Day-biting Mosquitoes Research Articles

Do tigers hunt during the day? Diel activity of the Asian tiger mosquito, Aedes albopictus (Diptera: Culicidae), in urban and suburban habitats of North America

BackgroundAedes (Stegomyia) albopictus (Skuse) impacts human outdoor activity because of its aggressive biting behavior, and as a major vector of mosquito-borne diseases, it is also of public health importance. Although most mosquito species exhibit crepuscular activity by primarily host seeking at dawn and dusk, Ae. albopictus has been traditionally characterized as a diurnal or day-biting mosquito. With the global expansion and increased involvement of Ae. albopictus in mosquito-borne diseases, it is imperative to elucidate the diel activity of this species, particularly in newly invaded areas.Methodology and principal findingsHuman sweep netting and carbon dioxide-baited rotator traps were used to evaluate the diel activity of Ae. albopictus in two study sites. Both trapping methods were used in New Jersey’s Mercer County, USA (temperate/urban), while only human sweep netting was used in Florida’s Volusia County, USA (subtropical/suburban). Human sweep netting was performed to determine adult mosquito activity at Sunrise, Solar Noon, Sunset, and Lunar Midnight. Because New Jersey is in a temperate area, diel activity was investigated during the early season (3–19 July), peak season (25 July-19 September), and late season (22 September- 22 October). Aedes albopictus showed the highest activity during peak and late seasons at Solar Noon (P < 0.05). At Sunrise and Sunset during the peak season, Ae. albopictus activity was similar. Lunar Midnight activity was significantly lower than Sunrise and Solar Noon (P < 0.05) but was similar to that of Sunset. In the late season, the highest activity was observed during Solar Noon while the least activity was observed during Sunrise and Lunar Midnight (P<0.05). Bottle rotator traps used in conjunction with the human sweep net technique exhibited similar results. Seasonal activity was not differentiated in Florida due to the consistent subtropical climate. The highest adult activity was observed at Sunrise using human sweep netting, but it was not significantly different from Solar Noon and Sunset. The lowest adult activity was observed at Lunar Midnight; however, it was not significantly different from Solar Noon and Sunset. These results provide evidence that the diel activity of Ae. albopictus, contrary to the common perception of its diurnal activity, is much more varied.Conclusion/SignificanceInvolvement of Ae. albopictus in the transmission of debilitating mosquito-borne pathogens such as chikungunya, dengue, and Zika virus, coupled with its affinity to thrive in human peridomestic environments, substantiates that our findings have global implications in areas where Ae. albopictus populations established. It also highlights the importance of behavioral studies of vector species which will not only help mosquito control professionals plan the timing of their control efforts but also provides empirical evidence against conventional wisdoms that may unjustly persist within public health stewards.

Circadian Regulation of Light-Evoked Attraction and Avoidance Behaviors in Daytime- versus Nighttime-Biting Mosquitoes

Mosquitoes pose widespread threats to humans and other animals as disease vectors [1]. Day- versus night-biting mosquitoes occupy distinct time-of-day niches [2, 3]. Here, we explore day- versus night-biting female and male mosquitoes' innate temporal attraction/avoidance behavioral responses to light and their regulation by circadian circuit and molecular mechanisms. Day-biting mosquitoes Aedes aegypti, particularly females, are attracted to light during the day regardless of spectra. In contrast, night-biting mosquitoes, Anopheles coluzzii, specifically avoid ultraviolet (UV) and blue light during the day. Behavioral attraction to/avoidance of light in both species change with time of day and show distinct sex and circadian neural circuit differences. Males of both diurnal and nocturnal mosquito species show reduced UV light avoidance in anticipation of evening onset relative to females. The circadian neural circuits of diurnal/day- and nocturnal/night-biting mosquitoes based on PERIOD (PER) and pigment-dispersing factor (PDF) expression show similar but distinct circuit organizations between species. The basis of diurnal versus nocturnal behaviors is driven by molecular clock timing, which cycles in anti-phase between day- versus night-biting mosquitoes. Observed differences at the neural circuit and protein levels provide insight into the fundamental basis underlying diurnality versus nocturnality. Molecular disruption of the circadian clock severely interferes with light-evoked attraction/avoidance behaviors in mosquitoes. In summary, attraction/avoidance behaviors show marked differences between day- versus night-biting mosquitoes, but both classes of mosquitoes are circadian and light regulated, which may be applied toward species-specific control of harmful mosquitoes.

