Bridging Vectors of Dengue Fever: The Endless Cycle (original) (raw)
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Ecology of Aedes Mosquitoes, the Major Vectors of Arboviruses in Human Population
Dengue Fever - a Resilient Threat in the Face of Innovation, 2019
Aedes aegypti (Stegomyia) has been human vectors for many human diseases globally. In recent years, dengue virus has been diagnosed in different regions such as Asia and Latin America vectored by Aedes spp. mosquitoes. Dengue cases have been reported again in the several parts of African and other continental hospital. The different types of breeding sites have been found to be abundant in both urban and rural areas. The abundance of adult Ae. aegypti and habitat productivity in different settings escalates the risk of dengue transmission if viruses are found in asymptomatic population. The insecticide resistance has been found to occur in the wild population of Aedes aegypti to insecticides commonly used for indoor residual spray and long-lasting insecticidal net treatments. The control of human vector population is still a challenge as the vector has a diurnal feeding and outdoor resting behavior. Environmental management is still the best practice to be adopted in many countries for Aedes aegypti control. The currently discovered dengue vaccine might be an immediate arsenal for the community immunization.
Consequences of the Expanding Global Distribution of Aedes albopictus for Dengue Virus Transmission
PLoS Neglected Tropical Diseases, 2010
The dramatic global expansion of Aedes albopictus in the last three decades has increased public health concern because it is a potential vector of numerous arthropod-borne viruses (arboviruses), including the most prevalent arboviral pathogen of humans, dengue virus (DENV). Ae. aegypti is considered the primary DENV vector and has repeatedly been incriminated as a driving force in dengue's worldwide emergence. What remains unresolved is the extent to which Ae. albopictus contributes to DENV transmission and whether an improved understanding of its vector status would enhance dengue surveillance and prevention. To assess the relative public health importance of Ae. albopictus for dengue, we carried out two complementary analyses. We reviewed its role in past dengue epidemics and compared its DENV vector competence with that of Ae. aegypti. Observations from ''natural experiments'' indicate that, despite seemingly favorable conditions, places where Ae. albopictus predominates over Ae. aegypti have never experienced a typical explosive dengue epidemic with severe cases of the disease. Results from a meta-analysis of experimental laboratory studies reveal that although Ae. albopictus is overall more susceptible to DENV midgut infection, rates of virus dissemination from the midgut to other tissues are significantly lower in Ae. albopictus than in Ae. aegypti. For both indices of vector competence, a few generations of mosquito colonization appear to result in a relative increase of Ae. albopictus susceptibility, which may have been a confounding factor in the literature. Our results lead to the conclusion that Ae. albopictus plays a relatively minor role compared to Ae. aegypti in DENV transmission, at least in part due to differences in host preferences and reduced vector competence. Recent examples of rapid arboviral adaptation to alternative mosquito vectors, however, call for cautious extrapolation of our conclusion. Vector status is a dynamic process that in the future could change in epidemiologically important ways.
Aedes Mosquitoes and Aedes-Borne Arboviruses in Africa: Current and Future Threats
International journal of environmental research and public health, 2018
The Zika crisis drew attention to the long-overlooked problem of arboviruses transmitted by Aedes mosquitoes in Africa. Yellow fever, dengue, chikungunya and Zika are poorly controlled in Africa and often go unrecognized. However, to combat these diseases, both in Africa and worldwide, it is crucial that this situation changes. Here, we review available data on the distribution of each disease in Africa, their Aedes vectors, transmission potential, and challenges and opportunities for Aedes control. Data on disease and vector ranges are sparse, and consequently maps of risk are uncertain. Issues such as genetic and ecological diversity, and opportunities for integration with malaria control, are primarily African; others such as ever-increasing urbanization, insecticide resistance and lack of evidence for most control-interventions reflect problems throughout the tropics. We identify key knowledge gaps and future research areas, and in particular, highlight the need to improve knowl...
The dengue vector Aedes aegypti: what comes next
Microbes and Infection, 2010
Aedes aegypti is the urban vector of dengue viruses worldwide. While climate influences the geographical distribution of this mosquito species, other factors also determine the suitability of the physical environment. Importantly, the close association of A. aegypti with humans and the domestic environment allows this species to persist in regions that may otherwise be unsuitable based on climatic factors alone. We highlight the need to incorporate the impact of the urban environment in attempts to model the potential distribution of A. aegypti and we briefly discuss the potential for future technology to aid management and control of this widespread vector species.
