Malaria remains a significant global health concern, with sub-Saharan Africa bearing the highest burden, particularly due to Plasmodiumfalciparum, which causes the deadliest form of the disease. Malaria has historically been considered a disease confined to rural locations [1][2]. Over 90 million people worldwide face a risk of contracting malaria every year. Nigeria alone accounts for a disproportionate share of the global malaria burden, contributing approximately 29% of all malaria cases and 26% of malaria-related deaths worldwide, according to recent World Health Organization estimates [3]. In 2023, this translated to over 75 million estimated malaria cases in Nigeria, underscoring the country’s position as the epicentre of malaria transmission in sub-Saharan Africa [3]. Recent analyses of urban malaria transmission dynamics in south-eastern Nigeria further highlight how persistent vector populations and increasing insecticide resistance sustain this exceptionally high burden [4].

Current urbanization and immigration to urban centers have led to widespread urban agriculture, neglected green space, and unplanned urban sprawl with inadequate water management in cities. Such regions have similarities with rural locations, and thus mosquito vectors potentially harboring both Anophelesarabiensis and Anophelesgambiae can sustain malaria transmission at even 30% to 40% prevalence in some situations [5].

Since the Horn of Africa’s Djibouti City reported an uncommon urban malaria outbreak in 2012, there have been yearly reports of outbreaks that are getting worse. Further research revealed the existence of An. stephensi, an Asian mosquito species that is known to flourish in urban settings. The World Health Organization issued a vector alert urging aggressive mosquito surveillance in the area after An. stephensi was discovered in Ethiopia, Sudan, and Nigeria since that initial report [6].

An. stephensi, indigenous to regions across South Asia and the Arabian Peninsula, has been extending its distribution throughout Africa in the past decade. It is reported to flourish in urban environments, in contrast to other malaria species that predominantly inhabit rural areas. Originating from its native region, it is recognized as an efficient vector for malaria, mostly due to its ability to transmit both Plasmodiumvivax and the more lethal P. falciparum, which are responsible for the majority of human malaria cases [3].

An. stephensi favors artificial water storage, which enables it to persist throughout the year and maintain activity during arid periods, in contrast to An. gambiae, which flourishes in rural areas and during the wet season. Additionally, studies reveal that An. stephensi prefers to rest within barns or sheds instead of houses; thus, methods of controlling mosquitoes like protective nets and indoor chemical spraying might not work. The discovery of An. stephensi in Africa, which was first observed in Djibouti in 2012, took the continent by surprise because of the remarkable strides it had achieved in the fight against malaria. Although it has been further observed in Nigeria, Somalia, and Sudan, it might also exist in other nations. According to a recent study in The Lancet Global Health, immediate action is required to stop the proliferation of this vector because malaria could infect nations where the disease is not normally endemic [7]. Its capacity to survive dry seasons and flourish in urban environments has raised serious concerns. Given that over 40% of Africans live in cities, a 2020 study calculated that the An. stephensi mosquito would render a further 126 million individuals vulnerable to malaria infection [8].

Malaria is a mosquito-borne disease transmitted exclusively by female Anopheles mosquitoes and remains a major public health challenge in tropical and subtropical regions, particularly sub-Saharan Africa [3]. While mosquitoes are also vectors of other diseases such as dengue, yellow fever, chikungunya, lymphatic filariasis, and viral encephalitides, malaria continues to account for the greatest burden of morbidity and mortality in the region [9][10].

Traditionally, malaria transmission in Africa has been associated with rural environments, where dominant vectors such as Anophelesgambiae complex species breed in natural or semi-natural water bodies. However, rapid urbanization, population growth, and inadequate urban infrastructure have increasingly altered malaria epidemiology. Urban malaria transmission is now sustained by human-modified environments, including informal settlements, poor drainage systems, construction sites, and widespread domestic water storage practices, which provide stable breeding habitats for mosquitoes even in densely populated cities.

The emergence of Anophelesstephensi in Africa represents a fundamental shift in urban malaria risk. Unlike indigenous African vectors, An. stephensi is highly adapted to urban and peri-urban settings, readily exploiting artificial containers such as overhead tanks, wells, barrels, and discarded receptacles for breeding. Its ability to thrive in polluted water, tolerate a wide range of temperatures, and coexist closely with human populations has enabled it to drive major urban malaria outbreaks in South Asia and, more recently, the Horn of Africa.

