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PubMed1995

Identification of a region of the alcelaphine herpesvirus-1 genome associated with virulence for rabbits.

The gammaherpesvirus Alcelaphine Herpesvirus 1 (AHV-1) causes the fatal lymphoproliferative disease known as malignant catarrhal fever (MCF), in susceptible hosts. The virulent C500 isolate of AHV-1 became attenuated for the laboratory model, the rabbit, as a result of serial passage in cells of bovine origin. This work describes the identification of a region of the central unique sequence of the C500 genome, located close to the terminal repeat units of the molecule, which is altered on attenuation. The virulent C500 genome contains two copies of a sequence of approximately 2 kbp, contained within a 7 kbp region of the unique DNA located adjacent to the terminal repeats at the left end of the molecule. In the genome of the attenuated virus, there are also two copies of the 2 kbp sequence but they are located at the ends of the attenuated genome unique region, adjacent to the terminally repeated sequences. One open reading frame (ORF), designated putative polypeptide 5, was altered on attenuation such that the 3' sequence was lost. The location of this ORF, coupled with the loss of its 3' sequence, suggests that this ORF may encode a gene involved in the virulent mechanisms of this virus, in a manner similar to that of the transforming proteins of Herpesvirus saimiri (HSV).

Amino Acid Sequence↗

PubMed2002

Surface expression of an immunodominant malaria protein B cell epitope by yellow fever virus.

The yellow fever 17D virus (YF17D) has several characteristics that are desirable for the development of new, live attenuated vaccines. We approached its development as a vector for heterologous antigens by studying the expression of a humoral epitope at the surface of the E protein based on the results of modelling its three-dimensional structure. This model indicated that the most promising insertion site is between beta-strands f and g, a site that is exposed at the external surface of the virus. The large deletion of six residues from the fg loop of the E protein from yellow fever virus, compared to tick-born encephalitis virus, leaves space at the dimer interface for a large insertion without creating steric hindrance. We have tested this hypothesis by inserting a model humoral epitope from the circumsporozoite protein of Plasmodium falciparum consisting of triple NANP repeats. Recombinant virus (17D/8) expressing this insertion flanked by two glycine residues at each end, is specifically neutralized by a monoclonal antibody to the model epitope. Furthermore, mouse antibodies raised to the recombinant virus recognize the parasite protein in an ELISA assay. Serial passage analysis confirmed the genetic stability of the insertion made in the viral genome and the resulting 17D/8 virus is significantly more attenuated in mouse neurovirulence tests than the 17DD vaccine. The fg loop belongs to the dimerization domain of the E protein and lies at the interface between monomers. This domain undergoes a low pH transition, which is related to the fusion of the viral envelope to the endosome membrane. It is conceivable that a slower rate of fusion, resulting from the insertion close to the dimer interface, may delay the onset of virus production and thereby lead to a milder infection of the host. This would account for the more attenuated phenotype of the recombinant virus in the mouse model and lower extent of replication in cultured cells. The vectorial capacity of the yellow fever virus is being further explored for the expression and presentation of other epitopes, including those mediating T-cell responses.

Amino Acid Sequence↗

PubMed1995

De novo generation of defective interfering-like RNAs in broad bean mottle bromovirus.

Broad been mottle virus (BBMV) is the only member of the bromoviruses that is known to accumulate defective-interfering (DI) RNAs (Romero et al., Virology 194, 576-584, 1993). De novo generation of DI-like RNAs was demonstrated during serial passages of BBMV in broad bean using either DI RNA-free virion RNA preparations or transcribed genomic RNA inocula. As for previously described DI RNAs, all but one of the characterized de novo generated DI-like RNAs were derived by a single in-frame deletion from the RNA2 component. The sole exception was derived by two shorter in-frame deletions from RNA2. The maintenance of an open reading frame by all DI-like RNAs suggests the importance of coding capacity and/or the shortened 2a protein in the accumulation of these RNAs during infection. The deletion junction sites were between nucleotides 1152 and 2366, suggesting that the retained regions are essential for the efficient accumulation of BBMV DI-like RNAs in planta. Short regions of sequence similarity and/or complementarity were revealed at the 5' and 3' junction borders. We speculate that these regions can facilitate DI (DI-like) RNA formation. In addition to DI-like RNAs, the full-length nucleotide sequences of RNA2 components of the Type and Morocco strains of BBMV are presented.

