Progress in research on mosquito-borne viruses: Understanding infection, transmission, and control

Abstract

Mosquito-borne viruses (MBVs) are a group of arboviruses belonging to diverse families and genera. Transmitted through mosquito bites, MBVs are a significant public health concern. These pathogens can cause a spectrum of mosquito-borne viral diseases (MBVDs) ranging from rashes, mild fever, and arthralgia to severe conditions, such as shock, encephalitis, microcephaly, hemorrhagic fever and even death. MBVDs are primarily endemic in tropical and subtropical regions, putting half of the global population at risk. Evolutionarily, these viruses are highly adapted to both mosquito and mammalian hosts, efficiently exploiting multiple characteristics of both hosts to facilitate the infection and transmission cycle. In this study, we review the current knowledge of the infection and transmission of major pathogenic MBVs, the underlying mechanisms thereof, and recent advances in preventing and controlling these viruses. We also highlight key challenges in MBV control, infection, and transmission while discussing prospective directions for future research.

1. Introduction

Mosquito-borne viruses (MBVs) comprise a large group of arthropod-borne viruses (arboviruses) transmitted through mosquito bites, encompassing dozens of viruses from at least four families: Flaviviridae, Togaviridae, Peribunyaviridae, and Phenuiviridae.^[1] Of these viruses, the major human pathogens include dengue virus (DENV), Zika virus (ZIKV), West Nile virus (WNV), Japanese encephalitis virus (JEV), and yellow fever virus (YFV), which belong to the genus Flavivirus in the family Flaviviridae;^[2] Chikungunya virus (CHIKV), Sindbis virus (SINV), Eastern equine encephalitis virus (EEEV), and Venezuelan equine encephalitis virus (VEEV), which are part of the genus Alphavirus in the family Togaviridae;^[3,4] La Crosse virus (LACV), Jamestown Canyon virus (JCV), Snowshoe Hare virus (SSHV), and California encephalitis virus (CEV), which are grouped under the genus Orthobunyavirus in the family Peribunyaviridae;^[5,6,7,8] and Rift Valley fever virus (RVFV), which belongs to the genus Phlebovirus in the family Phenuiviridae (Table 1).^[9]

Table 1.

Mosquito-borne viruses and mosquito-borne viral diseases (MBVDs)

Family and genus	Representative viruses	Vector mosquitoes	Associated human diseases
Flaviviridae Flavivirus	Dengue virus	Aedes aegypti,Aedes albopictus[149]	Dengue disease, including dengue fever, dengue hemorrhagic fever, and dengue shock syndrome, is the most prevalent MBVD in the world, causing the biggest threat among arboviruses to both global health and socioeconomic development.[10,149,150]
	Zika virus	Aedes aegypti,Aedes albopictus[149]	Zika disease, include Zika fever, microcephaly and other birth defects, and neurological complications, is an important re-emerging MBVD.[151,152,153]
	Yellow fever virus	Aedes aegypti[149]	Yellow fever can range from mild fever to severe life-threatening conditions, such as bleeding, organ failure, and jaundice.[154,155]
	West Nile virus (WNV)	Culex pipiens,Culex quinquefasciatus[156,157]	WNV disease, including West Nile fever, West Nile encephalitis, and West Nile meningoencephalitis, is the most important MBVD in North America.[158,159,160]
	Japanese encephalitis virus (JEV)	Culex tritaeniorhynchus[161]	JEV disease can manifest from mild fever to life-threatening Japanese encephalitis (JE), whose fatality rate is as high as 50%.[162] The survivors may also suffer from long-term neurological sequelae. JE is a leading cause of viral encephalitis in the world.[162,163]
Togaviridae Alphavirus	Chikungunya virus	Aedes aegypti,Aedes albopictus[149]	Chikungunya fever usually manifests a sudden high fever, severe arthralgia and myalgia. It is rarely fatal, the joint pain can be debilitating and may persist for a long period even after other symptoms have subsided.[39,164,165]
	Sindbis virus	Culex pipiens, Culex torrentium[166,167]	Sindbis fever is generally mild and can include fever, rash, arthralgia, and fatigue.[168]
	Eastern equine encephalitis virus (EEEV)	Culiseta melanura[169]	EEEV disease can range from mild flu-like illness to severe encephalitis with a fatality rate as high as 30%–70%, and survivors often experience significant neurological sequelae.[170,171]
	Venezuelan equine encephalitis virus (VEEV)	Culex (Melanoconion) gnomatus, Culex (Melanoconion) vomerifer[172,173]	VEEV disease can range from a mild flu-like illness to severe encephalitis, whose fatality rate is lower than that of EEEV.[174]
Peribunyaviridae Orthobunyavirus	La Crosse virus (LACV)	Aedes triseriatus[175,176]	LACV disease can range from mild fever illness to severe encephalitis, which is a leading cause of pediatric arboviral encephalitis in the United States.[175]
	Jamestown Canyon virus (JCV)	Aedes, Culiseta, Anopheles[6,177,178]	JCV disease usually manifests as a mild febrile illness, sometimes encephalitis or meningitis.[5,6,179]
	Snowshoe Hare virus (SSHV)	Aedes, Culiseta, Anopheles[180,181]	SSHV disease usually manifests a mild febrile illness, sometimes an encephalitis.[180,182]
	California encephalitis virus (CEV)	Aedes squamiger[183]	CEV disease usually manifests as a mild febrile illness, sometimes encephalitis or meningitis.[6]
Phenuiviridae Phlebovirus	Rift Valley fever virus	Aedes, Culex[9,184]	Rift Valley fever can range from a mild febrile illness to a severe hemorrhagic fever.[9]

Infection with MBVs can generate mosquito-borne viral diseases (MBVDs), of which billions of cases are reported annually worldwide, along with hundreds of thousands of deaths, posing a severe threat to global public health.^[1,10,11] With the global warming of the climate, expansion of mosquito habitats, and ever-expanding transportation of people and goods, the incidence and geographic distribution of MBVDs have further increased.^[12] Using cartographic approaches, Bhatt et al.^[10] estimated that there are 390 million (95% confidence interval [CI]: 284–528) dengue infections per year worldwide, of which 96 million (95% CI: 67–136) are apparent. Table 1 summarizes the major pathogenic MBVs and corresponding MBVDs.

