By Giancarlo Ceccarelli, Ph.D., Francesco Branda, Ph.D., Cecilia Ceccarelli, B.Arch(c), and Massimo Ciccozzi, Ph.D.

Las Vegas has long been regarded as an unlikely environment for Aedes aegypti.

Characterised by high temperatures, limited precipitation, and desert ecological conditions, the city does not align with the environmental profile typically associated with this species, the primary vector of dengue, Zika, chikungunya, and yellow fever. However, recent surveillance data have documented not only its presence but also its progressive establishment across several areas of the metropolitan region. This indicates that Aedes aegypti can persist in dry urban settings, although the factors supporting its presence in such environments are not yet fully understood.

Urban Form as an Ecological Framework

The distribution of Aedes aegypti has traditionally been interpreted through climatic variables, particularly temperature, rainfall, and humidity. While these factors remain fundamental, they may not fully capture the ecological conditions created within contemporary urban environments.

Cities can be understood as complex ecological systems, where built form, infrastructure, and human activity collectively shape local microenvironmental conditions. In arid settings such as Las Vegas, features including shaded spaces, irrigated vegetation, impermeable surfaces, and dense building configurations can generate localised microclimates in which temperature, humidity, and water availability differ substantially from the surrounding desert environment.

Within these microenvironments, even small and transient accumulations of water—found in domestic containers, drainage systems, or urban infrastructure—may be sufficient to support the development of immature mosquito stages. These habitats are often dispersed, intermittent, and difficult to identify, potentially limiting the effectiveness of control strategies based solely on source reduction or targeted chemical interventions. From this perspective, the presence of Aedes aegypti may be understood not only in relation to climate but also to the ecological characteristics of the built environment.

To that point, in an article we published in February in the Journal of Medical Entomology, we argue that an ecological characteristic particularly relevant to the built environment of Las Vegas should also be studied as a factor: artificial light at night.

Artificial Light and Temporal Ecology

Among the various components of urban environments, artificial light at night has received comparatively limited attention in vector ecology. Yet, in highly illuminated cities, the distinction between day and night is partially diminished, with potential implications for organisms regulated by circadian rhythms.

Experimental evidence suggests that artificial illumination can influence several aspects of mosquito biology, including activity cycles, host-seeking behaviour, and reproductive timing. Under certain conditions, light exposure has been associated with extended periods of activity and changes in biting patterns. These effects do not appear to be species-specific, but rather they reflect a broader influence of artificial light on circadian regulation across multiple mosquito species. In the case of Aedes aegypti, however, the potential relevance may be greater, given its close association with human environments and its predominantly diurnal biting behaviour, which may extend into twilight or nighttime periods under artificial illumination.

The extent to which these experimentally observed effects occur in real-world urban environments remains uncertain. Nonetheless, it is plausible that artificial light at night may alter the timing of mosquito activity, increasing the overlap between periods of vector activity and human presence. From an ecological standpoint, this would represent a shift not in spatial distribution but in the timing of interactions between vectors, hosts, and the environment.

Interactions Within the Urban System

The role of artificial light becomes more meaningful when considered alongside other features of urban environments. Cities concentrate several factors known to support Aedes aegypti, including consistent access to human hosts, widespread availability of artificial breeding sites, and microclimatic buffering that moderates environmental extremes. These conditions are well recognised as key determinants of mosquito-borne virus transmission dynamics.

Within this framework, artificial light may be viewed as an additional modifier that interacts with existing environmental conditions, potentially influencing the timing and frequency of human–mosquito encounters. The magnitude of this contribution, however, remains to be quantified.

Implications for Urban Design and Mosquito Control

These observations suggest that the relationship between urban environments and vector ecology may be more closely coupled than traditionally assumed. Control strategies for mosquitoes and other vectors (e.g., ticks) have historically focused on surveillance, chemical interventions, and habitat reduction. While these approaches remain essential, they often address vector populations after favourable ecological conditions have already been established.

A complementary perspective is to consider how elements of urban design contribute to the creation of such conditions. Water management systems, infrastructure maintenance, waste management, and building design are already recognised as important components of integrated vector control.

Within this broader context, lighting systems may also warrant consideration. Parameters such as intensity, spectral composition, and spatial distribution of artificial light could, in principle, influence mosquito behaviour, although current evidence does not yet allow for the definition of specific operational thresholds or design recommendations.

Towards an Interdisciplinary Research Agenda

The role of artificial light at night in shaping the ecology of Aedes aegypti remains only partially understood. Further research is needed to examine how lighting conditions interact with mosquito behaviour in real-world urban settings, how these interactions vary across different urban forms, and whether they translate into measurable differences in transmission risk.

Addressing these questions will require interdisciplinary collaboration across entomology, epidemiology, urban studies, and environmental sciences, consistent with a One Health perspective in which human health outcomes emerge from interactions between biological systems and their environments.

Rethinking Vector Ecology in the Built Environment

The establishment of Aedes aegypti in cities such as Las Vegas suggests that the ecological limits of vector species may increasingly be shaped by urbanisation. Climate remains a fundamental constraint, but it operates within a context that is profoundly modified by human design. The built environment does not merely host vector populations; it may actively contribute to the conditions that enable their persistence.

Artificial light at night represents one component of this system that has yet to be fully integrated into models of vector ecology. Clarifying its role will be important not only for advancing ecological understanding but also for informing future approaches to vector control in urban settings where traditional assumptions about environmental suitability may no longer fully apply.

Giancarlo Ceccarelli, M.D., Ph.D., is an infectious diseases consultant at Policlinico Umberto I in Rome, Italy, and adjunct professor at Sapienza University, with a focus on emerging vector-borne diseases, global health, and the interaction between urban environments and infectious risk. Email: giancarlo.ceccarelli@uniroma1.it. Francesco Branda, Ph.D., is an assistant professor at Università Campus Bio-Medico in Rome, focusing on epidemiological modelling, data analysis, and AI-driven public health research. Cecilia Ceccarelli, B.Arch(c), is in the final stage of her degree in Architectural Sciences at Roma Tre University. Her expertise includes the interaction between urban design, environmental conditions, and infectious disease dynamics, including vector-related risks. Massimo Ciccozzi, Ph.D., is a full professor of epidemiology and head of medical statistics and epidemiology at Università Campus Bio-Medico in Rome. His research focuses on viral genomics and evolution, with particular expertise in emerging infections.