Amino Acid Sequence↗

PubMed2004

Two amino acid mutations in the capsid protein of type 2 porcine circovirus (PCV2) enhanced PCV2 replication in vitro and attenuated the virus in vivo.

Porcine circovirus type 2 (PCV2) is the primary causative agent of postweaning multisystemic wasting syndrome (PMWS) in pigs. To identify potential genetic determinants for virulence and replication, we serially passaged a PCV2 isolate 120 times in PK-15 cells. The viruses harvested at virus passages 1 (VP1) and 120 (VP120) were biologically, genetically, and experimentally characterized. The PCV2 VP120 virus replicated in PK-15 cells to a titer similar to that of the PK-15 cell line-derived nonpathogenic PCV1 but replicated more efficiently than PCV2 VP1 with a difference of about 1 log unit in the titers. The complete genomic sequences of viruses at passages 0, 30, 60, 90, and 120 were determined. After 120 passages, only two nucleotide mutations were identified in the entire genome, and both were located in the capsid gene: the mutations were located at nucleotide positions 328 (C328G) and 573 (A573C). The C328G mutation, in which a proline at position 110 of the capsid protein changed to an alanine (P110A), occurred at passage 30 and remained in the subsequent passages. The second mutation, A573C, resulting in a change from an arginine to a serine at position 191 (R191S), appeared at passage 120. To experimentally characterize the VP120 virus, 31 specific-pathogen-free pigs were randomly divided into three groups. Ten pigs in group 1 received phosphate-buffered saline as negative controls. Each pig in group 2 (11 pigs) was inoculated intramuscularly and intranasally with 10(4.9) 50% tissue culture infective doses (TCID(50)) of PCV2 VP120. Each pig in group 3 (10 pigs) was similarly inoculated with 10(4.9) TCID(50) of PCV2 VP1. Viremia was detected in 9 of 10 pigs in the PCV2 VP1 group with a mean duration of 3 weeks, but in only 4 of 11 pigs in the PCV2 VP120 group with a mean duration of 1.6 weeks. The PCV2 genomic copy numbers in serum in the PCV2 VP1 group were significantly higher than those in the PCV2 VP120 group (P < 0.0001). Gross and histopathologic lesions in pigs inoculated with PCV2 VP1 were more severe than those inoculated with PCV2 VP120 at both day 21 and 42 necropsies (P = 0.0032 and P = 0.0274, respectively). Taken together, the results from this study indicated that the P110A and R191S mutations in the capsid of PCV2 enhanced the growth ability of PCV2 in vitro and attenuated the virus in vivo. This finding has important implications for PCV2 vaccine development.

Animals↗

PubMed1993

Derivation of highly mefloquine-resistant lines from Plasmodium falciparum in vitro.

Serial passage of a multidrug-resistant clone of Plasmodium falciparum in concentrations of mefloquine hydrochloride ranging from 30 to 2,400 ng/ml resulted in the derivation of increasingly resistant parasite lines in vitro. Parasite lines isolated in mefloquine concentrations greater than 300 ng/ml demonstrated increased vacuolization, enhanced pigment production, and increased growth rates as compared with the progenitor clone, W2-mef. Although microdilution incorporation assays demonstrated that the 50% inhibitory concentration (IC50) of mefloquine were similar for all lines, the IC90, IC95, and IC99 levels were significantly increased. Growth rate assays performed in 5% hematocrit suspensions demonstrated different levels of mefloquine resistance among these lines. Under these conditions the most resistant line, Mef 2.4, grew efficiently in approximately 10-fold higher concentrations of mefloquine than the progenitor clone W2-mef. Analysis of drug susceptibility profiles to mefloquine hydrochloride, chloroquine diphosphate, quinine sulfate, and halofantrine hydrochloride indicated that selection for high levels of mefloquine resistance had resulted in significant increases in resistance to halofantrine and increased sensitivity to chloroquine. The phenotypic changes demonstrated in the most resistant line, Mef 2.4, reflect a multidrug resistant-like phenotype, and appear to mimic changes recently reported in drug susceptibility profiles of recrudescent isolates following mefloquine treatment failures in Thailand.

Animals↗

PubMed1994

Loss of conserved cysteine residues in the attachment (G) glycoprotein of two human respiratory syncytial virus escape mutants that contain multiple A-G substitutions (hypermutations).

