Detection of West Nile virus-specific antibodies and nucleic acid in horses and mosquitoes, respectively, in Nuevo Leon State, northern Mexico, 2006-2007.

In the last 5 years, there has been only one reported human case of West Nile virus (WNV) disease in northern Mexico. To determine if the virus was still circulating in this region, equine and entomological surveillance for WNV was conducted in the state of Nuevo Leon in northern Mexico in 2006 and 2007. A total of 203 horses were serologically assayed for antibodies to WNV using an epitope-blocking enzyme-linked immunosorbent assay (bELISA). Seroprevalences for WNV in horses sampled in 2006 and 2007 were 26% and 45%, respectively. Mosquito collections in 2007 produced 7365 specimens representing 15 species. Culex mosquitoes were screened for WNV RNA and other genera (Mansonia, Anopheles, Aedes, Psorophora and Uranotaenia) were screened for flaviviruses using reverse-transcription (RT)-PCR. Two pools consisting of Culex spp. mosquitoes contained WNV RNA. Molecular species identification revealed that neither pool included Culex quinquefasciatus (Say) (Diptera:Culicidae) complex mosquitoes. No evidence of flaviviruses was found in the other mosquito genera examined. These data provide evidence that WNV is currently circulating in northern Mexico and that non-Cx. quinquefasciatus spp. mosquitoes may be participating in the WNV transmission cycle in this region.

Risk indicators for the tick Ixodes ricinus and Borrelia burgdorferi sensu lato in Sweden.

The distributional area of the tick Ixodes ricinus (L.), the primary European vector to humans of Lyme borreliosis spirochaetes (Borrelia burgdorferi sensu lato) and tick-borne encephalitis virus, appears to be increasing in Sweden. It is therefore important to determine which environmental factors are most useful to assess risk of human exposure to this tick and its associated pathogens. The geographical distribution of I. ricinus in Sweden was analysed with respect to vegetation zones and climate. The northern limit of I. ricinus and B. burgdorferi s.l. in Sweden corresponds roughly to the northern limit of the southern boreal vegetation zone, and is characterized climatically by snow cover for a mean duration of 150 days and a vegetation period averaging 170 days. The zoogeographical distribution of I. ricinus in Sweden can be classified as southerly-central, with the centre of the distribution south of the Limes Norrlandicus. Ixodes ricinus nymphs from 13 localities in different parts of Sweden were examined for the presence of B. burgdorferi s.l. and found to be infected with Borrelia afzelii and Borrelia garinii. Tick sampling localities were characterized on the basis of the density of Borrelia-infected I. ricinus nymphs, presence of specific mammals, dominant vegetation and climate. Densities of I. ricinus nymphs and Borrelia-infected nymphs were significantly correlated, and nymphal density can thus serve as a general indicator of risk for exposure to Lyme borreliosis spirochaetes. Analysis of data from this and other studies suggests that high densities of Borrelia-infected nymphs typically occur in coastal, broadleaf vegetation and in mixed deciduous/spruce vegetation in southern Sweden. Ixodes ricinus populations consistently infected with B. burgdorferi s.l. can occur in: (a) biotopes with shrews, rodents, hares and birds; (b) biotopes with shrews, rodents, hares, deer and birds, and (c) island locations where the varying hare (Lepus timidus) is the only mammalian tick host.

Climate-based model predicting acarological risk of encountering the human-biting adult life stage of Dermacentor andersoni (Acari: Ixodidae) in a key habitat type in Colorado.

