Incidence of dengue and chikungunya viruses in mosquitoes and human patients in border provinces of Vietnam.

BACKGROUND: Dengue virus remains a major threat in Vietnam, while chikungunya virus is expected to become one. Surveillance was conducted from 2012 to 2014 in Vietnam to assess the presence of dengue and chikungunya viruses in patients hospitalized with acute fever in five Vietnam provinces neighboring Lao PDR and Cambodia. Surveillance was extended to mosquitoes present in the vicinity of the patients' households. RESULTS: A total 558 human serum samples were collected along with 1104 adult mosquitoes and 12,041 larvae from 2250 households. Dengue virus was found in 17 (3%) human serum samples and in 9 (0.8%) adult mosquitoes. Chikungunya virus was detected in 2 adult mosquitoes (0.18%) while no chikungunya virus was detected in humans. Differing densities of mosquito populations were found, with the highest in the Long An Province border with Cambodia. Long An Province also displayed the lowest rate of infection, despite a very high Breteau Index, high human population density and presence of the main cross border road system. The highest incidence was found in Dac Nong Province, where the Breteau and Container indices were the second lowest. Dengue virus was detected in five Aedes albopictus, three Aedes aegypti and one Culex vishnui. Chikungunya virus was detected in two Ae. aegypti. All infected mosquitoes belonged to haplotypes described in other parts of the world and a number of novel haplotypes were found among uninfected mosquitoes. CONCLUSIONS: Dengue is considered to be regularly introduced to Vietnam from Cambodia, mostly through human movement. The data reported here provides a complementary picture. Due to intensive international trade, long-distance transportation of mosquito populations may play a role in the regular importation of dengue in Vietnam through Ho Chi Minh City. It is important to decipher the movement of mosquitoes in Vietnam, not only at the Lao PDR and Cambodia borders but also through international trade routes. Mosquito surveillance programs should address and follow mosquito populations instead of mosquito species.

Surveillance of dengue and chikungunya infection in Dong Thap, Vietnam: A 13-month study

OBJECTIVE@#To establish a surveillance in Dong Thap, at the border with Cambodia by assessing the presence of DENV serotypes and CHIKV among patients hospitalized at Dong Thap general hospital.@*METHODS@#Cross-sectional descriptive analysis was conducted on a cohort of 131 patients hospitalized with acute fever and symptoms compatible with dengue or chikungunya. The study was conducted from January 2012 to February 2013. The full clinical picture was established as well as serological and molecular detection. Serological analysis was sequentially performed on blood samples collected on admission and an average of seven days after admission. The detection of IgM antibody to DENV was performed by IgM capture ELISA and the detection of DENV and CHIKV RNA was done by reverse-transcription multiplex PCR.@*RESULTS@#101 patients out of 131 (77%) were confirmed with dengue. All four dengue serotypes were detected with a predominance of DENV2 and DENV4. No chikungunya infection was detected although reported in neighboring Cambodia. A differential efficiency of serological dengue detection was observed. Efficiency was 29% upon admission and 53% after seven days on the same patients. 30 patients out of 131 (23%) were negative with both DENV and CHIKV.@*CONCLUSIONS@#Dengue is at risk of being underestimated and chikungunya is not systematically detected. Changes in detection and surveillance procedures are therefore discussed to increase efficiency of dengue detection and continue the monitoring the emergence of CHIKV in Dong Thap province and in Vietnam.

Surveillance of dengue and chikungunya infection in Dong Thap, Vietnam: A 13-month study

Objective: To establish a surveillance in Dong Thap, at the border with Cambodia by assessing the presence of DENV serotypes and CHIKV among patients hospitalized at Dong Thap general hospital. Methods: Cross-sectional descriptive analysis was conducted on a cohort of 131 patients hospitalized with acute fever and symptoms compatible with dengue or chikungunya. The study was conducted from January 2012 to February 2013. The full clinical picture was established as well as serological and molecular detection. Serological analysis was sequentially performed on blood samples collected on admission and an average of seven days after admission. The detection of IgM antibody to DENV was performed by IgM capture ELISA and the detection of DENV and CHIKV RNA was done by reverse-transcription multiplex PCR. Results: 101 patients out of 131 (77%) were confirmed with dengue. All four dengue serotypes were detected with a predominance of DENV2 and DENV4. No chikungunya infection was detected although reported in neighboring Cambodia. A differential efficiency of serological dengue detection was observed. Efficiency was 29% upon admission and 53% after seven days on the same patients. 30 patients out of 131 (23%) were negative with both DENV and CHIKV. Conclusions: Dengue is at risk of being underestimated and chikungunya is not systematically detected. Changes in detection and surveillance procedures are therefore discussed to increase efficiency of dengue detection and continue the monitoring the emergence of CHIKV in Dong Thap province and in Vietnam.

