A commercial autogenous injection vaccine protects ballan wrasse (Labrus bergylta, Ascanius) against Aeromonas salmonicida vapA type V.

Atypical Aeromonas salmonicida (aAs) and Vibrionaceae related species are bacteria routinely recovered from diseased ballan wrasse used as cleaner fish in the Atlantic salmon farming industry. Autogenous (i.e. farm specific inactivated) multivalent vaccines formulated from these microorganisms are widely used to protect farmed wrasse despite limited experimental proof that they are primary pathogens. In this study, the components of a commercial multivalent injection vaccine containing four strains of Aeromonas salmonicida and one strain of Vibrio splendidus previously isolated from ballan wrasse in Scotland, were tested for infectivity, pathogenicity and virulence via intra peritoneal injection at pre-deployment size (25-50 g) and the efficacy of the vaccine for protection against aAs assessed. Injection with 3.5 × 109, 8 × 109 1.8 × 109 and 5 × 109 cfu/fish of Vibrio splendidus, V. ichthyoenteri, Aliivibrio logeii and A. salmonicida, respectively, did not cause significant mortalities, lesions or clinical signs after a period of 14 days. IP injection with both aAs and Photobacterium indicum successfully reproduced the clinical signs and internal lesions observed during natural outbreaks of the disease. Differences in virulence (LD50 at day 8-post infection of 3.6 × 106 cfu/fish and 1.6 × 107 cfu/fish) were observed for two aAs vapA type V isolates. In addition, the LD50 for Photobacterium indicum was 2.2 × 107 cfu/fish. The autogenous vaccine was highly protective against the two aAs vapA type V isolates after 700-degree days of immunisation. The RPSFINAL values for the first isolate were 95 and 91% at 1 × 106 cfu/fish and 1 × 107 cfu/fish, respectively, and 79% at 1 × 107 cfu/fish for the second isolate tested. In addition, significantly higher anti aAs seral antibodies (IgM), were detected by ELISA in vaccinated fish in contrast with control (mock vaccinated) fish. These results suggest wrasse can be effectively immunised and protected against aAs infection by injection with oil adjuvanted vaccines prepared with inactivated homologous isolates.

Disrupted seasonal biology impacts health, food security and ecosystems.

The rhythm of life on earth is shaped by seasonal changes in the environment. Plants and animals show profound annual cycles in physiology, health, morphology, behaviour and demography in response to environmental cues. Seasonal biology impacts ecosystems and agriculture, with consequences for humans and biodiversity. Human populations show robust annual rhythms in health and well-being, and the birth month can have lasting effects that persist throughout life. This review emphasizes the need for a better understanding of seasonal biology against the backdrop of its rapidly progressing disruption through climate change, human lifestyles and other anthropogenic impact. Climate change is modifying annual rhythms to which numerous organisms have adapted, with potential consequences for industries relating to health, ecosystems and food security. Disconcertingly, human lifestyles under artificial conditions of eternal summer provide the most extreme example for disconnect from natural seasons, making humans vulnerable to increased morbidity and mortality. In this review, we introduce scenarios of seasonal disruption, highlight key aspects of seasonal biology and summarize from biomedical, anthropological, veterinary, agricultural and environmental perspectives the recent evidence for seasonal desynchronization between environmental factors and internal rhythms. Because annual rhythms are pervasive across biological systems, they provide a common framework for trans-disciplinary research.

Low-coverage vaccination strategies for the conservation of endangered species.

The conventional objective of vaccination programmes is to eliminate infection by reducing the reproduction number of an infectious agent to less than one, which generally requires vaccination of the majority of individuals. In populations of endangered wildlife, the intervention required to deliver such coverage can be undesirable and impractical; however, endangered populations are increasingly threatened by outbreaks of infectious disease for which effective vaccines exist. As an alternative, wildlife epidemiologists could adopt a vaccination strategy that protects a population from the consequences of only the largest outbreaks of disease. Here we provide a successful example of this strategy in the Ethiopian wolf, the world's rarest canid, which persists in small subpopulations threatened by repeated outbreaks of rabies introduced by domestic dogs. On the basis of data from past outbreaks, we propose an approach that controls the spread of disease through habitat corridors between subpopulations and that requires only low vaccination coverage. This approach reduces the extent of rabies outbreaks and should significantly enhance the long-term persistence of the population. Our study shows that vaccination used to enhance metapopulation persistence through elimination of the largest outbreaks of disease requires lower coverage than the conventional objective of reducing the reproduction number of an infectious agent to less than one.

