Mosquito-borne Viral Infection Research Articles

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.

Modeling Dynamic Introduction of Chikungunya Virus in the United States

Chikungunya is a mosquito-borne viral infection of humans that previously was confined to regions in central Africa. However, during this century, the virus has shown surprising potential for geographic expansion as it invaded other countries including more temperate regions. With no vaccine and no specific treatment, the main control strategy for Chikungunya remains preventive control of mosquito populations. In consideration for the risk of Chikungunya introduction to the US, we developed a model for disease introduction based on virus introduction by one individual. Our study combines a climate-based mosquito population dynamics stochastic model with an epidemiological model to identify temporal windows that have epidemic risk. We ran this model with temperature data from different locations to study the geographic sensitivity of epidemic potential. We found that in locations with marked seasonal variation in temperature there also was a season of epidemic risk matching the period of the year in which mosquito populations survive and grow. In these locations controlling mosquito population sizes might be an efficient strategy. But, in other locations where the temperature supports mosquito development all year the epidemic risk is high and (practically) constant. In these locations, mosquito population control alone might not be an efficient disease control strategy and other approaches should be implemented to complement it. Our results strongly suggest that, in the event of an introduction and establishment of Chikungunya in the US, endemic and epidemic regions would emerge initially, primarily defined by environmental factors controlling annual mosquito population cycles. These regions should be identified to plan different intervention measures. In addition, reducing vector: human ratios can lower the probability and magnitude of outbreaks for regions with strong seasonal temperature patterns. This is the first model to consider Chikungunya risk in the US and can be applied to other vector borne diseases.

The 1α,25-dihydroxy-vitamin D3 reduces dengue virus infection in human myelomonocyte (U937) and hepatic (Huh-7) cell lines and cytokine production in the infected monocytes

Dengue is the most important mosquito-borne viral infection in humans. Recent evidence suggests that vitamin D influences virus replication. In this work, the effect of vitamin D treatment on dengue virus infection in human hepatic Huh-7 cells and on virus infection and cytokine production in the human monocytic U937 cells was evaluated. Exposure to 1α,25-dihydroxy-vitamin D3, resulted in a significant reduction in the number of infected cells, in conditions where cell viability was not affected. Viral replication in monocytic cells was more susceptible to vitamin D3 than replication in the hepatic cells. Moreover, vitamin D3 significantly reduced the levels of proinflammatory cytokines (TNF-α, IL-6, IL-12p70 and IL-1β) produced by infected U937 cells. These results suggest that vitamin D3 may represent a potentially useful antiviral compound.

Evaluation of testing strategies for reliable measurement of rates of subclinical mosquito-borne viral infections

Aim Insect-transmitted viral infections remain a significant public health concern in Australia. The positive predictive value (PPV) for detection of anti-viral antibodies in donors was assessed using commercially-available kits. Methods Blood samples collected from Australian blood donors were tested by ELISA for IgM or IgG specific for either Dengue virus (DENV), Ross River virus (RRV) or Barmah Forest virus (BFV). The PPV was determined by comparison with results from reference laboratories. Results For the commercially-available kits: anti-DENV IgG, 225 kit-positive, 213 confirmed, PPV 94.7%; anti-RRV IgG, 315 kit-positive, 239 confirmed, PPV 75.9%; anti-BFV IgG, 127 kit-positive, 47 confirmed, PPV 37.0%; anti-DENV IgM, 118 kit-positive, 7 confirmed, PPV 5.9%; anti-RRV IgM, 138 kit-positive, 45 confirmed, PPV 32.6%; anti-BFV IgM, 142 kit-positive, 71 confirmed, PPV 50.0%. Some potential sources of unexpected kit-positives were investigated, however, these contributed minimally to the unacceptable PPVs. Conclusions These kits are designed for diagnostic testing of symptomatic patients, however, it would be expected that reliability for investigation of sub-clinical infection would be equal. PPVs, with the exception of 94.7% for IgG anti-DENV, were less than 80%. To measure rates of subclinical infection an investigation algorithm including exploration of unexpected positives and reliable confirmatory testing is required.

