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Biomedical subjects

D Waltner-Toews

Publications and source records attributed to D Waltner-Toews.

At least 19 recordsLinked to original sources
PubMed2006

Prevalence of zoonotic agents in dogs visiting hospitalized people in Ontario: implications for infection control.

Visitation of hospitalized people by dogs is becoming commonplace, but little is known about the potential health risks of introducing dogs to healthcare settings. This cross-sectional study evaluated the prevalence of zoonotic agents in a group of 102 visitation dogs from a variety of sources across Ontario. Between May and July 2004, owners were interviewed by a standardized questionnaire while dogs underwent a standardized physical examination. One specimen of faeces, hair-coat brushings and one rectal, aural, nasal, oral and pharyngeal swab were collected from each dog and tested for 18 specific pathogens. All dogs were judged to be in good health. Zoonotic agents were isolated from 80 out of 102 (80%) dogs. The primary pathogen was Clostridium difficile, which was isolated from 58 (58%) faecal specimens. Seventy-one percent (41/58) of these isolates were toxigenic. Extended-spectrum beta-lactamase Escherichia coli was isolated from one (1%) dog, extended-spectrum cephalosporinase E. coli was isolated from three (3%) dogs, and organisms of the genus Salmonella were isolated from three (3%) dogs. Pasteurella multocida or Pasteurella canis was isolated from 29 (29%) oral swabs, and Malassezia pachydermatis was isolated from eight (8%) aural swabs. Giardia antigen was present in the faeces of seven (7%) dogs, while Toxocara canis and Ancylostoma caninum were detected in two (2%) dogs and one (1%) dog, respectively. Methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, Campylobacter spp., Microsporum canis, group A streptococci, Pseudomonas aeruginosa and Cryptosporidium spp. were not detected. Further information is needed before the full implications of these findings for infection control can be assessed properly.

Animals↗
PubMed2006

Investigation of ground level and remote-sensed data for habitat classification and prediction of survival of Ixodes scapularis in habitats of southeastern Canada.

In southeastern Canada, most populations of Ixodes scapularis Say, the Lyme disease vector, occur in Carolinian forests. Climate change projections suggest a northward range expansion of I. scapularis this century, but it is unclear whether more northerly habitats are suitable for I. scapularis survival. In this study, we assessed the suitability of woodlands of the Lower Great Lakes/St. Lawrence Plain region for I. scapularis by comparing tick egg survival in four different woodlands. Woodlands where I. scapularis are established, and sand dune where I. scapularis do not survive, served as positive and negative control sites, respectively. At two woodland sites, egg survival was the same as at the positive control site, but at two of the sites survival was significantly less than either the positive control site, or one of the other test sites. Egg survival in all woodland sites was significantly higher than in the sand dune site. Ground level habitat classification discriminated among woodlands in which tick survival differed. The likelihood that I. scapularis populations could persist in the different habitats, as deduced using a population model of I. scapularis, was significantly associated with variations in Landsat 7 ETM+ data (normalized difference vegetation index [NDVI] and Tasselled Cap indices). The NDVI index predicted habitat suitability at Long Point, Ontario, with high sensitivity but moderate specificity. Our study suggests that I. scapularis populations could establish in more northerly woodland types than those in which they currently exist. Suitable habitats may be detected by ground-level habitat classification, and remote-sensed data may assist this process.

Animals↗
PubMed2006

Drinking water consumption patterns of residents in a Canadian community.

A cross-sectional survey using computer-assisted telephone interviewing was performed to assess the drinking water consumption patterns in a Canadian community, and to examine the associations between these patterns and various demographic characteristics. The median amount of water consumed daily was four 250 ml servings (1.01), although responses were highly variable (0 to 8.01). Bottled water consumption was common, and represented the primary source of drinking water for approximately 27% of respondents. Approximately 49% of households used water treatment devices to treat their tap water. The observed associations between some demographic characteristics and drinking water consumption patterns indicated potential differences in risk of exposure to waterborne hazards in the population. Our results lend support to the federal review of the bottled water regulations currently in progress in Canada. Additionally, they may lend support to a provincial/territorial government review of bottled water regulations, and both federal and provincial/territorial level reviews of the water treatment device industry. Further investigation of the use of alternative water sources and the perceptions of drinking water in Canada is also needed to better understand, and subsequently address, concerns among Canadians.

