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Since 2005, cases of chikungunya (CHIK) were caused by an unusual vector, Aedes albopictus. This mosquito, present in Europe since 1979, has gained importance since its involvement in the first CHIK outbreak in Italy in 2007. The species is capable of transmitting experimentally 26 arboviruses. However, the vectorial status of its temperate populations has remained little investigated. In 2010, autochthonous cases of CHIK and dengue (DEN) were reported in southeastern France. We evaluated the potential of a French population of Ae. albopictus in the transmission of both viruses. We used two strains of each virus, CHIK AND DEN: one strain was isolated from an imported case, and one from an autochthonous case. We used as controls Aedes aegypti from India and Martinique, the source of the imported cases of CHIK and DEN, respectively. We showed that Ae. albopictus from Cagnes-sur-Mer (AL-CSM) was as efficient as the typical tropical vector Ae. aegypti from India to experimentally transmit both CHIK strains isolated from patients in Fréjus, with around 35-67% of mosquitoes delivering up to 14 viral particles at day 3 post-infection (pi). The unexpected finding came from the high efficiency of AL-CSM to transmit both strains of DENV-1 isolated from patients in Nice. Almost 67% of Ae. albopictus AL-CSM which have ensured viral dissemination were able to transmit at day 9 pi when less than 21% of the typical DEN vector Ae. aegypti from Martinique could achieve transmission. Temperate Ae. albopictus behaves differently compared to its counterpart from tropical regions, where recurrent epidemic outbreaks occur. Its potential responsibility for outbreaks in Europe should not be minimized.

We conducted a retrospective phylogenetic analysis of Mayaro virus (MAYV) detected in French Guiana during 1996-2024. Analysis revealed circulation of MAYV genotype D sublineage 2 and suggested introduction from Brazil and spread to Haiti and Venezuela. Phylogenetic findings support endemic circulation and reinforce the need for MAYV surveillance in the region.

Introduced transinfections of the inherited bacteria Wolbachia can inhibit transmission of viruses by Aedes mosquitoes, and in Ae. aegypti are now being deployed for dengue control in a number of countries. Only three Wolbachia strains from the large number that exist in nature have to date been introduced and characterized in this species. Here novel Ae. aegypti transinfections were generated using the wAlbA and wAu strains. In its native Ae. albopictus, wAlbA is maintained at lower density than the co-infecting wAlbB, but following transfer to Ae. aegypti the relative strain density was reversed, illustrating the strain-specific nature of Wolbachia-host co-adaptation in determining density. The wAu strain also reached high densities in Ae. aegypti, and provided highly efficient transmission blocking of dengue and Zika viruses. Both wAu and wAlbA were less susceptible than wMel to density reduction/incomplete maternal transmission resulting from elevated larval rearing temperatures. Although wAu does not induce cytoplasmic incompatibility (CI), it was stably combined with a CI-inducing strain as a superinfection, and this would facilitate its spread into wild populations. Wolbachia wAu provides a very promising new option for arbovirus control, particularly for deployment in hot tropical climates.

Accurate serological tools are essential for monitoring the transmission of arboviruses with pandemic potential, yet cross-reactivity between closely related viruses hampers diagnostics and surveillance. Here, we develop a high-throughput multiplex serological assay to quantify antibody responses to 28 antigens from nine arboviruses (dengue, Zika, yellow fever, West Nile, Usutu, Japanese encephalitis, chikungunya (CHIKV), Mayaro (MAYV), and O’nyong-nyong virus) and apply it to over 4000 samples from epidemiologically distinct sites on four continents. We implement a flexible analytical method based on Bayesian finite mixture models and Receiver Operating Characteristic analysis to evaluate assay performance and define seropositivity thresholds. As a case study, we resolve cross-reactive and virus-specific responses for CHIKV and the emerging MAYV by combining competitive immunoassays with mathematical modelling of multiplex serological and epidemiological data. This approach yields cross-reactivity-adjusted estimates of local transmission dynamics, in agreement with existing epidemiological evidence, and reveals that CHIKV is more prone to induce cross-reactive antibody responses than MAYV. Our results demonstrate the power of combining multiplex serology with experimental validation and modelling to disentangle exposure histories in the face of serological cross-reactivity. This integrative approach holds promise for improving arbovirus surveillance, particularly in settings with overlapping transmission of multiple viruses and limited diagnostic capacity. Arboviruses often co-circulate, but cross-reactivity hampers serological diagnostics. Here, the authors paired multiplex serology with competitive immunoassays and Bayesian modelling to quantify antibody cross-reactivity and extract virus-specific signals from exposure data, enabling reconstruction of transmission dynamics.

As of early August, more than half a million cases of chikungunya virus infection had been reported in the Americas. The rapid spread is probably attributable to a lack of population immunity and the broad distribution in the Americas of vectors capable of transmitting the virus. In December 2013, the first local transmission of chikungunya virus in the Western Hemisphere was reported, beginning with autochthonous cases in Saint Martin. Since then, local transmission has been reported in 31 countries or territories throughout the Americas, including locations in the United States and its territories (Florida, Puerto Rico, and the U.S. Virgin Islands) (see figure). As of August 8, 2014, a total of 576,535 suspected and laboratory-confirmed chikungunya cases had been reported in the Americas, a case count that had nearly doubled over the previous month (see interactive graphic, available with the full text of this article at . . .

