Measuring the impacts of aquatic animal diseases: the role of economic analysis.

Aquaculture is an important industry both economically and socially. The majority of this industry is focused on the production of aquatic animals, which may be substantially adversely affected by disease. Economic analyses may be used to inform decision-makers on the aquatic animal disease control choices that are economically optimal. Examples of such analyses are presented in this paper, ranging from basic cost estimates of disease impact to complex, spatial- temporal, bio-economic models. Regardless of the complexity of the analysis, there is a consistent need to collect and analyse good quality data measuring both the production and health of aquatic animals. This would require a variety of individuals and groups, including farmers, scientists and the government, to collaboratively contribute to this end. Given the necessary data, more sophisticated models may be better used to inform decision-making from the farm to the national level. Finally, economic analyses should not be limited to simple aggregated cost and benefit results but rather should include the social and gender impacts of financial decisions, as well as the potential externalities both within and among the various impacted sectors in order to optimise investment at both the farm and national levels.

Le secteur de l'aquaculture joue un rôle important aux plans tant économique que social. La majorité des filières du secteur sont axées sur la production d'animaux aquatiques, espèces susceptibles à des maladies à l'impact souvent considérable. Les décideurs ont la possibilité de recourir à des analyses économiques afin de sélectionner les stratégies de lutte contre les maladies des animaux aquatiques optimales au plan économique. L'auteur présente quelques exemples de ce type d'analyses, qui vont de l'estimation basique des coûts liés à l'impact d'une maladie à des modèles analytiques complexes, spatiotemporels et bioéconomiques. Indépendamment de la complexité de l'analyse, il est à chaque fois indispensable de collecter et d'analyser des données de bonne qualité concernant la production et la santé des animaux aquatiques. La réussite d'une telle entreprise nécessite la contribution d'un large éventail d'acteurs individuels et collectifs travaillant en collaboration, dont les éleveurs, les chercheurs et les instances gouvernementales. Dès lors que l'on dispose des données nécessaires, des modèles plus sophistiqués pourront être utilisés afin d'étayer les prises de décision depuis les élevages jusqu'au niveau national. Enfin, les analyses économiques ne devraient pas se limiter à de simples résultats agrégés des coûts et des bénéfices mais devraient prendre en compte les impacts sociaux des décisions financières et leurs répercussions sexospécifiques, ainsi que les effets externes potentiels sur et parmi les divers secteurs affectés, dans le but d'optimiser les investissements réalisés aussi bien au niveau des élevages qu'à l'échelle nationale.

La acuicultura es una actividad industrial importante, a la vez económica y socialmente. El grueso del sector está dedicado a la producción de animales acuáticos, en los que pueden hacer estragos las enfermedades. Los análisis económicos pueden ser utilizados por las instancias decisorias para decidir con conocimiento de causa acerca de las líneas de actuación económicamente idóneas para combatir las enfermedades de dichos animales. El autor presenta ejemplos de este tipo de análisis, que van desde estimaciones básicas del costo de las consecuencias de una enfermedad hasta complejos modelos bioeconómicos que integran la dimensión espaciotemporal. Ahora bien, sea cual sea el nivel de complejidad del análisis, siempre es necesario reunir y analizar datos de buena calidad que midan tanto la producción como el estado de salud de los animales acuáticos. Para hacer posible tal objetivo sería menester que diversas personas y colectividades, entre ellas productores, científicos y administraciones públicas, trabajaran de consuno con este fin. Habida cuenta de los datos necesarios, es posible dar un mejor uso a modelos más sofisticados para fundamentar los procesos decisorios a todos los niveles, desde la explotación hasta el ámbito nacional. Los resultados de los análisis económicos, por último, lejos de ofrecer meras sumas de costos y beneficios, deberían también dar cuenta de los efectos sociales o ligados al género de las decisiones de índole económica, así como de eventuales influencias externas que se dejen sentir en los diversos sectores afectados, o que se ejerzan de uno a otro de esos sectores, con el fin de optimizar las inversiones tanto en cada explotación como a escala nacional.

Economics for assisting policy-makers to take decisions about new and endemic diseases.