Adolescent↗
PubMed2005

Climate change and the potential for range expansion of the Lyme disease vector Ixodes scapularis in Canada.

We used an Ixodes scapularis population model to investigate potential northward spread of the tick associated with climate change. Annual degree-days >0 degrees C limits for I. scapularis establishment, obtained from tick population model simulations, were mapped using temperatures projected for the 2020s, 2050s and 2080s by two Global Climate Models (the Canadian CGCM2 and the UK HadCM3) for two greenhouse gas emission scenario enforcings 'A2'and 'B2' of the Intergovernmental Panel on Climate Change. Under scenario 'A2' using either climate model, the theoretical range for I. scapularis establishment moved northwards by approximately 200 km by the 2020s and 1000 km by the 2080s. Reductions in emissions (scenario 'B2') had little effect on projected range expansion up to the 2050s, but the range expansion projected to occur between the 2050s and 2080s was less than that under scenario 'A2'. When the tick population model was driven by projected annual temperature cycles (obtained using CGCM2 under scenario 'A2'), tick abundance almost doubled by the 2020s at the current northern limit of I. scapularis, suggesting that the threshold numbers of immigrating ticks needed to establish new populations will fall during the coming decades. The projected degrees of theoretical range expansion and increased tick survival by the 2020s, suggest that actual range expansion of I. scapularis may be detectable within the next two decades. Seasonal tick activity under climate change scenarios was consistent with maintenance of endemic cycles of the Lyme disease agent in newly established tick populations. The geographic range of I. scapularis-borne zoonoses may, therefore, expand significantly northwards as a consequence of climate change this century.

Animals↗
PubMed2005

A dynamic population model to investigate effects of climate on geographic range and seasonality of the tick Ixodes scapularis.

A dynamic population model of Ixodes scapularis, the vector of a number of tick-borne zoonoses in North America, was developed to simulate effects of temperature on tick survival and seasonality. Tick development rates were modelled as temperature-dependent time delays, calculated using mean monthly normal temperature data from specific meteorological stations. Temperature also influenced host-finding success in the model. Using data from stations near endemic populations of I. scapularis, the model reached repeatable, stable, cyclical equilibria with seasonal activity of different instars being very close to that observed in the field. In simulations run using data from meteorological stations in central and eastern Canada, the maximum equilibrium numbers of ticks declined the further north was the station location, and simulated populations died out at more northerly stations. Tick die-out at northern latitudes was due to a steady increase in mortality of all life stages with decreasing temperature rather than a specific threshold event in phenology of one life stage. By linear regression we investigated mean annual numbers of degree-days >0 degrees C (DD>0 degrees C) as a readily mapped index of the temperature conditions at the meteorological stations providing temperature data for the model. Maximum numbers of ticks at equilibrium were strongly associated with the mean DD>0 degrees C (r2>0.96, P<0.001), when the Province of origin of the meteorological station was accounted for (Quebec>Ontario, beta=103, P<0.001). The intercepts of the regression models provided theoretical limits for the establishment of I. scapularis in Canada. Maps of these limits suggested that the range of southeast Canada where temperature conditions are currently suitable for the tick, is much wider than the existing distribution of I. scapularis, implying that there is potential for spread. Future applications of the model in investigating climate change effects on I. scapularis are discussed.

Animals↗
PubMed2004

Investigation of relationships between temperature and developmental rates of tick Ixodes scapularis (Acari: Ixodidae) in the laboratory and field.

Relationships between temperature and preoviposition, preeclosion, and premolt developmental periods for the tick Ixodes scapularis Say were investigated by holding field-collected ticks in the laboratory at temperatures of 0 to 32 degrees C at constant daylength. The duration of these developmental periods decreased significantly with increasing temperature. Host of origin, prior storage at 4 degrees C, and season of collection of the ticks were also significantly associated with variations in the duration of the preoviposition period. For each developmental stage, the effect of temperature on development rate was best described as a power relationship. Laboratory-derived relationships were used to predict dates for molting, oviposition, and eclosion of engorged larvae and nymphs, engorged adult females and egg masses, respectively, placed in the field during 1989-1992. Predicted dates for oviposition by adult females, eclosion of eggs, and molting of engorged larvae were within 2 wk of the observed dates, and field-observed seasonal activity of questing larvae and nymphs also was predicted well by laboratory data. Molting of engorged nymphs and seasonal activity of questing adult ticks were, however, poorly predicted. Our findings suggest that duration of development in the field, of larvae from engorged adult females, and of nymphs from engorged larvae, may be explained largely by temperature effects alone, whereas emergence of adult I. scapularis from engorged nymphs may depend on temperature-independent diapause phenomena. The significance of these findings for understanding current and future distributions of I. scapularis, and of the pathogens it transmits, is discussed.

