Prevalence and abundance of Ixodes pacificus immatures (Acari: Ixodidae) infesting western fence lizards (Sceloporus occidentalis) in northern California: temporal trends and environmental correlates.

The prevalence and abundance of immature Ixodes pacificus ticks on western fence lizards (Sceloporus occidentalis) were examined in relation to time of year, host attributes (i.e., age, gender, and presence or absence of blood parasites), and 5 environmental characteristics, including topographic exposure and ground cover substrate, over a 2-year period in northern California. Lizards were infested with subadult ticks from early March until late July or early August, with peak median numbers of larvae and nymphs recorded in late April and early May of both years. Peak larval and nymphal abundances differed between years. The overall ratio of larvae to nymphs on adult male lizards was low, ranging from 0.80 in 1999 to 2.41 in 2000. Such intensive feeding of nymphs versus larvae on these lizards, which are reservoir-incompetent for Borrelia burgdorferi spirochetes, may explain previous observations of decreasing spirochetal infection prevalence from the nymphal to adult stage in northwestern California. Adult male lizards were more likely to be infested with nymphs and harbored greater abundances of larvae and nymphs than adult females. Lizards uninfected with blood parasites had more nymphs than infected lizards. The measured environmental characteristics could explain only a small percentage of the total variation observed in larval prevalence (22%) and in larval and nymphal abundance (12 and 3%, respectively).     

The role of medium-sized mammals as reservoirs of Borrelia burgdorferi in southern New York

The ability of raccoons (Procyon lotor), striped skunks (Mephitis mephitis) and opossums (Didelphis virginiana) to serve as reservoirs of Borrelia burgdorferi, the spirochetal agent of Lyme disease, was compared with that of white-footed mice (Peromyscus leucopus). Twenty-eight (28) medium-sized mammals and 34 white-footed mice were captured in Westchester County, New York (USA) in summer 1986. Animals were caged over pans of water for 1 to 2 days to recover engorged tick larvae (Ixodes dammini) that detached from the hosts after feeding. With the exception of mice, numbers of engorged tick larvae recovered exceeded those counted during initial examinations of the hosts by 30% (opossums) to nearly 90% (raccoons). Newly-molted nymphal ticks derived from the engorged larvae were examined for the presence of spirochetes by darkfield microscopy. Percentage infection was 5% (n = 22) for ticks from skunks and 14% (n = 191) for ticks from raccoons. None of 24 nymphs from larvae that fed on opossums survived long enough for spirochete examination. By comparison, 40% (n = 72) of nymphs from larvae which fed on white-footed mice were infected. Of the individual hosts from which molted nymphs had fed as larvae, 67% of mice, 33% of skunks, and 55% of raccoons produced spirochete-positive ticks.     

Lyme disease and migrating birds in the Saint Croix River Valley

During a study of migrating land birds in 1987, we examined over 9,200 individual birds representing 99 species from the Saint Croix River Valley, a Lyme disease-endemic area of east central Minnesota and northwestern Wisconsin. We found that 250 deer tick (Ixodes dammini) larvae and nymphs infested 58 birds from 15 migrant species; 56 ticks (22.4%) were positive for the Lyme disease spirochete Borrelia burgdorferi. Five ground-foraging migrant bird species favoring mesic habitats, veery (Catharus fuscescens), ovenbird (Seiurus aurocapillus), northern waterthrush (S. novaboracensis), common yellowthroat (Geothlypis trichas), and swamp sparrow (Melospiza georgiana), accounted for nearly three-quarters of parasitized individuals. Nearly half of the spirochete-positive ticks were removed from migrating birds taken in a riparian floodplain forest. Recaptured migrants with infected ticks indicate that they transmit B. burgdorferi to hexapod larvae. We suggest that birds may be both an important local reservoir in the upper Mississippi Valley and long-distance dispersal agents for B. burgdorferi-infected ticks to other regions of the continent.     

Lyme disease and migrating birds in the Saint Croix River Valley.

During a study of migrating land birds in 1987, we examined over 9,200 individual birds representing 99 species from the Saint Croix River Valley, a Lyme disease-endemic area of east central Minnesota and northwestern Wisconsin. We found that 250 deer tick (Ixodes dammini) larvae and nymphs infested 58 birds from 15 migrant species; 56 ticks (22.4%) were positive for the Lyme disease spirochete Borrelia burgdorferi. Five ground-foraging migrant bird species favoring mesic habitats, veery (Catharus fuscescens), ovenbird (Seiurus aurocapillus), northern waterthrush (S. novaboracensis), common yellowthroat (Geothlypis trichas), and swamp sparrow (Melospiza georgiana), accounted for nearly three-quarters of parasitized individuals. Nearly half of the spirochete-positive ticks were removed from migrating birds taken in a riparian floodplain forest. Recaptured migrants with infected ticks indicate that they transmit B. burgdorferi to hexapod larvae. We suggest that birds may be both an important local reservoir in the upper Mississippi Valley and long-distance dispersal agents for B. burgdorferi-infected ticks to other regions of the continent.     

