9,207 research outputs found
Biological Control of the Chagas Disease Vector Triatoma infestans with the Entomopathogenic Fungus Beauveria bassiana Combined with an Aggregation Cue: Field, Laboratory and Mathematical Modeling Assessment
Background: Current Chagas disease vector control strategies, based on chemical insecticide spraying, are growingly threatened by the emergence of pyrethroid-resistant Triatoma infestans populations in the Gran Chaco region of South America. Methodology and findings: We have already shown that the entomopathogenic fungus Beauveria bassiana has the ability to breach the insect cuticle and is effective both against pyrethroid-susceptible and pyrethroid-resistant T. infestans, in laboratory as well as field assays. It is also known that T. infestans cuticle lipids play a major role as contact aggregation pheromones. We estimated the effectiveness of pheromonebased infection boxes containing B. bassiana spores to kill indoor bugs, and its effect on the vector population dynamics. Laboratory assays were performed to estimate the effect of fungal infection on female reproductive parameters. The effect of insect exuviae as an aggregation signal in the performance of the infection boxes was estimated both in the laboratory and in the field. We developed a stage-specific matrix model of T. infestans to describe the fungal infection effects on insect population dynamics, and to analyze the performance of the biopesticide device in vector biological control. Conclusions: The pheromone-containing infective box is a promising new tool against indoor populations of this Chagas disease vector, with the number of boxes per house being the main driver of the reduction of the total domestic bug population. This ecologically safe approach is the first proven alternative to chemical insecticides in the control of T. infestans. The advantageous reduction in vector population by delayedaction fungal biopesticides in a contained environment is here shown supported by mathematical modeling.Fil: Forlani, Lucas. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de Investigaciones BioquĂmicas de La Plata ; ArgentinaFil: Pedrini, Nicolás. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de Investigaciones BioquĂmicas de La Plata ; ArgentinaFil: Girotti, Juan Roberto. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de Investigaciones BioquĂmicas de La Plata ; ArgentinaFil: Mijailovsky, Sergio Javier. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de Investigaciones BioquĂmicas de La Plata ; ArgentinaFil: Cardozo, RubĂ©n Marino. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Salta. Instituto de PatologĂa Experimental. Universidad Nacional de Salta. Facultad de Ciencias de la Salud. Instituto de PatologĂa Experimental; Argentina. Provincia de Salta. Ministerio de Salud PĂşblica. CoordinaciĂłn de GestiĂłn EpidemiolĂłgica; ArgentinaFil: Gentile, Alberto G.. Provincia de Salta. Ministerio de Salud PĂşblica. CoordinaciĂłn de GestiĂłn EpidemiolĂłgica; ArgentinaFil: Hernández Suárez, Carlos. Universidad de Colima. Facultad de Ciencias; MĂ©xicoFil: Rabinovich, Jorge Eduardo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Centro de Estudios ParasitolĂłgicos y de Vectores. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Estudios ParasitolĂłgicos y de Vectores; ArgentinaFil: Juarez, Marta Patricia. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de Investigaciones BioquĂmicas de La Plata ; Argentin
Who acquires infection from whom and how? Disentangling multi-host and multi-mode transmission dynamics in the 'elimination' era
Multi-host infectious agents challenge our abilities to understand, predict and manage disease dynamics. Within this, many infectious agents are also able to use, simultaneously or sequentially, multiple modes of transmission. Furthermore, the relative importance of different host species and modes can itself be dynamic, with potential for switches and shifts in host range and/ or transmission mode in response to changing selective pressures, such as those imposed by disease control interventions. The epidemiology of such multi-host, multi-mode infectious agents thereby can involve a multi-faceted community of definitive and intermediate/secondary hosts or vectors, often together with infectious stages in the environment, all of which may represent potential targets, as well as specific challenges, particularly where disease elimination is proposed. Here, we explore, focusing on examples fromboth human and animal pathogen systems, why and how we should aim to disentangle and quantify the relative importance of multi-host multi-mode infectious agent transmission dynamics under contrasting conditions, and ultimately, how this can be used to help achieve efficient and effective disease control.
This article is part of the themed issue 'Opening the black box: re-examining the ecology and evolution of parasite transmission'
From eggs to bites: do ovitrap data provide reliable estimates of Aedes albopictus biting females?
Background. Aedes albopictus is an aggressive invasive mosquito species that represents
a serious health concern not only in tropical areas, but also in temperate regions due
to its role as vector of arboviruses. Estimates of mosquito biting rates are essential to
account for vector-human contact in models aimed to predict the risk of arbovirus
autochthonous transmission and outbreaks, as well as nuisance thresholds useful for
correct planning of mosquito control interventions. Methods targeting daytime and
outdoor biting Ae. albopictus females (e.g., Human Landing Collection, HLC) are
expensive and difficult to implement in large scale schemes. Instead, egg-collections
by ovitraps are the most widely used routine approach for large-scale monitoring of
the species. The aim of this work was to assess whether ovitrap data can be exploited
to estimate numbers of adult biting Ae. albopictus females and whether the resulting
relationship could be used to build risk models helpful for decision-makers in charge
of planning of mosquito-control activities in infested areas.
