Domestic Dogs as Sentinels for West Nile Virus but not Aedes-borne Flaviviruses, Mexico

We tested 294 domestic pet dogs in Mexico for neutralizing antibodies for mosquito-borne flaviviruses. We found high (42.6%) exposure to West Nile virus in Reynosa (northern Mexico) and low (1.2%) exposure in Tuxtla Gutierrez (southern Mexico) but very limited exposure to Aedes-borne flaviviruses. Domestic dogs may be useful sentinels for West Nile virus.

Meta-Analysis of the Relative Abundance of Nuisance and Vector Mosquitoes in Urban and Blue-Green Spaces

Blue-green spaces (BGSs), urban areas characterized by the presence of vegetation and or water, and infrastructure form a potential solution for public health threats from increasing urbanization. We conducted a meta-analysis to test the hypothesis that blue-green spaces increase the abundance of nuisance and vector mosquito species compared to non-greened urban areas. After screening 7306 studies published since 1992, we identified 18 studies containing sufficient data from both traditional urban areas and BGSs. We found no significant difference in mean abundance of all mosquito taxa in three genera (Aedes, Culex, Anopheles) when comparing blue-green spaces and non-greened urban spaces. Similarly, a separate analysis of each individual genera found no significant differences. An analysis of the taxa by larval habitat guilds found no differences for container-breeding mosquitoes. Flood-water species tended to be more abundant in blue-green spaces, but the differences were not significant. The individual taxa of Aedes albopictus and the Culex pipiens complex showed no differences between blue-green and urban spaces, while the abundance of Aedes aegypti was significantly higher in traditional urban spaces. Due to the variety existing between and among the several types of blue-green spaces, further studies comparing each unique type of blue-green space or infrastructure will be necessary to draw conclusions regarding the influence of each structure on for urban mosquito communities.

Anopheles albimanus (Diptera: Culicidae) Ensemble Distribution Modeling: Applications for Malaria Elimination

Simple Summary

Costa Rica is near malaria elimination. However, sporadic outbreaks still occur, and while control strategies have been focused on delivering efficient treatments for infected patients, an open question is whether control measures targeting the dominant vector, Anopheles albimanus, are appropriately designed given their ecology and distribution. Here, we illustrate the use of an ensemble species distribution model (SDM) as a tool to assess the potential exposure to An. albimanus in palm and pineapple plantations, and to also assess the potential involvement of this mosquito vector in transmission foci where entomological surveillance is not feasible. We found that both oil palm and pineapple plantations are very likely to harbor An. albimanus. By contrast, environments at the Crucitas open-pit gold mine, the epicenter of malaria transmission in 2018 and 2019, have low suitability for this mosquito species. Our results suggest that medium to high resolution SDMs can be used to plan vector control activities. Finally, we discuss the high suitability of oil palm and pineapple plantations for An. albimanus in reference to recently developed social science theory about the Plantationocene.

Abstract

In the absence of entomological information, tools for predicting Anopheles spp. presence can help evaluate the entomological risk of malaria transmission. Here, we illustrate how species distribution models (SDM) could quantify potential dominant vector species presence in malaria elimination settings. We fitted a 250 m resolution ensemble SDM for Anopheles albimanus Wiedemann. The ensemble SDM included predictions based on seven different algorithms, 110 occurrence records and 70 model projections. SDM covariates included nine environmental variables that were selected based on their importance from an original set of 28 layers that included remotely and spatially interpolated locally measured variables for the land surface of Costa Rica. Goodness of fit for the ensemble SDM was very high, with a minimum AUC of 0.79. We used the resulting ensemble SDM to evaluate differences in habitat suitability (HS) between commercial plantations and surrounding landscapes, finding a higher HS in pineapple and oil palm plantations, suggestive of An. albimanus presence, than in surrounding landscapes. The ensemble SDM suggested a low HS for An. albimanus at the presumed epicenter of malaria transmission during 2018–2019 in Costa Rica, yet this vector was likely present at the two main towns also affected by the epidemic. Our results illustrate how ensemble SDMs in malaria elimination settings can provide information that could help to improve vector surveillance and control.