Two escape mutants (R10c/1 and R10c/10) of the human respiratory syncytial (RS) virus Long strain were selected after serial passage in the presence of monoclonal antibody c793 directed against the G glycoprotein. This antibody recognizes an epitope which is shared by all viruses of the two antigenic subgroups in which human RS virus isolates have been subdivided. The mutant viruses had lost most of the G protein conserved and subgroup-specific epitopes but maintained the strain-variable epitopes. The two mutants had 10 or 11 nucleotide changes in the central region of the G protein gene when compared to the Long sequence, and almost all of those changes were different between the two mutants. The majority of the nucleotide changes involved A-G transitions (U-C in the positive sense) that resulted in amino acid substitutions. Each mutant had a total of six amino acid changes, and the changes were different between the two mutants. Unexpectedly, each mutant lost one of the four conserved cysteines of the G protein, and a different cysteine (Cys 182 or 186) was lost in each mutant. They are, in fact, the first reported RS viruses with only three cysteines in the G protein ectodomain. The genetic mechanism that generated the escape mutants and its relevance for the natural history of RS virus are discussed.

Antibodies, Monoclonal↗

PubMed1995

Genomic analysis of a transposition-deletion variant of orf virus reveals a 3.3 kbp region of non-essential DNA.

Restriction endonuclease analysis of the DNA extracted orf virus strain NZ2, which had been serially passaged in primary bovine testis cells, revealed a population of variants that had over-grown the wild-type virus. At least three distinct mutant forms were identified in which the right end of the genome had been duplicated and translocated to the left end, accompanied by deletions of sequences at the left end. Sequencing of a single variant isolated from the heterogeneous population revealed that recombination had occurred between non-homologous sequences. In this case, 6.6 kb of DNA at the left end of the genome had been replaced by 19.3 kb from the right end. The transposition resulted in the deletion at the left end of 3.3 kb of DNA encoding three genes and the terminal sequences of a fourth gene. The three genes completely deleted were a homologue of dUTPase, a gene that encodes a protein containing ankyrin-like repeats and a homologue of the 5K gene of the vaccinia virus WR strain. Experimental inoculation of sheep showed that the genes are also non-essential in vivo, but that the size of the lesion was reduced, compared with that induced by the wild-type, and resolved more rapidly.

Animals↗

PubMed1991

In vitro homotypic and heterotypic interference by defective interfering particles of West Nile virus.

Defective interfering (DI) particles of the flavivirus West Nile (WN) were generated after as few as two high multiplicity serial passages in Vero and LLC-MK2 cells. Six cell lines (Vero, LLC-MK2, L929, HeLa, BHK-21 and SW13) were used to assay interference by DI particles in a yield reduction assay. Interference was found to vary depending on the cell type used. The highest levels of interference were obtained in LLC-MK2 cells, whereas no detectable effect was observed in BHK-21 and SW13 cells. The ability of DI virus to be propagated varied depending on the cell line used; no detectable propagation of DI virus was observed in SW13 cells. Optimum interference was obtained following co-infection of cells with DI virus and standard virus at a multiplicity of 5. Interference between DI and standard viruses occurred only when they were co-infected or when cells were infected with DI virus 1 h before standard virus. Investigation of heterotypic interference by DI particles of WN virus strains from Sarawak, India and Egypt revealed that interference was dependent on the strain of WN virus or flavivirus used as standard virus. A measure of the similarity between five strains of WN virus and other flaviviruses was made on the basis of interference by DI viruses, and was found to be similar to that based on haemagglutination inhibition tests using a panel of monoclonal antibodies.

Animals↗

PubMed1994

Molecular analysis of the glycoprotein C-negative phenotype of attenuated Marek's disease virus.

Serial passage of oncogenic serotype 1 Marek's Disease virus (MDV) in cultured avian cells results in attenuation of viral oncogenicity and pathogenicity. Coincident with attenuation, expression of MDV glycoprotein C (gC) is significantly reduced. Regulation of MDV gC may have important implications for virus-host interactions and have important consequences in the process of viral attenuation. To investigate the mechanism by which MDV gC expression is reduced during attenuation of the very virulent serotype 1 MDV strain Md11, protein levels, gene structure, steady-state RNA levels, and transcription rates of MDV gC from oncogenic and attenuated isolates of Md11 were determined. Comparison of these data with similar studies on MDV proteins whose expression is not altered during attenuation indicates that reduced expression of MDV gC is directly related to reduction in transcription rate of the MDV gC gene in attenuated Md11. Reduced transcription rates and lack of any gross structural alterations in the attenuated MDV gC gene suggest that MDV regulatory protein(s) which interact with the MDV gC promoter are altered during attenuation of MDV strain Md11. This conclusion is supported by DNA sequence data which indicate that the promoters of oncogenic and attenuated Md11 gC genes are identical.

