Invasions by Eurasian Avian Influenza Virus H6 Genes and Replacement of Its North American Clade

This study showed frequent cross-hemisphere virus movement, which can affect the risk posed to poultry and humans

Spatial Re-Establishment Dynamics of Local Populations of Vectors of Chagas Disease

Chagas disease is transmitted by blood-sucking bugs (vectors) and presents a severe public health threat in the Americas. Worldwide there are approximately 10 million people infected with Chagas disease, a disease for which there is currently no effective cure. Vector suppression is the main strategy to control the spread of this disease. Unfortunately, the vectors have been resurgent in some areas. It is important to understand the dynamics of reinfestation where it occurs. Here we show how different models fitted to patch-level bug infestation data can elucidate different aspects of re-establishment dynamics. Our results demonstrated a 6-month time lag between detection of a new infestation and dispersal events, seasonality in dispersal rates and effects of previous vector infestation on subsequent vector establishment rates. In addition we provide estimates of dispersal distances and the effect of insecticide spraying on rates of vector re-establishment. While some of our results confirm previous findings, the effects of season and previous infestation on bug establishment challenge our current understanding of T. infestans ecology and highlight important gaps in our knowledge of T. infestans dispersal

Emergence and Genetic Variation of Neuraminidase Stalk Deletions in Avian Influenza Viruses

When avian influenza viruses (AIVs) are transmitted from their reservoir hosts (wild waterfowl and shorebirds) to domestic bird species, they undergo genetic changes that have been linked to higher virulence and broader host range. Common genetic AIV modifications in viral proteins of poultry isolates are deletions in the stalk region of the neuraminidase (NA) and additions of glycosylation sites on the hemagglutinin (HA). Even though these NA deletion mutations occur in several AIV subtypes, they have not been analyzed comprehensively. In this study, 4,920 NA nucleotide sequences, 5,596 HA nucleotide and 4,702 HA amino acid sequences were analyzed to elucidate the widespread emergence of NA stalk deletions in gallinaceous hosts, the genetic polymorphism of the deletion patterns and association between the stalk deletions in NA and amino acid variants in HA. Forty-seven different NA stalk deletion patterns were identified in six NA subtypes, N1–N3 and N5–N7. An analysis that controlled for phylogenetic dependence due to shared ancestry showed that NA stalk deletions are statistically correlated with gallinaceous hosts and certain amino acid features on the HA protein. Those HA features included five glycosylation sites, one insertion and one deletion. The correlations between NA stalk deletions and HA features are HA-NA-subtype-specific. Our results demonstrate that stalk deletions in the NA proteins of AIV are relatively common. Understanding the NA stalk deletion and related HA features may be important for vaccine and drug development and could be useful in establishing effective early detection and warning systems for the poultry industry

The effect of intra- and interspecific aggression on patch residence time in Negev Desert gerbils: a competing risk analysis

We observed patch-use behavior by two gerbil species in a field setting and investigated how aggression and intrinsic decision-making interact to influence patch residence times. Results were interpreted by using a competing risk analysis model, which uniquely enabled us to estimate the intrinsic patch-leaving decisions independently of external interruptions of foraging bouts by aggression. The experiment was conducted in two 1-ha field enclosures completely surrounded by rodent-proof fences and included allopatric (only Gerbillus andersoni allenbyi) and sympatric (G. a. allenbyi and G. pyramidum) treatments. We predicted that increased food patch quality (i.e., habitat quality) should decrease intrinsic patch-leaving rates and increase rates of aggressive interactions involving the forager feeding in the patch (i.e., the occupant individual). We also anticipated that increasing population density should result in an increase in the rate of aggressive interactions involving the occupant individual. Our results supported the first two predictions, indicating a trade-off between foraging and aggression. However, the third prediction was realized only for G. a. allenbyi in allopatry. Furthermore, in allopatry, occupant G. a. allenbyi individuals with high competitive ranks were involved in aggressive interactions at lower rates than those with low competitive ranks. However, in sympatry, patch-use behavior of occupant G. a. allenbyi individuals was mainly influenced by aggressive behavior of G. pyramidum, which did not respond to their competitive rank. Thus, it should pay less for G. a. allenbyi to be aggressive in sympatric populations. The observed reduction in intraspecific aggression among individual G. a. allenbyi in the presence of G. pyramidum supports this assertion. We suggest that this reduction likely weakens the negative effect of intra- and interspecific density on the per capita growth rate of G. a. allenbyi. Because this would change the slope of the isocline of G. a. allenbyi, it could be an important mechanism promoting coexistence when habitat selection is constrained. Copyright 2003.aggression; competing risk method; intrinsic decision-making; patch residence time; patch use; survival analysis