A Study on Outbreak of Dengue from Bihar, India-Establishing New Foci, Attributable to Climatic Changes Ragini Mishra1* and Prashant Kumar2

Dengue fever (DF) is a mosquito-borne viral infection which is emerging fast in terms of mortality and morbidity in humans worldwide, particularly in tropical and subtropical countries. DF is characterized clinically by headache, retro-orbital pain, myalgia, arthralgia, integumentary rashes, and sometimes with haemorrhagic manifestations. Aedes aegypti, the main vector species of dengue fever/dengue haemorrhagic fever (DHF) is commonly found in urban areas which can be attributed to the availability of breeding sites such as water storage containers due to poor management of water and limited supply of drinking water, non degradable tyres, long lasting plastic containers and ineffective community participation in eliminating the breeding places. However, new foci are a major concern for public health by affecting the epidemiology of this disease such as rural and semi-urban areas, which may be linked to climate change. Climate change has led to unusual rainfall pattern leading to excess rain in some parts and deficient rainfall in other parts. This is accompanied by overall rise in average temperature which favors fast circulation of the vector and consequently of dengue virus in the environment. Thus, epidemiological, environmental and entomological observations were made to confirm the aetiology of a focal outbreak of dengue fever in rural and semi-urban areas providing breeding sites for larval growth. The present research aimed to record outbreak of dengue from new foci from Bihar, India, and correlates it with climate change. Bihar was said to be free from dengue but in September, 2010, outbreaks have been reported specially from three districts: Patna, Munger and Begusarai. The epidemiological investigation of probable cases showed clustered distribution of cases in adjacent houses and streets and absence of travellers to dengue endemic regions, though many cases of migration was also noted during early phase of outbreak. Cases reported from Patna were mostly related to migration from different areas in order to get better treatment facilities. Entomological investigations were carried out in 60, 94 and 75 houses in the districts of Patna, Munger and Begusarai respectively. The index of House, Container and Breteau from Patna, Munger and Begusarai found were 20, 40 and 29, 11.11, 43 and 31, and 26, 91.48 and 56, respectively, thereby indicating the high receptivity of Munger to DF/DHF transmission which can subsequently be confirmed with the number of cases reported from there. The environmental investigations included in this study were average temperature, humidity and rainfall of three affected districts. The averages temperatures during the outbreak from Patna were 32.21 (maximum) and 25.09 (minimum), from Munger were 32.39 (maximum) and 25.19 (minimum) and from Begusarai were 32.33 (maximum) and 25.43 (minimum). The rate of humidity from Patna were 86.29 (morning) and 82.43 (evening), from Munger were 84.97 (morning) and 82.86 (evening) and from Begusarai were 84.12 (morning) and 83.43 (evening). The rate of rainfall in the year 2010 was 226.9, 220.00 and 224.45 mm for Patna, Munger and Begusarai respectively. The reasons for death may be attributed to absence of herd immunity in new foci. Key words: Rural areas, new foci of dengue, Aedes aegypti, house index, container index, Breteau index, climate change.

Dengue Control: The Challenge Ahead

Dengue Control: The Challenge Ahead

Neuralgic amyotrophy associated with dengue fever

Dengue is an acute mosquito borne viral infection caused by one of the four distinct serotype of dengue viruses (type 1-4), belonging to flavivirus family. Dengue fever, an arboviral infection is known to cause various neurological complications. Commonly reported neurological manifestations associated with dengue infection are encephalopathy, myelopathy, stroke, Guillain-Barre syndrome and hypokalemic paralysis. Brachial amyotrophy associated with dengue infection were not described previously. Here, we describe three patients presenting with brachial neuritis associated with dengue infection. Dengue infection should be considered in the etiological list of brachial neuritis in dengue endemic areas, especially if preceded by history of febrile illness compatible with dengue illness.

