Eric Pearce Caragata

Wolbachia Blocks Currently Circulating Zika Virus Isolates in Brazilian Aedes aegypti Mosquitoes

Summary The recent association of Zika virus with cases of microcephaly has sparked a global health crisis and highlighted the need for mechanisms to combat the Zika vector, Aedes aegypti mosquitoes. Wolbachia pipientis, a bacterial endosymbiont of insect, has recently garnered attention as a mechanism for arbovirus control. Here we report that Aedes aegypti harboring Wolbachia are highly resistant to infection with two currently circulating Zika virus isolates from the recent Brazilian epidemic. Wolbachia-harboring mosquitoes displayed lower viral prevalence and intensity and decreased disseminated infection and, critically, did not carry infectious virus in the saliva, suggesting that viral transmission was blocked. Our data indicate that the use of Wolbachia-harboring mosquitoes could represent an effective mechanism to reduce Zika virus transmission and should be included as part of Zika control strategies.

Exploiting Intimate Relationships: Controlling Mosquito-Transmitted Disease with Wolbachia

Mosquito-transmitted diseases impose a growing burden on human health, and current control strategies have proven insufficient to stem the tide. The bacterium Wolbachia is a novel and promising form of control for mosquito-transmitted disease. It manipulates host biology, restricts infection with dengue and other pathogens, and alters host reproduction to promote rapid spread in the field. In this review, we examine how the intimate and diverse relationships formed between Wolbachia and their mosquito hosts can be exploited for disease control purposes. We consider these relationships in the context of recent developments, including successful field trials with Wolbachia-infected mosquitoes to combat dengue, and new Wolbachia infections in key malaria vectors, which have enhanced the disease control prospects of this unique bacterium.

From Lab to Field: The Influence of Urban Landscapes on the Invasive Potential of Wolbachia in Brazilian Aedes aegypti Mosquitoes

Background The symbiotic bacterium Wolbachia is currently being trialled as a biocontrol agent in several countries to reduce dengue transmission. Wolbachia can invade and spread to infect all individuals within wild mosquito populations, but requires a high rate of maternal transmission, strong cytoplasmic incompatibility and low fitness costs in the host in order to do so. Additionally, extensive differences in climate, field-release protocols, urbanization level and human density amongst the sites where this bacterium has been deployed have limited comparison and analysis of Wolbachia’s invasive potential. Methodology/Principal Findings We examined key phenotypic effects of the wMel Wolbachia strain in laboratory Aedes aegypti mosquitoes with a Brazilian genetic background to characterize its invasive potential. We show that the wMel strain causes strong cytoplasmic incompatibility, a high rate of maternal transmission and has no evident detrimental effect on host fecundity or fertility. Next, to understand the effects of different urban landscapes on the likelihood of mosquito survival, we performed mark-release-recapture experiments using Wolbachia-uninfected Brazilian mosquitoes in two areas of Rio de Janeiro where Wolbachia will be deployed in the future. We characterized the mosquito populations in relation to the socio-demographic conditions at these sites, and at three other future release areas. We then constructed mathematical models using both the laboratory and field data, and used these to describe the influence of urban environmental conditions on the likelihood that the Wolbachia infection frequency could reach 100% following mosquito release. We predict successful invasion at all five field sites, however the conditions by which this occurs vary greatly between sites, and are strongly influenced by the size of the local mosquito population. Conclusions/Significance Through analysis of laboratory, field and mathematical data, we show that the wMel strain of Wolbachia possesses the characteristics required to spread effectively in different urban socio-demographic environments in Rio de Janeiro, including those where mosquito releases from the Eliminate Dengue Program will take place.

Inhibition of Zika virus by Wolbachia in Aedes aegypti

Through association with cases of microcephaly in 2015, Zika virus (ZIKV) has transitioned from a relatively unknown mosquito-transmitted pathogen to a global health emergency, emphasizing the need to improve existing mosquito control programs to prevent future disease outbreaks. The response to Zika must involve a paradigm shift from traditional to novel methods of mosquito control, and according to the World Health Organization should incorporate the release of mosquitoes infected with the bacterial endosymbiont Wolbachia pipientis. In our recent paper [Dutra, HLC et al., Cell Host & Microbe 2016] we investigated the potential of Wolbachia infections in Aedes aegypti to restrict infection and transmission of Zika virus recently isolated in Brazil. Wolbachia is now well known for its ability to block or reduce infection with a variety of pathogens in different mosquito species including the dengue (DENV), yellow fever, and chikungunya viruses, and malaria-causing Plasmodium, and consequently has great potential to control mosquito-transmitted diseases across the globe. Our results demonstrated that the wMel Wolbachia strain in Brazilian Ae. aegypti is a strong inhibitor of ZIKV infection, and furthermore appears to prevent transmission of infectious viral particles in mosquito saliva, which highlights the bacterium’s suitability for more widespread use in Zika control.