Excito-repellency Activity of Andrographis paniculata (Lamiales: Acanthaceae) Against Colonized Mosquitoes.

Excito-repellency activity of plant extracts have been increasingly studied as mosquito repellents. In this study, the crude extract of Andrographis paniculata was evaluated for its noncontact repellency, contact excitation (irritancy + repellency), and knockdown/toxicity response against five colonized mosquitoes; Aedes aegypti (L.), Aedes albopictus (Skuse), Anopheles dirus Peyton & Harrison, Anopheles epiroticus Linton & Harbach, and Culex quinquefasciatus Say (Diptera: Culicidae) using an excito-repellency assay system under laboratory-controlled conditions. The escape responses were observed at four different concentrations (0.5-5.0% w/v) with A. paniculata showing strong spatial repellency against Ae. albopictus (96.7% escape) and Ae. aegypti (71.7% escape) at the 2.5% and 0.5% concentrations, respectively. At 0.5% and 5.0% concentrations, the greatest repellency was seen for An. dirus (48.2% escape) and Cx. quinquefasciatus (59.7% escape), respectively. Comparatively, low repellency action was observed against An. epiroticus (1.6-15.0% escape). Escape in contact assays (before adjustment) was generally less pronounced compared to noncontact spatial repellency, with Ae. albopictus showing highest percent escape (71.4% escape) in the contact assay at 1.0% concentration. After adjusting for spatial repellency, escape due to contact irritancy alone was either not present or an insignificant contribution to the overall avoidance response for all species. No knockdown or mortality at 24-h postexposure was observed in any trials. These findings indicate that the A. paniculata crude extract is more active against day-biting mosquitoes; however, this may be a reflection of the time of testing. This study demonstrates compelling evidence that A. paniculata extract performs primarily as a spatial repellent. Further investigations exploring the use A. paniculata as a potential active ingredient in repellent products are needed.

A review on test methods for insecticidal fabrics and the need for standardisation.

Insecticidal fabrics are effective personal protective measures against disease vectors and unlike bed nets, these fabrics can provide protection from day-biting mosquitoes and in outdoor environments. The rapid geographical expansion of day-biting mosquitoes and their role in disease transmission necessitate technological interventions, which can be effectively used during the daytime. There is a renewed interest in insecticidal fabrics mainly due to the recent outbreaks and geographical spread of dengue and chikungunya and with the emerging threat of Zika virus infection. Insecticidal fabrics are useful for protection from night-biting mosquitoes and also in situations were sleeping under a bed net is not possible. They are also effective against other biting arthropods like ticks, mites, tsetse flies, sand flies and body lice. Although long-lasting insecticidal fabrics factory-treated with permethrin are now commercially available for military and civilian use, there are no international guidelines for testing their efficacy. The different methods employed so far for testing bioefficacy, washing and quantification of permethrin are compiled in this review. The future prospects and challenges ahead for long-lasting insecticidal fabrics are discussed in the context of the increased threat from day-biting mosquitoes and the diseases transmitted by them. The review focuses on the need for standardisation of the test methods for ensuring adequate bioefficacy and safety to the user. The differences between long-lasting insecticidal nets and long-lasting insecticidal fabrics are elaborated, and the need for a separate registration and licencing procedure for long-lasting insecticidal fabrics is highlighted. A test procedure for insecticidal fabrics is described, which could be used until internationally accepted guidelines are available.

Inferences about spatiotemporal variation in dengue virus transmission are sensitive to assumptions about human mobility: a case study using geolocated tweets from Lahore, Pakistan

Billions of users of mobile phones, social media platforms, and other technologies generate an increasingly large volume of data that has the potential to be leveraged towards solving public health challenges. These and other big data resources tend to be most successful in epidemiological applications when utilized within an appropriate conceptual framework. Here, we demonstrate the importance of assumptions about host mobility in a framework for dynamic modeling of infectious disease spread among districts within a large urban area. Our analysis focused on spatial and temporal variation in the transmission of dengue virus (DENV) during a series of large seasonal epidemics in Lahore, Pakistan during 2011–2014. Similar to many directly transmitted diseases, DENV transmission occurs primarily where people spend time during daytime hours, given that DENV is transmitted by a day-biting mosquito. We inferred spatiotemporal variation in DENV transmission under five different assumptions about mobility patterns among ten districts of Lahore: no movement among districts, movement following patterns of geo-located tweets, movement proportional to district population size, and movement following the commonly used gravity and radiation models. Overall, we found that inferences about spatiotemporal variation in DENV transmission were highly sensitive to this range of assumptions about intra-urban human mobility patterns, although the three assumptions that allowed for a modest degree of intra-urban mobility all performed similarly in key respects. Differing inferences about transmission patterns based on our analysis are significant from an epidemiological perspective, as they have different implications for where control efforts should be targeted and whether conditions for transmission became more or less favorable over time.

