Vector Competence Research Articles

Diagnosis of Imported Dengue and Zika Virus Infections in Italy from November 2015 to November 2022: Laboratory Surveillance Data from a National Reference Laboratory.

Dengue (DENV) and Zika (ZIKV) viruses are mosquito-borne human pathogens. In Italy, the presence of the competent vector Aedes albopictus increases the risk of autochthonous transmission, and a national plan for arboviruses prevention, surveillance, and response (PNA 2020-2025) is in place. The results of laboratory diagnosis of both viruses by the National Reference Laboratory for arboviruses (NRLA) from November 2015 to November 2022 are presented. Samples from 655 suspected cases were tested by both molecular and serological assays. Virus and antibody kinetics, cross-reactivity, and diagnostic performance of IgM ELISA systems were analysed. Of 524 cases tested for DENV, 146 were classified as confirmed, 7 as probable, while 371 were excluded. Of 619 cases tested for ZIKV, 44 were classified as confirmed, while 492 were excluded. All cases were imported. Overall, 75.3% (110/146) of DENV and 50% (22/44) of ZIKV cases were confirmed through direct virus detection methods. High percentages of cross reactivity were observed between the two viruses. The median lag time from symptoms onset to sample collection was 7 days for both DENV molecular (range 0-20) and NS1 ELISA (range 0-48) tests, with high percentages of positivity also after 7 days (39% and 67%, respectively). For ZIKV, the median lag time was 5 days (range 0-22), with 16% positivity after 7 days. Diagnostic performance was assessed with negative predictive values ranging from 92% to 95% for the anti-DENV systems, and of 97% for the ZIKV one. Lower positive predictive values were seen in the tested population (DENV: 55% to 91%, ZIKV: 50%). DENV and ZIKV diagnosis by molecular test is the gold standard, but sample collection time is a limitation. Serological tests, including Plaque Reduction Neutralization Test, are thus necessary. Co-circulation and cross-reactivity between the two viruses increase diagnostic difficulty. Continuous evaluation of diagnostic strategies is essential to improve laboratory testing.

Ehrlichia chaffeensis Co-Opts Phagocytic Hemocytes for Systemic Dissemination in the Lone Star Tick, Amblyomma americanum

Introduction: Hematophagous arthropods can acquire and transmit several pathogens of medical importance. In ticks, the innate immune system is crucial in the outcome between vector-pathogen interaction and overall vector competence. However, the specific immune response(s) elicited by the immune cells known as hemocytes remains largely undefined in Ehrlichia chaffeensis and its competent tick vector, Amblyomma americanum. Methods: We utilized injection of clodronate liposome to deplete tick granulocytes combined with infection with E. chaffeensis to demonstrate their essential role in microbial infection. Results: Here, we show that granulocytes, professional phagocytic cells, are integral in eliciting immune responses against commensal and pathogen infection. The chemical depletion of granulocytes led to decreased phagocytic efficiency of tissue-associated hemocytes. We demonstrate that E. chaffeensis can infect circulating hemocytes, and both cell-free plasma and hemocytes from E. chaffeensis-infected ticks can establish Ehrlichia infection in recipient ticks. Lastly, we provide evidence to show that granulocytes play a dual role in E. chaffeensis infection. Depleting granulocytic hemocytes increased Ehrlichia load in the salivary gland and midgut tissues. In contrast, granulocyte depletion led to a reduced systemic load of Ehrlichia. Conclusion: This study has identified multiple roles for granulocytic hemocytes in the control and systemic dissemination of E. chaffeensis infection.

Intrinsic factors driving mosquito vector competence and viral evolution: a review.

Mosquitoes are responsible for the transmission of numerous viruses of global health significance. The term "vector competence" describes the intrinsic ability of an arthropod vector to transmit an infectious agent. Prior to transmission, the mosquito itself presents a complex and hostile environment through which a virus must transit to ensure propagation and transmission to the next host. Viruses imbibed in an infectious blood meal must pass in and out of the mosquito midgut, traffic through the body cavity or hemocoel, invade the salivary glands, and be expelled with the saliva when the vector takes a subsequent blood meal. Viruses encounter physical, cellular, microbial, and immunological barriers, which are influenced by the genetic background of the mosquito vector as well as environmental conditions. Collectively, these factors place significant selective pressure on the virus that impact its evolution and transmission. Here, we provide an overview of the current state of the field in understanding the mosquito-specific factors that underpin vector competence and how each of these mechanisms may influence virus evolution.