Vector behavioural adaptability further complicates control efforts in urban environments. Although Anopheles mosquitoes are generally nocturnal, changes in biting behaviour, such as earlier evening feeding prior to bed net use, have been observed in African settings, partly in response to widespread insecticide-treated net coverage [11]. Such behavioural plasticity may enhance the transmission potential of An. stephensi in urban Nigeria, where conventional malaria control strategies have largely been designed for rural vectors.

Given Nigeria’s rapid urban expansion and existing challenges in water management and vector surveillance, the establishment of An. stephensi poses a serious threat to malaria control gains. Its presence raises concerns about sustained urban transmission, an increased malaria burden in cities, and reduced effectiveness of traditional control interventions. Understanding the changing epidemiology of urban malaria is therefore critical for developing targeted surveillance and control strategies suited to Nigeria’s evolving urban landscape.

Human malaria is transmitted primarily by infected female Anopheles mosquitoes, with transmission dynamics strongly influenced by vector ecology, behaviour, and adaptation to human environments [12]. In Nigeria and much of sub-Saharan Africa, malaria transmission has historically been driven by indigenous vectors within the Anophelesgambiae sensu lato complex; principally Anophelesgambiaesensustricto, Anophelescoluzzii, and Anophelesarabiensis, as well as Anophelesfunestus in many settings [12][13].

These native vectors are typically associated with rural and peri-urban environments, breeding in natural or semi-permanent water bodies such as puddles, marshes, rice fields, and stream margins. Behaviourally, An. gambiaes.l. exhibits strong anthropophily, nocturnal feeding, and predominantly endophagic and endophilic tendencies, making it a highly efficient vector and particularly susceptible to indoor interventions such as long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) [14][15].

In contrast, Anophelesstephensi represents a distinct ecological and behavioural departure from Nigeria’s traditional malaria vectors. Unlike An. gambiaes.l., An. stephensi is highly adapted to urban environments, exploiting artificial container habitats such as overhead tanks, barrels, wells, construction sites, and discarded containers for larval development [16][17]. This container-breeding behaviour closely resembles that of Aedes mosquitoes rather than African Anopheles species, enabling An. stephensi to thrive in densely populated cities where natural breeding sites are limited [6][18].

Feeding and resting behaviours also differ markedly. While An. gambiaes.l. is predominantly endophagic, An. stephensi displays greater behavioural plasticity, feeding both indoors and outdoors and resting in diverse locations, which may reduce the effectiveness of indoor-focused control strategies [17]. Additionally, An. stephensi demonstrates flexible host-feeding patterns, maintaining anthropophily while also feeding opportunistically on animals, facilitating its persistence across heterogeneous urban landscapes [16].

These contrasts have major implications for malaria control in Nigeria. Current national strategies have been optimized for rural, indoor-biting vectors such as An. gambiaes.l. and An. funestus. The introduction of An. stephensi, with its urban, container-breeding ecology and behavioural flexibility, threatens to undermine existing gains by expanding malaria transmission into urban settings traditionally considered lower-risk [6][18]. Consequently, the emergence of An. stephensi necessitates a re-evaluation of vector control paradigms in Nigeria, with increased emphasis on urban surveillance, larval source management, and community-based habitat reduction alongside established indoor interventions.

Among the approximately 500 recognized species within the genus Anopheles, only about 30 are considered efficient malaria vectors, including Anophelesstephensi [19]-[21]. This species exists in three recognized biological forms: type, intermediate, and mysorensis, which can be differentiated based on egg morphology [19]-[21]. These forms exhibit distinct ecological and behavioural traits that influence their vectorial capacity. The mysorensis form is predominantly zoophilic and is therefore considered a less effective malaria vector, whereas the type and intermediate forms are highly anthropophilic and play a significant role in malaria transmission [15][22].

Anophelesstephensi displays several biological characteristics that distinguish it from indigenous African malaria vectors and facilitate its success in urban environments. The species is strongly anthropophilic, exhibits endophagic feeding behavior (feeding indoors), and shows endophilic resting tendencies, traits that enhance human-vector contact in densely populated settings [23]. Unlike many African vectors that rely on natural or semi-natural aquatic habitats, the immature stages of An. stephensi are commonly found in anthropogenic water-holding containers such as overhead tanks, barrels, wells, fountains, cisterns, and other artificial receptacles prevalent in urban and peri-urban areas [22][23].

