are only some of the issues, and the fact remains that there is a paucity of clear, solid data. Folklore has become the standard of practice in many areas of medicine; it is richly found in nutrition support. We must be careful not to get caught up in the trappings of our beliefs about nutrition support. Instead, we must continue to evaluate our own practices and fine-tune our skills of clinical assessment and common sense.

Nutrition support for the mechanically ventilated patient

Nutrition support is a hotly debated topic in most intensive care units. Is enteral nutrition or TPN best? Is gastric or small-bowel feeding safer? Are specialized formulas needed? These are only some of the issues, and the fact remains that there is a paucity of clear, solid data. Folklore has become the standard of practice in many areas of medicine; it is richly found in nutrition support. We must be careful not to get caught up in the trappings of our beliefs about nutrition support. Instead, we must continue to evaluate our own practices and fine-tune our skills of clinical assessment and common sense.

Feline calicivirus capsid protein expression and capsid assembly in cultured feline cells

The capsid protein of feline calicivirus (FCV) was expressed by using plasmids containing cytomegalovirus, simian virus 40, or T7 promoters. The strongest expression was achieved with the T7 promoter and coinfection with vaccinia virus expressing the T7 RNA polymerase (MVA/T7pol). The FCV precursor capsid protein was processed to the mature-size protein, and these proteins were assembled in to virus-like particles.

Antigenic and genetic analysis of canine parvoviruses in southern Africa

Canine parvovirus (CPV) is a significant pathogen of domestic and free-ranging carnivores all over the world. It suddenly appeared at the end of the 1970s and most likely emerged as a variant of the well known feline panleukopenia virus (FPV). During its adaptation to the new host, the domestic-dog, the virus has changed its antigenic profile twice giving rise to two new antigenic types, CPV-2a and CPV-2b. These new types have replaced the original type CPV-2 in the United States of America, Europe and Japan. However, no data about the prevalence of the new antigenic types on the African continent are available. In this study, 128 recent parvovirus isolates from South Africa and Namibia were antigenically typed with type-specific monoclonal antibodies. No original CPV-2 viruses were found and its complete replacement by the new antigenic types conforms to the situation in other parts of the world. The predominant strain found in southern Africa was CPV-2b (66%), which differs from the situation in Europe and Japan where CPV-2a is the most prevalent type. Analysis of the capsid protein DNA-sequences of four selected African isolates gave no hint of a specific African parvovirus lineage.

Assaying for structural variation in the parvovirus capsid and its role in infection

The capsid of canine parvovirus (CPV) was assayed for susceptibility to proteases and for structural variation. The natural cleavage of VP2 to VP3 in CPV full (DNA containing) particles recovered from tissue culture occurred within the sequence Arg-Asn-Glu-Arg Ala-Thr. Trypsin, chymotrypsin, bromelain, and cathepsin B all cleaved >90% of the VP2 to VP3 in full but not in empty capsids and did not digest the capsid further. Digestion with proteinase K, Pronase, papain, or subtilisin cleaved the VP2 to VP3 and also cleaved at additional internal sites, causing particle disintegration and protein degradation. Several partial digestion products produced by proteinase K or subtilisin were approximately 31-32.5 kDa, indicating cleavage within loop 3 of the capsid protein as well as other sites. Protease treatment of capsids at pH 5.5 or 7.5 did not significantly alter their susceptibility to digestion. The isoelectric point of CPV empty capsids was pH 5.3, and full capsids were 0.3 pH more acidic, but after proteolysis of VP2 to VP3, the pI of the full capsids became the same as that of the empty capsids. Antibodies against various capsid protein sequences showed the amino termini of most VP2 molecules were on the outside of full but not empty particles, that the VP1-unique sequence was internal, and that the capsid could be disintegrated by heat or urea treatment to expose the internal sequences. Capsids added to cells were localized within the cell cytoplasm in vesicles that appeared to be lysosomes. Microinjected capsids remained primarily in the cytoplasm, although a small proportion was observed to be in the nucleus after 2 h. After CPV capsids labeled with [35S]methionine were bound to cells at 0 degrees C and the cells warmed, little cleavage of VP1 or VP2 was observed even after prolonged incubation. Inoculation of cells with virus in the presence of proteinase inhibitors did not significantly reduce the infection.

