Autochthonous Transmission Of Chikungunya Virus Research Articles

Expression of anti-chikungunya single-domain antibodies in transgenic Aedes aegypti reduces vector competence for chikungunya virus and Mayaro virus.

Chikungunya virus (CHIKV) and Mayaro virus (MAYV) are closely related alphaviruses that cause acute febrile illness accompanied by an incapacitating polyarthralgia that can persist for years following initial infection. In conjunction with sporadic outbreaks throughout the sub-tropical regions of the Americas, increased global travel to CHIKV- and MAYV-endemic areas has resulted in imported cases of MAYV, as well as imported cases and autochthonous transmission of CHIKV, within the United States and Europe. With increasing prevalence of CHIKV worldwide and MAYV throughout the Americas within the last decade, a heavy focus has been placed on control and prevention programs. To date, the most effective means of controlling the spread of these viruses is through mosquito control programs. However, current programs have limitations in their effectiveness; therefore, novel approaches are necessary to control the spread of these crippling pathogens and lessen their disease burden. We have previously identified and characterized an anti-CHIKV single-domain antibody (sdAb) that potently neutralizes several alphaviruses including Ross River virus and Mayaro virus. Given the close antigenic relationship between MAYV and CHIKV, we formulated a single defense strategy to combat both emerging arboviruses: we generated transgenic Aedes aegypti mosquitoes that express two camelid-derived anti-CHIKV sdAbs. Following an infectious bloodmeal, we observed significant reduction in CHIKV and MAYV replication and transmission potential in sdAb-expressing transgenic compared to wild-type mosquitoes; thus, this strategy provides a novel approach to controlling and preventing outbreaks of these pathogens that reduce quality of life throughout the tropical regions of the world.

Estimating chikungunya virus transmission parameters and vector control effectiveness highlights key factors to mitigate arboviral disease outbreaks

BackgroundViruses transmitted by Aedes mosquitoes have greatly expanded their geographic range in recent decades. They are considered emerging public health threats throughout the world, including Europe. Therefore, public health authorities must be prepared by quantifying the potential magnitude of virus transmission and the effectiveness of interventions.MethodologyWe developed a mathematical model with a vector-host structure for chikungunya virus transmission and estimated model parameters from epidemiological data of the two main autochthonous chikungunya virus transmission events that occurred in Southern France, in Montpellier (2014) and in Le Cannet-des-Maures (2017). We then performed simulations of the model using these estimates to forecast the magnitude of the foci of transmission as a function of the response delay and the moment of virus introduction.ConclusionsThe results of the different simulations underline the relative importance of each variable and can be useful to stakeholders when designing context-based intervention strategies. The findings emphasize the importance of, and advocate for early detection of imported cases and timely biological confirmation of autochthonous cases to ensure timely vector control measures, supporting the implementation and the maintenance of sustainable surveillance systems.

Countries at risk of importation of chikungunya virus cases from Southern Thailand: A modeling study.

Southern Thailand has been experiencing a large chikungunya virus (CHIKV) outbreak since October 2018. Given the magnitude and duration of the outbreak and its location in a popular tourist destination, we sought to determine international case exportation risk and identify countries at greatest risk of receiving travel-associated imported CHIKV cases. We used a probabilistic model to estimate the expected number of exported cases from Southern Thailand between October 2018 and April 2019. The model incorporated data on CHIKV natural history, infection rates in Southern Thailand, average length of stay for tourists, and international outbound air passenger numbers from the outbreak area. For countries highly connected to Southern Thailand by air travel, we ran 1000 simulations to estimate the expected number of imported cases. We also identified destination countries with conditions suitable for autochthonous CHIKV transmission. Over the outbreak period, we estimated that an average of 125 (95% credible interval (CrI): 102–149) cases would be exported from Southern Thailand to international destinations via air travel. China was projected to receive the most cases (43, 95% CrI: 30–56), followed by Singapore (7, 95% CrI: 2–12) and Malaysia (5, 95% CrI: 1–10). Twenty-three countries were projected to receive at least one imported case, and 64% of these countries had one or more regions that could potentially support autochthonous CHIKV transmission. The overall risk of international exportation of CHIKV cases associated with the outbreak is Southern Thailand is high. Our model projections are consistent with recent reports of CHIKV in travelers returning from the region. Countries should be alert to the possibility of CHIKV infection in returning travelers, particularly in regions where autochthonous transmission is possible.

