Biology subjects

Murdock, C.

Publications and source records attributed to Murdock, C..

7 recordsLinked to original sources

bioRxiv2026

The Effects of Mean Temperature and Diurnal Temperature Range on West Nile Virus Transmission

Temperature is a major driver of arbovirus transmission, and a changing climate is expected to affect this process significantly. Most experimental studies rely on constant temperatures and overlook realistic daily temperature fluctuations that impact vector-pathogen interactions. The nonlinear relationship between temperature and vector traits responsible for pathogen transmission suggests that daily fluctuating temperatures produce phenotypes important for transmission distinct from those at constant temperatures. Here, we tested whether realistic variations in mean temperature and diurnal temperature range (DTR) influence West Nile virus (WNV) transmission. We experimentally infected colonized Culex tarsalis with WNV-infectious blood meals and maintained them under constant and fluctuating temperature regimes. We quantified how temperature, DTR, and incubation time shaped several outcomes (infection, dissemination, infectiousness, WNV loads in mosquito saliva and mosquito survival). We also integrated survival and infectiousness probabilities to infer implications for transmission. We observed strong effects of temperature on the WNV infection dynamics, viral loads and mosquito survival. Although the probability of initial infection was similar among all temperature regimes, dissemination and infectiousness were constrained by temperature. Dissemination and infectiousness were highest at 26{degrees}C and reduced at cooler (22{degrees}C) and warmer (30{degrees}C) temperatures. Fluctuating temperatures significantly decreased infection and dissemination probabilities, while the probability of becoming infectious was driven primarily by mean temperature rather than DTR. Mosquito survival probability was temperature dependent, and fluctuating regimes increased mortality risk by 1.95-fold. Integrating mosquito survival and infectiousness dynamics demonstrated that, although at higher temperatures the extrinsic incubation period is shorter, reduced mosquito lifespan can limit viral transmission. Together, these results indicate that overall WNV transmission is affected by temperature-dependent viral dynamics and host physiological constraints. Fluctuating temperature regimes significantly delay viral dissemination within the host, especially at the optimal temperature (26{degrees}C). Measurement of infection outcomes under constant temperatures treatments may lead to over/under estimation of transmission parameters in epidemiological models, therefore integrating fluctuating temperature treatments into mechanistic models of transmission can improve estimates of when and where WNV transmission is most likely to occur.

ecology↗

bioRxiv2026

Impact of thermal variation on the transcriptome of Plasmodium falciparum infected Anopheles stephensi

Temperature is a key determinant of malaria transmission, influencing both parasite development and mosquito physiology, yet the underlying mechanisms remain poorly understood. Here, we examined how temperature and time modulate gene expression in Anopheles stephensi infected with Plasmodium falciparum. Using RNA-sequencing over 1-19 days post-blood meal and three temperature regimes (20, 24, and 28{degrees}C with diurnal fluctuations of 9{degrees}C), we characterize transcriptome responses to infection with P. falciparum at the site of infection in the midgut, and systemically, in the carcasses. Oocyst prevalence and density declined over the thermal gradient, albeit with distinct, non-linear temporal dynamics in parasite development rates. Although infection contributed minimally to global variation in gene expression relative to temperature and time, infection-associated genes in the midgut showed coordinated transcriptional responses enriched in canonical Plasmodium associated extracellular, proteolytic, immune, and metabolic functions; notably, decline in oocyst infections in the midguts over the thermal gradient was reflected in reduced expression of immune genes known to regulate P. falciparum. Network analysis demonstrated that these genes participate in a significantly interconnected protein-protein interaction network, within which a small number of high betweenness centrality proteins act as bottlenecks linking immune, metabolic, reproductive and behavioral processes. Our results suggest responses to infection may be mediated through coordinated physiological networks rather than large-scale transcriptional changes. Our findings also indicate that differences in thermal conditions may be an important factor when comparing mechanisms of vector- parasite interactions between Plasmodium species. Together, our results highlight the importance of integrating thermal context into mechanistic studies of vector-parasite interactions.

ecology↗

bioRxiv2020

Assessing temperature-dependent competition between two invasive mosquito species