We exploited an elevation (climate) gradient ranging from 1,700 to 2,500 m in Poudre Canyon of Larimer County, CO, to determine climatic correlates of abundance per 15-s drag sampling time unit (hereafter referred to as abundance) of the human-biting adult life stage of the Rocky Mountain wood tick, Dermacentor andersoni Stiles (Acari: Ixodidae), in a key risk habitat for tick exposure: south/west-facing, rocky hillsides with mixed grass-brush-conifer vegetation. The relationship between elevation and abundance was parabolic, with peak tick abundances occurring at mid-range elevations (2,200-2,400 m) and tick abundances approaching zero at approximately 2,100 and 2,500 m. Regression modeling demonstrated that abundance of host-seeking adult ticks in south/west-facing exposures was accurately predicted by several climate variables related to temperature (e.g., mean annual minimum temperature, maximum temperature, and base 10 degrees C growing degree-days, and median length of annual freeze-free period; r2 values ranging from 0.771 to 0.864), whereas mean annual precipitation, snowfall, or relative humidity were uninformative in this respect (r2 values ranging from 0.020 to 0.316). Abundance of D. andersoni adults peaked at a mean annual maximum temperature of approximately 10 degrees C and a mean annual growing degree-day value of approximately 650. Relationships between climate variables and abundance of D. andersoni adults were used to create geographic information system (GIS)-based models for predicted tick abundance in south/west-facing exposures in Larimer County. This is the first GIS-based model developed for spatial patterns of abundance of D. andersoni. Finally, preliminary data from Poudre Canyon indicate a shift toward peak abundances of D. andersoni adults occurring in sheltered northern/eastern exposures, rather than in drier and hotter southern/ western exposures, at elevations below 2,100 m.

A call for renewed research on tick-borne Francisella tularensis in the Arkansas-Missouri primary national focus of tularemia in humans.

Arkansas-Missouri has emerged as the primary U.S. focus of tularemia, which is caused by the National Institute of Allergy and Infectious Diseases Category A Priority Pathogen Francisella tularensis, over the past 30 yr. There are several pieces of indirect evidence suggesting that a key role of ticks in the transmission of F. tularensis to humans in Arkansas-Missouri is the primary reason why tularemia has remained a prominent disease of humans in this two-state area while fading away from other central or eastern states after a general decline in rabbit-associated tularemia cases. The primary tick vector(s) in Arkansas-Missouri can, based on a comparison of seasonal patterns of human tularemia cases and peak host-seeking activity of commonly human-biting tick species and life stages, be narrowed down to Amblyomma americanum (L.) nymphs, A. americanum adults, or Dermacentor variabilis (Say) adults. Unfortunately, currently available data cannot be used to further elucidate the relative roles of these ticks as vectors of F. tularensis to humans in Arkansas-Missouri. To address the fact that we do not know which tick species is the primary vector of F. tularensis to humans in the most prominent U.S. focus of tularemia, we need to determine (1) relative contributions of different tick species and life stages as human biters in Arkansas-Missouri; (2) natural rates of infection with F. tularensis tularensis (type A) and F. tularensis holarctica (type B) of the most prominent human-biting ticks in areas of Arkansas-Missouri hyperendemic for tularemia; (3) experimental vector efficiency of these ticks for both F. tularensis tularensis and F. tularensis holarctica; and (4) presence of infection with F. tularensis tularensis or F tularensis holarctica in ticks collected from humans in Arkansas-Missouri.

Seasonal pattern of host-seeking activity by the human-biting adult life stage of Dermacentor andersoni (Acari: Ixodidae).

Nonremoval drag sampling was conducted in multiple sites in Larimer County, CO, from March to July 2006 to determine the seasonal pattern of host-seeking activity by the human-biting adult life stage of the Rocky Mountain wood tick, Dermacentor andersoni Stiles (Acari: Ixodidae). Four sites, at elevations ranging from 1,790 to 2,470 m, consistently yielded host-seeking ticks. Ticks were active from March until late June; the length of the active period ranged from 84 to 104 d. Based on site-specific linear regression models of increase and decrease in tick host-seeking activity over time, densities of D. andersoni adults were estimated to reach 50% of their peaks between 2 and 11 April, to peak between 21 and 28 April, and to fall below 50% of the peaks between 24 and 27 May. The length of the periods with tick densities exceeding 50 and 75% of the peak was 43-52 and 21-26 d, respectively. Rapid increases in tick numbers in late March to early April followed a stretch of days with daily maximum temperatures exceeding 5 degrees C, whereas rapidly declining tick numbers in mid- to late May were associated with daily maximum temperatures consistently exceeding 20 degrees C and daily minimum relative humidity commonly falling below 20%. Densities of D. andersoni adults exceeded 50% of the peak when daily maximum temperatures were in the 16-19 degrees C range and daily minimum relative humidity was > 20%. Finally, tick seasonality may be adapted to local climatic conditions within Larimer County; site-specific daily maximum temperatures at the time of peak tick host-seeking activity in late April were positively associated with site-specific mean daily maximum temperatures for April.

