The importance of fisheries and aquaculture production for nutrition and food security.

Aquatic food has a significant role to play in global nutrition and food security but is often ignored in that debate. Understanding its potential role is made difficult by the fact that aquatic food covers a large number of species which come from both capture fisheries and aquaculture and the marine and freshwater environments, including finfish, crustacea, molluscs, echinoderms, aquatic plants and other aquatic animals. Further complications arise from the fact that both supply and consumption vary significantly between countries. There are several criteria which need to be considered when discussing nutrition and food security. These include: how much food is produced, whether that production is sustainable, whether the production supports livelihoods, what the nutritional content of the food is and whether that food is safe. The authors conclude that there are many benefits to aquatic food under each of these criteria but there are also some hurdles which need to be overcome. Increased production to feed a growing global population relies on the growth of aquaculture. Challenges to such growth include the supply of raw ingredients for aquafeeds, losses due to disease outbreaks, being able to ensure high standards of food safety and overcoming environmental limitations to expansion. There are also problems with welfare conditions for people working in the supply chain which need to be addressed. Given the challenges to nutrition and food security which the world is currently facing, it is essential that aquatic food is brought into the debate and the significant benefits that aquatic foods provide are acknowledged and exploited.

Les denrées alimentaires d'origine aquatique contribuent de manière significative à la sécurité nutritionnelle et alimentaire mondiale ; or, elles sont souvent ignorées dans les discussions sur le sujet. Il est d'autant plus difficile de se faire une idée exacte de la contribution potentielle des aliments d'origine aquatique que ceuxci recouvrent un grand nombre d'espèces provenant aussi bien des pêches de capture que de l'aquaculture et issues de milieux tant marins que d'eau douce, comme les poissons, les crustacés, les mollusques, les échinodermes, mais aussi la flore aquatique et bien d'autres espèces d'animaux aquatiques. À ces difficultés s'ajoutent celles liées aux variations importantes de l'offre et de la consommation de ces denrées suivant les pays. Un certain nombre de critères sont à examiner lorsqu'on traite des questions de sécurité nutritionnelle et alimentaire. Il convient notamment d'examiner les quantités d'aliments produites, le caractère durable ou non de chaque production, son rôle dans l'économie de subsistance, le contenu nutritionnel des aliments et leur innocuité. Les auteurs concluent que si les aliments d'origine aquatique présentent nombre d'avantages au regard de chacun de ces critères, des obstacles subsistent auxquels il convient de remédier. Les possibilités de produire davantage d'aliments afin de nourrir une population mondiale toujours plus nombreuse sont tributaires de la croissance de l'aquaculture. Cette croissance est limitée par divers facteurs, notamment la disponibilité des matières premières utilisées pour l'alimentation des espèces aquatiques, les pertes dues aux maladies, la nécessité de garantir un niveau élevé de sécurité sanitaire des aliments à travers des normes appropriées et la capacité de résoudre les contraintes environnementales liées à cette expansion. Il faut également apporter une réponse aux problèmes de bien-être professionnel dans la filière. Compte tenu des défis posés par la sécurité nutritionnelle et alimentaire au niveau mondial, il est essentiel d'inscrire les aliments d'origine aquatique à l'ordre du jour des discussions afin que les avantages significatifs de ces productions soient reconnus et exploités.

Aunque revisten importancia para la seguridad nutricional y alimentaria del mundo, los alimentos de origen acuático son a menudo los grandes olvidados de los debates en la materia. La dificultad de aprehender la posible función de estos alimentos estriba en el hecho de que abarcan un gran número de especies procedentes tanto de la pesca de captura como de la acuicultura y de medios tanto marinos como de agua dulce: peces, crustáceos, moluscos, equinodermos y otros animales acuáticos, así como también plantas acuáticas. La cuestión resulta tanto más compleja cuanto que el suministro y el consumo difieren sensiblemente de un país a otro. Existen varios criterios que conviene tener en cuenta al reflexionar sobre cuestiones de seguridad nutricional y alimentaria, entre ellos los siguientes: qué cantidad de alimento se produce; el carácter sostenible o insostenible de la producción; el hecho de que la producción forme parte o no de los medios de subsistencia; el contenido nutricional de los alimentos; o el nivel de inocuidad que estos ofrecen. Los autores llegan a la conclusión de que, a la luz de cada uno de estos criterios, los alimentos acuáticos aportan muchos beneficios, pero también presentan una serie de problemas que es preciso resolver. El logro de una mayor producción destinada a alimentar a la creciente población mundial reposa en el crecimiento de la acuicultura, crecimiento que está sujeto a limitaciones como el aprovisionamiento en ingredientes para los piensos destinados a animales acuáticos, las pérdidas causadas por brotes infecciosos, el cumplimiento de criterios estrictos de inocuidad de los alimentos o la posibilidad, o no, de superar los límites que el medio ambiente impone a la expansión de la actividad. También hay problemas ligados a las condiciones de bienestar de los trabajadores de la cadena de suministro que es preciso abordar. En vista de los problemas de seguridad nutricional y alimentaria a los que ahora mismo hace frente el mundo, es indispensable integrar los alimentos acuáticos en los procesos de debate y reflexión y saber reconocer y aprovechar los importantes beneficios que traen consigo.

