Dengue Virus Surveillance Research Articles

Laboratory-Based Surveillance and Molecular Characterization of Dengue Viruses in Taiwan, 2014

We present the results of a laboratory-based surveillance of dengue in Taiwan in 2014. A total of 240 imported dengue cases were identified. The patients had arrived from 16 countries, and Malaysia, Indonesia, the Philippines, and China were the most frequent importing countries. Phylogenetic analyses showed that genotype I of dengue virus type 1 (DENV-1) and the cosmopolitan genotype of DENV-2 were the predominant DENV strains circulating in southeast Asia. The 2014 dengue epidemic was the largest ever to occur in Taiwan since World War II, and there were 15,492 laboratory-confirmed indigenous dengue cases. Phylogenetic analysis showed that the explosive dengue epidemic in southern Taiwan was caused by a DENV-1 strain of genotype I imported from Indonesia. There were several possible causes of this outbreak, including delayed notification of the outbreak, limited staff and resources for control measures, abnormal weather conditions, and a serious gas pipeline explosion in the dengue hot spot areas in Kaohsiung City. However, the results of this surveillance indicated that both active and passive surveillance systems should be strengthened so appropriate public health measures can be taken promptly to prevent large-scale dengue outbreaks.

Persistent dengue emergence: the 7 years surrounding the 2010 epidemic in Nepal.

Dengue fever (DF) is an emerging public health problem in Nepal, and yet neither the magnitude of the DF burden or its epidemiological trends are well understood. We conducted a sero-epidemiological, seasonal trend and demographic analysis of the trends in DF in the Terai region of Nepal, from 2007 to 2013. In that period, 2002 serum samples were collected from febrile patients suspected of dengue virus infection. Samples were screened by IgM antibody ELISA analysis for the presence of anti-dengue IgM antibodies. The overall prevalence of DF cases was found to range from 26.1 to 55.4%. Infection was found to be more common among adults and males. Seasonal trends revealed that cases peaked in October and November. The study offers perspective on the dengue fever burden before, during and after a major epidemic and can now be used as a basis for formulating strategies by policy makers that will enhance and develop relevant control and preventive measures against dengue fever. The findings of this study reinforce the perceived need for urgent dengue virus surveillance to enhance dengue control strategies that need to be developed for future preparedness. In the light of the recent earthquakes, future major outbreaks of vector borne disease are likely to recur.

Arbovirus Surveillance and First Report of Chikungunya Virus in Wild Populations of Aedes aegypti from Guerrero, Mexico.

We carried out dengue (DENV) and chikungunya virus (CHIKV) surveillance in wild populations of Aedes aegypti from Guerrero, Mexico, from 2012 to 2014 following a standard national protocol of the Mexican Dengue Control Program. A total of 284 pools (15-30 specimens/pool) of female mosquitoes were tested with real-time reverse transcriptase-polymerase chain reaction to detect DENV and CHIKV. We report for the 1st time the detection of CHIKV from field-collected mosquitoes at Acapulco and Juchitán in 2014. Results from DENV are also reported.

System Analysis of Dengue Virus Surveillance in BBTKL PP Surabaya Year 2012–2014

ABSTRACTChanging the distribution of dengue virus serotypes has occurred in Indonesia. This condition should be monitored continuously through the Dengue Virus Surveillance. Implementation of Dengue Virus Surveillance also conducted by BBTKL PP Surabaya. The purpose of this study was to determine the workflow, identify problems, set priority problem, find the cause of the problem, and provide the alternative solution related to problems of Dengue Virus Surveillance in BBTKL PP Surabaya. This is a operational research and the informants are officers of Dengue Virus Surveillance in BBTKL PP Surabaya. Data in this study was analyzed descriptive and presented narrative. Results showed that the workflow of Dengue Virus Surveillance in BBTKL PP Surabaya are collecting of patient’s blood and vector specimen, vector survey and collecting the supporting data, Rapid Diagnostic Test (RDT) and Polymerase Chain Reaction (PCR), processing and data analysis, and dissemination the information. The main problems of Dengue Virus Surveillance in BBTKL PP Surabaya is the low quality of the information. Tree problem analysis showed that the cause of problem that can be intervene are incomplete supporting data and data storage. Alternative solution related to problems of Dengue Virus Surveillance in BBTKL PP Surabaya is use of Epi Info.Keyword: surveillance, dengue virus, data management