Mosquito-Borne Arboviruses Occurrence and Distribution in the Last Three Decades in Central Africa: A Systematic Literature Review.

Arboviruses represent a real public health problem globally and in the Central African subregion in particular, which represents a high-risk zone for the emergence and re-emergence of arbovirus outbreaks. Furthermore, an updated review on the current arbovirus burden and associated mosquito vectors is lacking for this region. To contribute to filling this knowledge gap, the current study was designed with the following objectives: (i) to systematically review data on the occurrence and distribution of arboviruses and mosquito fauna; and (ii) to identify potential spillover mosquito species in the Central African region in the last 30 years. A web search enabled the documentation of 2454 articles from different online databases. The preferred reporting items for systematic reviews and meta-analyses (PRISMA) and the quality of reporting of meta-analyses (QUORUM) steps for a systematic review enabled the selection of 164 articles that fulfilled our selection criteria. Of the six arboviruses (dengue virus (DENV), chikungunya virus (CHIKV), yellow fever virus (YFV), Zika virus (ZIKV), Rift Valley fever virus (RVFV), and West Nile virus (WNV)) of public health concern studied, the most frequently reported were chikungunya and dengue. The entomological records showed >248 species of mosquitoes regrouped under 15 genera, with Anopheles (n = 100 species), Culex (n = 56 species), and Aedes (n = 52 species) having high species diversity. Three genera were rarely represented, with only one species included, namely, Orthopodomyia, Lutzia, and Verrallina, but individuals of the genera Toxorhinchites and Finlayas were not identified at the species level. We found that two Aedes species (Ae. aegypti and Ae. albopictus) colonised the same microhabitat and were involved in major epidemics of the six medically important arboviruses, and other less-frequently identified mosquito genera consisted of competent species and were associated with outbreaks of medical and zoonotic arboviruses. The present study reveals a high species richness of competent mosquito vectors that could lead to the spillover of medically important arboviruses in the region. Although epidemiological studies were found, they were not regularly documented, and this also applies to vector competence and transmission studies. Future studies will consider unpublished information in dissertations and technical reports from different countries to allow their information to be more consistent. A regional project, entitled "Ecology of Arboviruses" (EcoVir), is underway in three countries (Gabon, Benin, and Cote d'Ivoire) to generate a more comprehensive epidemiological and entomological data on this topic.

Implications of migratory and exotic birds and the mosquito community on West Nile virus transmission

Background Vector-borne diseases like West Nile virus (WNV) pose a global health challenge, with rising incidence and distribution. Culex mosquitoes are crucial WNV vectors. Avian species composition and bird community diversity, along with vector communities, influence WNV transmission patterns. However, limited knowledge exists on their impact in southwestern Spain, an area with active WNV circulation in wild birds, mosquitoes, and humans. Methods To address this, we conducted a comprehensive study investigating the contributions of migratory and exotic bird species to WNV transmission and the influence of mosquito community composition. Results Analysing 1194 serum samples from 44 avian species, we detected WNV antibodies in 32 samples from 11 species, four for the first time in Europe. Migratory birds had higher WNV exposure likelihood than native and exotic species, and higher phylogenetic diversity in bird communities correlated with lower exposure rates. Moreover, in 5859 female mosquitoes belonging to 12 species, we identified WNV competent vectors like Cx. pipiens s.l. and the Univittatus subgroup. Birds with WNV antibodies were positively associated with competent vector abundance, but negatively with overall mosquito species richness. Conclusions These findings highlight the complex interactions between bird species, their phylogenetics, and mosquito vectors in WNV transmission. Understanding these dynamics will help to implement effective disease control strategies in southwestern Spain.