Mosquitoes are the critical vectors that mediate the transmission cycle of MBVs. Various protein components in mosquito saliva can regulate infection with MBVs and their pathogenicity at the bite site in the skin and systemically throughout the mammalian host.^[2] Conversely, multiple components in mammalian blood, derived from both the mammalian host and the MBVs, can modulate infectiousness and dissemination of MBVs within the mosquito vector.^[13]

Currently, the primary methods of blocking MBV transmission are vector control and vaccination, with vector control remaining the most critical and effective strategy.^[14] While there are many MBVs, vaccine availability is limited. Nevertheless, vaccination significantly reduces the incidence of certain MBV diseases, such as yellow fever, which is caused by YFV, and Japanese encephalitis, caused by JEV.^[15,16] Recent advances have deepened our understanding of MBV transmission mechanisms, leading to the development of novel transmission-blocking strategies that target key sites, which have demonstrated promising results in laboratory settings.^{[17,18,19,20,21,22]} Future research should focus on field trials at multiple scales to validate the efficacy of these strategies. Overall, MBV transmission control requires an integrated, multifaceted approach, as its benefits substantially surpass those of any single intervention.

In this paper, we review the current knowledge of the infection and transmission of major pathogenic MBVs, their underlying mechanisms, and recent advances in their prevention and control. Simultaneously, we review critical challenges in MBV infection, control, and transmission along with future research directions.

2. Infection with MBVs

MBVs can effectively infect both mosquito vectors and mammalian hosts; some are also capable of infecting avian species. Given the substantial differences between mosquitoes and mammals in terms of physiology, biochemistry, metabolism, and immunity, the processes underlying MBV infection and dissemination in the two distinct host types exhibit specialized characteristics. The following sections detail MBV infections in mammalian hosts and mosquito vectors.

2.1. MBV infection in mammalian hosts

2.1.1. Infection at the mosquito bite site and systemic dissemination

When MBVs are transmitted to a mammalian host through a mosquito bite, they are introduced along with mosquito saliva into both the epidermis and dermis layers of the skin. MBVs typically infect multiple cell types within skin tissue, including monocytes, macrophages, keratinocytes, Langerhans cells, and dendritic cells.^{[23,24,25,26]} Mosquito salivary proteins (MSPs) can stimulate resident immune cells in the skin, such as macrophages and mast cells, inducing the production of multiple proinflammatory cytokines.^[19,27,28] This draws additional virus-susceptible myeloid immune cells to the bite site, facilitating viral infection of these cells and promoting the drainage of infected immune cells to the lymph nodes (Figure 1).^{[19,29,30,31]}

Figure 1.

Mosquito salivary protein (MSP)-enhanced mosquito-borne virus (MBV)-infection. When a mosquito bites a host, MBVs and MSPs are delivered into the epidermis and dermis. MSPs can activate skin resident immune cells, including macrophages and mast cells, triggering the production of pro-inflammatory mediators. This response attracts MBV-susceptible myeloid cells, such as monocytes, macrophages, and dendritic cells, to the bite site, enhancing viral infection and promoting the spread of infected immune cells to the lymph nodes and bloodstream.

The viruses at the mosquito bite site can then return to the draining lymph nodes either as free viral particles or via infected skin immune cells in a Trojan horse-like mechanism. In the spleen and lymph nodes, the viruses can replicate extensively, generating progeny viruses that enter the bloodstream and cause viremia. These progeny viruses then spread systemically through the bloodstream, reaching diverse target organs and infecting them, thereby driving the process of systemic viral dissemination.^[31]

2.1.2. Tissue and cellular tropism of MBVs in mammalian hosts

Viral infections typically exhibit distinct tissue and cellular tropisms closely associated with factors such as virulence, infection routes, receptor distribution patterns, and the distribution in cells and tissues of the components required for viral replication. Mosquito-borne flaviviruses and alphaviruses demonstrate a clear tissue and cellular tropism. Flaviviruses typically infect various skin cell types at mosquito bite sites, including keratinocytes, macrophages, skin fibroblasts, and dendritic cells. Additionally, they infect myeloid immune cells primarily monocytes, macrophages, and dendritic cells, which subsequently traffic to draining lymph nodes and spleens, where viral replication is greatly amplified. This infection process is a common feature of all MBVs.^[2,32]

Certain MBVs exhibit a specific tissue tropism. For instance, JEV, WNV, ZIKV, and VEEV are neurotropic pathogens capable of crossing the blood–brain barrier to infect neurons, glial cells, and neural stem cells, leading to encephalitis, neurodevelopmental disorders, and other neuropathological damage.^{[33,34,35,36,37]} Other MBVs display joint tropism, infecting fibroblasts, chondrocytes, macrophages, and synovial cells within joint tissues, resulting in inflammatory responses and pathological damage in these areas.^{[38,39,40,41]}

2.1.3. Receptors that mediate MBV infection in mammalian hosts

There is a diverse range of receptor molecules for MBVs, particularly flaviviruses, which employ a wide range of receptor types. These include carbohydrate molecules (e.g., glycosaminoglycans, sulfated polysaccharides, and glycosphingolipids),^[42,43,44] α_vβ₃ integrins,^[45,46] C-type lectin receptors (e.g., DC-SIGN/L-SIGN, CLEC5A, and mannose receptors),^[46,47,48] and phosphatidylserine receptors (e.g., TIM, TYRO3, AXL, and MERT).^[49,50] These membrane molecules can either assist or directly mediate flavivirus infection. Notably, the absence of one or more receptor molecules does not compromise flavivirus infection, as other receptor molecules can fully compensate for the missing ones.

However, for certain MBVs, especially some alphaviruses, Zhang et al.^[51] have identified critical receptor molecules whose absence significantly reduces the efficiency of viral infection. For instance, using a genome-wide CRISPR-Cas9-based screen assay, researchers have identified matrix remodeling associated 8 (Mxra8), a plasma membrane protein widely expressed in mammalian myeloid, epithelial, and mesenchymal cells, as an entry mediator for multiple arthritogenic alphaviruses, including CHIKV, Mayaro, Ross River, and O’nyong nyong viruses. Mxra8 directly binds to CHIKV particles, facilitating their attachment to and internalization into host cells. Mechanistically, Mxra8 interacts with a surface-exposed region across the A and B domains of the CHIKV E2 protein, a region thought to mediate attachment. Furthermore, administering Mxra8-Fc protein or anti-Mxra8 blocking antibodies in mice significantly reduces CHIKV and O’nyong nyong virus infection and pathogenesis.

