Arbovirus phenotype alters transmission potential

Extrinsic and environmental factors are known to affect the transmission of arthropod-borne viruses (arboviruses), including variations in the arthropod vector populations. Differences among these factors have been associated with differential transmission and are sometimes used to control the spread of an arbovirus through a vertebrate population in an effort to prevent or disrupt an outbreak. However, diversity in intrinsic viral populations, such as genetic and phenotypic variability, is not often accounted for when considering alterations in transmission. Presented in this dissertation are four experimental studies that explore the contribution of viral intrinsic factors, especially phenotypic variability, to the transmission potential of arboviruses as judged by modeling parameters such as vectorial capacity (VC) and the basic reproductive number (R0). The overall hypothesis of this research is that phenotypic differences of arboviruses alter the transmission potential of these arboviruses by conferring fitness advantages in either the vector or the vertebrate. Further, these phenotypic differences need not be large in magnitude to affect the relative transmission potential. To investigate this hypothesis, this research determined 1) whether intrinsic viral characteristics can lead to differential transmission in a given locale, 2) whether variability of viral fitness in the mosquito vector can lead to significant differential transmission potential, 3) how our newly formulated methods from our preceding aim could aid in the explanation of a currently puzzling phenomenon in the field of arbovirology, 4) whether phenotypic differences in the vertebrate host alters the potential for transmission, and 5) how identified phenotypic differences in both the vector and vertebrate hosts could act synergistically or antagonistically to alter transmission potential of arboviruses. The research in this dissertation offers a more accurate tool for assessing transmission potential in the vector, provides a new model assessing transmission potential in the vertebrate, and provides several of the necessary steps towards a more appropriate calculation of R0. Our use of R0 based on dynamic phenotypic differences provides a framework for a more dynamic formulation of transmission models, and provides an accessible framework for output validation and reporting to public health stakeholders

A Method for Repeated, Longitudinal Sampling of Individual Aedes aegypti for Transmission Potential of Arboviruses

Mosquito-borne viruses are the cause of significant morbidity and mortality worldwide, especially in low- and middle-income countries. Assessing risk for viral transmission often involves characterization of the vector competence of vector–virus pairings. The most common determination of vector competence uses discreet, terminal time points, which cannot be used to investigate variation in transmission aspects, such as biting behavior, over time. Here, we present a novel method to longitudinally measure individual biting behavior and Zika virus (ZIKV) transmission. Individual mosquitoes were exposed to ZIKV, and from 9 to 24 days post-exposure, individuals were each offered a 180 μL bloodmeal every other day. Biting behavior was observed and characterized as either active probing, feeding, or no bite. The bloodmeal was then collected, spun down, serum collected, and tested for ZIKV RNA via qRT-PCR to determine individuals’ vector competence over time. This included whether transmission to the bloodmeal was successful and the titer of expectorated virus. Additionally, serum was inoculated onto Vero cells in order to determine infectiousness of positive recovered sera. Results demonstrate heterogeneity in not only biting patterns but expectorated viral titers among individual mosquitoes over time. These findings demonstrate that the act of transmission is a complex process governed by mosquito behavior and mosquito–virus interaction, and herein we offer a method to investigate this phenomenon

Credit Card Usage of College Students: Evidence from Louisiana State University (Research Information Sheet #107)

In recent years, there has been a dramatic growth in credit card usage among college students. How are Louisiana State University undergraduates using credit cards? Are LSU students managing credit card debt wisely? What can LSU do to offer the appropriate kinds of help to enable students to be financially literate? These are the issues addressed in this publication.https://digitalcommons.lsu.edu/agcenter_researchinfosheets/1007/thumbnail.jp

No Evidence That Salt Water Ingestion Kills Adult Mosquitoes (Diptera: Culicidae)