Larval development in An. stephensi is particularly well-suited to urban conditions. The larvae of the type and intermediate forms preferentially exploit clean water stored in domestic containers, while the mysorensis form is more frequently associated with natural habitats [22]. This capacity to utilize a wide range of artificial breeding sites allows An. stephensi populations to persist independently of rainfall patterns, supporting continuous transmission in cities. Rapid development in these stable container habitats further enhances population growth and vector density in urban settings.

Adult survival and feeding behaviour further contribute to the vectorial efficiency of An. stephensi. Upon emergence, adults seek sugar sources for energy-demanding activities such as mating, flight, and host-seeking, while females require blood meals to support egg development [24]. Although feeding is predominantly nocturnal, urban studies have shown a strong preference for human hosts, even in environments where alternative animal hosts are available, increasing the risk of sustained human-to-human transmission [19]-[22]. Under favourable conditions, adult An. stephensi mosquitoes can survive for a month or longer, providing sufficient time for parasite development and onward transmission [25].

Seasonal survival strategies may further enhance the persistence of An. stephensi populations. Aestivation during hot or dry periods has been proposed as a mechanism enabling survival through unfavourable environmental conditions, while diapause may occur in populations inhabiting the northern limits of the species’ range [26]. These adaptive traits collectively underscore the capacity of An. stephensi to establish stable populations in urban environments and pose a substantial challenge to malaria control strategies traditionally designed for rural vectors.

Accurate identification of Anopheles mosquito species is fundamental to effective malaria vector surveillance and control, as control strategies and insecticide selection depend heavily on species-specific behavioural and ecological traits [35]. Precise species identification enables assessments of vector competence, insecticide susceptibility, feeding and resting behaviour, and breeding ecology, all of which are essential for designing targeted and cost-effective vector control interventions.

In Nigeria, malaria transmission has historically been driven by indigenous vectors such as Anophelesgambiae, Anophelescoluzzii, and Anophelesarabiensis [12][36], alongside several secondary vectors including Anophelesmerus, Anophelesrivulorum, Anophelesparensis, Anophelesvaneedeni, and Anophelesleesoni [37][38]. These species often coexist in ecologically interdependent assemblages, with distinct behavioural patterns and insecticide susceptibility profiles that influence malaria transmission dynamics [12][39].

The emergence of Anophelesstephensi presents a significant diagnostic challenge within this established vector landscape. Morphologically, An. stephensi shares similarities with members of the An. gambiae complex, particularly An. arabiensis, increasing the likelihood of misidentification when using conventional morphological keys alone. While morphological identification remains a cost-effective and widely applied approach at state and local levels, it may be insufficient for reliably detecting An. stephensi, especially in early invasion stages or mixed-species populations.

The consequences of misidentification can be substantial. Historical evidence from Zimbabwe demonstrated how confusion between vector and non-vector species within the An. gambiae complex led to inappropriate insecticide policy decisions and masked insecticide resistance in the true vector population [39]-[41]. Similar misclassification involving An. stephensi could result in ineffective control strategies, particularly in urban settings where this species exhibits distinct breeding and feeding behaviours.

Molecular diagnostic tools, therefore, play a critical role in confirming species identity. Multiplex PCR assays targeting species-specific genetic markers are routinely used in national reference laboratories and research institutions to distinguish closely related Anopheles species [42][43]. Additionally, DNA sequencing of mitochondrial and nuclear markers, particularly the cytochrome oxidase subunit I (COI) gene and the internal transcribed spacer 2 (ITS2) region (Table 1), has proven highly effective for species differentiation, phylogenetic analysis, and confirmation of invasive populations [38][44]-[47][48]. The ITS2 locus, in particular, is increasingly used as a diagnostic marker due to its ability to resolve cryptic species within anopheline complexes [45].

Table 1. Details of Anopheles spp. and their sequence accession numbers [49].

Despite their accuracy, molecular approaches are often constrained by cost, infrastructure requirements, and technical expertise, limiting their routine deployment in many malaria-endemic settings [49]. As a result, reliance on morphology alone remains common in routine surveillance, potentially contributing to the under-detection or delayed recognition of An. stephensi incursions.The morphological similarity betweenAn. stephensi and indigenous African vectors, combined with historical gaps in molecular surveillance capacity, may partly explain why the species remained undetected in Africa until its confirmed emergence in the Horn of Africa [18][50].