Genetic characterization of the complete genome of a strain of Chikungunya virus circulating in Brazil

The Chikungunya virus (CHIKV) is a single-stranded positive-sense RNA virus that belongs to the Alphavirus genus of the Togaviridae family. It is primarily transmitted by Aedes aegypti and albopictus mosquitoes. Its genome encodes four non-structural proteins (NSP 1-4) and three structural proteins (C, E1, and E2). Four lineages of this virus have been identified, namely the West African, East African, Central and South African (ECSA), Asian (AL), and Indian Ocean Lineages (IOL). CHIKV is an endemic arbovirus circulating in 51 countries in the Americas. Clinical manifestations attributed to it include high fever, rash, myalgia, and episodes of arthralgia, which subsequently lead to chronic pain and disability, especially in the joints. Sequencing the complete genome of the Chikungunya virus is essential to understand its biology, evolution, and spread and to develop effective strategies for prevention, diagnosis, and treatment. This information is crucial for combating the disease and minimizing its impact on public health. For these reasons, the complete genome of the Chikungunya virus strain br33, identified in the northeastern city of Recife, in the state of Pernambuco, Brazil, was sequenced. The genome has a size of 11,601 nucleotides and contains coding regions for two polyproteins. A phylogenetic analysis indicates that the recent Brazilian strain of CHIKV belongs to the East, Central, and South African lineage (ECSA). This phylogenetic identification is important because this particular genotype has been associated with greater damage and clinical severity. Until 2016, the CHIKV virus was directly associated with travel, and its transmission was limited. Subsequently, the largest outbreak occurred in the state associated with the introduction of a new ECSA lineage, as identified in this study. It is highly likely that new CHIKV outbreaks will occur in the near future due to the abundance of competent vectors in Brazil and a susceptible population, exposing more than 11 million inhabitants to an increasing risk of infection.

The impact of anthropogenic climate change on pediatric viral diseases.

The adverse effects of climate change on human health are unfolding in real time. Environmental fragmentation is amplifying spillover of viruses from wildlife to humans. Increasing temperatures are expanding mosquito and tick habitats, introducing vector-borne viruses into immunologically susceptible populations. More frequent flooding is spreading water-borne viral pathogens, while prolonged droughts reduce regional capacity to prevent and respond to disease outbreaks with adequate water, sanitation, and hygiene resources. Worsening air quality and altered transmission seasons due to an increasingly volatile climate may exacerbate the impacts of respiratory viruses. Furthermore, both extreme weather events and long-term climate variation are causing the destruction of health systems and large-scale migrations, reshaping health care delivery in the face of an evolving global burden of viral disease. Because of their immunological immaturity, differences in physiology (e.g., size), dependence on caregivers, and behavioral traits, children are particularly vulnerable to climate change. This investigation into the unique pediatric viral threats posed by an increasingly inhospitable world elucidates potential avenues of targeted programming and uncovers future research questions to effect equitable, actionable change. IMPACT: A review of the effects of climate change on viral threats to pediatric health, including zoonotic, vector-borne, water-borne, and respiratory viruses, as well as distal threats related to climate-induced migration and health systems. A unique focus on viruses offers a more in-depth look at the effect of climate change on vector competence, viral particle survival, co-morbidities, and host behavior. An examination of children as a particularly vulnerable population provokes programming tailored to their unique set of vulnerabilities and encourages reflection on equitable climate adaptation frameworks.

Dehydration stress and Mayaro virus vector competence in Aedes aegypti.

Relative humidity (RH) is an environmental variable that affects mosquito physiology and can impact pathogen transmission. Low RH can induce dehydration in mosquitoes, leading to alterations in physiological and behavioral responses such as blood-feeding and host-seeking behavior. We evaluated the effects of a temporal drop in RH (RH shock) on mortality and Mayaro virus vector competence in Ae. aegypti. While dehydration induced by humidity shock did not impact virus infection, we detected a significant effect of dehydration on mosquito mortality and blood-feeding frequency, which could significantly impact transmission dynamics.