Kidenga: Public engagement for detection and prevention of Aedes -borne viral diseases

Objective(1) Early detection ofAedes-borne arboviral disease; (2) improveddata onAe. aegyptiandAe. albopictusdistribution in the UnitedStates (U.S.); and (3) education of clinicians and the public.IntroductionZika, chikungunya, and dengue have surged in the Americas overthe past several years and pose serious health threats in regions of theU.S. whereAe. aegyptiandAe. albopictusmosquito vectors occur.Ae. aegyptihave been detected up to 6 months of the year or longer inparts of Arizona, Florida, and Texas where mosquito surveillance isregularly conducted. However, many areas in the U.S. lack basic dataon vector presence or absence. The Zika, dengue, and chikungunyaviruses range in pathogenicity, but all include asymptomatic or mildpresentations for which individuals may not seek care. Traditionalpassive surveillance systems rely on confirmatory laboratory testingand may not detect emergent disease until there is high morbidity in acommunity or severe disease presentation. Participatory surveillanceis an approach to disease detection that allows the public to directlyreport symptoms electronically and provides rapid visualization ofaggregated data to the user and public health agencies. Several suchsystems have been shown to be sensitive, accurate, and timelierthan traditional surveillance. We developed Kidenga, a mobilephone app and participatory surveillance system, to address someof the challenges in early detection of day-biting mosquitoes andAedes-borne arboviruses and to enhance dissemination of informationto at-risk communities.MethodsKidenga sends a weekly push notification prompting users toreport symptoms, travel history, and day-biting mosquito activity.If an individual reports through Kidenga that they or a family memberhave had symptoms consistent with Zika, dengue, or chikungunya,they receive an email with educational information about the diseases,prevention strategies, and treatment/testing information for clinicians.Upon registration, users can opt in to have additional follow-up viaemail. At any time, users may also view maps of aggregated userreports, confirmed case counts by county from public health partners(in pilot areas),Aedesdistribution maps, information about preventionand control strategies, and news on the diseases and vectors from acurated newsfeed. Users in select pilot areas may also receive pressreleases issued by their state or local public health department relatedto the diseases and their vectors. University of Arizona owns andmaintains the app and its data. Local and state health departmentsthat want more detailed information on user symptoms and mosquitoactivity may request and monitor the data at no cost. A marketingcampaign to recruit a broad user base is being implemented inArizona, Texas, and Florida.ResultsKidenga was developed with significant input from public healthstakeholders and launched in September 2016,accompanied byEnglish and Spanish radio public service announcements in selectArizona markets, press releases, and a social marketing campaign.A Spanish version of the app is under development. We willdescribe the results of user registration and survey submissions,challenges identified during development and deployment of thisnovel surveillance system, plans for data use and evaluation, andcollaborations with public health partners.ConclusionsThe utility of Kidenga as a surveillance system will depend onbroad and consistent participation among diverse user populations,particularly in low-risk areas; strategies to integrate health reports forhigh-risk populations who may not have smartphones; validation ofdata and development of sensitive and specific algorithms for takingpublic health action, and buy-in from public health departments touse the data and advocate for this novel surveillance tool. Kidenga’ssecondary function as an education tool onAedes-borne viruses is lessdependent upon a large user base and can be evaluated separately.Participatory surveillance systems that specifically monitorAedes-borne pathogens are relatively new, and the challenges associatedwith their early detection may differ from those of other diseases.

Effectiveness of autodissemination stations containing pyriproxyfen in reducing immature Aedes albopictus populations

