Growth characteristics of ChimeriVax-DEN2 vaccine virus in Aedes aegypti and Aedes albopictus mosquitoes

The chimeric yellow fever (YF) 17D-dengue type 2 (ChimeriVax-DEN2) vaccine virus developed by Acambis, Inc. (Cambridge, MA) contains the prM and E genes of wild-type (wt) dengue 2 (DEN-2) (strain PUO-218) virus in the YF vaccine virus (strain 17D) backbone. The potential of ChimeriVax-DEN2 virus to infect and be transmitted by Aedes aegypti, the principal DEN and YF virus mosquito vector, and Aedes albopictus, a species that occurs in areas of active transmission of YF and DEN viruses, was evaluated. Mosquitoes were intrathoracically (IT) inoculated with virus or were fed a virus-laden blood meal, and the replication kinetics of ChimeriVax-DEN2 were compared with the wt DEN-2 and YF 17D vaccine viruses. Replication of YF 17D virus is attenuated in cultured Ae. albopictus C6/36 mosquito cells and in Ae. aegypti and Ae. albopictus mosquitoes. Growth of ChimeriVax-DEN2 virus similarly was restricted in C6/36 cells and in mosquitoes. ChimeriVax-DEN2 replicated in 56% of IT inoculated Ae. aegypti, and virus disseminated to head tissue in 36%, with a mean viral titer of 1.8 log10 PFU/mosquito. Of mosquitoes, 16% of Ae. aegypti and 24% of Ae. albopictus were infected 14 days after a blood meal containing ChimeriVax-DEN2, but virus did not disseminate to head tissue. In contrast, DEN-2 replicated in all IT inoculated and orally infected Ae. aegypti (mean titer 5.5 log10 PFU/mosquito), and virus disseminated to head tissue in 95%. Of Ae. albopictus, 84% were infected after a blood meal containing DEN-2 virus; dissemination occurred in 36%. Replication of ChimeriVax-DEN2 virus in mosquitoes corresponded to that of YF 17D vaccine virus, which is restricted in its ability to infect and replicate in mosquitoes. Therefore, transmission of ChimeriVax-DEN2 virus by vector mosquitoes is unlikely.     

Transovarial transmission of dengue viruses by mosquitoes: Aedes albopictus and Aedes aegypti

Transovarial transmission of all four dengue serotypes was demonstrated in Aedes albopictus mosquitoes. The rates of such transmission varied with the serotype and strain of virus. In general, the highest rates were observed with strains of dengue type 1 and the lowest with dengue type 3. Surprisingly, despite the use of viral strains of the four dengue serotypes which gave the highest rates with Ae. albopictus, transovarial transmission was observed in Aedes aegypti only with dengue type 1, and then only at a relatively low rate. Five different strains of Ae. aegypti were employed, including one that was known to be relatively susceptible to oral infection with dengue viruses. The findings support the view that Ae. aegypti, while of major importance from the point of view of transmission of dengue to man, may be relatively unimportant in the overall natural history of dengue viruses.     

Limited potential for transmission of live dengue virus vaccine candidates by Aedes aegypti and Aedes albopictus

To evaluate the transmission risk of four live dengue (DEN) vaccine candidates developed by the U.S. Army (DEN-1, 45AZ5 PDK 20; DEN-2, S16803 PDK 50; DEN-3, CH53489 PDK 20; and DEN-4, 341750 PDK 20), we tested 3,010 Aedes aegypti and 1,576 Aedes albopictus mosquitoes blood-fed on 21 volunteers who had been administered one of the four vaccine candidates or the licensed yellow fever (YF) vaccine (17D). We used an indirect immunofluorescence assay (IFA) to detect DEN or YF viral antigen in the heads of mosquitoes. Corresponding to the lack of a detectable viremia among volunteers inoculated 8-13 days previously with live DEN-1 or DEN-2 vaccine candidates, only six mosquitoes developed disseminated infections after feeding on these volunteers. These six mosquitoes included 4 of 247 Ae. albopictus fed on volunteers inoculated with the DEN-1 vaccine candidate and 2 of 528 Ae. aegypti fed on volunteers inoculated with the DEN-2 vaccine candidate. Infection was confirmed in each of these IFA-positive mosquitoes by isolating infectious virus from the mosquito's body in Vero-cell culture. None of the 1,252 or the 969 mosquitoes fed on DEN-3 or DEN-4 recipients, respectively, were infected. Overall, dissemination rates in Ae. albopictus and Ae. aegypti were low. Dissemination rates were 0.5%, 0.3%, < 0.1%, and < 0.1% for the DEN-1 through DEN-4 vaccine candidates, respectively. Because of the observed low dissemination rates, it is unlikely that these vaccine viruses would be transmitted under natural conditions.     