System Analysis of Dengue Virus Surveillance in BBTKL PP Surabaya Year 2012–2014

Changing the distribution of dengue virus serotypes has occurred in Indonesia. This condition should be monitored continuously through the Dengue Virus Surveillance. Implementation of Dengue Virus Surveillance also conducted by BBTKL PP Surabaya. The purpose of this study was to determine the workflow, identify problems, set priority problem, find the cause of the problem, and provide the alternative solution related to problems of Dengue Virus Surveillance in BBTKL PP Surabaya. This is a operational research and the informants are officers of Dengue Virus Surveillance in BBTKL PP Surabaya. Data in this study was analyzed descriptive and presented narrative. Results showed that the workflow of Dengue Virus Surveillance in BBTKL PP Surabaya are collecting of patient’s blood and vector specimen, vector survey and collecting the supporting data, Rapid Diagnostic Test (RDT) and Polymerase Chain Reaction (PCR), processing and data analysis, and dissemination the information. The main problems of Dengue Virus Surveillance in BBTKL PP Surabaya is the low quality of the information. Tree problem analysis showed that the cause of problem that can be intervene are incomplete supporting data and data storage. Alternative solution related to problems of Dengue Virus Surveillance in BBTKL PP Surabaya is use of Epi Info.Keyword: surveillance, dengue virus, data management

Vector competence of the Aedes aegypti population from Santiago Island, Cape Verde, to different serotypes of dengue virus.

BackgroundDengue is an arboviral disease caused by dengue virus (DENV), whose main vectors are the mosquitoes Aedes aegypti and Aedes albopictus. A. aegypti is the only DENV vector in Cape Verde, an African country that suffered its first outbreak of dengue in 2009. However, little is known about the variation in the level of vector competence of this mosquito population to the different DENV serotypes. This study aimed to evaluate the vector competence of A. aegypti from the island of Santiago, Cape Verde, to four DENV serotypes and to detect DENV vertical transmission.MethodsMosquitoes were fed on blood containing DENV serotypes and were dissected at 7, 14 and 21 days post-infection (dpi) to detect the virus in the midgut, head and salivary glands (SG) using RT-PCR. Additionally, the number of copies of viral RNA present in the SG was determined by qRT-PCR. Furthermore, eggs were collected in the field and adult mosquitoes obtained were analyzed by RT-PCR and the platelia dengue NS1 antigen kit to detect transovarial transmission.ResultsHigh rates of SG infection were observed for DENV-2 and DENV-3 whereas for DENV-1, viral RNA was only detected in the midgut and head. DENV-4 did not spread to the head or SG, maintaining the infection only in the midgut. The number of viral RNA copies in the SG did not vary significantly between DENV-2 and DENV-3 or among the different periods of incubation and the various titers of DENV tested. With respect to DENV surveillance in mosquitoes obtained from the eggs collected in the field, no samples were positive.ConclusionAlthough no DENV positive samples were collected from the field in 2014, it is important to highlight that the A. aegypti population from Santiago Islands exhibited different degrees of susceptibility to DENV serotypes. This population showed a high vector competence for DENV-2 and DENV-3 strains and a low susceptibility to DENV-1 and DENV-4. Viral RNA copies in the SG remained constant for at least 21 dpi, which may enhance the vector capacity of A. aegypti and suggests the presence of a mechanism modulating virus replication in the SG.

Dengue virus 4 (DENV-4) re-emerges after 30 years in Brazil: cocirculation of DENV-2, DENV-3, and DENV-4 in Bahia.