The surveillance and detection of zoonotic pathogens in animals is essential for predicting disease transmission pathways and the risks of spillover, but challenges include the costs, ethics and technical expertise required for vertebrate trapping, serum sampling and antibody or virus screening. Surveillance using haematophagous arthropods as a sampling tool offers a unique opportunity to obtain blood samples from a wide range of vertebrate species, allowing the study of host-mosquito associations, and host exposure to pathogens. We explored vertebrate diversity and potential Ross River virus (RRV) transmission pathways by analysing blood-fed mosquitoes collected in Brisbane, Australia. Host origins were identified using barcode sequencing, and host exposure to RRV was assessed using a modified plaque reduction neutralisation test. In total, 480 blood-fed mosquitoes were collected between February 2021 and May 2022. The host origins of 346 (72%) bloodmeals were identified, with humans (73%) and cattle (9%) comprising the dominant hosts. RRV seroprevalence was high in both vertebrate species with evidence of RRV exposure in 70% (21/30) of cattle and 52% (132/253) of humans. This is a novel, non-invasive method of estimating seroprevalence in vertebrate host populations. Our results highlight the potential of blood-fed mosquitoes to provide species-specific insights into pathogen transmission dynamics.

Key Points Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that provokes arthralgia and, potentially, severe complications in humans. A multidisciplinary effort, carried out over the past 5 years, allowed a thoughtful characterization of this mysterious virus. Recently, there was an unexpectedly severe epidemic of CHIKV in countries of the Indian Ocean region. This outbreak seems to have been the result of a striking adaptation of the virus to a new arthropod, Aedes albopictus (the tiger mosquito). Analyses of isolates from this outbreak have resulted in several interesting findings regarding the clinical onset and physiopathology of this virus. Progress has also been made to further our understanding of the interactions of CHIKV with its human host, the cellular tropism of the virus and the mechanisms of triggering the innate immune response. Clinical development has also seen recent advances. Chikungunya virus is a re-emerging alphavirus that recently caused an epidemic in countries of the Indian Ocean. At the time, little was known about the biology and pathogenesis of this virus compared with other viruses, but recent multidisciplinary efforts have furthered our understanding of this pathogen and its interaction with the host. Chikungunya virus (CHIKV) is a re-emerging mosquito-borne alphavirus responsible for a recent, unexpectedly severe epidemic in countries of the Indian Ocean region. Although many alphaviruses have been well studied, little was known about the biology and pathogenesis of CHIKV at the time of the 2005 outbreak. Over the past 5 years there has been a multidisciplinary effort aimed at deciphering the clinical, physiopathological, immunological and virological features of CHIKV infection. This Review highlights some of the most recent advances in our understanding of the biology of CHIKV and its interactions with the host.

Chikungunya is an arboviral disease transmitted by aedes mosquitoes. The virus was first isolated in 1953 in Tanzania. Chikungunya virus is a member of the genus Alphavirus and the family Togaviridae. The disease typically consists of an acute illness characterised by fever, rash, and incapacitating arthralgia. The word chikungunya, used for both the virus and the disease, means “to walk bent over” in some east African languages, and refers to the effect of the joint pains that characterise this dengue-like infection. Chikungunya is a specifically tropical disease, but it is geographically restricted and outbreaks are relatively uncommon. It is only occasionally observed in travellers and military personnel. More than 266 000 people have been infected during the ongoing outbreak in Réunion, in which Aedes albopictus is the presumed vector. In the ongoing Indian outbreak, in which Aedes aegypti is the presumed vector, 1 400 000 cases of chikungunya were reported during 2006. The reasons for the re-emergence of chikungunya on the Indian subcontinent, and for its unprecedented incidence rate in the Indian Ocean region, are unclear. Plausible explanations include increased tourism, chikungunya virus introduction into a naive population, and viral mutation.

Alphavirus infections are transmitted by mosquitoes, but the mode of transmission for Mycobacterium ulcerans, which causes Buruli ulcer, is contested. Using notification data for Victoria, Australia, during 2017-2022, adjusted for incubation period, we show close alignment between alphavirus and Buruli ulcer seasons, supporting the hypothesis of mosquito transmission of M. ulcerans.

Outbreaks of zoonotic arboviruses originating in Africa occur amidst complex ecological changes and are increasingly emerging as important neglected tropical diseases. Despite sporadic epizootics and human cases of Wesselsbron virus (WSLV), Sindbis virus (SINV), and Middelburg virus (MIDV) in Africa, knowledge of associated risks remains insufficient for prevention. We developed species distribution models for the three viruses alongside five key vectors, Aedes circumluteolus and Aedes mcintoshi for WSLV; Culex univittatus and Culex pipiens for SINV; and Mansonia africana and Aedes mcintoshi for MIDV that indicate areas with ecological suitability for the arboviruses in Africa. We integrated virus and mosquito species occurrence data with climate and land-use data for current (2015) and future (2021 - 2040) scenarios under two shared socioeconomic pathways of emission and climate projections. We applied the Maxent algorithm and evaluated over 100 candidate models per species, selecting those with above-random predictive performance based on high mean Area Under the Curve ratios (Range = 1.45 - 1.88). Our models revealed high ecological suitability for the five mosquitoes in Equatorial and Southern Africa and predict emerging ecologically suitable hotspots for arboviral presence in Southern and Eastern regions, with potential future expansion into North and West Africa. Changing patterns in precipitation, especially precipitation in dry and warm seasons, urbanization, human population, livestock density, and climate change exacerbated the geographic expansion of vectors and ecological risk for arbovirus presence. While the ecological risk to arbovirus presence was currently higher in rural areas, our projections indicated a potential future shift towards urban areas. Our study describes how ecological changes are shaping current and future ecological risk of neglected arboviral diseases in Africa and provides spatial maps to aid intersectoral targeted surveillance and vector control as part of early-warning systems.