The failure of success: cyclic recurrences of a globally invasive pest.

In the six decades since 1960, the oriental fruit fly, Bactrocera dorsalis (Hendel), has been announced successfully eradicated in California by the U.S. Department of Agriculture a total of 564 times. This includes eradication declarations in one city a total of 25 different years, in 12 cities 8-19 different years, and in 101 cities 2-7 different years. We here show that the false negatives in declaring elimination success hinge on the easily achieved regulatory criteria, which have virtually guaranteed the failure of complete extirpation of this pest. Analyses of the time series of fly detection over California placed on a grid of 100-km2 cells revealed (1) partial success of the eradication program in controlling the invasion of the oriental fruit fly; (2) low prevalence of the initial detection in these cells is often followed by high prevalence of recurrences; (3) progressively shorter intervals between years of consecutive detections; and (4) high likelihood of early-infested cells also experiencing the most frequent outbreaks. Facing the risk of recurrent invasions, such short-term eradication programs have only succeeded annually according to the current regulatory criteria but have failed to achieve the larger goal of complete extirpation of the oriental fruit fly. Based on the components and running costs of the current programs, we further estimated the efficiency of eradication programs with different combinations of eradication radius, duration, and edge impermeability in reducing invasion recurrences and slowing the spread of the oriental fruit fly. We end with policy implications including the need for agricultural agencies worldwide to revisit eradication protocols in which monitoring and treatments are terminated when the regulatory criteria for declaring eradication are met. Our results also have direct implications to invasion biologists and agriculture policy makers regarding long-term risks of short-term expediency.

Investigation of a mortality cluster in wild adult yellow-eyed penguins (Megadyptes antipodes) at Otago Peninsula, New Zealand.

We investigated an epidemic mortality cluster of yellow-eyed penguins (Megadyptes antipodes) that involved 67 moribund or dead birds found on various beaches of the Otago Peninsula, New Zealand, between 21 January and 20 March 2013. Twenty-four carcases were examined post-mortem. Histological lesions of pulmonary, hepatic and splenic erythrophagocytosis and haemosiderosis were found in 23 of 24 birds. Fifteen birds also had haemoglobin-like protein droplets within renal tubular epithelial cells. Despite consistent histological lesions, a cause of death could not be established. Virology, bacteriology and molecular tests for avian influenza, avian paramyxovirus-1, avipoxvirus, Chlamydia psittaci, Plasmodium spp., Babesia spp., Leucocytozoon spp. and Toxoplasma gondii were negative. Tissue concentrations of a range of heavy metals (n = 4 birds) were consistent with low level exposure, while examination of proventricular contents and mucus failed to detect any marine biotoxins or Clostridium botulinum toxin. Hepatic concentrations of total polycyclic aromatic hydrocarbons (PAHs) (n = 5 birds) were similar to background concentrations of polycyclic aromatic hydrocarbons previously found in yellow-eyed penguins from the South Island of New Zealand, but there were significantly higher concentrations of 1-methylnapthelene and 2-methylnapthelene in the birds found dead in this mortality cluster. The biological significance of this finding is unclear. A temporal investigation of the epidemic did not indicate either a common source or propagative epidemic pattern. Although our investigation did not definitively implicate a toxic or infectious agent, we could not rule out causes such as toxic marine organisms or mycoplasmosis. Further investigations should therefore by carried out in the event of future mortality clusters.

Comparison of enzootic risk measures for predicting West Nile disease, Los Angeles, California, USA, 2004-2010.

In Los Angeles, California, USA, 2 epidemics of West Nile virus (WNV) disease have occurred since WNV was recognized in 2003. To assess which measure of risk was most predictive of human cases, we compared 3 measures: the California Mosquito-Borne Virus Surveillance and Response Plan Assessment, the vector index, and the Dynamic Continuous-Area Space-Time system. A case-crossover study was performed by using symptom onset dates from 384 persons with WNV infection to determine their relative environmental exposure to high-risk conditions as measured by each method. Receiver-operating characteristic plots determined thresholds for each model, and the area under the curve was used to compare methods. We found that the best risk assessment model for human WNV cases included surveillance data from avian, mosquito, and climate sources.