Dengue fever (DF) is a mosquito-borne viral disease of great concern in tropical and subtropical regions of the world. One important cause of the increase in DF is rapid development and urbanization has led to proliferation of the Aedes aegypti mosquito, the vector responsible for transmission of the illness. Surveillance of dengue virus (DENV) infection in Brazil shows the predominance of DENV-1, DENV-2, and DENV-3 until 2010. This study reports the reappearance of DENV-4 in Brazil for the first time in 30 years. Serum samples were collected from individuals (n = 214) exhibiting fever and muscular pain in Bahia, Brazil, during 2011-2012. These samples were subjected to reverse transcription-polymerase chain reaction (RT-PCR)/nested PCR, which revealed that 82% of samples were positive for DENV-4; most were older age groups and exhibited a serological pattern consistent with a primary infection. The cocirculation of multiple DENV serotypes within the same city places the population at risk for a fatal form of the disease. Therefore, with the increasing incidence of severe DF cases, early diagnosis will be a priority for public health efforts in Brazil.

Temporal correlations between mosquito-based dengue virus surveillance measures or indoor mosquito abundance and dengue case numbers in Mérida City, México.

Surveillance of dengue virus (DENV) in Aedes (Stegomyia) aegypti (L.) females is of potential interest because human DENV infections are commonly asymptomatic, which decreases the effectiveness of dengue case surveillance to provide early warning of building outbreaks. Our primary aim was to examine if mosquito-based virological measures--monthly percentages of examined Ae. aegypti females infected with DENV or examined homes from which at least one DENV-infected Ae. aegypti female was collected--are correlated with reported dengue cases in the same or subsequent months within study neighborhoods in Méida City, México. The study encompassed approximately 30 neighborhoods in the southern and eastern parts of the city. Mosquitoes were collected monthly over a 15-mo period within study homes (average of 145 homes examined per month); this produced approximately 5,800 Ae. aegypti females subsequently examined for DENV RNA. Although monthly dengue case numbers in the study neighborhoods varied > 100-fold during the study period, we did not find statistically significant positive correlations between monthly data for mosquito-based DENV surveillance measures and reported dengue cases in the same or subsequent months. Monthly average temperature, rainfall, and indoor abundance of Ae. aegypti females were positively correlated (P < or = 0.001) with dengue case numbers in subsequent months with lag times of 3-5, 2, and 1-2 mo, respectively. However, because dengue outbreak risk is strongly influenced by serotype-specific susceptibility of the human population to DENV, the value of weather conditions and entomological indices to predict outbreaks is very limited. Potential ways to improve the sensitivity of mosquito-based DENV surveillance are discussed.

Natural vertical transmission of dengue-1 virus in Aedes aegypti populations in Acapulco, Mexico.

We carried out dengue virus surveillance in Aedes aegypti populations from 47 neighborhoods of Acapulco during the rainy season of 2011 following a standard national protocol and as an improvement of the entomological surveillance of the Mexican Dengue Control Program. A total of 4,146 Ae. aegypti adults collected indoors and/or emerged from eggs, larvae, or pupae from households with dengue reports (probable or confirmed cases), were grouped into pools and processed using a standardized serotype-specific 4-plex real-time reverse transcriptase-polymerase chain reaction assay. Overall, only 2 (0.9%) of 226 pools of Ae. aegypti adults (1 pool of adults emerged from field-collected larvae, and another of indoor-collected adults) were positive for dengue virus 1 (DENV-1). This is appears to be the 1st report of evidence on the vertical and transovarial transmission of DENV-1 in field-caught Ae. aegypti in Mexico.