Refractoriness of the western fence lizard (Sceloporus occidentalis) to the Lyme disease group spirochete Borrelia bissettii.

The western fence lizard, Sceloporus occidentalis, is refractory to experimental infection with Borrelia burgdorferi sensu stricto, one of several Lyme disease spirochetes pathogenic for humans. Another member of the Lyme disease spirochete complex, Borrelia bissettii, is distributed widely throughout North America and a similar, if not identical, spirochete has been implicated as a human pathogen in southern Europe. To determine the susceptibility of S. occidentalis to B. bissettii, 6 naïve lizards were exposed to the feeding activities of Ixodes pacificus nymphs experimentally infected with this spirochete. None of the lizards developed spirochetemias detectable by polymerase chain reaction for up to 8 wk post-tick feeding, infected nymphs apparently lost their B. bissettii infections within 1-2 wk after engorgement, and xenodiagnostic L. pacificus larvae that co-fed alongside infected nymphs did not acquire and maintain spirochetes. In contrast, 3 of 4 naïve deer mice (Peromyscus maniculatus) exposed similarly to feeding by 1 or more B. bissettii-infected nymphs developed patent infections within 4 wk. These and previous findings suggest that the complement system of S. occidentalis typically destroys B. burgdorferi sensu lato spirochetes present in tissues of attached and feeding I. pacificus nymphs, thereby potentially reducing the probability of transmission of these bacteria to humans or other animals by the resultant adult ticks.

Color correction in planar optics configurations.

Color correction in planar optics configurations can be achieved by resorting to gradient-index rather than uniform-refractive-index substrates. The basic configuration, principle of correction, and calculated and experimental results are presented. The results reveal that, with an appropriate refractive index distribution along the thickness of the substrates, the color can be corrected over a wavelength range up to 155 nm depending on incidence angles.

Geographical distribution patterns and habitat suitability models for presence of host-seeking ixodid ticks in dense woodlands of Mendocino County, California.

We used drag sampling to examine the geographical distribution patterns of ixodid ticks engaging in open (non-nidicolous) host-seeking behavior in dense woodland habitats of the climatically and ecologically diverse Mendocino County in north coastal California. The findings based on this sampling methodology reflect risk of human exposure to host-seeking ticks rather than the true distribution of the ticks. Drag sampling in 78 sites yielded 7,860 nymphal or adult Ixodes pacificus Cooley & Kohls, 220 Dermacentor occidentalis Marx, 150 Ixodes spinipalpis Hadwen & Nuttall, 15 Hemaphysalis leporispalustris (Packard), 12 Ixodes angustus Neumann, 12 Ixodes auritulus Neumann, and a single Dermacentor variabilis (Say). I. pacificus, which is the primary vector of the Lyme disease spirochete Borrelia burgdorferi to humans in California, occurred in all 78 sites examined. D. occidentalis, another tick species commonly biting humans in California, and H. leporispalustris typically were encountered in oak-associated woodlands in the central or eastern parts of the county. In contrast, three species of Ixodes ticks (I. angustus, I. auritulus, and I. spinipalpis) most commonly were found questing openly in woodlands with redwood present in the western part of the county. I. angustus and I. spinipalpis are occasional human biters and known experimental vectors of B. burgdorferi. Our study represents the first collection of large numbers of openly host-seeking I. spinipalpis ticks. Univariate tests of associations between presence of ticks (D. occidentalis, H. leporispalustris, I. angustus, I. auritulus, or I. spinipalpis) and environmental geographical information systems-remote sensing (GIS/ RS)-based data indicated that elevation, number of growing degree-days, and tasseled cap brightness, greenness, and wetness are especially useful predictors of presence of openly hostseeking ticks. Combinations of the above-mentioned GIS/RS-based data yielded significant logistic regression models for habitat suitability of host-seeking ticks for all five above-mentioned species. The model equations were used to create spatial surfaces of predicted presence of suitable habitat for openly host-seeking ticks in Mendocino County dense woodlands.

