Mar 5, 2007

Travel to dengue-endemic areas is a risk for contracting dengue fever (DF) and dengue hemorrhagic fever (DHF).

Currently, there is no vaccine available for prevention of dengue infections; however, research is ongoing and it is expected that an effective dengue vaccine will be available within five to ten years.

Visitors to endemic areas are advised to protect against the dengue virus vector – the Aedes aegypti mosquito. The Aedes aegypti mosquito is also the vector for yellow fever, so dengue and yellow fever infection prevention strategies are similar, although a yellow fever vaccine is available and immunization is recommended when traveling to endemic areas (Yellow fever prevention). Avoiding mosquito bites is the best way to reduce the risk of dengue virus infection. Aedes aegypti is a daytime biting mosquito that prefers humans. The most common exposure times are early morning and late afternoon and evening.

Avoiding mosquito bites:

• Wear clothes that cover the arms and legs.
• Wear light-colored clothing (mosquitos are attracted to dark colors).
• Do not wear scented products.
• Apply DEET-containing insect repellent to skin and clothing every 6 hours.
• Remain in well-screened or air-conditioned areas when possible.
• Use mosquito netting.

Travel to dengue-endemic areas is a risk for contracting dengue fever (DF) and dengue hemorrhagic fever (DHF).

Currently, there is no vaccine available for prevention of dengue infections; however, research is ongoing and it is expected that an effective dengue vaccine will be available within five to ten years.

Visitors to endemic areas are advised to protect against the dengue virus vector – the Aedes aegypti mosquito. The Aedes aegypti mosquito is also the vector for yellow fever, so dengue and yellow fever infection prevention strategies are similar, although a yellow fever vaccine is available and immunization is recommended when traveling to endemic areas (Yellow fever prevention). Avoiding mosquito bites is the best way to reduce the risk of dengue virus infection. Aedes aegypti is a daytime biting mosquito that prefers humans. The most common exposure times are early morning and late afternoon and evening.

Read more: http://microbiology.suite101.com/article.cfm/travel_associated_dengue#ixzz0NZlK3THp

School of Biological Sciences, University of Queensland, St Lucia, Queensland, Australia.

ABSTRACT

BACKGROUND: The reduced rainfall in southeast Australia has placed this region’s urban and rural communities on escalating water restrictions, with anthropogenic climate change forecasts suggesting that this drying trend will continue. To mitigate the stress this may place on domestic water supply, governments have encouraged the installation of large domestic water tanks in towns and cities throughout this region. These prospective stable mosquito larval sites create the possibility of the reintroduction of Ae. aegypti from Queensland, where it remains endemic, back into New South Wales and other populated centres in Australia, along with the associated emerging and re-emerging dengue risk if the virus was to be introduced. METHODOLOGY/PRINCIPAL FINDINGS: Having collated the known distribution of Ae. aegypti in Australia, we built distributional models using a genetic algorithm to project Ae. aegypti’s distribution under today’s climate and under climate change scenarios for 2030 and 2050 and compared the outputs to published theoretical temperature limits. Incongruence identified between the models and theoretical temperature limits highlighted the difficulty of using point occurrence data to study a species whose distribution is mediated more by human activity than by climate. Synthesis of this data with dengue transmission climate limits in Australia derived from historical dengue epidemics suggested that a proliferation of domestic water storage tanks in Australia could result in another range expansion of Ae. aegypti which would present a risk of dengue transmission in most major cities during their warm summer months. CONCLUSIONS/SIGNIFICANCE: In the debate of the role climate change will play in the future range of dengue in Australia, we conclude that the increased risk of an Ae. aegypti range expansion in Australia would be due not directly to climate change but rather to human adaptation to the current and forecasted regional drying through the installation of large domestic water storing containers. The expansion of this efficient dengue vector presents both an emerging and re-emerging disease risk to Australia. Therefore, if the installation and maintenance of domestic water storage tanks is not tightly controlled, Ae. aegypti could expand its range again and cohabit with the majority of Australia’s population, presenting a high potential dengue transmission risk during our warm summers.

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Department of Entomology, University of California, One Shields Avenue, Davis, CA 95616, USA. Louis.Lambrechts@mpl.ird.fr

ABSTRACT

BACKGROUND: Several observations support the hypothesis that vector-driven selection plays an important role in shaping dengue virus (DENV) genetic diversity. Clustering of DENV genetic diversity at a particular location may reflect underlying genetic structure of vector populations, which combined with specific vector genotype x virus genotype (G x G) interactions may promote adaptation of viral lineages to local mosquito vector genotypes. Although spatial structure of vector polymorphism at neutral genetic loci is well-documented, existence of G x G interactions between mosquito and virus genotypes has not been formally demonstrated in natural populations. Here we measure G x G interactions in a system representative of a natural situation in Thailand by challenging three isofemale families from field-derived Aedes aegypti with three contemporaneous low-passage isolates of DENV-1. RESULTS: Among indices of vector competence examined, the proportion of mosquitoes with a midgut infection, viral RNA concentration in the body, and quantity of virus disseminated to the head/legs (but not the proportion of infected mosquitoes with a disseminated infection) strongly depended on the specific combinations of isofemale families and viral isolates, demonstrating significant G x G interactions. CONCLUSION: Evidence for genetic specificity of interactions in our simple experimental design indicates that vector competence of Ae. aegypti for DENV is likely governed to a large extent by G x G interactions in genetically diverse, natural populations. This result challenges the general relevance of conclusions from laboratory systems that consist of a single combination of mosquito and DENV genotypes. Combined with earlier evidence for fine-scale genetic structure of natural Ae. aegypti populations, our finding indicates that the necessary conditions for local DENV adaptation to mosquito vectors are met.