Public Acceptance of and Willingness to Pay for Mosquito Control, Texas, USA

Mosquito control is essential to reduce vectorborne disease risk. We surveyed residents in Harris, Tarrant, and Hidalgo Counties, Texas, USA, to estimate willingness-to-pay for mosquito control and acceptance of control methods. Results show an unmet demand for expanded mosquito control that could be funded through local taxes or fees.

The effect of anticoagulants in artificial blood meals on the mortality, fecundity, and fertility of Culex quinquefasciatus and Aedes aegypti (Culicidae)

Blood sources used for insect colonies and their effects on fecundity and fertility have been studied in multiple mosquito species, but the effect of anticoagulants that prevent clotting of blood has received minimal attention. Here, we identify the effect two anticoagulants have on the mortality, fecundity, and fertility of Culex quinquefasciatus (Sebring and BCS strains) and Aedes aegypti Liverpool. Each mosquito species was provided with one of three treatments: direct feeding on live chicken (LC), blood from freshly exsanguinated chicken treated with heparin (EXS) or commercially purchased chicken blood treated with Alsever's solution (ART). No significant effect of treatment on mortality was observed. Both Cx. quinquefasciatus Sebring and BCS strains demonstrated a significant effect of treatment type on fecundity with the number of eggs laid for LC being 1.40-fold higher than EXS and 2.14-fold higher than ART for Sebring. For BCS strain mosquitoes, LC was 1.55-fold higher than ART, and EXS was 1.57-fold higher than ART, but there was no significant difference between LC and EXS. For Ae. aegypti mosquitoes, only a significant difference in mean egg counts was observed between LC and ART treatments, with LC laying 1.46-fold more eggs. No significant effect on fertility was observed among any mosquitoes for any treatment. These results demonstrate the negative effect of anticoagulants on the fecundity for multiple mosquito taxa. This may affect the ability of labs to produce large numbers of mosquitoes or colonize wild mosquito populations and should be taken into account when considering colony maintenance or vector biology research.

Variable coverage in an Autocidal Gravid Ovitrap intervention impacts efficacy of Aedes aegypti control

Control of the arboviral disease vector Aedes aegypti has shown variable levels of efficacy around the globe. We evaluated an Autocidal Gravid Ovitrap (AGO) intervention as a stand-alone control tool for population suppression of A. aegypti in US communities bordering Mexico.We conducted a cluster randomized crossover trial with weekly mosquito surveillance of sentinel households from July 2017 to December 2018. The intervention took place from August to December of both years. Multilevel models (generalized linear and additive mixed models) were used to analyse the changes in population abundance of female A. aegypti.We observed that female populations were being suppressed 77% (2018) and four times lower outdoor female abundance when AGO coverage (number of intervention AGO traps that surrounded a sentinel home) was high (2.7 AGOs/house). However, we also observed that areas with low intervention AGO coverage resulted in no difference (2017) or slightly higher abundance compared to the control. These results suggest that coverage rate might play a critical role on how populations of female A. aegypti are being modulated in the field. The lack of larval source habitat reduction and the short duration of the intervention period might have limited the A. aegypti population suppression observed in this study. Synthesis and applications. The mosquito, A. aegypti, is a public health concern in most tropical and subtropical regions. With the rise of insecticide resistance, the evaluation of non-chemical tools has become pivotal in the fight against arboviral disease transmission. Our study shows that the AGO intervention, as a stand-alone control tool, is limited by its coverage in human settlements. Vector control programmes should consider, that if the target coverage rate is not achieved, measures will be ineffective unless coupled with other control approaches. Although our multilevel modelling was focused on A. aegypti and the AGO, the approach can be applied to other mosquito vector species.