Past and future perspectives on mathematical models of tick-borne pathogens.

Ticks are vectors of pathogens which are important both with respect to human health and economically. They have a complex life cycle requiring several blood meals throughout their life. These blood meals take place on different individual hosts and potentially on different host species. Their life cycle is also dependent on environmental conditions such as the temperature and habitat type. Mathematical models have been used for the more than 30 years to help us understand how tick dynamics are dependent on these environmental factors and host availability. In this paper, we review models of tick dynamics and summarize the main results. This summary is split into two parts, one which looks at tick dynamics and one which looks at tick-borne pathogens. In general, the models of tick dynamics are used to determine when the peak in tick densities is likely to occur in the year and how that changes with environmental conditions. The models of tick-borne pathogens focus more on the conditions under which the pathogen can persist and how host population densities might be manipulated to control these pathogens. In the final section of the paper, we identify gaps in the current knowledge and future modelling approaches. These include spatial models linked to environmental information and Geographic Information System maps, and development of new modelling techniques which model tick densities per host more explicitly.

The impact of increased dispersal in response to disease control in patchy environments.

This paper uses a mathematical framework to investigate the impact of increased movement in response to disturbance caused by disease control strategies. Implementation of invasive disease control strategies such as culling may cause species to disperse beyond their natural range, thus aiding the spread of infection to otherwise infection free areas. Both linear and non-linear dispersal functions are compared with constant per capita dispersal in a coupled two patch SI model. For highly virulent or infrequently transmitted pathogens, it is found that an increase of dispersal due to control requires a higher level of disease control than in the constant dispersal model. Patches which may be sources or reservoirs of infection are investigated and it is found that if dispersal increases in response to control, then all patches, reservoir or not, must be targeted. The single host two patch model is then extended to a two host wildlife/livestock system with one species 'wildlife' free to move between patches and the other 'livestock' confined. In the two host case, control of one species alone will only achieve successful pathogen exclusion if that species is a reservoir for infection.

An alternative to killing? Treatment of reservoir hosts to control a vector and pathogen in a susceptible species.

Parasite-mediated apparent competition occurs when one species affects another through the action of a shared parasite. One way of controlling the parasite in the more susceptible host is to manage the reservoir host. Culling can cause issues in terms of ethics and biodiversity impacts, therefore we ask: can treating, as compared to culling, a wildlife host protect a target species from the shared parasite? We used Susceptible Infected Recovered (SIR) models parameterized for the tick-borne louping ill virus (LIV) system. Deer are the key hosts of the vector (Ixodes ricinus) that transmits LIV to red grouse Lagopus lagopus scoticus, causing high mortality. The model was run under scenarios of varying acaricide efficacy and deer densities. The model predicted that treating deer can increase grouse density through controlling ticks and LIV, if acaricide efficacies are high and deer densities low. Comparing deer treated with 70% acaricide efficacy with a 70% cull rate suggested that treatment may be more effective than culling if initial deer densities are high. Our results will help inform tick control policies, optimize the targeting of control methods and identify conditions where host management is most likely to succeed. Our approach is applicable to other host-vector-pathogen systems.

A model to test how ticks and louping ill virus can be controlled by treating red grouse with acaricide.

Ticks are the most important vectors of disease-causing pathogens in Europe. In the U.K., Ixodes ricinus L. (Ixodida: Ixodidae) transmits louping ill virus (LIV; Flaviviridae), which kills livestock and red grouse, Lagopus lagopus scoticus Lath. (Galliformes: Phasianidae), a valuable game bird. Tick burdens on grouse have been increasing. One novel method to reduce ticks and LIV in grouse may be acaricide treatment. Here, we use a mathematical model parameterized with empirical data to investigate how the acaricide treatment of grouse might theoretically control ticks and LIV in grouse. Assuming a situation in which ticks and LIV impact on the grouse population, the model predicts that grouse density will depend on deer density because deer maintain the tick population. In low deer densities, no acaricide treatment is predicted to be necessary because abundances of grouse will be high. However, at higher deer densities, the model predicts that grouse densities will increase only if high numbers of grouse are treated, and the efficacy of acaricide is high and lasts 20 weeks. The qualitative model predictions may help to guide decisions on whether to treat grouse or cull deer depending on deer densities and how many grouse can be treated. The model is discussed in terms of practical management implications.

