Papaverine-sensitive phosphodiesterase activity is measured in bovine spermatozoa.

Cyclic adenosine monophosphate (cAMP) plays a crucial role as a signaling molecule for capacitation, motility, and acrosome reaction in mammalian spermatozoa. It is well-known that cAMP degradation by phosphodiesterase (PDE) enzyme has a major impact on sperm functions. This study was undertaken to characterize cAMP-PDE activity in bovine spermatozoa. Total cAMP-PDE activity in cauda epididymal and ejaculated spermatozoa was 543.2 ± 49.5 and 1252.6 ± 86.5 fmoles/min/106 spermatozoa, respectively. Using different family-specific PDE inhibitors, we showed that in cauda epididymal and ejaculated spermatozoa, the major cAMP-PDE activity was papaverine-sensitive (44.5% and 57.5%, respectively, at 400 nm, papaverine is a specific inhibitor of the PDE10 family). These data are supporting the functional presence of PDE10 in bovine spermatozoa and were further confirmed by western blot to be PDE10A. Using immunocytochemistry, we showed immunoreactive signal for PDE10A present on the post-acrosomal region of the head and on the flagella of ejaculated spermatozoa. Using papaverine, we showed that it promotes tyrosine phosphorylation of sperm proteins, phosphorylation of Erk1 and Erk2, and Ca2+ release from Ca2+ store. These results suggest that PDE10 is functionally present in bovine spermatozoa and is affecting different molecular events involved in capacitation, most probably by cAMP local regulation.

A simple geometric validation approach to assess the basic behaviour of space- and time- distributed models of epidemic spread - an example using the Ontario rabies model.

Dynamic mathematical modelling and stochastic simulation of disease-host systems for the purpose of epidemiological analysis offer great opportunities for testing hypotheses, especially when field experiments are impractical or when there is a need to evaluate multiple experimental scenarios. This, combined with the ever increasing computer power available to researchers, has contributed to the development of many mathematical models for epidemic simulations, such as the individual-based model (IBM). Nevertheless, few of these models undergo extensive validation and proper assessment of intrinsic variability. The Ontario rabies model (ORM) will be used here to exemplify some advantages of appropriate model behaviour validation and to illustrate the use of a simple geometric procedure for testing directional bias in distributed stochastic dynamic model of spread of diseases. Results were obtained through the comparison of 10 000 epizootics resulting from 100 epidemic simulations started using 100 distinct base populations. The analysis results demonstrated a significant directional bias in epidemic dispersion, which prompted further verification of the model code and the identification of a coding error, which was then corrected. Subsequent testing of the corrected code showed that the directional bias could no longer be detected. These results illustrate the importance of proper validation and the importance of sufficient knowledge of the model behaviour to ensure the results will not confound the objectives of the end-users.

Bioeconomic modelling of raccoon rabies spread management impacts in Quebec, Canada.

Beginning in 2006, point infection control operations and aerial distribution of oral rabies vaccines along the US border were performed in Quebec, Canada, to control the potential spread of raccoon rabies. A benefit-cost analysis assessed the economic efficiency of this rabies control programme into the future. In this study, a mathematical simulation model was used to determine the potential spread of raccoon rabies from the 2006 index case, and incidence rates of human post-exposure prophylaxis (PEP), animal testing and human exposure investigations were calculated. Benefits were calculated as the potential savings from reduced numbers of human PEP, animal testing and human exposure investigations owing to control, which ranged from $47 million to $53 million. Programme cost scenarios were based on projections of total expenditures, which ranged from $33 million to $49 million. Economic efficiency was indicated for approximately half of the modelled scenarios, with the greatest benefit-cost ratios resulting from reduced future programme costs.

Effects of estrogen and progesterone on cerebrovascular responses to euoxic hypercapnia in women.