Dengue virus surveillance in a medium size city in Brazil reveals a complex pattern of serotypes and strains circulation

Dengue virus surveillance in a medium size city in Brazil reveals a complex pattern of serotypes and strains circulation

Field Validation of the GravidAedesTrap (GAT) for Collection ofAedes aegypti(Diptera: Culicidae)

Current surveillance methods for adult Aedes aegypti (L.) are expensive, require electrical power (e.g., the BG-Sentinel trap, BGS), are labor intensive (aspirators), or require difficult to use and costly adhesives (sticky ovitraps). Field trials were conducted in Cairns (Australia) to compare the efficacy of the newly designed Gravid Aedes Trap (GAT) against existing sticky ovitraps (MosquiTRAP and double sticky ovitrap) and the BGS. Latin square design trials confirmed that alarge GAT using a 9.2-liters bucket treated with Mortein Barrier Outdoor Surface Spray ([AI] 0.3 g/kg imiprothrin and 0.6 g/kg deltamethrin) outperformed a smaller 1.2-liters GAT and collected, on average, 3.7x and 2.4X more female Ae. aegypti than the MosquiTRAP and double sticky ovitrap, respectively. Field trials showed that the GAT collected 10-50% less female Ae. aegypti than the BGS trap but 30% more gravid mosquitoes than the BGS. Trials using the BGS and the GAT indicated that there was no difference in capture rates between female Ae. aegypti uninfected and infected with the wMel strain of Wolbachia, and wMel infection rates were nearly identical at >90% to field captured Ae. aegypti. The potential for the GAT to be used for dengue virus surveillance was also demonstrated with dengue virus type 3 RNA detected in five-sixths and six-sixths pools ofAe. aegypti stored in a GAT held at 28 degreeC and 60% relative humidity for 7 and 14 d, respectively. Mosquito knock down in GATs treated with Mortein surface spray set in 30, 70, and 99% shade was comparable for up to 2 mo, with only approximately 10% of adults escaping. The GAT is therefore a useful tool for capturing adult Ae. aegypti and may be suitable for other container-inhabiting species such as Aedes albopictus (Skuse) and Culex quinquefasciatus Say. The low cost and practicality of operation make the GAT suitable for vector surveillance and projects requiring monitoring of mosquitoes for Wolbachia and arboviruses, especially in developing countries.

Detection of DENV-4 genotype I from mosquitoes collected in the city of Manaus, Brazil

BackgroundDengue epidemics have been reported in Brazil since 1981. In Manaus, a large city in the Amazon region, dengue is endemic with all four-virus serotypes (DENV-1, -2, -3, and -4) simultaneously causing human disease. In 2008, during a surveillance of dengue virus in mosquitoes in the district of Tancredo Neves in Manaus, 260 mosquitoes of Aedes genus were captured, identified and grouped into pools of 10 mosquitoes.FindingsRNA extracts of mosquito pools were tested by a RT-Hemi-Nested-PCR for detection of flaviviruses. One amplicon of 222 bp, compatible with dengue virus serotype 4, was obtained from a pool of Aedes aegypti. The nucleotide sequence of the amplicon indicated that the mosquitoes were infected with DENV-4 of genotype I. This virus of Asian origin has been described in Manaus in 2008 infecting acute febrile illness patients.ConclusionThis is the first report of dengue virus serotype 4 genotype I infecting Aedes aegypti in the Americas.

Virological surveillance for early warning of dengue epidemics in the State of Rio de Janeiro, Brazil

The state of Rio de Janeiro has been important since 1986 as a portal for the introduction of dengue virus (DENV) into Brazil and dissemination of the virus throughout the country. This study describes an active surveillance of DENV in the state of Rio de Janeiro from 2004 to 2008. A total of 14408 samples from patients suspected to be infected with DENV were tested by virus isolation, and nested reverse transcriptase (RT)-PCR assay or anti-DENV dengue IgM antibody capture ELISA (MAC-ELISA), or both. By the use of these different methods, a total of 2324 (16.1%) cases were confirmed as dengue infection. The study covers an inter-epidemic period (2004-2005), the DENV-3 circulation in 2006, the re-emergence of DENV-2 in 2007 and the severe epidemic caused by DENV-2 in the summer of 2008. During the period, 69 dengue fatal cases were reported, 14 (20.2%) deaths being attributable to DENV-3 and 55 (79.7%) to DENV-2. Our results emphasize the role of the laboratory in the early detection of dengue virus transmission and provide information on the dynamics of DENV introduction and spread, important for the assessment of intervention strategies.