BackgroundAedes albopictus, the Asian tiger mosquito, is an aggressive, highly anthropophilic, day-biting mosquito with an expanding geographic range. Suppression of Ae. albopictus is difficult because of the abundance and prevalence of larval habitats within peridomestic environments, particularly cryptic habitats such as corrugated extension spouts, fence post openings, discarded food containers, etc. Because of the challenges of eliminating or treating larval habitats of this species, we tested an autodissemination concept to contaminate these habitats with the insect growth regulator pyriproxyfen.MethodsOur study was conducted in the City of Trenton (Mercer County), New Jersey, USA (40°12′N, 74°44′W). We selected six hot spots, where five or more Ae. albopictus males or females were collected based on weekly trap surveillance. A trapping unit was a city block, approximately 0.8 ha (hot spot), where we deployed 26 to 28 autodissemination stations per treatment plot. To gauge efficacy, we deployed BGS traps, oviposition cups, and sentinel cups in treatment and control locations.ResultsWe found a significant reduction in eggs (P < 0.0001) and larval populations (P < 0.0001) as a result of treatment. Pupal mortality, as determined through bioassays, was also significantly higher in the treatment sites (P < 0.0001).ConclusionOur results clearly show the potential and unique use of the autodissemination stations to control immature Ae. albopictus in urban areas. Penetration of larvicides with existing methods are difficult to reach cryptic habitats, but the autodissemination approach, which exploits the oviposition behavior of the target pest, can be integrated into intervention programs. New tools are urgently needed to curb the expansion and public health implications of Ae. albopictus and other container-inhabiting species.

Outbreak of Zika virus disease in the Americas and the association with microcephaly, congenital malformations and Guillain–Barré syndrome

Prior to 2007, Zika virus (ZIKV) was generally considered an arbovirus of limited importance, causing a mild self-limiting febrile illness in tropical Africa and Southeast Asia. Now, a large, ongoing...

Vigilance to Limit the Bidirectional Introduction and Co-circulation of Virus Serotypes Aims to Reduce Risk of Severe Dengue Disease in North East India

Dengue is a serious re-emerging arboviral disease that presents a global human health challenge. Infection is caused by one of several recognised serotypes of dengue virus, a member of the mosquito-transmitted Flaviviridae family of human pathogens, which also includes yellow fever, Zika and West Nile viruses. The greatest burden of dengue is borne by countries in the Asia Pacific region, in particular South East Asia and the Indian subcontinent where infection breaks out with increasing frequency and intensity. The World Health Organization South East Asia Region has a population of 1.3 billion people and includes 11 countries, of which Thailand, Myanmar and India have the highest reported incidence of dengue. Infection outcomes vary from the commonly asymptomatic or a self-limiting fever to more severe manifestations such as dengue haemorrhagic fever and dengue shock syndrome. Although primary infection with one serotype elicits lifelong immunity against homologous reinfection, severe dengue is linked to an antibody-related immunopathological response that is triggered by secondary infection with a heterologous serotype. The principal vectors of transmission are the day-biting mosquitoes Aedes aegypti and Ae. albopictus, the respective preference of which for urban and rural habitats has facilitated the rapid and continued spread of dengue across tropical and sub-tropical climatic zones. The narrow elevated corridor of North East India was considered historically to be non-endemic for dengue and as such separated areas of high endemicity in the Bengal Delta and the other zones of India from those in Thailand and Myanmar. In these regions the predominant serotype is usually distinct, so a breach of this geographical bottleneck would potentially enable the co-circulation of virus serotypes, thus posing an increased risk of severe disease upon secondary infection. This alarming scenario may now be realized following the notification of clinical cases in the states of Arunachal Pradesh, Assam and Manipur in recent years. While incidence is still sporadic in North East India limitation of local outbreaks is required through vigilant adherence to the integrated implementation of clinical management, diagnosis, surveillance and vector control in order to prevent the transcontinental spread of dengue.

Use of insecticide-treated school uniforms for prevention of dengue in schoolchildren: a cost-effectiveness analysis.

BackgroundDengue-related illness is a leading cause of hospitalization and death, particularly among children. Practical, acceptable and affordable measures are urgently needed to protect this age group. Schools where children spend most of their day is proposed as an ideal setting to implement preventive strategies against day-biting Aedes mosquitoes. The use of insecticide-treated school uniforms is a promising strategy currently under investigation.MethodsUsing a decision-analytic model, we evaluated the cost-effectiveness of the use of insecticide-treated school uniforms for prevention of dengue, compared with a “do-nothing” alternative, in schoolchildren from the societal perspective. We explored how the potential economic value of the intervention varied under various scenarios of intervention effectiveness and cost, as well as dengue infection risk in school-aged children, using data specific to Thailand.ResultsAt an average dengue incidence rate of 5.8% per year in school-aged children, the intervention was cost-effective (ICER≤$16,440) in a variety of scenarios when the intervention cost per child was $5.3 or less and the intervention effectiveness was 50% or higher. In fact, the intervention was cost saving (ICER<0) in all scenarios in which the intervention cost per child was $2.9 or less per year and the intervention effectiveness was 50% or higher. The results suggested that this intervention would be of no interest to Thai policy makers when the intervention cost per child was $10.6 or higher per year regardless of intervention effectiveness (ICER>$16,440).ConclusionsOur results present the potential economic value of the use of insecticide-treated uniforms for prevention of dengue in schoolchildren in a typical dengue endemic setting and highlight the urgent need for additional research on this intervention.