OBJECTIVES: To determine the cerebral blood flow response to step changes in end-tidal Pco(2) in premenopausal women (n = 10; mean age±standard deviation 27.0±6.4 years) during the follicular (FP), mid-cycle (MC) and luteal (LP) phases of the menstrual cycle. METHODS: Transcranial Doppler ultrasound was used to measure beat-by-beat averaged peak blood flow velocity (V(p)) in the middle cerebral artery in response to 20 min of euoxic hypercapnia (end-tidal PO(2) = 88 Torr; end-tidal PCO(2) = 7.0 Torr above resting values). The V(p) responses to euoxic hypercapnia were fitted to a simple mathematical model that included gain terms for the on (G(on)) and off (G(off)) responses, time constants for the on (τ(on)) and off (τ(off)) responses, baseline terms and a time delay (T(d)). RESULTS: Serum progesterone levels were significantly greater for LP compared to FP and MC (40.6±13.2 vs. 32.6±1.4 nmol/l (p < 0.001) and 8.8±3.8 nmol/l (p < 0.001), respectively). Serum estrogen concentrations were significantly lower in FP compared to MC and LP (150.9±51.2 vs. 506.5±220.5 pmol/l (p = 0.002) and 589.1±222.8 pmol/l (p < 0.001), respectively). Arterial PCO(2) was significantly greater in MC compared to LP (35.0±2.1 and 32.6±1.4 Torr, respectively; p = 0.02). There was a significant increase in G(off) during LP compared with FP and MC (3.38±0.68 vs. 2.79±0.82 cm s(-1) Torr(-1) (p = 0.021) and 2.74±0.90 (p = 0.018) cm s(-1) Torr2(1), respectively). Progesterone and the estrogen/progesterone ratio contributed to the observed differences in G(off). CONCLUSION: There is an increase in G(off) during LP that is explained, at least in part, by increases in serum progesterone and estrogen and a decrease in arterial PCO(2).

Spatio-temporal variations and age effect on Toxoplasma gondii seroprevalence in seals from the Canadian Arctic.

Toxoplasmosis is a significant public health threat for Inuit in the Canadian Arctic. This study aimed to investigate arctic seals as a possible food-borne source of infection. Blood samples collected from 828 seals in 7 Canadian Arctic communities from 1999 to 2006 were tested for Toxoplasma gondii antibodies using a direct agglutination test. Polymerase chain reaction (PCR) was used to detect T. gondii DNA in tissues of a subsample of seals. Associations between seal age, sex, species, diet, community and year of capture, and serological test results were investigated by logistic regression. Overall seroprevalence was 10·4% (86/828). All tissues tested were negative by PCR. In ringed seals, seroprevalence was significantly higher in juveniles than in adults (odds ratio=2·44). Overall, seroprevalence varied amongst communities (P=0·0119) and by capture year (P=0·0001). Our study supports the hypothesis that consumption of raw seal meat is a significant source of infection for Inuit. This work raises many questions about the mechanism of transfer of this terrestrial parasite to the marine environment, the preponderance of infection in younger animals and the natural course of infection in seals. Further studies to address these questions are essential to fully understand the health risks for Inuit communities.

Effects of intermittent hypoxia on erythropoietin, soluble erythropoietin receptor and ventilation in humans.

Erythropoietin (EPO) and soluble EPO receptors (sEPOR) have been proposed to play a central role in the ventilatory acclimatisation to continuous hypoxia in mice. In this study, we demonstrated for the first time in humans (n = 9) that sEPOR is downregulated upon daytime exposure to 4 days of intermittent hypoxia (IH; 6 h·day⁻¹, cycles of 2 min of hypoxia followed by 2 min of reoxygenation; peak end-tidal oxygen tension (P(ET,O2)) 88 Torr, nadir P(ET,O2)) 45 Torr), thereby allowing EPO concentration to rise. We also determined the strength of the association between these haematological adaptations and alterations in the acute hypoxic ventilatory response (AHVR). We observed a nadir in sEPOR on day 2 (-70%), concomitant with the peak in EPO concentration (+50%). Following exposure to IH, tidal volume (V(T)) increased, respiratory frequency remained unchanged, and minute ventilation (V'(E)) was increased. There was a negative correlation between EPO and sEPOR (r = -0.261; p = 0.05), and between sEPOR and V(T) (r = -0.331; p = 0.02). EPO was positively correlated with V'(E) (r = 0.458; p = 0.001). In conclusion, the downregulation of sEPOR by IH modulates the subsequent EPO response. Furthermore, the alterations in AHVR and breathing pattern following IH appear to be mediated, at least in part, by the increase in EPO.

The analysis of crow population dynamics as a surveillance tool.