Chikungunya virus outbreak in Sint Maarten, 2013–2014

ABSTRACTThis report describes the outbreak of chikungunya virus (CHIKV) in Sint Maarten, a constituent country of Kingdom of the Netherlands comprising the southern part of the Caribbean island of Saint Martin, from 22 December 2013 (first reported case) through 5 December 2014. The outbreak was first reported by the French overseas collectivity of Saint-Martin in the northern part of the island—the first site in the Americas to report autochthonous transmission of CHIKV. By 5 December 2014, Sint Maarten had reported a total of 658 cases—an overall attack rate of 1.76%. Actual prevalence may have been higher, as some cases may have been misdiagnosed as dengue. Fever and arthralgia affected 71% and 69% of reported cases respectively. Of the 390 laboratory-confirmed cases, 61% were female and the majority were 20–59 years old (mean: 42; range: 4–92). The spread of CHIKV to Sint Maarten was inevitable given the ease of movement of people, and the vector, island-wide. Continuing their history of collaboration, the French and Dutch parts of the island coordinated efforts for prevention and control of the disease. These included a formal agreement to exchange epidemiological information on a regular basis and provide alerts in a timely manner; collaboration among personnel through joint island-wide planning of mosquito control activities, especially along borders; notification of all island visitors, upon their arrival at airports and seaports, of preventative measures to avoid being bitten by mosquitoes; dissemination of educational materials to the public; and island-wide public awareness campaigns, particularly in densely populated areas, for both residents and visitors. The information provided in this report could help increase understanding of the epidemiological characteristics of CHIKV and guide other countries dealing with vector-borne epidemics.

First report of naturally infected Aedes aegypti with chikungunya virus genotype ECSA in the Americas.

BackgroundThe worldwide expansion of new emergent arboviruses such as Chikungunya and Zika reinforces the importance in understanding the role of mosquito species in spreading these pathogens in affected regions. This knowledge is essential for developing effective programs based on species specificity to avoid the establishment of endemic transmission cycles sustained by the identified local vectors. Although the first autochthonous transmission of Chikungunya virus was described in 2014 in the north of Brazil, the main outbreaks were reported in 2015 and 2016 in the northeast of Brazil.Methodology/Principal findingsDuring 5 days of February 2016, we collected mosquitoes in homes of 6 neighborhoods of Aracaju city, the capital of Sergipe state. Four mosquito species were identified but Culex quinquefasciatus and Aedes aegypti were the most abundant. Field-caught mosquitoes were tested for Chikungunya (CHIKV), Zika (ZIKV) and Dengue viruses (DENV) by qRT-PCR and one CHIKV-infected Ae. aegypti female was detected. The complete sequence of CHIKV genome was obtained from this sample and phylogenetic analysis revealed that this isolate belongs to the East-Central-South-African (ECSA) genotype.ConclusionsOur study describes the first identification of a naturally CHIKV-infected Ae. aegypti in Brazil and the first report of a CHIKV from ECSA genotype identified in this species in the Americas. These findings support the notion of Ae. aegypti being a vector involved in CHIKV outbreaks in northeast of Brazil.

Assessment of the Probability of Autochthonous Transmission of Chikungunya Virus in Canada under Recent and Projected Climate Change.

