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Biomedical subjects

A Spielman

Publications and source records attributed to A Spielman.

At least 109 records · Page 6Linked to original sources
PubMed1993

Diversionary role of hoofed game in the transmission of Lyme disease spirochetes.

To determine whether the presence of ungulates may inhibit transmission of the agent of Lyme disease (Borrelia burgdorferi) while promoting the abundance of its European vector tick (Ixodes ricinus), we compared the feeding density of subadult ticks on roe deer (Capreolus capreolus), red deer (Cervus elaphus), fallow deer (Dama dama), and wild sheep (Ovis ammon) near Berlin and in Brandenburg State, Germany. The prevalence of spirochetal infection in these ticks was compared with that in ticks swept from nearby vegetation. Spirochetes are present in nearly one-fifth of nonfed, questing nymphal and adult wood ticks in the region. Many ungulates in this intensely enzootic region fail to mount a detectable humoral response against the agent of Lyme disease, even when exposed to numerous infected ticks. During the height of the summer, each ungulate may support the feeding of hundreds of subadult ticks. Larvae feed lower on the bodies of hoofed game than do nymphs. Few ticks retain infection by the Lyme disease spirochete after feeding on hoofed game animals. We conclude that numerous I. ricinus ticks feed on ungulates, but that such host-contact fails to infect these ticks while eliminating pre-existing spirochetal infection.

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PubMed1992

A comprehensive multiple matrix model representing the life cycle of the tick that transmits the agent of Lyme disease.

An extension of Leslie matrix methodology was developed to describe the life cycle of Ixodes dammini, the tick that transmits the agent of Lyme disease in eastern North America. Thereby, we described the seasonally changing pattern of interactions of the tick with its various hosts in a well-studied site on Nantucket Island, Massachusetts. Particular numerical values representing the site were estimated mainly on the basis of published values and interpreted on the basis of experience. The model was used to predict seasonal abundance and annual rate of increase of this vector tick. Although these ticks quest for hosts during two consecutive feeding seasons, all but a few feed during the first such season. The relative distribution of developmental stages of the tick stabilized after 35 years. Abundance of the simulated population increased exponentially and doubled every 6 years. The simulations produced realistic seasonal feeding distributions of the ticks in its various developmental stages.

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PubMed1992

Elimination of Borrelia burgdorferi from vector ticks feeding on OspA-immunized mice.

Although recombinant outer surface protein A (OspA) of Borrelia burgdorferi protects mice against injected Lyme disease spirochetes, the mode of protection has not yet been explored. Indeed, the efficacy of vaccine-induced immunity against a realistic vector-mediated challenge remains unexplored. Accordingly, we determined whether this immunogen protects mice against spirochetes delivered by nymphal Ixodes dammini ticks. Following challenge by tick bite, no spirochetes could be cultured from immunized mice, and no characteristic histopathology was found. The spirochete was not detected in ticks that fed on immunized animals and was present in virtually all ticks that fed on nonimmunized mice. We conclude that OspA-immunized mice are protected from spirochetal infection, at least in part, because the spirochete is destroyed in the infecting tick.

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PubMed1992

Stage-associated risk of transmission of the Lyme disease spirochete by European Ixodes ticks.

To more closely define the risk of infection by the agent of Lyme disease in Europe, we determined whether spirochetal prevalence increases throughout the development of the Ixodes ricinus vector tick. Of all ticks that could be flagged from vegetation, I. ricinus were by far the most abundant. Spirochetal infection rates in the adult stage of this tick (15%) are no higher than those in nymphs (18%) but greatly exceed those in larvae (0.7%). This tick therefore appears to attain infection mainly from the host of its larval stage, generally feeds on hosts that are noncompetent as reservoirs in its nymphal stage, and rarely inherits infection. Risk of human infection mainly derives from contact with the nymphal stage of the vector tick because the larva is rarely infected and the adult is large enough to be noticed and promptly removed.

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PubMed1992

Loss of Lyme disease spirochetes from Ixodes ricinus ticks feeding on European blackbirds.