A proposed framework for the development and qualitative evaluation of West Nile virus models and their application to local public health decision-making

West Nile virus (WNV) is a globally distributed mosquito-borne virus of great public health concern. The number of WNV human cases and mosquito infection patterns vary in space and time. Many statistical models have been developed to understand and predict WNV geographic and temporal dynamics. However, these modeling efforts have been disjointed with little model comparison and inconsistent validation. In this paper, we describe a framework to unify and standardize WNV modeling efforts nationwide. WNV risk, detection, or warning models for this review were solicited from active research groups working in different regions of the United States. A total of 13 models were selected and described. The spatial and temporal scales of each model were compared to guide the timing and the locations for mosquito and virus surveillance, to support mosquito vector control decisions, and to assist in conducting public health outreach campaigns at multiple scales of decision-making. Our overarching goal is to bridge the existing gap between model development, which is usually conducted as an academic exercise, and practical model applications, which occur at state, tribal, local, or territorial public health and mosquito control agency levels. The proposed model assessment and comparison framework helps clarify the value of individual models for decision-making and identifies the appropriate temporal and spatial scope of each model. This qualitative evaluation clearly identifies gaps in linking models to applied decisions and sets the stage for a quantitative comparison of models. Specifically, whereas many coarse-grained models (county resolution or greater) have been developed, the greatest need is for fine-grained, short-term planning models (m-km, days-weeks) that remain scarce. We further recommend quantifying the value of information for each decision to identify decisions that would benefit most from model input.

Culex quinquefasciatus (Diptera: Culicidae) survivorship following the ingestion of bird blood infected with Haemoproteus sp. parasites

Arthropod vectors are frequently exposed to a diverse assemblage of parasites, but the consequence of these infections on their biology and behavior are poorly understood. We experimentally evaluated whether the ingestion of a common protozoan parasite of avian hosts (Haemoproteus spp.; Haemosporida: Haemoproteidae) impacted the survivorship of Culex quinquefasciatus (Say) (Diptera: Culicidae). Blood was collected from wild northern cardinals (Cardinalis cardinalis) in College Station, Texas, and screened for the presence of Haemoproteus spp. parasites using microscopic and molecular methods. Experimental groups of Cx. quinquefasciatus mosquitoes were offered Haemoproteus-positive cardinal blood through an artificial feeding apparatus, while control groups received Haemoproteus-negative cardinal blood or domestic canary (Serinus canaria domestica) blood. Culex quinquefasciatus mosquitoes exposed to Haemoproteus infected cardinal blood survived significantly fewer days than mosquitoes that ingested Haemoproteus-negative cardinal blood. The survival of mosquitoes fed on positive cardinal blood had a median survival time of 18 days post-exposure and the survival of mosquitoes fed on negative cardinal blood exceeded 50% across the 30 day observation period. Additionally, mosquitoes that fed on canary controls survived significantly fewer days than cardinal negative controls, with canary control mosquitoes having a median survival time of 17 days. This study further supports prior observations that Haemoproteus parasites can be pathogenic to bird-biting mosquitoes, and suggests that Haemoproteus parasites may indirectly suppress the transmission of co-circulating vector-borne pathogens by modulating vector survivorship. Our results also suggest that even in the absence of parasite infection, bloodmeals from different bird species can influence mosquito survivorship.

SARS-CoV-2 Infections and Viral Isolations among Serially Tested Cats and Dogs in Households with Infected Owners in Texas, USA

