Vector-borne pathogens (VBPs) are disease agents (e.g., viruses, parasites or bacteria) of human and animal illness transmitted by arthropod vectors including flies, fleas, midges, mites, ticks and most deadly, mosquitoes (1). Over the past decades, the emergence or re-emergence of VBPs has accelerated, posing a heavy burden on public health and biodiversity conservation (2–5). According to the World Health Organization, for example, the annual number of estimated cases of dengue and malaria were up to 390 and 249 million, respectively, accounting for a considerable portion of the global infectious disease burden (6, 7). Blooming global trade and travel has most likely facilitated the movement of VBPs via infected humans, livestock, or vectors. As a result, many VBPs are expanding their distribution ranges, some even breaking through the intercontinental barriers and threatening new regions remote from their native ranges (5). A notorious recent example likely involving infected travelers was Zika virus (8), whose endemic regions consist of Africa and with infections later sporadically occurring in Asia. Following introduction to Yap Island in the western Pacific in 2007 and then French Polynesia in the southern Pacific in 2013-2014, a large epidemic occurred in Brazil in 2015-2016 and the virus continued to spread through Latin America, the Caribbean, and parts of Europe (9, 10). In Brazil, studies have shown that subsequent lower levels of incidence following the large outbreaks were most likely caused by the build-up of population immunity (11). Although there was no major outbreak of Zika in the US, locally acquired cases were also reported in Southern Texas and Florida in 2016-2017 ( (12) and references therein). Another example is the transmission of West Nile virus (WNV). Originally discovered in Uganda in 1937, WNV gradually spread throughout Africa, Middle East and Europe over the course of 60 years, and it spread to the Western hemisphere starting from the outbreak of WNV infection in avian communities in New York 1999, followed by thousands of reported human cases, including hundreds of deaths in the US and Canada in 2002 and 2003 ( (13) and references therein). This is a prime example of an arbovirus that not only was introduced and led to major outbreaks, but then rapidly spread over the course of a 4-year period across the continental United States and has become established in local avian populations (14).

Given these examples of recent invasions of vector-borne pathogens, and the threat associated with potential novel invasive pathogens, understanding the drivers for local and regional expansion of VBPs is of top priority. Global trade and travel have been suggested as the main driver for the introduction of VBPs into novel regions while land use and social changes (e.g., poverty) are more likely drivers of local expansion of already-circulating VBPs (5). In addition, global climate change may also contribute to the range expansion or shifts of VBPs if increasing temperatures enable certain vectors to expand their distribution range by latitude or elevation (15). In this context, the introduction of VBPs in novel regions can be facilitated by modern transportation carrying infected hosts and/or vectors, while the circulation of both novel and endemic VBPs relies on host and vector population dynamics that are regulated by environmental changes ( Figure 1 ). Ultimately, the transmission of VBPs from an infected host to a new one depends on the blood-sucking behavior of vectors, and mosquitoes serve as primary vectors of many VBPs, such as avian Plasmodium and WNV (16, 17). Some VBPs circulate between humans, but others mainly infect animals, with humans and livestock acting as incidental hosts.

As a bridge between VBPs and their vertebrate hosts, mosquitoes play a central role in the transmission of VBPs. And those invasive mosquitoes become a research focus because they have the potential to become competent vectors of both novel and endemic VBPs and hence, significantly contribute to the expansion of VBPs. This review will focus on invasive mosquitoes, their introduction pathways, and the ecological factors that limit their establishment and spread. It will also examine the role these mosquitoes play in the transmission of VBPs during their introduction, establishment and spread, with particular attention to how the addition of an invasive mosquito can alter transmission intensity or pathways.

