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PubMed1997

Protective effect of exposure to non-virulent Trypanosoma cruzi clones on the course of subsequent infections with highly virulent clones in mice.

The protective effect of primary infection with non-virulent Trypanosoma cruzi clones against subsequent infection with highly virulent clones was determined in groups of BALB/c mice. All mice inoculated with the highly virulent m3 and m4 clones succumbed in < or = 16 days. Mice inoculated with the non-virulent h1 and h2 clones survived and were superinfected with the m3 and m4 clones. Low degrees of parasitaemia were observed in mice challenged with the highly virulent clones. The survival ratios of the superinfected mice were not statistically different from those seen in mice that received a single injection of non-virulent T. cruzi. Mice given a non-virulent infection and subsequently challenged with a virulent clone differed from those given only a non-virulent infection in showing more frequently an inflammatory infiltrate in the heart, skeletal muscle and intestines.

Animals↗
PubMed1988

Monoclonal antibodies to a virulent strain of transmissible gastroenteritis virus: comparison of reactivity with virulent and attenuated virus.

Twelve hybridomas secreting monoclonal antibodies (MAbs) against Miller virulent strain of transmissible gastroenteritis virus (TGEV) were generated and characterized. In a cell culture immunofluorescence (CCIF) assay, three MAbs directed against peplomer protein (E2) had perinuclear fluorescence and four unclassified MAbs showed cell membrane fluorescence. Six of these seven MAbs neutralized both attenuated and virulent TGEV, and the seventh (an unclassified MAb) neutralized only the latter virus. Two MAbs able to bind the cell membrane of infected cells had low neutralizing antibody titers (8 to 72) but were able to distinguish between virulent and attenuated TGEV (9- to 72-fold differences in neutralizing titers). Two E2-specific MAbs had higher neutralizing antibody titers (782 to 34,117) and showed 4- to 13-fold differences in titers against the attenuated and virulent TGEV strains. Five MAbs which were specific for nucleocapsid (N) protein had cytoplasmic, particulate fluorescence in CCIF, and did not neutralize TGEV. Comparison of CCIF antibody titers of MAbs to the virulent and attenuated strains of TGEV indicated that differences existed in titers of most E2 and all N-specific MAbs, with titers consistently higher against virulent TGEV (homologous strain). Hyperimmune antisera prepared in gnotobiotic pigs against the attenuated, virulent and a recent isolate of TGEV immunoprecipitated the 3 major structural proteins of both the attenuated and virulent TGEV strains. Relative mol. wt. differences in the E1 and E2 proteins between the two virus strains were revealed using either the hyperimmune pig sera or MAbs. In addition to the 48 K N protein, a 44 K protein was coimmunoprecipitated by the hyperimmune sera and MAbs, but mainly from lysates of attenuated TGEV.

Animals↗
PubMed1987

Comparison of virulent trypomastigotes with low-virulent ones derived from a single strain of Trypanosoma cruzi: infectivity to new fibroblasts from various organs of the mouse.

Previous experiments have shown that the infectivity of virulent trypomastigotes in L-cell culture was much more intensive not only for macrophages but also for newly cultured fibroblasts from the mouse heart as compared to low-virulent trypomastigotes in L-cell culture which had been derived from the same strain. On the other hand, the infectivity of virulent trypomastigotes for L-cells was less intensive. In the present work, new fibroblasts derived from muscles, skin, heart and kidney of newborn mice and established fibroblasts from mouse muscles were examined in terms of their susceptibility to trypomastigotes of different virulence. A slight difference of susceptibility to virulent trypomastigotes among new fibroblasts from different sources was found, i.e. fibroblasts derived from muscles and skin were more susceptible than those from heart and kidney. Growth of low-virulent trypomastigotes was suppressed in all new fibroblasts. This suppression was explained by the result that amastigote proliferation of a low-virulent strain was much slower in new fibroblasts from mouse muscles in spite of a similar penetrative ability of both kinds of trypomastigotes. Furthermore, a slight decrease in the susceptibility of new fibroblasts to virulent trypomastigotes was found depending on the length of time fibroblasts had been maintained.