Animal health policy-makers are frequently faced with making decisions concerning the control and exclusion of diseases in livestock and wildlife populations. Economics is one of the tools they have to aid their decision-making. It can enable them to make objective decisions based on the expected costs and benefits of their policy. In addition, economics can help them determine both the distribution impact and the indirect impact of their decisions. However, economics is only one of many tools available to policy-makers, who also need to consider non-economic outcomes in their decision-making process. While there are sophisticated epidemic and economic (epinomic) models that are available to help evaluate complex problems, these models typically require extensive data and well-trained analysts to run and interpret their results. In addition, effective communication between analysts and policy-makers is important to ensure that results are clearly conveyed to the policy-makers. This may be facilitated by early and continued discussions between these two potentially disparate groups. If successfully performed and communicated, economic analyses may present valuable information to policy-makers, enabling them to not only better understand the economic implications of their policy, but also to communicate the policy to relevant stakeholders, further ensuring their likelihood of participating in the planned policy and hence increasing its likelihood of success.

Les responsables des politiques de santé animale sont souvent confrontés à la nécessité de prendre des décisions au sujet de la lutte à mener contre les maladies animales affectant les populations domestiques et sauvages ou de leur éradication. L'économie est l'un des outils d'aide à la décision à leur disposition. L'économie peut les aider à prendre des décisions objectives basées sur les coûts et les avantages attendus des politiques envisagées. Elle peut aussi les aider à déterminer l'impact de leurs décisions en termes de portée et d'effets indirects. Néanmoins, l'économie n'est qu'un des nombreux outils disponibles et les décideurs doivent également intégrer les résultats non économiques lors de leur processus décisionnel. Un certain nombre de modèles épidémiques et économiques (« épinomiques ¼) sophistiqués permettent d'évaluer des problèmes complexes ; ils nécessitent cependant un volume considérable de données ainsi que des analystes qualifiés pour les mettre en oeuvre et en interpréter les résultats. En outre, une communication efficace doit être mise en place entre les analystes et les décideurs afin de s'assurer que les résultats obtenus sont rapportés à ces derniers dans un langage clair. Ceci peut être facilité par des échanges précoces et permanents entre ces deux groupes potentiellement hétérogènes. Des analyses économiques bien réalisées et faisant l'objet d'une bonne communication fournissent aux décideurs des informations de qualité grâce auxquelles ils peuvent appréhender plus clairement les conséquences économiques de leurs politiques, mais aussi expliquer ces politiques aux principales parties prenantes, ce qui accroît la probabilité de les faire adhérer aux mesures planifiées et améliore d'autant les chances de succès.

Los planificadores de políticas zoosanitarias se ven con frecuencia en la tesitura de adoptar decisiones acerca del control y la exclusión de enfermedades en poblaciones de ganado o de animales salvajes. La economía es una de las herramientas en las que pueden apoyarse para ello, pues les ayuda a tomar decisiones objetivas basándose en los costos y beneficios previstos de determinada política. Además, la economía puede serles útil para determinar tanto el impacto distributivo como el impacto indirecto de sus decisiones. Sin embargo, la economía es solo una de las muchas herramientas de que disponen los planificadores, que en su proceso decisorio también deben tener en cuenta efectos de carácter no económico. Si bien para ayudarles a aprehender problemas complejos existen sofisticados modelos epidemiológicos y económicos (epinómicos), estos suelen requerir un gran número de datos, así como el concurso de analistas cualificados para aplicar los modelos e interpretar sus resultados. Asimismo, para que los resultados obtenidos por los analistas lleguen con claridad a los planificadores es importante que existan cauces eficaces de comunicación entre los primeros y los segundos, lo que puede verse facilitado si estos dos grupos, en potencia tan dispares, dialogan desde buen comienzo y de forma continua. Si se llevan a cabo y se comunican correctamente, los análisis económicos pueden ofrecer información útil a los planificadores, que les sirva no solo para aprehender mejor las consecuencias económicas de sus políticas, sino también para explicar determinada política a todos los interlocutores del sector, con lo cual estos serán más proclives a participar en dicha política y esta tendrá más probabilidades de éxito.

Cost-benefit analyses of supplementary measles immunisation in the highly immunized population of New Zealand.