Animals↗

PubMed2004

Influence of decreased penicillin susceptibility on growth rate of beta haemolytic streptococci.

BACKGROUND & OBJECTIVES: Beta haemolytic streptococci (BHS), especially group A are still highly susceptible to penicillin. One possible explanation for this could be reduced growth capability in penicillin resistant BHS mutants. The present study was therefore undertaken to analyze the growth rates of BHS with decreased susceptibility to penicillin. METHODS: Serial passages in the medium with subinhibitory concentration of penicillin were done to induce resistance to this antibiotic in 12 clinical isolates of BHS serogroups A, B, C, and G. Both penicillin susceptible (parental) and variants with decreased susceptibility to penicillin (laboratory strains) were grown in three different media and their growth rates were determined by counting the number of bacterial colonies and by measuring optical density of bacterial culture. RESULTS: The lowest increase in minimal inhibitory concentration (MIC) value for penicillin (8-16 times) was obtained in BHS group A isolates, while the increase in MIC values of BHS groups B, C and G strains was higher (64-128 times) and they reached the level of complete resistance. Laboratory variants differed significantly from parental in their morphological and cultural characteristics. There were no statistically significant differences between the growth rates of penicillin susceptible and variants with decreased susceptibility to penicillin, though a delay in multiplication of the laboratory strains during exponential phase of growth was noted. INTERPRETATION & CONCLUSION: Though significant differences in phenotypic characteristics of penicillin susceptible and laboratory variants were noted, the results of this study provides no support to the assumption that variants of BHS with decreased susceptibility to penicillin of BHS were incapable for normal growth. Further studies needs to be done to find out the association between the decreased susceptibility to penicillin in the BHS and decreased growth capability in these bacteria.

Culture Media↗

PubMed2003

Characterization of a novel ranavirus isolated from grouper Epinephelus tauvina.

A large icosahedral virus was isolated from diseased grouper Epinephelus tauvina. The virus grew well in several cultured fish cell lines, with stable and high infectivity after serial passages in grouper cell line (GP). The virus was sensitive to both acid and heat treatments. Virus replication was inhibited by 5-iodo-2-deoxyuridine (IUDR), indicative of a DNA-containing genome. The virus infectivity was reduced with ether treatment, suggesting that the virus was lipid-enveloped. Electron micrographs showed abundant cytoplasmic icosahedral virons in the virus-infected GP cells. The size of the intracellular nucleocapsid was 154 nm between the opposite sides, or 176 nm between the opposite vertices with an inner electron-dense core of 93 nm. Virus particles were released through budding from plasma membranes with a size of 200 nm in diameter. SDS-PAGE of purified virus revealed 20 structural protein bands and a major capsid protein (MCP) of 49 kDa. A DNA fragment of approximately 500 nucleotides was successfully amplified by polymerase chain reaction (PCR) using the primers from conserved regions of the MCP gene of frog virus 3 (FV3), the type species of Ranavirus. Subsequent multiple alignment and phylogenetic analysis showed that the newly isolated grouper virus was closely related to largemouth bass virus (LMBV), FV3 and Regina ranavirus (RRV). Our data suggests that the virus isolate is a novel member of genus Ranavirus, family Iridoviridae. We tentatively name the virus as Singapore grouper iridovirus (SGIV). SGIV was able to cause serious systemic disease capable of killing 96% of grouper fry.

Amino Acid Sequence↗

PubMed1989

Isolation and characterization of low- and high-metastatic clones from murine RCT (Radiological, Chiba, and Toyama) sarcoma.