Animals↗
PubMed1991

The Salmonella typhimurium virulence plasmid encodes a positive regulator of a plasmid-encoded virulence gene.

The 90-kb virulence plasmid of Salmonella typhimurium is necessary for invasion beyond the Peyer's patches to the mesenteric lymph nodes and spleens of orally inoculated mice. Two Tn5 insertions located on the left side of a previously identified 14-kb virulence region (P. A. Gulig and R. Curtiss III, Infect. Immun. 58:3262-3271, 1988) and mapping 272 bp from each other exhibited opposite effects on splenic infection of mice after oral inoculation. spvR23::Tn5 decreased splenic infection by 1,000-fold, whereas a spv-14::Tn5 mutant outcompeted wild-type S. typhimurium for splenic infection by 27-fold in mice fed mixtures of mutated and wild-type S. typhimurium. spvR23::Tn5 was complemented by a virulence plasmid subclone with an insert sequence encoding only an 891-bp open reading frame specifying a 33,000-molecular-weight protein. The amino acid sequence of this open reading frame had significant homology to members of the LysR family of positive regulatory proteins; thus, the gene was named spvR (salmonella plasmid virulence). To examine the possible regulatory effects of spvR on other virulence genes, we constructed a lacZ operon fusion in a downstream virulence gene, spvB. When spvR subcloned behind the lac promoter was provided on a separate plasmid in trans to the spvB-lacZ operon fusion, transcription of spvB increased 15-fold. spv-14::Tn5, which conferred a competitive advantage to S. typhimurium, increased the expression of a spvR-lacZ operon fusion in cis. spvR is therefore a positive regulator of spvB and an essential virulence gene of S. typhimurium. As opposed to having spvR subcloned behind the lac promoter, the wild-type spvR gene present on the virulence plasmid did not function to positively regulate spvB-lacZ in trans when salmonellae were grown to the log phase in L broth, suggesting that this regulatory system is activated in vivo during infection.

Amino Acid Sequence↗
PubMed1961

The virulence in the guinea-pig of tubercle bacilli isolated before treatment from South Indian patients with pulmonary tuberculosis. 3. Virulence related to pretreatment status of disease and to response to chemotherapy.

This is the last of a series of three reports from the Tuberculosis Chemotherapy Centre Madras, on a study undertaken with the object of finding out whether differences in the virulence in the guinea-pig of tubercle bacilli isolated from South Indian tuberculous patients before the start of chemotherapy are related to the severity of the patients' disease on admission to treatment and to the subsequent response to chemotherapy. The 281 patients in this study were drawn from the patients admitted to a 1-year comparison of four domiciliary chemotherapeutic regimens: (a) 3.9-5.5 mg/kg isoniazid plus 0.2-0.3 g/kg sodium PAS daily, divided into two doses (PH series); (b) 7.8-9.6 mg/kg isoniazid alone daily in one dose (HI-1 series); (c) 7.8-9.6 mg/kg isoniazid alone daily, divided into two doses (HI-2 series); (d) 3.9-5.5 mg/kg isoniazid alone daily, divided into two doses (H series).No evidence was found of an association between the virulence of the organisms and any pretreatment condition of known prognostic importance. There was no association between pretreatment virulence and progress during treatment in the PH series (the most effective regimen). In the other series, however, the progress was more satisfactory in patients infected with organisms of low virulence than in those infected with organisms of high virulence, the association between virulence and progress attaining statistical significance in the combined HI-2 and H series (the least effective regimens) and only just failing to do so in the smaller HI-1 series.Possible explanations are put forward both for the absence of an association between virulence and severity of disease on admission and for the presence of an association between virulence and response in the patients treated with isoniazid alone.

Aged↗
PubMed2000

Pathogenicity caused by high virulent and low virulent strains of Steinernema carpocapsae to Galleria mellonella.