Understanding the ecological and epidemiological roles of pets in the transmission of SARS-CoV-2 is critical for animal and human health, identifying household reservoirs, and predicting the potential enzootic maintenance of the virus. We conducted a longitudinal household transmission study of 76 dogs and cats living with at least one SARS-CoV-2-infected human in Texas and found that 17 pets from 25.6% of 39 households met the national case definition for SARS-CoV-2 infections in animals. This includes three out of seventeen (17.6%) cats and one out of fifty-nine (1.7%) dogs that were positive by RT-PCR and sequencing, with the virus successfully isolated from the respiratory swabs of one cat and one dog. Whole-genome sequences of SARS-CoV-2 obtained from all four PCR-positive animals were unique variants grouping with genomes circulating among people with COVID-19 in Texas. Re-sampling showed persistence of viral RNA for at least 25 d-post initial test. Additionally, seven out of sixteen (43.8%) cats and seven out of fifty-nine (11.9%) dogs harbored SARS-CoV-2 neutralizing antibodies upon initial sampling, with relatively stable or increasing titers over the 2–3 months of follow-up and no evidence of seroreversion. The majority (82.4%) of infected pets were asymptomatic. ‘Reverse zoonotic’ transmission of SARS-CoV-2 from infected people to animals may occur more frequently than recognized.

SARS-CoV-2 B.1.1.7 variant of concern detected in a pet dog and cat after exposure to a person with COVID-19, USA

As part of a longitudinal household transmission study of pets living with persons with COVID‐19 in Texas, two pets were confirmed to be infected with the SARS‐CoV‐2 B.1.1.7 variant of concern (VOC). The pets were a dog and a cat from the same household, sampled two days after their owner tested positive for COVID‐19. The oral, nasal and fur swabs for both pets tested positive for SARS‐CoV‐2 by qRT‐PCR and consensus whole‐genome sequences from the dog and cat were 100% identical and matched the B.1.1.7 VOC. Virus was isolated from the cat's nasal swab. One month after initial detection of infection, the pets were re‐tested twice at which time only the fur swabs (both pets) and oral swab (dog only) remained positive, and neutralizing antibodies for SARS‐CoV‐2 were present in both animals. Sneezing by both pets was noted by the owner in the weeks between initial and follow‐up testing. This study documents the first detection of B.1.1.7. in companion animals in the United States, and the first genome recovery and isolation of B.1.1.7 variant of concern globally in any animal.

Global patterns of aegyptism without arbovirus

The world's most important mosquito vector of viruses, Aedes aegypti, is found around the world in tropical, subtropical and even some temperate locations. While climate change may limit populations of Ae. aegypti in some regions, increasing temperatures will likely expand its territory thus increasing risk of human exposure to arboviruses in places like Europe, Northern Australia and North America, among many others. Most studies of Ae. aegypti biology and virus transmission focus on locations with high endemicity or severe outbreaks of human amplified urban arboviruses, such as dengue, Zika, and chikungunya viruses, but rarely on areas at the margins of endemicity. The objective in this study is to explore previously published global patterns in the environmental suitability for Ae. aegypti and dengue virus to reveal deviations in the probability of the vector and human disease occurring. We developed a map showing one end of the gradient being higher suitability of Ae. aegypti with low suitability of dengue and the other end of the spectrum being equal and higher environmental suitability for both Ae. aegypti and dengue. The regions of the world with Ae. aegypti environmental suitability and no endemic dengue transmission exhibits a phenomenon we term 'aegyptism without arbovirus'. We then tested what environmental and socioeconomic variables influence this deviation map revealing a significant association with human population density, suggesting that locations with lower human population density were more likely to have a higher probability of aegyptism without arbovirus. Characterizing regions of the world with established populations of Ae. aegypti but little to no autochthonous transmission of human-amplified arboviruses is an important step in understanding and achieving aegyptism without arbovirus.

The Eco-Bio-Social Factors That Modulate Aedes aegypti Abundance in South Texas Border Communities

Simple Summary

The Aedes aegypti mosquito is distributed worldwide and has become a major public health concern due to its proclivity for the urban environment, human feeding behavior, and ability to transmit agents of diseases such as Zika, chikungunya, and dengue. In the continental United States, the region known as the Lower Rio Grande Valley is one of the few areas with local mosquito transmission of these pathogens transmitted by Ae. aegypti. With limited resources for mosquito control in this region, understanding the ecological, biological, and social factors that affect Ae. aegypti population can help guide and improve current control efforts. We were able to observe widespread knowledge regarding Zika, but with very low importance given to mosquitoes as a problem. We found that the presence of window-mounted air conditioning units, number of windows and doors, characteristics of the property, and presence of children in the household all influenced the abundance of Ae. aegypti. The current results not only show a need for improved community engagement for increasing disease and mosquito risk awareness, but also provide risk factors that can guide current vector control activities.