Quantifying the Impact of Mosquitoes on Quality of Life and Enjoyment of Yard and Porch Activities in New Jersey

The recent expansion of Aedes albopictus, a day-biting mosquito, to densely inhabited areas in the northeastern Atlantic states of the USA has dramatically increased the problem that mosquitoes create for urban and suburban residents. We quantified the impact of mosquitoes on residents' quality of life within the context of a comprehensive area-wide integrated pest management program to control Ae. albopictus in two counties (Mercer and Monmouth) in New Jersey. We interviewed residents of 121 randomly selected households in both counties between October and November 2010. We asked residents about their experience with mosquitoes in their neighborhood and the importance of the ability to relax outdoors without mosquitoes compared to other neighborhood characteristics (1 = not important, 5 = extremely important). We rated residents' utility based on paired comparisons to known states from the EuroQol health description system. The majority (54.6%) of respondents considered mosquitoes to be a problem. Respondents reported an average of 7.1 mosquito bites in a typical week during that summer. Mosquitoes prevented 59.5% of residents from enjoying their outdoor activities at least to some extent. Residents rated the mosquito acceptability (mean ± standard deviation) during that summer on a scale of 0 (mosquito invasion) to 100 (no mosquitoes) at 56.7±28.7, and their overall utility at 0.87±0.03. This is comparable to living with up to two risk factors for diabetes (i.e., abdominal obesity, body mass index of 28 or more, reported cholesterol problems, diagnosis of hypertension, or history of cardiovascular disease) or women experiencing menstrual disorders. Respondents rated the importance of enjoying outdoor activities without mosquitoes (4.69±0.80) comparable to that of neighborhood safety (4.74±0.80) and higher than that of a clean neighborhood (4.59±0.94). In conclusion, New Jersey residents reported that mosquitoes decreased their utility by 0.13, comparable to the loss from worrisome health risk factors, underscoring the importance of controlling this problem.

Child Outdoor Physical Activity is Reduced by Prevalence of the Asian Tiger Mosquito,Aedes albopictus

We tested the hypothesis that day-biting mosquitoes contribute to child obesity by reducing opportunities for summer outdoor play. The influence of Asian tiger mosquito (Aedes albopictus) prevalence on child outdoor physical activity was compared in 2 matched urban communities, one treated for mosquito abatement and one untreated. More time was spent outdoors by children where abatement took place.

A New Threat Looming over the Mediterranean Basin: Emergence of Viral Diseases Transmitted by Aedes albopictus Mosquitoes

A New Threat Looming over the Mediterranean Basin: Emergence of Viral Diseases Transmitted by Aedes albopictus Mosquitoes

Insecticide resistance in the dengue vector Aedes aegypti from Martinique: distribution, mechanisms and relations with environmental factors.

Dengue is an important mosquito borne viral disease in Martinique Island (French West Indies). The viruses responsible for dengue are transmitted by Aedes aegypti, an indoor day-biting mosquito. The most effective proven method for disease prevention has been by vector control by various chemical or biological means. Unfortunately insecticide resistance has already been observed on the Island and recently showed to significantly reduce the efficacy of vector control interventions. In this study, we investigated the distribution of resistance and the underlying mechanisms in nine Ae. aegypti populations. Statistical multifactorial approach was used to investigate the correlations between insecticide resistance levels, associated mechanisms and environmental factors characterizing the mosquito populations. Bioassays revealed high levels of resistance to temephos and deltamethrin and susceptibility to Bti in the 9 populations tested. Biochemical assays showed elevated detoxification enzyme activities of monooxygenases, carboxylesterases and glutathione S-tranferases in most of the populations. Molecular screening for common insecticide target-site mutations, revealed the presence of the “knock-down resistance” V1016I Kdr mutation at high frequency (>87%). Real time quantitative RT-PCR showed the potential involvement of several candidate detoxification genes in insecticide resistance. Principal Component Analysis (PCA) performed with variables characterizing Ae. aegypti from Martinique permitted to underline potential links existing between resistance distribution and other variables such as agriculture practices, vector control interventions and urbanization. Insecticide resistance is widespread but not homogeneously distributed across Martinique. The influence of environmental and operational factors on the evolution of the resistance and mechanisms are discussed.

