Passive surveillance for I. scapularis ticks: enhanced analysis for early detection of emerging Lyme disease risk.

Lyme disease (LD) is emerging in Canada because of the northward expansion of the geographic range of the tick vector Ixodes scapularis (Say). Early detection of emerging areas of LD risk is critical to public health responses, but the methods to do so on a local scale are lacking. Passive tick surveillance has operated in Canada since 1990 but this method lacks specificity for identifying areas where tick populations are established because of dispersion of ticks from established LD risk areas by migratory birds. Using data from 70 field sites in Quebec visited previously, we developed a logistic regression model for estimating the risk of I. scapularis population establishment based on the number of ticks submitted in passive surveillance and a model-derived environmental suitability index. Sensitivity-specificity plots were used to select an optimal threshold value of the linear predictor from the model as the signal for tick population establishment. This value was used to produce an "Alert Map" identifying areas where the passive surveillance data suggested ticks were establishing in Quebec. Alert Map predictions were validated by field surveillance at 76 sites: the prevalence of established I. scapularis populations was significantly greater in areas predicted as high-risk by the Alert map (29 out of 48) than in areas predicted as moderate-risk (4 out of 30) (P < 0.001). This study suggests that Alert Maps created using this approach can provide a usefully rapid and accurate tool for early identification of emerging areas of LD risk at a geographic scale appropriate for local disease control and prevention activities.

Active and passive surveillance and phylogenetic analysis of Borrelia burgdorferi elucidate the process of Lyme disease risk emergence in Canada.

BACKGROUND: Northward expansion of the tick Ixodes scapularis is driving Lyme disease (LD) emergence in Canada. Information on mechanisms involved is needed to enhance surveillance and identify where LD risk is emerging. OBJECTIVES: We used passive and active surveillance and phylogeographic analysis of Borrelia burgdorferi to investigate LD risk emergence in Quebec. METHODS: In active surveillance, we collected ticks from the environment and from captured rodents. B. burgdorferi transmission was detected by serological analysis of rodents and by polymerase chain reaction assays of ticks. Spatiotemporal trends in passive surveillance data assisted interpretation of active surveillance. Multilocus sequence typing (MLST) of B. burgdorferi in ticks identified likely source locations of B. burgdorferi. RESULTS: In active surveillance, we found I. scapularis at 55% of sites, and we were more likely to find them at sites with a warmer climate. B. burgdorferi was identified at 13 I. scapularis-positive sites, but infection prevalence in ticks and animal hosts was low. Low infection prevalence in ticks submitted in passive surveillance after 2004-from the tick-positive regions identified in active surveillance-coincided with an exponential increase in tick submissions during this time. MLST analysis suggested recent introduction of B. burgdorferi from the northeastern United States. CONCLUSIONS: These data are consistent with I. scapularis ticks dispersed from the United States by migratory birds, founding populations where the climate is warmest, and then establishment of B. burgdorferi from the United States several years after I. scapularis have established. These observations provide vital information for public health to minimize the impact of LD in Canada.

Risk maps for range expansion of the Lyme disease vector, Ixodes scapularis, in Canada now and with climate change.

BACKGROUND: Lyme disease is the commonest vector-borne zoonosis in the temperate world, and an emerging infectious disease in Canada due to expansion of the geographic range of the tick vector Ixodes scapularis. Studies suggest that climate change will accelerate Lyme disease emergence by enhancing climatic suitability for I. scapularis. Risk maps will help to meet the public health challenge of Lyme disease by allowing targeting of surveillance and intervention activities. RESULTS: A risk map for possible Lyme endemicity was created using a simple risk algorithm for occurrence of I. scapularis populations. The algorithm was calculated for each census sub-division in central and eastern Canada from interpolated output of a temperature-driven simulation model of I. scapularis populations and an index of tick immigration. The latter was calculated from estimates of tick dispersion distances by migratory birds and recent knowledge of the current geographic range of endemic I. scapularis populations. The index of tick immigration closely predicted passive surveillance data on I. scapularis occurrence, and the risk algorithm was a significant predictor of the occurrence of I. scapularis populations in a prospective field study. Risk maps for I. scapularis occurrence in Canada under future projected climate (in the 2020s, 2050s and 2080s) were produced using temperature output from the Canadian Coupled Global Climate Model 2 with greenhouse gas emission scenario enforcing 'A2' of the Intergovernmental Panel on Climate Change. CONCLUSION: We have prepared risk maps for the occurrence of I. scapularis in eastern and central Canada under current and future projected climate. Validation of the risk maps provides some confidence that they provide a useful first step in predicting the occurrence of I. scapularis populations, and directing public health objectives in minimizing risk from Lyme disease. Further field studies are needed, however, to continue validation and refinement of the risk maps.

Detection and differentiation of Entamoeba histolytica and Entamoeba dispar isolates in clinical samples by PCR and enzyme-linked immunosorbent assay.

Differential diagnosis of Entamoeba histolytica (pathogenic) and Entamoeba dispar (nonpathogenic), which are two morphologically identical species of amebae, is essential both for treatment decision and public health knowledge. The study reported here was designed to choose a reference differentiation technique. Stool samples (n = 95) were tested by microscopy, TechLab enzyme-linked immunosorbent assays (ELISAs), and an in-house PCR. The target for the PCR amplification was a small region (135 bp) of the SSU rRNA selected to increase the sensitivity of the test. Sixty-eight specimens tested positive by PCR: 2 for E. histolytica and 66 for E. dispar. For detection of E. dispar, ELISA performance was lower than that of microscopy in this reference context, while PCR was much more sensitive than microscopy. Given the low proportion of E. histolytica cases, test performance for this species is difficult to assess. However, for differentiation, PCR performed well on simulated samples, while ELISA gave a discordant result for one of the two samples PCR positive for E. histolytica during the study. This report also confirms that E. dispar infection is significantly higher among travelers and underlines the possibility of acquiring E. histolytica infection in regions that are not areas of endemicity. Because of its lower sensitivity, the interest of ELISA for Entamoeba detection and differentiation in stools seems questionable in nontropical regions. On the other hand, results suggest that PCR should be useful as a reference test for sensitive differentiation of both species and to contribute to physicians' decision in treatment of E. histolytica- or E. dispar-infected patients.