Differential Susceptibilities of Aedes aegypti and Aedes albopictus from the Americas to Zika Virus

BackgroundSince the major outbreak in 2007 in the Yap Island, Zika virus (ZIKV) causing dengue-like syndromes has affected multiple islands of the South Pacific region. In May 2015, the virus was detected in Brazil and then spread through South and Central America. In December 2015, ZIKV was detected in French Guiana and Martinique. The aim of the study was to evaluate the vector competence of the mosquito spp. Aedes aegypti and Aedes albopictus from the Caribbean (Martinique, Guadeloupe), North America (southern United States), South America (Brazil, French Guiana) for the currently circulating Asian genotype of ZIKV isolated from a patient in April 2014 in New Caledonia.Conclusions/SignificanceThis study suggests that although susceptible to infection, Ae. aegypti and Ae. albopictus were unexpectedly low competent vectors for ZIKV. This may suggest that other factors such as the large naïve population for ZIKV and the high densities of human-biting mosquitoes contribute to the rapid spread of ZIKV during the current outbreak.     

Morphogenesis of Sindbis virus in cultured Aedes albopictus cells.

Cultured mosquito cells were found to produce Sindbis virus nearly as efficiently as BHK-21 cells at 28 C. In virtually all of the cells observed in the electron microscope, virus morphogenesis was found to occur within complex vesicular structures which developed after viral infection. Viral nucleocapsids were first seen in these vesicles and appeared to be enveloped within these structures. The process of envelopment within these inclusions differed in some respects from the process previously described for the envelopment of nucleocapsids at the plasma membrane of vertebrae cells. Free nucleocapsids were only rarely seen in the cytoplasm of infected mosquito cells, and budding of virus from the cell surface was detected so infrequently that this process of virus production could not account for the amount of virus produced by the infected cells. The vast majority of extracellular virus was produced by the fusion of the virus-containing vesicles with the plasma membrane releasing mature virions and membrane nucleocapsid complexes in various stages of development.     

登革Ⅱ型病毒经白纹伊蚊滞育卵的传递

采用C6/36细胞培养分离病毒的方法检测感染登革Ⅱ型病毒的白纹伊蚊Aedes albopictus滞育卵孵化的F₁代蚊虫感染率,从第一个生殖营养周期子代蚊虫中未分离到病毒,第二与第三生殖营养周期子代蚊虫最低感染率没有显著性差异（χ²=0.01,P＞0.0 5）,感染子代的批阳性率为9.1%,最低感染率为1∶330;间接免疫荧光检测结果表明感染登革Ⅱ型病毒的白纹伊蚊滞育卵孵化的子代成蚊能通过叮咬将登革病毒传播给敏感乳鼠。这些研究结果表明登革病毒能在媒介滞育卵内存活并传至子代,子代蚊虫能通过叮咬敏感宿主水平传播病毒。     

Semliki Forest virus multiplication in clones of Aedes albopictus cells.

A total of 115 clones of Aedes albopictus cells were examined for their response to infection with Semliki Forest virus. Virus yield and cytopathology showed a bimodal distribution. More than 68% of the clones gave low yields of virus (between 8 x 10(6) and 2 x 10(8) PFU/ml) with no discernable cytopathology, and 30% gave high yields of virus (between 1 x 10(9) and 8 x 10(9) PFU/ml) and showed moderate to severe cytopathology. To determine the level at which restriction in virus growth occurs in the low-virus-producing clones, we compared the nature and extent of several virus-directed events in selected low-virus-producing clones with the same events in high-virus-producing clones. Specifically, we compared virus-specified polypeptide synthesis, positive- and negative-strand RNA synthesis, adsorption, uncoating, and transfection with virion 42S RNA. These studies showed that whereas events before negative-strand RNA synthesis and all subsequent virus-specified events were markedly reduced in the low-virus-producing lines, compared with the high-virus-producing lines. Thus, the restriction in virus growth in the low-virus-producing lines occurs at the level of synthesis of negative-strand RNA. The consequence of this restriction in an early step in the virus multiplication cycle is discussed in terms of the survival of invertebrate cells after alphavirus infection.     