To determine whether blackbirds (Turdus merula), the most abundant and most abundantly tick-infested ecotonal bird of Central Europe, may contribute to the transmission of the Lyme disease spirochete (Borrelia burgdorferi), we compared the infectivity to ticks of naturally as well as experimentally infected blackbirds and rodents. European blackbirds experience intense exposure to Ixodes ricinus ticks and to the pathogens that they transmit. In nature, subadult I. ricinus ticks found feeding on these birds generally contain no spirochetes, although infection is universal in those found on black-striped mice (Apodemus agrarius). Those found on yellow-necked mice (A. flavicollis) are less frequently infected. Ticks lose infection in the course of feeding on blackbirds and fail to infect them. Subadult I. ricinus ticks readily feed on blackbirds, black-striped mice, and jirds (Meriones unguiculatus), but engorge less fully on the bird than on the rodents. Although birds may burden human health by establishing new infestations of I. ricinus ticks, our observations indicate that particular birds may benefit health by locally diminishing transmission of the Lyme disease spirochete.

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PubMed1992

Vegetation structure influences the burden of immature Ixodes dammini on its main host, Peromyscus leucopus.

To determine whether the relative abundance of immature Ixodes dammini (the vector of Lyme disease and human babesiosis) is related to habitat structure, we examined tick burdens on their main host, the white-footed mouse (Peromyscus leucopus), in 4 structurally diverse sites on Great Island, Massachusetts, USA. Vegetation structure at each site was quantified with respect to 25 habitat variables. Principal components analysis was used to reduce this set of habitat variables to seven new and orthogonal variables. Immature tick abundance varied widely among grids. Regression analysis of tick burdens on the habitat principal components showed that larval burdens were related strongly to the density of woody vegetation and negatively to herbaceous vegetation. Nymphal burdens were related negatively to herbaceous vegetation, but the relationship was not as strong as in the case of larvae. An experimental reduction in the abundance of white-tailed deer (Odocoileus virginianus), the main host of adult ticks, substantially reduced tick burdens and altered their relationships to habitat structure. Nymphal burdens were unrelated to habitat structure following deer removal. Manipulating habitat structure may have utility as a control strategy against this important vector.

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PubMed1992

Capacity of European animals as reservoir hosts for the Lyme disease spirochete.

The abundance of spirochete-infected Ixodes ricinus ticks naturally derived from endemic rodents was compared to identify the reservoir hosts of the agent of Lyme disease at a series of enzootic sites in Central Europe. Black-striped mice appear to be the most important rodent host for the tick and infect more ticks with Borrelia burgdorferi than do other mice and voles tested. Although rodents infect about half of the ticks that feed on them, lizards infect none. These spirochete-incompetent hosts dilute the force of transmission because many nymphal ticks feed on them. Older male hosts are more heavily infested by subadult ticks than are younger or female hosts. The intensity of transmission of the agent of Lyme disease at particular Central European sites appears to correlate directly with the presence of black-striped mice and inversely with that of lizards.

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PubMed1992

Delayed dissemination of Lyme disease spirochetes from the site of deposition in the skin of mice.

To determine whether the agent of Lyme disease disseminates in vertebrate hosts directly after deposition by an infecting tick, a 6-mm disk of skin was excised from the sites where nymphal Ixodes dammini ticks infected by Lyme disease spirochetes, Borrelia burgdorferi, had fed. Infection in each mouse was tested by examining xenodiagnostic ticks that had engorged on these mice 4 weeks later and by serologic testing. Generalized infection was aborted when the site of inoculation was excised within 2 days after the infecting tick detached but not after 2 weeks. In contrast, all mice became infected when the bite site remained intact. Spirochetes could be cultured from the tissues around the site of attachment solely when the sample was ablated within a week after infecting ticks detached. These observations suggest that infecting ticks deliver the agent of Lyme disease directly into the skin and that such spirochetes multiply locally for some days before disseminating to remote sites.

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PubMed1992

Ribosomal DNA probe for differentiation of Babesia microti and B. gibsoni isolates.

The objective of this study was to determine whether different isolates of Babesia microti could be distinguished from morphologically similar isolates of B. gibsoni by using a ribosomal DNA (rDNA) probe. A Babesia-specific rDNA probe was obtained by polymerase chain reaction amplification of sequences from B. microti DNA using universal primers directed against highly conserved portions of the eukaryotic 16S-like rRNA gene. The chemiluminescent rDNA probe hybridized to Southern blots of restriction endonuclease-digested DNA preparations of different isolates of B. gibsoni from infected dogs and B. microti from infected humans and white-footed mice. Restriction fragment length polymorphisms served to differentiate these species. Although the hybridization patterns seen with DNAs from six B. microti isolates did not vary, those of the five B. gibsoni isolates did indicate genotypic variation. We concluded that isolates of B. microti and B. gibsoni can be differentiated on the basis of restriction fragment length polymorphism detected with a chemiluminescent rDNA probe.

