Spatio-temporal changes in chronic wasting disease risk in wild deer during 14 years of surveillance in Alberta, Canada

Disease risk modeling is a key first step to understand the spatio-temporal dynamics of wildlife disease and to direct cost-effective surveillance and management. In Alberta, active surveillance for chronic wasting disease (CWD) in wild cervids began in 1998 with the first case detected in free-ranging cervids in 2005. Following the detection, a herd reduction program was implemented during 2005-2008 and in 2006 the ongoing hunter-based CWD Surveillance Program became mandatory in high-risk Wildlife Management Units (WMU). We used data collected during the CWD surveillance program to 1) document growth in sex-specific CWD prevalence (proportion of deer in sample that is CWD-positive) in hunter-harvest deer in 6 WMUs consistently monitored from 2006 to 2018, 2) document landscape features associated with where CWD-positive compared to CWD-negative deer were removed during hunter harvest and herd reduction in an early (2005-2012) and in a late period (2013-2017), and 3) to map the spatial risk of harvesting a deer infected with CWD in the prairie parklands of Alberta. In the 6 continuously monitored WMUs, risk of a harvested deer being CWD positive increased from 2006 to 2018 with CWD prevalence remaining highest in male mule deer whereas overall growth rate in CWD prevalence was greater in female mule deer, but similar to male white-tailed deer. We found no evidence that the 3-year herd reduction program conducted immediately after CWD was first detected affected the rate at which CWD grew over the course of the invasion. Risk of deer being CWD-positive was the highest in animals taken near small stream drainages and on soils with low organic carbon content in the early period, whereas risk became highest in areas of agriculture especially when far from large river drainages where deer often concentrate in isolated woody patches. The change in the influence of proximity to known CWD-positive cases suggested the disease was initially patchy but became more spatially homogeneous over time. Our results indicate that a targeted-removal program will remove more CWD positive animals compared to hunter harvest. However, the discontinuation of targeted removals during our research program, restricted our ability to assess its long term impact on CWD prevalence.

Hierarchical, Memory-Based Movement Models for Translocated Elk (Cervus canadensis)

The use of spatial memory is well-documented in many animal species and has been shown to be critical for the emergence of spatial learning. Adaptive behaviors based on learning can emerge thanks to an interdependence between the acquisition of information over time and movement decisions. The study of how spatio-ecological knowledge is constructed throughout the life of an individual has not been carried out in a quantitative and comprehensive way, hindered by the lack of knowledge of the information an animal already has of its environment at the time monitoring begins. Identifying how animals use memory to make beneficial decisions is fundamental to developing a general theory of animal movement and space use. Here we propose several mobility models based on memory and perform hierarchical Bayesian inference on 11-month trajectories of 21 elk after they were released in a completely new environment. Almost all the observed animals exhibited preferential returns to previously visited patches, such that memory and random exploration phases occurred. Memory decay was mild or negligible over the study period. The fact that individual elk rapidly become used to a relatively small number of patches was consistent with the hypothesis that they seek places with predictable resources and reduced mortality risks such as predation.

Functional response of wolves to human development across boreal North America

AIM

The influence of humans on large carnivores, including wolves, is a worldwide conservation concern. In addition, human-caused changes in carnivore density and distribution might have impacts on prey and, indirectly, on vegetation. We therefore tested wolf responses to infrastructure related to natural resource development (i.e., human footprint).

LOCATION

Our study provides one of the most extensive assessments of how predators like wolves select habitat in response to various degrees of footprint across boreal ecosystems encompassing over a million square kilometers of Canada.

METHODS

We deployed GPS-collars on 172 wolves, monitored movements and used a generalized functional response (GFR) model of resource selection. A functional response in habitat selection occurs when selection varies as a function of the availability of that habitat. GFRs can clarify how human-induced habitat changes are influencing wildlife across large, diverse landscapes.

RESULTS

Wolves displayed a functional response to footprint. Wolves were more likely to select forest harvest cutblocks in regions with higher cutblock density (i.e., a positive functional response to high-quality habitats for ungulate prey) and to select for higher road density in regions where road density was high (i.e., a positive functional response to human-created travel routes). Wolves were more likely to use cutblocks in habitats with low road densities, and more likely to use roads in habitats with low cutblock densities, except in winter when wolves were more likely to use roads regardless of cutblock density.