Role of Aedes aegypti and Aedes albopictus during the 2011 dengue fever epidemics in Hanoi, Vietnam

OBJECTIVE@#To record the human cases of dengue fever (DF) and investigate the Aedes mosquito species circulating during the Hanoi 2011 DF epidemics.@*METHODS@#24 different outbreak points were recorded in 8 districts between August and December 2011.@*RESULTS@#140 patients were hospitalized following dengue diagnostic with a predominance of males (59.3%) and the 15-34 age class. Only DENV-1 (11.27%) and DENV-2 (88.73%) serotypes were detected in human samples. Mosquito sampling performed in and around patients households revealed the predominance of Aedes aegypti (A. aegypti) (95.15%) versus Aedes albopictus (4.85%).@*CONCLUSIONS@#There is a positive correlation between the population density of A. aegypti and the number of human cases and duration of outbreaks. This was not observed for Aedes albopictus. Three pools of A. aegypti were positive with dengue virus, two with DENV-1 and one with DENV-2.

Role of Aedes aegypti and Aedes albopictus during the 2011 dengue fever epidemics in Hanoi, Vietnam

Objective: To record the human cases of dengue fever (DF) and investigate the Aedes mosquito species circulating during the Hanoi 2011 DF epidemics. Methods: 24 different outbreak points were recorded in 8 districts between August and December 2011. Results: 140 patients were hospitalized following dengue diagnostic with a predominance of males (59.3%) and the 15-34 age class. Only DENV-1 (11.27%) and DENV-2 (88.73%) serotypes were detected in human samples. Mosquito sampling performed in and around patients households revealed the predominance of Aedes aegypti (A. aegypti) (95.15%) versus Aedes albopictus (4.85%). Conclusions: There is a positive correlation between the population density of A. aegypti and the number of human cases and duration of outbreaks. This was not observed for Aedes albopictus. Three pools of A. aegypti were positive with dengue virus, two with DENV-1 and one with DENV-2.

The isolation of Japanese encephalitis and Nam Dinh viruses in Gia Lai, 2004

In 2004, 13 mosquito samples and 31 pig blood samples were collected at reveral districts, Gia Lai province for virus isolating. Isolating virus was carried out by Aedes albopictus clone C6/36 cells. Identifying virus was implemented by RT-PCR with generate primers of Alpha, Bunya, Flavi viruses and specific primers of Japanese encephalitis and Nam dinh virus. Result: one Japanese encephalitis virus strain was isolated from pig blood samples at Ia Grai, Gialai and six Nam dinh virus strains were isolated from Clux tritaeniorhynchus, Culex vishnui and Culex gelidus at Chu se, Gia Lai.

Preparation of Nam Dinh virus antigen to diagnosis of viral acute encephalitis syndrome, 1998-2004

From 2000ml supernatant fluid of infected Aedes albopictus cells clone C6/36, Nam Dinh virus antigen was prepared by ultracentrifuge generating 5ml purified antigen. Protein content of the purified antigen is 4.4 mg/ml and antigen titer stabilizes for two years at - 80oC. The purified antigen was used for detecting IgM against Nam Dinh virus in cerebrospinal fluid from acute encephalitis syndrome patients by indirect IgM-ELISA. The examination of 814 cerebrospinal fluid samples of acute encephalitis syndrome, which were confirmed non-Japanese encephalitis during 1998 - 2004. The positive proportion with Nam Dinh virus antigen has been found to be 6.59 % - 20.06%. Most of positive cases in children were under 15 years old. Acute encephalitis syndrome cases due to Nam Dinh virus mainly occurred in May, June and July, in the same season of Japanese encephalitis in the Northern area of Vietnam.

Applying mac-elisa for etiological surveillance of Japanese encephalitis, West Nile and Nam Dinh viruses cause acute encephalitis syndrome, 2003-2004

During 2003 - 2004, in total 976 sera and cerebrospinal fluid samples from patients with acute encephalitis syndrome (AES) were collected from Pediatric Hospital, several Centers of Preventive Medicine and National Institute of Hygiene and Epidemiology, Tay Nguyen for screening viral pathogens cause AES using MAC-ELISA with Japanese encephalitis (JE), West Nile and Nam Dinh virus antigens. Results: Out of 976 sera and cerebrospinal fluid samples of AES patients were screened using JE virus antigen, 46.1% (454/976) cases were confirmed to be JE virus infection. Out of 239 cerebrospinal fluid samples of AES patients were screened by Nam Dinh virus antigen, 13.4% (32/239) cases were confirmed to be Nam Dinh virus infection. Out of 103 sera and cerebrospinal fluid samples of AES patients were screened by West Nile virus antigen, there were no positive result was confirmed with this antigen. To date, JE virus is leading cause of AES in Vietnam, with over 80% cases in children under 15 years old. It should be intensive JE vaccination for all children under 15 years old in order to control JE soon.

