A Novel Sphingosine Kinase Inhibitor Suppresses Chikungunya Virus Infection

Chikungunya virus (CHIKV) is a re-emerging arbovirus in the alphavirus genus. Upon infection, it can cause severe joint pain that can last years in some patients, significantly affecting their quality of life. Currently, there are no vaccines or anti-viral therapies available against CHIKV. Its spread to the Americas from the eastern continents has substantially increased the count of the infected by millions. Thus, there is an urgent need to identify therapeutic targets for CHIKV treatment. A potential point of intervention is the sphingosine-1-phosphate (S1P) pathway. Conversion of sphingosine to S1P is catalyzed by Sphingosine kinases (SKs), which we previously showed to be crucial pro-viral host factor during CHIKV infection. In this study, we screened inhibitors of SKs and identified a novel potent inhibitor of CHIKV infection—SLL3071511. We showed that the pre-treatment of cells with SLL3071511 in vitro effectively inhibited CHIKV infection with an EC₅₀ value of 2.91 µM under both prophylactic and therapeutic modes, significantly decreasing the viral gene expression and release of viral particles. Our studies suggest that targeting SKs is a viable approach for controlling CHIKV replication.     

Case Report: A Case of Diabetic Ketoacidosis Following Chikungunya Virus Infection

Chikungunya is a mosquito-borne viral disease that has recently become endemic in the Caribbean, including the island of Puerto Rico. We present the case of a 50-year-old Puerto Rican man who traveled to St. Louis for business and was diagnosed with acute chikungunya virus infection with atypical features causing diabetic ketoacidosis. This case highlights the need to keep tropical infectious diseases on the differential diagnosis in appropriate individuals and the ways in which tropical infectious diseases can masquerade as part of common presentations.     

Decadal Change in Seroprevalence of Chikungunya Virus Infection in Pune City,India

Chikungunya virus (CHIKV) is an arthropod-borne virus capable of causing large outbreaks. We aimed to determine the decadal change in the extent of chikungunya virus infection from 2009 to 2019. We implemented a prospective cross-sectional survey in Pune City using a 30-cluster approach with probability-proportion-to-size (PPS) sampling, with blood samples collected from 1654 participants in early 2019. The study also included an additional 799 blood samples from an earlier serosurvey in late 2009. The samples were tested by an in-house anti-CHIKV IgG ELISA assay. The overall seroprevalence in 2019 was 53.2% (95% CI 50.7–55.6) as against 8.5% (95% CI 6.5–10.4) in 2009. A fivefold increase in seroprevalence was observed in a decade (p < 0.00001). The seroprevalence increased significantly with age; however, it did not differ between genders. Modeling of age-stratified seroprevalence data from 2019 coincided with a recent outbreak in 2016 followed by the low-level circulation. The mean estimated force of infection during the outbreak was 35.8% (95% CI 2.9–41.2), and it was 1.2% after the outbreak. To conclude, the study reports a fivefold increase in the seroprevalence of chikungunya infection over a decade in Pune City. The modeling approach considering intermittent outbreaks with continuous low-level circulation was a better fit and coincided with a recent outbreak reported in 2016. Community engagement and effective vector control measures are needed to avert future chikungunya outbreaks.     

BHK-21 Cell Clones Differ in Chikungunya Virus Infection and MXRA8 Receptor Expression

Baby hamster kidney-21 (BHK-21) cells are widely used to propagate and study many animal viruses using infection and transfection techniques. Among various BHK-21 cell clones, the fibroblast-like BHK-21/C-13 line and the epithelial-like BHK-21/WI-2 line are commonly used cell clones for alphavirus research. Here we report that BHK-21/WI-2 cells were significantly less susceptible to primary infection by the alphavirus chikungunya virus (CHIKV) than were BHK-21/C-13 cells. The electroporation efficiency of alphavirus RNA into BHK-21/WI-2 was also lower than that of BHK-21/C-13. The growth of CHIKV was decreased in BHK-21/WI-2 compared to BHK-21/C-13, while primary infection and growth of the alphavirus Sindbis virus (SINV) were equivalent in the two cell lines. Our results suggested that CHIKV entry could be compromised in BHK-21/WI-2. Indeed, we found that the mRNA level of the CHIKV receptor MXRA8 in BHK-21/WI-2 cells was much lower than that in BHK-21/C-13 cells, and exogenous expression of either human MXRA8 or hamster MXRA8 rescued CHIKV infection. Our results affirm the importance of the MXRA8 receptor for CHIKV infection, and document differences in its expression in two clonal cell lines derived from the original BHK-21 cell cultures. Our results also indicate that CHIKV propagation and entry studies in BHK-21 cells will be significantly more efficient in BHK-21/C-13 than in BHK-21/WI-2 cells.     