Method. Ovitrap collections and HLCs were carried out in hot-spots of Ae. albopictus
abundance in Rome (Italy) along a whole reproductive season. The relationship between
the two sets of data was assessed by generalized least square analysis, taking into account
meteorological parameters.
Result. The mean number of mosquito females/person collected by HLC in 150
(i.e.,
females/HLC) and the mean number of eggs/day were 18.9 ± 0.7 and 39.0 ± 2.0,
respectively. The regression models found a significant positive relationship between
the two sets of data and estimated an increase of one biting female/person every five
additional eggs found in ovitraps. Both observed and fitted values indicated presence of
adults in the absence of eggs in ovitraps. Notably, wide confidence intervals of estimates
of biting females based on eggs were observed. The patterns of exotic arbovirus outbreak
probability obtained by introducing these estimates in risk models were similar to those
based on females/HLC (R0 > 1 in 86% and 40% of sampling dates for Chikungunya and
Zika, respectively; R0 < 1 along the entire season for Dengue). Moreover, the model
predicted that in this case-study scenario an R0 > 1 for Chikungunya is also to be
expected when few/no eggs/day are collected by ovitraps.
Discussion. This work provides the first evidence of the possibility to predict mean
number of adult biting Ae. albopictus females based on mean number of eggs and to
compute the threshold of eggs/ovitrap associated to epidemiological risk of arbovirus
transmission in the study area. Overall, however, the large confidence intervals in the
model predictions represent a caveat regarding the reliability of monitoring schemes
based exclusively on ovitrap collections to estimate numbers of biting females and plan
control interventions
Chapter 9 Gene Drive Strategies for Population Replacement
Gene drive systems are selfish genetic elements capable of spreading into a population despite a fitness cost. A variety of these systems have been proposed for spreading disease-refractory genes into mosquito populations, thus reducing their ability to transmit diseases such as malaria and dengue fever to humans. Some have also been proposed for suppressing mosquito populations. We assess the alignment of these systems with design criteria for their safety and efficacy. Systems such as homing endonuclease genes, which manipulate inheritance through DNA cleavage and repair, are highly invasive and well-suited to population suppression efforts. Systems such as Medea, which use combinations of toxins and antidotes to favor their own inheritance, are highly stable and suitable for replacing mosquito populations with disease-refractory varieties. These systems offer much promise for future vector-borne disease control
Vector-borne diseases with non-stationary vector populations: the case of growing and decaying populations
Since the last century, deterministic compartmental models have emerged as
powerful tools to predict and control epidemic outbreaks, in many cases helping
to mitigate their impacts. A key quantity for these models is the so-called
Basic Reproduction Number, that measures the number of secondary infections
produced by an initial infected individual in a fully susceptible population.
Some methods have been developed to allow the direct computation of this
quantity provided that some conditions are fulfilled, such that the model has a
pre-pandemic disease-free equilibrium state. This condition is only fulfilled
when the populations are stationary. In the case of vector-borne diseases, this
implies that the vector birth and death rates need to be balanced, what is not
fulfilled in many realistic cases in which the vector population grow or
decrease. Here we develop a vector-borne epidemic model with growing and
decaying vector populations and study the conditions under which the standard
methods to compute work and discuss an alternative when they fail. We
also show that growing vector populations produce a delay in the epidemic
dynamics when compared to the case of the stationary vector population.
Finally, we discuss the conditions under which the model can be reduced to the
SIR model with fewer compartments and parameters, which helps in solving the
problem of parameter unidentifiability of many vector-borne epidemic models.Comment: 16 pages, 6 figure
Hybridization in parasites: consequences for adaptive evolution, pathogenesis and public health in a changing world
[No abstract available
Using A Dynamic Model To Assess Maintenance Of Deer Tick Virus Via Horizontal Transmission In Ixodes Scapularis Populations
IntroductionDeer Tick Virus—a lineage of Powassan Virus—is an emerging tick-borne flavivirus associated with high rates of morbidity and mortality. Although DTV infection is rare, there has been an observed increase in the number of human cases in recent decades, necessitating more public health attention. Ixodes scapularis ticks are known to be the primary vector of DTV. However, the enzootic cycle has yet to be fully characterized and there is evidence that horizontal transmission alone may be insufficient for DTV maintenance; it is hypothesized that vertical and co-feeding transmission are also necessary for sustained transmission.
MethodsA dynamic model was developed to analyze DTV maintenance in the absence of vertical and co-feeding transmission. Multiple parameters—including host population density, host-to-larva and nymph-to-host transmission rates, and duration of host viremia—were modified to assess their impact on DTV transmission dynamics.
Results/ConclusionsDTV infection rates within the I. scapularis population declined dramatically within the tick population during the first year of the model’s run-time, and DTV prevalence dropped to zero early in the second year. The model output indicates that, in isolation, horizontal transmission is unlikely to be sufficient for sustaining DTV long-term. A combination of increased duration of host viremia, host population density, and transmission rates resulted in DTV stability within the tick population over time. Therefore, in order for viremic transmission to act as the sole form of transmission in nature, a combination of parameters must be modified, including host density, host viremic period, and/or horizontal transmission rates
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