MAIN CONCLUSIONS

These interactions suggest that wolves trade-off among human-impacted habitats, and adaptively switch from using roads to facilitate movement (while also risking encounters with humans), to using cutblocks that may have higher ungulate densities. We recommend that conservation managers consider the contextual and interacting effects of footprints when assessing impacts on carnivores. These effects likely have indirect impacts on ecosystems too, including on prey species.

Moving in the Anthropocene: Global reductions in terrestrial mammalian movements

Animal movement is fundamental for ecosystem functioning and species survival, yet the effects of the anthropogenic footprint on animal movements have not been estimated across species. Using a unique GPS-tracking database of 803 individuals across 57 species, we found that movements of mammals in areas with a comparatively high human footprint were on average one-half to one-third the extent of their movements in areas with a low human footprint. We attribute this reduction to behavioral changes of individual animals and to the exclusion of species with long-range movements from areas with higher human impact. Global loss of vagility alters a key ecological trait of animals that affects not only population persistence but also ecosystem processes such as predator-prey interactions, nutrient cycling, and disease transmission.

Chronic Wasting Disease: Transmission Mechanisms and the Possibility of Harvest Management

We develop a model of CWD management by nonselective deer harvest, currently the most feasible approach available for managing CWD in wild populations. We use the model to explore the effects of 6 common harvest strategies on disease prevalence and to identify potential optimal harvest policies for reducing disease prevalence without population collapse. The model includes 4 deer categories (juveniles, adult females, younger adult males, older adult males) that may be harvested at different rates, a food-based carrying capacity, which influences juvenile survival but not adult reproduction or survival, and seasonal force of infection terms for each deer category under differing frequency-dependent transmission dynamics resulting from environmental and direct contact mechanisms. Numerical experiments show that the interval of transmission coefficients β where the disease can be controlled is generally narrow and efficiency of a harvest policy to reduce disease prevalence depends crucially on the details of the disease transmission mechanism, in particular on the intensity of disease transmission to juveniles and the potential differences in the behavior of older and younger males that influence contact rates. Optimal harvest policy to minimize disease prevalence for each of the assumed transmission mechanisms is shown to depend on harvest intensity. Across mechanisms, a harvest that focuses on antlered deer, without distinguishing between age classes reduces disease prevalence most consistently, whereas distinguishing between young and older antlered deer produces higher uncertainty in the harvest effects on disease prevalence. Our results show that, despite uncertainties, a modelling approach can determine classes of harvest strategy that are most likely to be effective in combatting CWD.

Empirical Estimation of R0 for Unknown Transmission Functions: The Case of Chronic Wasting Disease in Alberta

We consider the problem of estimating the basic reproduction number R₀ from data on prevalence dynamics at the beginning of a disease outbreak. We derive discrete and continuous time models, some coefficients of which are to be fitted from data. We show that prevalence of the disease is sufficient to determine R₀. We apply this method to chronic wasting disease spread in Alberta determining a range of possible R₀ and their sensitivity to the probability of deer annual survival.

Wildlife disease elimination and density dependence

Disease control by managers is a crucial response to emerging wildlife epidemics, yet the means of control may be limited by the method of disease transmission. In particular, it is widely held that population reduction, while effective for controlling diseases that are subject to density-dependent (DD) transmission, is ineffective for controlling diseases that are subject to frequency-dependent (FD) transmission. We investigate control for horizontally transmitted diseases with FD transmission where the control is via culling or harvest that is non-selective with respect to infection and the population can compensate through DD recruitment or survival. Using a mathematical model, we show that culling or harvesting can eradicate the disease, even when transmission dynamics are FD. Eradication can be achieved under FD transmission when DD birth or recruitment induces compensatory growth of new, healthy individuals, which has the net effect of reducing disease prevalence by dilution. We also show that if harvest is used simultaneously with vaccination, and there is high enough transmission coefficient, application of both controls may be less efficient than vaccination alone. We illustrate the effects of these control approaches on disease prevalence for chronic wasting disease in deer where the disease is transmitted directly among deer and through the environment.