Vector-Borne and Zoonotic Diseases
Emerging mosquito-borne viruses continue to cause serious health problems and economic burden among billions of people living in and near the tropical belt of the world. The highly invasive mosquito species Aedes aegypti and Aedes albopictus have successively invaded and expanded their presence as key vectors of Chikungunya virus, dengue virus, yellow fever virus, and Zika virus, and that has consecutively led to frequent outbreaks of the corresponding viral diseases. Of note, these two mosquito species have gradually adapted to the changing weather and environmental conditions leading to a shift in the epidemiology of the viral diseases, and facilitated their establishment in new ecozones inhabited by immunologically naive human populations. Many abilities of Ae. aegypti and Ae. albopictus, as vectors of significant arbovirus pathogens, may affect the infection and transmission rates after a bloodmeal, and may influence the vector competence for either virus. We highlight that many collaborating risk factors, for example, the global transportation systems may result in sporadic and more local outbreaks caused by mosquito-borne viruses related to Ae. aegypti and/or Ae. albopictus. Those local outbreaks could in synergy grow and produce larger epidemics with pandemic characters. There is an urgent need for improved surveillance of vector populations, human cases, and reliable prediction models. In summary, we recommend new and innovative strategies for the prevention of these types of infections.
Aedes Aegypti and Dengue Virus Infections
Journal of the Egyptian Society of Parasitology
Aedes-borne diseases (Dengue, Chikungunya, Yellow Fever and Zika) are an emerging problem worldwide, escalating overall risk and burden of disease worldwide. Dengue viruses are members of the family Flaviviridae, genus flavivirus with four anti-genically related but distinct viruses; all are mosquito-borne human pathogens. The four dengue virus serotypes are associated with fever, rash, and the more severe forms, hemorrhagic fever and shock syndrome. Susceptible humans become infected after being bitten by an infected female Aedes mosquito. Viremia in humans begins at the end of a four-six-day incubation period and persists until fever abates. An uninfected Aedes spp. may acquire the virus after feeding on a patient at the vermeil period. Infected mosquitoes carry the virus for their lifespan and pass the virus to its immature stages (Trans-ovarian transmission) and remain infective for humans, Several factors have combined to produce epidemiological conditions in developing countries in the tropics and subtropics that favor viral transmission by the main mosquito vector, Aedes as the rapid population growth, rural-urban migration, inadequate basic urban infrastructure (eg. the unreliable water supply leading householders to store water in containers close to homes) and the increase in volume of solid waste, such as discarded plastic containers and other abandoned items which provide larval habitats in urban areas. Geographical expansion of the mosquito has been aided by the international commercial trade particularly in used car-tyres which easily accumulate rainwater. Increased air travel and the breakdown of vector control measures have also contributed greatly to the global burden of dengue and DH fevers.
POTENTIAL ROLE OF SYLVATIC AND DOMESTIC AFRICAN MOSQUITO SPECIES IN DENGUE EMERGENCE
2005
Dengue virus 2 (DENV-2) strains that circulate in sylvatic habitats of Senegal and other parts of west Africa are believed to represent ancestral forms that evolved into endemic/epidemic strains that now circulate widely in urban areas of the tropics. Previous studies suggested that the evolution of the endemic/epidemic strains was mediated by adaptation to the peridomestic mosquito vectors Aedes aegypti and Ae. albopictus. We conducted experimental infections using sylvatic and peridomestic Senegalese mosquitoes, and both sylvatic and urban DENV-2 strains to determine if endemic DENV-2 adaptation was vector species specific, and to assess ancestral vector susceptibility. Aedes furcifer and Ae. luteocephalus, probable sylvatic vectors, were highly susceptible to both sylvatic and urban DENV-2 strains. In contrast, sylvatic Ae. vittatus and both sylvatic and peridomestic populations of Ae. aegypti were relative refractory to all DENV-2 strains tested. These results indicate that adaptation of DENV-2 to urban vectors did not result in a loss of infectivity for some African sylvatic vectors. Implications for dengue emergence in west Africa are discussed. Acknowledgment: We thank Wenli Kang for excellent technical assistance.