Role of Aedes aegypti and Aedes albopictus during the 2011 dengue fever epidemics in Hanoi,Vietnam

Objective: To record the human cases of dengue fever(DF) and investigate the Aedes mosquito species circulating during the Hanoi 2011 DF epidemics. Methods: 24 different outbreak points were recorded in 8 districts between August and December 2011. Results: 140 patients were hospitalized following dengue diagnostic with a predominance of males(59.3%) and the 15-34 age class. Only DENV-1(11.27%) and DENV-2(88.73%) serotypes were detected in human samples. Mosquito sampling performed in and around patients households revealed the predominance of Aedes aegypti(95.15%) versus Aedes albopictus(4.85%). There is a positive correlation between the population density of Aedes aegypti and the number of human cases and duration of outbreaks. Conclusions: This was not observed for Aedes albopictus. 3 pools of Aedes aegypti were positive with dengue virus, two with DENV-1 and one with DENV-2.     

Evaluation of Aedes aegypti,Aedes albopictus,and Culex quinquefasciatus Mosquitoes Competence to Oropouche virus Infection

The emergence of new human viral pathogens and re-emergence of several diseases are of particular concern in the last decades. Oropouche orthobunyavirus (OROV) is an arbovirus endemic to South and Central America tropical regions, responsible to several epidemic events in the last decades. There is little information regarding the ability of OROV to be transmitted by urban/peri-urban mosquitoes, which has limited the predictability of the emergence of permanent urban transmission cycles. Here, we evaluated the ability of OROV to infect, replicate, and be transmitted by three anthropophilic and urban species of mosquitoes, Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus. We show that OROV is able to infect and efficiently replicate when systemically injected in all three species tested, but not when orally ingested. Moreover, we find that, once OROV replication has occurred in the mosquito body, all three species were able to transmit the virus to immunocompromised mice during blood feeding. These data provide evidence that OROV is restricted by the midgut barrier of three major urban mosquito species, but, if this restriction is overcome, could be efficiently transmitted to vertebrate hosts. This poses a great risk for the emergence of permanent urban cycles and geographic expansion of OROV to other continents.     

Population genetic structure and competence as a vector for dengue type 2 virus of Aedes aegypti and Aedes albopictus from Madagascar.

Starch gel electrophoresis was used to assess the polymorphism of 7 isoenzymes in single mosquitoes (field-collected F0 or F1 generation) for Aedes albopictus (8 strains) from northern Madagascar. Mosquitoes of the F2 generation (3 strains of Aedes aegypti and 10 strains of Ae. albopictus) were tested for oral susceptibility to dengue type 2 virus. Aedes aegypti was less susceptible to viral infection than Ae. albopictus. The genetic differentiation was less high between Ae. albopictus populations collected in agglomerations connected by highly frequented roads, indicating that human ground transportation favors mosquito dispersal. These results have implications for the ecology, pattern of migration, and relative importance in epidemic transmission of dengue viruses between the 2 Aedes species.     

