Biomedical subjects

A Spielman

Publications and source records attributed to A Spielman.

At least 127 records · Page 7Linked to original sources

PubMed1991

Hosts on which nymphal Ixodes ricinus most abundantly feed.

To identify hosts that may serve as European reservoirs for the agent of Lyme disease, Borrelia burgdorferi, we determined whether nymphal Ixodes ricinus feed mainly on particular mice (Apodemus flavicollis or A. agrarius), voles (Clethrionomys glareolus) or on sand lizards (Lacerta agilis) and whether the abundance of these hosts corresponds to the seasonal activity of the subadult stages of the vector tick. In all sites, the mice appeared most heavily infested by larvae; at least seven parasitized each mouse, about three per vole and four per lizard. Many fewer nymphal I. ricinus parasitized A. flavicollis and C. glareolus than did larvae. Although more than 30 times as many larval than nymphal ticks parasitized the two most abundant hosts (C. glareolus and A. flavicollis), about 15 times as many fed on A. agrarius and twice as many on lizards. Nymphal and larval ticks fed on rodents at about the same time. Lizards were most abundantly parasitized by nymphs somewhat earlier than by larvae. Early in the season of transmission of Lyme disease, virtually all A. agrarius as well as lizards were potentially exposed to spirochetes borne by nymphal I. ricinus. We concluded that larval and nymphal I. ricinus differentially parasitize different hosts. Because so many of these nymphs feed on them, A. agrarius may more effectively serve as reservoirs for the agent of Lyme disease than do other putative reservoir hosts. The presence of lizards may inhibit transmission.

Animals↗

PubMed1991

A Brugia species infecting rabbits in the northeastern United States.

Brugia sp. microfilariae were observed in more than 60% of wild rabbits collected on Nantucket Island, Massachusetts. The microfilariae measured 294-344 microns in length and had the characteristic subterminal and terminal nuclei observed in other Brugia microfilariae. The microfilaria is similar to those described for Brugia leporis in rabbits in Louisiana. This may be the Brugia species responsible for 21 documented cases of human infection in the northeastern United States.

Animals↗

PubMed1991

Relationship of Borrelia burgdorferi to its arthropod vectors.

At the IV International Conference on Lyme Borreliosis, a workshop was held to identify the unique development of the Lyme disease spirochete, Borrelia burgdorferi, in its established and suspected arthropod vectors. The following is a summary of the panel's discussions of research aspects concerning relationship(s) of this borrelia to its vectors, and the mode(s) of its transmission to animal hosts.

Animals↗

PubMed1991

Differential detachment from resting hosts of replete larval and nymphal Ixodes ticks.

To determine whether replete subadult Ixodes ticks detach more frequently from resting than from active hosts, diverse rodents and lizards were caged in an apparatus designed to record the ticks' sites of detachment relative to the resting site of the host. Replete larval Ixodes ricinus and Ixodes dammini accumulated mainly beneath the resting places of the mice (Apodemus agrarius and Peromyscus leucopus) most frequently parasitized in nature. Although nymphal I. ricinus similarly detached where these mice rested, nymphal I. dammini detached more randomly. When lizards were used as hosts, both subadult stages of I. ricinus tended to detach away from their main resting sites; these ticks detached from squirrels more randomly. Detachment ratios for other rodent hosts, that are abundantly infested by the larvae of these ticks in nature (Apodemus flavicollis and Clethrionomys glareolus), could not be derived because nymphs generally failed to attach. Our observations are consistent with reports that both subadult stages of I. dammini, but not the adult, feed on the same kind of nest-dwelling hosts and that the host range of I. ricinus is less focused. Detachment of mouse-feeding larvae from resting mice promotes subsequent nymphal attachment to conspecific hosts, and the absence of such behavior among nymphs facilitates access of the resulting adults to deer.

Animals↗

PubMed1991

Emerging vector-borne infections.

The principles that regulate the transmission of vector-borne infectious agents are briefly described. In particular, the circumstances that may lead to human exposure to various North American zoonoses are analyzed.

Animals↗

PubMed1990

Detection of Borrelia burgdorferi DNA in museum specimens of Ixodes dammini ticks.

In order to investigate the potential for Borrelia burgdorferi infection before the recognition of Lyme disease as a clinical entity, the polymerase chain reaction (PCR) was used to examine museum specimens of Ixodes dammini (deer ticks) for the presence of spirochete-specific DNA sequences. One hundred and thirty-six archival tick specimens were obtained representing various continental U.S. locations; DNA sequences characteristic of modern day isolates of B. burgdorferi were detected in 13 1940s specimens from Montauk Point and Hither Hills, Long Island, New York. Five archival specimens of Dermacentor variabilis (dog tick) from the same collection and 118 Ixodes specimens from other endemic and nonendemic sites were negative. These data suggest that the appearance of the Lyme disease spirochete in suitable arthropod vectors preceded, by at least a generation, the formal recognition of this disease as a clinical entity in the United States.