Lack of Evidence of Chikungunya Virus Infection among Blood Donors during the Chikungunya Outbreak in Lazio Region,Italy, 2017

Background: The latest European Chikungunya virus (CHIKV) outbreak occurred in Italy in 2017, in the municipalities of Anzio and Rome (Lazio Region), with a secondary outbreak in the Calabrian Region. Most CHIKV infections are symptomatic but about 15% of people who acquire the infection may be asymptomatic. A retrospective study was conducted with the aim of assessing the prevalence of recent/ongoing CHIKV infections on the blood donor population in the Lazio Region, during the 2017 outbreak (including in the period before it was detected). Methods: The study was conducted on 4595 plasma samples from donors who donated in 14 different Blood Establishments in the Lazio Region, in the period June–November 2017. A total of 389 of these samples were collected in provinces not affected by the outbreak and were used as negative controls. All samples were tested for IgM detection by the use of an ELISA test, and positive samples were tested for confirmation through the use of a PRNT. Molecular tests were performed on sera that were found to be IgM-positive or borderline. Results: A total of 41 (0.89%) blood donors tested positive for IgM. None of these positive IgM ELISA results was confirmed either by PRNT or by molecular tests. Conclusions: Our study has shown no evidence of recent/ongoing CHIKV infection in blood donors of the affected area.     

Symptomatic Chikungunya Virus Infection and Pregnancy Outcomes: A Nested Case-Control Study in French Guiana

During the Chikungunya epidemic in the Caribbean and Latin America, pregnant women were affected by the virus in French Guiana. The question of the impact of the virus on pregnancy was raised because of the lack of scientific consensus and published data in the region. Thus, during the Chikungunya outbreak in French Guiana, a comparative study was set up using a cohort of pregnant women. The objective was to compare pregnancy and neonatal outcomes between pregnant women with Chikungunya virus (CHIKV) infection and pregnant women without CHIKV. Of 653 mothers included in the cohort, 246 mothers were included in the case-control study: 73 had CHIKV fever during pregnancy and 173 had neither fever nor CHIKV during pregnancy. The study did not observe any severe clinical presentation of CHIKV in the participating women. There were no intensive care unit admissions. In addition, the study showed no significant difference between the two groups with regard to pregnancy complications. However, the results showed a potential excess risk of neonatal ICU admission of the newborn when the maternal infection occurred within 7 days before delivery. These results suggest that special attention should be paid to neonates whose mothers were infected with CHIKV shortly before delivery.     

Predictable Chikungunya Infection Dynamics in Brazil

Chikungunya virus (CHIKV) was first imported into the Caribbean in 2013 and subsequently spread across the Americas. It has infected millions in the region and Brazil has become the hub of ongoing transmission. Using Seasonal Autoregressive Integrated Moving Average (SARIMA) models trained and validated on Brazilian data from the Ministry of Health’s notifiable diseases information system, we tested the hypothesis that transmission in Brazil had transitioned from sporadic and explosive to become more predictable. Consistency weighted, population standardized kernel density estimates were used to identify municipalities with the most consistent inter-annual transmission rates. Spatial clustering was assessed per calendar month for 2017–2021 inclusive using Moran’s I. SARIMA models were validated on 2020–2021 data and forecasted 106,162 (95%CI 27,303–200,917) serologically confirmed cases and 339,907 (95%CI 35,780–1035,449) total notifications for 2022–2023 inclusive, with >90% of cases in the Northeast and Southeast regions. Comparing forecasts for the first five months of 2022 to the most up-to-date ECDC report (published 2 June 2022) showed remarkable accuracy: the models predicted 92,739 (95%CI 20,685–195,191) case notifications during which the ECDC reported 92,349 case notifications. Hotspots of consistent transmission were identified in the states of Para and Tocantins (North region); Rio Grande do Norte, Paraiba and Pernambuco (Northeast region); and Rio de Janeiro and eastern Minas Gerais (Southeast region). Significant spatial clustering peaked during late summer/early autumn. This analysis highlights how CHIKV transmission in Brazil has transitioned, making it more predictable and thus enabling improved control targeting and site selection for trialing interventions.     