Background:Chikungunya virus (CHIKV) is a reemerging pathogen transmitted by Aedes aegypti and Aedes albopictus mosquitoes. The ongoing Caribbean outbreak is of concern due to the potential for infected travelers to spread the virus to countries where vectors are present and the population is susceptible. Although there has been no autochthonous transmission of CHIKV in Canada, there is concern that both Ae. albopictus and CHIKV will become established, particularly under projected climate change. We developed risk maps for autochthonous CHIKV transmission in Canada under recent (1981–2010) and projected climate (2011–2040 and 2041–2070).Methods:The risk for CHIKV transmission was the combination of the climatic suitability for CHIKV transmission potential and the climatic suitability for the presence of Ae. albopictus; the former was assessed using a stochastic model to calculate and the latter was assessed by deriving a suitability indicator (SIG) that captures a set of climatic conditions known to influence the ecology of Ae. albopictus. and SIG were calculated for each grid cell in Canada south of , for each time period and for two emission scenarios, and combined to produce overall risk categories that were mapped to identify areas suitable for transmission and the duration of transmissibility.Findings:The risk for autochthonous CHIKV transmission under recent climate is very low with all of Canada classified as unsuitable or rather unsuitable for transmission. Small parts of southern coastal British Columbia become progressively suitable with short-term and long-term projected climate; the duration of potential transmission is limited to 1–2 months of the year.Interpretation:Although the current risk for autochthonous CHIKV transmission in Canada is very low, our study could be further supported by the routine surveillance of Ae. albopictus in areas identified as potentially suitable for transmission given our uncertainty on the current distribution of this species in Canada. https://doi.org/10.1289/EHP669

Epidemic outbreak of Chikungunya in two neighboring towns in the Colombian Caribbean: a survival analysis

BackgroundThe first autochthonous Chikungunya virus transmission in Colombia was reported in September 2014. Three months later, every town in the Caribbean region was affected, including the bordering towns of Ovejas and Corozal, in the department of Sucre. The objective of the study was to analyze and compare the temporal dynamics of the outbreak of Chikungunya in two towns of the department of Sucre.MethodsHouseholds with suspicious cases with clinical symptomatology for Chikungunya were enrolled. In each house an epidemiological questionnaire was applied to collect economic and social information and methods for vector control.ResultsThe study analyzed data collected between 09/01/2014 and 01/31/2015; 458 families in Corozal and 516 families in Ovejas were identified with Chikungunya cases. Estimated attack rates were 10,621 cases and 1640 cases per 100,000 inhabitants, in Ovejas and Corozal, respectively. The 75-day survival curve was 27.2% lower (0.632, CI = 0.614–0.651) in Ovejas than in Corozal (0.904, CI = 0.891–0.917). After 120 days, both curves showed a stable horizontal slope, close to a survival probability of 0.54, indicating the end of the epidemic period. The log-rank test (X2 = 94.6, 1fd, p-value = 0.000) showed the improved survival of Chikungunya in the town of Corozal. The relative risk between the two towns was 0.863 (CI = 0.809–0.921; p-value < 0.001).ConclusionsThe dynamics of the temporal distribution of CHIKV could be influenced by socioeconomic and preventable risk factors. Poor socioeconomic conditions such as the lack and poor efficiency of water supply and waste collection services could be determining factors in the proliferation of CHIKV. The survival analysis proved to be a suitable method for studying the presentation of CHIKV and can be applied to other prevalent vector-borne diseases such as the ZIKA and Dengue.

Dengue, zika e chikungunya - desafios do controle vetorial frente à ocorrência das três arboviroses - Parte I