West Nile virus (WNV) infection, a zoonotic disease for which birds act as a reservoir, first appeared in North America in August 1999. It was first reported in Quebec in 2002. The Quebec surveillance system for WNV has several components, including the surveillance of mortality in corvid populations, which includes the American crow (Corvus brachyrhynchos). The main objectives of this study are to better understand the population dynamics of this species in Quebec and to evaluate the impact of WNV on these dynamics. We obtained observation data for living crows in this province for the period of 1990-2005 and then conducted a spectral analysis of these data. To study changes in crow population dynamics, the analysis was carried out before and after the appearance of WNV and space was divided in two different areas (urban and non-urban). Our results show the importance of cycles with periods of less than 1 year in non-urban areas and cycles with periods of greater than 1 year in urban areas in the normal population dynamics of the species. We obtained expected fluctuations in bird densities using an algorithm derived from spectral decomposition. When we compared these predictions with data observed after 2002, we found marked perturbations in population dynamics beginning in 2003 and lasting up to 2005. In the discussion, we present various hypotheses based on the behaviour of the American crow to explain the normal population dynamics observed in this species and the effect of type of area (urban versus non-urban). We also discuss how the predictive algorithm could be used as a disease surveillance tool and as a measure of the impact of a disease on wild fauna.

Sexual and marital trajectories and HIV infection among ever-married women in rural Malawi.

OBJECTIVE: To explore how sexual and marital trajectories are associated with HIV infection among ever-married women in rural Malawi. METHODS: Retrospective survey data and HIV biomarker data for 926 ever-married women interviewed in the Malawi Diffusion and Ideational Change Project were used. The associations between HIV infection and four key life course transitions considered individually (age at sexual debut, premarital sexual activity, entry into marriage and marital disruption by divorce or death) were examined. These transitions were then sequenced to construct trajectories that represent the variety of patterns in the data. The association between different trajectories and HIV prevalence was examined, controlling for potentially confounding factors such as age and region. RESULTS: Although each life course transition taken in isolation may be associated with HIV infection, their combined effect appeared to be conditional on the sequence in which they occurred. Although early sexual debut, not marrying one's first sexual partner and having a disrupted marriage each increased the likelihood of HIV infection, their risk was not additive. Women who both delayed sexual debut and did not marry their first partner are, once married, more likely to experience marital disruption and to be HIV-positive. Women who marry their first partner but who have sex at a young age, however, are also at considerable risk. CONCLUSIONS: These findings identify the potential of a life course perspective for understanding why some women become infected with HIV and others do not, as well as the differentials in HIV prevalence that originate from the sequence of sexual and marital transitions in one's life. The analysis suggests, however, the need for further data collection to permit a better examination of the mechanisms that account for variations in life course trajectories and thus in lifetime probabilities of HIV infection.

Acceptance of repeat population-based voluntary counselling and testing for HIV in rural Malawi.

OBJECTIVE: To examine the acceptance of repeat population-based voluntary counselling and testing (VCT) for HIV in rural Malawi. METHODS: Behavioural and biomarker data were collected in 2004 and 2006 from approximately 3000 adult respondents. In 2004, oral swab specimens were collected and analysed using ELISA and confirmatory Western blot tests, while finger-prick rapid testing was done in 2006. We used cross-tabulations with chi(2) tests and significance tests of proportions to determine the statistical significance of differences in acceptance of VCT by year, individual characteristics and HIV risk. RESULTS: First, over 90% of respondents in each round accepted the HIV test, despite variations in testing protocols. Second, the percentage of individuals who obtained their test results significantly increased from 67% in 2004, when the results were provided in randomly selected locations several weeks after the specimens were collected, to 98% in 2006 when they were made available immediately within the home. Third, whereas there were significant variations in the sociodemographic and behavioural profiles of those who were successfully contacted for a second HIV test, this was not the case for those who accepted repeat VCT. This suggests that variations in the success of repeat testing might come from contacting the individuals rather than from accepting the test or knowing the results. CONCLUSIONS: Repeat HIV testing at home by trained healthcare workers from outside the local area, and with either saliva or blood, is almost universally acceptable in rural Malawi and, thus, likely to be acceptable in similar contexts.

Projected effects of climate change on tick phenology and fitness of pathogens transmitted by the North American tick Ixodes scapularis.

