Hydrological modelling of Toxoplasma gondii oocysts transport to investigate contaminated snowmelt runoff as a potential source of infection for marine mammals in the Canadian Arctic.

Toxoplasma gondii (T. gondii) is a zoonotic protozoan that sometimes causes serious illness in humans and other animals worldwide, including the Canadian Arctic. Wild and domestic felids, the only hosts able to shed T. gondii oocysts, are practically non-existent in the Canadian Arctic. So here the hypothesis that T. gondii oocysts, shed in the southern areas of the boreal watershed, could contaminate the Arctic coastal marine environment via surface runoff, particularly during the spring snowmelt period, was explored. A watershed model was applied to simulate the hydrological transport of T. gondii oocysts during the snowmelt period and test the possible efficiency of river-to-sea transport as a potential source of marine organisms' exposure to this pathogen. Simulations were run for two pilot watersheds with the ultimate aim of extrapolating the results across the Canadian Arctic watersheds. Results suggest that daily stream flow concentrations of T. gondii oocysts at the river outlet are likely to be very low. However, accumulation of oocysts in the estuarine areas may be large enough to contaminate estuarine/marine filter-feeding molluscs and snails on which seals and other marine mammals may feed. Potential maximum concentrations of T. gondii oocysts in runoff are reached at the beginning of the snowmelt period with maxima varying with discharge rates into rivers and how far upstream oocysts are discharged. Meteorological conditions during the snowmelt period can affect simulated concentrations of oocysts. These findings support the hypothesis that T. gondii oocysts carried in snowmelt runoff could be a source of T. gondii infection for marine mammals in the Canadian Arctic, and for Arctic human populations that hunt and consume raw meat from marine mammals.

Geographical variation of Crohn's disease residual incidence in the Province of Quebec, Canada.

BACKGROUND: Crohn's disease (CD) is clinically expressed as a chronic affection of the gastrointestinal tract currently known to have a multifactorial etiology involving a complex pathophysiological host response modulated by genetic susceptibilities, demographic determinants and environmental factors. With more than 20 cases per 100,000 person-years, the province of Quebec, Canada is among regions of the world with highest reported occurrence of CD in relation to other places where comparable estimates are available. This ecological study was designed to provide a medium-scale spatial exploration of CD incidence after accounting for the influence of known population and regional determinants. Health records of consulting patients in southern Quebec were compiled from 1995 to 2000 and used to estimate age and sex standardized rates per health area (n = 156). Various statistical models taking into account the regional effect of Jewish ethnicity, aboriginal ancestry, material deprivation, prescription for oral contraceptives, reportable enteric infection incidence, smoking as well as latitude and longitude locations were fitted. RESULTS: The final regression model presented a coefficient of determination of 22.8% and there was evidence of an eastern trend in the residual incidence (p = 0.018). Overall, the smoothed residual incidence presented a heterogeneous spatial pattern with evidence of patches (multiple health areas) of high, low and contrasting values. Health areas with most extreme incidence residuals where also distributed over the whole province including one area in the metropolitan area of Montreal and others in surrounding areas. CONCLUSIONS: These findings suggest that known populational and regional factors derived through census information only explain a limited fraction of the geographical variation of CD incidence and lead to speculate that the effects of these factors may be incompletely captured (imperfect construction of proxy variables) or that other important factors remain unmeasured. In this view, markers of genetic profiles of homogeneous sub-populations, and other factors linked to agroenvironmental microbial exposure should be further investigated. Once accounting for known factors, it would also be worth comparing adjacent geographical areas demonstrating abrupt changes in residual incidence rates to further explore effect linked to regional factors from those resulting from various reporting systems.

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.

Relationship of trade patterns of the Danish swine industry animal movements network to potential disease spread.