Three closely related herpesviruses are associated with fibropapillomatosis in marine turtles

Green turtle fibropapillomatosis is a neoplastic disease of increasingly significant threat to the survivability of this species. Degenerate PCR primers that target highly conserved regions of genes encoding herpesvirus DNA polymerases were used to amplify a DNA sequence from fibropapillomas and fibromas from Hawaiian and Florida green turtles. All of the tumors tested (n = 23) were found to harbor viral DNA, whereas no viral DNA was detected in skin biopsies from tumor-negative turtles. The tissue distribution of the green turtle herpesvirus appears to be generally limited to tumors where viral DNA was found to accumulate at approximately two to five copies per cell and is occasionally detected, only by PCR, in some tissues normally associated with tumor development. In addition, herpesviral DNA was detected in fibropapillomas from two loggerhead and four olive ridley turtles. Nucleotide sequencing of a 483-bp fragment of the turtle herpesvirus DNA polymerase gene determined that the Florida green turtle and loggerhead turtle sequences are identical and differ from the Hawaiian green turtle sequence by five nucleotide changes, which results in two amino acid substitutions. The olive ridley sequence differs from the Florida and Hawaiian green turtle sequences by 15 and 16 nucleotide changes, respectively, resulting in four amino acid substitutions, three of which are unique to the olive ridley sequence. Our data suggest that these closely related turtle herpesviruses are intimately involved in the genesis of fibropapillomatosis.

No evidence for a role of modified live virus vaccines in the emergence of canine parvovirus

In this study the early evolution and potential origins of canine parvovirus (CPV) were examined. We cloned and sequenced the VP2 capsid protein genes of three German CPV strains isolated in 1979-1980, as well as two feline panleukopenia virus (FPV) vaccine viruses that were previously shown to have some restriction enzyme cleavage sites in common with CPV. Other partial VP2 gene sequences were obtained by amplifying CPV DNA from paraffin-embedded tissues of dogs which were early parvovirus disease cases in Germany in 1978-1979. Sequences were analysed with respect to their evolutionary relationships to other CPV and FPV isolates. Those analyses did not support the hypothesis that CPV emerged as a variant of an FPV vaccine virus. Neither did they reveal ancestral sequences among the very early CPV isolates examined. Other possible sources for the origin of CPV are examined, including the involvement of viruses from wild carnivores.

Detection of a novel bovine lymphotropic herpesvirus

Degenerate PCR primers which amplify a conserved region of the DNA polymerase genes of the herpesvirus family were used to provide sequence evidence for a new bovine herpesvirus in bovine B-lymphoma cells and peripheral blood mononuclear cells (PBMC). The sequence of the resultant amplicon was found to be distinct from those of known herpesvirus isolates. Alignment of amino acid sequences demonstrated 70% identity with ovine herpesvirus 2, 69% with alcelaphine herpesvirus 1, 65% with bovine herpesvirus 4, and 42% with bovine herpesvirus 1. Phylogenetic analysis placed this putative virus within the tumorigenic Gammaherpesvirinae subfamily, and it is tentatively identified as bovine lymphotropic herpesvirus. This novel agent was expressed in vitro from infected PBMC, and cell-free supernatants were used to transfer infection to a bovine B-cell line, BL3. Analysis, with specific PCR primers, of DNA from bovine PBMC and lymphoma cells identified infection in blood of 91% of adult animals (n = 101), 63% of lymphomas (n = 32), and 38% of juveniles (n = 13). Of the adults, herpesvirus infection was present in 94% of animals that were seropositive for bovine leukemia virus (BLV) (n = 63) and in 87% of BLV-seronegative animals (n = 38). Of the seropositive group, 17 animals exhibited persistent lymphocytosis, and 100% of these were herpesvirus positive by PCR. A role for bovine lymphotropic herpesvirus as a cofactor in BLV pathogenesis is considered.