Evaluation of a commercial Dengue NS1 enzyme-linked immunosorbent assay for early diagnosis of dengue infection

Purpose: Dengue is one of the most serious mosquito-borne viral infections affecting tropical and subtropical countries in the world. Since there is no immunoprophylactic or specific antiviral therapy available, timely and rapid diagnosis plays a vital role in patient management and implementation of control measures. This paper evaluates a commercially available NS1 antigen capture ELISA vis-a-vis SD bioline Dengue NS1 antigen test for early detection of dengue virus. Materials and Methods: To evaluate a commercial NS1 antigen detection kit vis-a-vis SD bioline Dengue NS1 antigen test, a total of 91 clinical samples were tested. Virological investigations with regard to dengue virus, viz. NS1 antigen capture ELISA (Panbio, Australia), SD bioline Dengue NS1 antigen test, RT-PCR and virus isolation were performed. Results: Out of 91 samples, 24 (26%) were positive by NS1 antigen capture ELISA, 15 (16%) by SD bioline Dengue NS1 antigen test and 11(12%) positive by RT-PCR analysis. The RT-PCR-positive samples were further subjected to virus isolation and resulted in three isolates. The results of the Panbio NS1 antigen capture ELISA, SD bioline Dengue NS1 antigen test, RT-PCR and virus isolation were correlated among themselves. Conclusions: The present study comprehensively established the utility of NS1 antigen ELISA in early diagnosis of dengue infection.

Co-infection with Dengue Virus and Pandemic (H1N1) 2009 Virus

Co-infection with Dengue Virus and Pandemic (H1N1) 2009 Virus

Incidence of Chikungunya Fever in Singapore: Implications of Public Health Measures and Transnational Movements of People

In addition to Dengue virus infection, another mosquito-borne viral infection has become a significant health hazard. After the first domestic case of Chikungunya fever was reported in the Republic of Singapore, the outbreak was brought under control in 18 days. Despite the quick and thorough public health measures including intensive vector control, this country known as a developed island state could not stop the subsequent outbreaks as both domestic and imported cases surged. Our in-depth investigation benefiting from field activities recapitulates the governmental interventions to control the re-emerging infectious disease. We discuss potential factors contributing to the subsequently increased cases in Singapore and then review strategies that other governments may consider in controlling vector-borne infectious diseases in urban areas with transnational movements of people.

Print Media Representations Of An Unusual Health Event: Chikungunya virus, risk and identity on Réunion Island

In 2005-6, the French Indian Ocean island of Réunion experienced a massive epidemic of the mosquito-borne viral infection Chikungunya. Reporting on the epidemic in the print media demonstrates a considerable lag compared to the realtime evolution of the epidemic, and this paper explores possible reasons for that delay. We analyse the content of print media articles about Chikungunya from two Reunionese newspapers (Témoignages and Clicanoo) and two newspapers from metropolitan France (Le Figaro and Le Monde). In the Reunionese newspapers, the delay in acknowledging the public health risk posed by the virus suggests passive denial in the early stages of the epidemic, followed by acceptance with blame attributed to the French metropolitan government – reflecting the uneasy historical relationship between the Reunionese and the government. In the French metropolitan newspapers, the delay is even greater and may reflect the influence of residual colonialist thinking on the priority placed on reporting on an epidemic in a remote tropical location: once a risk to metropolitan France is identified, reporting intensifies considerably. The media representations also highlight the importance of belief systems as modulators of people’s risk perception and their subsequent health-protection behaviour. We suggest that a better understanding of these drivers of health behaviour in multicultural societies may provide important opportunities to reduce the community burden of disease.

