Assessing the potential impact of vector-borne disease transmission following heavy rainfall events: a mathematical framework.

Predicting the impact of natural disasters such as hurricanes on the transmission dynamics of infectious diseases poses significant challenges. In this paper, we put forward a simple modelling framework to investigate the impact of heavy rainfall events (HREs) on mosquito-borne disease transmission in temperate areas of the world such as the southern coastal areas of the USA. In particular, we explore the impact of the timing of HREs relative to the transmission season via analyses that test the sensitivity of HRE-induced epidemics to variation in the effects of rainfall on the dynamics of mosquito breeding capacity, and the intensity and temporal profile of human population displacement patterns. The recent Hurricane Harvey in Texas motivates the simulations reported. Overall, we find that the impact of vector-borne disease transmission is likely to be greater the earlier the HREs occur in the transmission season. Simulations based on data for Hurricane Harvey suggest that the limited impact it had on vector-borne disease transmission was in part because of when it occurred (late August) relative to the local transmission season, and in part because of the mitigating effect of the displacement of people. We also highlight key data gaps related to models of vector-borne disease transmission in the context of natural disasters. This article is part of the theme issue 'Modelling infectious disease outbreaks in humans, animals and plants: approaches and important themes'. This issue is linked with the subsequent theme issue 'Modelling infectious disease outbreaks in humans, animals and plants: epidemic forecasting and control'.

The Effect of the Post 2001 Reforms on FMD Risks of the International Live Animal Trade.

The 2001 UK foot and mouth disease (FMD) epidemic marked a change in global FMD management, focusing less on trade isolation than on biosecurity within countries where FMD is endemic. Post 2001 policy calls for the isolation of disease-free zones in FMD-endemic countries, while increasing the opportunities for trade. The impact of the change on disease risk has yet to be tested. In this paper, we estimate an empirical model of disease risk that tests for the impact of trade volumes before and after 2001, controlling for biosecurity measures. In the pre 2001 regime, we find that poor biosecurity was associated with the probability of reporting an outbreak. In the post 2001 regime, the risks changed, with trade being a much greater source of risk. We discuss the trade-off between trade restrictions and biosecurity measures in the management of FMD disease risks.

Economic Incentives in the Socially Optimal Management of Infectious Disease: When [Formula: see text] is Not Enough.

Does society benefit from encouraging or discouraging private infectious disease-risk mitigation? Private individuals routinely mitigate infectious disease risks through the adoption of a range of precautions, from vaccination to changes in their contact with others. Such precautions have epidemiological consequences. Private disease-risk mitigation generally reduces both peak prevalence of symptomatic infection and the number of people who fall ill. At the same time, however, it can prolong an epidemic. A reduction in prevalence is socially beneficial. Prolongation of an epidemic is not. We find that for a large class of infectious diseases, private risk mitigation is socially suboptimal-either too low or too high. The social optimum requires either more or less private mitigation. Since private mitigation effort depends on the cost of mitigation and the cost of illness, interventions that change either of these costs may be used to alter mitigation decisions. We model the potential for instruments that affect the cost of illness to yield net social benefits. We find that where a disease is not very infectious or the duration of illness is short, it may be socially optimal to promote private mitigation effort by increasing the cost of illness. By contrast, where a disease is highly infectious or long lasting, it may be optimal to discourage private mitigation by reducing the cost of disease. Society would prefer a shorter, more intense, epidemic to a longer, less intense epidemic. There is, however, a region in parameter space where the relationship is more complicated. For moderately infectious diseases with medium infectious periods, the social optimum depends on interactions between prevalence and duration. Basic reproduction numbers are not sufficient to predict the social optimum.

Foot and mouth disease: the risks of the international trade in live animals.