Nonstructural protein-2 and the replication of canine parvovirus

The nonstructural protein-2 (NS2) of canine parvovirus (CPV) is produced from the left-hand open reading frame of the viral genome and contains 87 amino-terminal amino acids in common with nonstructural protein 1 (NS1) joined to 78 amino acids from an alternative open reading frame. In the minute virus of mice parvovirus NS2 plays a role in controlling capsid protein assembly and translation in a host-specific manner. The predicted NS2 of CPV is divergent from the proteins of the rodent parvoviruses, and the protein and its functions have not been described. We characterized the large and the small splices of CPV using reverse transcriptase-PCR, NS2 was identified using anti-peptide antibodies against the predicted C-terminal sequence and also by expressing the protein from a plasmid vector. The protein could be detected at low levels in the nucleus and the cytoplasm of a proportion of CPV-infected cells, as well as in cells transfected with the expression plasmid. Virus genomes were prepared with mutations in the splice donor or acceptor sites of the NS2-specific intron or with three different termination codons in the NS2-unique exon. Both splice donor and acceptor mutations resulted in the use of previously cryptic splice sites, and the virus containing the splice donor mutation replicated inefficiently. However, the other four mutant viruses were all viable and replicated efficiently in cat and dog cells, and two mutant viruses that were tested appeared to assemble their capsids in the same manner as did the wildtype. After inoculation of dogs an NS2 mutant virus with a termination codon in the NS2-unique exon replicated to titers similar to those seen for wildtype CPV in several tissues examined.

Canine parvovirus host range is determined by the specific conformation of an additional region of the capsid

We analyzed a region of the capsid of canine parvovirus (CPV) which determines the ability of the virus to infect canine cells. This region is distinct from those previously shown to determine the canine host range differences between CPV and feline panleukopenia virus. It lies on a ridge of the threefold spike of the capsid and is comprised of five interacting loops from three capsid protein monomers. We analyzed 12 mutants of CPV which contained amino acid changes in two adjacent loops exposed on the surface of this region. Nine mutants infected and grew in feline cells but were restricted in replication in one or the other of two canine cell lines tested. Three other mutants whose genomes contain mutations which affect one probable interchain bond were nonviable and could not be propagated in either canine or feline cells, although the VP1 and VP2 proteins from those mutants produced empty capsids when expressed from a plasmid vector. Although wild-type and mutant capsids bound to canine and feline cells in similar amounts, infection or viral DNA replication was greatly reduced after inoculation of canine cells with most of the mutants. The viral genomes of two host range-restricted mutants and two nonviable mutants replicated to wild-type levels in both feline and canine cells upon transfection with plasmid clones. The capsids of wild-type CPV and two mutants were similar in susceptibility to heat inactivation, but one of those mutants and one other were more stable against urea denaturation. Most mutations in this structural region altered the ability of monoclonal antibodies to recognize epitopes within a major neutralizing antigenic site, and that site could be subdivided into a number of distinct epitopes. These results argue that a specific structure of this region is required for CPV to retain its canine host range.

Tropic determinant for canine parvovirus and feline panleukopenia virus functions through the capsid protein VP2

Canine parvovirus (CPV) can productively infect canine and feline cell lines whereas feline panleukopenia virus (FPV) is restricted to the latter. The major determinants of tropism are two amino acids in the sequence shared by the capsid proteins, VP1 and VP2. We have shown that a rodent parvovirus-derived transducing genome, containing the luciferase reporter, can be packaged by VP1 and VP2 from separate helper sources. Canine A72 cells and feline CFK cells were transduced with recombinant virions generated using VP1 and VP2 combinations from CPV and FPV. Both VP1 and VP2 were necessary for production of transducing virions. Efficient transduction of A72 cells required VP2 of CPV. Therefore, the capsid determinants of tropism for CPV and FPV are in VP2, although a source of VP1 is also necessary to produce infectious particles. The results extend similar observations on the tropic determinants of different strains of minute virus of mice.