Abstract

Aedes aegypti control requires dedicated resources that are usually scarce, limiting the reach and sustainability of vector control programs. This generates a need to focus on areas at risk of disease transmission and also understand the factors that might modulate local mosquito abundance. We evaluated the eco-bio-social factors that modulate indoor and outdoor relative abundance of female Ae. aegypti in communities of South Texas. We conducted housing quality and Knowledge Attitudes and Practices surveys in households that were part of a weekly mosquito surveillance program in November of 2017 and 2018. Our results showed widespread knowledge of mosquitoes and Zika virus by our participants. However, less than 35% considered them as serious problems in this region. The presence of window-mounted air conditioning units increased the risk of female mosquito relative abundance indoors. An increase in outdoor relative abundance was associated with larger properties and a higher number of children between 6 to 17 years of age. Interestingly, we observed that an increasing number of children <5 years of age modulated both indoor and outdoor relative abundance, with a 52% increase indoors and 30% decrease outdoors. The low perception of mosquito and disease risk highlights engagement needs for vector-borne disease prevention in this region. The identified risk factors can help guide public health officials in their efforts to reduce human and vector contact.

Identification of Host Bloodmeal Source in Ornithodoros turicata Dugès (Ixodida: Argasidae) Using DNA-Based and Stable Isotope-Based Techniques

The ecology and host feeding patterns of many soft ticks (Ixodida: Argasidae) remain poorly understood. To address soft tick-host feeding associations, we fed Ornithodoros turicata Dugès on multiple host species and evaluated quantitative PCR (qPCR) and stable isotope analyses to identify the vertebrate species used for the bloodmeal. The results showed that a qPCR with host-specific probes for the cytochrome b gene successfully identified bloodmeals from chicken (Gallus gallus L.), goat (Capra aegagrus hircus L), and swine (Sus scrofa domesticus) beyond 330 days post-feeding and through multiple molting. Also, qPCR-based bloodmeal analyses could detect multiple host species within individual ticks that fed upon more than one species. The stable isotope bloodmeal analyses were based on variation in the natural abundance of carbon (13C/12C) and nitrogen (15N/14N) isotopes in ticks fed on different hosts. When compared to reference isotope signatures, this method discerned unique δ13C and δ15N signatures in the ticks fed on each host taxa yet could not discern multiple host species from O. turicata that fed on more than one host species. Given the significance of soft tick-borne zoonoses and animal diseases, elucidating host feeding patterns from field-collected ticks using these methods may provide insight for an ecological basis to disease management.

Host Bloodmeal Identification in Cave-Dwelling Ornithodoros turicata Dugès (Ixodida: Argasidae), Texas, USA

Tick-host bloodmeal associations are important factors when characterizing risks of associated pathogen transmission and applying appropriate management strategies. Despite their biological importance, comparatively little is known about soft tick (Argasidae) host associations in the United States compared to hard ticks (Ixodidae). In this study, we evaluated a PCR and direct Sanger sequencing method for identifying the bloodmeal hosts of soft ticks. We collected 381 cave-associated Ornithodoros turicata near San Antonio, Texas, USA, and also utilized eight colony-reared specimens fed artificially on known host blood sources over 1.5 years ago. We correctly identified the vertebrate host bloodmeals of two colony-reared ticks (chicken and pig) up to 1,105 days post-feeding, and identified bloodmeal hosts from 19 out of 168 field-collected soft ticks, including raccoon (78.9%), black vulture (10.5%), Texas black rattlesnake (5.3%), and human (5.3%). Our results confirm the retention of vertebrate blood DNA in soft ticks and advance the knowledge of argasid host associations in cave-dwelling O. turicata.