Low-density lipoprotein (LDL) receptor class A domain containing 3 (LDLRAD3) is a conserved plasma membrane protein of the LDL scavenger receptor family. It is expressed in muscle tissues, myeloid cells, mammalian neurons, and the epithelial cells of the gastrointestinal tract. LDLRAD3 binds directly to VEEV particles and enhances their attachment to and internalization into host cells. Notably, VEEV pathogenesis is abolished in mice with deletions in the Ldlrad3 gene, and administering LDLRAD3(D1)-Fc prevents diseases caused by several VEEV subtypes, including highly virulent strains. These findings indicate that LDLRAD3 is a key receptor that mediates VEEV infection in vitro and in vivo.^[52,53]

Clark et al.^[52] demonstrated that the very low-density lipoprotein receptor (VLDLR) serves as a receptor for the prototypical alphavirus, Semliki Forest virus (SFV). They showed that the E2 and E1 glycoproteins (E2-E1) of SFV, EEEV, and SINV interact with the ligand-binding domains (LBDs) of VLDLR and apolipoprotein E receptor 2 (ApoER2), two closely related receptors. The ectopic expression of either receptor enhances cellular attachment and the internalization of virus-like particles. Conversely, a VLDLR LBD-Fc fusion protein or a ligand-binding antagonist can block SFV E2-E1-mediated infection in human and mouse neurons in vitro. Additionally, administering a VLDLR LBD-Fc fusion protein protects neonatal mice against SFV infection, which can quickly become fatal. Interestingly, invertebrate receptor orthologues taken from worms and mosquitoes can also serve as functional alphavirus receptors. These findings suggest that alphaviruses may have evolutionarily selected conserved lipoprotein receptors to facilitate their infection of both mammalian and mosquito hosts.

2.2. Infection of mosquitoes with MBVs

As they feed on mammalian blood, mosquitoes may become infected by viruses present in the blood. First, the virus typically infects the mosquito’s midgut epithelial cells, releasing progeny viruses into the hemolymph. These viruses then disseminate through the hemolymph into various tissues, infecting suitable organs. MBVs essentially act as enteric viruses in mosquitoes, which is a markedly different role from their transmission route in mammals. This also indicates that the process through which mosquitoes are infected with MBVs differs significantly from that in mammals.

2.2.1. Infection of midgut epithelial cells and systemic dissemination

After a mosquito ingests virus-containing blood, the virus enters its midgut, where it directly interacts with and infects midgut epithelial cells. Following extensive replication in the midgut, the virus breaches the midgut epithelial barrier, crossing the escape barrier into the hemolymph. It then disseminates via the hemolymph to other organs and tissues within the mosquito, infecting additional cell types, such as fat body and muscle cells. The virus continues replicating and spreading at these sites, ultimately reaching the salivary glands, where it undergoes further replication and is secreted along with the mosquito’s saliva.^[54,55] The period from when a mosquito ingests a blood meal containing the viruses through their replication in the midgut epithelial cells, dissemination in the hemolymph, and amplification in the salivary glands, until the viruses can be stored and transmitted to the next host, is known as the extrinsic incubation period (EIP).^[56,57] EIP is of great significance for predicting and simulating the transmission of MBVs and for developing appropriate control strategies.^[57,58]

The mosquito midgut hosts a diverse range of microorganisms that can influence MBV infection by modulating the gut microenvironment. Serratia marcescens, a symbiont in the mosquito midgut, facilitates MBV infection through a secreted protein called SmEnhancin, which digests membrane-bound mucins on the mosquito gut epithelium, thereby promoting viral dissemination.^[59] In the midgut of Aedes albopictus, another symbiont, Rosenbergiella sp. YN46, secretes glucose dehydrogenase (RyGDH), which acidifies the gut lumen in mosquitoes that have fed. This acidification induces irreversible conformational changes in the flavivirus envelope protein, preventing viral entry into cells. Rosenbergiella_YN46 manifests effective transstadial transmission in field mosquitoes, blocking the transmission of DENV by newly emerged adult mosquitoes and thereby providing a safe, promising candidate for flavivirus biocontrol.^[22]

2.2.2. Tissue and cellular tropisms of MBVs in mosquitoes

Vector mosquitoes are generally highly susceptible to the viruses they transmit, with multiple cell types and tissues in the mosquito body being susceptible to arboviral infection.^[60,61] Once the virus successfully infects the midgut epithelial cells, it replicates extensively within these cells and releases progeny viruses into the mosquito hemocoel. This hemocoel contains various immune cells, including prohemocytes, phagocytic cells (plasmatocytes), granulocytes, and oenocytoids. Among these, phagocytic cells and granulocytes are particularly susceptible to arboviruses such as DENV or WNV. These infected hemocytes play a crucial role in mediating viral dissemination.^[62]

The fat body is an important organ for nutrition, metabolism, immunity, and endocrine function in mosquitoes, and it is essential for normal physiological activities.^[63,64,65] It is also a critical tissue for arboviral infection.^[66] Infection of the fat body by arboviruses can disrupt normal physiological functions, threatening the survival of the mosquito vector.^[67] In addition, arboviruses can infect mosquitos’ neural tissue, and salivary glands; the last is of significant importance to public health. Once the virus infects the salivary gland cells, it replicates extensively and releases progeny viruses in the saliva, enabling mosquito-to-mammal transmission of the viruses.^[68]

In general, except for certain highly virulent MBVs (e.g., JEV and WNV), MBV infection does not significantly affect the physiological functions or survival of the mosquito. As a result, virus-infected mosquitoes can survive for extended periods and continue to transmit the viruses.