From phenotype to genotype: a Bayesian solution.

The study of biological systems commonly depends on inferring the state of a 'hidden' variable, such as an underlying genotype, from that of an 'observed' variable, such as an expressed phenotype. However, this cannot be achieved using traditional quantitative methods when more than one genetic mechanism exists for a single observable phenotype. Using a novel latent class Bayesian model, it is possible to infer the prevalence of different genetic elements in a population given a sample of phenotypes. As an exemplar, data comprising phenotypic resistance to six antimicrobials obtained from passive surveillance of Salmonella Typhimurium DT104 are analysed to infer the prevalence of individual resistance genes, as well as the prevalence of a genomic island known as SGI1 and its variants. Three competing models are fitted to the data and distinguished between using posterior predictive p-values to assess their ability to predict the observed number of unique phenotypes. The results suggest that several SGI1 variants circulate in a few fixed forms through the population from which our data were derived. The methods presented could be applied to other types of phenotypic data, and represent a useful and generic mechanism of inferring the genetic population structure of organisms.

Critical interplay between parasite differentiation, host immunity, and antigenic variation in trypanosome infections.

Increasing availability of pathogen genomic data offers new opportunities to understand the fundamental mechanisms of immune evasion and pathogen population dynamics during chronic infection. Motivated by the growing knowledge on the antigenic variation system of the sleeping sickness parasite, the African trypanosome, we introduce a mechanistic framework for modeling within-host infection dynamics. Our analysis focuses first on a single parasitemia peak and then on the dynamics of multiple peaks that rely on stochastic switching between groups of parasite variants. A major feature of trypanosome infections is the interaction between variant-specific host immunity and density-dependent parasite differentiation to transmission life stages. In this study, we investigate how the interplay between these two types of control depends on the modular structure of the parasite antigenic archive. Our model shows that the degree of synchronization in stochastic variant emergence determines the relative dominance of general over specific control within a single peak. A requirement for multiple-peak dynamics is a critical switch rate between blocks of antigenic variants, which implies constraints on variant surface glycoprotein (VSG) archive genetic diversification. Our study illustrates the importance of quantifying the links between parasite genetics and within-host dynamics and provides insights into the evolution of trypanosomes.

Population biology of multihost pathogens.

The majority of pathogens, including many of medical and veterinary importance, can infect more than one species of host. Population biology has yet to explain why perceived evolutionary advantages of pathogen specialization are, in practice, outweighed by those of generalization. Factors that predispose pathogens to generalism include high levels of genetic diversity and abundant opportunities for cross-species transmission, and the taxonomic distributions of generalists and specialists appear to reflect these factors. Generalism also has consequences for the evolution of virulence and for pathogen epidemiology, making both much less predictable. The evolutionary advantages and disadvantages of generalism are so finely balanced that even closely related pathogens can have very different host range sizes.

Dynamics of the 2001 UK foot and mouth epidemic: stochastic dispersal in a heterogeneous landscape.

Foot-and-mouth is one of the world's most economically important livestock diseases. We developed an individual farm-based stochastic model of the current UK epidemic. The fine grain of the epidemiological data reveals the infection dynamics at an unusually high spatiotemporal resolution. We show that the spatial distribution, size, and species composition of farms all influence the observed pattern and regional variability of outbreaks. The other key dynamical component is long-tailed stochastic dispersal of infection, combining frequent local movements with occasional long jumps. We assess the history and possible duration of the epidemic, the performance of control strategies, and general implications for disease dynamics in space and time.

Overviews of pathogen emergence: which pathogens emerge, when and why?