Given the public health implications of An. stephensi establishment in Nigerian cities, there is a growing need to integrate molecular confirmation into routine surveillance systems. The adoption of simplified PCR protocols, portable molecular platforms, or other rapid field-deployable diagnostic tools could bridge the gap between accuracy and feasibility. Strengthening diagnostic capacity will be essential for early detection, monitoring spread, and implementing timely, evidence-based vector control strategies tailored to the unique biology of An. stephensi.

Since its first appearance outside Asia in 2012, Anophelesstephensi has rapidly spread into urban areas across the Horn of Africa and beyond. These invasions, captured through entomological and molecular surveillance, have been published in peer-reviewed literature. Table 2 identifies representative emergence events.

Table 2.Documented the first records of Anophelesstephensi in non-native urban locations.

*For some countries, first detections were initially reported through WHO-coordinated entomological surveillance and vector alerts prior to publication in peer-reviewed journals.

Recent entomological surveillance has confirmed the presence of Anophelesstephensi in Nigeria. The first documented detection occurred in 2020 in the Biliri Local Government Area of Gombe State, northeastern Nigeria (Figure 2). Mosquito specimens were collected from artificial water-holding containers within urban and peri-urban settings, consistent with the known ecology of An. stephensi.

Figure 2. Map indicating the location of the initial discovery of Anophelesstephensi in Nigeria [56].

Initial identification was conducted using morphological keys to screen Anopheline larvae and adults suspected to be non-native vectors. Due to the morphological similarity between An. stephensi and indigenous members of the Anophelesgambiaesensulato complex, molecular confirmation was subsequently performed using PCR-based species identification assays at national reference laboratories in collaboration with the Nigerian Institute of Medical Research (NIMR) and the National Malaria Elimination Programme (NMEP).

This detection represents a significant milestone in malaria vector surveillance in Nigeria, as An. stephensi is uniquely adapted to urban transmission environments, where over half of Nigeria’s population resides. Its establishment, therefore, poses a heightened risk of increased malaria transmission in densely populated cities [54].

Nigeria’s NMEP, with technical support from the U.S. President’s Malaria Initiative (PMI), has since expanded surveillance capacity for An. stephensi. In November 2022, PMI supported targeted training of entomology technicians and researchers across multiple Nigerian states to strengthen morphological screening and molecular diagnostic capabilities for the early detection and monitoring of this invasive vector [56].

The introduction and spread of An. stephensi in Nigeria is likely facilitated by increased urbanization, climate suitability, and international trade and transport networks, which collectively enhance opportunities for passive dispersal and establishment in urban centers.

Nigeria bears the highest malaria burden globally, accounting for a substantial proportion of cases and deaths worldwide, and the introduction of Anophelesstephensi threatens to further complicate malaria control efforts in the country [54]. Unlike indigenous African malaria vectors that predominantly sustain transmission in rural settings, An. stephensi is highly adapted to urban environments, where it breeds efficiently in artificial water containers and thrives in close proximity to dense human populations [8][22].

Evidence from the Horn of Africa illustrates the epidemiological consequences of An. stephensi establishment in urban areas. In Djibouti, malaria incidence increased dramatically following the detection of An. stephensi in 2012, rising from fewer than 3000 reported cases annually to tens of thousands within a decade, coinciding with the vector’s urban proliferation [16][57]. Similarly, entomological and epidemiological investigations in Ethiopia have confirmed widespread urban colonization by An. stephensi, with the vector demonstrating competence for transmitting both Plasmodiumfalciparum and Plasmodiumvivax [58][59].

Modeling studies further underscore the magnitude of this threat. Using climatic suitability and urbanization trends, Sinka et al. [22] estimated that the continued spread of An. stephensi could place over 120 million additional people in Africa at risk of malaria, predominantly in urban and peri-urban settings. In Ethiopia, projections suggest that An. stephensi establishment could lead to substantial increases in malaria incidence, particularly in cities previously considered low-risk, if existing control strategies remain unchanged [59].

Nigeria’s rapid urban growth amplifies this concern. More than 40% of Nigeria’s population now resides in urban areas, many characterized by informal settlements, unreliable piped water supply, and widespread household water storage; conditions highly favourable for An. stephensi breeding [6][60]. If transmission dynamics similar to those observed in the Horn of Africa were to emerge in Nigerian cities such as Lagos, Kano, or Ibadan, the result could be a marked increase in urban malaria prevalence, placing additional strain on already burdened health systems.