Animals↗

PubMed1990

Time of repletion of subadult Ixodes ricinus ticks feeding on diverse hosts.

For a comparison of the times of day at which the subadult stages of Ixodes ricinus detach from nocturnal vs diurnal hosts, these ticks were placed on a variety of indigenous and experimental animals. The time of detachment appears to depend more on properties of the host than on the periodicity of tick behavior. Ticks on rodents, regardless of host periodicity, tended to detach late in the afternoon; those on the hedgehog detached around midnight, and those on lizards and birds, during the morning. Ticks on carnivores (dog, cat) detached throughout the daylight hours. The ability of these parasites to survive to the next developmental stage and, ultimately, to come into contact with another suitable host may be influenced by the identity of the host and, hence, by the circumstances of detachment. Subadult I. ricinus probably concentrate in the host's nest when feeding on mammals but are scattered over the ground when feeding on lizard or avian hosts, an aspect of engorgement behavior that may profoundly affect the capacity of this tick as a vector of agents of Lyme disease and other infections.

Animals↗

PubMed1990

Borrelia burgdorferi and Babesia microti: efficiency of transmission from reservoirs to vector ticks (Ixodes dammini).

In endemic regions, Peromyscus leucopus, the mouse reservoir of the Lyme disease spirochete (Borrelia burgdorferi) and the piroplasm causing human babesiosis (Babesia microti), is nearly universally infected with both agents. Paradoxically, spirochetal infection is nearly twice as prevalent as is babesial infection in populations of field-collected nymphal Ixodes dammini, the tick vector. In the laboratory, a similarly disproportionate rate of infection was observed among nymphal ticks, feeding as larvae, on either B. burgdorferi- or B. microti-infected mice. Ticks which fed on mice with concurrent spirochetal and babesial infections also exhibited twice the incidence of spirochetal infection over that of the piroplasm. These data suggest that the efficiency of acquisition and transstadial passage of B. burgdorferi and B. microti infection differ by a factor of two. This discrepancy may explain differences observed both in the prevalence of infection in ticks collected in the field, as well as the apparently greater risk of spirochetal infection to humans in endemic areas.

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PubMed1990

The behaviour of common measures of association used to assess a vaccination programme under complex disease transmission patterns--a computer simulation study of malaria vaccines.

Case-control studies have been evoked as important alternatives to randomized clinical trials in the evaluation of infectious disease interventions. Using computer simulations, we compare the behaviour of common measures of association derived from case-control studies in the context of a malaria vaccine programme administered under complex transmission conditions. Several simplifying assumptions of previous workers have been relaxed and the simulated conditions are endemic rather than epidemic. The common estimators of association used in case-control studies remain unbiased only in limited circumstances. The term dependent happenings, first defined by Ross in 1916, is resurrected. Since the number of people becoming infected is dependent on the number of people already infected, control programmes in infectious diseases produce direct as well as indirect effects. Three different study designs with different pairs of comparison populations are defined. The choice of comparison population can be used to differentiate direct from indirect effects. In order to clarify the direct effects of a vaccination programme the comparison groups must be subjected to identical transmission intensities. In contrast, the referent group must remain unaffected by consequences of the intervention to determine indirect effects.

Brazil↗

PubMed1990

Motility of Lyme disease spirochetes in fluids as viscous as the extracellular matrix.

When properties of extracellular fluids that might regulate the ability of the Lyme disease spirochete to locomote were investigated, the rate of progression correlated with viscoelasticity. Such spirochetes flexed and rotated but did not progress in relatively nonviscous fluids and migrated increasingly rapidly as the viscous characteristics of the medium increased. The viscoelastic properties of various kinds of hyaluronic acid resembled those of a methylcellulose standard. The maximum velocity that spirochetes achieved in such solutions related directly to viscoelasticity rather than to chemical composition. Spirochetes remained motile during 3 h of observation despite 100-fold dilution of the standard nutrient medium. The immobility of Lyme disease spirochetes in media less viscous in character than fixed tissue suggests dissemination via the intercellular ground substance of skin.

Borrelia burgdorferi Group↗

PubMed1990

Duration and regulation of the developmental cycle of Ixodes dammini (Acari: Ixodidae).