Acarologic risk of exposure to Borrelia burgdorferi spirochaetes: long-term evaluations in north-western California, with implications for Lyme borreliosis risk-assessment models.

Over a 5-year period (1997-2001) the population densities of Ixodes pacificus Cooley & Kohls (Acari: Ixodidae) nymphs infected with spirochaetes of Borrelia burgdorferi sensu lato (s.l.) were evaluated in areas of 2000 ha at two localities (CHR, nine sites; HREC, seven sites) 25 km apart in Mendocino County, north-western California. The 5-year median density of infected nymphs was significantly higher at CHR than at HREC (0.51 vs. 0.09 per 100 m(2) and site-specific yearly densities exceeding one infected nymph per 100 m2 were 10-fold more likely to occur at CHR than at HREC. The importance of long-term data in acarologic risk assessment was demonstrated by significantly higher median yearly densities of infected nymphs at CHR from 1997 to 1999, whereas both areas had similar densities during 2000-2001. Overall, the causative agent of Lyme borreliosis in North America, B. burgdorferi Johnson et al. sensu stricto (s.s.) accounted for 76% of 46 genetically characterized B. burgdorferi s.l. infections from I. pacificus nymphs. Tremendous variability in acarologic risk was recorded within both areas: yearly densities of infected nymphs varied 11-97-fold between sites at CHR and 8-30-fold at HREC. Part of this variation could be explained by environmental traits, most notably deer usage. However, correlations between environmental factors and density of infected nymphs (for CHR and HREC combined) did not necessarily apply when these areas were considered separately. Thus, a Lyme borreliosis ecology model developed in one of these areas needs testing in the other area.

Seasonal activity patterns of Ixodes pacificus nymphs in relation to climatic conditions.

In western North America, the tick Ixodes pacificus Cooley & Kohls (Acari: Ixodidae) is the primary vector to humans and domestic animals of the disease agents causing Lyme disease and granulocytic ehrlichiosis. We examined the seasonal activity patterns of I. pacificus nymphs over a 4-year period, including the wet and cold El Niño winter/spring of 1998, in a dry oak/madrone woodland, and for one year in a cooler and moister redwood/tanoak woodland in Mendocino County, California. Linear regressions were used to estimate when nymphal densities first exceeded and then fell below 25, 50 and 75% of the recorded yearly peak densities. In oak/madrone woodland, nymphs typically were active by mid-March, reached 50% of their yearly peak densities in early to mid-April, peaked by early May, fell below 50% of their peak densities by early to mid-June, and were absent by late July to mid-August. The lengths of the periods with nymphal densities exceeding 50 and 75% of the recorded yearly peaks in oak/madrone woodland were associated positively with rainfall and negatively with maximum air temperatures during April-May. Moreover, nymphal numbers typically reached 50% of their peak 10-15 days later, remained at levels above 50% of the peak 1.3-1.5 times longer, and started declining 4-6 weeks later under cooler, moister climatic conditions (oak/madrone woodland in 1998 and redwood/tanoak woodland in 2000) relative to warmer, drier conditions (oak/madrone woodland in 2000-2001). In oak/madrone woodland, nymphal densities typically started to decline when mean maximum daily air temperatures exceeded 23 degrees C. Nymphal densities were higher in dry oak/madrone relative to moist redwood/tanoak woodland from mid-March to late May 2000, similar in both habitat types in early June, but higher in redwood/tanoak woodland from late June onwards. We conclude that large-scale studies of the density of I. pacificus nymphs in California need to consider spatial variation in the length of nymphal activity periods and select temporal sampling regimens that yield representative data for all included habitat types.