A common definition of invasive alien species are animals, plants or microorganisms that are introduced to a non-native ecosystem as a direct or indirect consequence of human actions, where they cause harm by threatening economic development, public health, food security or biodiversity (18–20). A number of mosquitoes that were introduced to new regions meet this definition and can be defined as invasive mosquitoes. For example, the southern house mosquito Culex quinquefasciatus, which is a native species of Africa, has been introduced to most of the world (see Table 1 ). The introduction of this species along with pathogens (such as avian malaria and poxvirus) they are able to spread to Hawaii has been regarded as the major driver for the decline and extinction of native avifauna (71). Anopheles stephensi, another invasive species whose native regions are Southern Asia and Arabian Peninsula, has been introduced to the Horn of Africa in recent years and has been tied to an increase in malaria cases in Djibouti following its introduction in 2012 (64). There is considerable concern about the range expansion of this malaria vector that relate to how its presence could alter the previously established transmission patterns. Particularly, this species is well adapted to urban environments and uses man-made containers as oviposition and larval development sites. This differs from the primary sub-Saharan African malaria vectors that tend to be associated with ephemeral larval habitats in rural environments. There is thus concern that the spread of this invasive mosquito could lead to a surge in urban malaria in the African continent. Further, it has been found that due to the use of man-made containers, this species appears to be capable of persisting and remaining active and abundant throughout the dry season, which poses the threat of year-round malaria (72). Its role in spreading drug-resistant malaria has recently been documented (73). Due to these threats, an initiative to mitigate the further spread of this vector has been initiated by the World Health Organization (74). We provide a table to summarize the native and invaded regions, primary hosts and vectors as well as the recent outbreak of VBPs associated with several major invasive mosquitoes from the genus of Aedes, Culex and Anopheles in Table 1 .

The record of mosquito invasion dates back to the 16^th century, when Ae. aegypti hitchhiked in the bilges of slave ships or in casks of drinking water from West Africa to the Americas (75, 76). Transoceanic ships were the major introduction pathway of invasive mosquitoes at that time. With the growth and development of the global economy and international transportation networks, modern trade and carriers have grown in importance as unintended pathways for mosquito invasion in new regions and even new continents. These pathways include two major trades via sea transportation (trades of used tires and Lucky bamboo), as well as air and ground transportation ((77) and references therein). In addition, natural dispersal of mosquitoes across terrestrial borders of adjacent countries may also be involved in range expansions (78).

Invasive mosquitoes may pose a great threat to wildlife and human health, for instance through the introduction of invasive mosquitoes that are capable of transmitting exotic pathogens to native host populations lacking herd immunity. The introduction of invasive mosquitoes may play varying roles in the transmission of vector-borne pathogens, depending on their competence for transmitting native or novel pathogens and the ways in which their introduction shifts vectorial capacity of the local mosquito community for different pathogens (see Box 1 for an example). Some mosquito vectors and pathogens may be associated in their native ranges but are introduced separately into new regions, which is considered as the most common cause of disease outbreak in the invaded regions (21). In other cases, some mosquito vectors and pathogens are introduced simultaneously into new regions, or introduced mosquitoes are already capable of transmitting endemic pathogens.

Separate introductions of novel vector and pathogens are likely to occur in introduction events as a consequence of mosquitoes and pathogens having different introduction pathways. For instance, the propagule pressure for mosquitoes could be greatest due to long distance travel of containers, and uninfected mosquitoes (e.g., transported in the egg stage) will arrive in a much greater volume than infected mosquitoes. At the same time, the pathogen might be introduced much less frequently through movement of the vector, compared to the movements of infected hosts such as humans, livestock, or migratory birds (5). Following establishment, introduced mosquitoes may acquire an association with separately introduced pathogens and create a new threat to susceptible hosts. For instance, the separate introductions of Cx. quinquefasciatus and avian Plasmodium in Hawaii have caused the outbreak of avian malaria and the decline of Hawaiian birds, particularly in those avian fauna at low elevations (149). Another example is the separate introduction of Culex pipiens complex and West Nile virus in North America where the pathogen was introduced long after the mosquito (150).

Simultaneous introductions of novel vectors and pathogens likely occurs much more rarely. However, it may still have the potential to cause large outbreaks of diseases, given native host populations are relatively naïve to novel pathogens. For example, the historical introductions of Ae. aegypti in North and South Americas have caused immediate outbreak of yellow fever and dengue, respectively, upon the arrival of slave ships from Africa that were presumably carrying yellow fever and dengue virus that were novel to these regions at that time (21).

Invasive mosquitoes can also be competent for existing native pathogens and modify local transmission cycles of vector-borne diseases. If the introduced vectors are highly competent, the disease transmission rates and risk to public health could be enhanced. But if the introduced vectors are less efficient or through competitive interactions lower the population densities or exclude existing primary vectors, the disease transmission rates could decrease. An example of this is Ae. aegypti which is an invasive species in Asia, originating in sub-Saharan Africa, and becomes a major vector of dengue in tropical Asia. Although it is possible that dengue originated in Africa, there is compelling evidence that dengue virus is native to Asia (151).