Seroprevalence of dengue virus antibodies in healthy Jamaicans

Dengue fever, a mosquito borne viral infection, is endemic to Jamaica. The seroprevalence of dengue IgG and IgM antibodies were determined in 277 healthy Jamaicans by enzyme linked immunosorbent assay (ELISA). The seroprevalence of dengue IgG antibodies was 100% (277/277) while dengue IgM antibodies were found in 3.6% (10/277). A statistically significant association was found between the presence of dengue IgM antibodies and gender (males 10/105, 9.5% vs females 0/172, 0.0%); chi(2) = 17.0, p=0.000.The high seroprevalence rate of dengue IgG antibodies and the presence of dengue IgM in the healthy population are in keeping with the endemicity of the virus in Jamaica. Therefore tests for dengue IgG antibodies are of limited usefulness in Jamaica and can be safely excluded from diagnostic testing as a cost saving measure. Serological diagnosis of current dengue infection should be centred around the dengue IgM tests although the limitations in the predictive values of such tests should also be considered. The results also suggest that the risk of emergence of the more severe forms of dengue, dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS) in the Jamaican population, due to the presence of enhancing antibodies, is high.

Predicted RNA secondary structures for the conserved regions in dengue virus

Dengue fever, dengue hemorrhagic fever and dengue shock syndrome are the prevalent mosquito borne viral infections worldwide. The dengue virus belongs to the genus flavivirus with conserved RNA domains peptidase_S7 and dexHc among its members. The secondary structures for RNA domains peptidase_S7 and DexHc are hence predicted and discussed with other known viral RNA structures to glean structural insights through comparison.

Mosquito-borne viral infections and the traveller

This article reviews the mosquito-borne infections yellow fever, Chikungunya virus, West Nile virus, dengue fever and eastern equine encephalitis. It provides advice on symptoms, diagnosis and preventive strategies to inform nursing practice during pre-travel consultations.

Vaccination against mosquito borne viral infections: current status.

Mosquito borne infectious diseases are among important group of diseases worldwide. Vaccination is available for some tropical mosquito-borne diseases, especially for Japanese encephalitis virus infection and yellow fever. There are also several attempts to develop new vaccines for the other mosquito-borne diseases such as malaria, dengue infection and West Nile virus infection. In this article, the author reviews the issues on vaccination of some important tropical mosquito borne infectious diseases.

Patterns of disease in Sri Lankan dengue patients

Background: Dengue is the most important mosquito borne viral infection in the world. Nearly 90% of infections occur in children. At present, prospective information on clinical and laboratory findings in...

Multi-level analyses of spatial and temporal determinants for dengue infection

BackgroundDengue is a mosquito-borne viral infection that is now endemic in most tropical countries. In Thailand, dengue fever/dengue hemorrhagic fever is a leading cause of hospitalization and death among children. A longitudinal study among 1750 people in two rural and one urban sites in northern Thailand from 2001 to 2003 studied spatial and temporal determinants for recent dengue infection at three levels (time, individual and household).MethodsDeterminants for dengue infection were measured by questionnaire, land-cover maps and GIS. IgM antibodies against dengue were detected by ELISA. Three-level multi-level analysis was used to study the risk determinants of recent dengue infection.ResultsRates of recent dengue infection varied substantially in time from 4 to 30%, peaking in 2002. Determinants for recent dengue infection differed per site. Spatial clustering was observed, demonstrating variation in local infection patterns. Most of the variation in recent dengue infection was explained at the time-period level. Location of a person and the environment around the house (including irrigated fields and orchards) were important determinants for recent dengue infection.ConclusionWe showed the focal nature of asymptomatic dengue infections. The great variation of determinants for recent dengue infection in space and time should be taken into account when designing local dengue control programs.

Molecular epidemiology of type 1 and 2 dengue viruses in Brazil from 1988 to 2001

Dengue is a mosquito-borne viral infection that in recent decades has become a major international public health concern. Epidemic dengue fever reemerged in Brazil in 1981. Since 1990 more than one dengue virus serotype has been circulating in this tropical country and increasing rates of dengue hemorrhagic fever and dengue shock syndrome have been detected every year. Some evidence supports the association between the introduction of a new serotype and/or genotype in a region and the appearance of dengue hemorrhagic fever. In order to study the evolutionary relationships and possible detection of the introduction of new dengue virus genotypes in Brazil in the last years, we analyzed partial nucleotide sequences of 52 Brazilian samples of both dengue type 1 and dengue type 2 isolated from 1988 to 2001 from highly endemic regions. A 240-nucleotide-long sequence from the envelope/nonstructural protein 1 gene junction was used for phylogenetic analysis. After comparing the nucleotide sequences originally obtained in this study to those previously studied by others, and analyzing the phylogenetic trees, we conclude that, after the initial introduction of the currently circulating dengue-1 and dengue-2 genotypes in Brazil, there has been no evidence of introduction of new genotypes since 1988. The increasing number of dengue hemorrhagic fever cases seen in Brazil in the last years is probably associated with secondary infections or with the introduction of new serotypes but not with the introduction of new genotypes.