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Entomology, University of California, Davis, California, United States of America.

ABSTRACT

BACKGROUND: Human movement is a key behavioral factor in many vector-borne disease systems because it influences exposure to vectors and thus the transmission of pathogens. Human movement transcends spatial and temporal scales with different influences on disease dynamics. Here we develop a conceptual model to evaluate the importance of variation in exposure due to individual human movements for pathogen transmission, focusing on mosquito-borne dengue virus. METHODOLOGY AND PRINCIPAL FINDINGS: We develop a model showing that the relevance of human movement at a particular scale depends on vector behavior. Focusing on the day-biting Aedes aegypti, we illustrate how vector biting behavior combined with fine-scale movements of individual humans engaged in their regular daily routine can influence transmission. Using a simple example, we estimate a transmission rate (R(0)) of 1.3 when exposure is assumed to occur only in the home versus 3.75 when exposure at multiple locations-e.g., market, friend’s-due to movement is considered. Movement also influences for which sites and individuals risk is greatest. For the example considered, intriguingly, our model predicts little correspondence between vector abundance in a site and estimated R(0) for that site when movement is considered. This illustrates the importance of human movement for understanding and predicting the dynamics of a disease like dengue. To encourage investigation of human movement and disease, we review methods currently available to study human movement and, based on our experience studying dengue in Peru, discuss several important questions to address when designing a study. CONCLUSIONS/SIGNIFICANCE: Human movement is a critical, understudied behavioral component underlying the transmission dynamics of many vector-borne pathogens. Understanding movement will facilitate identification of key individuals and sites in the transmission of pathogens such as dengue, which then may provide targets for surveillance, intervention, and improved disease prevention.

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Abstract.

The rDEN4delta30-200,201 is a live attenuated DENV-4 vaccine candidate specifically designed to further
attenuate the rDEN4delta30 parent virus. In the present study, 28 healthy adult volunteers were randomized to receive either 105 plaque-forming unit (PFU) of vaccine (20) or placebo (8) as a single subcutaneous injection. Volunteers were evaluated for safety every other day for 16 days. Serum neutralizing antibody titer against DEN4 was determined at study day 28, 42, and 180. The vaccine infected all vaccinees and was well tolerated without inducing alanine aminotransferase (ALT) elevations. Although virus was not recovered from the serum of any vaccinee, moderate levels of neutralizing antibody were induced in all volunteers. Thus the restricted replication of rDEN4delta30-200,201 previously documented in animal models was confirmed in humans. The rDEN4delta30-200,201  is a promising candidate and can be considered for inclusion in a tetravalent dengue virus (DENV) vaccine.

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Arbovirus Diseases Branch, Division of Vector-Borne Infectious Diseases, Centers for Disease Control and Prevention, Public Health Service, US Department of Health and Human Service, Fort Collins, CO, USA. wcrill@cdc.gov

Abstract

Dengue virus (DENV) is a serious mosquito-borne pathogen causing significant global disease burden, either as classic dengue fever (DF) or in its most severe manifestation dengue hemorrhagic fever (DHF). Nearly half of the world’s population is at risk of dengue disease and there are estimated to be millions of infections annually; a situation which will continue to worsen with increasing expansion of the mosquito vectors and epidemic DF/DHF. Currently there are no available licensed vaccines or antivirals for dengue, although significant effort has been directed toward the development of safe and efficacious dengue vaccines for over 30 years. Promising vaccine candidates are in development and testing phases, but a better understanding of immune responses to DENV infection and vaccination is needed. Humoral immune responses to DENV infection are complex and may exacerbate pathogenicity, yet are essential for immune protection. In this report, we develop DENV-2 envelope (E) protein epitope-specific antigens and measure immunoglobulin responses to three distinct epitopes in DENV-2 infected human serum samples. Immunoglobulin responses to DENV-2 infection exhibited significant levels of individual variation. Antibody populations targeting broadly cross-reactive epitopes centered on the fusion peptide in structural domain II were large, highly variable, and greater in primary than in secondary DENV-2 infected sera. E protein domain III cross-reactive immunoglobulin populations were similarly variable and much larger in IgM than in IgG. DENV-2 specific domain III IgG formed a very small proportion of the antibody response yet was significantly correlated with DENV-2 neutralization, suggesting that the highly protective IgG recognizing this epitope in murine studies plays a role in humans as well. This report begins to tease apart complex humoral immune responses to DENV infection and is thus important for improving our understanding of dengue disease and immunological correlates of protection, relevant to DENV vaccine development and testing.

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