2.2.3. Receptors that mediate MBV infection in mosquitoes

The mosquito midgut serves as the initial site and critical gateway for arbovirus infection. Certain membrane proteins expressed in midgut epithelial cells may act as key receptors to mediate MBV infection. For example, two glycoproteins with molecular weights of 38 kDa and 60 kDa, which are expressed on the brush border membrane of the Aedes aegypti midgut, have been proposed to mediate CHIKV infection.^[69] A 45-kDa membrane protein broadly expressed in the midgut, ovaries, and salivary glands of Aedes aegypti has been identified as a receptor that facilitates DENV infection.^[70] Mucin has also been reported to bind to domain III of the DENV E protein and mediate DENV infection of midgut epithelial cells in Aedes aegypti.^[71]

Additionally, in the midgut of Aedes aegypti, and in C6/36 cells derived from Aedes albopictus, R67 and R80 have been identified as critical receptors that mediate infection with all four DENV serotypes.^[72] Cheng et al.^[73] demonstrated that an Aedes aegypti C-type lectin, mosGCTL-1, is induced by WNV, interacts with WNV in a calcium-dependent manner, and facilitates infection both in vitro and in vivo. A mosquito homolog of human CD45, called mosPTP-1, recruits mosGCTL-1 to mediate viral attachment and enhance viral entry into cells. Similar mechanisms were observed in Culex quinquefasciatus, a natural WNV vector, further confirming the involvement of these molecules in WNV infection. Subsequently, the same group identified nine Aedes aegypti mosGCTL genes as key susceptibility factors for DENV serotype 2 (DENV-2) infection, with mosGCTL-3 exhibiting the strongest effect. MosGCTL-3 is induced by DENV-2 in mosquito tissues and interacts with the DENV-2 E protein and virions in vitro and in vivo. Other mosGCTLs also interact with the DENV-2 E protein, suggesting that DENV uses multiple mosGCTLs as ligands to facilitate infection.^[74]

In fact, a diverse array of receptor molecules mediate MBV infection in mosquitoes, much as they do in mammalian hosts. A single MBV may employ multiple receptor molecules to establish infections within mosquito cells, while different arboviruses may share common receptors. This multiplicity of receptor molecules ensures efficient MBV infection across various tissues and organs within the mosquito.

2.3. Differences and similarities between MBV infection in mammals and mosquitoes

2.3.1. Differences

There are profound physiological and biochemical differences between mammals and mosquitoes. Accordingly, MBV infection unfolds in different ways in the two hosts.

Infection routes: In mammalian hosts, MBVs are transmitted via mosquito bites that inoculate the virus into the dermis and epidermis, where it first infects resident skin cells, such as keratinocytes and Langerhans cells. Subsequently, the virus infects chemotactically recruited myeloid cells at the bite site, which traffic to draining lymph nodes, leading to extensive viral replication. Virions are then released into the bloodstream, disseminating systemically to infect target organs.^{[23,24,25,26,31]} In contrast, mosquitoes acquire MBVs by feeding on blood; the viruses initially replicate extensively in the midgut epithelium, and progeny virions then enter the hemolymph and directly infect hemocytes and other tissues.^[54,55]

Ease of viral replication: MBV replication is more challenging in mammals due to their robust innate and adaptive immune defenses, which the viruses must overcome to establish infections.^{[75,76,77,78]} Mosquitoes lack strong immune mechanisms to suppress MBV replication, enabling prolific viral replication within their bodies.^[79]

Influence of environmental factors: Mammals are homeothermic, maintaining relatively stable physiological and biochemical states, so environmental factors have minimal influence on viral replication. Mosquitoes are poikilothermic miniature insects whose physiology varies significantly with environmental conditions; accordingly, the environment has a strong impact on viral replication in mosquitoes.^{[80,81,82,83]}

Infection outcomes: In mammals, MBV infection can lead to overt symptoms arising from direct viral cytopathology and immune-mediated pathology. Over time, infections are usually cleared by the immune system; mortality is rare.^[84] Conversely, in mosquitoes, MBVs replicate extensively and persist at a relatively stable titer without causing significant harm to the mosquitoes’ survival or ecological fitness, although the mechanisms behind this tolerance remain unclear.^[85]

2.3.2. Similarities

Despite these differences, MBV infections in mammals and mosquitoes share the following features:

Target organ diversity: MBVs infect multiple tissues and organs in both hosts, facilitating viral spread.^[54,86]

Receptor diversity: MBVs, especially mosquito-borne flaviviruses, exploit multiple receptor molecules in mammalian and mosquito cells. These receptors are fully functionally redundant.

Similarity in target cells: MBV infections exhibit tropisms for immune cells in both hosts. Infection of immune cells may aid systemic dissemination, as these cells traffic through the blood and lymph.^{[23,24,25,26,62]}

In summary, MBV infections in mammals and mosquitoes demonstrate marked differences as well as shared characteristics, reflecting MBVs’ different routes of evolutionary adaptation to the two distinct hosts.

3. MBV transmission

The transmission of MBVs involves two primary processes, passing from mosquitoes to mammals and from mammals to mosquitoes.

3.1. Transmission of MBVs from mosquitoes to mammals

MBVs are transmitted from mosquitoes to mammals through mosquito bites. Mammalian skin serves as a complex barrier and immune system. Using piercing-sucking mouthparts, mosquitoes penetrate the epidermis and dermis to locate capillaries.^[87,88] Once a capillary wall is breached, the mosquito accesses the lumen to feed on blood. Throughout this process, from the initial contact with the host’s skin to the completion of blood-feeding, mosquitoes continuously secrete saliva.^[89,90] Mosquito saliva contains hundreds of different types of MSPs, which are the main bioactive components in mosquito saliva.^[2] These MSPs facilitate piercing and feeding by acting as lubricants, anticoagulants, anesthetics, and analgesics, thereby minimizing host pain and itching to avoid detection.^{[54,91,92,93]}

While the specialized functions of most MSPs remain unclear, they are the pivotal factors that mediate mosquito–mammal interaction. Ample solid evidence has demonstrated that MSPs can significantly facilitate the transmission of MBVs from mosquitoes to mammals, which also reflects the viruses’ long-term evolutionary adaptation to both mosquito and mammalian hosts.