Endovascular repair of para-anastomotic aneurysms of the aorta and iliac arteries: preferred treatment for a complex problem.

PURPOSE: Standard surgical repair of para-anastamotic aneurysms (PAAs) of the abdominal and thoracic aorta and the iliac arteries has been associated with high morbidity and mortality rates. We reviewed our continuing experience with endovascular repair of these lesions to determine whether this approach is favorable and durable. METHODS: All patients with PAAs of the aorta or iliac arteries who underwent endovascular treatment of their lesions between August 1993 and July 1999 were prospectively followed up, and data on age, previous aortic pathology and surgery, size of PAA, time to diagnosis, and symptoms at presentation were recorded. Preoperative, intraoperative, and postoperative imaging studies were analyzed. All patients had endovascular stent-grafts placed under digital fluoroscopic guidance in the operating room. Data on intraoperative and postoperative complications, mortality, and endoleaks were reviewed. RESULTS: From August 1993 to July 1999, 28 patients (20 men, 8 women) had 35 PAAs of the aorta or iliac arteries. There were 5 thoracic aortic, 12 abdominal aortic, and 18 iliac artery PAAs. Three patients had a contained rupture of their PAA. All patients who had originally undergone reconstruction for occlusive disease had lesions consistent with false aneurysms, whereas 73% of the aortic or iliac PAAs in patients originally treated for aneurysm disease appeared to be true aneurysms. Thirty-four of 35 PAAs were successfully excluded with stent-grafts (97%). There was one death at 30 days (3.6%) in a patient who was successfully treated endovascularly for a contained rupture of a thoracic PAA. There were four major postoperative complications (14.2%) in the 28 patients who were treated. One patient had continued perfusion of a thoracic aortic PAA (type I endoleak). The in-hospital length of stay after endovascular repair of PAA was 4 days (range, 1-18 days). The mean follow-up period was 21 months (range, 1-68 months). CONCLUSION: Endovascular repair of aortic and iliac artery PAAs is technically feasible and provides a high rate of lesion exclusion. Morbidity and mortality rates appear lower than those reported for open surgical repair. These patients can typically be discharged by the second postoperative day. Endovascular therapy for stable ruptured PAAs can be successfully performed and should be considered as an option only when appropriate devices and expertise are available. For uncomplicated PAAs of the aorta and iliac arteries, endovascular therapy may be more favorable than surgical repair.

Intentional internal iliac artery occlusion to facilitate endovascular repair of aortoiliac aneurysms.