We have established low- and high-metastatic clones, named RCT(-) and RCT(+) cells, respectively, from the RCT (Radiological, Chiba, and Toyama) sarcoma spontaneously developed in a C3H/He male mouse by the limiting-dilution method in vitro or by the combination of the lung passages and limiting-dilution methods. After 20 serial passages in vitro, the metastatic potential of each clone did not alter. Morphologically, both cells were spindle-shaped, but RCT(+) cells were slightly thicker and larger than RCT(-) cells. The organization of actin-containing filaments was slightly poorer in RCT(+) cells than that in RCT(-) cells. Marked differences were observed in their growth characteristics and adhesiveness to plastic or collagen-coated surfaces, that is, RCT(+) cells grew more slowly but could adhere more rapidly and firmly to the surfaces than RCT(-) cells. RCT(+) cells were agglutinated by all lectins used but several lectins could not agglutinate RCT(-) cells. These results could be a reflection of the difference in oligosaccharide residues on the surface of each cell and, in part, might reflect the difference in organization of the actin-containing filaments that regulate the mobility of lectin receptors. No significant difference between these cell clones was noted in their sensitivity to natural-killer-cell-mediated cytotoxicity in vitro. RCT(-) and RCT(+) cells are considered to be the most useful experimental model for the study of the certain sarcomas.

Animals↗

PubMed2003

[Experimental study of xenogeneic heart valve material].

OBJECTIVE: To explore the possibility of improving the performance of tissue engineering valve by means of preendothelialization with cultured human umbilical vein endothelial cell(hUVEC) and to develop a new xenogenic bioprosthesis valve material. METHODS: The porcine aortic valves treated by use of glutaraldehyde(GA), epoxychloropropane(EC), L-glutamic acid(L-GA) and cellular extraction(CE) respectively were divided into four groups; group 1(GA), group 2(EC), group 3(EC + L-GA), and group 4(EC + L-GA + CE). The cultured hUVECs were seeded onto the treated porcine aortic valve, then that stuff were examined by means of EC VIII factor staining, living cells counting and microscopy. RESULTS: The cultured hUVEC could adhere to culturing bottle wall an hour later, and propagated to two passages after seven days. The cells increased with serial passage at a 7-day interval. But the hUVEC grew slowly when seeded onto the treated valve material except group 4. The cells in group 4 covered the surface of valve completely seven days later, which could also be seen in group 3 but not completely. There was no cell growing in group 1, and only fewer in group 2. The living cell in groups 3 and 4 were significantly more than in groups 1 and 2 on the 3rd, 7th and 14th days (P < 0.01), meanwhile, the number of cells in group 4 were also significantly more than that in group 3 (P < 0.05). The covering area of cultured cell on the valve material in groups 3 and 4 was significantly larger than that in groups 1 and 2. The covering area of cell in group 4 was over 95%, and higher than that in group 3(60%-70%). The hUVEC of group 4 arranged in pattern of three dimension. So it could resist rising of foreign power from the cardiac cavity of high pressure and flowing volume. There was no cell on the leaflet surface in group 1, and only a few pinch of cells could be seen in group 2. CONCLUSION: The porcine aortic valve can be used to be an ideal xenogeneic valve scaffold; the scaffold of porcine aortic valve should be treated by use of epoxy-chloropropane, L-glutamic acid and cellular extraction, so that a best growing environment to the hUVEC would be given; the cultured hUVECs used to be source of seed living cell had a boundless prospects; the growing velocity of cultured hUVEC was controllable, which facilitated clinical application; and the endothelial cells of xenogeneic valve material which grew compactly onto the scaffold can resist rising of foreign power from the cardiac cavity itself.

Animals↗

PubMed1976

Studies on the effects of furazolidon and P-rosaniline on the kinetoplast of Trypanosoma gambiense in mice.

p-Rosaniline-sensitive and -resistant strains of Trypanosoma gambiense were separately passaged in mice treated with furazolidon. After 10 serial passages in mice, the trypanosomes were found to be resistant to furazolidon when tested in mice. The rate of appearance of AK forms after injection of furazolidon into mice infected with a clone obtained from the p-rosaniline resistant strain by repeated treatment with furazolidon (WRF) was lower than that in mice infected with a clone obtained from the p-rosaniline sensitive strain by the same treatment with furazolidon (WSF). Moreover, WSF was resistant to p-rosaniline, although it had not been exposed to it. These results indicate that there is an interaction between the actions of furazolidon and p-rosaniline on the kinetoplast. The existence of this interaction was supported by electron microscopic observations on the kinetoplasts of trypanosomes after the injection with p-rosaniline and furazolidon into mice infected with the p-rosaniline resistant clones, WSF and WRF.