3.1.1. MSPs directly facilitate MBV infection in target cells

Some MSPs can directly enhance viral replication in target skin cells. For example, AaVA-1, a venom allergen protein in Aedes aegypti mosquito saliva, competes with Beclin-1 for binding to LRPPRC, freeing Beclin-1 to activate autophagy in mononuclear macrophages and thereby promoting viral infection.^[94] CLIPA3, a serine protease in Aedes aegypti saliva, promotes DENV infection by proteolyzing extracellular matrix proteins, thereby enhancing viral attachment to heparan sulfate.^[95] LTRIN, a salivary protein found in Aedes aegypti mosquitoes, binds to the cell surface receptor LTβR, inhibiting NF-κB signaling and the inflammatory response. Additionally, it upregulates Axl, a coreceptor that facilitates the entry of ZIKV and DENV.^[96] Keratinocytes have been proposed as an important target cell for MBVs. Mosquito saliva has been shown to facilitate infection with DENV, CHIKV, and WNV by suppressing the antiviral response in human keratinocytes.^[97,98]

3.1.2. MSPs facilitate MBV transmission by recruiting susceptible cells

As shown in Figure 1, MSPs are alien to mammals. They can stimulate localized inflammatory responses, attracting immune cells, such as monocytes, macrophages, and dendritic cells, all key targets for MBVs, to the bite site. These cells enhance local infection and facilitate viral dissemination via the lymphatic fluid to the lymph nodes and remote tissues.^[31] For example, AaNRP, a salivary protein from Aedes aegypti, binds to TLR1/4 on macrophages in mammalian skin, activating the MyD88/NF-κB pathway and inducing the release of CXCL1/2/3. These chemokines recruit neutrophils to the bite site, which in turn attract virus-susceptible myeloid cells, enhancing local infection and systemic spread.^[19]

In nature, mammals are often repeatedly exposed to mosquito bites, leading to specific immune responses against MSPs. These immune responses may modulate MBV infection and pathogenesis. The host’s specific humoral immune response may neutralize the MPSs that facilitate viral transmission, thereby mitigating viral infection by mosquito bites. For instance, Aedes aegypti salivary proteins NeSt1 and AgBR1 enhance ZIKV infection.^[99,100] Passive immunization with antibodies targeting these proteins improves survival and reduces viral loads in mice, demonstrating their potential to inhibit mosquito-mediated viral enhancement.^[101] However, not all immune responses are protective. Vaccination with D7, a strong immunogenic salivary protein in Aedes aegypti, exacerbates the severity of mosquito-transmitted WNV infection. Passive transfer of sera from vaccinated mice to naïve mice increases mortality upon subsequent infection, suggesting that a humoral response to the D7 protein may enhance viral pathogenesis.^[102]

Research on specific immune responses to MSPs and their impact on viral transmission remains limited, necessitating further investigation. Additionally, the effect of continued mosquito exposure on viral infection and pathogenesis in hosts already infected with MBVs have not yet been unexplored.

3.1.3. Altered host-seeking or blood-feeding behavior promotes mosquito-to-mammal transmission of MBVs

MBV infection in mosquitoes can alter their host-seeking and blood-feeding behaviors, thereby enhancing viral transmission from mosquitoes to mammals.^[103] For example, Xiang et al.^[104] demonstrated that DENV infection elevates mosquitoes’ attraction to mammalian hosts while reducing their biting efficiency. This inefficiency leads infected mosquitoes to bite more frequently to consume the same level of blood as uninfected mosquitoes. Consequently, the increase in biting frequency facilitates successive transmission, and the behavioral changes induced by the infection triple the mosquitoes’ transmission capacity. MBVs can establish persistent, asymptomatic infections in the mosquitoes’ central nervous system while still influencing their physiology and behavior. Gao et al.^[105] discovered that DENV2 and ZIKV infection reinforce mosquito locomotor activity and blood-feeding propensity throughout the day, thus facilitating the transmission of these viruses.

3.1.4. Mutation of MBVs significantly modulates their transmission from mosquitoes to mammals

When they mutate, MBVs’ transmission capacity can be significantly affected because these mutations alter their viral replication capacity. Cheng et al.^[106] reported that two adjacent amino acid substitutions, threonine to lysine at position 226 (T226K) and glycine to glutamic acid at position 228 (G228E) in the DENV2 Asian I genotype, enhance viral infectivity in both mosquito vectors and mammalian hosts. These mutations thereby facilitate the transmission of the virus. Mechanistic studies suggest that the polarity changes induced by these substitutions increase the binding affinity of the E protein for host C-type lectins. Regla-Nava et al.^[107] reported that an isoleucine-to-valine mutation (I39V) in the NS2B protein of ZIKV enhances viral fitness and enables escape from preexisting DENV immunity. Introducing I39V or I39T, a similar mutation found in recent ZIKV isolates, enhances the replication of wild-type ZIKV in human neuronal precursor cells and lab-reared mosquitoes. These mutations may accelerate the ZIKV transmission cycle.

In summary, the main factors that promote MBV transmission from mosquito to mammalian hosts are the MSPs, the mutations of MBVs, and the altered host-seeking or blood-feeding behaviors induced by MBV infection. Recent research on the impact of MSPs on MBV transmission has largely focused on their direct effects while overlooking the influence of MSP-induced host-specific immune responses on viral transmission. Additionally, since hosts are often repeatedly bitten by mosquitoes after arbovirus infection, the effects of MSPs on viral replication and pathogenesis within the host remain unexplored. Future studies are needed to address these aspects and fully elucidate the critical role of MSPs in accelerating the transmission cycle of MBVs.

3.2. Transmission of MBVs from mammals to mosquitoes

The transmission of MBVs from mammals to mosquitoes is another critical aspect of their life cycle. Studies have identified multiple factors in mammalian host blood that can regulate the infection of mosquito vectors by these viruses.