Building a mechanistic understanding of predation with GPS-based movement data

Quantifying kill rates and sources of variation in kill rates remains an important challenge in linking predators to their prey. We address current approaches to using global positioning system (GPS)-based movement data for quantifying key predation components of large carnivores. We review approaches to identify kill sites from GPS movement data as a means to estimate kill rates and address advantages of using GPS-based data over past approaches. Despite considerable progress, modelling the probability that a cluster of GPS points is a kill site is no substitute for field visits, but can guide our field efforts. Once kill sites are identified, time spent at a kill site (handling time) and time between kills (killing time) can be determined. We show how statistical models can be used to investigate the influence of factors such as animal characteristics (e.g. age, sex, group size) and landscape features on either handling time or killing efficiency. If we know the prey densities along paths to a kill, we can quantify the 'attack success' parameter in functional response models directly. Problems remain in incorporating the behavioural complexity derived from GPS movement paths into functional response models, particularly in multi-prey systems, but we believe that exploring the details of GPS movement data has put us on the right path.

Preventing tobacco use in young people: strategies for the nurse practitioner

The use of tobacco is considered to be one of the most serious public health issues in America today. Each day thousands of young people start smoking or begin to use smokeless tobacco, both of which are known to increase the rate of illness, particularly heart disease and cancer. This article provides important and useful information in educating in health promotion strategies for the nurse practitioner working with families and communities to reduce tobacco use by young people.

Low density lipoprotein cholesterol and whole blood viscosity

Whole blood viscosity (WBV) was measured in a normal population and was analyzed in relation to packed cell volume, (hematocrit, PCV), fibrinogen, white blood cell count (WBC), platelet count, and plasma lipids, including total cholesterol, triglycerides, high density lipoprotein cholesterol (HDLc) and low density lipoprotein cholesterol (LDLc). Conventional assays were used for all blood and lipid measurements. Whole blood viscosity was measured under disaggregating conditions with a disposable, porous bed viscometer. As expected, the strongest correlation was seen between WBV and PCV (r = 0.78, p < 0.001). Significant positive correlations also were demonstrated between WBV and cholesterol (r = 0.22, p < 0.001), triglycerides (r = 0.14, p < 0.001) and LDLc (r = 0.21, p < 0.001). A significant negative correlation was found between HDLc and WBV (r = -0.20, p < 0.001). Correlation analysis by sex showed only the correlation of LDLc was significant for both men and women. A stepwise multiple regression analysis of WBV indicated that LDLc, fibrinogen (Fbg) and platelet (Plt) counts correlated independently of PCV to WBV. The equation derived from multiple regression and partial correlation analysis was: WBV (mPa.sec) = -9.317 + 0.0047 (LDLc) + 0.381 (PCV) + 0.00152 (Plt) + 0.0021 (Fbg). The calculated mean specific contribution of PCV was 90.8 percent, LDLc 3.5 percent, and fibrinogen 3.3 percent to observed mean WBV. This study shows that LDLc is the principal lipoprotein independently influencing whole blood viscosity and its effect is similar in magnitude to fibrinogen. Further studies to elucidate the mechanism and clinical significance of the effects of LDLc on WBV are indicated.

The estimation of whole blood viscosity by a porous bed method

A significant impediment in determining the relative contribution of whole blood viscosity to the pathogenesis of cardiovascular and cerebrovascular disease has been the lack of an uncomplicated method to measure whole blood viscosity. To address this problem, a simplified porous bed viscometer has been developed to measure whole blood viscosity. Whole blood is passed through a porous bed of branching channels with a mean pore diameter of 69.6 +/- 20.2 microns and an estimated mean shear rate of 19.6 seconds-1. The effects of sample collection, sample storage, and temperature are described. The mean whole blood viscosity of 242 healthy persons was 22.7 +/- 5.3 seconds, which, when corrected to centipoise using Darcy's equation, corresponds to an apparent viscosity of 5.7 +/- 1.3 cp. There was a significant difference in the whole blood viscosity of normal men and women related to their different packed cell volumes. Platelets and granulocytes influenced whole blood viscosity in proportion to their contribution to the total packed cell volume. Fibrinogen levels did not significantly influence measured whole blood viscosity, which is consistent with the disaggregating conditions and the mean shear rate of the instrument. The porous bed viscometer is a convenient means to measure whole blood viscosity and it should be useful as a screening test for clinical and epidemiologic studies.