Bird-feeding ticks transstadially transmit Borrelia burgdorferi that infect Syrian hamsters

Bird-feeding Ixodes dammini ticks were documented for the first time to successfully molt and transstadially pass Borrelia burgdorferi spirochetes that were indistinguishable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis from the type B31 strain. Forty-six of 73 blood-engorged larvae and 50 of 66 fully-fed nymphs, removed from wild-caught birds, successfully molted. Borreliae were isolated from 21 of 78 partially- and fully-fed larvae off birds, including six specimens that molted. Spirochete-positive cultures also were obtained from 35 of 60 partially- and fully-fed nymphs that had fed from birds, including 20 nymphs that molted into adult ticks. Transstadially passed borreliae by bird-feeding larval and nymphal I. dammini were infectious to hamsters, leading us to suggest that these ticks are capable of subsequently transmitting infectious spirochetes to mammals, including humans. An isolated of B. burgdorferi, recovered from a bird-feeding larval Ixodes dentatus, was indistinguishable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis from the B31 strain. This isolate, unlike another from I. dentatus off a cottontail rabbit (Sylvilagus floridanus), had a protein band with a molecular weight of approximately 31,000 that reacted with murine monoclonal antibodies H3TS and H5332 in western blot analysis. Thus, closely related borreliae are present in both I. dentatus and I. dammini.     

Spirochetes in ticks and antibodies to Borrelia burgdorferi in white-tailed deer from Connecticut, New York State, and North Carolina

Ticks were screened for spirochetes and serum samples from white-tailed deer (Odocoileus virginianus) were assayed for antibodies to Borrelia burgdorferi during 1983-1984. Using fluorescein isothiocyanate-labeled rabbit antibodies produced to B. burgdorferi, the etiologic agent of Lyme disease, spirochetes were detected in Ixodes dammini (10.5% of 1,193) and Dermacentor albipictus (0.6% of 157) adults from Connecticut, I. dammini nymphs (49.1% of 108) and adults (64.7% of 99) from Armonk, New York, and in I. scapularis (0.4% of 531) and Amblyomma americanum (3.5% of 173) adults from North Carolina. Infected ticks were either seeking hosts or feeding on deer during the summer and fall. Direct fluorescent antibody staining also revealed spirochetes in two larvae of I. scapularis that emerged from eggs deposited by separate females in the laboratory. Using indirect immunofluorescence tests, antibodies to B. burgdorferi were identified in white-tailed deer living in tick-infested areas of all three states. Aside from minor cross-reactivity, there was no serologic evidence of Treponema or Leptospira infections. Ixodes dammini is a primary vector of B. burgdorferi in northeastern United States, but in North Carolina, other ixodid ticks may transmit this spirochete to humans and wildlife.     

Birds and their ticks in northwestern California: minimal contribution to Borrelia burgdorferi enzootiology

Birds and their attendant ticks were surveyed for infection with the Lyme disease spirochete Borrelia burgdorferi, in chaparral and woodland-grass habitats in northwestern California from March to July, 1998 to 1999. In total, 234 birds were captured and recaptured (15%); nearly 2.5 times more birds were captured in chaparral than in woodland-grass. Overall, 34 species representing 15 families were collected during this study; of these, 24 species were caught in chaparral, 19 in woodland-grass, and 9 in both vegetational types. The most frequently captured birds were sage sparrows (Amphispiza belli) in chaparral, and American robins (Turdus migratorius) and oak titmice (Baelophus inornatus) in woodland-grass. Birds hosted 35 Ixodes pacificus (15 larvae, 20 nymphs) and 9 Haemaphysalis leporispalustris (3 larvae, 5 nymphs, 1 adult) ticks, of which 32 were removed from chaparral birds and 12 from woodland birds. The prevalence of tick infestation was 13% (21/167) in chaparral and 5% (3/67) in woodland-grass, but the relative and mean tick intensities of 0.19 and 1.5 for chaparral birds, and 0.18 and 4.0 for woodland birds, respectively, did not differ significantly by habitat. Spirochetes were not detected in either bird-blood or tick-tissue samples when tested by culture, immunofluorescence, or Giemsa-staining. In contrast, over 90% (86/94) of western fence lizards (Sceloporus occidentalis) collected in June or July were infested with an average of 6.9 and 8.9 immature I. pacificus in chaparral and woodland-grass, respectively. We conclude that birds contribute little to the enzootiology of B. burgdorferi in chaparral and woodland-grass habitats in northwestern California because of their limited parasitism by tick vectors and lack of detectable spirochetemias.     