Assessing alternative low pathogenic avian influenza virus surveillance strategies in a live bird market.

Surveillance, comprised of sampling and testing, of low pathogenic avian influenza virus (LPAIV) in a live bird market (LBM) may enable the detection of the virus, reducing its spread within the market to humans and birds and to other markets within the LBM system. In addition, detection of infected birds would also reduce the probability of reassortment and possible change from a LPAIV to a highly pathogenic avian influenza virus, which would have a devastating impact on the economy, trade, and society. In this paper we present results from a computer simulation model based on previously collected survey and experimental transmission data. Once we validated the model with experimental transmission data, we applied it to address some of the questions that need to be answered in order to create an efficient surveillance system in an LBM. We have identified effective sampling times, patterns, and sizes that would enhance the probability of an early detection of LPAIV if present and minimize the associated labor and cost. The model may be modified to evaluate different sized and structured LBMs. It also provides the basis to evaluate an entire LBM system for the United States or other countries.

Alternative scan-based approaches to identify space-time clusters of highly pathogenic avian influenza virus H5N1 in wild birds in Denmark and Sweden in 2006.

The objective of this study was to demonstrate the effects of the nature of the information collected through passive surveillance on the detection of space-time clusters of highly pathogenic avian influenza virus (HPAIV) H5N1 cases reported among dead wild birds in Denmark and Sweden in 2006. Data included 1469 records (109 cases, 1360 controls) collected during the regional epidemic between February and June by passive surveillance of dead wild birds. Laboratory diagnoses were obtained by PCR methods and/or virus isolation. The nature of available information influences both the type of model suitable for analysis and its parameterization. Here, we explored four alternative scan-based methods, suitable for detection of clusters only when case data (univariate permutation model), case and hypothesized epidemiological variables (multivariate permutation model), case and control data (univariate Bernoulli model), and case, control, and hypothesized epidemiological variables (multivariate Bernoulli model) are available. Tufted ducks were particularly common among infected wild bird species detected in Denmark and Sweden during the initial phases of this epidemic, and species group (tufted ducks [62 cases, 57 controls] vs. other wild bird species [47 cases, 1303 controls]) was considered in the multivariate models as a covariate potentially associated with clustering. Bernoulli and permutation scan analyses both detected multiple significant (P < 0.01) clusters with similar locations, but with certain differences in their numbers and sizes. The observed-to-expected case ratios in the two clusters detected by the multivariate Bernoulli scan model were substantially heterogeneous. However, the permutation model detected only one of the Swedish clusters and only pinpointed the heterogeneity between species on clustering in the same Danish cluster as detected by the Bernoulli model. The output of the methods described here were shown to be highly sensitive to the choice of the probability model for cases and the choice of plausible assumptions to parameterize the scan statistic tests. The results of the multivariate Bernoulli suggest that with noncase information regarding a potential risk factor, such as species of birds, this method is sensitive and efficient in identifying high-risk areas and time periods for regional occurrence of HPAIV and potentially for similar infectious diseases. Results here demonstrate the impact that the nature of the collected information has on the epidemiological investigation of outbreaks. Results show the importance of collecting information on control data and on variables hypothesized to influence disease risk on the identification of periods of time and locations at high risk for the disease and risk factors associated with clustering as part of the national and international surveillance systems.

Prevalence of low pathogenicity avian influenza virus during 2005 in two U.S. live bird market systems.

