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Biomedical subjects

M Labuda

Publications and source records attributed to M Labuda.

At least 19 recordsLinked to original sources
PubMed2000

Inhibition of the antiviral action of interferon by tick salivary gland extract.

The saliva of haematophagous arthropods (e.g. mosquitoes, sandflies and ticks) contains potent immunomodulatory activities that counter their hosts' haemostatic, inflammatory and immune responses to facilitate blood-feeding. Such effects are exploited by arthropod-transmitted pathogens to promote their transmission. We investigated the ability of tick saliva to enhance arthropod-borne virus (arbovirus) transmission by determining its effect on the antiviral action of murine interferon (IFN alpha/beta). Salivary gland extract (SGE) was prepared from partially fed adult female Dermacentor reticulatus ticks that had been feeding on mice for either 3 or 5 days (SGED3 and SGED5, respectively). We demonstrated that SGE inhibits the antiviral effect of IFN as measured by a biological assay using vesicular stomatitis virus (VSV), and by two-dimensional electrophoretic analysis of the appearance of selected VSV proteins. The most pronounced effect was observed when mouse L cells were treated with SGE prior to IFN treatment. Following pretreatment with SGE, virus multiplication (which was fully blocked by IFN treatment alone) achieved yields similar to those obtained from infected cells not treated with IFN. Contemporaneous treatment, or treatment with SGE after IFN, was less effective. In parallel with these findings, formation of early viral proteins, N (nucleocapsid protein) and P (phosphoprotein), which was blocked by IFN, was detectable following pretreatment with SGE. The ability to inhibit the antiviral action of IFN was higher for SGED3 compared to SGED5. Demonstration that tick SGE can promote virus replication by suppressing the action of IFN helps explain why ticks are such efficient vectors of arboviruses.

Animals↗
PubMed1999

A nonpathogenic GAAGGA repeat in the Friedreich gene: implications for pathogenesis.

An individual with late-onset ataxia was found to be heterozygous for an unusual (GAAGGA)65 sequence and a normal GAA repeat in the frataxin gene. No frataxin point mutation was present, excluding a form of Friedreich ataxia. (GAAGGA)65 did not have the inhibitory effect on gene expression in transfected cells shown by pathogenic GAA repeats of similar length. GAA repeats, but not (GAAGGA)65, adopt a triple helical conformation in vitro. We suggest that such a triplex structure is essential for suppression of gene expression.

Aged↗
PubMed1999

Friedreich's ataxia: point mutations and clinical presentation of compound heterozygotes.

Friedreich's ataxia is the most common inherited ataxia. Ninety-six percent of patients are homozygous for GAA trinucleotide repeat expansions in the first intron of the frataxin gene. The remaining cases are compound heterozygotes for a GAA expansion and a frataxin point mutation. We report here the identification of 10 novel frataxin point mutations, and the detection of a previously described mutation (G130V) in two additional families. Most truncating mutations were in exon 1. All missense mutations were in the last three exons coding for the mature frataxin protein. The clinical features of 25 patients with identified frataxin point mutations were compared with those of 196 patients homozygous for the GAA expansion. A similar phenotype resulted from truncating mutations and from missense mutations in the carboxy-terminal half of mature frataxin, suggesting that they cause a comparable loss of function. In contrast, the only two missense mutations located in the amino-terminal half of mature frataxin (D122Y and G130V) cause an atypical and milder clinical presentation (early-onset spastic gait with slow disease progression, absence of dysarthria, retained or brisk tendon reflexes, and mild or no cerebellar ataxia), suggesting that they only partially affect frataxin function. The incidence of optic disk pallor was higher in compound heterozygotes than in expansion homozygotes, which might correlate with a very low residual level of normal frataxin produced from the expanded allele.

Adolescent↗
PubMed1999

Survival strategy of tick-borne encephalitis virus: cellular basis and environmental determinants.