Various products and insecticides are available that purport to reduce wild populations of adult mosquitoes. Recently, several manufacturers and general public comments on the internet have promoted devices that claim that ingestion of salt will significantly reduce populations of wild mosquitoes to near zero; there are no known scientific efficacy data that support these claims. We tested the survival of nine mosquito species of pest and public health importance across four adult diets: Water Only, Sugar Water Only (8.00%), Salt Water Only (1.03%), and Sugar + Salt Water. Species included the following: Aedes aegypti (L.), Aedes albopictus (Skuse), Aedes dorsalis (Meigen), Aedes notoscriptus (Skuse), Aedes vigilax (Skuse), Anopheles quadrimaculatus (Say), Culex pipiens (L.), Culex quinquefasciatus (Say), and Culex tarsalis (Coquillett). Male and female mosquitoes were placed in cages and allowed to feed on liquid diets under controlled environmental conditions for 1 wk. For seven of the nine species, adult survival was significantly higher in the presence (Sugar Water, Sugar + Salt Water) versus the absence (Water Only, Salt Only) of sugar, with no indication that salt had any effect on survival. Anopheles quadrimaculatus showed intermediate survival in Sugar + Salt to either Sugar Only or no sugar diets, whereas Aedes dorsalis showed low survival in Salt Only versus other diets. Based on our data and coupled with the fact that mosquitoes have physiological and behavioral adaptations that allow them to avoid or process excess salt (as found in blood meals), we conclude that there is no scientific foundation for salt-based control methods of mosquitoes

Development of a transmission model for dengue virus

BACKGROUND: Dengue virus (DENV) research has historically been hampered by the lack of a susceptible vertebrate transmission model. Recently, there has been progress towards such models using several varieties of knockout mice, particularly those deficient in type I and II interferon receptors. Based on the critical nature of the type I interferon response in limiting DENV infection establishment, we assessed the permissiveness of a mouse strain with a blunted type I interferon response via gene deficiencies in interferon regulatory factors 3 and 7 (IRF3/7 (−/− −/−)) with regards to DENV transmission success. We investigated the possibility of transmission to the mouse by needle and infectious mosquito, and subsequent transmission back to mosquito from an infected animal during its viremic period. METHODS: Mice were inoculated subcutaneously with non-mouse adapted DENV-2 strain 1232 and serum was tested for viral load and cytokine production each day. Additionally, mosquitoes were orally challenged with the same DENV-2 strain via artificial membrane feeder, and then allowed to forage or naïve mice. Subsequently, we determined acquisition potential by allowing naïve mosquitoes on forage on exposed mice during their viremic period. RESULTS: Both needle inoculation and infectious mosquito bite(s) resulted in 100% infection. Significant differences between these groups in viremia on the two days leading to peak viremia were observed, though no significant difference in cytokine production was seen. Through our determination of transmission and acquisition potentials, the transmission cycle (mouse-to mosquito-to mouse) was completed. We confirmed that the IRF3/7 (−/− −/−) mouse supports DENV replication and is competent for transmission experiments, with the ability to use a non-mouse adapted DENV-2 strain. A significant finding of this study was that this IRF3/7 (−/− −/−) mouse strain was able to be infected by and transmit virus to mosquitoes, thus providing means to replicate the natural transmission cycle of DENV. CONCLUSION: As there is currently no approved vaccine for DENV, public health monitoring and a greater understanding of transmission dynamics leading to outbreak events are critical. The further characterization of DENV using this model will expand knowledge of key entomological, virological and immunological components of infection establishment and transmission events

Spatiotemporal dynamics of vector-borne disease risk across human land-use gradients: examining the role of agriculture, indigenous territories, and protected areas in Costa Rica