Detection of Chikungunya Virus in Nepal

Chikungunya virus (CHIKV) is an emerging alphaviral disease and a public health problem in South Asia including Nepal in recent years. In this study, sera were collected from patients presenting with fever, headache, muscular pain, fatigue, and joint pain of both upper and lower extremities. A total of 169 serum samples were tested for CHIKV and dengue virus (DENV) by using Immunoglobulin M (IgM) and Immunoglobulin G (IgG) antibody using enzyme-linked immunosorbent assay (ELISA) method during August to November 2013. Results showed that 3.6% and 27.8% samples were positive for CHIKV and DENV IgM positive, respectively. Similarly, results of IgG showed 3.0% samples were positive for CHIKV IgG and 29.0% were for DENV IgG positive. Further, a 50% focal reduction neutralization test (FRNT₅₀) was performed to confirm the presence of CHIKV, which demonstrated that 8.9% of CHIKV IgM and/or IgG ELISA positive possessed neutralizing anti-CHIK antibodies. To our knowledge, this is the first report in which the presence of CHIKV is confirmed in Nepalese patients by FRNT₅₀. Basic scientists and clinicians need to consider CHIKV as a differential diagnosis in febrile Nepalese patients, and policy makers should consider appropriate surveillance and actions for control strategies.Chikungunya virus (CHIKV) is a mosquito-borne febrile illness that is transmitted to humans through the bite of infected Aedes aegypti and Ae. albopictus mosquitoes.¹ CHIKV belongs to the Alphavirus genus of the Togaviridae family whereas dengue viruses (DENVs) belong to genus Flavivirus of the family Flaviviridae. Both CHIKV and DENV are transmitted by the same mosquito vectors. The CHIKV was first isolated and characterized in humans and mosquitoes during an outbreak in Tanzania and Mozambique in 1955.² Afterwards, several outbreaks of CHIKV occurred and affected millions of people in eastern, southern, central Africa and Asia.³ CHIKV was introduced in the Americas in October 2013. As of April 2015, over 1,322,893 cases have been suspected and 30,309 confirmed to be CHIKV in the Americas.⁴ It generally causes mild illness but sometimes can lead to severe and life-threatening complications. The disease is characterized by an acute illness with fever, chills, headache, nausea, vomiting, joint pain with or without swelling, low back pain, and skin rash. DENV can progress to dengue hemorrhagic fever and dengue shock syndrome while CHIKV causes arthralgia, which may persist for months.⁵ There is similarity in signs and symptoms of CHIK and DEN, which increases risks for misdiagnosis and underreporting of CHIKV infection in DEN-endemic areas.⁵ The incubation period of CHIKV is usually 2–10 days, with constitutional symptoms lasting up to 7 days. The symptoms usually resolve within days to a few weeks; but in severe cases, these symptoms may last for months. Herein, we report a serological study of possible CHIKV infection with confirmation by 50% focal reduction neutralization test (FRNT₅₀) among febrile patients for the first time in Nepal.During August to November 2013, physicians observed more patients presenting with fever and joint pain in three large hospitals of Terai region of Nepal namely Narayani Sub-Regional Hospital, Birgunj, Parsa; Rapti Zonal Hospital, Ghorahi, Dang; and Mahakali Zonal Hospital, Mahendranagar, Kanchanpur (Figure 1 ). The clinical features of those patients were consistent with DEN fever and included fever, rashes, and thrombocytopenia. These patients were initially diagnosed clinically as DEN and managed accordingly. A blood sample was collected from all febrile patients at the time of admission to the hospitals (1–7 days after onset of fever). Samples were centrifuged and maintained at 4°C until they arrived in our research center at Kathmandu. The sera were stored at − 70°C until assayed.Open in a separate windowFigure 1.Map of Nepal showing three ecological zones, five development regions, 75 districts, and study sites.Initially, serum samples were screened for the presence of Immunoglobulin G (IgG) and Immunoglobulin M (IgM) antibodies against DENV using a microtiter plate enzyme-linked immunosorbent assay (ELISA) (Standard Diagnostics Inc., Korea) at Kathmandu, Nepal. The ELISA test was performed according to the manufacture''s protocol and interpreted either positive or negative on