Stocking methods and parasite-induced reductions in capture: modelling Argulus foliaceus in trout fisheries.

Argulus foliaceus is a macroparasite which can have a significant impact on yield in recreational trout fisheries, partly by increasing fish mortalities but also by reducing the appetite of infected fish, making them less likely to respond to bait. The aim of this paper is to determine the impact of four commonly used fish stocking methods both on the parasite dynamics, and on fisheries' yields. The wider consequences of the resultant reduction in host feeding are also of interest. To this end four different stocking methods were incorporated into Anderson and May's macroparasite model, which comprises three differential equations representing the host, attached parasite and free-living parasite populations. To each of these a reduction in the fish capture rate, inversely linked to the mean parasite burden, is added and the effects interpreted. Results show that (1) the common practise of increasing the stocking rate as catches drop may be counterproductive; (2) in the absence of any wild population of reservoir hosts, the parasite will be unable to survive if the stocking rate does not exceed the rate of capture; (3) compensatory stocking to account for fish mortalities can have disastrous consequences on yield; and (4) the parasite can, under certain circumstances, maintain the host population by preventing their capture.

Environmental forcing, invasion and control of ecological and epidemiological systems.

Destabilising a biological system through periodic or stochastic forcing can lead to significant changes in system behaviour. Forcing can bring about coexistence when previously there was exclusion; it can excite massive system response through resonance, it can offset the negative effect of apparent competition and it can change the conditions under which the system can be invaded. Our main focus is on the invasion properties of continuous time models under periodic forcing. We show that invasion is highly sensitive to the strength, period, phase, shape and configuration of the forcing components. This complexity can be of great advantage if some of the forcing components are anthropogenic in origin. They can be turned into instruments of control to achieve specific objectives in ecology and disease management, for example. Culling, vaccination and resource regulation are considered. A general analysis is presented, based on the leading Lyapunov exponent criterion for invasion. For unstructured invaders, a formula for this exponent can typically be written down from the model equations. Whether forcing hinders or encourages invasion depends on two factors: the covariances between invader parameters and resident populations and the shifts in average resident population levels brought about by the forcing. The invasion dynamics of a structured invader are much more complicated but an analytic solution can be obtained in quadratic approximation for moderate forcing strength. The general theory is illustrated by a range of models drawn from ecology and epidemiology. The relationship between periodic and stochastic forcing is also considered.

The effect of seasonal host birth rates on disease persistence.

In this paper, we add seasonality to the birth rate of an SIR model with density dependence in the death rate. We find that disease persistence can be explained by considering the average value of the seasonal term. If the basic reproductive ratio R(0)>1 with this average value then the disease will persist and if R(0)<1 with this average value then the disease will die out. However, if the underlying non-seasonal model displays oscillations towards the equilibrium then the dynamics of the seasonal model can become more complex. In this case, the seasonality can interact with the underlying oscillations, resonate and the population can display a range of complex behaviours including chaos. We discuss these results in terms of two examples, Cowpox in bank voles and Rabbit Haemorrhagic disease in rabbits.

The effect of seasonal host birth rates on population dynamics: the importance of resonance.

Many of the simple mathematical models currently in use often fail to capture important biological factors. Here we extend current models of insect-pathogen interactions to include seasonality in the birth rate. In particular, we consider the SIR model with self-regulation when applied to specific cases--rabbit haemorrhagic disease and fox rabies. In this paper, we briefly summarize the results of the model with a constant time-independent birth rate, a, which we then replace with the time dependent birth rate a(t), to investigate how this effects the dynamics of the host population. We can split parameter space into an area in which the model without seasonality has no oscillations, in which case a simple averaging rule predicts the behaviour. Alternatively, in the area where oscillations to the equilibrium do occur in the non-seasonal model, disease persistence is more complicated and we get more complex dynamical behaviour in this case. We apply resonance techniques to discover the structure of the subharmonic modes of the SIR model with self-regulation. We then look at whether many biological systems are likely to display these "resonant" dynamics and find that we would expect them to be widespread.

Epidemiological consequences of a pathogen having both virulent and avirulent modes of transmission: the case of rabbit haemorrhagic disease virus.