Oropharyngeal and cloacal swabs were collected from poultry sold in two live bird market (LBM) systems to estimate the prevalence of low pathogenicity avian influenza virus (LPAIV) shedding during the summer and fall of 2005. Random sampling was conducted in three LBMs in Minnesota where 50 birds were sampled twice weekly for 4 wk, and in three LBMs in a California marketing system. A stratified systematic sampling method was used to collect samples from Southern California LBMs, where LPAIV was detected during routine surveillance. No LPAIV was detected in the LBM system in Minnesota where realtime reverse transcription-PCR (RT-PCR) was conducted on oropharyngeal samples. RT-PCR was performed on swabs taken from 290 of 14,000, 65 of 252, and 60 of 211 birds at the three Southern California LBMs. The number of samples collected was based on the number of birds, age of the birds, and number of species present in the LBM. Virus isolation, subtyping, and sequencing of the hemagglutinin, neuraminidase, and other internal protein genes was performed on AIV-positive samples. The estimated prevalence of LPAIV in California was 0.345% in an LBM/supply farm with multiple ages of Japanese quail, 3% in an LBM with multiple ages and strains of chickens present, and 49.8% in an LBM with multiple species, multiple strains, and multiple ages. The positive virus samples were all LPAIV H6N2 and closely related to viruses isolated from Southern California in 2001 and 2004. Little or no comingling of poultry may contribute to little or no LPAIV detection in the LBMs.

Identifying errors in avian influenza virus gene sequences and implications for data usage of public databases.

Public gene sequence databases have become important research tools to understand viruses and other organisms. Evidence suggests that the identifying information for some of the sequences in these databases might not belong to the sequences they are associated with. We developed two tests to conduct a comprehensive analysis of all published sequences of the hemaglutinin and neuramidase genes of avian influenza viruses (AIVs) to identify sequences that may have been misclassified. One test identified sequence pairs with highly similar nucleotide sequences despite a difference of several years between their sampling dates. Another test, which was applied to samples sequenced and deposited more than once, detected sequences with more nucleotide differences to their own than to their closest relatives. All sequences identified as misclassified were further traced to relevant publications to assess the likelihood of contamination and determine if any conclusions were associated with the use of these sequences. Our results suggested that among 4040 published gene sequences examined, approximately 0.8% might be misclassified and that publications using these sequences may include inaccurate statements. Findings from this report suggest that using laboratory-adapted strains and handling multiple samples simultaneously increases the risk of contamination. The tests reported here may be useful for screening new submissions to public sequence databases.

Distinctive egg-laying patterns in terminal versus non-terminal periods in three fruit fly species.

The specific objective of this study was to use a logistic regression model for determining the degree to which egg laying patterns of individual females at the end of life (i.e., terminal segments) in each of three different fruit fly species could be distinguished from the egg-laying patterns over a similar period in midlife (i.e., non-terminal segments). Extracting data from large-scale databases for 11-day terminal and 11-day non-terminal segments in the vinegar fly (Drosophila melanogaster), the Mexican fruit fly (Anastrepha ludens) and the Mediterranean fruit fly (Ceratitis capitata) and organizing the model's results in a 2 × 2 contingency table, we found that: (1) daily egg-laying patterns in fruit flies can be used to distinguish terminal from non-terminal periods; (2) the overall performance metrics such as precision, accuracy, false positives and true negatives depended heavily on species; (3) differentiating between terminal and non-terminal segments is more difficult when flies die at younger ages; and (4) among the three species the best performing metrics including accuracy and precision were those produced using data on D. melanogaster. We conclude that, although the reliability of the prediction of whether a segment occurred at the end of life is relatively high for most species, it does not follow precisely predicting remaining life will also be highly reliable since classifying an end of life period is a fundamentally different challenge than is predicting an exact day of death.

Exploring the effects of visual and literary arts interventions on psychosocial well-being of diverse older adults: a mixed methods pilot study.

BACKGROUND: Engagement in the arts may have health benefits for older adults. Most research has focused on music and dance; less is known about the benefits of other arts interventions. The purpose of this study was to examine the effects of visual (ceramics and collage) and literary arts (storytelling and writing) on well-being. METHODS: We used mixed methods to examine the effects of a 12-week visual or literary arts intervention on well-being. Adults age 55 and over from four housing sites were assigned to start an intervention immediately (intervention) or wait 12 weeks (controls). The study included pre/post-test measures of well-being and focus groups about perceived benefits. RESULTS: Compared to controls, participants in the ceramics intervention had significant improvements in interest in life and mastery, while no changes were observed after the storytelling intervention. Seven psychosocial benefits were identified . CONCLUSIONS: Participation in visual and literary arts for older adults was associated with well-being media.