As endemic measles is eliminated from countries through increased immunisation, the economic benefits of enhanced immunisation programs may come into question. New Zealand has suffered from outbreaks after measles introductions from abroad and we use it as a model system to understand the benefits of catch up immunisation in highly immunised populations. We provide cost-benefit analyses for measles supplementary immunisation in New Zealand. We model outbreaks based on estimates of the basic reproduction number in the vaccinated population (Rv, the number of secondary infections in a partially immunised population), based on the number of immunologically-naïve people at district and national levels, considering both pre- and post-catch up vaccination scenarios. Our analyses suggest that measles Rv often includes or exceeds one (0.18-3.92) despite high levels of population immunity. We calculate the cost of the first 187 confirmed and probable measles cases in 2014 to be over NZ$1 million (∼US$864,200) due to earnings lost, case management and hospitalization costs. The benefit-cost ratio analyses suggest additional vaccination beyond routine childhood immunisation is economically efficient. Supplemental vaccination-related costs are required to exceed approximately US$66 to US$1877 per person, depending on different scenarios, before supplemental vaccination is economically inefficient. Thus, our analysis suggests additional immunisation beyond childhood programs to target naïve individuals is economically beneficial even when childhood immunisation rates are high.

Global importation and population risk factors for measles in New Zealand: a case study for highly immunized populations.

As endemic measles is eliminated through immunization, countries must determine the risk factors for the importation of measles into highly immunized populations to target control measures. Despite eliminating endemic measles, New Zealand suffers from outbreaks after introductions from abroad, enabling us to use it as a model for measles introduction risk. We used a generalized linear model to analyze risk factors for 1137 measles cases from 2007 to June 2014, provide estimates of national immunity levels, and model measles importation risk. People of European ethnicity made up the majority of measles cases. Age is a positive risk factor, particularly 0-2-year-olds and 5-17-year-old Europeans, along with increased wealth. Pacific islanders were also at greater risk, but due to 0-2-year-old cases. Despite recent high measles, mumps, and rubella vaccine immunization coverage, overall population immunity against measles remains ~90% and is lower in people born between 1982 and 2005. Greatest measles importation risk is during December, and countries predicted to be sources have historical connections and highest travel rates (Australia and UK), followed by Asian countries with high travel rates and higher measles incidences. Our results suggest measles importation due to travel is seeding measles outbreaks, and immunization levels are insufficient to continue to prevent outbreaks because of heterogeneous immunity in the population, leaving particular age groups at risk.

Invited review: A systematic literature review and meta-analysis of mortality and culling in dairy cattle.

Dairy industries and individual farmers are concerned about mortality and culling of dairy animals. This is because the timing and fates of animals that exit dairy farms have important animal welfare and economic consequences that reflect the conditions under which they are farmed and the efficiency of their production systems. Reports from a few countries have indicated increased incidence of mortality, and occasionally culling, of dairy animals in recent decades, and these changes have been associated with intensification of production systems. Dairy industries and farmers need benchmarks for culling and mortality against which they can compare themselves, as well as improved understanding of the extent of any change and of any associated factors. We reasoned that a systematic literature review and meta-analysis of scientific articles published between 1989 and 2014 would allow us to determine whether these reports were universal, to quantify any change over time, and to investigate whether production systems or study factors were associated with culling and mortality. From 3,275 articles retrieved from databases and manual searching of cited articles, 118 articles were appraised independently by 2 assessors, and 51 articles representing 54 studies were determined to be eligible for review and meta-analysis. We estimated that both the annual incidence risk (IR) and incidence density of mortality of cows had increased significantly from 0.02 per cow and 2.32 per 100 cow-years, to 0.04 per cow and 3.75 per 100 cow-years, an increase per decade of 0.02 per cow and 1.42 per 100 cow-years, respectively. We also estimated that the annual IR of culling attributed to low production had declined significantly from 0.07 to 0.05 and that the IR of perinatal, but not neonatal, mortality had increased significantly from 0.04 to 0.06 per decade. We found no evidence of change in overall annual IR of culling of cows over time or any association between study design factors and the IR or incidence density of culling or mortality. These findings provide benchmarks for describing culling and mortality, and should encourage farmers and researchers in countries with modern dairy industries to discover and implement management strategies to reduce the animal welfare and economic costs associated with these changes.