Structural analysis of a mutation in canine parvovirus which controls antigenicity and host range

A single mutation in canine parvovirus (CPV) of VP2 residue 300 from alanine to aspartic acid causes a loss of canine host range and alters the antigenic properties of the virus. The three-dimensional structure of this mutant has been solved to 3.25 A resolution. Crystals of full particles were triclinic, with cell dimensions of a = 267.6, b = 268.5, c = 274.3 A. alpha = 61.9, beta = 62.6, and gamma = 60.2 degrees. The native structure of CPV was used as an initial model. Phases were improved by real-space electron density averaging. In spite of the relative low percentage of observed reflections (32.5% of the data between 15.0 and 3.25 A resolution), the presence of 60-fold noncrystallographic redundancy allowed the averaging procedure to converge smoothly. The mutant aspartic acid at residue 300 forms a salt bridge with Arg81 in an icosahedrally threefold-related subunit, inducing local changes within the antigenic site B on the CPV surface. In addition, the loop between residues 359 and 374 adopts a conformation similar to that displayed by feline panleukopenia virus. The ability of the Ala300-->Asp mutant to evade antibody binding can be associated with the change of charge distribution and structure in the antigenic binding site. The variation in host range behavior may be due to the increased stability as a result of formation of the salt bridge between adjacent subunits.

Analysis of the serotype-specific epitopes of avian infectious bronchitis virus strains Ark99 and Mass41

The Ark and Mass serotype-specific epitopes of infectious bronchitis virus were studied by immunofluorescence and immunoprecipitation of mutant and recombinant spike glycoproteins (S protein) expressed in mouse L cells. Serotype-specific monoclonal antibodies could bind to the recombinant proteins of Ark99 and Mass41 expressed from the chimeras in which the N-terminal thirds of the S1 sequences were reciprocally exchanged. Therefore, it appears that the respective serotype-specific epitopes of both strains were localized within the C-terminal two-thirds of the S1 proteins. Deletion and insertion of a five-amino-acid fragment on the S1 proteins of Ark99 and Mass41, altered the serotype-specific epitopes. This result implies that the five-amino-acid insertion on the S1 protein of the Ark serotype was involved in determining the conformation of the protein, probably acting as a spacer. In addition, it appears that an interaction between sequences of the N-terminal third and the remaining portion of the S1 protein determines the tertiary structure of the protein as well as the conformation of the serotype-specific epitope.

Evolution of canine parvovirus involved loss and gain of feline host range

Canine parvovirus (CPV) type-2 emerged as a new virus infecting dogs in 1978, and it was probably derived as a variant of feline panleukopenia virus or of a closely related virus infecting another carnivore. CPV type-2 was subsequently replaced in nature by antigenically variant viruses (CPV type-2a and CPV type-2b) which now coexist in dog populations worldwide. We show that CPV type-2 isolates did not replicate in cats, but that both CPV type-2a and CPV type-2b isolates replicated efficiently. About 10% of the viruses isolated from cats with natural parvovirus disease were antigenically indistinguishable from CPV type-2a or type-2b. The capsid protein gene sequence of a 1990 feline parvovirus isolate ("FPV-24") was essentially identical to the sequence of CPV type-2b viruses from dogs. The loss and reacquisition of the feline host range in CPV was most likely due in each case to small numbers of changes in a region of the virus capsid where three protein monomers interact.

Evolution of the feline-subgroup parvoviruses and the control of canine host range in vivo

A related group of parvoviruses infects members of many different carnivore families. Some of those viruses differ in host range or antigenic properties, but the true relationships are poorly understood. We examined 24 VP1/VP2 and 8 NS1 gene sequences from various parvovirus isolates to determine the phylogenetic relationships between viruses isolated from cats, dogs, Asiatic raccoon dogs, mink, raccoons, and foxes. There were about 1.3% pairwise sequence differences between the VP1/VP2 genes of viruses collected up to four decades apart. Viruses from cats, mink, foxes, and raccoons were not distinguished from each other phylogenetically, but the canine or Asiatic raccoon dog isolates formed a distinct clade. Characteristic antigenic, tissue culture host range, and other properties of the canine isolates have previously been shown to be determined by differences in the VP1/VP2 gene, and we show here that there are at least 10 nucleotide sequence differences which distinguish all canine isolates from any other virus. The VP1/VP2 gene sequences grouped roughly according to the time of virus isolation, and there were similar rates of sequence divergence among the canine isolates and those from the other species. A smaller number of differences were present in the NS1 gene sequences, but a similar phylogeny was revealed. Inoculation of mutants of a feline virus isolate into dogs showed that three or four CPV-specific differences in the VP1/VP2 gene controlled the in vivo canine host range.