Animals↗
PubMed2001

An ecosystem approach to health and its applications to tropical and emerging diseases.

Disease and health outcomes occur within a complex socio-ecological context characterized by feedback loops across space and time, self-organization, holarchies, and sudden changes in organization when thresholds are reached. Disease control programs, even if they are successful, may undermine health; conversely, programs in agriculture and economic development designed to improve health may simply alter disease patterns. A research and development strategy to promote sustainable health must therefore incorporate multiple scales, multiple perspectives, and high degrees of uncertainty. The ecosystem approach developed by researchers in the Great Lakes Basin meets these criteria. This has implications for community involvement in research, development policies, and for understanding and controlling tropical and emerging diseases. Even if unsuccessful in achieving specific outcome targets, however, the requirements of this approach for open and democratic communication, negotiation, and ecological awareness make its implementation worthwhile.

Agriculture↗
PubMed2000

Risk factors for acute diarrhoea among inhabitants of Kampala District, Uganda.

OBJECTIVE: To identify modifiable individual and household risk factors for diarrhoea among people of all ages in Kampala district, Uganda. DESIGN: A cross-sectional, analytical study. SETTING: Multi-stage sampling. Four purposively selected parishes, two each from low and high socio-economic residential areas in Kampala district. Two randomly selected zones per parish with 60 households randomly selected from each zone. STUDY GROUP: All members present in each household at time of study. Individual and household information collected by means of personal interview using a questionnaire. MAIN OUTCOME MEASURES: Odds of diarrhoea among individuals or households exposed to a study factor compared with the odds of diarrhoea among those not exposed to the factor. RESULTS: Drinking raw chicken eggs was significantly (P < 0.01) and strongly (odds ratio (OR) = 99) associated with diarrhoea among residents of Kampala district. The odds of diarrhoea in households that 'cooked just enough food per meal' was significantly less (OR = 0.42) than in those that did not. People who used municipal water supplies and those who boiled their drinking water were significantly less likely (OR = 0.27, OR = 0.33, respectively) than those who used other water sources and/or who did not boil drinking water to report an episode of diarrhoea in the 2 weeks preceding the survey. The odds of diarrhoea were 2.6 times greater for individuals who reported a pest problem than for those who did not, while keeping pets was found to be protective (OR = 0.43). The number of income earners was also significantly (P < 0.5) and negatively (OR = 0.59) associated with the occurrence of diarrhoea in a member of the household. CONCLUSIONS: The findings of this study underscore the importance of proper food handling, preparation and eating habits as well as safe water, sanitation practices and socio-economic factors in the epidemiology of diarrhoea in developing countries.

Chi-Square Distribution↗
PubMed1999

From 'ecopathology' to 'agroecosystem health'.

The 'epidemiologic revolution' of the 1960s arose in response to the inability of reductionist methods to provide practical solutions to the complex problems of health and production in livestock systems. In a farm, there are not only interactions between animal factors and herd husbandry factors such as feeding, housing, and microbiological environment, but also with a number of other 'non-animal' factors. For this reason, a 'global' or 'holistic' approach, aimed at explaining animal health status within the overall dynamic of a livestock production system, was developed in France under the title of 'ecopathology'. In ecopathology, the discipline of epidemiology is integrated into a systemic approach, including: the development of a preliminary conceptual model, sampling based on the structure of the livestock production system, the establishment of a field study by a multidisciplinary team, the organization and management of the animal health and production information, data analysis, the distribution of results to all participants and the development of a preventive medicine programme. The farm is also influenced by the social, economic and environmental setting to which it belongs. To account for this, a change of scale is necessary. The three elements of the livestock production system considered in ecopathology (farmer, herd and resources), at the level of the agroecosystem become a human community (farmers, consumers, decision-makers), an animal population, and the complex of human, social and economic conditions within the system. The concept of agroecosystem health is closely linked to the overall principle of improving the sustainability of the system. This and other measures of the health status of an agroecosystem can be assessed with methods developed by epidemiologists and other disciplines within a system's perspective. In this systems view, ecopathology provides a basis for assessing herd health whereas agroecosystem health develops the broader context into which ecopathology contributes.