Long before the emergence of the Chikungunya virus (CHIKV) and the Zika virus (ZIKV) in the Americas and in Brazil between 2013 and 2015, with a record of major epidemics(1-3), there was already a consensus that the traditional model of vector control alone was not capable of stopping the geographical spread of dengue throughout areas hitherto unaffected(4,5). On the other hand, the academic community concluded that a global initiative for immunization, with a large-scale development of vaccines against dengue, will not considerably reduce the transmission of the virus (DENV) if not coupled with other interventions(6). The combination of a more efficient vector control – which has an impact on the force of disease transmission – with the vaccination of large populations – to decrease the proportion of susceptible individuals – appears to be a promising strategy(6,7). However, realistically, the lack of an effective cost-effective vaccine against all four serotypes of DENV and the unavailability of treatment and specific immunobiological drugs against CHIKV and ZIKV still highlight the battle against Aedes aegypti as a central strategy for the containment of arboviruses. However, vector control will only succeed if it includes new technologies and tools that can – in conjunction with those already in effect – achieve more satisfactory results proven to reduce the burden of disease and not only improve entomological indicators(7). Arboviruses: magnitude of the problem Dengue is a viral disease transmitted by arthropods (arbovirus) responsible for the largest number of cases and deaths worldwide, representing a serious public health problem on a global scale(7). The exponential increase in the incidence of the disease and its geographic expansion are impressive given that by the end of 1960 only nine countries had reported outbreaks with autochthonous transmission. In 2016, dengue has become endemic in more than 120 countries, with 100 million estimated cases every year and four billion people living in areas considered at risk for infection by DENV(4,6,8). Brazil accounts for about 70% of all cases reported in the Americas each year. In 2010, twenty-five years after the re-emergence of the disease in the country, more than one million cases were reported by Brazilian states, which overwhelmed health services with nearly a hundred thousand hospitalizations and 678 deaths – half of which were of people under 42 years(9). The potential association between ZIKV and the occurrence of microcephaly and other congenital abnormalities in fetuses and babies whose infection was vertically transmitted in the Americas led the World Health Organization to declare that it is a Public Health Emergency of International Concern (PHEIC) in February 2016(10,11). The association, which would be recognized as causal relationship by the US Centers for Disease Control and Prevention (CDC) and the WHO two months later, was suggested by Brazilian neurologists from September 2015 based on the increase in cases of microcephaly in areas with previous epidemic history ofZIKV(10-13). In August 2016, the Ministry of Health reported 1,806 confirmed cases of microcephaly and/or CNS changes suggestive of congenital infection accumulated since they started to be counted in November 2015(14). The ZIKV was first isolated in Brazil in blood samples obtained in March 2015 in Bahia(15), but reports of an unknown rash disease date back to the end of 2014 and it is likely that its introduction in Brazil has actually occurred in 2013(12,16). Since then, Brazil started to identify in some states the simultaneous circulation of three arboviruses as autochthonous transmission of Chikungunya virus (CHIKV) was already reported since September 2014(2). Throughout 2015 and 2016, explosive outbreaks of Chikungunya fever occurred in several states of Northeastern Brazil. Last year alone, there were more than 170,000 probable cases in Brazil(17). The reasons for the rapid spread of arboviruses are complex and not well understood. However, it can be said that in addition to intrinsic factors related to pathogenic agents themselves, climatic, demographic and social changes have contributed to this process. Particularly, the increased movement of people across countries (migration or leisure) appears to have been instrumental in introducing both CHIKV and ZIKV in the Americas(2,16). The rapid and unplanned urbanization in most developing countries, for example, is related to the increase in infections by DENV as it expands the habitat of primary vectors, particularly Aedes aegypti, in densely populated areas(18,19). The circulation of viruses emerging in areas where the mosquito is endemic, the poor sanitation and a totally susceptible population allows to exacerbate this association. This issue is currently giving rise to new studies and research given its impact on global health and it is not totally covered in this Editorial, which allows the debate to continue, which will be held in the nextissue of the Brazilian Journal in Health Promotion.

Chikungunya virus infections among travellers returning to Spain, 2008 to 2014.

Since the first documented autochthonous transmission of chikungunya virus in the Caribbean island of Saint Martin in 2013, the infection has been reported within the Caribbean region as well as North, Central and South America. The risk of autochthonous transmission of chikungunya virus becoming established in Spain may be elevated due to the large numbers of travellers returning to Spain from countries affected by the 2013 epidemic in the Caribbean and South America, as well as the existence of the Aedes albopictus vector in certain parts of Spain. We retrospectively analysed the laboratory diagnostic database of the National Centre for Microbiology, Institute of Health Carlos III (CNM-ISCIII) from 2008 to 2014. During the study period, 264 confirmed cases, of 1,371 suspected cases, were diagnosed at the CNM-ISCIII. In 2014 alone, there were 234 confirmed cases. The highest number of confirmed cases were reported from the Dominican Republic (n = 136), Venezuela (n = 30) and Haiti (n = 11). Six cases were viraemic in areas of Spain where the vector is present. This report highlights the need for integrated active case and vector surveillance in Spain and other parts of Europe where chikungunya virus may be introduced by returning travellers.

