in november 2009 , saudi military forces previously stationed in other parts of the country were deployed to jazan province . this situation enabled us to look at baseline arbovirus seroprevalence in a group of new arrivals , stratified by province of origin . during may 812 , 2010 , we enrolled 1,026 soldiers in 5 jazan administrative units near the border with yemen in a study to evaluate serologic reactivity to ahfv , cchfv , denv , and rvfv . after receiving consent and assigning numeric identifiers to anonymize data , we used questionnaires to record jazan arrival dates , home province , previous administrative residence , health histories , vector exposures , and other risk factors . serum samples from each soldier were labeled , archived , frozen , stored at 80c , and transferred to the ministry of health central laboratory in riyadh for testing . questionnaire and testing data were entered in epi info software ( wwwn.cdc.gov/epiinfo ) and then transferred to spss version 19.0 ( ibm , somers , ny , usa ) for analysis . a total of 197 ( 19% ) enrolled soldiers reported symptomatic illness during deployment , 49 ( 25% ) of whom were hospitalized . reported signs and symptoms were fever ( n = 81 ) , rash ( n = 50 ) , and musculoskeletal complaints ( n = 128 ) . a diagnosis of malaria was recorded for 27 febrile soldiers and dengue fever for 1 . as expected given the number of malaria cases , reported arthropod exposures favored mosquitoes over ticks , with 875 ( 85% ) soldiers reporting mosquito contact compared with 153 ( 15% ) reporting tick encounters . thirty - seven ( 3% ) soldiers reported contact with livestock carcasses , blood , or body fluids . serologic testing was completed for 1,024 soldiers ; initial screening by igg to each of the 4 viruses was followed by igm testing of all igg - reactive samples . dengue antibodies were tested by using panbio elisa igg ( e - den02 g ; inverness medical innovations , sinnamon park , qld , australia ) and igm ( e - den01 m ; inverness medical innovations ) following manufacturer recommendations and protocols . igg and igm testing for ahfv , cchv , and rvfv was done with centers for disease control and prevention ( atlanta , ga , usa ) reagents and protocols by using cell culture  derived antigens ( 7,10,11 ) . briefly , the elisa antigens used to coat plates ( for igg ) or detect captured igm were produced by infecting vero e6 cells with respective reference virus strains or by using uninfected cells for control . each sample was tested at 4 dilutions ( 100 , 400 , 1,600 , and 6,400 ) . igg reactivity / igm nonreactivity was considered evidence of past infection ; concurrent igg / igm reactivity was interpreted as infection within the previous 6 months . igg - seropositive persons without histories of illness were considered to have had subclinical or very mild infection . forty reactive serum samples were identified , for a combined seroprevalence of 3.9 cases/100 soldiers tested : rvf ( n = 20 ) , ahfv ( n = 13 ) , cchv ( n = 6 ) , and denv ( n = 1 ) ( table ) . one soldier who had a positive test result for igg and igm to rvfv had a rash but no history of fever . we did not observe cross - reactivity of antibodies often seen with flaviviruses , and no person had positive test results against > 1 antigen . * ahfv , alkhurma hemorrhagic fever virus ; cchf , crimean - congo hemorrhagic fever ; denv , dengue virus ; rvfv , rift valley fever virus . two hundred sixty - eight ( 26% ) soldiers were transferred to jazan from tabouk . this northern district accounted for most seropositive soldiers ( 8/13 ) , 6 of whom might have resided in or visited a previously known ahfv - endemic region before transfer . three ahfv - seropositive soldiers arrived from the eastern region ; none had a previous residence or travel history elsewhere . in contrast , most rvfv - seropositive soldiers ( 18/20 ) and all 6 cchv - seropositive soldiers had previously worked and resided in jazan or other previously affected region . the only rvfv igm - seropositive soldier listed a home residence and previous workplace in an ahfv - endemic region . numbers of soldiers with seropositive test results distributed according to saudi arabian province before transfer to jazan , 2009 . red ( n = 20 ) , seropositive for rift valley fever virus . map courtesy of al zahrani . although the full geographic distribution and severity of ahfv infection is still being characterized , data from this study imply a wider range of endemicity than previously reported . this finding is not surprising knowing the large geographic distribution of the suspected tick vectors , ornithodoros savignyi and hyalomma dromedarii ( 12,13 ) ; however , neither hemorrhagic fever nor ahfv infection has been reported from either region . nor did any ahfv - seropositive soldier disclose a history of severe illness , consistent with a 20062009 narjan outbreak study that found seropositive status to be highly correlated with mild or asymptomatic infection . although additional studies are required to further characterize alkhurma s natural history , case - fatality rates of 25%30% reported after earlier outbreaks in jeddah and makkah appear to be overestimates ( 14 ) . in contrast , all cchfv - seropositive and rvfv - seropositive soldiers had resided in jazan or an adjacent region previously endemic for those viruses . apart from the reported episodes of cchf surrounding the importation of infected livestock or ticks , our results showed that it is circulating at least in the western part of the country . a 2% rvfv seroprevalence in our study , although not necessarily generalizable to the entire population , is not surprising given the large number of cases during the 20002001 outbreak ( 1,15 ) . low dengue seroprevalence contrasts with large recurring outbreaks in jeddah and makkah and may have implications for future prevention strategies . although igm testing was not done on igg - seronegative samples , the absence of compatible illness in surveyed soldiers suggests igg was adequate for surveillance screening . other potential limitations include unknown specificity of some tests used to survey these viruses and recall accuracy of travel histories or residences reported by the study s participants . nonetheless , this study provides systematic evidence that alkhurma , crimean - congo hemorrhagic fever , dengue , and rift valley fever viruses are endemic to western , if not all provinces of , saudi arabia . a better understanding of their ecology , natural history , and epidemiology is needed to assess the potential risks to public health .
a 2009 deployment of military units from several saudi arabian provinces to jazan province , saudi arabia , enabled us to evaluate exposure to alkhurma , crimean - congo , dengue , and rift valley hemorrhagic fever viruses . 
 seroprevalence to all viruses was low ; however , alkhurma virus seroprevalence was higher ( 1.3% ) and less geographically restricted than previously thought .