Data-Driven Models of Foot-and-Mouth Disease Dynamics: A Review.

Foot-and-mouth disease virus (FMDV) threatens animal health and leads to considerable economic losses worldwide. Progress towards minimizing both veterinary and financial impact of the disease will be made with targeted disease control policies. To move towards targeted control, specific targets and detailed control strategies must be defined. One approach for identifying targets is to use mathematical and simulation models quantified with accurate and fine-scale data to design and evaluate alternative control policies. Nevertheless, published models of FMDV vary in modelling techniques and resolution of data incorporated. In order to determine which models and data sources contain enough detail to represent realistic control policy alternatives, we performed a systematic literature review of all FMDV dynamical models that use host data, disease data or both data types. For the purpose of evaluating modelling methodology, we classified models by control strategy represented, resolution of models and data, and location modelled. We found that modelling methodology has been well developed to the point where multiple methods are available to represent detailed and contact-specific transmission and targeted control. However, detailed host and disease data needed to quantify these models are only available from a few outbreaks. To address existing challenges in data collection, novel data sources should be considered and integrated into models of FMDV transmission and control. We suggest modelling multiple endemic areas to advance local control and global control and better understand FMDV transmission dynamics. With incorporation of additional data, models can assist with both the design of targeted control and identification of transmission drivers across geographic boundaries.

Prevalence, location and symmetry of noncatastrophic ligamentous suspensory apparatus lesions in California Thoroughbred racehorses, and association of these lesions with catastrophic injuries.

REASONS FOR PERFORMING STUDY: Knowledge of the site distribution of ligamentous injuries facilitates clinical diagnosis of suspensory apparatus conditions. OBJECTIVES: To determine if lesions within the suspensory ligament (SL) and distal ligaments of the proximal sesamoid bones (DSLs) were associated with suspensory apparatus failure or metacarpal lateral condylar fracture in California Thoroughbred racehorses. STUDY DESIGN: Cross-sectional study. METHODS: Suspensory apparatus specimens from 327 deceased Thoroughbred racehorses were sectioned within the SL body and branches, and oblique and straight DSLs. Purple lesions ≥2 mm in width were categorised as moderate and paler or smaller lesions as mild. Associations between moderate lesions and age, sex, racetrack and cause of death were evaluated using multivariable logistic regression. RESULTS: Moderate lesions were evident in 16% and milder lesions in 77% of racehorses. Moderate lesions occurred with similar frequency in SL branches and oblique DSLs. Moderate lesions were more likely to occur in horses that died as a result of suspensory apparatus failure (odds ratio [OR] = 4.60; 95% confidence interval [CI] 1.61-13.13; and P = 0.004) or metacarpal lateral condylar fracture (OR = 5.05; 95% CI 1.42-17.93; and P = 0.012) compared with horses that died from nonmusculoskeletal causes, and in horses aged ≥7 years horses compared with 2-year-old horses (OR = 5.33; 95% CI 1.44-19.75; and P = 0.012). CONCLUSIONS: Moderate lesions are common in the SL branches and oblique DSLs of racehorses, and may be associated with risk for suspensory apparatus failure and metacarpal condylar fracture. Monitoring health of the suspensory apparatus ligamentous structures may be a simple means of assessing fatigue in, and preventing more extensive injuries to, the forelimb suspensory apparatus and metacarpal condyles.

The role of fish movements and the spread of infectious salmon anemia virus (ISAV) in Chile, 2007-2009.