the basis of absorbance with respect to cutoff values. A sample was considered positive if the absorbance was greater than the cutoff value (0.3 + average of negative value).The serum samples were shipped to Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan to perform IgG, IgM ELISA and FRNT₅₀ for CHIKV. In-house IgM-capture ELISA was carried out using the protocol described by Bundo and Igarashi⁶ with minor modifications. Ninety-six-well microplates were coated with 100 μL (5.5 μg/100 μL) of anti-human IgM and incubated at 37°C for 1 hour. Wells were blocked with Block Ace and were incubated at room temperature (RT) for 1 hour. After incubation, wells were washed with phosphate buffer saline (PBS) containing 0.05% Tween 20 (PBS-T) three times. Test samples, positive and negative controls were diluted 1:100 in PBS-T and 100 μL aliquots were distributed into duplicate wells. The plate was incubated at 37°C for 1 hour and then washed as described above. CHIKV (strain: S-27 African prototype) antigen (128 ELISA units) was added 100 μL/well and incubated at 37°C for 1 hour. After washing, 100 μL/well of 1:150 dilution of HRP-conjugated anti-CHIKV rabbit polyclonal antibody was added and incubated at 37°C for 1 hour. In case of DENV IgM ELISA, tetravalent DENV antigen and 1:2,500 dilution of HRP-conjugated anti-flavi mouse monoclonal antibody was used.⁷ After washing, 100 μL/well of o-Phenylenediamine dihydrochloride substrate was added and was kept in the dark at RT for 1 hour. To terminate the reaction, 100 μL/well of 1 N sulfuric acid was added to each well, and then the optical density (OD) was read at 492 nm (Multiscan JX, model no. 353; Thermolab System, Tokyo, Japan). A positive control OD₄₉₂ (or sample)/negative control OD₄₉₂ ratio greater than or equal to 2.0 was considered positive. In-house indirect IgG ELISA, purified CHIKV (strain: S-27 African prototype) and was used as assay antigen for CHIK indirect ELISA. For DENV IgG indirect ELISA, was carried out following the protocol described previously.⁸ The protocol for CHIK IgG detection was the same as the IgM detection method except in, assay antigen purified was used for coating plate, dilution of the samples were 1:1,000 and HRP-conjugated anti-human IgG dilution was 1:30,000. A standard curve was prepared using the OD₄₉₂ values of the CHIKV-positive control sera starting with a 1,000-fold dilution, followed by serial 2-fold dilutions. A sample titer equal to or greater than 1:3,000 was considered to be positive.For FRNT₅₀, 150 μL of each dilution of the serum samples were mixed with an equal volume of CHIKV, which contained 60 focus-forming units, followed by incubation at 37°C for 1 hour for a virus-antibody neutralization reaction. The virus and serum mixture was inoculated into vero cell monolayer in a 96-well plate at 37°C for 1 hour. After incubation, the infected cells were overlaid with 1.25% methylcellulose 4,000 in 2% fetal calf serum (FCS) minimun essential medium (MEM). The plates were then incubated at 37°C for 30 hours. The plates were washed with PBS, fixed with 4% paraformaldehyde phosphate buffer solution for 30 minutes at RT, rinsed, and permeabilized with 1% NP-40 solution in PBS per well for 30 minutes at RT. After washing, the plates were blocked with Block Ace for 30 minutes at RT. In-house anti-CHIKV rabbit IgG (diluted 1:3,000), was then added, incubated at 37°C for 1 hour and washed. Subsequently, 1:1,000 diluted HRP-conjugated goat anti-rabbit IgG were added to the plates and incubated at 37°C for 1 hour. The staining was visualized by the addition of a 0.5 mg/mL solution of substrate 3, 3′-diaminobenzidine tetrahydrochloride in PBS with 0.03% of H₂O₂ added at RT for 10 minutes, and the staining reaction was allowed to proceed. After washing the stained cells, the number of foci per well were counted by using a microscope. The reciprocal of the end point serum dilution that provided a 50%, or greater, reduction in the mean number of foci relative to the control wells that contained no serum was considered to be the FRNT₅₀ titer.A total of 169 serum samples were tested for IgM and IgG against CHIKV and DENV by using IgM capture ELISAs and IgG ELISAs.⁸ Results of IgM capture ELISAs showed that six (3.6%) samples were positive for CHIKV IgM only, 47 (27.8%) for DENV IgM only, and three (1.8%) for both CHIKV and DENV IgM positive (