Vertebrate-Aedes aegypti and Culex quinquefasciatus (Diptera)-arbovirus transmission networks: Non-human feeding revealed by meta-barcoding and next-generation sequencing

Background

Aedes aegypti mosquito-borne viruses including Zika (ZIKV), dengue (DENV), yellow fever (YFV), and chikungunya (CHIKV) have emerged and re-emerged globally, resulting in an elevated burden of human disease. Aedes aegypti is found worldwide in tropical, sub-tropical, and temperate areas. The characterization of mosquito blood meals is essential to understand the transmission dynamics of mosquito-vectored pathogens.

Methodology/principal findings

Here, we report Ae. aegypti and Culex quinquefasciatus host feeding patterns and arbovirus transmission in Northern Mexico using a metabarcoding-like approach with next-generation deep sequencing technology. A total of 145 Ae. aegypti yielded a blood meal analysis result with 107 (73.8%) for a single vertebrate species and 38 (26.2%) for two or more. Among the single host blood meals for Ae. aegypti, 28.0% were from humans, 54.2% from dogs, 16.8% from cats, and 1.0% from tortoises. Among those with more than one species present, 65.9% were from humans and dogs. For Cx. quinquefasciatus, 388 individuals yielded information with 326 (84%) being from a single host and 63 (16.2%) being from two or more hosts. Of the single species blood meals, 77.9% were from dogs, 6.1% from chickens, 3.1% from house sparrows, 2.4% from humans, while the remaining 10.5% derived from other 12 host species. Among those which had fed on more than one species, 11% were from dogs and humans, and 89% of other host species combinations. Forage ratio analysis revealed dog as the most over-utilized host by Ae. aegypti (= 4.3) and Cx. quinquefasciatus (= 5.6) and the human blood index at 39% and 4%, respectively. A total of 2,941 host-seeking female Ae. aegypti and 3,536 Cx. quinquefasciatus mosquitoes were collected in the surveyed area. Of these, 118 Ae. aegypti pools and 37 Cx. quinquefasciatus pools were screened for seven arboviruses (ZIKV, DENV 1–4, CHIKV, and West Nile virus (WNV)) using qRT-PCR and none were positive (point prevalence = 0%). The 95%-exact upper limit confidence interval was 0.07% and 0.17% for Ae. aegypti and Cx. quinquefasciatus, respectively

Conclusions/significance

The low human blood feeding rate in Ae. aegypti, high rate of feeding on mammals by Cx. quinquefasciatus, and the potential risk to transmission dynamics of arboviruses in highly urbanized areas of Northern Mexico is discussed.

Elucidating arbovirus-vector-host contact networks is critical to understand and control mosquito-borne virus transmission, including pathogens such as ZIKV, DENV 1–4, CHIKV, and WNV. Here, we report the results of metabarcoding of blood meals of two primary pathogen mosquito vectors, Aedes aegypti and Culex quinquefasciatus. We found limited human blood feeding by Ae. aegypti and high preference for feeding on mammals by Cx. quinquefasciatus. Interestingly, blood meal analysis revealed dogs as the most utilized host for both vector species suggesting the potential for zooprophylaxis for human-amplified urban arboviruses. Pools of these vector species were tested for seven arboviruses and all were negative. We calculated vectorial capacity to discuss the potential risk and transmission dynamics of pathogens transmitted by these two important vectors in an urban location in Northern Mexico.