Seroprevalence of Anti-Chikungunya Virus Antibodies in Children and Adults in Managua, Nicaragua, After the First Chikungunya Epidemic, 2014-2015.

Chikungunya is a viral disease transmitted by Aedes aegypti and Ae. albopictus mosquitoes. In late 2013, chikungunya virus (CHIKV) was introduced into the Caribbean island of St. Martin. Since then, approximately 2 million chikungunya cases have been reported by the Pan American Health Organization, and most countries in the Americas report autochthonous transmission of CHIKV. In Nicaragua, the first imported case was described in July 2014 and the first autochthonous case in September 2014. Here, we conducted two studies to analyze the seroprevalence of anti-CHIKV antibodies after the first chikungunya epidemic in a community-based cohort study (ages 2–14 years) and in a cross-sectional survey of persons aged ≥15 years in the same area of Managua, Nicaragua. Routine annual serum samples collected from 3,362 cohort participants in March/April 2014 and 2015, and 848 age-stratified samples collected from persons ≥15 years old at the end of May-beginning of June 2015 were used to estimate the seroprevalence of anti-CHIKV antibodies after the first epidemic (October 2014 to February 2015 in the study population). Using an Inhibition ELISA assay that measures total anti-CHIKV antibodies, the seroprevalence was significantly higher in those aged ≥15 (13.1% (95%CI: 10.9, 15.5)) than in the pediatric population (6.1% (95%CI: 5.3, 6.9)). The proportion of inapparent infections was 58.3% (95%CI: 51.5, 65.1) in children and 64.9% (95%CI: 55.2, 73.7) in the ≥15 study population. We identified age, water availability, household size, and socioeconomic status as factors associated with the presence of anti-CHIKV antibodies. Overall, this is the first report of CHIKV seropositivity in continental Latin America and provides useful information for public health authorities in the region.

Viral exanthems.

Determining the viral cause of a rash presents significant diagnostic challenges. We review contemporary literature on viral exanthems and suggest a structured approach to aid diagnosis. Strains responsible for, and the clinical presentation of, enteroviral infections have diverged from classic descriptions. The causative relationship between antibiotic administration and rash in Epstein-Barr virus infection has been recently questioned. Major measles virus outbreaks have recently occurred in Europe and the USA. The largest Ebola virus outbreak in West Africa has resulted in importation of the virus to other countries and secondary local transmission. Autochthonous transmission of Chikungunya virus has occurred in nonendemic areas, including Europe, the Caribbean and Americas. Zika virus has re-emerged in the Pacific with local transmission from imported cases. Climate change, global warming and spillover of zoonotic viruses are contributing to the emergence and spread of viral diseases. Important clues to the diagnosis of viral exanthems include their distribution and morphology, geographic location and potential exposure to vector-borne or blood-borne viruses. Diagnosis is commonly made via serology, nucleic acid tests or, rarely, viral culture. Skin biopsy is not usually required. In general, viral exanthems are self-limiting and treatment is supportive.

Chikungunya Virus in the Caribbean: A Threat for All of the Americas.

The first known autochthonous transmission of chikungunya virus (CHIKV) fever in the Western Hemisphere occurred in October 2013 in the French sector of the island of Saint Martin, approximately 150 miles east from Puerto Rico [1]. Chikungunya virus is a mosquito-borne arbovirus widely distributed in Africa, Southeast Asia, and India, but until the last decade it was responsible mainly for sporadic, limited outbreaks of illness [2–5]. Its recent epidemic spread through the Caribbean now poses a threat to the continental countries of South, Central, and North America [6–10].

Geographic expansion of the invasive mosquito Aedes albopictus across Panama--implications for control of dengue and Chikungunya viruses.