Infectious salmon anemia virus (ISAV) infection is a constant major threat to farmed and wild Atlantic salmon worldwide. Many epidemics have recently been reported in the most important salmon farming regions of the world, including Chile (2007-2009), where ISAV generated the most important disease and economic crisis in history of the salmon industry of the country. The spread of ISAV within a region is most likely by local or neighborhood spread from an infected farm; however, there is evidence that anthropogenic activities, such as movement of live or harvested fish or their byproduct, may have played a more important role than environmental or passive transmission in the 2007-2009 outbreak. Atlantic salmon farms (n=421) were retrospectively followed from stocking to harvesting in southern Chile at the time of the ISAV epidemic (2007-2009). The effect of husbandry and spatial risk factors, in addition to contact-network risk factors, which were obtained from the social network analyses, on time to first ISAV infection was estimated using a multivariable Cox proportional hazards model. Five variables were retained in the final fitted model: co-existing multiple generations on a farm (hazard ratio [HR]=2.585), mean smolt weight at stocking greater than 120g (HR=1.165), farm area (perkm(2)) (HR=1.005), and increased number of shipments entering a farm, i.e. the farm input degree (HR=1.876) were associated with reduced time to infection; whereas time-to-infection was longer for farms located farther from an ongoing ISAV outbreak (HR=0.943). It was demonstrated that movements of latently infected fish resulted in approximately 7 outbreaks, and potentially explain about 6% of the total number of cases during the epidemic. Results from this study provide new information about the mechanisms of spread of ISAV in one the largest documented ISAV epidemics in the world. Findings may be used to support the design and implementation of risk-based surveillance and control programs that may help to prevent, detect and control future ISAV outbreaks.

Risk factors for foot-and-mouth disease in Zambia, 1981-2012.

The aim of this study was to describe the spatial distribution of foot-and-mouth disease (FMD) outbreaks in Zambia for the period January 1981-December 2012 and to quantify the association between geographical features (proximity to roads, national parks, wetland areas) and the spatial distribution of FMD using a Poisson point process model. Details of FMD outbreaks retrieved from the Zambian Department of Veterinary and Livestock Development included the date of onset of clinical signs and the name of the ward in which the index case enterprise was located. A total of 62 FMD outbreaks occurred throughout the study period. Outbreaks occurred in the south of the Southern province along the border with Namibia and Botswana (n=5), in the Western province (n=2), in the Southern and Central provinces on the Kafue flood plains (n=44), and in the north east of the country close to the border with Tanzania (n=11). Increases in distance to the nearest major international border crossing, distance to the nearest major road, distance to the wetland area of the Kafue flood plain, wetness index and elevation were all associated with a decrease in FMD-outbreak ward intensity. Our analyses support the hypothesis that in drier areas of the country cattle are more likely to aggregate around communal drinking pools. Aggregation of cattle provides conditions suitable for FMD spread and detection.

Within-farm spread of infectious salmon anemia virus (ISAV) in Atlantic salmon Salmo salar farms in Chile.

Spread of infectious salmon anemia virus (ISAV) at the cage level was quantified using a subset of data from 23 Atlantic salmon Salmo salar farms located in southern Chile. Data collected from official surveillance activities were systematically organized to obtain detailed information on infectious salmon anemia (ISA) outbreaks. Descriptive statistics for outbreak duration, proportion of infected fish, and time to secondary infection were calculated to quantify the magnitude of ISAV incursions. Linear and multiple failure time (MFT) regression models were used to determine factors associated with the cage-level reproduction number (Rc) and hazard rate (HR) for recurrent events, respectively. In addition, the Knox test was used to assess if cage-to-cage transmissions were clustered in space and time. Findings suggest that within farms, ISA outbreaks, on average, lasted 30 wk (median = 26 wk, 95% CI = 24 to 37 wk) and affected 57.3% (95% CI = 47.7 to 67.0%) of susceptible cages. The median time to secondarily diagnosed cages was 23 d. Occurrence of clinical ISAV outbreaks was significantly associated with increased Rc, whereas increased HR was significantly associated with clinical outbreaks and with a large number of fish. Spatio-temporal analysis failed to identify clustering of cage cases, suggesting that within-farm ISAV spread is independent of the spatial location of the cages. Results presented here will help to better understand ISAV transmission, to improve the design of surveillance programs in Chile and other regions in which salmon are intensively farmed, and to examine the economic impact of ISAV and related management strategies on various cost and demand shifting factors.

Co-infection patterns of infectious salmon anaemia and sea lice in farmed Atlantic salmon, Salmo salar L., in southern Chile (2007-2009).