Dirofilaria immitis in Italian Cats and the Risk of Exposure by Aedes albopictus.

Background: Dirofilaria immitis, the agent of canine and feline heartworm disease (HWD), is a widespread mosquito-borne helminth. The true prevalence of HW infection in cats is likely underestimated due to the difficulty in establishing a definitive diagnosis. Aedes albopictus, a recognized competent vector for D. immitis, is currently considered the most invasive mosquito species worldwide and Italy presents the highest abundance of Ae. albopictus in Europe. Materials and Methods: The present study was aimed at evaluating the current seroprevalence of D. immitis antibodies in cats in Italy. Further, the ecological niche model (ENM) was applied to evaluate the potential future risk of feline HWD associated with the presence of Ae. albopictus. Results: Sera of 812 Italian cats were analyzed, and the average prevalence of D. immitis antibodies was 12%. Seropositivity was significantly associated with age (<6 years), whereas there was no association with sex or geographical area. Data obtained with the risk map showed that the highest risk of infection was found in northern inland areas and along coastal areas, whereas the lowest risk was identified at higher altitudes. The ENM correctly classified most of the areas where D. immitis seropositive cats were found, with 80.4% occurring in high and very high-risk areas. Conclusions: Results of the present study suggest that cats in Italy are exposed to D. immitis infection, and that routine prevention should be part of the general health care protocols in cats. Moreover, the resulting risk maps indicate that areas with a suitable habitat for Ae. albopictus may put cats at risk of exposure to D. immitis.

Detection of a novel Babesia sp. in Amblyomma javanense, an ectoparasite of Sunda pangolins

BackgroundBabesia is a protozoal, tick-borne parasite that can cause life-threatening disease in humans, wildlife and domestic animals worldwide. However, in Southeast Asia, little is known about the prevalence and diversity of Babesia species present in wildlife and the tick vectors responsible for its transmission. Recently, a novel Babesia species was reported in confiscated Sunda pangolins (Manis javanica) in Thailand. To investigate the presence of this parasite in Singapore, we conducted a molecular survey of Babesia spp. in free-roaming Sunda pangolins and their main ectoparasite, the Amblyomma javanense tick.MethodsTicks and tissue samples were opportunistically collected from live and dead Sunda pangolins and screened using a PCR assay targeting the 18S rRNA gene of Babesia spp. DNA barcoding of the cytochrome oxidase subunit I (COI) mitochondrial gene was used to confirm the species of ticks that were Babesia positive.ResultsA total of 296 ticks and 40 tissue samples were obtained from 21 Sunda pangolins throughout the 1-year study period. Babesia DNA was detected in five A. javanense ticks (minimum infection rate = 1.7%) and in nine different pangolins (52.9%) located across the country. Phylogenetic analysis revealed that the Babesia 18S sequences obtained from these samples grouped into a single monophyletic clade together with those derived from Sunda pangolins in Thailand and that this evolutionarily distinct species is basal to the Babesia sensu stricto clade, which encompasses a range of Babesia species that infect both domestic and wildlife vertebrate hosts.ConclusionsThis is the first report documenting the detection of a Babesia species in A. javanense ticks, the main ectoparasite of Sunda pangolins. While our results showed that A. javanense can carry this novel Babesia sp., additional confirmatory studies are required to demonstrate vector competency. Further studies are also necessary to investigate the role of other transmission pathways given the low infection rate of ticks in relation to the high infection rate of Sunda pangolins. Although it appears that this novel Babesia sp. is of little to no pathogenicity to Sunda pangolins, its potential to cause disease in other animals or humans cannot be ruled out.Graphical abstract

Development and pre-clinical evaluation of a Zika virus diagnostic for low resource settings.