PURPOSE: The safety of intentional occlusion of patent internal iliac arteries (IIAs) to facilitate the endovascular repair of aortoiliac artery aneurysms (abdominal aortic aneurysms [AAAs] and iliac aneurysms [IAs]) was evaluated. METHODS: We analyzed the techniques and clinical sequelae of selective occlusion of one or both IIAs in 103 patients and correlated these findings with the results of preoperative angiograms to identify vascular anatomy that may predict postoperative pelvic ischemia. To quantify the clinical presentation of pelvic ischemia, we developed these criteria: class 0, no symptoms; class I, nonlimiting claudication with exercise; class II, new onset impotence, with or without moderate to severe buttock pain, leading to physical limitation with exercise; class III, buttock rest pain, colonic ischemia, or both. IIA occlusion was achieved in 100% of the patients by means of either catheter-directed embolization or orificial coverage with a stent-graft. No patient in this study had angiographic evidence of significant visceral occlusive disease before the procedure. Sixty-four patients had isolated AAAs, 23 patients had AAAs and IAs, and 16 patients had isolated IAs. Ninety-two patients had one IIA selectively occluded, and 11 patients had both IIAs selectively occluded. RESULTS: After IIA occlusion, 12 patients were categorized in class I, 9 patients were categorized in class II, and 1 patient was categorized in class III, for a total of 22 patients (21%) with pelvic ischemia. Sixteen (17%) of 92 patients had unilateral IIA occlusions, and six (17%) of 11 patients had bilateral IIA occlusions. Five patients in class I improved and had no symptoms within 1 year, and one patient in class II was downgraded to class I because of improved symptoms. Two unique preoperative angiographic findings were identified in the remaining 16 patients (16%) with chronic pelvic claudication: (1) stenosis of the remaining IIA origin (> 70%) with nonopacification of more than three of the six IIA branches (63%); and (2) small caliber, diseased or absent medial and lateral femoral circumflex arteries ipsilateral to the side of the IIA occlusion (25%). One patient with class III ischemia died of cardiovascular collapse associated with colon infarction caused by either acute ischemia or particulate embolization. CONCLUSION: The incidence of pelvic ischemia after IIA occlusion is 20% immediately after endovascular aortoiliac aneurysm repair. A total of 25% of patients had no symptoms within 1 year. Two preoperative radiologic findings may help identify patients who are at risk for pelvic ischemia: stenosis of the patent IIA and disease deep femoral ascending branches ipsilateral to the occluded IIA. The risk of colon ischemia appears to be small after selective IIA occlusion to facilitate endovascular AAA repair.

Histopathologic analysis of endovascular stent grafts from patients with aortic aneurysms: Does healing occur?

BACKGROUND: Research with animal models has demonstrated tissue healing of endovascular grafts in both native arterial segments and in experimentally created arterial aneurysms. Fundamental to the successful clinical use of endovascular grafts for the treatment of aneurysmal disease is the creation of a permanent hemostatic seal between the graft ends and the arterial wall. Characteristics of this healing process in patients with aneurysmal disease have not been fully studied. In this study, we analyzed the macroscopic and histopathologic changes of the arterial wall after endovascular repair of aortic aneurysms. METHODS: Over a 7-year period, 313 patients were treated with endovascular grafts to exclude arterial aneurysms of the thoracic and abdominal aorta. Of these patients, 11 had their endovascular grafts recovered for analysis. Five graft specimens were recovered during subsequent open aortic surgery. Six grafts were recovered at autopsy after the death of the patient of causes unrelated to the patient's endovascular graft. All specimens were fixed in formalin. Histologic analysis included light microscopy with hematoxylin and eosin and trichrome stains. Well-preserved specimens were selected after light microscopic examination and postfixed in 3% buffered glutaraldehyde for electron microscopy. The aortas from autopsy specimens were removed en bloc and fixed in formalin; representative regions of each graft were sectioned for analysis. Adherence of the graft to the vessel wall was categorized as densely adherent or easily separated after graft explantation. Traction applied to the graft-aortic anastomosis was equal to traction generated by suspending a standardized 2-kg weight. Infrarenal graft specimens were obtained with supraceliac aortic clamping, longitudinal aortotomy, and graft sampling before endograft revision. RESULTS: In eight patients, endograft fixation was found to be firmly adherent to the arterial wall. A translucent film of fibrinous material was consistently seen across the entire luminal surface of the endograft. Light and electron microscopy failed to demonstrate an endothelial layer or organized pseudointima at the graft-artery interface. CONCLUSION: Despite suggestive experimental data regarding endograft healing in animals, minimal graft incorporation was apparent in the stent grafts recovered in this study. A greater emphasis on the construction and mechanism of fixation of endograft attachment systems will be important for long-term device function.

Acarologic risk of exposure to emerging tick-borne bacterial pathogens in a semirural community in northern California.