To determine how long the various developmental stages of the deer tick (Ixodes dammini Spielman, Clifford, Piesman & Corwin) survive in nature and to establish the interval between blood feeding and ecdysis or oviposition as well as subsequent larval eclosion, we observed ticks confined in the field. Unless adults feed during their first season (fall through spring) of activity, they die and do not survive the summer. Nonfed nymphs survive through two seasons (May through August) of feeding activity such that annual cohorts overlap. Nonfed larvae survive less than one year, and because they hatch toward the end of the summer, cohorts of this developmental stage do not overlap. Larvae that feed before September molt promptly and overwinter as nymphs; those that feed later overwinter engorged and ecdyse during the following spring. Fed nymphs fail to survive the winter, and thus must feed before late summer. They develop to the adult stage in the same year in which they feed. Regardless of time of feeding, females lay eggs in early summer, and the resulting larvae synchronously eclose late in that season. Although the cycle of this tick can be completed in nature in two years, it may extend to four years when hosts are relatively scarce. The seasonal inversion of larvae and nymphs appears to be regulated by physiological mechanisms and by host abundance.

Animals↗

PubMed1990

Subadult Ixodes ricinus (Acari: Ixodidae) on rodents in Berlin, West Germany.

To identify hosts that may serve as reservoirs for the agent of Lyme disease in Central Europe, we determined whether Ixodes ricinus L. feed most frequently on certain rodents and whether the abundance of these hosts corresponds to the season of feeding activity of the tick in four sites in Berlin, Federal Republic of Germany. In addition, we correlated abundance of I. ricinus with that of particular rodent hosts. Two small rodents were more abundant than any others; a mouse, Apodemus flavicollis, predominated in a wooded site and a vole, Clethrionomys glareolus, in three brush- or grass-covered sites. The tick was most abundant in the mouse-infested site. Although A. flavicollis comprised only about a third of rodents collected, nearly 60% of all such rodent parasitizing I. ricinus fed on this mouse. These ticks were more abundant on mice than voles in each of the study sites and throughout the year, and more larvae fed on these rodents than did nymphs. Although larval as well as nymphal I. ricinus are most abundant during midsummer, they feed on rodents from April through October. Taken together, these observations suggest A. flavicollis as a potentially important reservoir host for I. ricinus-borne infections.

Animals↗

PubMed1990

Host-dependent differences in feeding and reproduction of Ixodes dammini (Acari: Ixodidae).

The frequencies with which adult Ixodes dammini Spielman, Clifford, Piesman and Corwin feed upon white-tailed deer (Odocoileus virginianus), raccoons (Procyon lotor), opossums (Didelphis virginiana), and domestic cats were compared in a wooded site in northeastern United States. By combining estimates of the quantity of ticks feeding on each host species with host densities, we derived the relative contribution made by each kind of host to the feeding of the tick population. To compare engorgement success and reproductive efficacy, we weighed ticks found on these hosts and compared tick weights with the quantity of eggs produced. Deer harbored the most female ticks per individual and, although deer were less abundant than raccoons, they harbored 94.6% of the feeding tick population. Raccoons, cats, and opossums, respectively, provided blood meals to 3.6, 1.6, and 0.2% of feeding adult ticks. Ticks engorged more successfully on cats and raccoons than on deer, and egg production correlated linearly with weight of female ticks collected from both cats and deer. Although these ticks engorged better on other hosts, the vast majority of eggs resulted from ticks that had fed on deer. We conclude that, in this site, the abundance of deer largely determines the abundance of I. dammini, the vector of the agent of Lyme disease.

Animals↗

PubMed1990

Microgeographic distribution of immature Ixodes dammini ticks correlated with that of deer.

In order to determine whether the small-scale distribution of immature Ixodes dammini Spielman et al. corresponds closely to the activity patterns of white-tailed deer, Odocoileus virginianus (Zimmerman), these relationships were examined in a site on Long Island, New York, U.S.A. We first determined the extent and temporal pattern of adult ticks feeding on deer by examining twenty-three resident deer tranquilized during September-December 1985. I. dammini adults infested deer throughout this fall period, most abundantly during October and November. With radio-telemetry collars attached to deer we determined the relative frequency that they occupied 0.25 ha quadrats of the study site. During the following summer, we examined white-footed mice, Peromyscus leucopus (Rafinesque), that inhabited these quadrats and removed immature ticks from each. 8975 larval and 163 nymphal I. dammini were removed from 208 mice trapped in forty-three such quadrats. The frequency of deer using these quadrats was positively correlated with both the number of larval and of nymphal ticks per mouse. These results suggest that risk of I. damminiborne zoonotic disease may be decreased by locally reducing deer density in sites that experience intense human activity.