The growth in world trade has generated significant benefits to humankind, but it has also generated costs. Among these is an increase in the dispersal of pests and pathogens across the globe. International trade has been implicated in outbreaks of several re-occurring livestock diseases. This paper is focused on the risk of foot and mouth disease (FMD) associated with the international trade in live animals. A model was used to estimate FMD risk as a function of the international trade in live animals, controlling for the biosecurity measures undertaken by importing and exporting countries, and for the presence of endemic FMD reservoirs. It was found that the indirect risks associated with exports may be as great as the direct risks associated with imports. For countries where livestock production occurs in disease-free zones (with or without vaccination), the trade risks vary with both species and trading partner. These findings may assist the targeting of disease risk mitigation activities.

La croissance du commerce international a apporté des bénéfices significatifs à l'humanité tout en générant certains coûts. Parmi ceux-ci figure la propagation accrue de parasites et d'agents pathogènes à l'échelle planétaire. Les échanges internationaux sont responsables de la résurgence de nombreuses maladies affectant le bétail. Les auteurs examinent en particulier le cas des risques de fièvre aphteuse associés aux échanges internationaux d'animaux vivants. Ils ont fait appel à un modèle pour estimer le risque de fièvre aphteuse en relation avec les échanges internationaux d'animaux vivants, le contrôle des mesures de biosécurité appliquées par les pays importateurs et exportateurs et la surveillance des réservoirs endémiques du virus. Il ressort de cette étude que les risques indirects associés aux exportations paraissent aussi importants que les risques directs associés aux importations. Dans les pays où l'élevage se déploie dans des zones indemnes de fièvre aphteuse (avec ou sans vaccination), les risques liés aux échanges varient en fonction de l'espèce et du partenaire commercial. Ces résultats peuvent contribuer à cibler les actions d'atténuation du risque de maladie.

El crecimiento del comercio mundial ha traído consigo importantes beneficios para la humanidad, pero también ha generado costos, entre ellos una mayor dispersión de plagas y patógenos por todo el planeta. El comercio internacional ha tenido cierto papel en la aparición de brotes recurrentes de varias enfermedades del ganado. Los autores se centran en el riesgo de fiebre aftosa ligado al comercio internacional de animales vivos. Con el empleo de un modelo para estimar el riesgo de fiebre aftosa como una función del comercio internacional de animales vivos, teniendo en cuenta las medidas de seguridad biológica implantadas por los países importadores y exportadores y la presencia de reservorios endémicos de fiebre aftosa, los autores descubrieron que los riesgos indirectos vinculados a las exportaciones pueden ser de igual magnitud que los riesgos directos ligados a las importaciones. En aquellos países donde la producción ganadera se sitúa en zonas libres de la enfermedad (con o sin vacunación), los riesgos ligados al comercio difieren en función de la especie y de cuál sea la contraparte comercial. Estas conclusiones pueden ayudar a seleccionar con más precisión las actividades de reducción del riesgo zoosanitario.

Integrating drivers influencing the detection of plant pests carried in the international cut flower trade.

This paper analyses the cut flower market as an example of an invasion pathway along which species of non-indigenous plant pests can travel to reach new areas. The paper examines the probability of pest detection by assessing information on pest detection and detection effort associated with the import of cut flowers. We test the link between the probability of plant pest arrivals, as a precursor to potential invasion, and volume of traded flowers using count data regression models. The analysis is applied to the UK import of specific genera of cut flowers from Kenya between 1996 and 2004. There is a link between pest detection and the Genus of cut flower imported. Hence, pest detection efforts should focus on identifying and targeting those imported plants with a high risk of carrying pest species. For most of the plants studied, efforts allocated to inspection have a significant influence on the probability of pest detection. However, by better targeting inspection efforts, it is shown that plant inspection effort could be reduced without increasing the risk of pest entry. Similarly, for most of the plants analysed, an increase in volume traded will not necessarily lead to an increase in the number of pests entering the UK. For some species, such as Carthamus and Veronica, the volume of flowers traded has a significant and positive impact on the likelihood of pest detection. We conclude that analysis at the rank of plant Genus is important both to understand the effectiveness of plant pest detection efforts and consequently to manage the risk of introduction of non-indigenous species.