An emerging pathogen has been defined as the causative agent of an infectious disease whose incidence is increasing following its appearance in a new host population or whose incidence is increasing in an existing population as a result of long-term changes in its underlying epidemiology (Woolhouse and Dye 2001). Although we appear to be in a period where novel diseases are appearing and old diseases are spreading at an unprecedented rate, disease emergence per se is not a new phenomenon. It is almost certain that disease emergence is a routine event in the evolutionary ecology of pathogens, and part of a ubiquitous response of pathogen populations to shifting arrays of host species. While our knowledge of emerging diseases is, for the most part, limited to the time span of the human lineage, this history provides us with a modern reflection of these deeper evolutionary processes, and it is clear from this record that at many times throughout human history, demographic and behavioural changes in society have provided opportunities for pathogens to emerge.

Molecular characterization of SAT-2 foot-and-mouth disease virus isolates obtained from cattle during a four-month period in 2001 in Limpopo Province, South Africa.

Foot-and-mouth disease (FMD) is an acute, highly contagious viral infection of domestic and wild cloven-hoofed animals. The virus is a single-stranded RNA virus that has a high rate of nucleotide mutation and amino acid substitution. In southern Africa the South African Territories (SAT) 1-3 serotypes of FMD virus are maintained by large numbers of African buffaloes (Syncerus caffer), which provide a potential source of infection for domestic livestock and wild animals. During February 2001, an outbreak of SAT-2 was recorded in cattle in the FMD control zone of South Africa, adjacent to the Kruger National Park (KNP). They had not been vaccinated against the disease since they form the buffer between the vaccination and free zones but in the face of the outbreak, they were vaccinated as part of the control measures to contain the disease. The virus was, however, isolated from some of them on several occasions up to May 2001. These isolates were characterized to determine the rate of genetic change in the main antigenic determinant, the 1 D/2A gene. Nucleotide substitutions at 12 different sites were identified of which five led to amino acid changes. Three of these occurred in known antigenic sites, viz. the GH-loop and C-terminal part of the protein, and two of these have previously been shown to be subject to positive selection. Likelihood models indicated that the ratio of non-synonymous to synonymous changes among the outbreak sequences recovered from cattle was four times higher than among comparable sequences isolated from wildlife, suggesting that the virus may be under greater selective pressure during rapid transmission events.

Molecular epidemiology identifies only a single rabies virus variant circulating in complex carnivore communities of the Serengeti.

Understanding the transmission dynamics of generalist pathogens that infect multiple host species is essential for their effective control. Only by identifying those host populations that are critical to the permanent maintenance of the pathogen, as opposed to populations in which outbreaks are the result of 'spillover' infections, can control measures be appropriately directed. Rabies virus is capable of infecting a wide range of host species, but in many ecosystems, particular variants circulate among only a limited range of potential host populations. The Serengeti ecosystem (in northwestern Tanzania) supports a complex community of wild carnivores that are threatened by generalist pathogens that also circulate in domestic dog populations surrounding the park boundaries. While the combined assemblage of host species appears capable of permanently maintaining rabies in the ecosystem, little is known about the patterns of circulation within and between these host populations. Here we use molecular phylogenetics to test whether distinct virus-host associations occur in this species-rich carnivore community. Our analysis identifies a single major variant belonging to the group of southern Africa canid-associated viruses (Africa 1b) to be circulating within this ecosystem, and no evidence for species-specific grouping. A statistical parsimony analysis of nucleoprotein and glycoprotein gene sequence data is consistent with both within- and between-species transmission events. While likely differential sampling effort between host species precludes a definitive inference, the results are most consistent with dogs comprising the reservoir of rabies and emphasize the importance of applying control efforts in dog populations.

Characterisation of a SAT-1 outbreak of foot-and-mouth disease in captive African buffalo (Syncerus caffer): clinical symptoms, genetic characterisation and phylogenetic comparison of outbreak isolates.