Emergence of Japanese encephalitis (JE) virus genotype 1 in North Vietnam

The analysis of evolutionary of JE virus in the North Vietnam was examined through 1,000 nucleotides of the envelope gene region encoded the E protein. 9 JE virus strains isolated from Vietnamese patients were sequenced and compared with previous published JE virus strains. The results showed that the Vietnamese strains isolated from human brain between 1986 and 1989 clustered in genotype 3. The strains isolated from mosquitoes and pigs between 2001 and 2002 clustered in genotype 1. The emerging JE virus genotype 1 in the North Vietnam among isolates from mosquitoes and pigs in the last few years was recorded for the first time. But JE virus genotype 1 was not detected among isolates from Vietnamese JE patients so far

Study on the pretence of Japanese encephalitis virus in nature

Haemagglutination Inhibition Technique was applied to study conversion anti-Japanese encephalitis (JE) virus antibodies in pigs in Hoai Duc, Ha Tay, in 2002. The results showed that antibody conversion in pigs occurs year-round. Vero and C6/36 cells were used to isolate JE virus. From 83 mosquito pools and 30 pig blood samples, 7 JE viruses strains were isolated from mosquito pools, and 4 JE viruses strains were isolated from pig blood samples. These JE viruses strains were isolated either in the epidemic or in the non epidemic season. Sequencing of E gene region of JE virus strains that were isolated from mosquitoes and pigs, circulating of genotype I of JE virus in North Vietnam in 2002

Detection of new viral encephalitis from cerebrospinal fluids of acute encephalitis syndrome patients in north VietNam

In the year 2002, a new arbovirus strain coded 02VN208 was isolated from cerebro- spinal fluid of patients with acute encephalitis syndrom by C6/36 mosquito cell lines. It’s a virus of 50nm spherical enveloped shape with ARN genetic materia. From a part of the extended sequence,specific primer pair was designed for determining the virus strains of the patients and the mosquitoes isolated by RT-PCR . 6 viral strains belonging to the same genotype of 02VN208 viral strain were confirmed. Results suggested that it’s a new arbovirus named Namdinh virus. Further study should be developed serologically and ultra morphologically

Japanese encephalitis in the North of Vietnam, 2002

453 cases of acute encephalitis syndrome were studied in the year 2002 at the National Institute of Pediatrics and 21 provinces of North Vietnam. Using Aedes albopictus clone C6/36, from CSF, 6 strains of Japanese encephalitis virus were isolated. By ELISA – Sandwich technique and indirect immunofluorescent assay, 4 virus strains were determined, including 4 strains of JE virus and 2 unknown viruses. 43.26% of cases of acute encephalitis syndrome were caused by JE virus. JE incidence in children of 1-4 years old reduced from 37.62% in 1989-1995 year period to 11.22% in 2002, due to the intensive immunization for children 1-5 years old.

Alphaviruses isolated from culex mosquitoes, 2001

In September – December 2001 period, from 4987 female Culex mosquitoes collected in Cat Que commune, Hoai Duc district, Ha Tay province, 4 viral species were isolated by clone C6/36 cells of Vero and Aedes albopictus. Among them, 2 species were alpha virus, 01VN61 virus was isolated from Culex tritaeniorhynchus and 01VN62 virus from Culex gelidus, both strains were adapted to 1-2 days age mice. By sequencing technique on E1 gene and 3 NCR gene area, 01VN62 virus was identified as Safiyama virus, a virus of alpha virus

Use of Mac-Elisa to determine the frequency of Japanese encephalitis (JE) infection among pig population in Ha Tay, 2001-2001

From 2001 September to 2002 August, 566 serum samples of 5-6 months pig at Hoai Duc district, Ha Tay province were supervised. Results showed very high frequency of JE infection among pig population during epidemic season with the percentage of positivity was 82% in June. By contrast during another months of non-epidemic season, the frequency of JE infection among pig population was very low, with the percentage of positivity was between 1.96% and 14%