Although TBE virus can be transmitted in the laboratory by a wide variety of ixodid tick species to a wide variety of vertebrate host species, nevertheless in nature endemic cycles of TBE virus depend principally on just two tick species, Ixodes ricinus in the western and I. persulcatus in the eastern Palaearctic. A complete transmission cycle, from tick to tick via vertebrates, occurs most efficiently between co-feeding ticks in the absence of a systemic viraemia. This non-systemic route depends on TBE virus replication within particular immunocompetent cells in the skin, and only certain vertebrate species, notably Apodemus mice, are susceptible to this. Amongst the potential tick vectors in Europe, only I. ricinus has the correct host relationships and appropriate natural life cycle to support such non-systemic transmission cycles. Within the wide European distribution of this tick-host relationship, only in certain places do larval and nymphal ticks feed together on the same hosts with sufficient coincidence to ensure TBE virus survival. The environmental factors that determine this seasonal coincidence are being identified with the help of remotely-sensed meteorological satellite imagery to create predictive risk maps of TBE foci.

Animals↗
PubMed1999

Incidence from coincidence: patterns of tick infestations on rodents facilitate transmission of tick-borne encephalitis virus.

Tick-borne encephalitis (TBE) virus has a highly focal distribution through Eurasia. Endemic cycles appear to depend on the transmission of non-systemic infections between ticks co-feeding on the same rodent hosts. The particular features of seasonal dynamics and infestation patterns of larval and nymphal Ixodes ricinus, but not Dermacentor reticulatus, from 4 regions within TBE foci in Slovakia, are such as to promote TBE virus transmission. The distributions of larvae and nymphs on their principal rodent hosts are highly aggregated and, rather than being independent, the distributions of each stage are coincident so that the same ca. 20% of hosts feed about three-quarters of both larvae and nymphs. This results in twice the number of infectible larvae feeding alongside potentially infected nymphs compared with the null hypothesis of independent distributions. Overall, co-feeding transmission under these circumstances brings the reproductive number (R0) for TBE virus to a level that accounts quantitatively for maintained endemic cycles. Essential for coincident aggregated distributions of larvae and nymphs is their synchronous seasonal activity. Preliminary comparisons support the prediction of a greater degree of coincident seasonality within recorded TBE foci than outside. This identifies the particular climatic factors that permit such patterns of tick seasonal dynamics as the primary predictors for the focal distribution of TBE.

Animals↗
PubMed1999

Mapping of a gene determining familial partial epilepsy with variable foci to chromosome 22q11-q12.

We identified two large French-Canadian families segregating a familial partial epilepsy syndrome with variable foci (FPEVF) characterized by mostly nocturnal seizures arising from frontal, temporal, and occasionally occipital epileptic foci. There is no evidence for structural brain damage or permanent neurological dysfunction. The syndrome is inherited as an autosomal dominant trait with incomplete penetrance. We mapped the disease locus to a 3. 8-cM interval on chromosome 22q11-q12, between markers D22S1144 and D22S685. Using the most conservative diagnostic scheme, the maximum cumulative LOD score was 6.53 at recombination fraction (straight theta) 0 with D22S689. The LOD score in the larger family was 5.34 at straight theta=0 with the same marker. The two families share an identical linked haplotype for >/=10 cM, including the candidate interval, indicating a recent founder effect. A severe phenotype in one of the probands may be caused by homozygosity for the causative mutation, as suggested by extensive homozygosity for the linked haplotype and a bilineal family history of epilepsy. An Australian family with a similar phenotype was not found to link to chromosome 22, indicating genetic heterogeneity of FPEVF.

Australia↗
PubMed1999

Recombination in Tula hantavirus evolution: analysis of genetic lineages from Slovakia.

To examine the evolution of Tula hantavirus (TUL), carried by the European common vole (Microtus arvalis and M. rossiaemeridionalis), we have analyzed genetic variants from Slovakia, the country where the virus is endemic. Phylogenetic analysis (PHYLIP) based on either partial (nucleotides [nt] 441 to 898) or complete N-protein-encoding sequences divided Slovakian TUL variants into two main lineages: (i) strains from eastern Slovakia, which clustered with Russian strains, and (ii) strains from western Slovakia situated closer to those from the Czech Republic. We found genetic diversity of 19% between the two groups and 4% within the western Slovakian TUL strains. Phylogenetic analysis of the 3' noncoding region (3'-NCR), however, placed the eastern Slovakian strains closer to those from western Slovakia and the Czech Republic, with a greater distance to the Russian strains, suggesting a recombinant nature of the S segment in the eastern Slovakian TUL lineage. A bootscan search of the S-segment sequences of TUL strains revealed at least two recombination points in the S sequences of eastern Slovakian TUL strains (nt 400 to 415 and around 1200) which agreed well with the pattern of amino acid substitutions in the N protein and deletions/insertions in the 3'-NCR of the S segment. These data suggest that homologous recombination events occurred in the evolution of hantaviruses.

