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Science - Biology (-tech,-chem,micro-) / Ixodes scapularis
|English term or phrase: Ixodes scapularis|
|The blacklegged tick, Ixodes scapularis, is an important vector of the Lyme disease spirochete, Borrelia burgdorferi, as well as the agents of human babesiosis, Babesia microti, and human granulocytic ehrlichiosis (HGE) (Des Vignes and Fish 1997). A significant feature in the transmission dynamics of B. burgdorferi is the importance of the nymphal stage\'s activity preceding that of the larvae which allows for an efficient transmission cycle (Spielman et al. 1985, Wilson and Spielman 1985). Before and during larval tick feeding, the naturally infected nymphs transmit B. burgdorferi to reservoir hosts. The newly hatched spirochete-free larvae (Piesman et al. 1986a) acquire the bacteria from the reservoir host and retain infection through the molting process. In the springtime, nymphs derived from infected larvae transmit infection to susceptible animals, which will serve as hosts for larvae later in the summer (Fish 1993). |
Human exposure to blacklegged ticks is greatest during the summer months when high nymphal I. scapularis activity and human outdoor activity coincide. Their small size, their vastly greater abundance over the adult stages and the difficulty in recognizing their bites (Berger 1989) tends to make nymphs the most important stage to consider for reducing disease risk.
Ixodes scapularis Suspect as Lyme Disease Vector
October 1989, 5.3 In the past few years, reports of human Lyme disease cases have increased exponentially in the Southeast.
Whether this observation represents a true \"outbreak\" in the South, as opposed to a
heightened diagnostic awareness by physicians and their patients, is a much debated question.
Regardless, much of the South is now considered endemic for Lyme disease, although prevalence of human infection remains much lower than the highly publicized New England region.
Information on Lyme disease in the South is sparse, and a very important piece of the puzzle is missing...identification of the tick vector or vectors.
Ixodes dammini was the first tick species proven to be a Lyme disease vector. Epidemiologic
studies in the Northeast and Upper Midwest clearly demonstrated that this tick readily transfers Lyme disease spirochetes (bacteria) by feeding upon infected rodents and, later, biting people or other animals.
As knowledge of Lyme disease increased, scientists learned that I . ricinus
transmitted Lyme disease in Europe and I. pacificus did the same in the Pacific Northwest.
None of the aforementioned ticks occur in the South, but a closely related species, I . scapularis, the black-legged tick, is present.
Therefore, a logical assumption is that I. scapularis may be the vector for the southeastern United States.
There are several reasons to consider I. scapularis as a prime suspect as the Lyme disease vector in the Southeast.
Experimentally, this tick species is capable of maintaining Lyme disease spirochetes and transferring them efficiently from animal to animal. Ixodes scapularis does this far better in the laboratory than American dog ticks (ermacentor variabilis) or lone star ticks
(mblyomma americanum). Larval and nymphal stages of I. scapularis feed on a variety of hosts, including small rodents, but they will bite humans as well. Furthermore, the geographic range of I. scapularis is widespread throughout much of the Southeast (see enclosed SCWDS data map).
Still, naturally infected I. scapularis have been extremely rare in the limited field surveys that
have been made in the South. It is obvious that further research is needed to determine if I.
scapularis is behaving like its notorious cousins or if the Lyme disease bacterium is employing other vector systems.
The blacklegged tick, Ixodes scapularis, principal vector of the pathogen causing Lyme disease in many area of the U. S., spends most of its life off of its hosts. It is important to know how well free-living survive in various common habitats in order to develop control and disease preventive strategies. Unfed and fed larvae and nymphs of the blacklegged tick confined in packets and vials were placed in the leaf litter in 4 types of habitat in Maryland, and their survival monitored. One of the 4 habitat types was characterized by profuse colonies of Nepal microstegium, an introduced grass that is expanding its range into areas of the northeast where blacklegged ticks are abundant. Although none of the 4 habitats appeared to be obviously more favorable or unfavorable for the survival of the confined ticks, host-seeking I. scapularis were scarce at sites in Virginia pine-southern red oak habitats. These findings benefit persons who might use or manage such habitats. Scientists investigating the ecology and control of the blacklegged tick will be interested in these results.