登革Ⅱ型病毒在白纹伊蚊体内分布的研究

利用蚊虫连续石蜡切片免疫组织化学技术,对登革Ⅱ型病毒(DEN-2)感染白纹伊蚊Aedes albopictus后的散播时间、程度及组织器官的感染顺序进行监测,以了解DEN-2在媒介白纹伊蚊体内的分布规律。结果表明：大剂量感染登革Ⅱ型病毒后,在蚊虫消化道的主要部位以及大多数组织器官包括神经及内分泌系统在内,如涎腺、脑、神经节等亦检测到病毒抗原。登革Ⅱ型病毒一旦感染并逸出中肠会迅速侵染其它组织。从各组织感染率的高低推断,病毒逸出中肠后通过血淋巴传播到其它组织的顺序通常为：前肠、涎腺、咽部神经节、脑及食管下神经节、后肠及复眼的小眼等。     

寨卡病毒及其疫苗研究

寨卡病毒与黄热病毒、登革热病毒、日本脑炎病毒、西尼罗病毒等都属于蚊媒传播的黄病毒属病毒。寨卡病毒分离于1947年,但由于分布区域有限,所致寨卡热症状较轻,很长一段时间并没有引起太多的关注。最近一些年,特别是2015年后,巴西的寨卡疫情暴发及其与新生儿小头畸形的关联,引起了全球越来越多的关注。疫苗是应对寨卡疫情的重要手段,目前全球有30余个机构在进行寨卡病毒疫苗的研发。本文综述了寨卡病毒的生物学、流行病学、临床特征以及当前不同类型寨卡病毒疫苗研发现状,同时对其他几种黄病毒属病毒批准和临床阶段疫苗情况进行了概述,以为相关研究人员提供参考。     

Geographic and ecological distribution of the dengue and chikungunya virus vectors Aedes aegypti and Aedes albopictus in three major Cameroonian towns

Aedes albopictus (Diptera: Culicidae) was first reported in Central Africa in 2000, together with the indigenous mosquito species Aedes aegypti (Diptera: Culicidae). Because Ae. albopictus can also transmit arboviruses, its introduction is a public health concern. We undertook a comparative study in three Cameroonian towns (Sahelian domain: Garoua; equatorial domain: Douala and Yaoundé) in order to document infestation by the two species and their ecological preferences. High and variable levels of pre‐imaginal Ae. aegypti and Ae. albopictus infestation were detected. Only Ae. aegypti was encountered in Garoua, whereas both species were found in Douala and Yaoundé, albeit with significant differences in their relative prevalence. Peridomestic water containers were the most strongly colonized and productive larval habitats for both species. No major differences in types of larval habitat were found, but Ae. albopictus preferentially bred in containers containing plant debris or surrounded by vegetation, whereas Ae. aegypti tended to breed in containers located in environments with a high density of buildings. These findings may have important implications for vector control strategies.     

The effect of sexual transmission on Zika virus dynamics

Journal of Mathematical Biology - Zika virus is a human disease that may lead to neurological disorders in affected individuals, and may be transmitted vectorially (by mosquitoes) or sexually. A...     

The effects of simulated rainfall on immature population dynamics of Aedes albopictus and female oviposition

Larvae of Aedes albopictus Skuse typically inhabit natural and artificial containers. Since these larval habitats are replenished by rainfall, Ae. albopictus may experience increased loss of immature stages in areas with high levels of rainfall. In this study, we investigated the effects of rainfall and container water level on population density, and oviposition activity of Ae. albopictus. In field and laboratory experiments, we found that rainfall resulted in the flushing of breeding habitats. Excess rain negatively impacted larval and pupal retention, especially in small habitats. When filled with water to overflowing, container habitats were significantly repellent to ovipositing females. Taken together, these data suggest that rainfall triggers population loss of Ae. albopictus and related species through a direct detrimental effect (flushing out) and an indirect effect (ovipositional repellency).     