Zika virus (ZIKV) is a re-emerging flavivirus that poses a significant public health threat. ZIKV exhibits a wide array of non-vector borne human transmission routes, such as sexual transmission, transplacental transmission and blood transfusion. Detection and surveillance of ZIKV is considered paramount in prevention of major outbreaks. With the majority of cases reported in low-resource locations, simple, low-cost detection methods are considered highly desirable. Here we have developed a sensitive and specific ZIKV diagnostic using reverse transcription recombinase-aided amplification (RT-RAA) coupled with lateral flow detection (LFD) targeting a highly conserved region of the ZIKV NS1 gene. We show our rapid, isothermal-ZIKV-diagnostic (Iso-ZIKV-Dx) can detect 500 copies of synthetic ZIKV RNA/μL in under 30 min at a constant 39°C. Using simulated urine samples, we observed that Iso-ZIKV-Dx also detects as low as 34.28 RNA copies/reaction of ZIKV (MR766 strain). Specificity testing confirmed that our test does not detect any co-circulating flaviviruses (dengue, West Nile, Japanese encephalitis, Murray Valley encephalitis and yellow fever viruses) or chikungunya virus. Sample processing results show complete inactivation of ZIKV (MR766 strain) in 5 min at room temperature using our novel viral RNA sample preparation reagent. Furthermore, lateral flow strips testing demonstrates positive diagnoses in as little as 5 min in running buffer. Contrary to conventional RT-qPCR, our Iso-ZIKV-Dx does not require expensive machinery, specialised laboratory settings or extensively trained personnel. Pre-clinical evaluation demonstrates that our test exhibits robust, in-field capabilities without compromising sensitivity or specificity. When compared to the gold-standard RT-qPCR, our Iso-ZIKV-Dx test offers an array of applications that extend beyond diagnostics alone, including potential for surveillance and monitoring of ZIKV vector competency.

Identifying Knowledge Gaps through the Systematic Review of Temperature-Driven Variability in the Competence of Aedes aegypti and Ae. albopictus for Chikungunya Virus.

Temperature is a well-known effector of several transmission factors of mosquito-borne viruses, including within mosquito dynamics. These dynamics are often characterized by vector competence and the extrinsic incubation period (EIP). Vector competence is the intrinsic ability of a mosquito population to become infected with and transmit a virus, while EIP is the time it takes for the virus to reach the salivary glands and be expectorated following an infectious bloodmeal. Temperatures outside the optimal range act on life traits, decreasing transmission potential, while increasing temperature within the optimal range correlates to increasing vector competence and a decreased EIP. These relatively well-studied effects of other Aedes borne viruses (dengue and Zika) are used to make predictions about transmission efficiency, including the challenges presented by urban heat islands and climate change. However, the knowledge of temperature and chikungunya (CHIKV) dynamics within its two primary vectors-Ae. aegypti and Ae. albopictus-remains less characterized, even though CHIKV remains a virus of public-health importance. Here, we review the literature and summarize the state of the literature on CHIKV and temperature dependence of vector competence and EIP and use these data to demonstrate how the remaining knowledge gap might confound the ability to adequately predict and, thus, prepare for future outbreaks.

Aedes aegypti microbiome composition covaries with the density of Wolbachia infection

BackgroundWolbachia is a widespread bacterial endosymbiont that can inhibit vector competency when stably transinfected into the mosquito, Aedes aegypti, a primary vector of the dengue virus (DENV) and other arboviruses. Although a complete mechanistic understanding of pathogen blocking is lacking, it is likely to involve host immunity induction and resource competition between Wolbachia and DENV, both of which may be impacted by microbiome composition. The potential impact of Wolbachia transinfection on host fitness is also of importance given the widespread release of mosquitos infected with the Drosophila melanogaster strain of Wolbachia (wMel) in wild populations. Here, population-level genomic data from Ae. aegypti was surveyed to establish the relationship between the density of wMel infection and the composition of the host microbiome.ResultsAnalysis of genomic data from 172 Ae. aegypti females across six populations resulted in an expanded and quantitatively refined, species-level characterization of the bacterial, archaeal, and fungal microbiome. This included 844 species of bacteria across 23 phyla, of which 54 species were found to be ubiquitous microbiome members across these populations. The density of wMel infection was highly variable between individuals and negatively correlated with microbiome diversity. Network analyses revealed wMel as a hub comprised solely of negative interactions with other bacterial species. This contrasted with the large and highly interconnected network of other microbiome species that may represent members of the midgut microbiome community in this population.ConclusionOur bioinformatic survey provided a species-level characterization of Ae. aegypti microbiome composition and variation. wMel load varied substantially across populations and individuals and, importantly, wMel was a major hub of a negative interactions across the microbiome. These interactions may be an inherent consequence of heightened pathogen blocking in densely infected individuals or, alternatively, may result from antagonistic Wolbachia-incompatible bacteria that could impede the efficacy of wMel as a biological control agent in future applications. The relationship between wMel infection variation and the microbiome warrants further investigation in the context of developing wMel as a multivalent control agent against other arboviruses.AACNEMfgWJ36enPNiFi-k-Video