Insecticide susceptibility tests of Anopheles minimus s.l., Aedes aegypti,Aedes albopictus,and Culex quinquefasciatus in northern Thailand

The susceptibility of Anopheles minimus s.l., Aedes aegypti, Ae. albopictus, and Culex quinquefasciatus to insecticide in northern Thailand was monitored by using the WHO standard susceptibility test. One- to two-day old female mosquitos, which were reared from wild caught females or immature stages, were exposed to discriminating dosages of insecticides for recommended exposure periods, and the 24-hour mortality recorded. The results revealed that, in general, An. minimus s.l. was still susceptible to DDT and permethrin, except in some areas where a slight increase in tolerance to DDT was observed. Ae. aegypti and Ae. albopictus were both highly resistant to DDT, but in some areas the former was also resistant to permethrin and deltamethrin. Cx. quinquefasciatus was resistant to DDT and etofenprox, with a slight increase in tolerance to permethrin, deltamethrin, malathion and fenitrothion. No resistance to lambda-cyhalothrin was detected in any of the species studied.     

Polygamy: the possibly significant behavior of Aedes aegypti and Aedes albopictus in relation to the efficient transmission of dengue virus

The polygamous behavior of male Aedes aegypti (L.) and Ae. albopictus (Skuse) was investigated by co-habiting a newly-emerged male and females in a 30 cm3 cage (1 male: 20 females) for up to 5 consecutive days. As determined by insemination rates, the results indicated that one Ae. aegypti and Ae. albopictus male could successfully mate with 1.10 (0-4), 4.10 (1-8), 5.40 (4-8), 5.10 (2-8), 5.15 (3-9) and 0.20 (0-3), 1.70 (0-3), 2.35 (1-4), 2.30 (0-4), 2.35 (1-4) Ae. aegypti and Ae. albopictus females, respectively on day 1,2,3,4 and 5 consecutively. The possibly significant role of their polygamy in relation to dengue virus transmission is discussed.     

High-Throughput Method for Detection of Arbovirus Infection of Saliva in Mosquitoes Aedes aegypti and Ae. albopictus

Vector competence refers to the ability of a vector to acquire, maintain, and transmit a pathogen. Collecting mosquito saliva in medium-filled capillary tubes has become the standard for approximating arbovirus transmission. However, this method is time-consuming and labor-intensive. Here we compare the capillary tube method to an alternative high-throughput detection method the collection of saliva on paper cards saturated with honey, with (FTA card) and without (filter paper) reagents for the preservation of nucleic acid for Aedes aegypti and Aedes albopictus mosquitoes infected with two emerging genotypes of the chikungunya virus (CHIKV). Model results showed that the Asian genotype CHIKV dissemination in the harvested legs of both Ae. aegypti and Ae. albopictus increased the odds of females having a positive salivary infection and higher salivary viral titers, while for the IOL genotype the same effect was observed only for Ae. aegypti. Of the three tested detection methods, the FTA card was significantly more effective at detecting infected saliva of Ae. aegypti and Ae. albopictus females than the capillary tube and filter paper was as effective as the capillary tube for the Asian genotype. We did not find significant effects of the detection method in detecting higher viral titer for both Asian and IOL genotypes. Our results are discussed in light of the limitations of the different tested detection methods.     

Transmission potential of two chimeric Chikungunya vaccine candidates in the urban mosquito vectors, Aedes aegypti and Ae. albopictus

Chikungunya virus (CHIKV) is an emerging, mosquito-borne alphavirus that has caused major epidemics in Africa and Asia. We developed chimeric vaccine candidates using the non-structural protein genes of either Venezuelan equine encephalitis virus (VEEV) attenuated vaccine strain TC-83 or a naturally attenuated strain of eastern equine encephalitis virus (EEEV) and the structural genes of CHIKV. Because the transmission of genetically modified live vaccine strains is undesirable because of the potentially unpredictable evolution of these viruses as well as the potential for reversion, we evaluated the ability of these vaccines to infect the urban CHIKV vectors, Aedes aegypti and Ae. albopictus. Both vaccine candidates exhibited significantly lower infection and dissemination rates compared with the parent alphaviruses. Intrathoracic inoculations indicated that reduced infectivity was mediated by midgut infection barriers in both species. These results indicate a low potential for transmission of these vaccine strains in the event that a vaccinee became viremic.     

