chikungunya ( chikv ) and dengue ( denv which is divided into 4 serotypes , 1 to 4 ) viruses are both arthropod - borne viruses belonging respectively to the genus alphavirus , togaviridae family and flavivirus , flaviviridae family , and transmitted to humans via a bite of infected aedes mosquitoes ( aedes aegypti , aedes albopictus ) . over the past two decades , they have caused multiple worldwide outbreaks , particularly in tropical and sub tropical areas .
recent chikv outbreaks started in kenya in 2004 , spread over the indian ocean region , reached india causing in all more than 1.5 million cases .
then , numerous imported cases were reported in different parts of the world , an outbreak occurred in italy , while autochthonous cases were reported in france .
in central africa , outbreaks occurred in democratic republic of congo , cameroon , gabon and republic of congo .
as for dengue fever ( df ) , its incidence has grown dramatically around the world , rising more than 30-fold in recent decades .
two fifths of the world 's population are at risk of infection , and who currently estimates there are 50 million dengue infections each year .
the disease is now endemic in more than 100 countries in africa , the americas , the eastern mediterranean , south - east asia and the western pacific . during the last decade ,
denv epidemics have occurred in some east and west african countries , including cape verde where more than 17,000 df cases due to serotype 3 were notified . in practice ,
the global picture of both chikungunya and df is similar in their classical forms , so they can be confused particularly in areas where they cocirculate . after variable incubation period ,
both diseases start abruptly with acute fever , arthralgias , myalgias , headaches , rash and fatigue .
arthralgias are often incapacitating in chikv infection and can persist for several years in some patients . for denv infection , after the initial febrile phase , hemorrhagic manifestations can occur , leading to dengue hemorrhagic fever ( dhf ) indeed dengue with shock syndrome ( dss ) . and finally , in addition to denv , reports of deaths in la reunion island were directly attributed to chikv .
furthermore , there is no comparative study of the two infections , still lesser in a concurrent outbreak . here
, we compare the clinical features and the laboratory findings for 343 laboratory - confirmed patients from the concurrent chikv / denv outbreak which occurred in gabon in 2010 .
franceville , the main town of the haut ogooue province , 512 km south - east from libreville ( capital of gabon ) , is located at altitude 333 meters , at the end of the transgabon railway and the national 3 road , in a savannah ecosystem constituted by forest gallery ( figure 1 ) .
there are 5 health care capacities ( hcc ) including 2 public hospitals with 170 beds in all and the medical unit of the centre international de recherches medicales de franceville ( cirmf ) .
a concomitant chikv/ denv outbreak raged 11 towns and one village of the southeast , from february to july 2010 , and recorded 1127 laboratory confirmed cases in franceville .
the cirmf was included as a partner of the moh , in the response to this outbreak , and implicated in active surveillance , case management and diagnostic . as part of these activities ,
a prospective study was initiated , and the investigations were considered as a component of the public health response and authorized by the regional health director . 

map of gabon with location of the gabonese chikungunya outbreak in 2010 . at the time of the outbreak ,
the moh provided a case definition including 2 categories : a suspected case was a patient presenting with at least one of the following symptoms : fever , arthralgias , myalgias , headaches , rash , fatigue , nausea , vomiting , diarrhea , bleeding , and jaundice ; a confirmed case was a suspected case with laboratory confirmation .
all suspected cases consulting in the cirmf medical unit were examined and demographic and clinical data collected in standardized questionnaire .
blood samples were collected in two 7-ml edta vacutainer tubes and one 7-ml dry tube ( vwr international , france ) .
the tubes were stored in the dark at + 4c until arrival at the laboratory .
thick and thin blood films were stained with 20% giemsa and examined for malaria parasites .
hematological ( hematology analyser act 10 , beckman coulter ) and biochemical ( creatinine , ast , alt ) tests were performed ( automatic analyser hitachi model 902 , roche diagnostics ) .
samples were tested for chikv and denv rna genomes by using taqman qrt - pcr technology and specific primers and probes . when used during the acute phase ( 17 days after onset of symptoms ) , the taqman qrt - pcr technology has a sensitivity of up to 80% and specificity of 100% .
results were expressed as averages ( with their sd ) and percentages ( with their 95% confidence interval , ic ) .
the student 's t test was used to compare laboratory parameters and continuous clinical variables . for qualitative variables , the chi square test or fisher 's exact test were used as appropriate .
franceville , the main town of the haut ogooue province , 512 km south - east from libreville ( capital of gabon ) , is located at altitude 333 meters , at the end of the transgabon railway and the national 3 road , in a savannah ecosystem constituted by forest gallery ( figure 1 ) .
there are 5 health care capacities ( hcc ) including 2 public hospitals with 170 beds in all and the medical unit of the centre international de recherches medicales de franceville ( cirmf ) .
a concomitant chikv/ denv outbreak raged 11 towns and one village of the southeast , from february to july 2010 , and recorded 1127 laboratory confirmed cases in franceville .
the cirmf was included as a partner of the moh , in the response to this outbreak , and implicated in active surveillance , case management and diagnostic . as part of these activities ,
a prospective study was initiated , and the investigations were considered as a component of the public health response and authorized by the regional health director . 