Infestation of mammals by Ixodes ricinus ticks (Acari: Ixodidae) in south-central Sweden

Infestation by Ixodes ricinus ticks on rodents, hares and cervids was examined at Bogesund, 10 km north of Stockholm, in south-central Sweden during 1991-1994 and on varying hares (Lepus timidus) at Stora Karlso and Gotska Sandon in the Baltic Sea during 1992-1993. At Bogesund, there were great differences between two consecutive years in the number of I. ricinus larvae infesting bank voles (Clethrionomys glareolus). The seasonal pattern of infestation by I. ricinus larvae and nymphs on bank voles was unimodal in 1991, with peaks in June-July and bimodal in 1992, with peaks in June and August. Male bank voles, compared to females and older voles, compared to young voles, harboured greater numbers of I. ricinus ticks. Apodemus mice, compared to bank voles, harboured greater numbers of I. ricinus ticks. Ixodes ricinus larvae engorged on Apodemus mice were heavier than larvae engorged on bank voles and resulted in larger nymphs. However, there was no difference in the proportions of viable nymphs resulting from larvae engorged on mice or voles. The ranges in the numbers of I. ricinus ticks infesting individual hosts were 1-451 for rodents, 16-2374 for hares and 428-2072 for roe deer (Capreolus capreolus). These ranges of tick numbers are estimated to represent potential blood losses from individual hosts of approximately 0.2-65% for rodents, 0.2-13% for hares and 0.3-9.0% for roe deer. Within the populations of all host species examined, the distributions of all stages of I. ricinus were clumped, with most host individuals harbouring few ticks and only a few individuals harbouring many ticks. The data suggest that, even though a small proportion of tick hosts may be severely affected, the direct effects of feeding by I. ricinus are unlikely to play an important role on mammal population dynamics.     

Host associations of ticks parasitizing rodents at Borrelia burgdorferi enzootic sites in South Carolina.

A total of 237 rodents was collected in 4 regions of South Carolina from July 1994 through December 1995. Eight species were collected, including cotton mouse, hispid cotton rat, eastern woodrat, marsh rice rat, white-footed mouse, eastern harvest mouse, golden mouse, and black rat. Of the 1,514 ticks recovered from these hosts, Ixodes minor Neumann, including larvae, nymphs, and adults, was the most abundant species, representing 54% of the total. Only immature stages of other tick species were found, including larvae and nymphs of Dermacentor variabilis (Say), Amblyomma maculatum Koch, Ixodes affinis Neumann, and Ixodes scapularis Say. All 5 tick species parasitized cotton mice, cotton rats, and woodrats, which were the most important small mammal hosts for ticks at the localities studied. Rice rats were hosts of A. maculatum, D. variabilis, and L. minor. Amblyomma maculatum was more strongly associated with cotton rats than other rodent species. Ixodes scapularis was most strongly associated with cotton mice, and I. minor was more strongly associated with both woodrats and cotton mice than other species of rodents. Ixodes minor parasitized hosts in the Coastal Zone only, where among spirochete-infected hosts, it was present in significantly greater numbers than other ticks. Furthermore, I. minor was the only tick species that showed a statistically significant positive association with spirochetal infection in rodents. More I. affinis parasitized spirochete-infected hosts than I. scapularis, but fewer than I. minor. The findings discussed herein provide evidence that implicates I. minor as the possible primary enzootic vector of the Lyme disease spirochete Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt and Brenner in the Coastal Zone of South Carolina. They also indicate that the high level of B. burgdorferi infection in rodents from this region may be a function of the combined involvement of I. minor, I. affinis, and I. scapularis in the enzootic transmission of the spirochete.     