Steinernema carpocapsae is an entomopathogenic nematode associated with a symbiotic bacterium, Xenorhabdus nematophilus. Both components of the complex participate in a pathogenic process in insects. This has raised two questions: how much does each one participate, and what mechanisms are involved? In this paper we compare the virulence of two strains of S. carpocapsae: a high virulent strain (Breton) and a low virulent strain (Az27), both of which are free of symbiotic bacteria. Breton and Az27 strains each one have similar ability to invade Galleria mellonella with median infectious times of 3.9 and 3.2 h, respectively. However, the LD(50) of the Breton and Az27 strains are 48.6 and 894.5 infective juveniles per insect, respectively. Breton strain takes 38 h to kill 100% of exposed insects, whereas Az27 takes three times longer. The lethal time of the low virulent strain in G. mellonella larvae is highly dependent on the number of nematodes which have penetrated the hemocelium, whereas it is not on the high virulent strain. Hemolymph patterns in SDS-PAGE of insects parasitized by the high virulent strain showed important differences in respect to the low virulent strain and control. Secretion/excretion products of the high virulent strain have important proteolytic activity as well as alpha-mannosidase and alpha-fucosidase activities, whereas, in secretion/excretion products of the avirulent strain, proteolytic activity was lower and alpha-mannosidase and alpha-fucosidase activities were undetected.

Animals↗
PubMed1997

Mixed vaginal infections of Balb/c mice with low virulent herpes simplex type 1 strains result in restoration of virulence properties: vaginitis/vulvitis and neuroinvasiveness.

Vaginal infections of BALB/c Ann mice with herpes simplex virus type 1 (HSV-1) were studied. Mice were inoculated with virulent strains ANG path and 17 syn+ or low-virulent recombinant strains 27/III and 17-syn3 that differ from parental strains in their glycoprotein B (gB) gene sequences. When low-virulent strains were inoculated separately, no vaginitis/vulvitis was produced despite replication in the vagina. In contrast, after coinfection of mice with the two low-virulent strains, vaginitis/vulvitis was produced and virus could be recovered from the central nervous system (CNS). Two of the CNS isolates produced vaginitis/vulvitis, neuroinvasiveness and death of mice after vaginal infection. Restriction fragment analysis and sequencing were used to assess recombination events in the gB gene sequence of the CNS isolates. After mixed vaginal infection recombination between non-virulent HSV strains occurs, resulting in vaginitis/vulvitis and neuroinvasiveness. No correlation was detected between the syncytial phenotype and local vaginal virulence. Virulence of HSV is not solely dependent on gB function; it seems to be more probable that several genes act in concert to induce virulence and neuroinvasiveness.

Amino Acid Sequence↗
PubMed1999

Detection of virulent strains of Streptococcus suis type 2 and highly virulent strains of Streptococcus suis type 1 in tonsillar specimens of pigs by PCR.

We developed a PCR assay for the rapid and sensitive detection of virulent Streptococcus suis type 2 and highly virulent S. suis type 1 in tonsillar specimens from pigs. The PCR primers were based on the sequence of the gene encoding the EF-protein of virulent S. suis type 2 strains (MRP+EF+) and highly virulent S. suis type 1 strains (MRP(s)EF+) and of the EF protein of weakly virulent S. suis type 2 strains (MRP+EF). The latter strains give rise to larger PCR products than the virulent strains of S. suis type 1 and 2. A positive control template was included in the assay to identify false negative results. The PCR was evaluated using tonsillar specimens from herds known (or suspected) to be infected and herds without an S. suis history. The results obtained with the PCR assay were compared with the results obtained with a newly developed bacteriological examination. In this bacteriological examination we were able to identify the EF-positive strains directly in the tonsillar specimens. From the 99 tonsils examined, 48 were positive in the PCR and 51 negative. All specimens from which EF-positive S. suis strains were isolated were also positive in the PCR assay. Three samples were positive in the PCR, but negative by bacteriological examination. The results demonstrated that the PCR is a highly specific and sensitive diagnostic tool for the detection of pigs carrying virulent strains of S. suis type 2 and highly virulent strains of type 1. Application of the assay may contribute to the control of S. suis infections.

Animals↗
PubMed1997

Leishmania major: a clone with low virulence for BALB/c mice elicits a Th1 type response and protects against infection with a highly virulent clone.