MOLECULAR CHARACTERIZATION OF DENGUE VIRUS AND VECTORIAL COMPETENCE OF AEDES MOSQUITOES: A LOCAL MODEL OF XENOMONITORING

Dengue is a major public health concern throughout tropical and sub-tropical regions of the world. Dengue virus is transmitted by infected female mosquitoes mainly of the species of Aedes aegypti and Ae. albopictus.Vector of Aedes mosquito populations may present different levels of competence for arbovirus transmission.Therefore, this study aimed at detecting DENV serotypes circulating and vectorial competence of adult field collected Aedes populations from selected local government areas of Kaduna State, Nigeria. A total of 233 mosquitoes were collected, identified morphologically to species level using coloured identification keys of Rueda and dissected under a dissecting microscope each species identified was tested in a pools of 20 individuals. Their bodies and head/salivary glands were separated and transferred to separate microtubes. RNA extraction was done using viral RNA extraction kit and semi-nested reverse transcription-polymerase chain reaction (RT-PCR) was used to amplified for DENV serotypes in the head/salivary glands of the Aedes mosquitoes. The study morphologically identified Ae. aegypti, Ae. vittatus and Ae. Furcifer. Aedes aegypti is the most abundant species 77.3%(180/233) while Ae. furcifer 10.3% (24/233) were the least. DENV serotypes were detected in 76.9%(10/13) of the pools of Aedes mosquitoes in the study areas. DENV1-3 serotypes were detected in Ae. Aegypti, DENV2 was detected in Ae. vittatus and DENV 2 and 3 were detected in Ae. Furcifer. Dengue virus 2 was the most detected serotypes in the study areas. PCR pools screening infectivity prevalence were found to be 7.07% (95% CI- 3.38-11.77). Thus, the finding...

The mosquito Aedes aegypti requires a gut microbiota for normal fecundity, longevity and vector competence

Mosquitoes shift from detritus-feeding larvae to blood-feeding adults that can vector pathogens to humans and other vertebrates. The sugar and blood meals adults consume are rich in carbohydrates and protein but are deficient in other nutrients including B vitamins. Facultatively hematophagous insects like mosquitoes have been hypothesized to avoid B vitamin deficiencies by carryover of resources from the larval stage. However, prior experimental studies have also used adults with a gut microbiota that could provision B vitamins. Here, we used Aedes aegypti, which is the primary vector of dengue virus (DENV), to ask if carryover effects enable normal function in adults with no microbiota. We show that adults with no gut microbiota produce fewer eggs, live longer with lower metabolic rates, and exhibit reduced DENV vector competence but are rescued by provisioning B vitamins or recolonizing the gut with B vitamin autotrophs. We conclude carryover effects do not enable normal function.

Attractive targeted sugar bait: the pyrrole insecticide chlorfenapyr and the anti-malarial pharmaceutical artemether–lumefantrine arrest Plasmodium falciparum development inside wild pyrethroid-resistant Anopheles gambiae s.s. mosquitoes