A comparison of methods for sampling the deer tick,Ixodes dammini,in a Lyme disease endemic area

The purpose of this study was to compare the trapping and examining of mice, drag sampling, and CO₂-baited traps for their ability to detect the presence and abundance of immature deer ticks,Ixodes dammini, in a Lyme disease endemic area in southern New York State. Eight study sites were sampled 14 times between 28 May and 31 August by setting 49 live-traps, four CO₂-baited traps, and drag sampling 500 m². A total of 1540 nymphs and 3079 larvae was collected during the study. Drag sampling collected the most nymphs (705), while more larvae were recovered from CO₂-baited traps (1105). Comparisons among the methods showed a significant difference in the numbers of both larval and nymphal ticks collected (P<0.01). There was a positive correlation between the numbers of nymphs collected by drag sampling and CO₂-baited tick traps (r _s=0.83,P<0.05), and between the numbers of larvae collected by drag sampling and mouse trapping (r _s=0.75,P<0.05). These results suggest that drag sampling would be the single most reliable method for quantitatively sampling immatureI. dammini populations in a Lyme disease endemic area.     

Short-tailed shrews as reservoirs of the agents of Lyme disease and human babesiosis

To determine whether short-tailed shrews (Blarina brevicauda) serve as reservoir hosts for the Lyme disease spirochete (Borrelia burgdorferi) and the agent of human babesiosis (Babesia microti), we examined nymphal ticks that had fed as larvae on shrews collected from 3 enzootic sites in coastal Massachusetts for evidence of infection by either or both of these agents. Xenodiagnosis indicated that 11 of 14 shrews were infected by B. burgdorferi. One of 3 piroplasm-infected shrews also infected ticks with B. microti. In a site where the piroplasm is endemic, 11 of 17 shrews showed patent parasitemias by thin blood smears. Of these, 4 had parasitemias exceeding 40%. Few immature ticks infested shrews, however, suggesting that B. brevicauda, although abundant in some endemic sites and serving as a competent reservoir, would contribute minimally to the population of infected nymphs.     

Avian and mammalian hosts for spirochete-infected ticks and insects in a Lyme disease focus in Connecticut.

Spirochetes and their vectors and reservoirs were studied in a Lyme disease focus in East Haddam, Connecticut, from mid-May through September 1983. Ixodes dammini subadults were comparable in number on white-footed mice (Peromyscus leucopus) (means = 2.9 +/- 3.6 SD) to those on 27 different species of birds (means = 2.3 +/- 4.2 SD) representing 11 families within the order Passeriformes. Less commonly found ticks on birds (means less than or equal to 0.1) were immature Ixodes dentatus and Haemaphysalis leporispalustris. Although spirochete-infected I. dammini larvae and nymphs were taken off eight and nine different species of birds, respectively, significantly fewer positive larvae were removed from birds than from white-footed mice. Spirochetes were detected in the midguts of I. dammini, Dermacentor variabilis, and H. leporispalustris and two species of insects (Cuterebra fontinella and Orchopeas leucopus). Possibly, arthropods other than I. dammini vector these spirochetes in northeastern United States. Spirochetes grew in a cell-free medium inoculated with bloods from four white-footed mice, one woodland jumping mouse (Napaeozapus insignis), one northern mockingbird (Mimus polyglottos), one gray catbird (Dumetella carolinensis), two prairie warblers (Dendroica discolor), one orchard oriole (Icterus spurius), one common yellowthroat (Geothlypis trichas), and one American robin (Turdus migratorius). We suggest that avian hosts, like mammals, develop spirochetemias of the causative agent of Lyme disease. Erythematous tissues from a white-footed mouse were infected with spirochetes.     

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.     

Borreliae in Ixodes ricinus ticks feeding on humans

A total of 298 Ixodes ricinus (L.) ticks (Acari: Ixodidae) feeding on humans in the Czech Republic were tested for borreliae (Borrelia burgdorferi sensu lato) by darkfield microscopy between 1997 and 2003. A majority (68%) of the supplied I. ricinus ticks were nymphs, 25% were females and 7% were larvae. Overall, 20% of 74 examined females and 9% of 203 examined nymphs (but none of 21 examined larvae) were infected with borreliae. The proportion of ticks with a high infection load (>100 spirochetes) was 4% in females and 2% in nymphal I. ricinus. During the year, the highest numbers and proportions of infected nymphal and female ticks were taken from humans in June. Detection of borreliae in the ticks feeding on humans might be helpful in the prophylaxis of Lyme borreliosis.     

Interstadial and Infestation Level-dependent Variation in the Transmission Efficiency of Borrelia Burgdorferi from Mice to Ixodes Ricinus Ticks

The efficiency with which the spirochaete Borrelia burgdorferi sensu stricto was transmitted from laboratory mice to larval and nymphal Ixodes ricinus ticks was assessed, using the polymerase chain reaction. The transmission efficiency to nymphs was significantly greater than to larvae when both fed together on the same host. Increased tick infestation levels of mice were correlated with significantly greater engorgement weights and higher B. burgdorferi transmission coefficients from mice to nymphs. These observations indicate that both the feeding success of ticks and the transmission coefficients from host to tick may be influenced by the tick infestation level of an infected host. The infestation level and the relative numbers of each life stage of the tick are factors which should be considered in the design of transmission experiments.     