The Asian tiger mosquito, Aedes (Stegomyia) albopictus, is an invasive species that has expanded its territory to over 40% of the earth’s terrestrial landmass in the last 30 years [1]. Ae. albopictus is an efficient vector of all serotypes of dengue, a disease that has increased in frequency over the past 30 years in the Americas [2], where it represents an annual cost of 2,100,000,000 USD per year [3]. This mosquito is also an efficient vector of the three genotypes of Chikungunya virus, a worldwide emerging pathogen that causes fever, fatigue, and joint swelling in humans. Since 2006, Chikungunya outbreaks have been increasingly recorded outside the virus’s native range in tropical Africa, perhaps because of a mutation in the virus’s envelope gene, which increases the replication and dissemination capacity of the virus in Ae. albopictus [4]. During the second quarter of 2014, Chikungunya has been detected throughout much of the Americas, with major outbreaks occurring in several Caribbean nations, and local transmission confirmed or suspected in the United States, Panama, Venezuela, Peru, and Chile, creating an imminent threat for humans throughout the Americas, who have no prior exposure to this infection [5]. The first cases of Chikungunya disease in Panama were reported in May 2014, occurring in nonresidents who most likely picked up the virus in their Caribbean countries of origin. On 23 July 2014, Panama’s health authority reported autochthonous transmission of Chikungunya virus. Coincidentally, the earliest cases involved patients located in Juan Diaz, an urban area on the eastern outskirts of Panama City, where the first specimen of invasive Ae. albopictus was collected in 2002. Ae. albopictus has expanded across much of Panama since that time, yet to date, no information exists about the degree of expansion or about the factors contributing to the geographic expansion of this important mosquito vector across Panama. Here, we map the temporal expansion of Ae. albopictus, use species distribution models to determine the ecological and nonecological factors associated with its expansion, and comment on the implications for vector and disease control programs in Panama and elsewhere in the American tropics.

Estimating Drivers of Autochthonous Transmission of Chikungunya Virus in its Invasion of the Americas

Estimating Drivers of Autochthonous Transmission of Chikungunya Virus in its Invasion of the Americas

Estimating drivers of autochthonous transmission of chikungunya virus in its invasion of the americas.

Background Chikungunya is an emerging arbovirus that has caused explosive outbreaks in Africa and Asia for decades and invaded the Americas just over a year ago. During this ongoing invasion, it has spread to 45 countries where it has been transmitted autochthonously, infecting nearly 1.3 million people in total. Methods Here, we made use of weekly, country-level case reports to infer relationships between transmission and two putative climatic drivers: temperature and precipitation averaged across each country on a monthly basis. To do so, we used a TSIR model that enabled us to infer a parametric relationship between climatic drivers and transmission potential, and we applied a new method for incorporating a probabilistic description of the serial interval distribution into the TSIR framework. Results We found significant relationships between transmission and linear and quadratic terms for temperature and precipitation and a linear term for log incidence during the previous pathogen generation. The lattermost suggests that case numbers three to four weeks ago are largely predictive of current case numbers. This effect is quite nonlinear at the country level, however, due to an estimated mixing parameter of 0.74. Relationships between transmission and the climatic variables that we estimated were biologically plausible and in line with expectations. Conclusions Our analysis suggests that autochthonous transmission of Chikungunya in the Americas can be correlated successfully with putative climatic drivers, even at the coarse scale of countries and using long-term average climate data. Overall, this provides a preliminary suggestion that successfully forecasting the future trajectory of a Chikungunya outbreak and the receptivity of virgin areas may be possible. Our results also provide tentative estimates of timeframes and areas of greatest risk, and our extension of the TSIR model provides a novel tool for modeling vector-borne disease transmission.

Large number of imported chikungunya cases in mainland France, 2014: a challenge for surveillance and response.

During the summer of 2014, all the pre-requisites for autochthonous transmission of chikungunya virus are present in southern France: a competent vector, Aedes albopictus, and a large number of travellers returning from the French Caribbean islands where an outbreak is occurring. We describe the system implemented for the surveillance of chikungunya and dengue in mainland France. From 2 May to 4 July 2014, there were 126 laboratory-confirmed imported chikungunya cases in mainland France.

Cases of chikungunya virus infection in travellers returning to Spain from Haiti or Dominican Republic, April-June 2014.

Ten cases of chikungunya were diagnosed in Spanish travellers returning from Haiti (n=2), the Dominican Republic (n=7) or from both countries (n=1) between April and June 2014. These cases remind clinicians to consider chikungunya in European travellers presenting with febrile illness and arthralgia, who are returning from the Caribbean region and Central America, particularly from Haiti and the Dominican Republic. The presence of Aedes albopictus together with viraemic patients could potentially lead to autochthonous transmission of chikungunya virus in southern Europe.