3' Untranslated Regions↗
PubMed1999

Short report: simultaneous occurrence of Dobrava, Puumala, and Tula Hantaviruses in Slovakia.

The prevalence of antibody to hantaviruses in Slovakia (serum panel n = 2,133) was lower in the western part (0.54%) and higher in the eastern part (1.91%) of the country and was found to be significantly enhanced in a group of forest workers from eastern Slovakia (5.88%). One-third of the IgM-negative convalescent phase sera from patients with hemorrhagic fever with renal syndrome exhibited antibodies reacting predominantly with Puumala virus antigen, while two-thirds had antibodies directed mainly against Hantaan virus antigen. Fine analysis of two Hantaan virus-reactive sera by a focus reduction neutralization test showed that Dobrava hantavirus was the source of these human infections. Initial results of rodent screening indicated the circulation of Dobrava virus in populations of striped field mice (Apodemus agrarius) in eastern Slovakia.

Animals↗
PubMed1998

Tick salivary gland extracts promote virus growth in vitro.

Saliva of blood-feeding arthropods promotes infection by the vector-borne pathogens they transmit. To investigate this phenomenon in vitro, cultures of mouse L cells were treated with a salivary gland extract (SGE) prepared from feeding ticks and then infected with vesicular stomatitis virus (VSV). At low input doses of VSV, viral yield was increased 100-fold to 10,000-fold by 16-23 h post-infection compared with untreated cultures, and depending on the SGE concentration. SGE-mediated acceleration of viral yield corresponded with the earlier appearance of VSV nucleocapsid protein as detected by 2-dimensional electrophoresis of infected cells. The observation that physiological doses of virus (i.e. doses likely to be inoculated by an infected arthropod vector into its vertebrate host during blood-feeding) respond to SGE treatment in vitro provides a new opportunity for identifying the factors in tick saliva that promote virus transmission in vivo.

Animals↗
PubMed1998

Genetics of vitamin D 1alpha-hydroxylase deficiency in 17 families.

Vitamin D-dependent rickets type I (VDDR-I), also known as pseudo-vitamin D-deficiency rickets, appears to result from deficiency of renal vitamin D 1alpha-hydroxylase activity. Prior work has shown that the affected gene lies on 12q13.3. We recently cloned the cDNA and gene for this enzyme, mitochondrial P450c1alpha, and we and others have found mutations in its gene in a few patients. To determine whether all patients with VDDR-I have mutations in P450c1alpha, we have analyzed the P450c1alpha gene in 19 individuals from 17 families representing various ethnic groups. The whole gene was PCR amplified and subjected to direct sequencing; candidate mutations were confirmed by repeat PCR of the relevant exon from genomic DNA from the patients and their parents. Microsatellite haplotyping with the markers D12S90, D12S305, and D12S104 was also done in all families. All patients had P450c1alpha mutations on both alleles. In the French Canadian population, among whom VDDR-I is common, 9 of 10 alleles bore the haplotype 4-7-1 and carried the mutation 958DeltaG. This haplotype and mutation were also seen in two other families and are easily identified because the mutation ablates a TaiI/MaeII site. Six families of widely divergent ethnic backgrounds carried a 7-bp duplication in association with four different microsatellite haplotypes, indicating a mutational hot spot. We found 14 different mutations, including 7 amino acid replacement mutations. When these missense mutations were analyzed by expressing the mutant enzyme in mouse Leydig MA-10 cells and assaying 1alpha-hydroxylase activity, none retained detectable 1alpha-hydroxylase activity. These studies show that most if not all patients with VDDR-I have severe mutations in P450c1alpha, and hence the disease should be referred to as "1alpha-hydroxylase deficiency."

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1998

Unusual EEG pattern linked to chromosome 3p in a family with idiopathic generalized epilepsy.