African buffalo (Syncerus caffer) play an important role in the maintenance of the SAT types of foot-and-mouth disease (FMD) in southern Africa. These long-term carriers mostly become sub-clinically infected, maintaining the disease and posing a threat to other susceptible wildlife and domestic species. During an unrelated bovine tuberculosis experiment using captive buffalo in the Kruger National Park (KNP), an outbreak of SAT-1 occurred and was further investigated. The clinical signs were recorded and all animals demonstrated significant weight loss and lymphopenia that lasted 100 days. In addition, the mean cell volume and mean cell haemoglobin values were significantly higher than before the outbreak started. Virus was isolated from several buffalo over a period of 167 days post infection and the molecular clock estimated to be 3 x 10(-5) nucleotide substitutions per site per day. Seven amino acid changes occurred of which four occurred in hypervariable regions previously described for SAT-1. The genetic relationship of the outbreak virus was compared to buffalo viruses previously obtained from the KNP but the phylogeny was largely unresolved, therefore the relationship of this outbreak strain to others isolated from the KNP remains unclear.

One Health contributions towards more effective and equitable approaches to health in low- and middle-income countries.

Emerging zoonoses with pandemic potential are a stated priority for the global health security agenda, but endemic zoonoses also have a major societal impact in low-resource settings. Although many endemic zoonoses can be treated, timely diagnosis and appropriate clinical management of human cases is often challenging. Preventive 'One Health' interventions, e.g. interventions in animal populations that generate human health benefits, may provide a useful approach to overcoming some of these challenges. Effective strategies, such as animal vaccination, already exist for the prevention, control and elimination of many endemic zoonoses, including rabies, and several livestock zoonoses (e.g. brucellosis, leptospirosis, Q fever) that are important causes of human febrile illness and livestock productivity losses in low- and middle-income countries. We make the case that, for these diseases, One Health interventions have the potential to be more effective and generate more equitable benefits for human health and livelihoods, particularly in rural areas, than approaches that rely exclusively on treatment of human cases. We hypothesize that applying One Health interventions to tackle these health challenges will help to build trust, community engagement and cross-sectoral collaboration, which will in turn strengthen the capacity of fragile health systems to respond to the threat of emerging zoonoses and other future health challenges. One Health interventions thus have the potential to align the ongoing needs of disadvantaged communities with the concerns of the broader global community, providing a pragmatic and equitable approach to meeting the global goals for sustainable development and supporting the global health security agenda.This article is part of the themed issue 'One Health for a changing world: zoonoses, ecosystems and human well-being'.

A centuries-long epidemic of scrapie in British sheep?

The apparent persistence of scrapie in British sheep for more than 250 years is difficult to explain. Susceptibility to scrapie is associated with particular alleles at a single locus, the PrP gene. As the only known effect of these alleles is to confer susceptibility to a fatal disease, natural selection is expected to reduce their frequency, as has been observed in practice during scrapie outbreaks in single sheep flocks. Susceptibility alleles, and hence scrapie itself, are therefore expected to become rare, yet the disease remains widespread. We suggest that the paradox of scrapie's persistence can be explained by the exceptionally long time-scales inherent in the epidemiology of the disease. It is proposed that scrapie should be regarded as epidemic in British sheep but, unlike more familiar epidemics, which have time-scales of months or years, the scrapie epidemic has a time-scale of centuries. This interpretation implies that scrapie should eventually disappear from the sheep population.

The influence of n-alkanols on the capacity per unit area of planar lipid bilayers.

The electrical capacities per unit area of planar lipid bilayers formed from monoolein/n-hexadecane, monoolein/ squalane (or squalene) and monoolein/triolein have been measured in the presence of a range of n-alkanols. For monoolein/n-hexadecane bilayers, the effects of the n-alkanols are complicated but can be rationalized in terms of the likely changes in lipid chain order and the influence of the n-alkanol in the Plateau-Gibbs border. Monoolein/ squalane (or squalene) and monoolein/triolein bilayers exhibit behaviour quite different from the n-hexadecane membranes. For both the squalane and triolein bilayers the shorter chain alkanols increase the capacity per unit area while the longer homologues have little effect. These results help to account for the influence of the n-alkanols on gramicidin single-channel lifetimes.