Insights from quantitative and mathematical modelling on the proposed WHO 2030 goals for Chagas disease

Chagas disease (CD) persists as one of the neglected tropical diseases (NTDs) with a particularly large impact in the Americas. The World Health Organization (WHO) recently proposed goals for CD elimination as a public health problem to be reached by 2030 by means of achieving intradomiciliary transmission interruption (IDTI), blood transfusion and transplant transmission interruption, diagnostic and treatment scaling-up and prevention and control of congenital transmission. The NTD Modelling Consortium has developed mathematical models to study Trypanosoma cruzi transmission dynamics and the potential impact of control measures. Modelling insights have shown that IDTI is feasible in areas with sustained vector control programmes and no presence of native triatomine vector populations. However, IDTI in areas with native vectors it is not feasible in a sustainable manner. Combining vector control with trypanocidal treatment can reduce the timeframes necessary to reach operational thresholds for IDTI (<2% seroprevalence in children aged <5 years), but the most informative age groups for serological monitoring are yet to be identified. Measuring progress towards the 2030 goals will require availability of vector surveillance and seroprevalence data at a fine scale, and a more active surveillance system, as well as a better understanding of the risks of vector re-colonization and disease resurgence after vector control cessation. Also, achieving scaling-up in terms of access to treatment to the expected levels (75%) will require a substantial increase in screening asymptomatic populations, which is anticipated to become very costly as CD prevalence decreases. Further modelling work includes refining and extending mathematical models (including transmission dynamics and statistical frameworks) to predict transmission at a sub-national scale, and developing quantitative tools to inform IDTI certification, post-certification and re-certification protocols. Potential perverse incentives associated with operational thresholds are discussed. These modelling insights aim to inform discussions on the goals and treatment guidelines for CD.Fil: Cohen, Joel E. The Rockefeller University; Estados UnidosFil: zu Dohna, Heinrich. The Rockefeller University; Estados UnidosFil: Gurtler, Ricardo Esteban. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin

Consequences of body size variation among herbivores on the strength of plant-herbivore interactions in a seasonal environment

Individual-based model Food web interactions Frequency-dependence Non-linearity Body size variation a b s t r a c t Classical theory in community ecology assumes that smaller-scale details such as individual traits can be abstracted safely and that community dynamics can be simply characterized in terms of net changes in population densities. Here we use a mechanistic simulation model of a three-level food web to explore the effect of initial body size variation among herbivores on final plant abundance resulting from a non-linear relationship between population demography and body size. We show that initial herbivore body size variation has a negative effect on their survival and consequently a positive effect on the final plant biomass. We then use trait distribution, in combination with body size-survival and body size-fitness curves estimated through simulations, to generate predictions for comparison with observed food web effects. We show that, owing to frequency-dependence, our ability to predict herbivore population dynamics is limited. However, at the community-level, this frequency-dependence, as well as changes in herbivore population size, can be abstracted safely and the strength of plant-herbivore interactions can be simply predicted from initial body size distribution in combination with the survival curve. Our findings suggest a need to revisit classical theory in community ecology. Doing so will require the mechanistic study of population demography and experimental testing of the effect of trait variation on community dynamics. © 2007 Elsevier B.V. All rights reserved. Introduction The way in which different organizational levels (e.g., individual, population, community) combine to influence population and community dynamics remains a fundamental research question in ecolog

The environment and species affect gut bacteria composition in laboratory co-cultured Anopheles gambiae and Aedes albopictus mosquitoes

The midgut microbiota of disease vectors plays a critical role in the successful transmission of human pathogens. The environment influences the microbiota composition; however, the relative mosquito-species contribution has not been rigorously disentangled from the environmental contribution to the microbiota structure. Also, the extent to which the microbiota of the adult sugar food source and larval water can predict that of the adult midgut and vice versa is not fully understood. To address these relationships, larvae and adults of Anopheles gambiae and Aedes albopictus were either reared separately or in a co-rearing system, whereby aquatic and adult stages of both species shared the larval water and sugar food source, respectively. Despite being reared under identical conditions, clear intra- and interspecies differences in midgut microbiota-composition were observed across seven cohorts, collected at different time points over a period of eight months. Fitting a linear model separately for each OTU in the mosquito midgut showed that two OTUs significantly differed between the midguts of the two mosquito species. We also show an effect for the sugar food source and larval water on the adult midgut microbiota. Our findings suggest that the mosquito midgut microbiota is highly dynamic and controlled by multiple factors