OBJECTIVE: To map the gene causing an unusual EEG pattern of delta bursts that appears to segregate as an autosomal dominant trait in an Italian family. The EEG pattern was observed in four family members affected by idiopathic generalized epilepsy (IGE) and in six other clinically unaffected members. METHODS: All available family members underwent clinical and EEG examination. DNA samples were obtained and used to perform a whole-genome scan with 270 microsatellite markers. After the first linked marker was identified, 12 additional markers in the same chromosomal region were tested to confirm linkage and define a candidate interval. RESULTS: The gene responsible for the EEG trait was mapped to an 11-cM interval on the proximal short arm of chromosome 3 (3p14.2-p12.1). CONCLUSION: In this family, a characteristic EEG activity is due to the effect of a single gene on chromosome 3p. A gene encoding a Ca2+ channel subunit maps in the interval and is a potential candidate for the trait. The clinical expression of epilepsy in four family members may reflect the interaction of additional genes, though environmental or other factors cannot be excluded.

Chromosome Mapping↗
PubMed1998

Incidence of dominant spinocerebellar and Friedreich triplet repeats among 361 ataxia families.

OBJECTIVE: To determine the incidence of spinocerebellar ataxia (SCA) types 1, 2, 3, 6, and 7 and Friedreich's ataxia (FA) among a large panel of ataxia families. BACKGROUND: The ataxias are a clinically and genetically heterogeneous group of neurodegenerative diseases that variably affect the cerebellum, brainstem, and spinocerebellar tracts. Trinucleotide repeat expansions have been shown to be the mutational mechanism for five dominantly inherited SCAs as well as FA. METHODS: We collected DNA samples and clinical data from patients representing 361 families with adult-onset ataxia of unknown etiology. Patients with a clinical diagnosis of FA were specifically excluded from our collection. RESULTS: Among the 178 dominant kindreds, we found SCA1 expansion at a frequency of 5.6%, SCA2 expansion at a frequency of 15.2%, SCA3 expansion at a frequency of 20.8%, SCA6 expansion at a frequency of 15.2%, and SCA7 expansion at a frequency of 4.5%. FA alleles were found in 11.4% of apparently recessive and 5.2% of apparently sporadic patients. Among these patients the repeat sizes for one or both FA alleles were relatively small, with sizes for the smaller allele ranging from 90 to 600 GAA repeats. The clinical presentation for these patients is atypical for FA, with one or more of the following characteristics: adult onset of disease, retained tendon reflexes, normal plantar response, and intact or partially intact sensory perceptions. CONCLUSIONS: Pathogenic trinucleotide repeat expansions were found among 61% of the dominant kindreds. Among patients with apparently recessive or negative family histories of ataxia, 6.8% and 4.4% tested positive for a CAG expansion at one of the dominant loci, and 11.4 and 5.2% of patients with apparently recessive or sporadic forms of ataxia had FA expansions. Because of the significant implications that a dominant versus recessive inheritance pattern has for future generations, it is important to screen patients who do not have a clearly dominant inheritance pattern for expansions at both the FA and the dominant ataxia loci.

Adult↗
PubMed1997

Tick-borne encephalitis virus transmission between ticks cofeeding on specific immune natural rodent hosts.

To determine whether the portion of a vertebrate host population having specific immunity to tick-borne encephalitis (TBE) virus can participate in the TBE virus transmission cycle, natural hosts immunized against TBE virus were challenged with infected and uninfected ticks. Yellow-necked field mice (Apodemus flavicollis) and bank voles (Clethrionomys glareolus) were either immunized with TBE virus by subcutaneous inoculation of the virus, or they were exposed to virus-infected Ixodes ricinus ticks. One month later, when serum neutralizing antibody was detectable, the animals were infested with infected (donor) adult female ticks and uninfected (recipient) nymphal ticks; recipients were allowed to feed either in close contact (chamber 1) or physically separated (chamber 2) from the infected donor ticks. Following challenge with infected (and uninfected) ticks, viremia developed in all the control, nonimmune animals, whereas viremia was undetectable in all those animals naturally immunized by previous exposure to infected ticks. Despite the presence of neutralizing antibodies in all the immunized animals, 89% (24/ 27) immune animals supported virus transmission between infected and uninfected cofeeding ticks. Most transmission was localized, occurring within chamber 1; disseminated transmission from chamber 1 to chamber 2 was reduced. Immunization by tick bite was more effective than immunization by syringe inoculation in blocking cofeeding virus transmission. Nevertheless 76% (9/12) animals with "natural" immunity still supported transmission. The results demonstrate that natural hosts having neutralizing antibodies to TBE virus (and no detectable viremia) can still support virus transmission between infected and uninfected ticks feeding closely together on the same animal. These observations have important epidemiological implications relating to the survival of TBE virus in Nature.