Impact of deltamethrin-resistance in Aedes albopictus on its fitness cost and vector competence

BackgroundAedes albopictus is one of the most invasive species in the world as well as the important vector for mosquito-borne diseases such as dengue fever, chikungunya fever and zika virus disease. Chemical control of mosquitoes is an effective method to control mosquito-borne diseases, however, the wide and improper application of insecticides for vector control has led to serious resistance problems. At present, there have been many reports on the resistance to pyrethroid insecticides in vector mosquitoes including deltamethrin to Aedes albopictus. However, the fitness cost and vector competence of deltamethrin resistant Aedes albopictus remain unknown. To understand the impact of insecticide resistant mosquito is of great significance for the prevention and control mosquitoes and mosquito-borne diseases.Methodology/Principal findingsA laboratory resistant strain (Lab-R) of Aedes albopictus was established by deltamethrin insecticide selecting from the laboratory susceptible strain (Lab-S). The life table between the two strains were comparatively analyzed. The average development time of Lab-R and Lab-S in larvae was 9.7 days and 8.2 days (P < 0.005), and in pupae was 2.0 days and 1.8 days respectively (P > 0.05), indicating that deltamethrin resistance prolongs the larval development time of resistant mosquitoes. The average survival time of resistant adults was significantly shorter than that of susceptible adults, while the body weight of resistant female adults was significantly higher than that of the susceptible females. We also compared the vector competence for dengue virus type-2 (DENV-2) between the two strains via RT-qPCR. Considering the results of infection rate (IR) and virus load, there was no difference between the two strains during the early period of infection (4, 7, 10 day post infection (dpi)). However, in the later period of infection (14 dpi), IR and virus load in heads, salivary glands and ovaries of the resistant mosquitoes were significantly lower than those of the susceptible strain (IR of heads, salivary glands and ovaries: P < 0.05; virus load in heads and salivary glands: P < 0.05; virus load in ovaries: P < 0.001). And then, fourteen days after the DENV-2-infectious blood meal, females of the susceptible and resistant strains were allow to bite 5-day-old suckling mice. Both stains of mosquito can transmit DENV-2 to mice, but the onset of viremia was later in the mice biting by resistant group as well as lower virus copies in serum and brains, suggesting that the horizontal transmission of the resistant strain is lower than the susceptible strain. Meanwhile, we also detected IR of egg pools of the two strains on 14 dpi and found that the resistant strain were less capable of vertical transmission than susceptible mosquitoes. In addition, the average survival time of the resistant females infected with DENV-2 was 16 days, which was the shortest among the four groups of female mosquitoes, suggesting that deltamethrin resistance would shorten the life span of female Aedes albopictus infected with DENV-2.Conclusions/SignificanceAs Aedes albopictus developing high resistance to deltamethrin, the resistance prolonged the growth and development of larvae, shorten the life span of adults, as well as reduced the vector competence of resistant Aedes albopictus for DENV-2. It can be concluded that the resistance to deltamethrin in Aedes albopictus is a double-edged sword, which not only endow the mosquito survive under the pressure of insecticide, but also increase the fitness cost and decrease its vector competence. However, Aedes albopictus resistant to deltamethrin can still complete the external incubation period and transmit dengue virus, which remains a potential vector for dengue virus transmission and becomes a threat to public health. Therefore, we should pay high attention for the problem of insecticide resistance so that to better prevent and control mosquito-borne diseases.     

Comparison of the insecticide susceptibilities of laboratory strains of Aedes aegypti and Aedes albopictus

A susceptible strain of Aedes albopictus derived from the Gainesville strain (Florida, USA) was established in our laboratory. The larvicidal efficacies of the neurotoxic insecticides temephos, permethrin and the pure cis and trans-permethrin isomers and the microbial insecticide Bacillus thuringiensis israelensis (Bti) against Ae. albopictus were estimated and compared to a susceptible strain of Aedes aegypti. The larvicidal effect of insect growth regulator pyriproxyfen was also evaluated in both mosquito strains. The median lethal concentration/median emergency inhibition values for Ae. aegypti and Ae. albopictus, respectively, were: temephos, 3.058 and 6.632 ppb, permethrin, 3.143 and 4.933 ppb, cis-permethrin, 4.457 and 10.068 ppb, trans-permethrin, 1.510 and 3.883 ppb, Bti, 0.655 and 0.880 ppb and pyriproxyfen, 0.00774 and 0.01642 ppb. Ae. albopictus was more tolerant than Ae. aegypti to all six larvicides evaluated. The order of susceptibility for Ae. aegypti was pyriproxyfen > Bti > trans-permethrin > temephos > permethrin > cis-permethrin and for Ae. albopictus was pyriproxyfen > Bti > trans-permethrin > permethrin > temephos > cis-permethrin. Because both species can be found together in common urban, suburban and rural breeding sites, the results of this work provide baseline data on the susceptibility of Ae. albopictus to insecticides commonly used for controlling Ae. aegypti in the field.     