The introduction of invasive mosquitoes into local mosquito communities can significantly impact the transmission risk (e.g., potential exposure for humans) and intensity (e.g., the basic reproduction number of the pathogen) of VBPs in their invaded areas. Invasive species may compete with native mosquitoes for ecological niches, such as breeding sites and nectar, and disrupt the existing host-vector interaction networks. These changes can lead to alterations in native mosquito population densities and modify the rates at which pathogens are transmitted to native hosts and vectors. For instance, Box 2 provides a case study on how the invasive species Ae. albopictus and Ae. j. japonicus can alter the host-vector interaction network of the native species Ae. triseriatus in North America.

We reviewed the literature for studies in North America that investigated the blood feeding patterns of a native mosquito, Ae. triseriatus, considered the primary vector of La Crosse encephalitis virus, and two invasive species, Ae. albopictus and Ae. j. japonicus, both of which are competent vectors under laboratory conditions (168) and have been found to be infected in the field with this virus as well (169, 170) In areas where these three species co-occur, ignoring possible effects they may exert on each other’s population density, the range of host species fed upon is considerably more diverse than in areas with only the native species. In the case of LACV, where the primary hosts are considered chipmunks and squirrels, the invasive species could potentially become exposed. The role of rabbits is less clear, although there have been suggestions, they may play a role as well (157). The larger impact of these invasive species however could be that rather than increasing R₀ in a meaningful way for a virus like LACV, they could however act as additional bridge vectors and increase the rate with which humans are bitten by infective mosquitoes. Theoretical models exploring these virus-vector-host networks, density-dependent interactions among vectors, and seasonal overlap, could shed light on exactly how VBP transmission would be altered by the introduction of one or more invasive species.

Current surveillance and control programs for invasive mosquitoes and vector-borne pathogens (VBPs) have shown varying degrees of effectiveness across different regions (171, 172). This variability is influenced by key factors such as the scope and enforcement of national and intergovernmental regulatory policies enacted for preventing the introduction, establishment, and spread of alien species, public investment in vector control and surveillance capacity, as well as efforts to reduce the vectorial capacities of invasive mosquitoes. For instance, the increased movement of goods and tourists poses significant challenges for controlling the entry of alien mosquitoes and VBPs at points of entry (5). Integrated Vector Management (IVM) remains the most effective strategy for mosquito control (173). IVM combines chemical, biological, and physical control methods and typically requires the use of insecticides and significant resources, including trained technicians. However, resource limitations, environmental concerns, and the development of insecticide resistance can hinder the effectiveness of IVM (174). Additionally, the ecological mechanisms underlying the establishment and spread of invasive mosquitoes in new regions remain largely unknown (54), making ecological control a significant challenge.

These challenges underscore the need to develop and implement newer, safer, more effective, and sustainable tools for invasive mosquito control. To address these challenges and the process of mosquito invasion, we propose several priority research questions for future study and control of invasive mosquitoes and VBPs: 1) Integrating advanced techniques (e.g., artificial intelligence (AI), quantitative risk assessments) for predicting future invasion risks, identifying high risk routes of entry, and enhancing the detection sensitivity and control of imported mosquito adults and eggs at entry points; 2) innovating surveillance techniques (e.g., high-throughput molecular tools and rapid detection kits) for mosquito and VBP identification and screening; 3) unravelling the ecological mechanisms behind the success of invasive mosquitoes in invaded regions, from establishment to spread, particularly their interactions with native mosquito species, vertebrate hosts, and how they change vector-host-pathogen networks; 4) Incorporating advanced tools such as AI, sterile insect techniques, and gene drive into IVM to effectively monitor, suppress, or replace invasive mosquito populations and reduce their vectorial capacities; 5) Enhancing control options for invasive mosquitoes by exploiting a wider range of their life cycle and behaviors, such as novel baitstations based on plant-derived volatiles; 6) Enhancing community engagement and education, as well as public integration in mosquito surveillance and control programs, such as through citizen science initiatives aimed at early detection of novel vector introduction and spread.

Mosquitoes can be introduced into novel regions by the transportations of used tires and lucky bamboo in global trade and by hitchhiking airplanes and ground vehicles in global travel. Local ecological factors including temperature, dryness, competition, predation, and parasitism may limit the establishment and spread of the introduced mosquitoes in novel regions. Invasive mosquitoes can play a critical role in the transmission of VBPs in their introduced regions, depending on whether they are introduced separately or simultaneously with already vectoring VBPs, or whether they can acquire the competence for novel pathogens in the invaded regions over generations. Management and control effort should be targeted at cutting off their introduction pathways as the frontline, limiting their establishment and spread using ecological measures and reducing their contact with local hosts and pathogens.