Analysis of the cell and erythrocyte binding activities of the dimple and canyon regions of the canine parvovirus capsid

Canine parvovirus (CPV) binds to a number of cell and erythrocyte receptors, some of which are involved in cell infection, while others are used for other viral functions. Little is known about the regions of the virus capsid which bind to the cell receptors. CPV binds sialic acid through a region within or adjacent to the dimple on the surface of the capsid (Barbis, D. P., Chang, S-F., and Parrish, C. R., 1992, Virology 191, 301-308). In order to map the sialic acid binding site in more detail and to examine other regions of the capsid for cell receptor binding, a variety of mutant capsids were analyzed which had changes in two depressions within the surface of the capsid--the "canyon" and "dimple." In most cases recombinant VP1 and VP2 proteins were stably expressed together in canine A72 cells from a plasmid expression vector. The purified empty capsids were tested for their ability to bind sialic acid and thereby hemagglutinate (HA) erythrocytes and for binding to permissive host cells. In addition, the ability of neutralizing monoclonal antibodies to block cell attachment was also examined. Mutations of amino acids on a wall of the dimple eliminated or severely decreased HA. Changing various residues within the canyon had no effect on binding to either sialic acids or other receptors on feline lymphoblastoid cells, suggesting that the canyon is not the site of cell receptor attachment. Neutralizing monoclonal antibodies against both major antigenic determinants had variable effects on cell binding, but no consistent inhibition of binding was observed by antibodies directed against either of those two major antigenic determinants of the capsid.

Pathogenesis of feline panleukopenia virus and canine parvovirus

Feline panleukopenia virus (FPV) and canine parvovirus (CPV) are autonomous parvoviruses which infect cats or dogs, respectively. Both viruses cause an acute disease, with virus replicating for less than seven days before being cleared by the developing immune responses. The viruses have a broad tropism for mitotically active cells. In neonatal animals the viruses replicate in a large number of tissues, and FPV infection of the germinal epithelium of the cerebellum leads to cerebellar hypoplasia, while CPV may infect the hearts of neonatal pups, causing myocarditis. In older animals the virus replicates systemically, primarily in the primary and secondary lymphoid tissues, and also in the rapidly replicating cells of the small intestinal epithelial crypts. A transient panleukopenia or relative lymphopenia is often observed after FPV or CPV infection, respectively. Whether the reduction in cell numbers in vivo is due to virus replicating in and killing cells, or due to other indirect effects, is not known. However, FPV kills both erythroid and myeloid colony progenitors in in vitro bone marrow cultures, and it has been suggested that virus replication in the myeloid cells in vivo could lead to the reduced neutrophil levels seen after FPV infection of cats.

There is nothing permanent except change. The emergence of new virus diseases

The sudden appearance of apparently new viruses with pathogenic potential is of fundamental importance in medical microbiology and a constant threat to humans and animals. The emergence of a "new" pathogen is not an isolated event, as for instance the frequent appearance of new influenza virus strains demonstrates. Often the new virus strains co-circulate with the older strains in a susceptible population, but a replacement of the older strains has been also observed. In rare instances the new viruses can cause dramatic epidemics or pandemics, such as those observed with the human immunodeficiency virus, canine parvovirus, or most recently, with the agent of bovine spongiform encephalopathy in the United Kingdom. The mechanisms of the emergence are not always clearly understood, but an altered host range appears to be a common event. Whether a true change in host range occurs, or whether the virus adapted to the host and replicated more efficiently, is often unknown. This review tries to summarize the facts that are known about a wide variety of "new" viruses of mammals, such as the simian, human and feline lentiviruses, the feline coronaviruses, the feline parvoviruses, the carnivore morbilliviruses, the influenza A viruses, and the transmissible spongiform encephalopathies. A particular emphasis will be put on the genetic mechanisms that might have taken place and that might have been responsible for their sudden appearance.