O_LIInvasive mosquitoes are expanding their ranges into new geographic areas and interacting with resident mosquito species. Understanding how novel interactions can affect mosquito population dynamics is necessary to predict transmission risk at invasion fronts. Mosquito life-history traits are extremely sensitive to temperature and this can lead to temperature-dependent competition between competing invasive mosquito species. C_LIO_LIWe explored temperature-dependent competition between Aedes aegypti and Anopheles stephensi, two invasive mosquito species whose distributions overlap in India, the Middle East, and North Africa. We followed mosquito cohorts raised at different intraspecific and interspecific densities across five temperatures (16{degrees}C - 32{degrees}C) to measure traits relevant for population growth and to estimate species' per capita growth rates. We then used these growth rates to derive each species competitive ability at each temperature. C_LIO_LIWe find strong evidence for asymmetric competition at all temperatures, with Ae. aegypti emerging as the dominant competitor. This was primarily due to differences in larval survival and development times across all temperatures that resulted in a higher estimated intrinsic growth rate and competitive tolerance estimate for Ae. aegypti compared to An. stephensi. C_LIO_LISynthesis and applications: The spread of An. stephensi into the African continent could lead to urban transmission of malaria, an otherwise rural disease, increasing the human population at risk and complicating malaria elimination efforts. Competition has resulted in habitat segregation of other invasive mosquito species, and our results suggest that it may play a role in determining the distribution of An. stephensi across its invasive range. C_LI

ecology↗

bioRxiv2019

Temperature Dramatically Shapes Mosquito Gene Expression with Consequences for Mosquito-Zika Virus Interactions

Vector-borne flaviviruses are emerging threats to human health. For successful transmission, the virus needs to efficiently enter mosquito cells, replicate within, and escape several tissue barriers while mosquitoes elicit major transcriptional responses to flavivirus infection. This process will not only be affected by the specific mosquito-pathogen pairing, but also variation in key environmental variables such as temperature. Thus far, few studies have examined the molecular responses triggered by temperature and how these responses modify infection outcomes despite substantial evidence showing strong relationships between temperature and transmission in a diversity of systems. To define the host transcriptional changes associated with temperature variation during the early infection process, we compared the transcriptome of mosquito midgut samples from mosquitoes exposed to Zika virus (ZIKV) and non-exposed mosquitoes housed at three different temperatures (20, 28, and 36{degrees}C). While the high temperature samples did not have significant changes from standard rearing conditions (28{degrees}C) 48 hr post-exposure, the transcriptome profile of mosquitoes housed at 20{degrees}C was dramatically different. The expression of genes most altered by the cooler temperature involved aspects of blood-meal digestion, ROS metabolism, and mosquito innate immunity. Further, we did not find significant differences in the viral RNA copy number between 24 and 48 hr post-exposure at 20{degrees}C, suggesting ZIKV replication is limited by cold-induced changes to the mosquito midgut environment. In ZIKV-exposed mosquitoes, vitellogenin, a lipid carrier protein, was the most up-regulated at 20{degrees}C. Our results provide a deeper understanding of the temperature-triggered transcriptional changes in Aedes aegypti and can be used to further define the molecular mechanisms driven by environmental temperature variation.\n\nContribution to the Field StatementA variety of methods for engineering refractory mosquitoes are currently being studied and show promise for disease control. Although considerable effort has been put into understanding the immune system of mosquitoes in response to infections, almost nothing is understood about environmental influences in regulating these responses. Here, we used RNA sequencing to study the effect of temperature on the mosquito transcriptome profile, as well as assess the changes in the immune response to ZIKV infection at three different temperatures. We found a remarkable effect of temperature on the transcriptome profile of mosquitoes exposed to cool conditions (20{degrees}C) after imbibing a blood meal, as well as accumulation of transcripts involved with different mechanisms associated with blood meal digestion, metabolism, and some components of the immune response in mosquitoes. Our results provide new insights in potential mechanisms that limit temperature-driven pathogen establishment and replication within the mosquito vector.

molecular biology↗

bioRxiv2019

Mosquito species and age influence thermal performance of traits relevant to malaria transmission

Models predicting disease transmission are a vital tool in the control of mosquito populations and malaria reduction as they can target intervention efforts. We compared the performance of temperature-dependent transmission models when mosquito life history traits were allowed to change across the lifespan of Anopheles stephensi, the urban malaria mosquito, to models parameterized with commonly derived estimates of lifetime trait values. We conducted an experiment on adult female An. stephensi to generate daily per capita values for lifespan, egg production, and biting rate at six constant temperatures. Both temperature and age significantly affected trait values. Further, we found quantitative and qualitative differences between temperature-trait relationships estimated based on daily rates versus directly observed lifetime values. Incorporating these temperature-trait relationships into an expression governing transmission suitability, relative R0(T), model resulted in minor differences in the breadth of suitable temperatures for Plasmodium falciparum transmission between the two models constructed from only An. stephensi trait data, but a substantial increase in breadth compared to a previously published model consisting of trait data from multiple mosquito species. Overall this work highlights the importance of considering how mosquito trait values vary with mosquito age and mosquito species when generating temperature-based environmental suitability predictions of transmission.

ecology↗

bioRxiv2018

Cryogenically preserved RBCs support gametocytogenesis of Plasmodium falciparum in vitro and gametogenesis in mosquitoes.