Animal Diseases↗
PubMed1999

Associations between stomach cancer incidence and drinking water contamination with atrazine and nitrate in Ontario (Canada) agroecosystems, 1987-1991.

BACKGROUND: Nitrate and atrazine are two chemicals that are heavily used in certain sectors of agriculture. They are suspected to be associated with the development of certain types of tumours. METHODS: Existing data were obtained on the incidence of specific types of cancers, contamination of drinking water with atrazine and nitrate, and related agricultural practices for the 40 ecodistricts in the province of Ontario. The data were merged into a georelational database for geographical and statistical analyses. Weighted (by population size) least squares regression analyses were conducted while controlling for confounding socioeconomic and lifestyle factors. Maximum likelihood spatial error models were estimated when least square regression error terms were found to be spatially autocorrelated using the Moran's I statistic. RESULTS: Atrazine contamination levels (range 50-649 ng/l, maximum acceptable concentration [MAC] = 60000 ng/l) were positively associated (P < 0.05) with stomach cancer incidence and negatively associated with colon cancer incidence. Nitrate levels, (range 0-91 mg/l, MAC = 10 mg/l) were negatively associated with stomach cancer incidence. CONCLUSION: The associations found at the ecodistrict level, both positive and negative, if confirmed by other studies, raise serious questions about maximum allowable limits for atrazine, as well as possibilities of complex trade-offs among disease outcomes, and interactions of biophysical and social mechanisms which might explain them. Although the negative associations appear to have no direct biological explanations, such counter-intuitive outcomes may occur in complex systems where social and biological variables interact.

Adult↗
PubMed1999

Influence of companion animals on the physical and psychological health of older people: an analysis of a one-year longitudinal study.

OBJECTIVE: To examine whether companion animals or attachment to a companion animal was associated with changes in physical and psychological health in older people and whether the relationships between physical and psychological health and human social networks were modified by the presence or absence of a companion animal. DESIGN: A 1-year longitudinal study with standardized telephone interview data collected at baseline and repeated at 1-year SETTING: Wellington County, Ontario, Canada PARTICIPANTS: An age- and sex stratified random sample (baseline n = 1054; follow-up n = 995) of noninstitutionalized adults aged 65 and older (mean age = 73, SD +/- 6.3) MEASUREMENTS: Social Network Activity was measured using a family and non-family social support scale, participation in an organized social group, involvement in the affairs of the social group, the practice of confiding in others, feelings of loneliness, and the perceived presence of support in a crisis situation. Chronic conditions were measured as the current number of selected health problems. Pet ownership was assessed by the report of owning a dog or a cat and the Lexington Attachment to Pets Scale score. Physical health was assessed as the ability to perform Activities of Daily Living (ADLs). Psychological health was measured as a summed score comprising the level of satisfaction regarding one's health, family and friend relationships, job, finances, life in general, overall happiness, and perceived mental health. Sociodemographic variables assessed include subject age, sex, marital status, living arrangements, education, household income, and major life events. RESULTS: Pet owners were younger, currently married or living with someone, and more physically active than non-pet owners. The ADL level of respondents who did not currently own pets deteriorated more on average (beta = -.270, P = .040) than that of respondents who currently owned pets after adjusting for other variables during the 1-year period. No statistically significant direct association was observed between pet ownership and change in psychological well-being (P > .100). However, pet ownership significantly modified the relationship between social support and the change in psychological well-being (P = .001) over a 1-year period. CONCLUSIONS: The results demonstrate the benefits of pet ownership in maintaining or slightly enhancing ADL levels of older people. However, a more complex relationship was observed between pet ownership and an older person's well-being.

Aged↗
PubMed1997

Emergent perplexity: in search of post-normal questions for community and agroecosystem health.