PLOS Neglected Tropical Diseases
Dengue fever (DEN) is the most common arboviral disease in the world and dengue virus (DENV) causes 390 million annual infections around the world, of which 240 million are inapparent and 96 million are symptomatic. During the past decade a changing epidemiological pattern has been observed in Africa, with DEN outbreaks reported in all regions. In Senegal, all DENV serotypes have been reported. These important changes in the epidemiological profile of DEN are occurring in a context where there is no qualified vaccine against DEN. Further there is significant gap of knowledge on the vector bionomics and transmission dynamics in the African region to effectively prevent and control epidemics. Except for DENV-2, few studies have been performed with serotypes 1, 3, and 4, so this study was undertaken to fill out this gap. We assessed the vector competence of Aedes (Diceromyia) furcifer, Ae. (Diceromyia) taylori, Ae. (Stegomyia) luteocephalus, sylvatic and urban Ae. (Stegomyia) aegypti populations from Senegal for DENV-1, DENV-3 and DENV-4 using experimental oral infection. Whole bodies and wings/legs were tested for DENV presence by cell culture assays and saliva samples were tested by real time RT-PCR to estimate infection, disseminated infection and transmission rates. Our results revealed a low capacity of sylvatic and urban Aedes mosquitoes from Senegal to transmit DENV-1, DENV-3 and DENV-4 and an impact of infection on their mortality. The highest potential transmission rate was 20% despite the high susceptibility and disseminated infection rates up to 93.7% for the 3 Ae. aegypti populations tested, and 84.6% for the sylvatic vectors Ae. furcifer, Ae. taylori and Ae. luteocephalus.
Natural vertical transmission of dengue viruses in Aedes aegypt in southern India
Transactions of the Royal Society of Tropical Medicine and Hygiene, 2000
Dengue is of great concern in various parts of the world, especially in tropical and subtropical countries where the mosquito vectors Aedes aegypti and Aedes albopictus are present. The transmission of this virus to humans, by what is known as horizontal transmission, occurs through the bite of infected females of one or other of the two mosquito species. Furthermore, an infected female or male parent, by what is known as vertical transmission, can transfer this arbovirus to some part of their offspring. Considering that vertical transmission may represent an important strategy for maintaining the circulation of arboviruses in nature, the verification of this phenomenon worldwide is extremely important and necessary to better understand its dynamic. In the present study, we conducted a literature review of the presence of natural vertical transmission of dengue virus in Ae. aegypti and Ae. albopictus worldwide. Searches were conducted in MEDLINE, sciELO and Lilacs and all the studies published in Portuguese, English and Spanish were read, evaluated and organized by mosquito species, serotype and the location at which the samples were collected. Forty-two studies were included in accordance with the exclusion criteria and methodology. The presence of natural vertical transmission in Ae. aegypti and Ae. albopictus was most clearly evidenced by dengue virus in endemic countries, especially in those in South America and Asia. Despite several African countries being considered endemic for dengue, there is a lack of publications on this subject on that continent, which highlights the importance of conducting studies there. Furthermore, the finding of natural vertical transmission in Ae. albopictus in countries where this species is not yet incriminated as a vector is of great concern as it demonstrates the circulation of this virus in populations of Ae. albopictus and alerts to the possibility of some other mosquito species playing a role in the transmission dynamics of this arbovirus. Parallel to this, the small number of studies of natural vertical transmission of chikungunya and Zika virus in the world may be explained by the recent entry of these arboviruses into most of the countries concerned.
PLOS Neglected Tropical Diseases, 2019
Dengue virus (DENV) is a flavivirus mainly transmitted to humans through the bite of infected mosquitoes notably Aedes aegypti and Aedes albopictus. In Central Africa where both vectors, Ae. aegypti and Ae. albopictus are well established, the role of each species in dengue transmission remains poorly investigated. Here, we assessed the vector competence of Ae. aegypti and Ae. albopictus collected in different ecological settings in Central Africa to transmit dengue 2 virus (DENV-2). We provide evidence that both Ae. aegypti and Ae. albopictus in Central Africa were able to transmit dengue virus with Ae. aegypti exhibiting a higher transmission rate. These findings could increase the risk of dengue outbreak in the region and emphasize the need for a comprehensive vector surveillance program to prevent and preparedness for an intervention in case of outbreaks.