An acarologic study was conducted in a semirural community in northern California to determine the relative abundance of, and the prevalence of infection with, three emerging bacterial pathogens in the western black-legged tick (Ixodes pacificus). These included the agents causing Lyme disease (Borrelia burgdorferi), human granulocytic ehrlichiosis [Ehrlichia phagocytophila (formerly Ehrlichia equi)], and human monocytic ehrlichiosis (Ehrlichia chaffeensis). The study area in Sonoma County consisted of two properties each with four residents and an uninhabited adjacent comparison area. Six of the eight residents had been either physician-diagnosed or serodiagnosed previously with Lyme disease, and, of these, one also had been serodiagnosed with human monocytic ehrlichiosis. Direct immunofluorescent/culture assays and bacterial species-specific polymerase chain reaction assays were used to test whole ticks individually for presence of B. burgdorferi and Ehrlichia spp., respectively. Overall, 6.5% of the nymphal (n = 589) and 1.6% of the adult ticks (n = 318) from the same generational cohort were found to contain B. burgdorferi. In contrast, none of 465 nymphs and 9.9% of 202 adults were infected with E. phagocytophila. Excised tissues from another 95 adult ticks yielded a comparable E. phagocytophila infection prevalence of 13.7%. E. chaffeensis was not detected in either nymphal or adult ticks. Using a combination of culture and polymerase chain reaction assays, coinfection of I. pacificus adults with B. burgdorferi and E. phagocytophila was demonstrated for the first time. The marked disparity in the infection prevalence of these pathogens in nymphal and adult ticks suggests that their maintenance cycles are inherently different.

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).

Efficiency of drag sampling for estimating population sizes of Ixodes pacificus (Acari: Ixodidae) nymphs in leaf litter.

Drag sampling is a commonly used method to obtain relative estimates of the density of questing nymphal Ixodes scapularis Say and I pacificus Cooley & Kohls ticks, which are primary vectors of Lyme disease spirochetes to humans in North America. However, the efficiency of drag sampling in determining absolute population densities of questing nymphs has not been evaluated previously. Therefore, we assessed the efficiency of a single drag-sampling occasion to estimate the total population size of questing I pacificus nymphs in a leaf-litter habitat in California. Repeated daily removal sampling was carried out in four areas, each covering 300 m2, on 17 occasions over a 23-d period in the spring of 1999. In total, 573 I. pacificus nymphs were collected, of which 55 (9.6%) were collected on the initial sampling occasion and 20 (3.5%) on the last occasion. The total population size of questing nymphs, i.e., the intersection with the horizontal axis of a linear regression of daily nymphal catch rates on the number of nymphs caught previously, was estimated to be 936. Thus, the efficiency of the initial sampling occasion to estimate the total population size was 5.9% (4.8, 5.0, 5.8, and 9.1%, respectively, for the four individual sampling areas). Further, the overall mean efficiencies of the two, five, and 10 first removal sampling occasions to estimate the absolute nymphal density was 5.2, 4.7, and 4.3%, respectively, and 13 sampling occasions were required to collect 50% of the estimated total nymphal population.

Abundance of ticks (Acari: Ixodidae) infesting the western fence lizard, Sceloporus occidentalis, in relation to environmental factors.

We examined the impact of environmental characteristics, such as habitat type, topographic exposure and presence of leaf litter, on the abundance of Ixodes pacificus ticks infesting the western fence lizard (Sceloporus occidentalis) at the University of California Hopland Research and Extension Center (HREC), Mendocino County, California. A total of 383 adult lizards were slip-noosed and examined for tick infestation in April and May 1998. At least 94% of the lizards were infested by ticks and at least 20% of the females and 33% of the males carried > 15 ticks. This intensive utilization of western fence lizards (which do not serve as natural reservoirs for Lyme disease spirochetes) by subadult ticks, is probably the primary reason for the low prevalence of infection with Borrelia burgdorferi in I. pacificus nymphs and adults previously recorded at the HREC. Tick loads were higher on male than female lizards. Also, male lizards were generally more heavily infested in late April than in late May. The prevalence of tick infestation exceeded 88% in all habitat types but males collected in woodland and grass/woodland edges had higher tick loads than those collected in open grassland. Male lizards captured in open, exposed grassland tended to carry heavier tick loads in northern/eastern, as compared to southern/western, exposures, and when leaf litter was present.

