reinforced surveillance systems aimed at monitoring the introduction of chikv have been implemented in 6 departments in southeastern france , including the var department , where ae . albopictus has spread since its introduction in 2004 , presumably from northern italy ( 4 ) . on august 29 , 2010 , a 7-year - old girl ( patient 1 ) with acute febrile syndrome , headache , and abdominal pain sought treatment in the city of frjus ( var ) 1 day after she had returned from rajasthan , india . continuous chikv circulation in northern india districts has been reported during 20092010 ( www.promedmail.org ) . three weeks after the notification of patient 1 , another young girl ( patient 2 ) experienced clinical symptoms that began on september 18 with fever , arthralgia , backache , headache , and retro - orbital pain . patient 2 s physician reported that a young girl ( patient 3 ) , a close friend of her patient , showed clinical symptoms compatible with chikv infection at the same time . patient 3 , who lives near patient 1 , had invited patient 2 to spend the night of september 15 at her home . a serum sample from patient 3 was collected 1 week after onset of fever and monoclonal antibody capture elisa detected high titers of specific anti - chikv immunoglobulin m. the serum sample also showed a weak rt - pcr signal for chikv . given that patients 2 and 3 did not report any recent travel to areas endemic for chikv no complications were recorded , but all 3 patients had persistent weakness and joint pain 3 months after the acute phase . intensive mosquito control measures , including spraying for adult mosquitoes and destroying breeding sites , were undertaken around the patients residences and areas visited by confirmed case - patients . no further cases were found by the active case finding system ( a local physician and laboratories network ) implemented for 45 days after the declaration of the last autochthonous case . a molecular study of france/2010 chikv strains isolated in frjus obtained from patients 1 ( imported case ) and 2 ( autochthonous case ) was performed . viral genomic rna was extracted from chikv grown once in mosquito c6/36 cells and then subjected to rt - pcr amplification by using a set of primers targeting the structural genes of chikv ( 7 ) . paired sequence analysis of the e26k e1 junction showed that the 2 france/2010 chikv strains display a divergence rate < 0.05% at the nucleotide level , whereas 100% identity was observed at the amino acid level . phylogenetic analysis demonstrated that these viral strains belong to a cluster that is closely related to strains from india within the ecsa lineage ( figure ) . the france/2010 chikv isolate from patient 2 might be derived from an indian strain introduced by patient 1 ( index case ) . genotypes e2 - 211 t , e2 - 312 m , e2 - 386a , 6k-8i , and e1 - 284e that are found in the currently circulating strains belonging to the ecsa lineage were identified in france/2010 chikv isolates ( 2,3,7 ) . these isolates also display the genotype e1 - 211e specifically shared by viral strains belonging to the asian phylogenetic group ( table ) . the residue ala at position e2 - 264 has not been previously described in any chikv strains . phylogenetic relationships among chikungunya virus isolates from cases of chikungunya fever in france , based on complete e2 - 6k - e1 nucleotide sequence ( 2,771 nt ) analysis . phylogenetic analysis was inferred by using the maximum - likelihood method as implemented in mega version 5 software ( www.megasoftware.net ) . the sequence of the strains from france described in this study has been deposited in genbank ( accession number pending ) ; other sequences were retrieved from genbank . * molecular signatures were based on the analysis of complete amino acid sequence e2 - 6k - e1 ( 923 aa ) . the numbering of amino acid positions refers to the african isolate s27 ( genbank access no . letters in parentheses after strain names refer to east / central / south africa ( a ) , asia ( b ) and west africa ( c ) phylogroups . recent attention has focused on the predominant role of e1 and e2 proteins in successful chikv infection of the anthropophilic ae . vector competence experiments with la runion/2006 chikv isolates demonstrated the importance of the newly acquired e1-ala226val substitution for efficient transmission by ae . albopictus from northern italy and from southeastern france showed disseminated infection rates ranging from 75%90% for chikv strains with e1 - 226v ( 10 ) . the 2 france/2010 chikv strains isolated in frjus have ala at position e1 - 226 ( table ) . the presence of an asp residue at position e2 - 60 , found in most of the ecsa chikv strains , may in part counterbalance the less favorable transmission of e1 - 226a strain in ae . albopictus ( table ) . the thr residue at position e2 - 211 potentiates the infectivity of chikv in ae . the presence of e2 - 211 t in chikv isolates from france underlines the risk for emergence of a fully adapted viral variant if the e1 - 226v genotype was selected during continuous transmission within ae . the efficient chikv transmission in italy and southeastern france sheds new light on its dissemination potential in europe from 1 index case , regardless of the viral genetic background and mosquito species in the region of origin of the imported chikv ( 1,10,11 ) . in emerging regions , such as italy and runion island , where the seroprevalence in the population was < 50% however , > 2 years passed since the end of the epidemic in runion island before a local transmission of chikv was again detected . in europe where sylvatic cycles are absent , vertical transmission may participate in the maintenance and/or cyclic reemergences of chikv . albopictus that may have more efficient vertical transmission than mosquito populations in eastern italy and tropical regions ( 11,12 ) . in 2010 , southeastern france faced the concomitant emergences of dengue virus ( denv ) and chikv ( 13 ) . for each of these viruses , only 2 autochthonous infections were confirmed , which suggests that rapid detection and control measures implemented around imported and autochthonous cases have been efficient . a recent report mentioned the dual emergence of chikv and denv in southeastern france and urged the implementation of specific surveillance and response measures to reduce the risk for arbovirus emergence ( 14 ) . since 2006 , a specific chikungunya / dengue national preparation and response plan based on rapid detection and investigation of imported and suspected autochthonous cases , mosquito control measures , and efficiency evaluation in the treated areas has been activated from may through november and then modified after annual debriefing meetings involving all partners . in 2010 , this model proved to be well adapted to the early detection and control of chikv and denv . albopictus mosquitoes and the successful emergence of chikv in italy and france , reinforced surveillance and response to chikv and denv dissemination should become a higher priority in europe ( 15 ) .
in september 2010 , autochthonous transmission of chikungunya virus was recorded in southeastern france , where the aedes albopictus mosquito vector is present . 
 sequence analysis of the viral genomes of imported and autochthonous isolates indicated new features for the potential emergence and spread of the virus in europe .