Infectious salmon anaemia virus (ISAV) caused a large epidemic in farmed Atlantic salmon in Chile in 2007-2009. Here, we assessed co-infection patterns of ISAV and sea lice (SL) based on surveillance data collected by the fish health authority. ISAV status and SL counts in all Atlantic salmon farms located in the 10th region of Chile were registered monthly from July 2007 through December 2009. Each farm was categorized monthly according to its ISAV and SL status. A multinomial time-space scan test using a circular window was applied to identify disease clusters, and a multivariate regression model was fitted to quantify the association between disease-clustering and farm-management factors. Most of the identified clusters (9/13) were associated with high SL burdens. There were significant associations (P < 0.05) between management factors and ISAV/SL status. Areas in which good management practices were associated with a reduced disease risk were identified. The findings of this study suggest that certain management practices can effectively reduce the risk of SL and ISAV in the face of an epidemic and will be helpful towards creating an effective disease control programme in Chile.

Evaluation of control and surveillance strategies for classical swine fever using a simulation model.

Classical swine fever (CSF) outbreaks can cause enormous losses in naïve pig populations. How to best minimize the economic damage and number of culled animals caused by CSF is therefore an important research area. The baseline CSF control strategy in the European Union and Switzerland consists of culling all animals in infected herds, movement restrictions for animals, material and people within a given distance to the infected herd and epidemiological tracing of transmission contacts. Additional disease control measures such as pre-emptive culling or vaccination have been recommended based on the results from several simulation models; however, these models were parameterized for areas with high animal densities. The objective of this study was to explore whether pre-emptive culling and emergency vaccination should also be recommended in low- to moderate-density areas such as Switzerland. Additionally, we studied the influence of initial outbreak conditions on outbreak severity to improve the efficiency of disease prevention and surveillance. A spatial, stochastic, individual-animal-based simulation model using all registered Swiss pig premises in 2009 (n=9770) was implemented to quantify these relationships. The model simulates within-herd and between-herd transmission (direct and indirect contacts and local area spread). By varying the four parameters (a) control measures, (b) index herd type (breeding, fattening, weaning or mixed herd), (c) detection delay for secondary cases during an outbreak and (d) contact tracing probability, 112 distinct scenarios were simulated. To assess the impact of scenarios on outbreak severity, daily transmission rates were compared between scenarios. Compared with the baseline strategy (stamping out and movement restrictions) vaccination and pre-emptive culling neither reduced outbreak size nor duration. Outbreaks starting in a herd with weaning piglets or fattening pigs caused higher losses regarding to the number of culled premises and were longer lasting than those starting in the two other index herd types. Similarly, larger transmission rates were estimated for these index herd type outbreaks. A longer detection delay resulted in more culled premises and longer duration and better transmission tracing increased the number of short outbreaks. Based on the simulation results, baseline control strategies seem sufficient to control CSF in low-medium animal-dense areas. Early detection of outbreaks is crucial and risk-based surveillance should be focused on weaning piglet and fattening pig premises.

The value of animal movement tracing: a case study simulating the spread and control of foot-and-mouth disease in California.

The purpose of this study was to estimate the benefits of an electronic animal tracing system and an improved paper-based system in terms of the potential spread of foot-and-mouth disease (FMD) if introduced in California. A spatial, stochastic simulation model and data for California were used to simulate FMD outbreaks originating from a dairy herd as the index case (IC). Descriptive statistics of the simulated FMD outbreak extent and duration were examined to determine the benefit of an electronic system or paper-based tracing systems of varying efficacies. According to the simulations, an electronic tracing system would reduce the median number of infected premises (IPs) by 8-81%, depending on size of the IC herd compared with the results expected from identifying IPs based on clinical signs alone. The benefit also varied by IP herd type, e.g. ≥ 50% for sheep farms, goat farms and calf and heifer raising operations and ≤ 20% for swine and beef premises. The electronic system simulated a decrease in the median duration from at least 200d to 42d, if the IC were a small dairy and from 110d to 45d if the IC were a large dairy. The impact of an introduction of FMD in California could be reduced substantially even without an electronic system, if paper-based tracing were more efficient; however, these benefits are far less than those that could be realized from an electronic animal identification system. Results show that substantial benefits, in terms of fewer IPs and infected animals and reduced epidemic duration, may be realized as a result of an efficient electronic animal identification system, compared with a paper-based animal tracing system; however, until then, an improvement in the current system, especially regarding the ability to trace movements the day prior to a premises being diagnosed with FMD, may be highly beneficial.

Stochastic, spatially-explicit epidemic models.