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PubMed1992

Detection of Babesia microti by polymerase chain reaction.

Human babesiosis, which is caused by infection with the intraerythrocytic malarialike protozoan Babesia microti, has recently been diagnosed with increasing frequency in residents of New England. Diagnosis is difficult because of the small size of the parasite and the sparse parasitemia that is characteristic of most infections with this pathogen. We generated B. microti-specific DNA sequence information by universal primer amplification of a portion of the eukaryotic 16S-like gene; this was followed by direct DNA sequence analysis. Specific primers were synthesized on the basis of this sequence information for use in the polymerase chain reaction (PCR). The PCR-based system demonstrates a strong bias for detection of B. microti as opposed to Babesia gibsoni and does not amplify vertebrate DNA. The analytical sensitivity of the system is approximately three merozoites. Blood specimens from 12 patients with clinically diagnosed and parasitologically confirmed babesiosis from Nantucket Island, Mass., were PCR positive in a blinded test of this procedure. Thus, DNA amplification may provide an adjunct to conventional methods for the diagnosis of human babesiosis and may provide a new means of monitoring therapy or enhancing epidemiological surveillance for this emerging pathogen.

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PubMed1992

Nonvascular delivery of Rift Valley fever virus by infected mosquitoes.

To determine whether virus-transmitting mosquitoes inoculate infectious particles extravascularly or directly into the vascular system, we permitted mosquitoes infected with Rift Valley fever virus to feed on the distal third of the tails of suckling mice. Amputation of the distal half of the tail within 5 min after their being bitten significantly increased mouse survival as compared with that of mice whose tails remained intact. Even when tails were amputated 10 or more min after mosquito feeding, the median time to death was significantly longer in the group with the amputated tails (53.5 hr) than in those mice with intact tails (46.0 hr). Mouse survival did not correlate with ingestion of blood by the infecting mosquito. We conclude that mosquitoes inoculate virus extravascularly, rather than directly into the vascular system, when feeding on a vertebrate host. Such extravascular delivery of virus by a transmitting mosquito may affect viral pathogenesis, antiviral activity, and vaccine efficacy.

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PubMed1992

Clustering of host-seeking nymphal deer ticks (Ixodes dammini) infected by Lyme disease spirochetes (Borrelia burgdorferi).

In areas where the agent of Lyme disease is intensely enzootic, the mouse reservoirs may be universally infected. Because a large proportion of the vector tick population appears to feed upon these hosts, the prevalence of infection in the vectors should approach 100%. However, infection in host-seeking nymphal ticks in nature rarely exceeds 40%. To help reconcile this apparent paradox, we examined whether estimates of prevalence might differ if we did not assume that infected ticks are randomly or uniformly distributed within a site. Nymphal Ixodes dammini were collected by dragging a series of 10-meter replicates within an intensely enzootic site. Estimates of the prevalence of spirochetal infection, based upon the monthly means of individual 10-meter collections, were then compared with estimates derived by pooling all samples. Host-seeking ticks tended to cluster. The Lyme disease spirochete was present in 15.6% of 469 pooled ticks. When the prevalence estimate was based solely on ticks in clusters that contained one or more infected ticks, however, at least 50% of the ticks were infected. We conclude that nymphal deer ticks infected by Lyme disease spirochetes tend to aggregate spatially in nature, and that prevalence estimates based upon a mean value for pools may be misleading.

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PubMed1992

[Comparison of mosquito larvicidal efficacy between microbial encapsulated BTI (EBTI) and standard BTI (SBTI)].

A comparative study was conducted on the efficacy of mosquito larvicides EBTI and SBTI. The results showed that: 1. The residual efficacy of EBTI was remarkably higher than that of SBTI at 0.007-0.002ppm BTI concentration (P < 0.01), the mosquito larvae mortality of EBTI remained 100% until the 4th week; in contrast, the mosquito larva mortality of SBTI gradually and obviously declined from the 2nd to 4th week after treatment (x2 = 8.17-24.08), and reached 0 at the 4th week. 2. The lowest BTI concentration of EBTI at which a high efficacy persisted for 4 weeks was 0.007ppm BTI, the mosquito larva mortality remaining 100%.

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PubMed1992

Babesiosis: an underdiagnosed disease of children.