Visualization and analysis of the Danish 2006 highly pathogenic avian influenza virus H5N1 wild bird surveillance data by a prototype avian influenza BioPortal.

Infection with highly pathogenic avian influenza virus H5N1 occurred for the first time in Denmark in 2006 during the last part of the European epidemic that mainly affected migrating wild birds. The total number of Danish wild bird cases was 45, of which only one was found through active surveillance using fecal sampling from resting areas for migrating species, whereas passive surveillance of dead wild birds provided 44 cases. One backyard, mixed poultry flock also became infected late in the epidemic. This study describes the spatial and temporal distribution of cases, initially characterized by a spatial-temporal cluster of affected tufted ducks that led to further spread to other wild bird species in the vicinity. The surveillance data also indicate an apparent die-off of the regional epidemic. As a tool in visualizing the spatial and temporal development of the epidemic, a prototype avian influenza (AI) BioPortal was used to provide online web-based access to the data. The AI BioPortal tools include mapping, graphing, phylogenetic tree construction, playback scenarios, and visualization of results of temporal-spatial analyses. Several of the features of this surveillance system compare favorably to the design of existing national and international surveillance information systems, and the AI BioPortal may become a useful tool for disease surveillance and for decision support in the event of future AI epidemics, both at national and international levels.

Potential impact of introduction of foot-and-mouth disease from wild pigs into commercial livestock premises in California.

OBJECTIVE: To estimate potential spread of foot-and-mouth disease (FMD) if introduced from wild pigs in California and to evaluate efficacies of various control strategies. SAMPLE POPULATION: Data for California livestock and from hunter surveys on wild pigs in California. PROCEDURES: A spatial, stochastic simulation model was used to simulate FMD epidemics that might occur if a dairy or beef herd were infected from contact with a wild pig. Index herd location and type were examined, in addition to different statewide movement ban (SWMB) durations, to determine their effect on extent of the epidemic. RESULTS: Duration, number of infected premises, size of simulated outbreak, number of culled animals, and spatial distribution of infected herds resulting from the simulated outbreaks varied considerably among geographic regions, depending on index case type and location. Outbreaks beginning in the southern region of California were consistently longest, whereas those beginning in the northern region were shortest. The largest outbreaks resulted from index cases located in the southern and valley regions, whereas outbreaks were smallest when originating in the Sonoma or northern regions. For all regions, when the index herd was a dairy herd, size and duration of the outbreak were consistently reduced with implementation of an SWMB >or= 3 days. CONCLUSIONS AND CLINICAL RELEVANCE: Introduction of FMDV from wild pigs into a dairy or beef herd could result in a large and rapidly spreading outbreak, potentially affecting large numbers of herds. Size and duration of the outbreak might be reduced with an SWMB; however, the impact is highly dependent on the index herd type and location.

Decoupling copolymer, lipid and carbon nanotube interactions in hybrid, biomimetic vesicles.

Bilayer vesicles that mimic a real biological cell can be tailored to carry out a specific function by manipulating the molecular composition of the amphiphiles. These bio-inspired and bio-mimetic structures are increasingly being employed for a number of applications from drug delivery to water purification and beyond. Complex hybrid bilayers are the key building blocks for fully synthetic vesicles that can mimic biological cell membranes, which often contain a wide variety of molecular species. While the assembly and morpholgy of pure phospholid bilayer vesicles is well understood, the functionality and structure dramaticlly changes when copolymer and/or carbon nanotube porins (CNTP) are added. The aim of this study is to understand how the collective molecular interactions within hybrid vesicles affect their nanoscale structure and properties. In situ small and wide angle X-ray scattering (SAXS/WAXS) and molecular dynamics simulations (MD) are used to investigate the morphological effect of molecular interactions between polybutadiene polyethylene oxide, lipids and carbon nanotubes (CNT) within the hybrid vesicle bilayer. Within the lipid/copolymer system, the hybrid bilayer morphology transitions from phase separated lipid and compressed copolymer at low copolymer loadings to a mixed bilayer where opposing lipids are mostly separated from the inner region. This transition begins between 60 wt% and 70 wt%, with full homogenization observed by 80 wt% copolymer. The incorporation of CNT into the hybrid vesicles increases the bilayer thickness and enhances the bilayer symmetry. Analysis of the WAXS and MD indicate that the CNT-dioleoyl interactions are much stronger than the CNT-polybutadiene.