Animal disease epidemic models are useful for better understanding both the spread and control of disease in a population. While it is advisable that models be only as complex as needed, it is often necessary to modify simplifying assumptions and thus increase model complexity to better reflect reality. Here, the author will examine the need for increasing model complexity by including randomness in a model and modifying the assumption of homogeneous mixing, by introducing a spatial component into the model. The costs and benefits of these changes will be examined.

Farm-level reproduction number during an epidemic of infectious salmon anemia virus in southern Chile in 2007-2009.

An epidemic of infectious salmon anemia virus (ISAV) has greatly impacted salmon production in Chile with devastating social and economic consequences. The epidemic is analyzed here and is likely the largest ISAV outbreak reported affecting one of the most productive regions for salmon farming activities in the world. After re-emerging in 2007, ISAV rapidly expanded the following two years, both in magnitude and geographic range, affecting about 65% and 50% of salmon farms located at the 10th and 11th regions of Chile, respectively. A useful metric for the control of infectious diseases that quantifies the progression of an epidemic is the reproduction number at the farm level (R(f)), which describes the mean number of secondary cases generated by an infectious farm. The parameter in this study was estimated for individual farms (R(fi)), specific phases (R(tf)), and for the entire epidemic (R(f)) by using several analytical approaches based on the characterization of the epidemic curves for the two regions. For the initial spread and the epidemic growth phase, initial and intrinsic growth rates were used to estimate R(tf). In addition, two approaches (epidemic final size and nearest neighbor analyses) were used to obtain an individual (R(fi)) and overall estimate of R(f) for the complete epidemic. In general, two distinct regional patterns of spread were identified. In the 10th region, after an explosive initial spread of ISAV in which R(tf) reached 12.0-16.9, a smaller epidemic growth of 1.6≤R(tf)≥2.5 and a final burnout with R(tf)<1 were observed. For the 11th region, R(tf) only reached 2.4 during the initial spread phase, ranged from 1.6≤R(tf)≥4.4 during the epidemic growth phases and ended when R(tf) was <1.0. The epidemic was characterized by clustering of ISAV 'superspreaders' farms i.e., farms with statistically significantly (P<0.047) higher R(fi) values. Distances between pairs of infected farms were statistically significantly (P=0.003) shorter in the 10th compared to the 11th region. Overall, R(f) ranged from 1.6 to 2.5 and 1.3 to 1.7 in the 10th and 11th regions, respectively. Our findings suggest that control efforts were able to protect 38-60% and 23-41% of the farms in the 10th and 11th regions, respectively, and may have resulted in the epidemic not spreading further. In addition, control strategies in highly populated areas using a control zone of at least 10km radius may be more effective than the 5km zone recommended by the World Animal Health Organization.

Factors associated with infection by Campylobacter fetus in beef herds in the Province of Buenos Aires, Argentina.

Campylobacter fetus is a major venereal pathogen of cattle that is considered to be widespread among the livestock population of Argentina. The disease accounts for a 10% reduction in the weaning rate of Argentine infected herds and annual losses of $165 million. A case-control, questionnaire-based study was developed with the objective of quantifying the association between C. fetus infection and demographic, husbandry, and sanitary factors in 196 herds located in the province of Buenos Aires, Argentina. Abortions observed in the herd (OR=3.08, 95% CI=1.52, 6.23), and trespassing of bulls from neighboring herds (OR=2.03, 95% CI=0.98, 4.20), were positively associated with the risk of finding C. fetus-infected bulls, whereas buying bulls was a protective factor for the disease (OR=0.53, 95% CI=0.26, 1.08). Results presented here will help to develop and implement actions aimed at preventing the spread and reducing the incidence of C. fetus infection in the beef cattle population of Argentina.

The spatial epidemiologic (r)evolution: a look back in time and forward to the future.