Dengue virus infection in travellers returning to Berlin, Germany: clinical, laboratory, and diagnostic aspects

Background: Dengue is a mosquito-borne viral infection endemic throughout the tropics and subtropics. The global prevalence of dengue has grown dramatically in recent years and it has been recognized as a potential hazard to tourists. Objective: In this study, we analyzed the epidemiology, clinical manifestations, laboratory features and serological/virological results in a series of German travellers returning to Berlin with acute dengue virus infection. Study design: Laboratory-confirmed dengue virus infections among German travellers returning to Berlin were studied retrospectively during the period of 1993–2001. Seventy-one patients tested positive for dengue fever and were included in this study. Results: The majority of patients (77.5%) contracted the disease in South Central and South East Asia. The most important clinical characteristics were fever and prostration (100%), headache, predominantly frontal or retroorbital (86%), arthralgia (79%), morbilliform rash (66%) and myalgia (48%). The most meaningful laboratory results were: marked leucopenia (72%), thrombocytopenia (70–89%), hyponatremia (41%) and increased hepatic enzymes ALAT (41%), ASAT (45%) and LDH (62%). Dengue virus infection was diagnosed by means of a matching clinico-epidemiological history and positivity of specific serology and/or virus isolation. Hemorrhagic phenomena appeared in 10 of the 71 patients (14%), out of which one was diagnosed with DHF according to WHO criteria. All patients recovered fully. Conclusion: Pretravel advice should be given to all travellers to dengue-endemic areas. DF must be included in the differential diagnosis of patients returning febrile from tropical areas.

Dengue virus infection.

Dengue fever is an acute self-limited mosquito-borne viral infection causing fever myalgia arthralgia headache rash and leukopenia. Thrombocytopenia and occasionally hemorrhage may develop in classic dengue fever but these are not prominent features. Dengue hemorrhagic fever (DHF) is a similar febrile illness except that increased capillary permeability and hemorrhage are major manifestations. Increased capillary permeability can lead to dengue shock syndrome (DSS; hemoconcentration profound shock and death from circulatory failure). The serotypes of dengue virus DEN-1 through DEN-4 all cause similar illness. The manifestations of DHF and DSS are thought to be primarily immune related and are likely caused by repeated infections by different dengue serotypes. Dengue virus is a zoonotic flavivirus containing a single positive sense RNA strand of 11 kb. The virion is spherical with an envelope containing the E (envelope) and M (membrane) glycoproteins. The E glycoprotein is essential for entry of the virus into host cells and contains several virusneutralizing epitopes. The four serotypes of dengue virus are transmitted throughout the tropics between 35 degrees north and 35 degrees south latitude closely matching the distribution of the principle mosquito vector of dengue virus Aedes aegypti. A. albopictus A. polynesiensis and other members of the subgenus Stegomyia transmit dengue in restricted geographic areas. The feeding behavior of Aedes mosquitoes influences the geographic pattern of dengue transmission; the mosquitoes are domestic are anthropophilic have short flight patterns and bite multiply before oviposition thus accentuating transmission of the virus in densely populated urban settings. A. aegypti breeds around houses in water pots gutters and discarded tires. In heavily endemic areas 1:20 may harbor an infected mosquito but such endemicity is not necessary for transmission. Dengue cases cluster tightly often within households. Of 30 household members 29 became infected in an extreme example from China. Despite the ability of the vector to migrate up to 2.5 km daily in 1 study only 0.7% of mosquitoes visited >4 houses reflecting limited vector migration between feedings. (excerpt)