Animals↗

PubMed1990

Nocturnal detachment of the tick Ixodes hexagonus from nocturnally active hosts.

To determine whether the pattern of engorgement of Ixodes hexagonus Leach (Acarina: Ixodidae) in Central Europe may influence host specificity, the host relationships of the sub-adult stages of this tick were examined and the time of detachment compared with the activity patterns of various candidate vertebrate hosts. The main hosts for I. hexagonus appear to be hedgehog and fox. This tick species seems to be incapable of feeding on any rodent commonly encountered in the study region, or on reptiles or birds. Virtually all of these ticks detach during the scotophase, becoming replete mainly during the late evening and early morning hours, regardless of the kind of host or of the time of attachment. These nocturnally detaching ticks, paradoxically, focus their feeding on nocturnally active hedgehogs and foxes, in spite of the possibility that such behaviour might cause them to disperse from the nests of the host. Dispersion is prevented, however, by the tendency of these ticks to detach while their host naps. The tick-host association of I. hexagonus with hedgehogs may serve to perpetuate such zoonotic, Ixodes-borne infections as Lyme disease.

Animals↗

PubMed1990

Detection of Borrelia burgdorferi infection in Ixodes dammini ticks with the polymerase chain reaction.

The polymerase chain reaction (PCR) was used to amplify DNA sequences of the etiologic agent of Lyme disease, Borrelia burgdorferi, and was applied to the detection of the spirochete in its tick vector. The target for PCR amplification was the OSP-A gene of strain B31; analysis of isolates from different geographical areas indicated that this gene could be used to identify most North American isolates. These methods were extended to the analysis of colony-derived and field-collected Ixodes dammini. OSP-A-specific sequences were identified in 15 of 15 colony-derived nymphal ticks that had fed previously on an infected animal; no such amplification products were detected in 8 control ticks. Segregated midgut tissues of field-collected adult and nymphal ticks from Nantucket Island, Mass., and the Crane Reserve, Ipswich, Mass., were examined by both direct fluorescent-antibody (DFA) staining and PCR. The DFA technique identified 16 infected ticks of 30 paired specimens; 15 of these specimens were positive by PCR. One specimen was positive by PCR that was DFA negative. Both live whole ticks and desiccated dead specimens were suitable for this analysis. Because only five ticks are suitable for DFA analysis, the use of PCR may extend the range of specimens that can be analyzed for the presence of the Lyme spirochete.

Animals↗

PubMed1990

Increased abundance, size, and longevity of food-deprived mosquito populations exposed to a fungal larvicide.

To determine whether the quantity of food available to mosquitoes in their aquatic environment limits the effectiveness of microbial pathogens as biological control agents, experimentally well-nourished and malnourished larval Aedes aegypti (Linn.) were exposed to graded inocula of the entomopathogenic fungus, Metarhizium anisopliae. First instar larvae were provided access either to 3 or to 5 mg of food, and lots from each food regimen were inoculated with 20, 40, 60, or 80 micrograms of fungal spores/ml water. Application of the fungus to well-nourished larvae reduced the proportion developing to the adult stage, and increased the size of those adults that developed; their survival was not affected. In the case of malnourished larvae, such applications appeared not to effect the proportion of larvae that matured, and, paradoxically, increased the size and longevity of these resulting adults. By destroying a portion of the larvae, the pathogen apparently reduced competition among malnourished larvae, thereby enhancing their survival, as well as the size of the resulting adults. Thus, biocontrol agents may fail when used as larvicides against such nutrient-deprived mosquitoes as frequently occur in nature.

Aedes↗

PubMed1990

Tropical extension of temperature zone Culex pipiens throughout Egypt.

To explore the southern limit of the temperate zone form of the Culex pipiens complex of mosquitoes in North Africa, we compared the structure of the copulatory structures of such male mosquitoes sampled along the length of Egypt. Larval mosquitoes were collected in 11 sites distributed along the entire Egyptian span of the Nile Valley as well as in sites along the central Red Sea coast and in the western desert. Four of these sites were sampled repeatedly, at various times of the year. A DV/D ratio was calculated for each adult male mosquito. Although all DV/D values conformed to criteria normally attributed to the temperate zone form, even at the southernmost site (22 degrees N), values tended toward those of the tropical form in southern sites and during the summer months. We concluded that Cx. pipiens mosquitoes of the Middle East are predominantly Mediterranean in form due to an isolating effect of the Sahara Desert which separates these temperate zone insects from those of tropical Africa.

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