BackgroundThe malaria Eradication Research Agenda (malERA) has identified human-to-mosquito transmission of Plasmodium falciparum as a major target for eradication. The cornerstone for identifying and evaluating transmission in the laboratory is small membrane feeding assays (SMFAs) where mature gametocytes of P. falciparum generated in vitro are offered to mosquitoes as part of a blood-meal. However, propagation of \"infectious\" gametocytes requires 10-12 days with considerable physico-chemical demands imposed on host RBCs and thus, \"fresh\" RBCs that are [≤]1-week old post-collection are generally recommended. However, in addition to the costs, physico-chemical characteristics unique to RBC donors may confound reproducibility and interpretation of SMFAs. Cryogenic storage of RBCs (cryo-preserved RBCs herein) is approved by the European and US FDAs as an alternative to refrigeration (4{degrees}C) for preserving RBC quality and while cryo-preserved RBCs have been used for in vitro cultures of other Plasmodia and the asexual stages of P. falciparum, none of the studies required RBCs to support parasite development for >4 days.\n\nResultsUsing the standard laboratory strain, P. falciparum NF54, we first demonstrate that cryo-preserved RBCs preserved in the gaseous phase of liquid nitrogen and thawed after storage for 1, 4, 8 and 12 weeks, supported gametocytogenesis in vitro and subsequent gametogenesis in Anopheles stephensi mosquitoes. Using data from 11 SMFAs and RBCs from 4 separate donors with 3 donors re-tested following various periods of cryo-preservation, we show that overall levels of sporogony in the mosquito, as measured by oocyst prevalence and burdens in the midguts and sporozoites in salivary glands, were similar or better than using [≤]1-week old refrigerated RBCs. Additionally, the potential for cryo-preserved RBCs to serve as a universal substrate for SMFAs is shown for a Cambodian isolate of P. falciparum.\n\nConclusionsConsidering the suitability of cryo-preserved RBCs for P. falciparum SMFAs, we suggest guidelines for their use and how they can be integrated into an existing laboratory/insectary framework with the potential to significantly reduce running costs and provide greater reliability. Finally, we discuss scenarios where cryo-preserved RBCs may be especially useful in enhancing our understanding and/or providing novel insights into the patterns and process underlying human-to-mosquito transmission.

microbiology↗

bioRxiv2016

Fine-scale variation in microclimate across an urban landscape changes the capacity of Aedes albopictus to vector arbovirus

Most statistical and mechanistic models used to predict mosquito borne disease transmission incorporate climate drivers of disease transmission by utilizing environmental data collected at scales that are potentially coarser than what mosquito vectors actually experience. Temperature and relative humidity can vary greatly between indoor and outdoor environments, and can be influenced strongly by variation in landscape features. In the Aedes albopictus system, we conducted a proof-of-concept study in the vicinity of the University of Georgia to explore the effects of fine-scale microclimate variation on mosquito life history and vectorial capacity (VC). We placed Ae. albopictus larvae in artificial pots distributed across three replicate sites within three different land uses - urban, suburban, and rural, which were characterized by high, intermediate, and low proportions of impervious surfaces. Data loggers were placed into each larval environment and in nearby vegetation to record daily variation in water and ambient temperature and relative humidity. The number of adults emerging from each pot and their body size and sex were recorded daily. We found mosquito microclimate to significantly vary across the season as well as with land use. Urban sites were in general warmer and less humid than suburban and rural sites, translating into decreased larval survival, smaller body sizes, and lower per capita growth rates of mosquitoes on urban sites. Dengue transmission potential was predicted to be higher in the summer than the fall. Additionally, the effects of land use on dengue transmission potential varied by season. Warm summers resulted in a higher predicted VC on the cooler, rural sites, while warmer, urban sites had a higher predicted VC during the cooler fall season.

ecology↗