A number of pathogens cause chronic infection in survivors of acute disease and this is believed to be a common means of persistence, including for highly virulent agents. We present a model in which transmission from chronically infected hosts causes chronic infection in naive individuals, without causing acute disease--indeed 'protecting' against it. Thus the pathogen obtains the benefit of virulence (high transmission rate), but mitigates against the cost (high host mortality). Recent findings suggest that rabbit haemorrhagic disease virus (RHDV), a highly contagious and virulent pathogen, may also utilize this alternative, 'avirulent', mode of transmission. The model may resolve the paradox of how RHDV can be highly prevalent in some populations, in the absence of mortality. Differences in host demography determine whether avirulent transmission prevents large-scale mortality (as in most UK populations) or not. Other pathogens may exhibit similar behaviour and the implications for emerging diseases in general are discussed.

The emergence of rabbit haemorrhagic disease virus: will a non-pathogenic strain protect the UK?

Rabbit haemorrhagic disease virus emerged in China in 1984, and has killed hundreds of millions of wild rabbits in Australia and Europe. In the UK there appears to be an endemic non-pathogenic strain, with high levels of seroprevalence being recorded, in the absence of associated mortality. Using a seasonal, age-structured model we examine the hypothesis that differences in rabbit population demography differentially affect the basic reproductive rates (R(0)) of the pathogenic and non-pathogenic strains, leading to each dominating in some populations and not others. The strain with the higher R(0) excluded the other, with the dynamics depending upon the ratio of the two R(0) values. When the non-pathogenic strain dominated, the pathogenic strain caused only transient mortality, although this could be significant when the two R(0) values were similar. When the pathogenic strain dominated, repeated epidemics led to host eradication. Seroprevalence data suggest that the non-pathogenic strain may be protecting some, but not all UK populations, with half being 'at risk' from invasion by the pathogenic strain and a fifth prone to significant transient mortality. We identify key questions for empirical research to test this prediction.

Re-assessing the infection strategies of the entomopathogenic nematode Steinernema feltiae (Rhabditidae; Steinernematidae).

Previous studies have indicated that between 60 and 80% of a population of entomopathogenic nematodes do not infect their insect hosts at any one period in time. Two hypotheses explain this behaviour: the first that there is a subpopulation of non-infectious nematodes and the second that the non-infectious group is created by inhibitory cues derived from infected insects. Through an experimental approach with the Galleria mellonella-Steinernema feltiae system we show that both mechanisms operate together. When conditions for infection were optimized, the sum of individual infection behaviours was similar to the number infecting as a population, implying observed infection rates are driven by intrinsic mechanisms. In addition, there was evidence that an infected host released a chemical cue into the environment which inhibited subsequent levels of infection. This degree of inhibition was independent of the number of infecting nematodes. Both these mechanisms are dynamic, so the observed proportion of infectious nematodes depended heavily on the time of exposure. The implications of these findings for both the design of laboratory trials and the use of entomopathogenic nematodes in biological control are discussed.

EPIFIL: the development of an age-structured model for describing the transmission dynamics and control of lymphatic filariasis.

Mathematical models of transmission dynamics of infectious diseases provide a useful tool for investigating the impact of community based control measures. Previously, we used a dynamic (constant force-of-infection) model for lymphatic filariasis to describe observed patterns of infection and disease in endemic communities. In this paper, we expand the model to examine the effects of control options against filariasis by incorporating the impact of age structure of the human community and by addressing explicitly the dynamics of parasite transmission from and to the vector population. This model is tested using data for Wuchereria bancrofti transmitted by Culex quinquefasciatus in Pondicherry, South India. The results show that chemotherapy has a larger short-term impact than vector control but that the effects of vector control can last beyond the treatment period. In addition we compare rates of recrudescence for drugs with different macrofilaricidal effects.

Steric hindrance regulation of the Pseudomonas aeruginosa amidase operon.

Expression of the amidase operon of Pseudomonas aeruginosa is controlled by AmiC, the ligand sensor and negative regulator, and AmiR the transcription antitermination factor activator. We have titrated out AmiC repression activity in vivo by increased AmiR production in trans and shown AmiC regulation of the antitermination activity of AmiR by a steric hindrance mechanism. In the presence of the co-repressor butyramide we have isolated a stable AmiC.AmiR complex. Addition of the inducing ligand acetamide to the complex trips the molecular switch, causing complex dissociation and release of AmiR. The AmiC.AmiR butyramide complex exhibits acetamide-dependent, sequence-specific RNA binding activity and a K(d) of 1.0 nm has been calculated for the AmiR.RNA interaction. The results show that amidase operon expression is controlled by a novel type of signal transduction system in which activity of a site-specific RNA binding activator is regulated via a sequestration mechanism.