Surface potential changes in lipid monolayers and the 'cut-off' in anaesthetic effects of N-alkanols.

The effects of 0.09 saturated solutions of the n-alkanols n-hexanol to n-tridecanol on the surface (compensation) potential of lipid monolayers have been examined. Actions on monolayers spread from pure egg phosphatidylcholine have been compared with effects on a system containing 2:1 mole ratio of egg phosphatidylcholine and cholesterol. The mean compensation potential for the pure phospholipid system was 475 +/- 9 mV; addition of cholesterol increased the potential to 503 +/- 10 mV. All n-alkanols tested reduced the surface potential in both systems. The reduction was larger in the pure phospholipid system but the difference in effect between lipid systems declined as the n-alkanol chainlength increased, becoming negligible by n-tridecanol. These results are considered in relation to the 'cut-off' in biological activity of n-alkanols around n-tridecanol.

The interaction of n-octanol with black lipid bilayer membranes.

The electrical capacities of black lipid films formed from monoolein + n-hexadecane and monoolein + squalane (or squalene) solutions have been measured in the presence of various concentrations of n-octanol. In addition, partition coefficients for n-octanol between n-hexadecane and 0.1 M NaCl, dielectric constants for octanol-hexadecane mixtures and the interfacial tension of films and film-forming lipid solutions against the aqueous phases have been determined. It is concluded that in "solvent-free" bilayers the octanol is unlikely to have changed the bilayer thickness by more than about 1 A. The bilayer tension, on the other hand, increases appreciably in the presence of octanol.

Kinetics and stability of alamethicin conducting channels in lipid bilayers.

It is already well-established that conduction in lipid bilayers containing alamethicin arises from the presence of complexes in which there are several molecules of the polypeptide. It is with the nature of these complexes that this paper is primarily concerned. While it is clear that increasing alamethicin concentration and increasing potential across the membrane favour their formation, the nature of the reactions involved has not yet been elucidated. Attempts have therefore been made to clarify the sequence of events leading to the establishment of a complex in its conducting state. It has been concluded that the most likely mechanism involves, initially, a non-field-dependent aggregation of the alamethicin, in the plane of the membrane, into non-conducting oligomers. These then appear to undergo movement normal to the membrane (which is field dependent) to form the conducting species. Temperature studies have shown that the various conducting states of the oligomer have effectively equal enthalpies, and that the activation energies for transitions between these states are all approx. 1.2kcal/mol. The corresponding rate constants are very sensitive to the lipid composition of the membrane and a variety of different systems has been examined in order to clarify the origins of this effect. The only conclusion from this part of the work is that lipid fluidity might be involved.

The adsorption of lysine vasopressin at ionized interfaces.

It has been shown by surface potential measurements that lysine vasopressin and oxytocin may be bound by ionic surfaces to very varied extents. To dodecyl sulphate and phosphatidylserine monolayers the binding is very strong and is comparable to that for biological receptors such as those in toad bladder. For dioleyl phosphate and the carboxyl group of the polypeptide alamethicin, the binding is rather weaker while, for the zwitterionic lipids phosphatidylcholine and phosphatidylethanolamine, and for the erythrocyte surface, which contains two varieties of carboxylic acid group, no interaction seems to take place. In no system does the lysyl amino group of the vasopressin appear necessary for adsorption and, in the dodecyl sulphate monolayers, the interaction is strong even when the ionization of the terminal alpha-amino group is suppressed.

The effects of homologous series of anaesthetics on a resting potassium conductance of the squid giant axon.

The effects of n-alkanes (n-pentane to n-octane), n-alkanols (n-pentanol to n-undecanol) and two carboxylic esters (methyl pentanoate and methyl octanoate) on the conductance of squid giant axons in a high potassium, zero sodium bathing solution have been examined. Sodium and delayed rectifier potassium channels were as far as possible pharmacologically blocked. A substantial fraction of the measured conductance is attributed to a recently-described, voltage-independent, potassium channel. Anaesthetics block this channel but its sensitivity is markedly different from those of other squid axon ion channels.