Dengue Control: The Challenge Ahead

Dengue Control: The Challenge Ahead

Bilateral periorbital ecchymosis in a case with dengue fever

Dear Editor, Dengue is caused by one of four closely related, but antigenically distinct, virus serotypes of the genus Flavivirus and spreads by Aedes aegypti, a domestic, day-biting mosquito that prefers to feed on humans.[1] Infections produce a spectrum of clinical illness ranging from a nonspecific viral syndrome to severe and fatal hemorrhagic disease resulting from increased vascular permeability and decreased platelet count.[1] Varying ocular findings in dengue, though rare are known,[24] petechial hemorrhages in conjunctiva being the commonest.[2] Maculopathy is another common manifestation.[5] We hereby, report a case of bilateral periorbital ecchymosis in a case of dengue hemorrhagic fever. A 22-year-old male patient admitted with the diagnosis of dengue hemorrhagic fever was referred from the medicine department of our hospital with complaints of bilateral periorbital swelling and bruising of one-day duration. There was no history of any blunt trauma to the orbit or the head. On examination, both the eyes had periorbital ecchymosis significantly worse in the right eye [Fig. 1]. Both the ocular globes were normal with no restriction of motility and a visual acuity of 20/20 in both eyes. Pupils were reactive to light in both eyes with no relative afferent pupillary defect. Intraocular pressure was 18 mm Hg in both eyes as measured by applanation tonometry. A dilated fundus examination revealed normal fundus with no evidence of hemorrhages or exudates. There was no evidence of ecchymosis elsewhere in the body. Complete blood counts of patient showed a significantly reduced platelet count of 16000/μL (normal range 150000 – 400000/μL). The diagnosis of dengue fever was confirmed by the detection of dengue IgM antibodies.Figure 1: Bilateral periorbital ecchymosis in a patient with dengue feverThe patient received six units of platelet concentrate and supportive therapy was given in the form of antipyretics and volume replacement. No specific treatment was added from the ophthalmic point of view. He was followed up after one week, and there was no change in the periorbital ecchymosis. Platelet count was 28000/μL at this point. Subsequently the patient was lost to follow-up. Dengue fever is considered to be rarely associated with ocular manifestations. The onset of symptoms appears to coincide with the resolution of fever and the nadir of thrombocytopenia.[6] Reported ocular manifestations of dengue fever include subconjunctival hemorrhage, vitreous hemorrhage, choroidal effusions, relative central scotoma, intraretinal hemorrhages, Roth spots, cotton-wool spots, retinal edema, blurring of the optic disk and maculopathy. Platelet count less than 50000/μL predisposes to ocular hemorrhages.[2] Nevertheless, periorbital ecchymosis has not been described as part of the clinical spectrum of dengue fever or any other viral fever. As it occurred with a significantly low platelet count, it appears to be related to thrombocytopenia. Patients with dengue fever who report visual symptoms should be evaluated promptly. Although there is no specific therapy, retinal hemorrhage may be an indication for early and aggressive correction of thrombocytopenia. Ocular alterations in dengue are usually self-limiting. Most of the findings resolve without specific treatment, but occasionally visual recovery may be prolonged or vision may remain permanently impaired in patients with a severe maculopathy.[4] To the best of our knowledge this is the first reported case of bilateral periorbital ecchymosis in a case of dengue hemorrhagic fever.