Exposure to chikungunya virus and adult longevity in Aedes aegypti (L.) and Aedes albopictus (Skuse)

Chikungunya virus (CHIKV) recently emerged as a global threat to public health through its adaptation to the cosmopolitan mosquito Aedes albopictus Skuse. Aedes albopictus is highly susceptible to the emergent strain of CHIKV, relative to the historical vector of CHIKV, Aedes aegypti (L.). We hypothesized that the high susceptibility of Ae. albopictus to CHIKV may have a cost in terms of longevity and fecundity among infected vs non‐infected mosquitoes, relative to Ae. aegypti. We performed a longevity experiment comparing Ae. aegypti and Ae. albopictus exposed to the emergent strain of CHIKV (LR‐2006OPY1). We found a small but significant decrease in longevity of Ae. albopictus, but not Ae. aegypti, in response to exposure to CHIKV. We did not observe significant differences in numbers of eggs laid by either species in response to exposure. Longevity and body titer of infected Ae. albopictus were significantly negatively correlated, such that individuals that lived longer had lower viral body titers when they died. The cost of exposure, while not high, suggests there may be physiological constraints in the evolution of viral infectiousness in its insect vector.     

Utilization of larval and pupal detritus by Aedes aegypti and Aedes albopictus

The utilization of detritus sources by mosquito larvae during development may significantly affect adult life history traits and mosquito population growth. Many studies have shown invertebrate carcasses to be an important detritus source in larval habitats, but little is known regarding how invertebrate carcasses are utilized by mosquito larvae. We conducted two studies to investigate the rate of detritus consumption and its effect on larval development and life history traits. Overall, we found that Aedes aegypti and Aedes albopictus larvae rapidly consumed larval detritus, while pupal detritus was consumed at a significantly slower rate. We also found that the consumption of larval detritus significantly increased larval survivorship and decreased male development time but did not significantly influence female development time or pupal cephalothorax length for either sex. Our results suggest that the direct consumption of larval detritus can support the production of adults in larval habitats that lack allochthonous detritus inputs or where such organic inputs are insufficient. These studies indicate that different forms of invertebrate detritus are utilized in distinct ways by mosquito larvae, and therefore different forms of invertebrate detritus may have distinct effects on larval development and adult life history traits.     

Comparing sources of mobility for modelling the epidemic spread of Zika virus in Colombia

Timely, accurate, and comparative data on human mobility is of paramount importance for epidemic preparedness and response, but generally not available or easily accessible. Mobile phone metadata, typically in the form of Call Detail Records (CDRs), represents a powerful source of information on human movements at an unprecedented scale. In this work, we investigate the potential benefits of harnessing aggregated CDR-derived mobility to predict the 2015-2016 Zika virus (ZIKV) outbreak in Colombia, when compared to other traditional data sources. To simulate the spread of ZIKV at sub-national level in Colombia, we employ a stochastic metapopulation epidemic model for vector-borne diseases. Our model integrates detailed data on the key drivers of ZIKV spread, including the spatial heterogeneity of the mosquito abundance, and the exposure of the population to the virus due to environmental and socio-economic factors. Given the same modelling settings (i.e. initial conditions and epidemiological parameters), we perform in-silico simulations for each mobility network and assess their ability in reproducing the local outbreak as reported by the official surveillance data. We assess the performance of our epidemic modelling approach in capturing the ZIKV outbreak both nationally and sub-nationally. Our model estimates are strongly correlated with the surveillance data at the country level (Pearson’s r = 0.92 for the CDR-informed network). Moreover, we found strong performance of the model estimates generated by the CDR-informed mobility networks in reproducing the local outbreak observed at the sub-national level. Compared to the CDR-informed networks, the performance of the other mobility networks is either comparatively similar or substantially lower, with no added value in predicting the local epidemic. This suggests that mobile phone data captures a better picture of human mobility patterns. This work contributes to the ongoing discussion on the value of aggregated mobility estimates from CDRs data that, with appropriate data protection and privacy safeguards, can be used for social impact applications and humanitarian action.