Genetic variation in the 3’ untranslated region of dengue virus serotype 3 strains isolated from mosquitoes and humans in Brazil

SummaryBackgroundDengue, a mosquito-borne viral infection caused by one of the four dengue virus (DENV) serotypes (DENV-1 to 4), replicate alternately on the mosquito vector and human host and are responsible for infections throughout tropical and subtropical regions of the world. In Brazil, the disease has become a major public health problem and the introduction of DENV-3 in 2000 in Rio de Janeiro (RJ) was associated with severe dengue epidemics. The potential emergence of strains associated with severe disease highlights the need for the surveillance of DENV in human host and vectors.MethodsAiming to contribute for DENV phylogenetic and vector-virus-human host studies, we sequenced the entire genome of one DENV-3 isolated from naturally infected Aedes aegypti from RJ in 2001 and characterized the 3’ UTR from strains isolated from mosquitoes and humans. Mosquitoes were pooled and submitted to virus isolation in Ae. albopictus C6/36 cells and the infecting serotype was identified by immunofluorescence using type-specific monoclonal antibody. Sequence analysis was performed using BioEdit software, the multiple alignments were performed using CLUSTAL W and the phylogenetic analysis by MEGA 5, using the Neighbor-joining method. Secondary structure prediction was performed by using the MFOLD program.ResultsExclusive substitutions and a substitution leading to a stop codon on the NS5 gene were observed in the DENV-3 isolated from a naturally infected Ae. aegypti and fully sequenced. As an 8- nucleotides deletion was observed within the 11- nucleotides (nts) insertion on the variable region (VR) from the 3′UTR in this isolate, we further sequenced other DENV-3 from both mosquitoes and humans. The majority of DENV-3 from RJ analyzed were characterized by the 11-nts insertion in the VR of the 3′UTR, despite the observation of strains carrying the 8-nts deletion. The latter presented similar secondary structures, however not all strains presenting the 11-nts insertion were similar in the predicted secondary structure.ConclusionsThe phylogeny based on the analysis of the complete genome and 3′UTR characterized the DENV-3 isolated from both vector and human host as belonging to Genotype III (GIII), despite the differences observed on the 3’ UTR. Further studies are needed to address the role of those mutations in the transmission of the different viral populations and vector competence.

Detection of Dengue Virus NS1 Antigen in Infected Aedes aegypti Using a Commercially Available Kit

Epidemic dengue has emerged throughout the tropical world. In the continued absence of a vaccine against dengue virus (DENV), mosquito vector surveillance and control programs are essential to reduce human infections. An effective test to detect DENV in infected mosquitoes would be a valuable addition to the surveillance effort. We investigated DENV detection in infected Aedes aegypti using a commercially available DENV non-structural protein 1 (NS1) ELISA kit (Platelia Dengue NS1 Ag), and by reverse transcription-polymerase chain reaction (RT-PCR) and virus isolation assays. The DENV-infected mosquitoes were subjected to field-relevant conditions and assayed individually and pooled with uninfected mosquitoes. Overall, DENV NS1 antigen was detected in 98% of infected mosquitoes/pools versus 79% for RT-PCR and 29% for virus isolation. Our results indicate that NS1 is an excellent analyte for detection of DENV in Ae. aegypti and that the tested NS1 antigen kit provides a sensitive, rapid, and convenient test for DENV surveillance in mosquitoes.