Diet-Induced Nutritional Stress and Pathogen Interference in Wolbachia-Infected Aedes aegypti

The pathogen interference phenotype greatly restricts infection with dengue virus (DENV) and other pathogens in Wolbachia-infected Aedes aegypti, and is a vital component of Wolbachia-based mosquito control. Critically, the phenotype’s causal mechanism is complex and poorly understood, with recent evidence suggesting that the cause may be species specific. To better understand this important phenotype, we investigated the role of diet-induced nutritional stress on interference against DENV and the avian malarial parasite Plasmodium gallinaceum in Wolbachia-infected Ae. aegypti, and on physiological processes linked to the phenotype. Wolbachia-infected mosquitoes were fed one of four different concentrations of sucrose, and then challenged with either P. gallinaceum or DENV. Interference against P. gallinaceum was significantly weakened by the change in diet however there was no effect on DENV interference. Immune gene expression and H2O2 levels have previously been linked to pathogen interference. These traits were assayed for mosquitoes on each diet using RT-qPCR and the Amplex Red Hydrogen Peroxide/Peroxidase Assay Kit, and it was observed that the change in diet did not significantly affect immune expression, but low carbohydrate levels led to a loss of ROS induction in Wolbachia-infected mosquitoes. Our data suggest that host nutrition may not influence DENV interference for Wolbachia-infected mosquitoes, but Plasmodium interference may be linked to both nutrition and oxidative stress. This pathogen-specific response to nutritional change highlights the complex nature of interactions between Wolbachia and pathogens in mosquitoes.

Wolbachia infection in Aedes aegypti mosquitoes alters blood meal excretion and delays oviposition without affecting trypsin activity

Blood feeding in Aedes aegypti is essential for reproduction, but also permits the mosquito to act as a vector for key human pathogens such as the Zika and dengue viruses. Wolbachia pipientis is an endosymbiotic bacterium that can manipulate the biology of Aedes aegypti mosquitoes, making them less competent hosts for many pathogens. Yet while Wolbachia affects other aspects of host physiology, it is unclear whether it influences physiological processes associated with blood meal digestion. To that end, we examined the effects of wMel Wolbachia infection in Ae. aegypti, on survival post-blood feeding, blood meal excretion, rate of oviposition, expression levels of key genes involved in oogenesis, and activity levels of trypsin blood digestion enzymes. We observed that wMel infection altered the rate and duration of blood meal excretion, delayed the onset of oviposition and was associated with a greater number of eggs being laid later. wMel-infected Ae. aegypti also had lower levels of key yolk protein precursor genes necessary for oogenesis. However, all of these effects occurred without a change in trypsin activity. These results suggest that Wolbachia infection may disrupt normal metabolic processes associated with blood feeding and reproduction in Ae. aegypti.

The impact of Wolbachia infection on the rate of vertical transmission of dengue virus in Brazilian Aedes aegypti

BackgroundWolbachia pipientis is a common endosymbiotic bacterium of arthropods that strongly inhibits dengue virus (DENV) infection and transmission in the primary vector, the mosquito Aedes aegypti. For that reason, Wolbachia-infected Ae. aegypti are currently being released into the field as part of a novel strategy to reduce DENV transmission. However, there is evidence that DENV can be transmitted vertically from mother to progeny, and this may help the virus persist in nature in the absence of regular human transmission. The effect of Wolbachia infection on this process had not previously been examined.ResultsWe challenged Ae. aegypti with different Brazilian DENV isolates either by oral feeding or intrathoracic injection to ensure disseminated infection. We examined the effect of Wolbachia infection on the prevalence of DENV infection, and viral load in the ovaries. For orally infected mosquitoes, Wolbachia decreased the prevalence of infection by 71.29%, but there was no such effect when the virus was injected. Interestingly, regardless of the method of infection, Wolbachia infection strongly reduced DENV load in the ovaries. We then looked at the effect of Wolbachia on vertical transmission, where we observed only very low rates of vertical transmission. There was a trend towards lower rates in the presence of Wolbachia, with overall maximum likelihood estimate of infection rates of 5.04 per 1000 larvae for mosquitoes without Wolbachia, and 1.93 per 1000 larvae for Wolbachia-infected mosquitoes, after DENV injection. However, this effect was not statistically significant.ConclusionsOur data support the idea that vertical transmission of DENV is rare in nature, even in the absence of Wolbachia. Indeed, we observed that vertical transmission rates were low even when the midgut barrier was bypassed, which might help to explain why we only observed a trend towards lower vertical transmission rates in the presence of Wolbachia. Nevertheless, the low prevalence of disseminated DENV infection and lower DENV load in the ovaries supports the hypothesis that the presence of Wolbachia in Ae. aegypti would have an effect on the vertical transmission of DENV in the field.

Wolbachia: Influence on Pathogeny, Treatment, and Control of Arthropod-Borne Diseases

Wolbachia pipientis is a naturally occurring bacterial endosymbiont of insects and other invertebrates that has recently gained prominence as a means for the biological control of important disease vector species. In this chapter we describe the biology of Wolbachia, its varied relationship with the invertebrates it infects, and how this relationship is a useful tool that is currently being exploited by novel and inventive means to reduce the capacity of insects to serve as vectors for a variety of diseases including dengue fever, lymphatic filariasis, and potentially even malaria.

Using an Endosymbiont to Control Mosquito-Transmitted Disease

Abstract The bacterial endosymbiont Wolbachia pipientis, more commonly referred to as Wolbachia, represents a promising agent of mosquito biological control that could potentially reduce mortality and morbidity associated with mosquito-transmitted pathogens including the parasites that cause malaria, and the viruses that cause dengue, chikungunya, and West Nile fever. Recent evidence also suggests Wolbachia could be an effective means to limit transmission of Zika virus—a fact that will likely lead to more widespread use of the bacterium in mosquito control. In this chapter we will discuss potential approaches and issues associated with using Wolbachia as a disease-control agent in mosquitoes.