at the time of the outbreak , the moh provided a case definition including 2 categories : a suspected case was a patient presenting with at least one of the following symptoms : fever , arthralgias , myalgias , headaches , rash , fatigue , nausea , vomiting , diarrhea , bleeding , and jaundice ; a confirmed case was a suspected case with laboratory confirmation .
all suspected cases consulting in the cirmf medical unit were examined and demographic and clinical data collected in standardized questionnaire .
blood samples were collected in two 7-ml edta vacutainer tubes and one 7-ml dry tube ( vwr international , france ) .
the tubes were stored in the dark at + 4c until arrival at the laboratory .
thick and thin blood films were stained with 20% giemsa and examined for malaria parasites .
hematological ( hematology analyser act 10 , beckman coulter ) and biochemical ( creatinine , ast , alt ) tests were performed ( automatic analyser hitachi model 902 , roche diagnostics ) .
samples were tested for chikv and denv rna genomes by using taqman qrt - pcr technology and specific primers and probes . when used during the acute phase ( 17 days after onset of symptoms )
, the taqman qrt - pcr technology has a sensitivity of up to 80% and specificity of 100% .
results were expressed as averages ( with their sd ) and percentages ( with their 95% confidence interval , ic ) .
the student 's t test was used to compare laboratory parameters and continuous clinical variables . for qualitative variables , the chi square test or fisher 's exact test were used as appropriate .
the sex ratio m / f was 0.99 and the mean age was 3015 ( range , 177 years ) . among these 433 patients ,
343 ( 79.2% ) were laboratory confirmed with 270 ( 62.3% ) chikv+ , 53 ( 12.2% ) denv+ .
the sex ratio m / f was 0.85 for the chikv group , 0.55 for the denv group and 1 for the chikv / denv group , and the mean age was respectively 3016 ( range 1 77 years ) , 3114 ( range , 576 years ) , and 3612 ( range , 174 ) .
hospitalization was required for 39 ( 14.4% ) chikv+ , 2 ( 3.7% ) denv+ ( p=0.02 ) , and 6 chikv / denv+ patients .
headaches and hemorrhage were more frequent ( p respectively 0.01 and 0.001 ) in the denv+ group than in the chikv+ group ( table 1 ) , and myalgias were more frequent in the chikv and denv groups than in the chikv / denv group ( p = 0.005 and 0.02 respectively ) .
similarly , leukopenia and lymphopenia were more frequent ( p respectively 0.02 and 0.001 ) in the denv+ group than in the chikv+ group ( table 2 ) .
there was no difference in biological parameters between the co - infected group and the other groups . 

table 1comparison of clinical signs between chikungunya and dengue - infected patients during the 2010 outbreak in gabon.chikv+denv+pn%n%hospitalization3914.323.60.02clinical symptomsfever234865292.90.16arthralgia22783.54783.90.93myalgia19571.74071.40.96headache19069.94885.70.01asthenia21478.74478.60.72skin rash11140.81526.80.06pruritus7326.81119.60.26digestive signs87321934.50.86hemorragy51.8712.50.001chikv , chikungunya virus ; denv , dengue virus . 
 
table 2comparison of biological parameters between chikungunya and dengue - infected patients during the 2010 outbreak in gabon.chikv+denv+pmeansdmeansdbiological parametershaemoglobin12.31.711.91.140.49leucocytes52431676339015170.02lymphocytes222821614012430.001platelets23308981750225600608240.77asat171118100.38alat453550340.58cratinine963288320.14chikv , chikungunya virus ; denv , dengue virus . 
 
we conducted a comparative study of clinical and biological data of patients with chikungunya and dengue viruses infections during a concurrent outbreak which occurred in south east gabon in 2010 .
of the 343 individuals included in the study , 270 were chik+ , 53 were denv+ , and 20 were co - infected ( chik+/den+ ) .
headaches , hemorrhage , leukopenia and lymphopenia were significantly more frequent in denv+ patients . in our opinion ,
thus , the circulation during this epidemic of other arboviruses such as west nile , rift valley fever and yellow fever viruses , can not be ruled out . to our knowledge , this is the first comparative study of these two diseases .
, chikungunya is described in the literature as a dengue - like disease , due to their common symptoms .
nevertheless , the existence of incapaciting joints pain located at the extremities seems specific of chikungunya .
this distinction is difficult in tropical areas where many other diseases , such as malaria , typhoid fever , influenza , share the same symptoms .
so , in our field experience , these diseases are clinically indistinguishable , and the problem of differential diagnosis may be compounded during concomitant chikv / denv outbreaks in a malaria endemic area . in their classical form , the hemorrhage constitutes an inconstant sign .
bleeding is generally minimal , non life - threathning , and can not assist for the differential diagnosis .
this entity is more recognizable , leading , with the shock syndrome , to the severity of the disease .
these hematological disorders are non specific and can not also assist for the differential diagnosis .
patients with mixed infection did not seem to have more severe symptoms or biological disorders , suggesting no additive effect of the two viruses .
the clinical and biological differences detected in our analysis are not useful in the field .
so , our study confirms that the two diseases are clinically similar and need for laboratory confirmation for their recognition . since their appearance in 2007 in the north of the country , these viruses have spread in the south east , together with the vector aedes albopitus .
 chikungunya ( chikv ) and dengue ( denv ) viruses , both arboviruses , have caused multiple outbreaks worldwide . 
 their clinical features are poorly described in africa and there is no comparative study , although chikungunya is considered as a dengue - like disease . 
 we conducted a comparative study of clinical and biological data from chikv and denv positive patients during the 2010 gabonese outbreak . 
 patients consulting with general symptoms and having laboratory confirmation for chikv or denv were included . 
 clinical and biological data were recorded . 
 statistical analyses were performed using epi info . 
 a p value < 0.05 was considered significant . in all , 270 chikv+ , 53 denv+ and 20 co - infected patients were included in the study . 
 headaches , hemorrhage , leukopenia and lymphopenia were significantly ( p respectively 0.01 , 0.001 , 0.02 and 0.001 ) more frequent in denv+ patients than in chikv+ . 
 there was no additive effect of the two viruses.these clinical and hematological disorders are non specific and can not assist for the differential diagnosis . 
 these diseases are clinically indistinguishable , and need for laboratory confirmation . 