Ticks and mosquitoes as vectors of Borrelia burgdorferi s. l. in the forested areas of Szczecin

The aim of the study was to determine the infection level of adult forms and larvae of ticks and mosquitoes with Borrelia burgdorferi in the forested areas of Szczecin. A total of 1699 ticks Ixodes ricinus, including 1422 nymphs, 277 adult forms and 2862 mosquito females representing the genera Aedes (89.6%) and Culex (10.4%) were collected between the years 2004 and 2005. A further 3746 larvae and 1596 pupae of Culex pipiens pipiens were colleted from water bodies. Borrelia burgdorferi s. l. was detected in the arthropods by the method of indirect immunofluorescence assay (IFA). A positive immunological reaction was detected in 16.6% of the adult forms and in 16.5% of the nymphs of Ixodes ricinus. Spirochetes were also detected in 1.7% of mosquito females, 3.2% of larvae and in 1.6% of pupae of Culex pipiens pipiens. The results of the present study confirm that contact with ticks constitutes the main risk of contracting Lyme disease, although mosquitoes play a role as vectors as well.     

Incompetence of catbirds as reservoirs for the Lyme disease spirochete (Borrelia burgdorferi)

We compared the relative infectivity to vector ticks of gray catbirds (Dumetella carolinensis) and white-footed mice (Peromyscus leucopus) for the Lyme disease spirochete (Borrelia burgdorferi). Of 28 catbirds captured in a site enzootic for this agent, 18 were infested by immature Ixodes dammini, the tick vector. By comparison, each of 32 mice sampled concurrently from the same site was infested, and by about 10 times as many ticks as were found infesting the 3 most commonly netted bird species. Although 76% of noninfected larval ticks placed on these mice in a xenodiagnosis became infected, none of the ticks similarly placed on 12 catbirds did so. Spirochetes were detected in ticks derived from 2 Carolina wrens (Thryothorus ludovicianus) and a common yellowthroat (Geothlypis trichas), but these species' potential contribution to infecting ticks does not compare with that of mice. Thus, although birds may help establish new foci of ticks, catbirds, at least, do not appear to contribute as reservoirs of infection.     

<Emphasis Type="Italic">Ixodes </Emphasis>(<Emphasis Type="Italic">Ixodes</Emphasis>) <Emphasis Type="Italic">pararicinus</Emphasis> Keirans &; Clifford, 1985 (Acari: Ixodidae): description of the immature stages,distribution, hosts and medical/veterinary importance

The immature stages of the Neotropical tick Ixodes (Ixodes) pararicinus Keirans & Clifford, 1985 are described from specimens in a laboratory colony initiated from engorged females collected on cattle and larvae fed on mice and chickens. The larva and nymph of I. pararicinus are described using SEM micrographs as well as drawings for some features of the larva. Additionally, immature stages of I. pararicinus collected on wild mice and birds in Uruguay and Argentina were compared with specimens from the laboratory colony. A taxonomic key to the nymphs of the species of the ricinus complex established in the Western Hemisphere is presented. The distribution of I. pararicinus comprises Argentina, Colombia and Uruguay, but it is also probably established in Bolivia, Brazil, Chile and Peru. Most adult ticks of this species have been found on introduced domestic artiodactyles, although Neotropical deer species must have been the ancestral host. Larvae and nymphs of I. pararicinus have also been found on sigmodontine rodents and passeriform birds. Although I. pararicinus is a member of the ricinus complex, which contains the main vectors of Borrelia burgdorferi (sensu lato), there are few studies concerning its potential for pathogen transmission.     

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.     

A microfilaria of exceptional size from the ixodid tick, Ixodes dammini, from Shelter Island, New York

Thirty or more microfilariae 0.70-1.32 mm in length were recovered from the hemocele of an unengorged adult tick, Ixodes dammini, that was collected from vegetation on Shelter Island, New York. Among approximately 500 I. dammini collected from the same area only 1 other was similarly infected. Outstanding features, in addition to size, were absence of a cephalic space and the presence of nuclei in 2 or 3 irregular rows extending to the end of a bluntly rounded tail. The microfilariae apparently were ingested in a blood meal that was taken when the ticks were larvae or nymphs, and had persisted alive without development.