BackgroundAttractive targeted sugar bait (ATSB) is a novel approach to vector control, offering an alternative mode of insecticide delivery via the insect alimentary canal, with potential to deliver a variety of compounds new to medical entomology and malaria control. Its potential to control mosquitoes was recently demonstrated in major field trials in Africa. The pyrrole chlorfenapyr is an insecticide new to malaria vector control, and through its unique mode of action—disruption of ATP mediated energy transfer in mitochondria—it may have direct action on energy transfer in the flight muscle cells of mosquitoes. It may also have potential to disrupt mitochondrial function in malarial parasites co-existing within the infected mosquito. However, little is known about the impact of such compounds on vector competence in mosquitoes responsible for malaria transmission.MethodsIn this study, ATSBs containing chlorfenapyr insecticide and, as a positive control, the anti-malarial drugs artemether/lumefantrine (A/L) were compared for their effect on Plasmodium falciparum development in wild pyrethroid-resistant Anopheles gambiae sensu stricto (s.s.) and for their capacity to reduce vector competence. Female mosquitoes were exposed to ATSB containing either sublethal dose of chlorfenapyr (CFP: 0.025%) or concentrations of A/L ranging from 0.4/2.4 mg/ml to 2.4/14.4 mg/ml, either shortly before or after taking infective blood meals. The impact of their component compounds on the prevalence and intensity of P. falciparum infection were compared between treatments.ResultsBoth the prevalence and intensity of infection were significantly reduced in mosquitoes exposed to either A/L or chlorfenapyr, compared to unexposed negative control mosquitoes. The A/L dose (2.4/14.4 mg/ml) totally erased P. falciparum parasites: 0% prevalence of infection in female mosquitoes exposed compared to 62% of infection in negative controls (df = 1, χ2 = 31.23 p < 0.001). The dose of chlorfenapyr (0.025%) that killed < 20% females in ATSB showed a reduction in oocyte density of 95% per midgut (0.18/3.43 per midgut).ConclusionThese results are evidence that chlorfenapyr, in addition to its direct killing effect on the vector, has the capacity to block Plasmodium transmission by interfering with oocyte development inside pyrethroid-resistant mosquitoes, and through this dual action may potentiate its impact under field conditions.

Genus Culex Linnaeus, 1758 (Diptera: Culicidae) as an Important Potential Arbovirus Vector in Brazil: An Integrative Review.

The genus Culex has 817 species subdivided into 28 subgenera. It has a cosmopolitan distribution, being most abundant in countries with a tropical climate. Understanding the ecology and diversity of viruses circulating in the species of this genus is important for understanding their role as arbovirus vectors in Brazil. To conduct an integrative review to identify the importance of the Culex genus as arbovirus vectors in Brazil. A search was carried out for scientific papers in the PubMed, BVSalud, Patuá-IEC and International Catalogue of Arboviruses: including certain other viruses of vertebrates databases. 36 publications describing arbovirus detections in Culex mosquitoes collected in the field in Brazil were evaluated. A total of 42 arbovirus species were detected, as well as studies analyzing the vector competence of C. quinquefasciatus for the transmission of four different arboviruses. The study of the Culex genus and its role as a vector of arboviruses in Brazil is essential for understanding transmission cycles, with the main aim of reducing cases of human infection. Thus, entomovirological surveillance guides the implementation of actions to detect circulating arboviruses among vectors to anticipate measures aimed at preventing or reducing the risk of arbovirus outbreaks in the country.

Cell fusing agent virus isolated from Aag2 cells does not vertically transmit in Aedes aegypti via artificial infection