Invasions by Eurasian avian influenza virus H6 genes and replacement of the virus' North American clade.

The spread of highly pathogenic avian influenza virus (AIV) (H5N1) underlines the potential for global AIV movement through birds. The phylogenies of AIV genes from avian hosts usually separate into Eurasian and North American clades, reflecting limited bird migration between the hemispheres. However, mounting evidence that some H6 sequences from North America cluster with Eurasian subtype H6 sequences calls the strict hemispheric divide into question. We conducted a comprehensive phylogenetic analysis of the extent and timing of cross-hemisphere movements by the H6 gene. Results suggested that Eurasian H6 subtype has invaded North America several times, with the first invasions occurring 10 years before the first detection of invading isolates. The members of the North American clade decreased from 100% in the 1980s to 20% in the 2000s among H6 isolates from North America. Unraveling the reasons for this large-scale gene movement between hemispheres might identify drivers of global AIV circulation.

Transmission of low-pathogenicity avian influenza virus of subtype H6N2 from chickens to Pekin ducks and Japanese quail (Coturnix coturnix japonica).

In this experiment we evaluated the transmission characteristics of a chicken-adapted low-pathogenicity avian influenza virus (LPAIV) of subtype H6N2, from infected chickens to Japanese quail and Pekin ducks, which are commonly sold in live bird markets located in Southern California. The layout of the cages and bird-handling practices were similar to those found in Southern California live bird markets. Five out of 20 chickens were inoculated with LPAIV H6N2, and placed in direct contact with five chickens and in indirect contact with 10 chickens, 10 Japanese quail and 10 Pekin ducks. Transmission of LPAIV was followed in each bird daily for 15 days post inoculation by real-time reverse transcriptase-polymerase chain reaction testing of oropharyngeal and cloacal swab samples. This strain of H6N2 LPAIV, isolated from commercial poultry in California, was transmitted to chickens, quail, and ducks from chickens. An antibody response was detected in ducks by haemagglutination inhibition tests, but avian influenza virus was only detected by reverse transcriptase-polymerase chain reaction in one duck. Avian influenza virus was detected in quail (5 and 7 days post inoculation) before chickens (8 and 9 days post inoculation), all of which were in indirect contact with infected chickens; however, this difference was not statistically significant.

Simulation of an early warning system using sentinel birds to detect a change of a low pathogenic avian influenza virus (LPAIV) to high pathogenic avian influenza virus (HPAIV).

The placement of sentinel birds in a commercial poultry flock infected with low pathogenic avian influenza virus (LPAIV) may be an effective way of detecting subsequent change in the isolate to a high pathogenic avian influenza virus (HPAIV). Data collected from the 2002 Chilean HPAIV outbreak, along with information from a literature review of laboratory studies involving A/chicken/Chile/176822/02 (H7N3/LP) and A/chicken/Chile/184240-1/02 (H7N3/HP) viruses, were used to construct a computer simulation model. Mortality rates of the original LPAIV-infected population and the sentinel population were compared to detect the presence of HPAIV. A total of 12 increased mortality threshold scenarios were examined, using one-day absolute (2, 3, or 4 birds) or relative (0.5, 1.0, or 1.5%) mortality thresholds, and two-day absolute (1, 2, or 3 birds) or relative (0.25, 0.50, or 1.00%) mortality thresholds, to indicate the change from LPAIV to HPAIV in the sentinel and original populations, respectively. Results showed that following a one-day approach, threshold mortalities occurred on average at 7.35, 7.82, and 8.17 (0.5, 1.0, or 1.5%) and 6.21, 6.38, and 6.45 (2, 3, or 4 birds) days after the first infectious case for the original and sentinel populations, respectively. The two-day approach delayed the occurrence of threshold mortalities, on average, to 7.64, 8.05, and 8.62 (0.25, 0.50, or 1.00%) and 6.86, 6.78, and 7.23 (1, 2, or 3 birds) days after the first infectious case for the original and sentinel populations, respectively. Although, significant (p<0.10) differences were observed among different combinations of detection times for the original and sentinel populations, the use of sentinel birds has a maximum mean advantage, over monitoring mortality exclusively in the original population, of 1.96 and 1.84 days for one- and two-day threshold moralities, respectively. Additionally, the early warning system based on a sentinel vs. original population presented a decrease of the probabilities of a false alarm, from 0.04-0.45 to <0.01-0.10%. These findings may be used by decision makers to evaluate the risk of not depopulating a flock infected with a H5 or H7 LPAIV strain and the benefit of using sentinel birds as an early warning system of a change to HPAIV.