Babesiosis is a malaria-like illness caused by the intraerythrocytic parasite Babesia microti and is transmitted by the same tick that transmits Borrelia burgdorferi, the causative agent of Lyme disease. Babesiosis is well recognized in adult residents of southern New England and New York but has been described in only five children. To determine whether children are infected with B microti less often than are adults, a prospective serosurvey was carried out on Block Island, RI, where babesiosis is endemic. Randomly recruited subjects completed a questionnaire and provided a blood sample. Antibodies against B microti and B burgdorferi were measured using a standard indirect immunofluorescence assay and enzyme-linked immunosorbent assay, respectively. Of 574 subjects, 9% tested positive for B microti, including 12% of the 52 children (7 months through 16 years) and 8% of the 522 adults (not significant, P less than .6). Although babesiosis had not been diagnosed in any of the Babesia-seropositive subjects, 25% of the children and 20% of the adults reported symptoms compatible with this infection during the previous year. Of the 6 children and 45 adults seropositive for B burgdorferi, 17% and 14%, respectively, were also seropositive for B microti. It is concluded that children are infected with B microti no less frequently than are adults and that this infection is underdiagnosed in all age groups. Physicians who practice where Lyme disease is endemic should become familiar with the clinical presentation and diagnosis of babesiosis, both in adults and children.

Adolescent↗
PubMed1991

Genetic similarity among Egyptian populations of Culex pipiens (Diptera: Culicidae).

Geographic variation among Culex pipiens L. populations was studied along a north-south transect across Egypt. Horizontal starch gel electrophoresis of 10 enzyme loci permitted estimates of adult polymorphism for 10 demes of Cx. pipiens. Levels of genetic variability, as indicated by a mean of 1.25 alleles per locus, a mean expected heterozygosity of 0.023, and a proportion of 0.25 of the loci being polymorphic, indicated limited genetic heterogeneity within and among demes. Nei's estimates of genetic divergence indicated considerable genetic exchange among demes (average genetic distance, 0.013). Thus, Cx. pipiens in Egypt was not differentiated into genetically isolated demes but, rather, seemed to consist of a single panmictic population.

Animals↗
PubMed1991

Rectal infusion and aspiration of material through the guts of ixodid ticks (Acari: Ixodidae).

A technique for inoculating and removing substances via the anus of vector ticks was devised to define features of vector competence precisely. Calibrated inocula (greater than 5 nanoliter) containing aqueous dye and polystyrene beads as well as infectious agents were infused into the rectal sacs of ticks using glass microcapillary pipettes placed within the expanded anal orifice. The guts of preadult and adult ticks, Ixodes dammini Spielman, Clifford, Piesman & Corwin, Dermacentor variabilis (Say), Hyalomma impeltatum Schulze & Schlottke, and Amblyomma americanum (L.), were thereby infused with these inocula. Distribution of inocula was determined by examining hemolymph and sectioned ticks and confirmed that material placed in the rectal sac spread throughout the midgut diverticula. Ticks survived for greater than 6 mo after this procedure and were able to feed, molt to the next stage, or oviposit. In contrast, fewer ticks survived after intracelomic inoculation. The course of infection in ticks receiving anal infusions of Borrelia burgdorferi (the Lyme disease spirochete) was assessed. Such infections appear to differ from those established by feeding on infected hosts. Contents of the tick gut can be sampled nondestructively by anal perfusion to diagnose infection by this spirochete.

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PubMed1991

Geographical and temporal distribution of babesial infection in Connecticut.

Human babesiosis was first recognized in Connecticut in 1989, nearly 15 years after Lyme disease, a similarly transmitted spirochetosis, was detected in the state. To determine the seroprevalence for the babesial pathogen and whether it was recently introduced, we used an indirect immunofluorescence assay to test for Babesia microti antibody in 1,285 Connecticut residents. Four groups were studied: I, people seropositive for Lyme disease, tested from 1986 to 1989; II, randomly selected outpatients tested in 1989; III, college students residing in Connecticut, tested from 1959 to 1989; and IV, healthy people without tick exposure or Lyme disease, tested in 1989. Babesia seropositivity was significantly higher in group I (9.5%; n = 735) than in groups II (2.6%; n = 304, P less than 0.0001) and III (1.0%; n = 206, P less than 0.0001) but not group IV (2.5%, n = 40). Babesia seropositivity for group I ranged from 9.2 to 10.2% between 1986 and 1989, and Babesia seropositivity for group III ranged from 0% between 1959 and 1985 to 2.9% between 1986 and 1989. There is a considerable risk of babesial infection among residents of the Connecticut mainland who are seropositive for Lyme disease, a risk that appears to have remained constant over the past 5 years.

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