Spatial epidemiology enables you to better understand diseases or ill-health processes; investigate relationships between the environment and the presence of disease; conduct disease cluster analyses; predict disease spread; evaluate control alternatives; and basically do things an epidemiologist otherwise would have been unable to do and avoid many errors that otherwise may have been committed. Recently, the discipline of spatial epidemiology has advanced substantially, owing to a combination of reasons. The introduction of the electronic computer has clearly led this advancement. Computers have facilitated the storage, management, display and analysis of data, which are critical to geographic information systems (GIS). Also, because of computers and their increased capabilities and capacities, data collection has greatly expanded and reached a new level owing in large part to the advent of geographic positioning systems (GPS). GPS enables the collection of spatial locations, which in turn present yet another attribute (location) amenable to consideration in epidemiologic studies. At the same time, spatial software has taken advantage of the evolution of computers and data, further enabling epidemiologists to perform spatial analyses that they may not have even conceived of 30 years before. Capitalizing on these now, non-binding technologic constraints, epidemiologists are more able to combine their analytic expertise with computational advances, to develop approaches, which enable them to make spatial epidemiologic methods an integral part of their toolkits. Instead of a novelty, spatial epidemiology is now more of a necessity for outbreak investigations, surveillance, hypothesis testing, and generating follow-up activities necessary to perform a complete and proper epidemiologic analysis.

Location of active transmission sites of Schistosoma japonicum in lake and marshland regions in China.

Schistosomiasis control in China has, in general, been very successful during the past several decades. However, the rebounding of the epidemic situation in some areas in recent years raises concerns about a sustainable control strategy of which locating active transmission sites (ATS) is a necessary first step. This study presents a systematic approach for locating schistosomiasis ATS by combining the approaches of identifying high risk regions for schisotosmiasis and extracting snail habitats. Environmental, topographical, and human behavioural factors were included in the model. Four significant high-risk regions were detected and 6 ATS were located. We used the normalized difference water index (NDWI) combined with the normalized difference vegetation index (NDVI) to extract snail habitats, and the pointwise 'P-value surface' approach to test statistical significance of predicted disease risk. We found complicated non-linear relationships between predictors and schistosomiasis risk, which might result in serious biases if data were not properly treated. We also found that the associations were related to spatial scales, indicating that a well-designed series of studies were needed to relate the disease risk with predictors across various study scales. Our approach provides a useful tool, especially in the field of vector-borne or environment-related diseases.

Risk assessment and cost-effectiveness analysis of Aujeszky's disease virus introduction through breeding and fattening pig movements into Spain.

Movement of infected animals is considered the most likely route of Aujeszky's disease virus (ADV) introduction into free areas and the main obstacle to eradicating Aujeszky's disease (AD) in those areas, which have achieved a low prevalence (>0 and < or =10%) status. For this reason, the Spanish AD control and eradication program has established measures to enhance security in animal movements in an attempt to protect areas with free or low prevalence status; however, no studies have quantified the effectiveness of the current or alternative ADV introduction prevention measures. We performed a probabilistic risk assessment and cost-effectiveness analysis, using Monte Carlo simulation, to evaluate the probability of introducing ADV-infected animals into free or low prevalence areas under the Spanish AD control and eradication program. We found the mean probability of introducing ADV-infected animals, when breeding pigs were quarantined but not tested prior to shipment, is likely (up to 21%), representing 13.6 times higher risk than when breeding pigs were tested prior to shipment. The strategy of testing pigs on fattening farms 15 days prior to shipment and using a sample size sufficient to detect a prevalence of 5% with a 95% of confidence, could reduce the probability of introducing ADV-infected animals by 91% with no additional cost. Similarly, testing pigs on breeding and fattening farms using a sample size sufficient to detect a prevalence of 1% with a 95% of confidence, could reduce the probability of introducing ADV-infected animals by 99%, but with an increased cost of 81%. Results reported in this study identify factors that contribute to risk of ADV introduction and should aid the control and eradication of AD in Spain.

Risk factors associated with Tritrichomonas foetus infection in beef herds in the Province of Buenos Aires, Argentina.

Bovine trichomonosis (BT) is a contagious disease, characterized by reproductive failure, embryonic losses, infertility, and abortions, which directly impacts the reproductive performance of cattle. In this cross-sectional questionnaire-based study, 56 veterinarians provided information on the geographic location and on the demographic, husbandry, and sanitary characteristics of 173 beef herds located in 26 (21%) counties of the Province of Buenos Aires, Argentina. Herds rearing beef cattle (OR=2.5, 95% CI=1.0, 6.3), with low pregnancy rate in cows (