BALB/c mice are highly susceptible to infection with Leishmania major and generally develop a severe, nonhealing form of disease following parasite inoculation. As opposed to protective Th1 type immune responses which develop in resistant strains of mice, BALB/c mice develop predominant Th2 type responses characterized by the production of high levels of IL-4, but only low levels of IFN-gamma. However, BALB/c mice will develop resistance and Th1 type responses following the inoculation of very low numbers of L. major promastigotes. In this study, we have examined the effects of parasite virulence on the immune response and disease phenotype in susceptible BALB/c mice. Two clones of L. major were isolated which differed with respect to their in vitro growth rates as promastigotes and their virulence for mice. One rapidly growing clone, L.m.F1, was highly virulent in BALB/c mice and produced nonhealing infections characterized by predominant Th2 type responses. In contrast, a slow-growing clone, L.m.S2, was less virulent in BALB/c mice and produced self-healing infections at parasite doses equivalent to those which produced progressive disease with the more virulent clone. Mice which healed infections with the L.m.S2 clone developed responses characterized by elevated production of IFN-gamma and were resistant to a challenge infection with the virulent L.m.F1 clone. These results suggest that the virulence of individual parasite clones may influence both the course of disease and the phenotype of the immune response which develops during infection.

Animals↗
PubMed1993

Non-toxigenic derivatives of the Ames strain of Bacillus anthracis are fully virulent for mice: role of plasmid pX02 and chromosome in strain-dependent virulence.

The toxin-encoding plasmid pX01 and capsule-associated plasmid pX02 are required for full virulence of Bacillus anthracis in some animals. However, the non-toxigenic pX01-cured derivatives of certain anthrax strains are not completely attenuated for mice, and their virulence is strain-dependent. The strain-related differences were partially associated with plasmid pX02 as demonstrated by pX02 transductants of the attenuated vaccine strain UM23-1 cured of pX01. To determine the virulence of non-toxigenic variants of virulent strains, we isolated pX01- derivatives of the Vollum 1B strain and the more 'vaccine-resistant' Ames strain which carried pX02 from either Ames or Vollum 1B. The 50% lethal dose (LD50) values of the derivatives of both strains which carried the Ames pX02 were not significantly different from the LD50s of the pX01+ pX02+ strains (and were lower than those of pX01+ pX02- strains). pX02+ derivatives of strain UM23-1 were less virulent than the comparable Ames and Vollum 1B strain derivatives, emphasizing a role for chromosomal loci in the virulence of the latter two strains. Non-toxigenic isolates which carried the Ames pX02 were more virulent for CBA/J mice than those with Vollum 1B pX02, and the differences were mouse strain-dependent. The pX01- pX02+ strains multiplied and achieved high concentrations systemically.

Animals↗
PubMed2004

The enhanced virulence of very virulent infectious bursal disease virus is partly determined by its B-segment.

There is a remarkable difference in virulence of infectious bursal disease virus (IBDV) strains ranging from sub-clinical infections for serotype 2 and cell culture adapted serotype 1 strains, to 100% mortality for very virulent serotype 1 strains in young SPF chickens. It is known that cell culture adaptation related attenuation is determined by distinct mutations in the hypervariable region of the VP2 outer capsid protein, encoded on the A-segment. Amino acid mutations in the hypervariable VP2 region however, offer no explanation for the difference in virulence of classical and very virulent serotype 1 strains. Here we show by in vitro and in vivo analysis of rescued segment re-asserted IBDVs that virulence factors are not only located on the A-segment, but on the RNA Dependent RNA Polymerase (VP1) encoding B-segment as well. Insight into the virulence factors of very virulent IBDV will contribute to the improvement of live IBDV vaccines.

Animals↗
PubMed1985

Comparison of structural and nonstructural proteins of virulent and less virulent Theiler's virus isolates using two-dimensional gel electrophoresis.