Natural SARS-CoV-2 infections, including virus isolation, among serially tested cats and dogs in households with confirmed human COVID-19 cases in Texas, USA

The natural infections and epidemiological roles of household pets in SARS-CoV-2 transmission are not understood. We conducted a longitudinal study of dogs and cats living with at least one SARS-CoV-2 infected human in Texas and found 47.1% of 17 cats and 15.3% of 59 dogs from 25.6% of 39 households were positive for SARS-CoV-2 via RT-PCR and genome sequencing or neutralizing antibodies. Virus was isolated from one cat. The majority (82.4%) of infected pets were asymptomatic. Re-sampling of one infected cat showed persistence of viral RNA at least 32 d-post human diagnosis (25 d-post initial test). Across 15 antibody-positive animals, titers increased (33.3%), decreased (33.3%) or were stable (33.3%) over time. A One Health approach is informative for prevention and control of SARS-CoV-2 transmission.

Sugar Feeding Patterns for Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae) Mosquitoes in South Texas

Effective mosquito surveillance and management depend on a thorough understanding of the biology and feeding patterns unique to species and sex. Given that a propensity to sugar feed is necessary for some mosquito surveillance and newer control strategies, we sought to document the amount of total sugar in wild Aedes aegypti (L.) and Culex quinquefasciatus (Say) captured from five different locations in the Lower Rio Grande Valley (LRGV) of South Texas over 2 yr. We used Biogents Sentinel 2 (BGS2) traps in year 1 and aspirators, BGS2, and CDC resting traps in years 2 and 3 to collect adult mosquitoes. The hot anthrone test was used to quantify total sugar content in each mosquito. Additionally, the cold and hot anthrone tests were used to distinguish fructose content from total sugars for mosquitoes captured in 2019. Overall, Ae. aegypti females had significantly lower total sugar content than Ae. aegypti males as well as both sexes of Cx. quinquefasciatus. However, the percentage of Ae. aegypti positive for fructose consumption was four to eightfold higher than Ae. aegypti previously reported in other regions. The difference between locations was significant for males of both species, but not for females. Seasonality and trapping method also revealed significant differences in sugar content of captured mosquitoes. Our results reinforce that sugar feeding in female Ae. aegypti is less than Cx. quinquefasciatus, although not absent. This study provides necessary data to evaluate the potential effectiveness of sugar baits in surveillance and control of both Ae. aegypti and Cx. quinquefasciatus mosquitoes.

Emergence of Arboviruses in the United States: The Boom and Bust of Funding, Innovation, and Capacity

Mosquito-borne viruses will continue to emerge and generate a significant public health burden around the globe. Here, we provide a longitudinal perspective on how the emergence of mosquito-borne viruses in the Americas has triggered reactionary funding by sponsored agencies, stimulating a number of publications, innovative development of traps, and augmented capacity. We discuss the return on investment (ROI) from the oscillation in federal funding that influences demand for surveillance and control traps and leads to innovation and research productivity.

Cell fusing agent virus (Flavivirus) infection in Aedes aegypti in Texas: seasonality, comparison by trap type, and individual viral loads

South Texas has experienced local transmission of Zika virus and of other mosquito-borne viruses such as chikungunya virus and dengue virus in the last decades. Using a mosquito surveillance program in the Lower Rio Grande Valley (LRGV) and San Antonio, TX, from 2016 to 2018, we detected the presence of an insect-specific virus, cell fusing agent virus (CFAV), in the Aedes aegypti mosquito population. We tested 6,326 females and 1,249 males from the LRGV and 659 females from San Antonio for CFAV by RT-PCR using specific primers. Infection rates varied from 0 to 261 per 1,000 mosquitoes in the LRGV and 115 to 208 per 1,000 in San Antonio depending on the month of collection. Infection rates per 1,000 individuals appeared higher in females collected from BG Sentinel 2 traps compared to Autocidal Gravid Ovitraps, but the ratio of the percentage of infected pools did not differ by trap type. The natural viral load in individual males ranged from 1.25 x 10² to 5.50 x 10⁶ RNA copies and in unfed females from 5.42 x 10³ to 8.70 x 10⁶ RNA copies. Gravid females were found to harbor fewer viral particles than males and unfed females.