Dengue Virus, Nepal

To the Editor: Dengue virus belongs to the genus Flavivirus, family Flaviviridae. It has 4 serotypes: dengue virus type 1 (DENV-1), dengue virus type 2 (DENV-2), dengue virus type 3 (DENV-3), and dengue virus type 4 (DENV-4). Dengue virus is maintained in a cycle between humans and Aedes aegypti, domestic day-biting mosquitoes. Dengue virus induces clinical illness, which ranges from a nonspecific viral syndrome (dengue fever [DF]) to severe and fatal hemorrhagic disease (dengue hemorrhagic fever [DHF]). DF/DHF occurs primarily in tropical and subtropical areas of the world. Domestic dengue virus infection occurs in >100 countries; >2.5 billion persons live in these areas. Approximately 100 million cases of DF, 500,000 cases of DHF, and several thousand deaths occur annually worldwide (1). During the past decades, dengue virus has emerged in southern Asia; DF/DHF epidemics have occurred in Bhutan, India, Maldives, Bangladesh, and Pakistan (2–4). From August through November 2006, the number of febrile patients increased in 4 major hospitals in the Terai region of Nepal: Nepalgunj Medical College, Bheri Zonal Hospital in Nepalgunj, Tribhuban Hospital in Dang, and Narayani subregional hospital in Birgunj. Patients with severe symptoms were referred to Sukraraj Tropical and Infectious Disease Hospital, Kathmandu, for diagnosis and treatment. The clinical features in most patients were consistent with signs of DF, but some patients showed signs (high fever, rash, ecchymosis, epistaxis, positive tourniquet test, liver dysfunction, and thrombocytopenia [platelet count <100,000/mm3]) consistent with the World Health Organization (WHO) definition of DHF. Ascites and plural effusion developed in 2 patients. Blood specimens were collected from all patients at the time of admission to the local hospitals. Particle agglutination (PA) assay (Pentax Ltd, Tokyo, Japan) (5) and immunoglobulin (Ig) M–capture ELISA (Dengue/JE IgM Combo ELISA kit, Panbio Ltd, Brisbane, Queensland, Australia) were performed. Dengue virus–specific IgM was detected in 11 patients who had fever, headache, and rash (Table). Each of these patients had negative results for Japanese encephalitis virus–specific IgM. Of the 11 patients, 10 had no history of travel to India or other dengue-endemic countries. DF or DHF was initially diagnosed for 7 patients, and viral encephalitis, typhoid fever, or viral fever was diagnosed for others without serologic tests. Reverse transcription–PCR and virus isolation were performed at Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan, but the dengue virus genome was not detected, and no virus was isolated, likely because sample collection was delayed and the sample was transported to Japan in a deteriorated condition. Table. Clinical and laboratory data for 11 patients admitted to hospitals and diagnosed with dengue fever or dengue hemorrhagic fever, Nepal, 2006* DF/DHF have been considered to be a possible public health threat to Nepal because DF/DHF epidemics have occurred recently in India and Pakistan, which reported several thousand cases and >100 deaths (6). The first DF case in Nepal was reported in 2004 (7). Further, the first DENV-2 strain of Nepal origin was isolated from a Japanese traveler who visited Nepal and in which DF developed after the patient returned to Japan. The isolated DENV-2 (GenBank accession no. {type:entrez-nucleotide,attrs:{text:AB194882,term_id:55771291}}AB194882) was 98% homologous with DENV-2 isolated in India (8). The prevalence of dengue virus antibody was reported to be 10.4% in the southwestern region of Nepal (9). These reports suggest that dengue virus has been circulating in Nepal for several years. Thus, DF/DHF has likely been misdiagnosed and illness caused by dengue virus underestimated in Nepal. In contrast, Japanese encephalitis has been a public health problem in southwestern region of Nepal, and large epidemics have occurred almost every year since 1978 (10). Nepal has no dengue surveillance programs, and health professionals do not usually consider dengue as a differential diagnosis. The emergence occurred in the lowland Terai belt region, which borders the state of Bihar, India. The Aedes mosquito is known to persist in this region. The emerging DENV-2 is likely to have been introduced into Nepal from India.

Discovery of a Widespread Infestation of Aedes albopictus in the Torres Strait, Australia

Aedes albopictus is a container-breeding Stegomyia mosquito that has dispersed widely from its origins in Southeast Asia. Because Ae. albopictus is a known dengue vector and a potential vector of a variety of arboviruses and it can tolerate cooler climates than Aedes aegypti, Australian quarantine and health authorities have strategies to detect and eliminate it from international ports. Following the detection of 42 adult Ae. albopictus in BG-Sentinel traps set on Yorke island in the Torres Strait of Australia in April 2005, extensive surveys were conducted to determine the distribution of Ae. albopictus in the Torres Strait and adjoining Cape York Peninsula. A total of 17 islands and the northern peninsula area of Cape York Peninsula were surveyed by collection of larvae and pupae from flooded containers and human bait collections of adult mosquitoes with aspirators and sweep nets. Aedes albopictus was detected on 10 islands and comprised 100% of the day-biting container-breeding mosquitoes on Yorke and Stephens Islands. No Ae. albopictus were detected in the mainland sites on Cape York. Retrospective genetic analysis of larvae collected in April 2004 and April 2005 on Yorke Island indicated that Ae. albopictus was present in low densities in 2004 and that there were 3 genetically distinct mitochondrial haplotypes on Yorke Island in April 2005. Additionally, on Yorke Island there is evidence that Ae. albopictus is displacing Aedes scutellaris.

