title: Co-circulation of the dengue with chikungunya virus during the 2013 outbreak in the southern part of Lao PDR.
abstract: BACKGROUND
  During the 2013 outbreak, 4638 infection cases and 32 deaths have been recorded in the southern part of Laos. In recent years, the chikungunya virus (CHIKV) emerged in the part of the country bordering Cambodia. Dengue virus (DENV) and CHIKV are transmitted by common mosquito vectors. Both diseases have similar clinical presentations; therefore, CHIKV infections might go undiagnosed in DENV-endemic areas. Thus, rapid detection and accurate diagnosis are crucial for differentiating between the two viruses (DENV and CHIKV). In this study, we demonstrated that CHIKV and two serotypes of DENV are circulating in Laos. In addition, we encountered patients that had been concurrently infected with multiple DENV serotypes or DENV and CHIKV.
  
  
  METHODS
  Plasma samples were collected from 40 patients with suspected DENV infections during an outbreak between July and August 2013. The reverse transcription polymerase chain reaction was performed to detect the four DENV serotypes and CHIKV using specific primers. Specifically, the complete envelope gene sequences of the viruses were sequenced and subjected to phylogenetic analysis.
  
  
  RESULTS
  Forty acute-phase plasma samples from patients with suspected dengue infections were tested for the presence of DENV viral RNA using molecular methods. Among the 40 samples, 14 samples were positive for DENV, 2 samples were positive for both viruses (DENV-2 and DENV-3), whereas DENV-1 and DENV-4 were not detected during the study period. We also encountered 10 samples that were positive for CHIKV. Of the 10 CHIKV-positive samples, 3 samples were co-infected by DENV-2, and 2 samples were co-infected by DENV-3. Phylogenetic analysis revealed that the 2013 dengue outbreak in Laos involved DENV-2 genotype Asian I and DENV-3 genotype II. Moreover, the Laotian CHIKV strains grouped together with those isolated during outbreaks on the Indian Ocean Islands within the East Central South African genotype.
  
  
  CONCLUSIONS
  These findings revealed that two serotypes (DENV-2 and DENV-3) and CHIKV were detected. Furthermore, infection of multiple DENV serotypes and CHIKV was also observed in the 2013 dengue outbreak. This is the first documented evidence of co-infection with CHIKV and one of two DENV serotypes.
authors.affiliation: Department of Public Health, Kansai Medical University, 2-5-1, Shinmachi, Hirakata-shi, Osaka, 573-1010 Japan.
authors.forename: Viengvaly
authors.initials: V
authors.lastname: Phommanivong
authors.affiliation: Department of Public Health, Kansai Medical University, 2-5-1, Shinmachi, Hirakata-shi, Osaka, 573-1010 Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Kanda
authors.affiliation: Department of Public Health, Kansai Medical University, 2-5-1, Shinmachi, Hirakata-shi, Osaka, 573-1010 Japan.
authors.forename: Takaki
authors.initials: T
authors.lastname: Shimono
authors.affiliation: Department of Public Health, Kansai Medical University, 2-5-1, Shinmachi, Hirakata-shi, Osaka, 573-1010 Japan.
authors.forename: Pheophet
authors.initials: P
authors.lastname: Lamaningao
authors.affiliation: Department of Public Health, Kansai Medical University, 2-5-1, Shinmachi, Hirakata-shi, Osaka, 573-1010 Japan.
authors.forename: Andrew Waleluma
authors.initials: AW
authors.lastname: Darcy
authors.affiliation: Department of Public Health, Kansai Medical University, 2-5-1, Shinmachi, Hirakata-shi, Osaka, 573-1010 Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Mishima
authors.affiliation: Champasak Provincial Health Department, Ministry of Health, Pakse, Champasak, Lao PDR.
authors.forename: Bounthanh
authors.initials: B
authors.lastname: Phaytanavanh
authors.affiliation: Department of Public Health, Kansai Medical University, 2-5-1, Shinmachi, Hirakata-shi, Osaka, 573-1010 Japan.
authors.forename: Toshimasa
authors.initials: T
authors.lastname: Nishiyama
keywords: Chikungunya virus; Co-circulation; Co-infection; Dengue virus; Outbreak; Phylogenetic analysis; RT-PCR