High Rate of Non-Human Feeding by Aedes aegypti Reduces Zika Virus Transmission in South Texas

Mosquito-borne viruses are emerging or re-emerging globally, afflicting millions of people around the world. Aedes aegypti, the yellow fever mosquito, is the principal vector of dengue, Zika, and chikungunya viruses, and has well-established populations across tropical and subtropical urban areas of the Americas, including the southern United States. While intense arboviral epidemics have occurred in Mexico and further south in the Americas, local transmission in the United States has been minimal. Here, we study Ae. aegypti and Culex quinquefasciatus host feeding patterns and vertebrate host communities in residential environments of South Texas to identify host-utilization relative to availability. Only 31% of Ae. aegypti blood meals were derived from humans, while 50% were from dogs and 19% from other wild and domestic animals. In Cx. quinquefasciatus, 67% of blood meals were derived from chicken, 22% came from dogs, 9% from various wild avian species, and 2% from other mammals including one human, one cat, and one pig. We developed a model for the reproductive number, R0, for Zika virus (ZIKV) in South Texas relative to northern Mexico using human disease data from Tamaulipas, Mexico. We show that ZIKV R0 in South Texas communities could be greater than one if the risk of human exposure to Ae. aegypti bites in these communities is at least 60% that of Northern Mexico communities. The high utilization of non-human vertebrates and low risk of human exposure in South Texas diminishes the outbreak potential for human-amplified urban arboviruses transmitted by Ae. aegypti.

Stable Isotope Marking of Laboratory-Reared Aedes aegypti (Diptera: Culicidae)

The use of stable isotope enrichment to mark mosquitoes has provided a tool to study the biology of vector species. In this study, we evaluated isotopic marking of Aedes aegypti (L.) (Diptera: Culicidae) in a laboratory setting. We determined the optimal dosage for marking adult Ae. aegypti mosquitoes with 13C and 15N. Additionally, Ae. aegypti mosquitoes were single and dually marked with 13C and 15N for up to 60 d postemergence without changes to adult body size or transgenerational marking. This report adds to the growing literature that explores the use of alternative marking methods for ecological and vector biology studies.

Landscape and demographic determinants of Culex infection with West Nile virus during the 2012 epidemic in Dallas County, TX

In 2012, the United States experienced one of the largest outbreaks of West Nile virus (WNV)-associated deaths, with the majority occurring in Dallas County (Co.), Texas (TX) and surrounding areas. In this study, logistic mixed models were used to identify associations between the landscape, human population, and WNV-infected Culex quinquefasciatus mosquitoes during the 2012 WNV epidemic in Dallas Co. We found increased probabilities for WNV-positive mosquitoes in north and central Dallas Co. The most significant predictors of the presence of WNV in Cx. quinquefasciatus pools were increased urbanization (based on an index composed of greater population density, lower normalized difference vegetation index, higher coverage of urban land types, and more impervious surfaces), older human populations, and lower elevation. These relationships between the landscape, sociodemographics, and risk of enzootic transmission identified regions of Dallas Co., TX with highest risk of spillover to human disease during the 2012 WNV epidemic.

Influence of herd immunity in the cyclical nature of arboviruses

We review and contrast the evidence for an effect of amplifying host herd immunity on circulation and human exposure to arboviruses. Herd immunity of short-lived West Nile virus avian amplifying hosts appears to play a limited role in levels of enzootic circulation and spillover infections of humans, which are not amplifiers. In contrast, herd immunity of nonhuman primate hosts for enzootic Zika, dengue, and chikungunya viruses is much stronger and appears to regulate to a large extent the periodicity of sylvatic amplification in Africa. Following the recent Zika and chikungunya pandemics, human herd immunity in the Americas quickly rose to ∼50% in many regions, although seroprevalence remains patchy. Modeling from decades of chikungunya circulation in Asia suggests that this level of herd immunity will suppress for many years major chikungunya and Zika epidemics in the Americas, followed by smaller outbreaks as herd immunity cycles with a periodicity of up to several decades.