Advances in dengue diagnosis.

Despite improvements in health, epidemics of infectious diseases continue to occur, and new diseases emerge and old diseases reemerge (113). Mosquito-borne flavivirus diseases are currently considered reemerging infections because of the increase in the incidences of yellow fever and, mainly, dengue fever and dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) observed in the last few years (30, 86). The dengue syndrome is an acute febrile viral exanthem, accompanied by headache, myalgia, anorexia, gastrointestinal disturbances, and postration, caused by viruses transmitted by mosquitoes (43). DHF is a severe febrile disease characterized by abnormalities of hemostasis and increased vascular permeability. DSS is the result of a hypovolemic shock observed in some DHF cases. DHF/DSS represents the severe form of dengue fever (52). The disease is caused by any one of the four distinct serotypes (1 to 4) of the dengue virus (52, 114). These viruses are members of the family Flaviviridae; they have a common morphology and genomic structure, and all members share common antigenic determinants. The four dengue virus serotypes are classified as a complex on the basis of clinical, biological, and immunological criteria. Dengue virus complex-specific antigenic determinants have been demonstrated by using neutralization assays, which also can differentiate the dengue virus complex into four antigenically distinct dengue virus serotypes, since each serotype presents a type-specific determinant (49, 52). The flaviviruses are transmitted by mosquitoes of the Stegomia family, mainly Aedes aegypti, a domestic, day-biting mosquito that prefers to feed on humans (52, 99). This is a highly urbanized mosquito, breeding in water stored for domestic use or collected rainwater. A jungle cycle has been proposed to exist in Southeast Asia, since there is a high rate of dengue transmission among different species of monkeys (52, 105). The genomic RNA of dengue viruses is single stranded and approximately 11 kb in length. The RNA is infectious and, as in the rest of the flaviviruses, it has a single open reading frame (103). The order of proteins encoded in the long open reading frame is 59-C-prM(M)-E-NS1-NS2A-NS2B-NS3-NS4A-NS4BNS5-39. The mature virion contains three structural proteins: C, the nucleocapside or core protein of 13.5 kDa; M, a membrane-associated protein of 8 kDa; and the E (envelope) protein of 51 kDa. The E protein has the sites for viral attachment to and transport through host cell plasma membranes. Functional domains responsible for the neutralization and hemagglutination of goose erythrocytes are associated with the E protein. It contains epitopes specific for serotype, dengue complex, and group (6, 48, 103, 115). Considering the technology currently used for the diagnosis of dengue viruses, a case definition in which laboratory confirmation is emphasized has been proposed. The laboratory criteria for confirmation of the infection and the disease include the isolation of dengue virus from serum and/or autopsy samples, the demonstration of a fourfold or greater increase in the titer of immunoglobulin G (IgG) or IgM antibody to one or more dengue virus antigens in paired serum samples, or the demonstration of dengue virus antigen in autopsy tissue or serum samples by immunohistochemistry, by immunofluorescence, or by the detection of the viral nucleic acid (98).

Dengue/dengue hemorrhagic fever: the emergence of a global health problem.

Dengue and dengue hemorrhagic fever (DHF) are caused by one of four closely related but antigenically distinct virus serotypes (DEN-1 DEN-2 DEN- 3 and DEN-4) of the genus Flavivirus. Infection with one of these serotypes does not provide cross-protective immunity so persons living in a dengueendemic area can have four dengue infections during their lifetimes. Dengue is primarily an urban disease of the tropics and the viruses that cause it are maintained in a cycle that involves humans and Aedes aegypti a domestic day-biting mosquito that prefers to feed on humans. Infection with a dengue virus serotype can produce a spectrum of clinical illness ranging from a nonspecific viral syndrome to severe and fatal hemorrhagic disease. Important risk factors for DHF include the strain and serotype of the virus involved as well as the age immune status and genetic predisposition of the patient. The first reported epidemics of dengue fever occurred in 1779-1780 in Asia Africa and North America; the near simultaneous occurrence of outbreaks on three continents indicates that these viruses and their mosquito vector have had a worldwide distribution in the tropics for more than 200 years. During most of this time dengue fever was considered a benign nonfatal disease of visitors to the tropics. Generally there were long intervals (10-40 years) between major epidemics mainly because the viruses and their mosquito vector could only be transported between population centers by sailing vessels. (excerpt)