3.2.1. Host blood factors significantly modulate the mammal-to-mosquito transmission of MBVs

As they replicate in mammalian hosts, viruses such as DENV, ZIKV, and JEV produce large quantities of secreted NS1 protein, with concentrations in host blood ranging from 70 to 15,000 ng/mL^[108] and reaching up to 50,000 ng/mL in exceptional cases.^[109] Host-derived flavivirus NS1 protein can facilitate viral infection in the mosquito gut by suppressing antiviral immune responses in intestinal epithelial cells.^[20,110]

Natural components of host blood can also significantly influence viral infection in mosquitoes. Glucose serves as a crucial energy source and metabolic precursor in the blood. Weng et al.^[111] demonstrated that blood glucose promotes DENV replication and facilitates viral transmission within mosquitoes through the AKT and TOR signaling pathways. Conversely, Zhu et al.^[21] reported that free iron ions in mammalian blood boost the production of reactive oxygen species in the mosquito gut, thereby inhibiting viral infection in the vector. MicroRNAs (miRNAs) in host blood also play a role in virus transmission. Hsa-miR-150-5p, an miRNA found in human blood, is transferred to the mosquito’s gut as it feeds on blood and remains stable for a period. This miRNA targets specific chymotrypsins in the mosquito midgut, reducing their expression and consequently inhibiting their antiviral effects; this ultimately promotes viral infection in the mosquito midgut.^[112]

3.2.2. Host attractiveness to mosquitoes modulates mammal-to-mosquito transmission of MBVs

Host attraction to mosquitoes represents a final critical mechanism for the transmission of MBVs from mammals to mosquitoes. Zhang et al.^[17] found that flavivirus infection can manipulate mammalian host skin microbiota to produce scents, primarily acetophenone, to attract mosquitoes. Mechanistically, flavivirus infection suppresses the expression of RELMα, a key antimicrobial protein on the host skin, leading to the proliferation of acetophenone-producing commensal bacteria and, consequently, elevated acetophenone levels. In addition to viral infection factors, other variables including the host’s genetic background, dietary factors, skin metabolism, and skin microbiome composition and abundance, as well as environmental humidity and temperature, can also influence the host’s odor profile. These changes may alter the host’s attractiveness to mosquitoes and biting behavior, ultimately impacting the efficiency of MBV transmission. Currently, research in these areas is limited. Future studies are urgently needed to elucidate the molecular mechanisms underlying host attraction to mosquitoes and their implications for the MBV transmission cycle, as this could help provide innovative strategies for blocking MBV spread.

3.2.3. Environmental factors influence mammal–mosquito transmission of MBVs

Mosquito vectors typically inhabit tropical and subtropical regions, where the climate is characterized by abundant sunshine, high temperatures, and high humidity, which happen to be the preferred conditions for their survival. Over the course of evolutionary history, MBVs have become highly adapted to the physiological and biochemical environments of their mosquito hosts. Generally, within suitable ranges, higher temperatures and humidity levels facilitate a more rapid replication and spread of viruses among mosquitoes, thereby enhancing their transmission competency.^[80,81]

The Mayaro virus (MAYV), an emerging MBV of public health concern, replicates and disseminates in A. aegypt significantly more rapidly at 30°C than at 20°C. Mosquitoes were found capable of transmitting MAYV as early as three days after a blood meal containing MAYV at 30°C, whereas the virus was only detectable in mosquito saliva after day 15 at 20°C.^[80] Temperature fluctuations can also influence the replication and dissemination of MBVs within mosquito vectors. Alto et al.^[81] observed that constant temperature conditions resulted in higher viral titers in the saliva of Aedes albopictus, whereas no such increase was detected in Aedes aegypti under comparable fluctuating temperature conditions.

Air humidity is another factor that influences the replication and dissemination of MBVs within mosquitoes, although research in this area remains limited. Abu et al.^[82] exposed Aedes aegypti to different humidity levels and measured components of vectorial capacity, including survival, blood-feeding rates, and ZIKV infection and dissemination. They found that mosquito survival decreased with lower humidity, while infection rates increased. Blood-feeding and disseminated infection rates peaked at 50% relative humidity but were similar at 30% and 80%. These findings suggest that humidity has a complex influence on ZIKV infection in Aedes aegypti.

3.2.4. Mutations of MBVs significantly modulate mammal–mosquito transmission of MBVs

Mutations of MBVs can significantly affect the transmission of MBVs from mammals to mosquitoes. This is mainly because these mutations alter the viruses’ replication capacity within the mosquitoes or within both the mosquitoes and mammals. Choi et al.^[113] reported that a single substitution of arginine for histidine at position 86 of the prM protein in the Tonga DENV-2 strain reduces viral protein translation and replication in mammalian cells, but not in Aedes aegypti midgut cells. In mosquito midgut cells, this prM mutation provides a selective infection advantage, likely due to the positively charged arginine introduced by the substitution. Using viruses derived from the DENV2 infectious clone 30P-NBX, Erb et al.^[114] observed a very low midgut infection rate when the viruses were delivered to female Aedes aegypti via an infectious blood meal. To determine whether adaptive mutations in the DENV2 envelope (E) glycoprotein could increase midgut infection rates, they serially passaged 30P-NBX in Aedes aegypti midguts. After four passages, a dominant, nonconservative K122E mutation emerged in E protein domain II, significantly enhancing the midgut infection rate. Site-directed mutagenesis showed that the reduction of the positive charge in E protein domain II promoted Aedes aegypti midgut infection.

In summary, climatic and environmental factors, host- and virus-derived factors in blood, host attractiveness to mosquitoes, and mutations of MBVs can all significantly influence the transmission of MBVs from mammals to mosquitoes. Notably, as micro-insects and poikilotherms, mosquitoes are highly sensitive to environmental factors, such as light, humidity, and temperature, which can naturally influence their physiological and biochemical conditions, thereby regulating the replication and dissemination of MBVs within these vectors. However, contemporary research on the impact of climatic factors on MBV transmission remains limited, focusing primarily on phenotypic traits without attaining in-depth mechanistic insights. Elucidating how climatic factors affect virus infection, dissemination, and vector competency in mosquitoes, and understanding the underlying mechanisms, is crucial for predicting outbreak risks and developing environmentally tailored vector control strategies.

4. Controlling MBV transmission

Given the significant threat that MBVs pose to public health and socioeconomic development, controlling and preventing their transmission are crucial. An integrated strategy combining vector control, vaccination, and novel approaches could effectively curb the transmission of MBVs.