Molecular surveillance of dengue virus in Bahia State, Brazil

Dengue is an important emerging viruses, posing a threat to one-third of the global human population. In 2002, the introduction of DENV-3 in the state of Bahia produced massive epidemic (about 35,000 cases detected) and the first cases of dengue hemorrhagic fever. To understand the nature of the virus circulating at Bahia, E/NS1 sequence was determined for 31 DENV viruses isolated in Bahia during the 2006 and 2007 transmission season, from patients presenting with different degrees of severity. The carboxi-terminal region of the E gene (220 nt) of 31 viruses, isolated from dengue patients with clinical diagnosis of dengue infection were used to determine the genetic variability of dengue 2 (DENV-2) and dengue 3 (DENV-3). Sequence data were used in phylogenetic comparisons with global samples of DENV-2 and DENV-3. DENV-2 sample grouped in the South East Indian genotype, while DENV-3 samples were grouped within Indian genotype. This study is the first report on Bahia isolates during two transmission seasons. Our data confirms reports from other parts of Brazil and different countries showing the DENV-3 (geno-type III) strains circulating in the Americas are closely related, and cluster within the genotype that has been associated with DHF epidemics in different conti-nents.

Dengue virus surveillance in Singapore reveals high viral diversity through multiple introductions and in situ evolution

Dengue fever, a vector-borne disease, has caused tremendous burden to countries in the tropics and sub tropics. Over the past 20years, dengue epidemics have become more widespread, severe and frequent. This study aims to understand the dynamics of dengue viruses in cosmopolitan Singapore. Envelope protein gene sequences of all four dengue serotypes (DENV-1–DENV-4) obtained from human sera in Singapore (2008–2010) revealed that constant viral introductions and in situ evolution contribute to viral diversity in Singapore and play important roles in shaping the epidemiology of dengue in the island state. The diversity of dengue viruses reported here could be a reflection of the on-going dengue situation in the region given Singapore’s location in a dengue hyperendemic region and its role as the regional hub for travels and trade. Though cosmopolitan genotype of DENV-2 has remained as the predominant strain circulating in Singapore, we uncovered evidence of in situ evolution which could possibly result in viruses with improved fitness. While we have previously shown that a switch in the predominant dengue serotype could serve as a warning for an impending outbreak, our current data shows that a replacement of a predominant viral clade, even in the absence of a switch in predominant serotype, could signal a possible increase in dengue transmission. The circulating dengue viruses in Singapore are highly diverse, a situation which could offer ample opportunities for selection of strains of higher fitness, thus increasing the risk of outbreaks despite a low Aedes population.

Dengue virus presence and surveillance in Okinawa (Review)

Recent reports have shown that the dengue virus (DENV) is a serious concern worldwide, especially in subtropical areas such as South-East Asia. With the development of transportation systems, the risk of DENV infection spreading is increasing. Since mosquitoes transmit DENV to humans, surveillance of DENV-infected mosquito vectors is the most effective approach for preventing DENV. Okinawa is the only prefecture located in a subtropical region in Japan and historically shows continuous importation of DENV-related mosquito vectors. In this review, we describe the current and historical status of DENV in Okinawa.

Prospective field study of transovarial dengue-virus transmission by two different forms of Aedes aegypti in an urban area of Bangkok, Thailand

A prospective field study was conducted to determine transovarial dengue-virus transmission in two forms of Aedes aegypti mosquitoes in an urban district of Bangkok, Thailand. Immature Aedes mosquitoes were collected monthly for one year and reared continuously until adulthood in the laboratory. Mosquitoes assayed for dengue virus were processed in pools and their dengue virus infection status was determined by one-step RT-PCR and nested-PCR methods. Of a total 15,457 newly emerged adult Ae. aegypti, 98.2% were dark and 1.8% of the pale form. The results showed that the minimum infection rate (MIR) by transovarial transmission (TOT) of dengue virus during the one-year study ranged between 0 to 24.4/1,000 mosquitoes. Dengue virus TOT increased gradually during the hot summer months, reaching a peak in April-June, while dengue cases peaked in September, a rainy month near the end of the rainy season. Therefore, mosquito infections due to TOT were prevalent four months before a high incidence of human infections. TOT dengue virus infections occurred in both forms of Ae. aegypti. All four dengue serotypes were detected, with DEN-4 predominant, followed by DEN-3, DEN-1, and DEN-2, respectively.

Imported Dengue Virus Serotype 3, Yemen to Italy, 2010

Imported Dengue Virus Serotype 3, Yemen to Italy, 2010