Animals↗

PubMed1992

The pathogenicity of two porcine rotaviruses differing in their in vitro growth characteristics and genes 4.

The pathogenicity of two rotavirus variants, 4F and 4S, obtained following adaptation to cell culture of rotavirus from a diarrhoeic pig in China, was compared by serial passage in 24 gnotobiotic piglets. The rotavirus variants have markedly different growth characteristics in vitro, and their genome profiles differ only in the relative migration of genes 4. Both cell culture-grown variants replicated to an equal extent in gnotobiotic piglets and neither caused disease, although weight gain was slightly affected in piglets inoculated with the 4F variant. During five serial pig-to-pig passages, variant 4F became highly pathogenic at the fourth and fifth passages, causing severe diarrhoea and weight loss, and premature death in two animals. Piglets inoculated with rotavirus variant 4S remained healthy during all passages although weight gain was slightly affected. Mean duration and peak infectivity titres of virus shedding were similar for both variants. Thus, variant 4F, which grew slowly and produced small plaques in vitro and had the faster migrating gene 4, was pathogenic in pigs, whereas variant 4S was apathogenic.

Adaptation, Biological↗

PubMedDate not supplied

Effects of heterophil adaptation on Salmonella enteritidis fecal shedding and egg contamination.

Serial passage of wild-type Salmonella enteritidis (SE) in chicken heterophils resulted in decreased shedding of SE in chicken feces and reduced egg contamination. When serially heterophil-passaged strains (heterophil-adapted SE [HASE]) were given to groups of 12 or more laying hens in drinking water at a dose of 10(8) colony-forming units for 3 consecutive days, the inoculum persisted in the feces at low frequency for a few days only. Two challenge wild-type strains, given in similar manner, persisted in feces at high frequency for 25 days or longer. The persistence of challenge strains in hens previously exposed to HASE was considerably shorter and occurred less frequently than persistence and frequency in challenge control hens. HASE strains were not isolated from any of 494 eggs laid after exposure to HASE. The challenge strain was isolated from 15 of 208 eggs (7.2%) after challenge of control hens and never from 461 eggs laid after challenge of "vaccinated" hens. I concluded that HASE clones obtained by five or more cycles of heterophil phagocytosis were avirulent and immunogenic.

Animals↗

PubMed1991

Rapid de novo generation of defective interfering RNA by cucumber necrosis virus mutants that do not express the 20-kDa nonstructural protein.

It is generally believed that serial passage at high multiplicity of infection (moi) is required for the generation of defective interfering (DI) particles. High levels of DI RNAs are found associated with persistent infections initiated with laboratory cultures of cucumber necrosis virus (CNV). Two synthetic CNV transcripts that were derived through site-directed mutagenesis of a highly infectious CNV cDNA clone and that do not express the CNV 20-kDa nonstructural protein were found to generate high levels of symptom-attenuating DI RNAs de novo without serial high-moi passage in transcript-inoculated plants. Such de novo generation of DI RNAs did not occur in infections initiated with wild-type transcript until at least eight serial high-moi passages. The observation that a CNV nonstructural protein mutant rapidly generates DI RNA de novo may provide insight into mechanisms that underly DI particle formation in RNA viruses in general.

Base Sequence↗

PubMed1991

Nucleotide sequence analysis of three different hepatitis delta viruses isolated from a woodchuck and humans.

We have investigated the extent of hepatitis delta virus (HDV) genetic variability after serial passages in chimpanzees and woodchucks and between different human isolates. A complete HDV genome, isolated from a woodchuck liver, was cloned after five serial transmissions. The 1679 nucleotide long genome revealed only point mutations and a nucleotide divergence of 0.65% and 0.89% with previously published sequences of two epidemiologically related HDVs. We have obtained partial nucleotide sequences of two unrelated human HDV cDNAs by using the polymerase chain reaction. When compared to the woodchuck HDV strain and other previously reported isolates, a perfectly conserved region of 90 nucleotides was shown in the region encompassing the delta antigen antigenomic self-cleavage site. In woodchuck and human HDV strains, the two forms of delta protein (195 and 214 amino acids) were potentially expressed. Our study indicates that only a limited genetic variability is generated by several passages in animals despite significant modification of pathogenicity during these transmissions.

Animals↗