Detection by PCR of wild-type canine parvovirus which contaminates dog vaccines

A method for detecting wild-type canine parvovirus (CPV) strains which contaminate vaccines for dogs has been developed by PCR. PCR primers which distinguish vaccine strains from the most common, recent strains of wild-type CPV in many countries, including Japan and the United States, were developed. This PCR is based on the differences in nucleotide sequences which determine the two antigenic types of this virus. CPV vaccine strains derived from antigenically old-type virus prevalent in former times were not detected by PCR with differential primers. Detection sensitivity of PCR was 100- to 10,000-fold higher than that of the culture method in Crandell feline kidney cells.

A novel variant of avian infectious bronchitis virus resulting from recombination among three different strains

An antigenic variant of avian infectious bronchitis virus (IBV), a coronavirus, was isolated and characterized. This strain, CU-T2, possesses a number of unusual features, which have not been previously observed in IBV. The S1 glycoprotein of CU-T2 carries virus-neutralizing and serotype-specific epitopes of two IBV serotypes, Arkansas (Ark) and Massachusetts (Mass). Sequence analysis revealed that the virus, originally an Ark serotype, has acquired the Mass-specific epitope by mutation(s). This provides evidence that point mutations may lead to generation of IBV antigenic variants in the field. It was further observed that two independent recombination events involving three different IBV strains had occurred in the S2 glycoprotein gene and N protein gene of CU-T2, indicating that genomic RNA recombination in IBV may occur in multiple genes in nature. It was especially significant that a sequence of Holland 52 (a vaccine strain) had replaced half of the N gene of CU-T2. This proves that recombination among vaccine strains is contributing to the generation of IBV variants in the field. Based on these observations it is predicted that every IBV field isolate could have unique genetic nature. Therefore, several recently reported diagnostic and serotyping methods of IBV which are based on dot-blot hybridization, restriction fragment length polymorphism (RFLP), and polymerase chain reaction (PCR), may not reveal the true antigenic and/or genetic nature of IBV isolates, and may in fact yield misleading information.

Localization of a neutralizing epitope on the envelope protein of dengue virus type 2

Two neutralization-resistant variants of dengue virus type 2 were selected using the neutralizing monoclonal antibody G8D11. Virus N-GV4 was derived from the New Guinea C strain and virus P-GV3 from the PUO-218 strain. Both variants had an identical change at nucleotide 919 in the E gene, causing a substitution of glutamic acid for lysine at residue 307 in the E glycoprotein. The substitution abolished the ability of antibody G8D11 to bind to the E glycoprotein in radioimmunoprecipitation experiments. The epitope was sensitive to treatment with SDS and was dependent on the formation of a disulfide bridge. This dependency was determined by mutagenesis of Cys residues 11 and 12 in the E glycoprotein.

The structure of a neutralized virus: canine parvovirus complexed with neutralizing antibody fragment

BACKGROUND

Members of the Parvovirus genus cause a variety of diseases in mammals, including humans. One of the major defences against viral infection is the presence of neutralizing antibodies that prevent virus particles from infecting target cells. The mechanism of neutralization is not well understood. We therefore studied the structure of canine parvovirus (CPV) complexed with the Fab fragment of a neutralizing antibody, A3B10, using image reconstruction of electron micrographs of vitrified samples, together with the already known structure of CPV from X-ray crystallographic data.

RESULTS

The structure of the complex of CPV with Fab A3B10 has been determined to 23 A resolution. The known CPV atomic structure was subtracted from the electron density of the complex, and the difference map was used to fit the atomic coordinates of a known Fab fragment, HyHEL-5. The long axis of each Fab molecule is oriented in a near radial direction, inclined away from the two-fold axes. The viral epitope consists of 14 amino acid residues found in loops 1, 2 and 3 on the capsid surface, which include previously identified escape mutations.

CONCLUSIONS

The mode of Fab binding suggests that the A3B10 neutralizing antibody cannot bind bivalently to the capsid across the two-fold axes, consistent with the observation that whole A3B10 antibody readily precipitates CPV. Since Fab A3B10 can also neutralize the virus, mechanisms of neutralization such as interference with cell attachment, cell entry, or uncoating, must be operative.