Chikungunya Virus Asian Lineage Infection in the Amazon Region Is Maintained by Asiatic and Caribbean-Introduced Variants

The simultaneous transmission of two lineages of the chikungunya virus (CHIKV) was discovered after the pathogen’s initial arrival in Brazil. In Oiapoque (Amapá state, north Brazil), the Asian lineage (CHIKV-Asian) was discovered, while in Bahia state, the East-Central-South-African lineage (CHIKV-ECSA) was discovered (northeast Brazil). Since then, the CHIKV-Asian lineage has been restricted to the Amazon region (mostly in the state of Amapá), whereas the ECSA lineage has expanded across the country. Despite the fact that the Asian lineage was already present in the Amazon region, the ECSA lineage brought from the northeast caused a large outbreak in the Amazonian state of Roraima (north Brazil) in 2017. Here, CHIKV spread in the Amazon region was studied by a Zika–Dengue–Chikungunya PCR assay in 824 serum samples collected between 2013 and 2016 from individuals with symptoms of viral infection in the Amapá state. We found 11 samples positive for CHIKV-Asian, and, from these samples, we were able to retrieve 10 full-length viral genomes. A comprehensive phylogenetic study revealed that nine CHIKV sequences came from a local transmission cluster related to Caribbean strains, whereas one sequence was related to sequences from the Philippines. These findings imply that CHIKV spread in different ways in Roraima and Amapá, despite the fact that both states had similar climatic circumstances and mosquito vector frequencies.     

树鼩实验感染后血清中抗基孔肯雅病毒IgM和IgG抗体检查

成年树经人工感染基孔肯雅病毒后，能产生2～6天的病毒血症。感染后第6天能产生特异性IgM抗体，第14～21天为高峰，以后逐渐下降。感染后第12天，IgG抗体开始出现，第30～60天为高峰，并持续不降，表明树对基孔肯雅病毒敏感。     

Spontaneous Abortion and Chikungunya Infection: Pathological Findings

Intrauterine transmission of the Chikungunya virus (CHIKV) during early pregnancy has rarely been reported, although vertical transmission has been observed in newborns. Here, we report four cases of spontaneous abortion in women who became infected with CHIKV between the 11th and 17th weeks of pregnancy. Laboratorial confirmation of the infection was conducted by RT-PCR on a urine sample for one case, and the other three were by detection of IgM anti-CHIKV antibodies. Hematoxylin and eosin (H&E) staining and an electron microscopy assay allowed us to find histopathological, such as inflammatory infiltrate in the decidua and chorionic villi, as well as areas of calcification, edema and the deposition of fibrinoid material, and ultrastructural changes, such as mitochondria with fewer cristae and ruptured membranes, endoplasmic reticulum with dilated cisterns, dispersed chromatin in the nuclei and the presence of an apoptotic body in case 1. In addition, by immunohistochemistry (IHC), we found a positivity for the anti-CHIKV antibody in cells of the endometrial glands, decidual cells, syncytiotrophoblasts, cytotrophoblasts, Hofbauer cells and decidual macrophages. Electron microscopy also helped in identifying virus-like particles in the aborted material with a diameter of 40–50 nm, which was consistent with the size of CHIKV particles in the literature. Our findings in this study suggest early maternal fetal transmission, adding more evidence on the role of CHIKV in fetal death.     

Seroprevalence of Asian Lineage Chikungunya Virus Infection on Saint Martin Island, 7 Months after the 2013 Emergence