Geriatric dermatology in chronic care and rehabilitation.

The skin care of disabled elders living in nursing homes and adult congregate, subacute, and home health settings requires special effort and consideration. Practitioners who regularly assist elders in these situations may be unfamiliar with dermatology problems related to chronic disability. As the U.S. population ages, skin care in the elderly and disabled will continue to be a challenge. However, if the diseases and problems can be addressed in a knowledgeable and problem-oriented manner, treatment can be maximized.

Crystal structure and induction mechanism of AmiC-AmiR: a ligand-regulated transcription antitermination complex.

Inducible expression of the aliphatic amidase operon in Pseudomonas aeruginosa is controlled by an antitermination mechanism which allows production of the full-length transcript only in the presence of small-molecule inducers, such as acetamide. Ligand-regulated antitermination is provided by AmiC, the ligand-sensitive negative regulator, and AmiR, the RNA-binding positive regulator. Under non-inducing or repressing growth conditions, AmiC and AmiR form a complex in which the activity of AmiR is silenced. The crystal structure of the AmiC-AmiR complex identifies AmiR as a new and highly unusual member of the response-regulator family of bacterial signal transduction proteins, regulated by sequestration rather than phosphorylation. Comparison with the structure of free AmiC reveals the subtle mechanism of ligand-induced release of AmiR.

Absence of genetic variation in some obesity candidate genes (GLP1R, ASIP, MC4R, MC5R) among Pima indians.

OBJECTIVE: To examine the obesity candidate genes glucagon-like-peptide receptor (GLP1R), agouti signaling protein (ASIP) and the melanocortin receptors 4 and 5 (MC4R and MC5R) for DNA polymorphisms in their coding regions. SUBJECTS: Unrelated, non-diabetic Pima Indians (8 to 12 from each extreme of body fat). MEASUREMENTS: DNA sequencing within the coding regions of each gene. RESULT: Only one variant was detected, a silent substitution in exon 6 of GLP1R. CONCLUSION: The exclusion of any common amino-acid polymorphisms (allele frequency > or = 0.20). implies that structural variants of these genes do not contribute to variation in the high level of obesity observed among the Pima Indians.

Epifil: a dynamic model of infection and disease in lymphatic filariasis.

The lack of a quantitative framework that describes the dynamic relationships between infection and morbidity has constrained efforts aimed at the community-level control of lymphatic filariasis. In this paper, we describe the development and validation of EPIFIL, a dynamic model of filariasis infection intensity and chronic disease. Infection dynamics are modeled using the well established immigration-death formulation, incorporating the acquisition of immunity to infective larvae over time. The dynamics of disease (lymphodema and hydrocele) are modeled as a catalytic function of a variety of factors, including worm load and the impact of immunopathological responses. The model was parameterized using age-stratified data collected from a Bancroftian filariasis endemic area in Pondicherry in southern India. The fitted parameters suggest that a relatively simple model including only acquired immunity to infection and irreversible progression to disease can satisfactorily explain the observed infection and disease patterns. Disease progression is assumed to be a consequence of worm induced damage and to occur at a high rate for hydrocele and a low rate for lymphodema. This suggests that immunopathology involvement may not be a necessary component of observed age-disease profiles. These findings support a central role for worm burden in the initiation and progression of chronic filarial disease.

A common variant in PPP1R3 associated with insulin resistance and type 2 diabetes.

Selected candidate genes have been analyzed in the Pima Indians of Arizona based on evidence that insulin resistance and type 2 diabetes have significant genetic determinants. An amino acid substitution at codon 905 of the glycogen-targeting subunit of type 1 protein phosphatase that regulates skeletal muscle glycogenesis was recently reported to be associated with changes in insulin action in Danish subjects. In addition to the variant at 905, we report here a novel substitution at codon 883 and common variant of an "ATTTA" element in the 3'-untranslated region (UTR) of the corresponding gene (PPP1R3). The 3'-UTR variant resembled the mRNA-destabilizing AT(AU)-rich elements (AREs) and resulted in a 10-fold difference in reporter mRNA half-life, was correlated with PPP1R3 transcript and protein concentrations in vivo, and was associated with insulin resistance and type 2 diabetes in the Pimas. The variant is more common in Pimas (0.56) than in Caucasians (0.40). Because of its apparent effect on expression of PPP1R3, it may, in part, contribute to the higher prevalence of type 2 diabetes in this Native American population.