Characterization of the feline host range and a specific epitope of feline panleukopenia virus

The feline parvovirus subgroup is comprised of viruses isolated from various carnivores, including the dog, cat, mink, raccoon, Arctic fox, and raccoon dog. Those viruses are > 98% identical in their DNA sequences and are very similar antigenically. We have shown that although canine parvovirus (CPV) replicates in numerous feline cell lines in vitro it does not infect cats after parenteral inoculation (U. Truyen and C. R. Parrish, (1992) J. Virol. 66, 5399-5408). Here we use recombination mapping to locate some viral determinants required for feline host range, and show that the ability to replicate in cats was determined by the right-hand 45% of the genome, most likely a function of the capsid protein gene. Efficient replication in the cat appeared to require feline panleukopenia virus sequences from both ends of the VP2 molecule, which contained differences of VP2 amino acid residues 80, 564, and 568. The difference at amino acid 80 was also associated with expression of an FPV-specific antigenic epitope. The differences which affected the feline host range were located in a region of the capsid structure where three VP2 molecules interact, and the mutations gave rise to changes in the conformation of loops of the three adjoining VP2 monomers. The mechanism(s) of the in vivo feline host range restriction were not defined, and we were unable to show in vitro inhibition of virus infectivity by feline serum components or erythrocytes.

Detection of canine parvovirus DNA in paraffin-embedded tissues by polymerase chain reaction

Canine Parvovirus (CPV) is seemingly a 'new' virus which suddenly appeared during the mid-1970's in an epizootic of disease in dogs. The virus is very similar to the feline panleukopenia virus (FPV), and recent studies have underlined the possible emergence of CPV as a variant of a virus from some other carnivore--possibly from FPV (Parrish, 1990). Several conserved amino-acid changes between CPV and FPV isolates have been defined by cloning and sequencing the capsid-protein gene. An alternative to cloning and sequencing the entire capsid-protein gene would be to use PCR amplification of short regions of the gene containing the appropriate variable amino-acid codons. In addition, use of PCR would also facilitate the study of virus samples which cannot be recovered as infectious agents, e.g. after having undergone formalaldehyde fixation and paraffin-embedding procedures. This study reports on the amplification of CPV DNA from 15-year-old tissue sections which have been prepared by formaldehyde or paraformaldehyde-lysine-periodate-glutaraldehyde fixation, using PCR with various primer pairs within the capsid-protein gene of CPV.

Characterization of canine parvovirus (CPV) interactions with 3201 T cells: involvement of GPI-anchored protein(s) in binding and infection

Binding of canine parvovirus (CPV) to the susceptible feline T cell line 3201 was quantitated by fluorescence-activated cell sorter (FACS) analysis. CPV bound to the cells in a dose-dependent manner, while no binding to the non-permissive MSB-1 avian lymphoma cell line was detected. Binding could be competitively inhibited by addition of excess unlabeled empty capsids, or by pre-incubation of virus with a CPV-specific monoclonal antibody. To characterize the biochemical nature of this binding, live cells were treated with a variety of enzymes prior to use in the binding assay. Treatment with neuraminidase removed a significant proportion of the wild-type virus binding activity, while both proteinase K and phosphatidylinositol-specific phospholipase C (PI-PLC) prevented binding of a non-hemagglutinating (non-HA), non-sialic acid binding mutant to 3201 cells. This suggests that CPV binds to sialic acid expressed on host cells as well as erythrocyte membranes, and that it also binds a protein moiety which is glycosylphosphatidylinositol (GPI)-anchored. The role of these components in CPV infection was also examined by pretreating cells with neuraminidase or PI-PLC prior to inoculating them with either wild-type CPV or the non-hemagglutinating mutant. Neuraminidase treatment had no effect on the ability of CPV to infect the cells, while infectivity was severely compromised by pretreating the cells with either proteinase K or PI-PLC. GPI-anchored proteins on 3201 cells were further characterized by Triton X-114 extraction and reactivity to anti-CRD after PI-PLC treatment.