Variation in the density of questing Ixodes pacificus (Acari:Ixodidae) nymphs infected with Borrelia burgdorferi at different spatial scales in California.

The density of, and prevalence of infection with Borrelia burgdorferi in, Ixodes pacificus nymphs as well as the density of infected nymphs were compared at 12 properties at a small rural community at high risk for Lyme disease (CHR) and at 12 areas at the University of California Hopland Research and Extension Center (HREC), Mendocino County, California. The mean infection prevalence and density of infected nymphs were 1.7% (range, 0-4.2%) and 0.10 infected nymphs per 100 m2 (range, 0-0.23 per 100 m2) at the HREC, and 12.4% (range, 3.9-41.3%) and 1.83 infected nymphs per 100 m2 (range, 0.29-22.17 per 100 m2) at the CHR. Thus, the mean density of infected nymphs differed 18-fold between CHR and HREC and 76-fold between properties at the CHR. Also, there was up to 10-fold variation in infection prevalence and 16-fold variation in density of infected nymphs between discrete areas within properties at the CHR. The high densities of infected nymphs recorded at the CHR suggest that, despite the low statewide incidence of Lyme disease, the medical community should be alerted that Lyme disease can be highly endemic in rural areas of northwestern California. The prevalence of spirochetal infection was higher for nymphs collected in southern/western, as compared to northern/eastern, exposures at both HREC and CHR. Infection prevalence and nymphal density were negatively associated at the HREC, whereas they tended to be associated positively at the CHR. A positive association was observed between nymphal density and density of infected nymphs when data from CHR and HREC were combined, and when data from the CHR were considered alone, but not for data from the HREC alone.

Intussusception in adults: institutional review.

BACKGROUND: Intestinal intussusception in the adult is a rare entity that differs greatly in etiology from its pediatric counterpart. Controversy remains regarding the optimal management of this problem in the adult patient. The purpose of this study was to determine the cause(s) of intussusception and to determine the role of intestinal reduction in the management of intussusception in adults. STUDY DESIGN: A retrospective review performed at The Mount Sinai Medical Center identified 27 patients, 16 years and older, with a diagnosis of intestinal intussusception. Data related to presentation, diagnosis, treatment, and pathology were analyzed. RESULTS: There were 13 males and 14 females. The median age of the group was 52 years with a range of 16 to 90 years. Abdominal pain was the most common presenting complaint. A preoperative diagnosis was suspected in 11 of 27 patients (40%). There were 22 small bowel lesions and 5 colonic lesions. A pathologic cause was identified in 85% of patients with 8 of 22 (36%) small bowel and 4 of 5 (80%) of large bowel lesions being malignant. All small bowel cancers represented metastatic disease and all large bowel malignancies were primary adenocarcinomas. The median age of patients with malignant disease was 60 years; it was 44 years for those with benign disease. Operative treatment consisted of resection alone in 58% of patients and resection after reduction in 42%. Three patients were treated nonoperatively. CONCLUSIONS: Our data support a selective approach to the operative treatment of intussusception in adults. Colonic lesions should not be reduced before resection because they most likely represent a primary adenocarcinoma. Small bowel intussusception should be reduced only in patients in whom a benign diagnosis has been made preoperatively or in patients in whom resection may result in short gut syndrome.

Managed competition in practice: 'value purchasing' by fourteen employers.

Many large U.S. companies have transformed their procurement of health benefits in the 1990s by combining the principles of managed competition with other business tactics to create a business-savvy hybrid of the private sector's own design, often referred to as "value purchasing." Until recently, few policymakers or health care observers believed that large firms would be a force in health system reform. Yet to implement value purchasing, the large companies in this study created new organizational forms, provided employees with financial incentives to select low-cost health plans, and used business tactics such as competitive bidding to negotiate more favorable rates and to improve quality among health plans. The financial results were impressive for the companies studied. In addition, the companies' demands on the health care delivery system are multiplying as the interface between business firms and health care organizations changes. These demands will only increase as the practices we found become more widespread.