This paper reports the results of a preliminary survey of fungal pathogens of deer ticks, the vector of the bacterium that causes Lyme disease, one of the most serious animal-borne diseases of humans to emerge in the NE quadrant if the US in recent years. This survey found a very low incidence of natural infection in adult female deer ticks by fungal pathogens are known to have wide host affinities for diverse insect hosts. While the low incidence of the natural infections is discouraging, it is important that the fungus found to affect the target populations is one that can be manipulated easily in culture and is already being used for practical biological control of aphids, whiteflies, and other insect pests in greenhouses in several parts of the world. This study provides some real hope that continuing research may lead to the practical utilization of fungi for the biological control of tick populations that transmit Lyme disease or other diseases to humans. The collections of ticks and fungal bioassays were done by University of Rhode Island scientists; the fungi were identified at and are preserved by the ARS Collection of Entomopathogenic Fungal Cultures (Ithaca, NY)
Rickettsia spp., obligately intracellular, gramnegative, vector-transmitted bacteria, are divided antigenically into the typhus group (TG) and the spotted fever group (SFG).
In nature, TG rickettsiae inhabit either flea (Rickettsia typhi and R. felis), louse (R. prowazekii), or tick (R. canada) arthropod hosts. Except for R. akari, whose invertebrate host is a mite, all SFG rickettsiae reside in tick hosts. SFG rickettsiae, excluding R. akari, are maintained in nature by a cycle involving both transovarial and transstadial passage of the microorganism in the tick and, for some species, amplification in small mammal hosts.
Ticks infected with pathogenic rickettsiae (i.e., R. rickettsii, R. conorii, R. sibirica, R. australis,
R. japonica, R. africae, and R. honei) that feed on humans, who are dead-end hosts, may transmit an SFG rickettsiosis (i.e., Rocky Mountain spotted fever [RMSF], boutonneuse fever, North Asian tick typhus, Queensland tick typhus, Japanese spotted fever, African tick bite fever, or Flinders Island spotted fever, respectively).
In the United States, Dermacentor andersoni and D. variabilis are the classic vectors of R.
rickettsii to humans; other recognized vectors include Rhipicephalus sanguineus for R. rickettsii in Mexico and for R. conorii in Eurasia and Africa, Amblyomma cajennense for R. rickettsii in Brazil, and Ixodes holocyclus for R. australis in Australia. Other rickettsiae, such as R. parkeri and R. amblyommii, have been isolated from human-biting ticks; however, these rickettsiae have not been proven pathogenic for humans.
The presence of apparently nonpathogenic rickettsiae whose vector host and geographic
distribution overlap with pathogenic rickettsiae may interfere with the transmission of
virulent rickettsiae to humans, as may be the case with R. peacockii (nonpathogenic) (1,2)
and R. rickettsii in D. andersoni in the Bitterroot Valley of Montana.
The black-legged tick, I. scapularis, is of major public health importance because it feeds
indiscriminately on numerous vertebrate hosts, including humans, and transmits Borrelia
burgdorferi, Babesia microti, and human granulocytotropic ehrlichia to humans.
Rickettsiae have been detected in I. scapularis (3-8); however, the ability of black-legged ticks to serve as vectors of rickettsiae to humans or to other small mammals important in maintaining and spreading rickettsiae in nature has not been examined. Because rickettsiae are regularly detected by immunofluorescence staining in I. scapularis specimens sent to the Texas Department of Health (5,7) and because the range of I. scapularis and RMSF cases overlaps in Texas (9), we characterized the immunofluorescencedetected microbial agent in this tick collected from Anderson County in eastern Texas. We examined the field-collected I. scapularis, preserved in alcohol, to determine species, sex,
5 hrs confidence:
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