Animals↗
PubMed1997

The Friedreich ataxia GAA triplet repeat: premutation and normal alleles.

The most common mutation causing Friedreich ataxia (FRDA), an autosomal recessive neurodegenerative disease, is the hyperexpansion of a polymorphic GAA triplet repeat localized within an Alu sequence (GAA-Alu) in the first intron of the frataxin (X25) gene. GAA-Alu belongs to the AluSx subfamily and contains several polymorphisms in strong linkage disequilibrium either with a subgroup of normal alleles, or with hyperexpanded FRDA-associated alleles. GAA repeat sizes in 300 normal chromosomes (97 from carriers and 203 from controls) were distributed in two separate groups: 83% of them contained between six and 10 triplets (small normal alleles), while the remaining 17% had more than 12 triplets, up to 36 (large normal alleles). Sequence analysis showed that no normal, stable allele contained more than 27 uninterrupted GAA triplets. All longer normal alleles were interrupted by a hexanucleotide repeat (GAGGAA). An allele containing an uninterrupted run of 34 GAA triplets was stably transmitted in four instances, but in one case underwent hyperexpansion to 650 triplets. Overall, our results suggest that the FRDA-associated expanded GAA repeats originate from normal alleles by recurrent expansions of alleles at risk.

Alleles↗
PubMed1997

Transmission of tick-borne bunyaviruses by cofeeding ixodid ticks.

Palma and Bhanja bunyaviruses replicated in Dermacentor marginatus, D. reticulatus, Rhipicephalus sanguineus, R. appendiculatus and Ixodes ricinus ticks after parenteral inoculation and appropriate incubation and feeding. Palma virus was transmitted to D. marginatus and D. reticulatus males, D. reticulatus and R. sanguineus females, and R. appendiculatus nymphs while cofeeding with infected ticks on laboratory mice. Bhanja virus was transmitted to D. marginatus males and R. appendiculatus nymphs. Laboratory mice developed low levels of viraemia detectable only by intracranial (i.c.) inoculation of newborne laboratory mice.

Animals↗
PubMed1996

Importance of localized skin infection in tick-borne encephalitis virus transmission.

Arboviruses are transmitted to vertebrates by the "bite" of infected arthropods. Events at the site of virus deposition are largely unknown despite increasing evidence that blood-sucking arthropods immunomodulate their skin site of feeding. This question is particularly relevant for ixodid ticks that feed for several days. To examine events under conditions mimicking tick-borne encephalitis (TBE) virus transmission in nature (i.e., infected and uninfected Ixodes ricinus ticks feeding on the same animal), infected adult and uninfected nymphal ticks were placed in one retaining chamber (skin site A) and uninfected nymphs were placed within a second chamber posteriorly (skin site B) on two natural host species, yellow-necked field mice (Apodemus flavicollis) and bank voles (Clethrionomys glareolus). Virus transmission from infected to uninfected cofeeding ticks was correlated with infection in the skin site of tick feeding. Furthermore, virus was recruited preferentially to the site in which ticks were feeding compared with uninfested skin sites. Viremia did not correspond with a generalized infection of the skin; virus was not detected in an uninfested skin site (C) of 12/13 natural hosts that had viremia levels > or = 2.0 log10 ic mouse LD50/0.02 ml blood. To characterize infected cells, laboratory mouse strains were infested with infected ticks and then explants were removed from selected skin sites and floated on culture medium. Numerous leukocytes were found to migrate from the skin explants of tick feeding sites. Two-color immunocytochemistry revealed viral antigen in both migratory Langerhans cells and neutrophils; in addition, the migratory monocyte/macrophages were shown to produce infectious virus. The results indicate that the local skin site of tick feeding is an important focus of viral replication early after TBE virus transmission by ticks. Cellular infiltration of tick feeding sites, and the migration of cells from such sites, may provide a vehicle for transmission between infected and uninfected cofeeding ticks that is independent of a patent viremia. The data support the hypothesis that viremia is a product, rather than a prerequisite, of tick-borne virus transmission.

Animals↗