Background Costa Rica has undergone significant changes to its forest ecosystems due, in part, to the proliferation of palm oil and other industrial agriculture operations. However, the country also boasts conservation programmes that are among the most robust in the neotropics. Consequently, gradients of anthropogenic to intact ecosystems are found throughout the country. Forest ecosystems may decrease vector-borne disease (VBD) risk by maintaining insect populations in a state of relative equilibrium; however, evidence suggests that intact forests foster biodiversity and may also amplify VBD risk in some circumstances. As a result, focal points of human-vector contact are likely idiosyncratic. This may be particularly true in indigenous territories, which have been shown to play a vital role in maintaining the ecological integrity of conservation areas. Here, we investigate the relationships between anthropogenic landscapes, indigenous territories, protected areas, and risk of VBD. Methods We quantified spatial dynamics of risk across three distinct categories of VBD in Costa Rica: emerging flaviviruses (Zika virus disease and dengue); neglected tropical diseases (cutaneous leishmaniasis and Chagas disease); and a disease nearing eradication (malaria). We collected district-level incidence data from between 2006 and 2017 and used spatial statistics to identify hotspots of elevated risk. We then quantified the associations between anthropogenic landscapes, intact forest ecosystems, and indigenous territories with both the presence and persistence of elevated transmission risk over time using multivariate hurdle models. Findings We detected clear patterns of non-random disease risk across each of the three categories of VBD. Compared with protected areas, districts with higher proportions of human-altered landscapes, particularly agricultural intensification, were at higher risk for VBD across all categories. Districts with the highest proportion of crop cover, compared with the lowest proportion, were significantly associated with the presence of hotspots for Zika virus disease (OR 15·19 [95% CI 6·19–37·26]), dengue (13·00 [7·24–23·35]), leishmaniasis (4·46 [1·18–16·84]), Chagas disease (3·09 [1·47–6·49]), and malaria (8·40 [3·56–19·83]). Interpretation A set of spatial epidemiology tools within a planetary health framework allowed for a refined understanding of the risk of VBD of global public health significance in a biodiversity hotspot. Our findings may be used to better guide targeted public health disease surveillance, control, and prevention programmes. Additional research to understand the role that socioeconomic factors play in the variating VBD risk would contribute additional context to these findings, as these factors are often also spatially associated

Antibodies to Aedes spp. salivary proteins: a systematic review and pooled analysis

Aedes spp. mosquitos are responsible for transmitting several viruses that pose significant public health risks, including dengue, Zika, yellow fever, chikungunya, and West Nile viruses. However, quantifying the number of individuals at risk and their exposure to Aedes spp. mosquitos over time is challenging due to various factors. Even accurate estimation of mosquito numbers at the population level may not fully capture the fluctuations in human exposure based on factors that affect biting rates of mosquitoes. Measuring the antibody response of humans to mosquito salivary proteins (MSP) has been proposed as a method to assess human exposure to mosquito bites and predict disease risk. The presence of antibodies to MSP can be quantified using the enzyme-linked immunosorbent assay (ELISA). While there is known variability in laboratory methods, the consistency of MSP measurements across different research groups has not been quantitatively examined. Variation in laboratory protocols, antigens used, and the human populations sampled all may contribute to differences observed in measured anti-MSP responses. In this study, we conducted a systematic review of the published literature focusing on antibody responses to MSP in humans and other vertebrate hosts. Whenever possible, we extracted individual-level anti-MSP IgG data from these studies and performed a pooled analysis of quantitative outcomes obtained from ELISAs, specifically optical densities (OD). We analyzed the pooled data to quantify variation between studies and identify sample and study characteristics associated with OD scores. Our candidate list of characteristics included the type of antigen used, age of human subjects, mosquito species, population-level mosquito exposure, collection season, Köppen-Geiger climate classification, and OD reporting method. Our findings revealed that the type of antigen, population-level mosquito exposure, and Köppen-Geiger climate classification were significantly associated with ELISA values. Furthermore, we developed a classification algorithm based on OD scores, which successfully distinguished samples from individuals living in areas where a specific mosquito species was present from those where it was not, with a high degree of accuracy. The pooled analysis we conducted provides a harmonized assessment of ELISA testing, which can be utilized to refine the use of antibody responses as markers for mosquito exposure. In conclusion, our study contributes to the understanding of antibody responses to MSP and their utility as indicators of mosquito exposure. By identifying the factors associated with variations in ELISA values, we have provided valuable insights for future research and the refinement of antibody-based assessments of mosquito exposure