An analysis of the importance of the "labile" fraction of glycosylated hemoglobin as determined by a minicolumn method

The authors have studied the contribution of the labile fraction of glycosylated hemoglobin to the total glycosylated hemoglobin (GH) in hospitalized, poorly controlled diabetic patients, and in a large group of outpatient diabetics using a conventional minicolumn method. A 5-hour saline incubation of erythrocytes or extensive dialysis of hemoglobin against a glucose-free buffer were used to remove the labile glycohemoglobin fraction. Equivalent results were obtained with either method. The change in GH after dialysis in a group of poorly controlled diabetics averaged 1.1%, but only 0.2% in a group of outpatients whose glycohemoglobin levels were being determined on a routine basis. In both groups, the size of the dialyzable fraction increased in proportion to the total GH level, and outpatients with a dialyzable fraction greater than or equal to 2.0% always had GH levels greater than or equal to 12.0%. In most cases where the total glycohemoglobin was less than 12%, the size of the dialyzable fraction approached the limits of the analytical variability of the minicolumn method (SD = approximately 0.3). The authors conclude that while saline incubation of erythrocytes is a practical procedure for removal of labile glycohemoglobin in a routine clinical laboratory, the use of this procedure is probably only necessary for patients with a high level of total glycosylated hemoglobin.

Heparin-Coated Surfaces that bind Antithrombin have Reduced Platelet Reactivity

Surfaces with heparin bound by covalent linkage react with platelets but are passivated by prior exposure to platelet free plasma (PFP), provided they are capable of adsorbing antithrombin III (AT). For example, heparin-agarose beads induce platelet adhesion and aggregation, which are reduced by preincubation of the beads with PFP, but PFP depleted of AT is not effective. The degree of passivation of the beads parallels their removal of AT from PFP. The beads are also passivated by a solution of purified AT.

Furthermore heparin-polymethyl acrylate copolymers made by radical polymerization initiated by Ce4+ bind AT, as demonstrated by measurement of AT remaining in solution after adsorption or eluted from the surface after plasma incubation. On such a surface, AT is activated just as by heparin in solution, measured by the ability of heparinized beads to inactivate thrombin (S-2160 chromogenic tripeptide substrate assay) in the presence of AT and by lack of inactivation of thrombin with AT-poor plasma and return of inactivating effect when AT is added back.

Aggregation of platelets by specific heparin fractions in solution appears to be an analogous phenomenon, which is inhibited by antithrombin.

In vitro assessment of interaction of blood with model surfaces

An in vitro system for the assessment of blood compatibility of artificial surfaces is described. Anticoagulated human whole blood was pumped through columns of beads and then analyzed for evidence of platelet retention and the release of platelet constitutents. Platelets were retained on the columns by adhesion to the beads and by aggregation. Experiments were conducted with PVAc, PC, PMA and PS beads to provide data on the reproducibility of the system and the effects of anticoagulants and RBC concentration on platelet adhesion and release. The system is versatile, inexpensive, reproducibile, and also suitable for studies of the effects of pharmacologic agents and other aspects of platelet-artificial surface interaction.

Interaction of human platelets with heparinized agarose gel

Platelet interaction with surfaces to which heparin had been covalently bonded was investigated with a chromatographic technique employing agarose gel beads heparinized via a cyanogen bromide reaction. Heparinization significantly increased platelet retention by the gel. Platelet retention was unchanged after pretreatment of the heparinized gel with albumin but increased after pretreatment with fibrinogen. Pretreatment with plasma or purified AT III decreased platelet retention. Reduction in platelet retention was correlated with the amount of AT III removed from plasma. Plasma with decreased levels of AT III was less effective in surface passivation. Pretreatment of heparinized gel with PF4 or protamine sulfate did not decrease platelet retention, but subsequent exposure to plasma did. The results suggest that a surface with covalently bonded heparin is reactive toward platelets but can be passivated by formation of a heparin/AT III complex.