Two dominant neutralizing antigenic determinants of canine parvovirus are found on the threefold spike of the virus capsid

The 25-nm diameter parvovirus capsid is assembled from 60 copies of a sequence common to the overlapping VP1 and VP2 proteins. Here we examine the epitope specificity's of 28 monoclonal antibodies (MAb) prepared against canine parvovirus (CPV), feline panleukopenia virus (FPV), and raccoon-dog parvovirus or blue (Arctic) fox parvovirus. Comparing the reactivity of those MAb with various MAb-selected escape mutants, or with natural variants of CPV or mink enteritis virus (MEV) which differ at known sequences, showed that the binding of 20 of those MAb was strongly affected by variations of two regions on the threefold spike of the CPV capsid. One region was adjacent to the tip of the threefold spike, and the second was around VP2 residue 300, on the shoulder of that structure. MAb recognizing both antigenic sites efficiently neutralized the virus infectivity and inhibited hemagglutination. Mutations leading to natural antigenic variation have also been observed in both those sites in naturally variant strains of CPV or MEV, suggesting that they are important antigenic structures on these parvoviruses. The bindings of several MAb were not affected by the mutations at those antigenic sites, indicating that they recognized other, and perhaps conserved, structures.

Structure determination of feline panleukopenia virus empty particles

Various crystal forms of the single-stranded DNA, feline panleukopenia virus (FPV), a parvovirus, have been grown of both full virions and empty particles. The structure of empty particles crystallized in an orthorhombic space group P2(1)2(1)2(1), with unit cell dimensions a = 380.1 A, b = 379.3 A, and c = 350.9 A, has been determined to 3.3 A resolution. The data were collected using oscillation photography with synchrotron radiation. The orientations of the empty capsids in the unit cell were determined using a self-rotation function and their positions were obtained with an R-factor search using canine parvovirus (CPV) as a model. Phases were then calculated, based on the CPV model, to 6.0 A resolution and gradually extended to 3.3 A resolution by molecular replacement electron density averaging. The resultant electron density was readily interpreted in terms of the known amino acid sequence. The structure is contrasted to that of CPV in terms of host range, neutralization by antibodies, hemagglutination properties, and binding of genomic DNA.

Determination of the detection limit of the polymerase chain reaction for chicken infectious anemia virus

Chicken infectious anemia virus (CIAV) DNA in infected cell cultures and chicken tissues was detected using a polymerase chain reaction (PCR) assay. The complete CIAV genome of several strains was amplified in two segments with two sets of primer pairs. The DNA segments of four CIAV strains and full-length Cux-1 strain DNA were cloned. After amplification, 100 original genome equivalents were detected by Southern hybridization. The sensitivity of the assay was enhanced considerably by performing a reamplification with nested primers. This modification permitted the detection of one molecule of CIAV DNA. Some problems of the assay and its possible application are discussed.

Multiple amino acids in the capsid structure of canine parvovirus coordinately determine the canine host range and specific antigenic and hemagglutination properties

Canine parvovirus (CPV) and feline panleukopenia virus (FPV) are over 98% similar in DNA sequence but have specific host range, antigenic, and hemagglutination (HA) properties which were located within the capsid protein gene. In vitro mutagenesis and recombination were used to prepare 16 different recombinant genomic clones, and viruses derived from those clones were analyzed for their in vitro host range, antigenic, and HA properties. The region of CPV from 59 to 91 map units determined the ability to replicate in canine cells. A complex series of interactions was observed among the individual sequence differences between 59 and 73 map units. The canine host range required that VP2 amino acids (aa) 93 and 323 both be the CPV sequence, and those two CPV sequences introduced alone into FPV greatly increased viral replication in canine cells. Changing any one of aa 93, 103, or 323 of CPV to the FPV sequence either greatly decreased replication in canine cells or resulted in an inviable plasmid. The Asn-Lys difference of aa 93 alone was responsible for the CPV-specific epitope recognized by monoclonal antibodies. An FPV-specific epitope was affected by aa 323. Amino acids 323 and 375 together determined the pH dependence of HA. Amino acids involved in the various specific properties were all around the threefold spikes of the viral particle.