The Theiler's murine encephalomyelitis viruses (TMEV) are important neurotropic picornaviruses because they persist in the central nervous system (CNS) and produce an inflammatory demyelinating disease in the mouse, their natural host. Insight into the pathogenesis of this disease may come from studying the genetic and biochemical compositions of these viruses; therefore, in this report, the structural and nonstructural proteins specified by both highly and less virulent TMEV were examined. Using two-dimensional gel electrophoresis, structural and nonstructural proteins, originating from each of the three regions of the picornavirus genome (Kitamura et al., 1981; Rueckert and Wimmer, 1984), from nine TMEV isolates were compared on the basis of isoelectric points (pI). Proteins of two virulent TMEV (GDVII and FA viruses) had almost indistinguishable pI values, whereas two of the three major capsid proteins of the less virulent TMEV varied considerably. For example, the structural proteins VP1 and VP3 from seven less virulent viruses ranged from pI 6.3 to 6.9 and 6.5 to 8.3, respectively. On the other hand, the pI values of VP2 and nonstructural proteins from the less virulent TMEV varied relatively little. In general, structural proteins of each TMEV group had pI ranges unique to their respective biological group, while most nonstructural proteins were similar for all TMEV. The virus-specified proteins of Vilyuisk virus, which is serologically related to the TMEV and a possible cause of encephalomyelitis in man, had pI values similar to the less virulent TMEV. Finally, VP3 not only showed the greatest variation in pI among the less virulent TMEV, but it also was preferentially radioiodinated in intact virus from each of the two biological groups using the lactoperoxidase technique.

Animals↗
PubMedDate not supplied

An unusual repetitive element from highly virulent isolates of Leptosphaeria maculans and evidence of its transfer to a weakly virulent isolate.

A 5,238-bp repetitive DNA element from a highly virulent isolate of Leptosphaeria maculans has been cloned and sequenced. The element is present in approximately 80 copies per haploid genome and hybridizes to every chromosome resolved by pulse field gel electrophoresis. The sequence is composed of 66% A+T and has numerous, very short, direct and inverted repeats. No RNA complementary to the element was detected in log phase cultures, and no open reading frames of significant length are present in the sequence. It has no structural similarity to other repetitive elements or significant homology to database sequences. We have designated the element LMR1. Southern blot hybridization indicated that the element is present in all isolates of L. maculans that are highly virulent to Brassica napus and B. rapa. The general structure of the element was conserved among isolates of different mating type, pathogenicity group, and geographic origin, as determined by both Southern blot analysis and primer-directed DNA amplification. LMR1 did not hybridize to DNA from weakly virulent strains of L. maculans, with the exception of one isolate. Phylogenetic analyses of restriction fragment length polymorphism and rDNA sequence indicated that the highly virulent and weakly virulent strains of L. maculans are not monophyletic. Therefore, the presence of the LMR1 element in a weakly virulent isolate may indicate that a rare transfer event has occurred. Surprisingly, the weakly virulent isolate that contains LMR1 is more pathogenic on B. napus and B. juncea than a similar isolate that lacks the element.

Ascomycota↗
PubMed1999

Effect of virulence on immunogenicity of single and double vaccinia virus recombinants expressing differently immunogenic antigens: antibody-response inhibition induced by immunization with a mixture of recombinants differing in virulence.

It has been shown recently that the residual virulence of vaccinia virus (VV) is an important factor that influences the outcome of immunization with VV recombinants. This study focused on the correlation of the residual virulence of several VV recombinants with antibody responses against the strongly immunogenic extrinsic glycoprotein E of varicella-zoster virus and the weakly immunogenic extrinsic protein preS2-S of hepatitis B virus and against VV proteins, with mice used as a model organism. Furthermore, the effects of mixing different recombinants on the antibody response were studied. The results obtained indicated that: (i) the antibody response depended on the residual virulence of the recombinants, more so in the case of the weakly immunogenic protein; (ii) the residual virulence, the growth rate of the VV recombinants in extraneural tissues and the immunogenicity were associated features; (iii) immunization with mixtures of two differently virulent recombinants or with unequal amounts of two similarly virulent recombinants sometimes led to the suppression of antibody response. The appearance of this suppression was dependent on three factors: the residual virulence of the recombinants, the immunogenicity of the extrinsic proteins and the ratio of the recombinants in the mixtures. Thus, the data obtained demonstrate that there are various limitations to the use of replicating VV recombinants for immunization purposes.

Animals↗