Growing awareness of the linkages between socioeconomic, ecological and human community health across various spatial and temporal scales has uncovered contradictions and ambiguities in the concept of health. Furthermore, conventional modes of inquiry are limited in their ability to handle these difficulties and may, indeed, reinforce them. Based on research into agroecosystems, and drawing on recent developments in our understanding of complex systems and what has been called post-normal science, a new type of question for health analysis is proposed. The question "Are the quality and quantity of internal and external resources sufficient, and is their organization appropriate for the system to meet its goals?" is implicitly integrative, context-sensitive, and attuned to emergent complexity. Unraveling the assumptions and implications of this question shifts the debate away from the causes of a particular disease to an exploration of the primary and operative goals inherent in the functioning of the system under investigation. It also becomes the basis for determining the roots of health problems and therefore pointing out what needs to be altered for improved health status. Using examples from research into agroecosystem health, the potential contributions of this new approach to health analysis are explored.

Agriculture↗
PubMed1997

Ecosystem health as a clinical rotation for senior students in Canadian veterinary schools.

We describe 4 years of an experimental rotation in ecosystem health offered to senior veterinary students in Canada. Faculty from the 4 Canadian veterinary colleges collaborated in offering the rotation once annually at 1 of the colleges. The 1st rotation was held in Guelph in 1993, followed in successive years by rotations at Saskatoon, Saint-Hyacinthe, and Charlottetown. The rotation is a predominantly field-based experience that allows students to work with veterinary and other role models who are actively engaged in clinical research related to ecosystem health. Five specific field studies that worked particularly well during the rotations are presented. These studies involved investigating mortality in wildlife due to botulism, designing an environmental surveillance system around herds of beef cattle, using belugas to evaluate the health of the St. Lawrence River, dealing with competition for water use by aquaculture and agriculture, and exploring the role of veterinarians during major coastal oil spills. The experience has resulted in our developing the subject matter, field examples, teaching approach, and confidence necessary to make ecosystem health the focus of a productive clinical rotation for senior year veterinary students.

Agriculture↗
PubMed1995

Cow, farm, and ecologic risk factors of clinical vesicular stomatitis on Costa Rican dairy farms.

Twenty-two Costa Rican dairy herds were actively monitored for vesicular diseases between November 1991 and March 1992, in anticipation of the annual dry season occurrence of vesicular stomatitis (VS). Thirty-nine confirmed cases of VS were concentrated on nine farms, resulting in an average herd incidence rate of 11.1% of mature cattle for the affected farms, or 2.6% for all farms. Affected cattle were generally older (average age = 5.4 years), with seven-year-old cows having the highest age-specific incidence rate (6.5%). The New Jersey serotype of VS was diagnosed for all but four cases, primarily manifesting as teat vesicles. Cases had high acute and convalescent antibody titers for both major VS serotypes, New Jersey and Indiana, with significant titer increases after clinical disease. Screening and multiple variable regression analyses of 140 cow, farm, and ecologic variables revealed that clinical disease was significantly associated with cows being in lactation, and with higher acute antibody titers to serotype Indiana, but not with any predisposing diseases. Significant farm factors were the presence of poultry and a longer calving interval on the farm, but not higher rates of other diseases. According to a prior epidemiologic hypothesis, two ecologic factors were forced to be included into the farm model: the reported presence of sand flies, and a higher proportion of the farm being in forest land, with subsequent stepwise regression. The resulting model containing only the two forced variables was significant (P < 0.003) and correctly classified 78% of farms into the correct group, as compared with 79% for the final stepwise model.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Distribution↗
PubMed1994

Echinococcus granulosus infections in the dogs of Kathmandu, Nepal.

The prevalence, incidence and risk factors of infection by Echinococcus granulosus were studied in the domestic and street dogs of Kathmandu, Nepal. Using an ELISA coproantigen test as a screening method, the highest prevalence (5/88 = 5.7%) was seen in domestic dogs from an area of the city used for slaughtering livestock. A prevalence of 1.8% (3/171) was found in domestic dogs seen at eight veterinary clinics distributed around the city. Although none of the 73 street dogs sampled in the ELISA screening survey was positive, three of 20 street dogs killed with poison as part of the city's dog-control programme harboured from one to five adult worms. As none of 99 dogs treated with an anthelmintic was found re-infected 3 months later, it was impossible to calculate accurately the of infection over a 3-month period. Information about the feeding, sleeping and roaming practices of the dogs was also gathered using questionnaires and direct observations.

Animals↗