Ixodes scapularis is the principal tick vector of the Lyme borreliosis agent Borrelia burgdorferi and other tick-borne zoonoses in northeastern North America. The degree of seasonal synchrony of nymphal and larval ticks may be important in influencing the basic reproductive number of the pathogens transmitted by I. scapularis. Because the seasonal phenology of tick vectors is partly controlled by ambient temperature, climate and climate change could shape the population biology of tick-borne pathogens. We used projected monthly normal temperatures, obtained from the second version of the Canadian Coupled Global Climate Model (CGCM2) under emissions scenario A2 of the Intergovernmental Panel on Climate Change for a site in southern Ontario, Canada, to simulate the phenology of I. scapularis in a mathematical model. The simulated seasonal abundance of ticks then determined transmission of three candidate pathogens amongst a population of white-footed mice (Peromyscus leucopus) using a susceptible-infected-recovered (SIR) model. Fitness of the different pathogens, in terms of resilience to changes in tick and rodent mortality, minima for infection duration, transmission efficiency and particularly any additional mortality of rodents specifically associated with infection, varied according to the seasonal pattern of immature tick activity, which was different under the temperature conditions projected for the 2020s, 2050s and 2080s. In each case, pathogens that were long-lived, highly transmissible and had little impact on rodent mortality rates were the fittest. However, under the seasonal tick activity patterns projected for the 2020s and 2050s, the fitness of pathogens that are shorter-lived, less efficiently transmitted, and more pathogenic to their natural hosts, increased. Therefore, climate change may affect the frequency and distribution of I. scapularis-borne pathogens and alter their evolutionary trajectories.

Role of migratory birds in introduction and range expansion of Ixodes scapularis ticks and of Borrelia burgdorferi and Anaplasma phagocytophilum in Canada.

During the spring in 2005 and 2006, 39,095 northward-migrating land birds were captured at 12 bird observatories in eastern Canada to investigate the role of migratory birds in northward range expansion of Lyme borreliosis, human granulocytic anaplasmosis, and their tick vector, Ixodes scapularis. The prevalence of birds carrying I. scapularis ticks (mostly nymphs) was 0.35% (95% confidence interval [CI] = 0.30 to 0.42), but a nested study by experienced observers suggested a more realistic infestation prevalence of 2.2% (95% CI = 1.18 to 3.73). The mean infestation intensity was 1.66 per bird. Overall, 15.4% of I. scapularis nymphs (95% CI = 10.7 to 20.9) were PCR positive for Borrelia burgdorferi, but only 8% (95% CI = 3.8 to 15.1) were positive when excluding nymphs collected at Long Point, Ontario, where B. burgdorferi is endemic. A wide range of ospC and rrs-rrl intergenic spacer alleles of B. burgdorferi were identified in infected ticks, including those associated with disseminated Lyme disease and alleles that are rare in the northeastern United States. Overall, 1.4[corrected]% (95% CI = 0.3 [corrected] to 0.41) of I. scapularis nymphs were PCR positive for Anaplasma phagocytophilum. We estimate that migratory birds disperse 50 million to 175 million I. scapularis ticks across Canada each spring, implicating migratory birds as possibly significant in I. scapularis range expansion in Canada. However, infrequent larvae and the low infection prevalence in ticks carried by the birds raise questions as to how B. burgdorferi and A. phagocytophilum become endemic in any tick populations established by bird-transported ticks.

Cerebral blood flow and ventilatory sensitivity to CO2 measured with the modified rebreathing method.

The ventilatory response to carbon dioxide (CO2) measured by modified rebreathing (SrVE) is closer to that measured by the steady-state method (SsVE) than is the response measured by Read's rebreathing method. Furthermore, the value estimated by the steady-state method depends upon the number of data points used to measure it. We planned to assess if these observations were also true for cerebral blood flow (CBF), as measured by steady-state (SsCBF) and modified rebreathing (SrCBF) tests. Six subjects undertook two protocols, one in the steady-state and one with modified rebreathing. SsVE depended upon the number of data points used to calculate it, and SsVE and SrVE were similar. However, this was not the case with SsCBF, and SsCBF was much higher than SrCBF. These findings are consistent with the notions that the specific CO2 stimulus differs for CBF control as compared with ventilation (VE) control, and that prior hypocapnia has an effect on CBF and VE for longer than the duration of the hypocapnia.