Furthermore, An. stephensi presents unique challenges for malaria control due to its behavioral and ecological plasticity, including container breeding, tolerance of polluted water, and documented resistance to multiple classes of insecticides [8][61]. These traits reduce the effectiveness of conventional vector control tools primarily designed for rural malaria vectors and highlight the risk of urban malaria resurgence.

These findings suggest that the establishment of An. stephensi in Nigeria could fundamentally alter malaria epidemiology by expanding transmission into urban environments. Proactive surveillance, urban-adapted vector control strategies, and the integration of An. stephensi into national malaria elimination frameworks is therefore critical to preventing a reversal of malaria control gains in Nigeria.

Nigeria’s current vector control measures mainly target the two main malaria vectors in sub-Saharan Africa, Anophelesgambiae and Anophelesfunestus. Because An. stephensi’s breeding grounds are frequently located in urban areas; these methods, which include indoor residual spraying (IRS) and insecticide-treated bed nets (ITNs), may be less successful against the species [56].

An increasing problem for malaria control efforts worldwide is insecticide resistance, and An. stephensi is no different. The efficiency of existing chemical control strategies is limited by reports that An. stephensi populations have acquired resistance against multiple insecticide classes. Since pyrethroids are a major component of vector management in Nigeria, the development of An. stephensi may compromise the performance of these treatments [54].

Active surveillance for Anophelesstephensi is essential in Nigeria, particularly in urban and peri-urban areas where the species is most likely to establish. The development of a coordinated network of entomological surveillance sites in high-risk locations can support the early detection of incursions and guide timely, evidence-based responses. Surveillance data are also critical for tailoring control strategies to local ecological conditions and for monitoring the effectiveness of interventions over time.

Given the container-breeding ecology of An. stephensi, Larval Source Management (LSM) represents one of the most immediate and practical control strategies. LSM approaches, including source reduction, environmental modification, larviciding, and improved water management, are particularly effective in urban settings where breeding sites are often fixed, accessible, and man-made [62]. Targeting overhead tanks, household water storage containers, construction sites, wells, and discarded receptacles can substantially reduce larval habitats and suppress adult mosquito populations. When systematically implemented, LSM can complement adult-focused interventions and reduce reliance on insecticides alone [63]-[65].

Community-based habitat reduction is a critical component of sustainable An. stephensi control. Public engagement initiatives that educate communities on the identification and elimination of potential breeding sites, such as emptying unused containers, covering water storage vessels, and improving sanitation, can significantly limit mosquito proliferation. Community participation is especially important in informal urban settlements where centralized vector control services may be limited. Empowering households and local leaders to take ownership of vector reduction enhances intervention coverage and long-term effectiveness [54][56][64].

Integrated Vector Management (IVM) provides a framework for combining these practical measures with chemical and biological interventions. In urban contexts, IVM strategies that prioritize environmental management and larval control are particularly well-suited to addressing the ecological flexibility of An. stephensi. Adult control measures, including targeted indoor residual spraying and insecticide-treated nets, may still play a role but are unlikely to be sufficient on their own given the vector’s breeding behaviour and potential for outdoor or early-evening biting [63].

Advanced technologies such as Wolbachia-based approaches and the sterile insect technique (SIT) offer promising long-term options for An. stephensi control. These methods aim to suppress mosquito populations or reduce vector competence through interference with reproduction. However, they remain largely experimental, require substantial infrastructure and technical capacity, and may not be immediately deployable at scale in Nigeria. As such, these approaches are best considered as complementary tools within a broader IVM strategy rather than standalone solutions [63][64].

Overall, effective control of An. stephensi in Nigeria will depend on prioritizing feasible, cost-effective, and community-driven interventions, particularly LSM and habitat reduction, while gradually integrating advanced technologies as surveillance capacity and operational readiness improve. Aligning these strategies with urban planning, water management policies, and community engagement initiatives will be essential to mitigating the public health threat posed by this invasive vector.

Anophelesstephensi’s invasion of Nigeria poses a serious threat to public health and could undo the progress achieved in combating malaria. In highly populated cities, An. stephensi, an urban-adapted vector with a high capacity for Plasmodiumfalciparum transmission, has the potential to significantly increase malaria transmission. Strict surveillance, innovative vector control techniques, and community involvement are all necessary to counter this menace. An. stephensi could further entrench malaria in Nigerian urban centres if prompt and concerted action is not taken, making the fight to eradicate malaria more difficult.