Spread of chikungunya from the Caribbean to mainland Central and South America: a greater risk of spillover in Europe?

After a decade of outbreaks in Africa, the Indian Ocean and Asia, chikungunya virus (CHIKV) is stepping out of the shadow of dengue virus [1]. Although these two mosquito-borne viruses share clinical characteristics and their main vectors, Aedes albopictus (the tiger mosquito) and Ae. aegypti, CHIKV has long remained exotic to the western hemisphere [2]. The emergence of the Indian Ocean lineage changed the views on CHIKV when it caused an unprecedented disease burden in India and the islands of the Indian Ocean between 2005 and 2008 [3,4]. More than the reports of single events of locallyacquired cases of chikungunya fever in Italy and France [5,6], the recent occurrence of autochthonous transmission of CHIKV in the Americas has redesigned the geographic distribution of the virus. An outbreak in the Caribbean caused by an Asian strain of the virus started in Saint Martin in October 2013 with Ae. aegypti as the primary vector. The dynamics of the spread of CHIKV was in line with that in outbreaks that occurred in the Indian Ocean [2]. In this issue of Eurosurveillance, Cauchemez et al. estimate the basic reproductive number (the mean number of new host cases generated by one infectious host in a completely susceptible human population) at between 2 and 4 in the initial phase of the outbreak in the French Caribbean [7]. This is close to estimates from the outbreaks in Italy in 2007 and on Reunion Island in 2006 (3.5 and 3.7, respectively) [8,9]. Data from epidemiological surveillance suggest that so far, six months after its introduction to the Caribbean, CHIKV has been responsible for over 350,000 suspected cases of chikungunya fever that have occurred throughout the region [10].

Emergence of chikungunya fever on the French side of Saint Martin island, October to December 2013

On 18 November 2013, five residents of Saint Martin presented with severe joint pain after an acute episode of dengue-like fever. Epidemiological, laboratory and entomological investigations provided evidence of the first autochthonous transmission of chikungunya virus in the Americas. The event indicates a risk of epidemics in America and Europe through substantial passenger traffic to and from continental France. We describe detection and confirmation of the first six cases and results of the first weeks of surveillance.

Chikungunya Virus and the Mosquito Vector Aedes aegypti in New Caledonia (South Pacific Region)

Chikungunya virus (CHIKV) is transmitted to humans through the bite of Aedes mosquitoes. During the 2005-2006 epidemic that occurred in the Indian Ocean Islands, a viral strain harboring a substitution of an alanine to valine at position 226 (E1-A226V) of the E1 glycoprotein enhanced the transmissibility of CHIKV by Aedes albopictus. In March 2011, autochthonous transmission of CHIKV was reported in New Caledonia (NC), an island located in the southwest Pacific Ocean. This was the first report of local chikungunya (CHIK) transmission in this region of the world. Phylogenetic analysis based on the complete genome demonstrated that the CHIKV-NC strain isolated from the first autochthonous human case belongs to the Asian lineage. This is consistent with the Indonesian origin of CHIK cases previously imported and detected. Thus the CHIKV-NC does not present a valine substitution at position E1-226. In New Caledonia, the putative vector of CHIKV is Aedes aegypti, since no other potential vector has ever been described. For example, A. albopictus is not found in NC. Vector competence experiments showed that A. aegypti from New Caledonia was able to transmit, as early as 3 days post-infection, two CHIKV strains: CHIKV-NC belonging to the Asian lineage, and CHIKV-RE from Reunion Island harboring the E1-A226V mutation. Thus the extrinsic incubation period of both CHIKV strains in this vector species could be considered to be quite short. These results illustrate the threat of the spread of CHIKV in the South Pacific region. From February to June 2011 (the end of the alert), only 33 cases were detected. Implementation of drastic vector control measures and the occurrence of the cold season probably helped to limit the extent of the outbreak, but other factors may have also been involved and are discussed.