Vector seasonality, host infection dynamics and fitness of pathogens transmitted by the tick Ixodes scapularis.

Fitness of tick-borne pathogens may be determined by the degree to which their infection dynamics in vertebrate hosts permits transmission cycles if infective and uninfected tick stages are active at different times of the year. To investigate this hypothesis we developed a simulation model that integrates the transmission pattern imposed by seasonally asynchronous nymphal and larval Ixodes scapularis ticks in northeastern North America, with a model of infection in white-footed mice (Peromyscus leucopus) reservoir hosts, using the bacteria Borrelia burgdorferi and Anaplasma phagocytophilum as examples. In simulations, survival of microparasites, their sensitivity to reduced rodent and tick abundance, and to 'dilution' by a reservoir-incompetent host depended on traits that allowed (i) highly efficient transmission from acutely-infected hosts, (ii) long-lived acute or 'carrier' host infections, and/or (iii) transmission amongst co-feeding ticks. Minimum values for transmission efficiency to ticks, and duration of host infectivity, necessary for microparasite persistence, were always higher when nymphal and larval ticks were seasonally asynchronous than when these instars were synchronous. Thus, traits influencing duration of host infectivity, transmission efficiency to ticks and co-feeding transmission are likely to be dominant determinants of fitness in I. scapularis-borne microparasites in northeastern North America due to abiotic forcings influencing I. scapularis seasonality.

Network analysis of Danish cattle industry trade patterns as an evaluation of risk potential for disease spread.

Trade patterns of animal movements in a specific industry are complex and difficult to study because there are many stakeholders, premises that are heterogeneously spread over the country, and a highly dynamic flow of animals exists among them. The Danish cattle industry was defined as a network of animal movements and graph theory was used to analyse the movements of cattle within this network. A premise was defined as a farm, an abattoir or a market. These premises constituted the network nodes in the graph and the animal movements between them were the links. In this framework, each premise had a sub-network of other premises to which it was linked by these animal movements. If no movement of animals were registered for a specific farm, then the sub-network for that premise consisted of only that premise. Otherwise, the sub-network linked the premise of interest to all premises from which and to which animals were moved, as long as there was a path linking animal movements to that specific premise. This approach allowed visualization and analyses of four levels of organization that existed in Denmark animal registers: (1) the animal that was moved, (2) the movements of all animals between two premises, (3) the specific premise network, and (4) the overall industry network. When contagious animals are moved from one premise to another, then to a third and so forth, these movements create a path for potential transfer of pathogens. The paths within which pathogens are present identify the transmission risks. A network of animal movements should provide information about pathogen transmission and disease spread. The network of the Danish cattle industry network was a directed scale-free graph (the direction of a movement was known), with an in-degree power of 2 an out-degree power of 1.46, consisted of 29,999 nodes, and 130,265 movements during a 6-month period. The in clustering coefficient was calculated to be 0.52 for the inward direction (movement to), while it was 0.02 for the outward direction (movement from). In Denmark, the cattle movements between premises demonstrated a large degree of heterogeneity. This heterogeneity in movements between farms should be used to evaluate the risk potential of disease transmission for each premise and must be considered when modelling disease spread between premises. The objective of this research was to describe the network of animal movements and not just the animal movements per se.

On-farm eradication of foot-and-mouth disease as an alternative to mass culling.

A control and eradication programme for foot-and-mouth disease (FMD) was initiated on a 1500-sow farm in Asia as an alternative to mass culling. The programme was based on mass vaccination and exposure to FMD virus to ensure the development of effective immunity throughout the population. Pigs are not long-term carriers of FMD virus and it should be eliminated by 21 days after infection. Entry of breeding stock was temporarily halted and the sow herd was partially depopulated in order to create a buffer between the infected and uninfected animals. After exposure to the virus and partial depopulation, the virus was eliminated through unidirectional pig flow and strict all-in/all-out procedures, and by thorough cleaning and disinfection of the buildings. Twelve months after the initial outbreak, the eradication plan was completed and successful. In parallel with the eradication programme, a small-scale isolated weaning project was carried out with the sow population that was moved out of the affected farm; 708 piglets were weaned to a separate facility 300 m away. No clinical signs of FMD were observed and the piglets remained serologically negative.

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.

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.