The movements of animals were analysed under the conceptual framework of graph theory in mathematics. The swine production related premises of Denmark were considered to constitute the nodes of a network and the links were the animal movements. In this framework, each farm will have a network of other premises to which it will be linked. A premise was a farm (breeding, rearing or slaughter pig), an abattoir or a trade market. The overall network was divided in premise specific subnets that linked the other premises from and to which animals were moved. This approach allowed us to visualise and analyse the three levels of organization related to animal movements that existed in the Danish swine production registers: the movement of animals between two premises, the premise specific networks, and the industry network. The analyses of animal movements were done using these three levels of organisation. The movements of swine were studied for the period September 30, 2002 to May 22, 2003. For daily movements of swine between two slaughter pig premises, the median number of pigs moved was 130 pigs with a maximum of 3306. For movements between a slaughter pig premise and an abattoir, the median number of pigs was 24. The largest percentage of movements was from farm to abattoir (82.5%); the median number of pigs per movement was 24 and the maximum number was 2018. For the whole period the median and maximum Euclidean distances observed in farm-to-farm movements were 22 km and 289 km respectively, while in the farm-to-abattoir movements, they were 36.2 km and 285 km. The network related to one specific premise showed that the median number of premises was mainly away from slaughter pig farms (3) or breeder farms (26) and mainly to an abattoir (1535). The assumption that animal movements can be randomly generated on the basis of farm density of the surrounding area of any farm is not correct since the patterns of animal movements have the topology of a scale-free network with a large degree of heterogeneity. This supported the opinion that the disease spread software assuming homogeneity in farm-to-farm relationship should only be used for large-scale interpretation and for epidemic preparedness. The network approach, based on graph theory, can be used efficiently to express more precisely, on a local scale (premise), the heterogeneity of animal movements. This approach, by providing network knowledge to the local veterinarian in charge of controlling disease spread, should also be evaluated as a potential tool to manage epidemics during the crisis. Geographic information systems could also be linked in the approach to produce knowledge about local transmission of disease.

Development of agroenvironmental indicators to evaluate the hygienic pressure of livestock production on human health.

Infections by enteropathogenic microorganisms linked to agroenvironmental contamination represent a significant threat to urban and rural communities. To better characterize and manage this risk, it is necessary, not only to accurately describe enteric illnesses occurring over time or across regions, but also to correctly assess exposure attributable to this environmental pollution. New agroenvironmental hygienic pressure indicators (AHPIs) were developed to synthesise relevant data expressing this exposure. They were derived from a conceptual framework for developing sustainable agriculture indicators and specifically adapted for describing the microbial risk of water contamination by livestock operations. The proposed indicators include two components, and five attributes whose values are calculated at the livestock operation level from a set of available data related to the fields of microbiology, animal production, agronomy, hydrology, and meteorology. They are then aggregated at a higher geographical level to better express exposure of human populations to potential of water contamination by zoonotic enteropathogens. The indicators are calculated separately by zoonotic enteropathogens, and by water source (surface or groundwater). They take into account the various animal species within each livestock operation. When validated, the proposed indicators will allow decision-makers and public health officials to better manage crucial issues in the area of water safety and agriculture.

Conceptual evaluation of population health surveillance programs: method and example.

Veterinary and public health surveillance programs can be evaluated to assess and improve the planning, implementation and effectiveness of these programs. Guidelines, protocols and methods have been developed for such evaluation. In general, they focus on a limited set of attributes (e.g., sensitivity and simplicity), that are assessed quantitatively whenever possible, otherwise qualitatively. Despite efforts at standardization, replication by different evaluators is difficult, making evaluation outcomes open to interpretation. This ultimately limits the usefulness of surveillance evaluations. At the same time, the growing demand to prove freedom from disease or pathogen, and the Sanitary and Phytosanitary Agreement and the International Health Regulations require stronger surveillance programs. We developed a method for evaluating veterinary and public health surveillance programs that is detailed, structured, transparent and based on surveillance concepts that are part of all types of surveillance programs. The proposed conceptual evaluation method comprises four steps: (1) text analysis, (2) extraction of the surveillance conceptual model, (3) comparison of the extracted surveillance conceptual model to a theoretical standard, and (4) validation interview with a surveillance program designer. This conceptual evaluation method was applied in 2005 to C-EnterNet, a new Canadian zoonotic disease surveillance program that encompasses laboratory based surveillance of enteric diseases in humans and active surveillance of the pathogens in food, water, and livestock. The theoretical standard used for evaluating C-EnterNet was a relevant existing structure called the "Population Health Surveillance Theory". Five out of 152 surveillance concepts were absent in the design of C-EnterNet. However, all of the surveillance concept relationships found in C-EnterNet were valid. The proposed method can be used to improve the design and documentation of surveillance programs. It complements existing surveillance evaluation methods. Conceptual evaluation is not a performance-oriented evaluation method and so it is particularly useful for surveillance programs with a valid conceptual framework but limited technical capacity and resources. Such programs would be penalized using existing performance-based evaluation methods. Applying conjointly the conceptual evaluation along with existing performance-oriented evaluation methods will better judge the worth of surveillance programs. We recommend developing a comprehensive surveillance evaluation framework for veterinary and public health surveillance programs that integrates all existing surveillance evaluation tools and provides an appropriate way to evaluate various types of surveillance programs.