Epidemiologic investigation of the re-emergence of infectious salmon anemia virus in Chile.

Reports from surveillance activities were analyzed to determine the epidemiology of the re-emergence of infectious salmon anemia virus (ISAV) in Atlantic salmon farms in Chile. The epidemic and spatial and spatiotemporal patterns were described, taking into account commercial compartmentalization of the farms. During the 64 wk study period, 76 ISAV-infected salmon farms, representing 17 companies, were reported in 65% of the management geographic zones of the 10th region in southern Chile. Approximately 20% of the farms at risk became infected, with the incidence rate increasing slightly over time. Results from epidemic analyses and observed spatial and spatiotemporal patterns suggested an initial dispersal and subsequent clustering of cases around the index case (IC) in a propagated epidemic mode. Results suggested that delayed depopulation may have been a key factor in the spread and persistence of ISAV. Clustering of cases supported the assumption that passive transmission in seawater from ISAV-infected farms (proximity) is a critical factor in controlling disease. The re-emergence of ISAV in Chile has resulted in one of the largest ISAV epidemics reported in the world and this study generates new hypotheses and provides useful information for spatial disease control planning in salmon farming areas.

Results of a survey to estimate cattle movements and contact rates among beef herds in California, with reference to the potential spread and control of foot-and-mouth disease.

OBJECTIVE: To estimate contact rates and movement variables for shipments of beef cattle to and from producer premises in California. DESIGN: Cross-sectional survey. SAMPLE POPULATION: 583 beef producers in California. PROCEDURES: Questionnaires were developed and distributed to beef cattle producers in California. The study period was from April 20, 2005, through September 7, 2006. Data from completed questionnaires were entered manually into an electronic format. Descriptive statistical analyses were performed. RESULTS: Median number of interstate animal movements (movement of cattle into or out of California) was 0.17/mo; on the basis of this median, beef cattle were moved interstate > 2 times/y. Respondents kept beef cattle at up to 5 locations throughout the year. More than 40% of the movements from the respondents' premises were to a sale yard or auction facility. CONCLUSIONS AND CLINICAL RELEVANCE: Frequency of animal movements in this statewide study differed from values in another study of monthly shipments of animals to and from beef operations in 3 counties of California. The survey reported here revealed more frequent movements of animals to and from beef operations of all sizes. In addition, there were more high-risk indirect contacts on beef operations than has been reported previously. However, the number of low-risk indirect contacts was similar for small beef operations but less for large beef operations than has been reported elsewhere. Epidemic simulation models for California based on data in earlier studies likely underpredicted disease transmission involving beef herds.

Life table invasion models: spatial progression and species-specific partitioning.