At the end of 2013, chikungunya virus (CHIKV) emerged in Saint Martin Island, Caribbean. The Asian lineage was identified. Seven months after this introduction, the seroprevalence was 16.9% in the population of Saint Martin and 39.0% of infections remained asymptomatic. This moderate attack rate and the apparent limited size of the outbreak in Saint Martin could be explained by control measures involved to lower the exposure of the inhabitants. Other drivers such as climatic factors and population genetic factors should be explored. The substantial rate of asymptomatic infections recorded points to a potential source of infection that can both spread in new geographic areas and maintain an inconspicuous endemic circulation in the Americas.Chikungunya virus (CHIKV) is a virus of the family Togaviridae, genus Alphavirus, transmitted by Aedes mosquitoes, first isolated in Tanzania in 1953.¹ The burden of the disease is related to persistent arthralgia that sometimes outlasts the initial characteristic triad: fever, arthritis, and rash.² CHIKV strains can be divided into three genetic lineages: west African, east/central/south African (ECSA), and Asian lineage.³ Over the last decade, the ECSA lineage became prevalent worldwide causing outbreaks in Europe, Africa, Indian Ocean, and south Asia.⁴Saint Martin Island is divided into two parts: in the north, the French overseas territory of Saint Martin (∼36,000 inhabitants) and in the south, Sint Maarten (∼40,000), country of the kingdom of the Netherlands. The first cases of CHIKV infection in the Americas were identified in Saint Martin in November 2013; the Asian lineage was involved.⁵ The spread of CHIKV from human to human by the widely distributed vector Aedes aegypti quickly evolved into an outbreak. By February 2014, weekly clinical cases of CHIKV infections diagnosed by general practitioners peaked at 226 (Figure 1 ). Since March, CHIKV circulation decreased in Saint Martin to a weekly average of 42 clinical cases.Open in a separate windowFigure 1.Number of weekly incident cases of chikungunya reported by the general practitioner surveillance system, Saint Martin.In early July, with the beginning of the wet season, we expected an increased activity of A. aegypti vector mosquitoes. To anticipate the dynamics of chikungunya in Saint Martin and inform decision making, we conducted a serosurvey to assess the level of herd immunity and the proportion of asymptomatic infections.For this serosurvey, we constituted a convenience sample, taking advantage of the sole laboratory of Saint Martin. Between July 3 and 8, 2014 (Figure 1), all individuals attending the laboratory for any type of biological analysis were offered a serological test for CHIKV. Only people living in Saint Martin for over 6 months were included. Participants or their legal guardian signed an informed consent and completed a questionnaire collecting information on gender, age, and possibly symptoms of CHIKV infection (joint pain and fever) during the last 6 months. A 5 mL sample of venous blood was collected from adults and 2 mL for children (those less than 6 months of age were excluded). The Advisory Ethical Committee of Paris and the French Data Protection Authority approved the study. Sera were collected and kept at −20°C for 1–6 days before being sent in dry ice to the regional French National Reference Center for Arboviruses, Institut Pasteur de Guyane. Both IgM and IgG anti-CHIKV-specific antibodies were screened in sera using an “in-house” enzyme-linked immunosorbent assay (IgM antibody capture ELISA and ELISA, respectively) as described by Talarmin and others.⁶ If IgM or IgG were detected, the serological test was considered positive.We performed statistical analysis using STATA version 10 (www.stata.com). After a direct standardization by gender and age using 2010 Census data of the French National Institute of Statistics and Economic Studies, we estimated the seroprevalence and the proportion of asymptomatic infections in the population.During the survey, 203 individuals were included (participation rate = 93%) and 42 (20.69%) tested positive for anti-CHIKV antibodies (19 for IgM, 36 for IgG, and 13 for both). Sample size n (%)Population of Saint Martin N (%)Standardized seroprevalence (%)^*Age group 6 months to 29 years37 (18.2)18,197 (0.49)14.8 (3.1–26.5) 30–44 years55 (27.1)9,070 (0.25)11.7 (3.0–20.4) 45–59 years66 (32.5)6,726 (0.18)21.6 (11.4–31.7) ≥ 60 years45 (22.2)2,983 (0.08)34.5 (20.5–48.7)Gender Men74 (36.5)17,519 (0.47)18.6 (9.5–27.8) Women129 (63.5)19,461 (0.53)15.2 (8.9–21.5)Total203 (100)36,98016.9 (11.6–22.1)Open in a separate windowCHIKV = chikungunya virus.^*Sex and age adjusted.This is the first CHIKV serosurvey in the Western Hemisphere since the 2013 emergence in the Caribbean. Seven months after this emergence, we estimated that 16.9% of Saint Martin inhabitants were infected. This moderated herd immunity indicated an intermediate stage of the outbreak in July 2014.Although a direct standardization by gender and age has been applied to limit the selection bias in patient recruitment, an underestimation of CHIKV seroprevalence in population could not be excluded. Access to health care could be easier for people coming to the laboratory than in the general population but should be unlikely as French regulation ensures a broad access to health care. Even if the geographic distribution of the individuals coming to the laboratory was not considered, CHIKV was widespread in all districts of Saint Martin.CHIKV circulated in the whole island; the seroprevalence should be comparable for Sint Maarten and Saint Martin because of the small size of the Island and the lack of physical or geographical separation between both countries facilitating population mixing. However, no surveillance data are available for Sint Maarten, hence the attack rate cannot be directly extrapolated for Sint Maarten.Seroprevalence reported in other surveys varied between 10.2% and 75% (8 the seroprevalence observed in Saint Martin in July 2014 was the lowest recorded. This moderate attack rate was pointing the persistence of the viral circulation in the following months (confirmed by the surveillance data; Figure 1). However, comparison with other surveys should be cautious because data were collected in different settings and at different times throughout the course of the outbreaks (elapsed time between emergence and serosurvey often missing).

Table 2

CHIKV seroprevalence and asymptomatic rates reported in other serosurveys