Spatiotemporal dynamics of Toxoplasma gondii infection in Canadian lynx (Lynx canadensis) in western Québec, Canada.

Toxoplasma gondii, one of the more common zoonotic parasites in the world, can cause serious illness in humans and other animals worldwide. Felids are the only known host that can shed T. gondii oocysts, which are essential to the perpetuation of the parasite. In much of boreal Canada, the Canadian lynx (Lynx canadensis) is the only wild felid host that could contribute to environmental contamination with T. gondii oocysts. We estimated the prevalence of T. gondii antibodies in Canadian lynx from western Québec and compared our results with earlier findings in the same region 12 yr earlier. We investigated factors associated with seroconversion, including age, sex, geographic location, and possible co-occurrence with domestic cats (Felis catus), and we assessed the proportion of lynx shedding T. gondii oocysts. Blood and fecal samples were collected from 84 lynx harvested by trappers in the eastern part of the study area during winter 2009-2010. Sera were tested for antibodies to T. gondii by the modified agglutination test (cutoff titer 1:50) and fecal samples for parasite eggs by fecal flotation. Antibodies to T. gondii were detected in sera of 14% of 84 lynx. Numerous helminth ova and coccidian oocysts were found in feces, whereas T. gondii-like oocysts were not detected. Antibody prevalence increased with age class (odds ratio [OR]=4.33, 95% confidence interval [CI]=1.57-11.99, P<0.01). Antibody prevalence (14%) in our study was significantly lower than in 84 lynx (36%) trapped in the western part of the study area during winter 1997-1998 (OR=0.18, 95% CI=0.08-0.44, P<0.001). Our results suggest there may be significant spatiotemporal dynamics of T. gondii infection in lynx in Canada, and we review possible abiotic and biotic ecologic factors supporting these findings.

A population health surveillance theory.

OBJECTIVES: Despite its extensive use, the term "Surveillance" often takes on various meanings in the scientific literature pertinent to public health and animal health. A critical appraisal of this literature also reveals ambiguities relating to the scope and necessary structural components underpinning the surveillance process. The authors hypothesized that these inconsistencies translate to real or perceived deficiencies in the conceptual framework of population health surveillance. This paper presents a population health surveillance theory framed upon an explicit conceptual system relative to health surveillance performed in human and animal populations. METHODS: The population health surveillance theory reflects the authors' system of thinking and was based on a creative process. RESULTS: POPULATION HEALTH SURVEILLANCE INCLUDES TWO BROAD COMPONENTS: one relating to the human organization (which includes expertise and the administrative program), and one relating to the system per se (which includes elements of design and method) and which can be viewed as a process. The population health surveillance process is made of five sequential interrelated steps: 1) a trigger or need, 2) problem formulation, 3) surveillance planning, 4) surveillance implementation, and 5) information communication and audit. CONCLUSIONS: The population health surveillance theory provides a systematic way of understanding, organizing and evaluating the population health surveillance process.

Risk factors associated with West Nile virus mortality in American Crow populations in Southern Quebec.

Soon after the appearance of West Nile virus (WNV) in North America, a number of public health authorities designated the American Crow (Corvus brachyrhynchos) a sentinel for WNV detection. Although preliminary studies have suggested a positive association between American Crow mortality and increased risk of WNV infection in humans, we still know little about dynamic variation in American Crow mortality, both baseline levels and mortality associated with WNV. We hypothesized that the complex social behavior of American Crows, which is shaped by age and seasonal factors, influences both baseline mortality and WNV mortality in American Crow populations. We examined American Crow mortality data from Quebec for the 2005 WNV surveillance year, which lasted from 5 June to 17 September 2005. The variables of interest were age, gender, body condition index, time of year, and land cover. We used a log-linear model to examine baseline mortality. Logistic regression and general linear regression models were constructed to examine variables associated with mortality due to WNV. We found that both age and time of year were key variables in explaining baseline mortality. These two variables were also risk factors for WNV mortality. The probability that a carcass tested positive for WNV increased with the age of the dead bird and as summer progressed. WNV-positive carcasses also had a lower body condition index than WNV-negative carcasses. We believe that the first major wave of American Crow mortality observed in the early summer of 2005 was the result of natural mortality among young American Crows. Because this mortality was not linked to WNV, it appears that American Crow may not be a good species for early detection of WNV activity. Our data also suggest that second-year American Crows play a major role in propagating WNV during their movements to urban land covers during midsummer.