BackgroundCell fusing agent virus (CFAV) was the first insect-specific virus to be characterized, and has been reported to negatively influence the growth of arboviruses such as dengue, Zika, and La Cross, making it a promising biocontrol agent for mosquito-borne disease prevention. Aedes aegypti Aag2 cells were naturally infected with CFAV. However, the ability of this virus to stably colonize an Ae. aegypti population via artificial infection and how it influences the vector competence of this mosquito have yet to be demonstrated.MethodsCFAV used in this study was harvested from Aag2 cells and its complete genome sequence was obtained by polymerase chain reaction and rapid amplification of complementary DNA ends, followed by Sanger sequencing. Phylogenetic analysis of newly identified CFAV sequences and other sequences retrieved from GenBank was performed. CFAV stock was inoculated into Ae. aegypti by intrathoracic injection, the survival of parental mosquitoes was monitored and CFAV copies in the whole bodies, ovaries, and carcasses of the injected F0 generation and in the whole bodies of the F1 generation on different days were examined by reverse transcription-quantitative polymerase chain reaction.ResultsThe virus harvested from Aag2 cells comprised a mixture of three CFAV strains. All genome sequences of CFAV derived from Aag2 cells clustered into one clade but were far from those isolated or identified from Ae. aegypti. Aag2-derived CFAV efficiently replicated in the mosquito body and did not attenuate the survival of Ae. aegypti. However, the viral load in the ovarian tissues was much lower than that in other tissues and the virus could not passage to the offspring by vertical transmission.ConclusionsThe results of this study demonstrate that Aag2-derived CFAV was not vertically transmitted in Ae. aegypti and provide valuable information on the colonization of mosquitoes by this virus.Graphical abstract

Increased blood meal size and feeding frequency compromise Aedes aegypti midgut integrity and enhance dengue virus dissemination.

Aedes aegypti is a highly efficient vector for numerous pathogenic arboviruses including dengue virus (DENV), Zika virus, and yellow fever virus. This efficiency can in part be attributed to their frequent feeding behavior. We previously found that acquisition of a second, full, non-infectious blood meal could accelerate virus dissemination within the mosquito by temporarily compromising midgut basal lamina integrity; however, in the wild, mosquitoes are often interrupted during feeding and only acquire partial or minimal blood meals. To explore the impact of this feeding behavior further, we examined the effects of partial blood feeding on DENV dissemination rates and midgut basal lamina damage in Ae. aegypti. DENV-infected mosquitoes given a secondary partial blood meal had intermediate rates of dissemination and midgut basal lamina damage compared to single-fed and fully double-fed counterparts. Subsequently, we evaluated if basal lamina damage accumulated across feeding episodes. Interestingly, within 24 hours of feeding, damage was proportional to the number of blood meals imbibed; however, this additive effect returned to baseline levels by 96 hours. These data reveal that midgut basal lamina damage and rates of dissemination are proportional to feeding frequency and size, and further demonstrate the impact that mosquito feeding behavior has on vector competence and arbovirus epidemiology. This work has strong implications for our understanding of virus transmission in the field and will be useful when designing laboratory experiments and creating more accurate models of virus spread and maintenance.

Transmission of Xanthomonas albilineans by the spittlebug, Mahanarva fimbriolata (Hemiptera: Cercopidae), in Brazil: first report of an insect vector for the causal agent of sugarcane leaf scald.

Leaf scald is a destructive sugarcane disease caused by the bacterium Xanthomonas albilineans (Ashby) Dowson. This pathogen presents the gene cluster SPI-1 T3SS, a conserved feature in pathogens vectored by animals. In this study, the competence of Mahanarva fimbriolata (Stål), a spittlebug commonly found in sugarcane fields in Brazil, was evaluated for the transmission of X.albilineans. Artificial probing assays were conducted to investigate the ability of M. fimbriolata adults to acquire X.albilineans from artificial diets containing the pathogen with subsequent inoculation of X.albilineans into pathogen-free diets. Plant probing assays with M. fimbriolata adults were conducted to evaluate the acquisition of X. albilineans from diseased source plants and subsequent inoculation of healthy recipient sugarcane plants. The presence of X.albilineans DNA in saliva/diet mixtures of the artificial probing assays and both insects and plants of the plant probing assays were checked using TaqMan assays. The artificial probing assays showed that M. fimbriolata adults were able to acquire and inoculate X.albilineans in diets. Plant probing assays confirmed the competence of M. fimbriolata to transmit X.albilineans to sugarcane. Over the entire experiment, 42% of the insects had acquired the pathogen and successful inoculation of the pathogen occurred in 18% of the recipient-susceptible sugarcane plants at 72 or 96 h of inoculation access period. Assays evidenced the vector competence of M. fimbriolata for transmission of X.albilineans, opening new pathways for investigating the biology and the economic impacts of the interaction between X.albilineans and M. fimbriolata.