Distribution of Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse) in small towns and villages of Penang Island, Malaysia--an ovitrap survey.

An ovitrap survey was carried out in April and May of 1975 at twenty-one locations scattered throughout Penang Island excluding the City of Georgetown. The results showed the ubiquitous presence of Ae. albopictus. Ae. aegypti was recorded only in Tanjung Tokong Lama, an area adjacent to the City of Georgetown. In the survey, Ae. albopictus females were found to prefer the outdoor ovitraps than indoor ones. The effectiveness of ovitrap in Aedes survey was discussed.     

Growth characteristics of the chimeric Japanese encephalitis virus vaccine candidate, ChimeriVax-JE (YF/JE SA14--14--2), in Culex tritaeniorhynchus, Aedes albopictus, and Aedes aegypti mosquitoes

The Japanese encephalitis (JE) virus vaccine candidate, ChimeriVax-JE, which consists of a yellow fever (YF) 17D virus backbone containing the prM and E genes from the JE vaccine strain JE SA14--14--2, exhibits restricted replication in non-human primates, producing only a low-level viremia following peripheral inoculation. Although this reduces the likelihood that hematophagous insects could become infected by feeding on a vaccinated host, it is prudent to investigate the replication kinetics of the vaccine virus in mosquito species that are known to vector the viruses from which the chimera is derived. In this study ChimeriVax-JE virus was compared to its parent viruses, as well as to wild-type JE virus, for its ability to replicate in Culex tritaeniorhynchus, Aedes albopictus, and Aedes aegypti mosquitoes. Individual mosquitoes were exposed to the viruses by oral ingestion of a virus-laden blood meal or by intrathoracic (IT) virus inoculation. ChimeriVax-JE virus did not replicate following ingestion by any of the three mosquito species. Additionally, replication was not detected after IT inoculation of ChimeriVax-JE in the primary JE virus vector, Cx. tritaeniorhynchus. ChimeriVax-JE exhibited moderate growth following IT inoculation into Ae. aegypti and Ae. albopictus, reaching titers of 3.6-5.0 log(10) PFU/mosquito. There was no change in the virus genotype associated with replication in mosquitoes. Similar results were observed in mosquitoes of all three species that were IT inoculated or had orally ingested the YF 17D vaccine virus. In contrast, all mosquitoes either IT inoculated with or orally fed wild-type and vaccine JE viruses became infected, reaching maximum titers of 5.4-7.3 log(10) PFU/mosquito. These results indicate that ChimeriVax-JE virus is restricted in its ability to infect and replicate in these mosquito vectors. The low viremia caused by ChimeriVax-JE in primates and poor infectivity for mosquitoes are safeguards against secondary spread of the vaccine virus.     

Breeding habitats and larval indices of Aedes aegypti and Ae. albopictus in the residential areas of Calcutta City.

Aedes aegypti and Ae. albopictus larvae were found breeding in almost all indoor and outdoor, temporary and/or permanent collections of water, either alone or in association with each other in residential areas of the city, the former throughout the year (June'97-May'98) and the latter during monsoons and post-monsoons only. Ae. aegypti showed preference for breeding in chowbachhas, indoors and Ae. albopictus for collections of water in flower pots and discarded containers and outdoors. The larval indices of both the species were highest during monsoons and post-monsoons.     

A survey of dengue viral infection in Aedes aegypti and Aedes albopictus from re-epidemic areas in the north of Thailand using nucleic acid sequence based amplification assay

Immature stages of Aedes aegypti and Ae. albopictus were collected from 17 dengue re-epidemic areas in Chiang Mai and Lampang Provinces, in the north of Thailand. They were reared to adults and tested for dengue viral RNA by a nucleic acid sequence based amplification assay (NASBA). Of a total of 9,825 Ae. aegypti and 150 Ae. albopictus examined, none of them were found positive for the virus, suggesting that transovarial transmission may be very low in the vector populations and may not play a significant role in the epidemiology of dengue infection in Thailand.     