Biological invasions are increasingly being considered important spatial processes that drive global changes, threatening biodiversity, regional economies, and ecosystem functions. A unifying conceptual model of the invasion dynamics could serve as a useful tool for comparison and classification of invasion processes involving different species across large geographic ranges. By dividing these geographic ranges that are subject to invasions into discrete spatial units, we here conceptualize the invasion process as the transition from pristine to invaded spatial units. We use California cities as the spatial units and a long-term database of invasive tropical tephritids to characterize the invasion patterns. A new life-table method based on insect demography, including the progression model of invasion stage transition and the species-specific partitioning model of multispecies invasions, was developed to analyze the invasion patterns. The progression model allows us to estimate the probability and rate of transition for individual cities from pristine to infested stages and subsequently differentiate the first year of detection from detection recurrences. Importantly, we show that the interval of invasive tephritid recurrence in a city declines with increasing invasion stages of the city. The species-specific partitioning model revealed profound differences in invasion outcome depending on which tephritid species was first detected (and then locally eradicated) in the early stage of invasion. Taken together, we discuss how these two life-table invasion models can cast new light on existing invasion concepts; in particular, on formulating invasion dynamics as the state transition of cities and partitioning species-specific roles during multispecies invasions. These models provide a new set of tools for predicting the spatiotemporal progression of invasion and providing early warnings of recurrent invasions for efficient management.

An economic analysis of a contingency model utilising vaccination for the control of equine influenza in a non-endemic country.

BACKGROUND: Equine influenza (EI) is an infectious respiratory disease of horses that has never been reported in New Zealand (NZ). However, the 2007 EI outbreak in Australia, previously EI free, spurred the NZ government and stakeholders into evaluating alternative EI control strategies in order to economically justify any future decision to eradicate or manage EI. To build on the policy debate, this paper presents an epinomic (epidemiologic and economic) modelling approach to evaluate alternative control strategies. An epidemiologic model to determine how alternative EI control strategies influence the distribution of EI. Model results were then input into a cost-benefit analysis framework, to identify the return and feasibility of alternative EI eradication strategies in NZ. METHODS: The article explores nine alternative eradication scenarios and two baseline strategies. The alternative scenarios consisted of three vaccination strategies (suppressive, protective or targeted) starting at three time points to reflect the commercial breeding-cycle. These alternatives were compared to two breeding-cycle adjusted baselines: movement restriction in the breeding season (August to January) or non-breeding season (February to July). The economic loss parameters were incursion response, impact to the commercial racing industry (breeding, sales and racing), horse morbidity and mortality, and compensation to industry participants. RESULTS AND CONCLUSIONS: Results suggest that the economic viability of the EI eradication programme is dependent on when within the breeding-cycle the EI outbreak occurs. If an outbreak were to occur, the return on each dollar invested for protective or suppressive vaccination strategies would be between NZD$3.67 to NZD$4.89 and between NZD$3.08 to NZD$3.50 in the breeding and non-breeding seasons, respectively. Therefore, protective or suppressive vaccination strategies could be prioritised, regardless of season. As multiple industry stakeholders benefit from these strategies, the study will enable policy development and to better formulate a user-pays eradication programme.

Risk factors associated with human infection during the 2006 West Nile virus outbreak in Davis, a residential community in northern California.

We collected a total of 15,329 mosquitoes during weekly sampling in Davis, CA, from April through mid-October 2006 at 21 trap sites uniformly spaced 1.5 km apart over an area of approximately 26 km(2). Of these mosquitoes, 1,355 pools of Culex spp. were tested by multiplex reverse transcriptase-polymerase chain reaction, of which 16 pools (1.2%) were positive for West Nile virus (WNV). A degree-day model with a developmental threshold of 14.3 degrees C accurately predicted episodic WNV transmission after three extrinsic incubation periods after initial detection. Kriging interpolation delineated that Culex tarsalis were most abundant at traps near surrounding agriculture, whereas Cx. pipiens clustered within residential areas and greenbelt systems in the old portion of Davis. Spatial-temporal analyses were performed to test for clustering of locations of WNV-infected dead birds and traps with WNV-positive Cx. tarsalis and Cx. pipiens; human case incidence was mapped by census blocks. Significant multivariate spatial-temporal clustering was detected among WNV-infected dead birds and WNV-positive Cx. tarsalis, and a WNV-positive Cx. pipiens cluster overlapped areas with high incidences of confirmed human cases. Spatial analyses of WNV surveillance data may be an effective method to identify areas with an increased risk for human infection and to target control efforts to reduce the incidence of human disease.