4.1. Vector control

Vector control measures, which include insecticides and biocontrol, are cost-effective methods of preventing the transmission of MBVs.^[14,115]

4.1.1. Mosquito eradication by insecticides

The first strategy primarily relies on the application of insecticides, such as organochlorines (e.g., DDT), organophosphates (e.g., malathion or dichlorvos), and pyrethroids (e.g., lambda-cyhalothrin or deltamethrin).^[116,117] The choice of insecticide depends on the target (adult mosquitoes or larvae), the application context (indoor or outdoor), and the mode of action (contact, stomach, or fumigation toxicity). The spraying methods include indoor residual spraying (IRS) and space spraying. IRS involves spraying long-lasting insecticides on indoor walls and ceilings, which kill mosquitoes upon contact. Meanwhile, space spraying involves delivering ultra-low-volume insecticides via vehicles or aircraft to rapidly kill adult mosquitoes in targeted areas.^[118,119] Insecticide-treated nets are also effective in both killing mosquitoes on contact and providing a physical barrier to repel them.^[120]

Since the dawn of the 21st century, a coordinated malaria control strategy has significantly reduced the global malaria burden. The key to this success has been vector control, especially via the widespread distribution of long-lasting impregnated nets (LLINs). The notion of treating nets with insecticide to improve their effectiveness originated in Benin in the late 1980s. Thanks to ongoing support from the World Health Organization and collaboration with industry, LLINs have become the central tool in malaria prevention, marking a major shift in control strategies.^[121] The remarkable success of LLINs in controlling malaria transmission offers promising prospects for controlling diseases caused by MBVs.

Applying appropriate insecticides through space spraying can effectively eliminate the primary vector mosquitoes that transmit MBVs, namely Aedes aegypti and Aedes albopictus. Karunaratne et al.^[122] conducted a study in Sri Lanka, reporting that space spraying experiments yielded 100% mortality at a 10-meter distance and over 50% mortality at a 50-meter distance using malathion, Pesguard, and Deltacide, even in areas with dense vegetation. In open areas and regions with minimal vegetation, Pesguard and Deltacide sprays achieved 100% mortality at up to 50 meters. In dense vegetation, both species exhibited over 50% mortality at a distance of 75 meters following Deltacide application. Laboratory larval bioassays revealed that a 1-ppm temephos solution could sustain a 100% larval mortality rate for up to 10 months, while the rate declined to 0% in the 11th month. In field conditions under which the concentration gradually decreased with water usage, 100% larval mortality was maintained only during the first four months, dropping to less than 50% in the subsequent two months and reaching zero eight months after application.

Although space spraying can effectively reduce the population density of adult mosquitoes and larva, its impact on lowering mosquito-borne disease transmission still requires further investigation. Pryce et al.^[123] conducted a meta-analysis of the effectiveness of space spraying in controlling malaria transmission. The review encompassed cluster-randomized controlled trials, interrupted time-series studies, randomized crossover studies, and controlled before-and-after studies comparing the capacity of space spraying to control malaria with no intervention. They found that evidence from a 30-year-old study conducted in one state in India hints at a potential effect of space spraying on malaria incidence. However, this evidence is far from certain. Conducting reliable research across diverse settings will be essential to determine whether and when this intervention may be beneficial. Esu et al.^[124] conducted a systematic review of the evidence regarding the effectiveness of peridomestic space spraying of insecticides in reducing wild Aedes mosquito populations and interrupting dengue transmission. They found no definitive evidence to recommend the efficacy of peridomestic space spraying as a standalone control measure. Instead, peridomestic space spraying is used more appropriately as part of an integrated vector management strategy.

However, prolonged insecticide application has promoted the development of resistance in mosquito populations.^{[125,126,127]} Implementing insecticide rotation and integrating chemical methods with biological control strategies can effectively mitigate resistance development and significantly improve mosquito control outcomes.

4.1.2. Biological control

As a complementary approach to chemical methods, biological control measures reduce the density of mosquito populations by introducing natural predators, introducing microbial agents that kill mosquitoes, or releasing genetically modified sterile mosquitoes.^[128,129] The biological control strategy has unique advantages: It does not cause mosquito resistance and is environmentally friendly and biodegradable.

Introducing predators of mosquitoes is a notable natural method of biological control. For example, a trial conducted in rice fields in California, which was intended to control Culex tarsalis, showed that the introduction of the mosquito fish Gambusia affinis followed by treatment with Bacillus thuringiensis israelensis (Bti) effectively prevented the resurgence of the mosquito population. In contrast, mosquito control groups treated only with Bti experienced a rebound in density.^[130] Introducing predatory Toxorhynchites mosquitoes is another example of predator-mediated biocontrol of vector mosquitoes such as Aedes aegypti.^{[131,132,133]} Toxorhynchites mosquitoes are autogenous and do not need to feed on blood; thus, they pose no additional risk of disease transmission.^[134]

Introducing microbes is an effective strategy for the biocontrol of vector mosquitoes. Wolbachia, a genus of gram-negative intracellular bacterial endosymbionts, has proven the most successful. Wolbachia can reduce the fitness of vectors (their ability to survive and reproduce) and suppress arbovirus replication, thereby limiting disease transmission.^[135,136] Utarini et al.^[128] conducted a cluster-randomized trial in Yogyakarta, Indonesia, releasing Aedes aegypti mosquitoes infected with a wMel strain of Wolbachia pipientis to control dengue. They found that the introgression of the strain into Aedes aegypti populations effectively reduced the incidence of symptomatic dengue and led to fewer dengue-related hospitalizations among the participants.

Gene drive technology is a method of genetic engineering designed to circumvent the traditional Mendelian inheritance rules by enabling a specific gene, including a sterile gene, a pathogen-resistant gene, or other detrimental genes, to spread through a population at a rate higher than the normal inheritance probability, which rapidly results in population suppression or replacement.^[137] Gene drives have been receiving increasing attention, and researchers have tested their capacity to control populations of vector mosquitoes in labs and fields.^[137] For instance, the transgenic Aedes aegypti line OX513A (Oxitec, Oxford, UK) has been evaluated as a “release of insects carrying a dominant lethal” (RIDL) strategy in multiple regions worldwide, including the Grand Cayman Islands and Brazil.^{[138,139,140]} This approach typically reduces adult mosquito populations by up to 80%–95%.^[138,139] Additionally, Hammond et al.^[141] demonstrated the suppressive efficacy of a gene drive system in age-structured Anopheles gambiae populations maintained in large indoor cages that allow for complex feeding and reproductive behaviors. They discovered that the gene-drive element rapidly disseminates throughout the population, achieving complete suppression within one year without provoking resistance to the drive in mosquitoes. These studies demonstrate the strong potential of gene drive technology for controlling vector populations and transmission of MBVs. Larger-scale field trials are needed in the future to validate the effectiveness and ecological safety of gene drives in controlling mosquito populations and MBV transmission.