Introduction, scenarios for establishment and seasonal activity of Aedes albopictus in The Netherlands

The Asian tiger mosquito Aedes albopictus was detected for the first time in the Netherlands in the summer of 2005. Aedes albopictus is a competent vector of several human viral diseases, and therefore the recent appearance of the vector is a concern to local public health authorities. In 2006 and 2007, the mosquito was found repeatedly and regularly at Lucky bamboo import companies. To assess whether imported Ae. albopictus could establish to produce subsequent generations in the following years or whether the winter conditions in the Netherlands would prove too cold to allow overwintering of diapausing eggs, predictions were made using a Geographic Information Systems (GIS) model based on January average temperature and the annual precipitation recorded in 2006. Seasonal activity of overwintering Ae. albopictus was estimated for temperate strains based on the weekly average temperature and weekly photoperiod using spring egg hatching thresholds of 10.5 degrees C and 11.25 hours, and egg diapause and adult survival thresholds of 9.5 degrees C and 13.5 hours. The analyses indicate that the climate conditions in the Netherlands over the past 10 years were favorable to allow overwintering of diapausing eggs of temperate strains of Ae. albopictus, particularly in the western coastal region. This region was also the area where adult Ae. albopictus were intercepted inside and surrounding plant glasshouses. The estimated number of weeks elapsing between first egg hatching in spring and the production of diapausing eggs in autumn ranged between 17 and 22 weeks in 2006.     

Mosquito-Producing Containers,Spatial Distribution,and Relationship between Aedes aegypti Population Indices on the Southern Boundary of its Distribution in South America (Salto,Uruguay)

A study was conducted in the city of Salto, Uruguay, to identify mosquito-producing containers, the spatial distribution of mosquitoes and the relationship between the different population indices of Aedes aegypti. On each of 312 premises visited, water-filled containers and immature Ae. aegypti mosquitoes were identified. The containers were counted and classified into six categories. Pupae per person and Stegomyia indices were calculated. Pupae per person were represented spatially. The number of each type of container and number of mosquitoes in each were analyzed and compared, and their spatial distribution was analyzed. No significant differences in the number of the different types of containers with mosquitoes or in the number of mosquitoes in each were found. The distribution of the containers with mosquito was random and the distribution of mosquitoes by type of container was aggregated or highly aggregated.     

Effect of temperature on the vector efficiency of Aedes aegypti for dengue 2 virus

The effect of temperature on the ability of Aedes aegypti to transmit dengue (DEN) 2 virus to rhesus monkeys was assessed as a possible explanation for the seasonal variation in the incidence of dengue hemorrhagic fever in Bangkok, Thailand. In two laboratory experiments, a Bangkok strain of Ae. aegypti was allowed to feed upon viremic monkeys infected with DEN-2 virus. Blood-engorged mosquitoes were separated into two groups and retained at constant temperatures. Virus infection and transmission rates were determined for Ae. aegypti at intervals ranging from 4 to 7 days during a 25-day incubation period. Results of the first experiment for mosquitoes infected with a low dose of DEN-2 virus and maintained at 20, 24, 26, and 30 degrees C, indicated that the infection rate ranged from 25% to 75% depending on the incubation period. However, DEN-2 virus was transmitted to monkeys only by Ae. aegypti retained at 30 degrees C for 25 days. In the second experiment, the infection rate for Ae. aegypti that ingested a higher viral dose, and incubated at 26, 30, 32, and 35 degrees C ranged from 67% to 95%. DEN-2 virus was transmitted to monkeys only by mosquitoes maintained at greater than or equal to 30 degrees C. The extrinsic incubation period was 12 days for mosquitoes at 30 degrees C, and was reduced to 7 days for mosquitoes incubated at 32 degrees C and 35 degrees C. These results imply that temperature-induced variations in the vector efficiency of Ae. aegypti may be a significant determinant in the annual cyclic pattern of dengue hemorrhagic fever epidemics in Bangkok.