In summary, vector control remains the most effective strategy for controlling the transmission of MBVs. The ideal vector control strategy should integrate chemical, biological, and gene drive approaches, which can significantly enhance vector control efficacy while minimizing the emergence of vector resistance.

4.2. Vaccination

Vaccination is an effective strategy for preventing MBVDs by protecting susceptible populations. Vaccines for certain MBVs, such as YFV and JEV, have been proven to significantly reduce disease incidence in vulnerable groups.^[15,16] Yellow fever vaccine 17D may be the most successful MBVD vaccine. In 1936, Max Theiler, Wray Lloyd, and Hugh Smith at the Rockefeller Foundation developed the 17D live attenuated vaccine.^[142] In 1951, Theiler was awarded the Nobel Prize in Medicine for the development of the 17D vaccine. Wherever high coverage rates of the 17D vaccine are achieved, the incidence of YF is diminished.^[16,143] JE vaccines, another successful type of MBVD prevention vaccine, have been available for decades in four types: live attenuated SA14-14-2, inactivated mouse brain-derived (JE-MB), inactivated Vero cell culture (JE-VC), and live attenuated chimeric (IMOJEV). These vaccines are widely used globally.^[144]

In Japan, China, Korea, and Thailand, childhood immunization programs have significantly reduced the incidence of JE in recent decades. Until recently, JE-MB was the primary vaccine used internationally, but it has now been largely replaced by cell culture–based vaccines.^[144] However, for some viruses, such as DENV and ZIKV, vaccine availability and suitability are limited. The potential for antibody dependent enhancement of infection (ADE) among different dengue serotypes and between DENV and ZIKV further restricts the safety of vaccination in controlling infections with these viruses.^{[145,146,147]} For many other MBVs, safe and effective vaccines are not yet available. Given the critical role of vaccines in preventing infectious diseases, researching and developing MBV vaccines remain urgent priorities in the future.

4.3. Novel strategies for interrupting MBV transmission

In addition to the traditional MBV control strategies discussed above, including vector control and vaccination, recent research advancements have yielded some innovative approaches for interrupting MBV transmission. These novel transmission-blocking methods can be classified into two categories based on the stage they target: they can block transmission from mosquitoes to mammals or from mammals to mosquitoes.

4.3.1. Inhibiting mosquito-to-mammal transmission

Research has revealed that mammalian hosts infected with mosquito-borne flaviviruses are more attractive to mosquitoes. This is due to virus-induced alterations in the host’s skin microbiota. These changes enhance the production of acetophenone, which attracts mosquitoes and improves virus transmission from mammals to mosquitoes. Retinoic acid can reverse these virus-induced changes in the skin microbiome, thereby inhibiting this transmission pathway.^[17] Manipulating host skin microbiota represents one potential approach to preventing mosquito-to-mammal virus transmission.^[18]

MSPs have been shown to significantly enhance MBV infection in mammalian hosts. Active immunization with certain MSPs or the passive transfer of antisera targeting these proteins can effectively compromise their infection-enhancing effects.^{[100,101,148]} MSPs facilitate viral infection by recruiting virus-susceptible myeloid immune cells.^[19,31] Resveratrol, a common plant-derived dietary supplement, can inhibit the recruitment of these myeloid cells when taken orally, thereby reducing MBV transmission from mosquitoes to mammals.^[19] These findings suggest that targeting MSPs or their mediated susceptible immune cell recruitment can help block mosquito-to-mammal virus transmission.

4.3.2. Inhibiting mammal-to-mosquito transmission

Flavivirus NS1 protein, which is produced during host infection, is released into peripheral blood and ingested by mosquitoes as they feed on the blood. In the mosquito gut, NS1 suppresses antiviral responses in intestinal epithelial cells, facilitating viral infection. Actively immunizing mice with NS1 protein not only prevents DENV-induced mortality but also significantly inhibits virus transmission from mammals to mosquitoes.^[20] Additionally, iron supplementation in individuals with iron deficiency can increase serum-free iron ion levels, which could reduce MBV transmission from hosts to mosquitoes.^[21] The gut commensal microbiota can significantly modulate viral infection in mosquitoes. YN46 (Rosenbergiella_YN46), a bacterium from the gut of field Aedes albopictus, renders the mosquitoes refractory to DENV and ZIKV infection. Moreover, in semifield conditions, YN46 exhibits effective transstadial transmission in field mosquitoes, blocking the transmission of DENV by newly emerged adult mosquitoes.^[22] Introducing this bacterium into the environment may offer an effective and safe strategy for flavivirus biocontrol.

In summary, these strategies have demonstrated significant efficacy under laboratory conditions and exhibit strong potential for practical application. However, they are currently unsupported by robust evidence from field trials. Therefore, future field or clinical intervention studies are needed to further validate their effectiveness.

5. Conclusion

MBVs are a significant group of arboviruses with profound public health importance. Diseases caused by these viruses are ubiquitous across multiple countries and regions globally, resulting in hundreds of millions of infections and hundreds of thousands of deaths annually. Over the course of their evolution, MBVs have developed a high degree of adaptation to both mosquito and mammalian hosts, efficiently exploiting specific factors from each host to facilitate transmission. Controlling MBVs requires an integrated approach, with vector management being the most critical preventive strategy at present. Additionally, the development of safe vaccines that are effective against MBVs remains an urgent priority. Some novel transmission-blocking methods have also shown promising application prospects, but their effectiveness needs to be further validated through field trials.

Author Contributions

Zhaoyang Wang conceived the framework of the manuscript, collected writing materials, and completed the writing and revision of the article. Yan Liang, Yufei Wang, and Tingting Li assisted in collecting materials and proofreading the manuscript and references. Gong Cheng conceived the framework of the manuscript, coordinated, and supervised the writing and revision process. All authors read and approved the final manuscript.

Conflicts of Interest

None.

Funding Statement

This review was supported by grants from the National Key Research and Development Plan of China (2023YFA1801004), Shenzhen Medical Research Fund (B2404002), the National Natural Science Foundation of China (32188101), the Shenzhen San-Ming Project for Prevention and Research on Vector-borne Diseases (SZSM202211023), the Science and Technology Project of Southwest United Graduate School of Yunnan (202302AO370010). The New Cornerstone Science Foundation through the New Cornerstone Investigator Program, and the XPLORER PRIZE.