Climate and the superimposed distribution of Aedes aegypti and Aedes albopictus on infestation of São Paulo State,Brazil

OBJECTIVE: To study the influence of climatic factors and superimposed distribution of Aedes aegypti and Aedes albopictus populations on their geographic dispersal in the state of S?o Paulo. METHODS: Data from government agencies on Ae. aegypti and Ae. albopictus foci and their distribution throughout counties of the state of S?o Paulo year by year, from 1985 to 1995, were obtained. Temperatures and rainfall data were also collected. Two indicators were used: infestation and rate. RESULTS AND CONCLUSIONS: The analysis indicated that the lower the temperature, the slower the geographic dispersal of Ae. aegypti population. This factor predominantly influenced the macro regional dispersal patterns of the species in the state of S?o Paulo. There was no clear influence of temperature on the dispersal of Ae. albopictus. The influence of rainfall on dispersal patterns was seen only for Ae. aegypti in a state area. No influence was detected on the prior presence of Ae. albopictus on the establishment of Ae. aegypti.     

Dominance of Aedes aegypti over Aedes albopictus in the southeastern coast of Brazil

OBJECTIVE: To assess infestation of Aedes aegypti and Aedes albopiticus and describe their association with weather conditions and container colonization in urban areas. METHODS: The town of S?o Sebasti?o in the southeastern coast of Brazil was selected. It was used data from the Dengue and Yellow Fever Vector Control Program of the State of S o Paulo, Brazil, that encompasses entomological surveillance at strategic positions, traps and foci demarcation. Strategic positions sites are fixed sites with containers in adequate conditions for larvae growth. Statistical analysis was performed using Kruskal-Wallis test, Dwass-Steel-Chritchlow-Fligne test and Mann-Whitney test. RESULTS: There was found an annual growth of positive traps and strategic positions of Ae. aegypti and a drop in Ae. albopictus population. An increase in immature Ae. aegypti and a drop of the other species were also seen. A gradual increase of positive dwellings for Ae. aegypti was noticed outgrowing Ae. albopictus population. There was a weak correlation of the Aedes species with abiotic factors. Higher numbers of immature mosquitoes of both species were found in artificial containers which could be eliminated. CONCLUSIONS: The study showed Ae. aegypti was predominant in urban areas, indicating that its growth seems to have affected the coexistence with other species. Natural selection could be in place contributing to Aedes aegypti and albopictus species separation.     

Invasion of cemeteries in Florida by Aedes albopictus.

Aedes albopictus has been found in 53 of the 67 Florida counties. The initial discoveries in 11 of these counties were made in cemeteries. At several locations, Ae. albopictus became well-established in cemeteries before appearing in nearby accumulations of waste tires. The recycling of plastic floral baskets may be aiding the spread of Ae. albopictus. Mosquitoes were commonly found in all types of flower-holding containers in cemeteries, except bronze vases. In the laboratory, most Aedes aegypti eggs laid in bronze vases hatched, but larvae subsequently died. The spread of Ae. albopictus in cemeteries seems to occur at the expense of Ae. aegypti populations. At one cemetery immature Ae. albopictus and Ae. aegypti were found in about 70% of the Aedes-positive containers at the start of a monitoring program. In subsequent collections from this site, Ae. albopictus was found in nearly all Aedes-positive containers, whereas there was a progressive decrease in containers with Ae. aegypti. This trend did not appear to be the result of any seasonal pattern because in a nearby cemetery where Ae. albopictus was absent, Ae. aegypti did not show a similar decline. Limiting flower-holding containers to those with drain holes or to bronze vases would greatly limit mosquito production.     

Diversity of oviposition containers and buildings where Aedes albopictus and Aedes aegypti can be found

OBJECTIVE: To assess the diversity of oviposition containers and buildings where females of Aedes albopictus and Aedes aegypti can be found. METHODS: A study was carried out in the city of Rio de Janeiro, Southern Brazil, between 2002 and 2003. Larvae in different types of buildings were investigated, and immature forms found were then sent to the laboratory for identification. The larval frequency for both mosquitoes was estimated in the oviposition containers available. The Breteau index and the building infestation index were calculated and differences were tested using the Chi-square test. RESULTS: The types of buildings that were positive for Aedes albopictus and Aedes aegypti were: dwellings (83.9%); churches, schools, clubs (6.8%); vacant land (6.4%); and businesses (2.8%). Of 9,153 larvae collected, 12.0% were Aedes albopictus and 88.0% were Aedes aegypti. Aedes albopictus were mostly found in drains (25.4%); cans, bottles, empty bottles (23.9%); and plant vases (16.2%). Aedes aegypti was much more frequently found than Aedes albopictus (chi(2)=145.067; p<0.001). Both species were significantly more frequent in artificial than in natural oviposition containers (chi(2)=31.46; p<0.001). The building infestation index and Breteau index for Aedes albopictus were 0.3% and 0.28% in 2002 and 0.4% and 0.5 in 2003, respectively. For Aedes aegypti, they were 1.0%, 1.16 in 2002 and 3.5% and 4.35 in 2003, respectively. CONCLUSIONS: The present study assessed the frequencies of Aedes albopictus and Aedes aegypti females in various types of oviposition containers and types of buildings. The abundant availability of artificial containers in dwellings, associated with the capacity of Ae. albopictus to be also found in natural oviposition containers, has greatly contributed for their gradual adaptation to human environment.     

Biology and distribution of Aedes albopictus and Aedes aegypti in Madagascar

The biology and distribution of the 2 Malagasy Stegomyia species, Aedes aegypti and Aedes albopictus, is updated and reported. Aedes aegypti is present in the western and southern regions and Ae. albopictus in the east and on the high plateau. Some unusual locations are noted. The ranges of Ae. albopictus and Ae. aegypti on Madagascar overlap only slightly. Aedes aegypti is present in the west and in the south, while the Ae. albopictus distribution area is in the east and on the central high plateau. Climatic factors (number of dry months, annual rainfall and temperature), rather than competitive interactions, appear to be the major determinants of the distribution of these species. Aedes aegypti is just slightly anthropophilic, contrary to Ae. albopictus. Babanki virus and MMP 158 virus were isolated from Ae. aegypti; no virus has been isolated from Ae. albopictus.     

Infection and dissemination of dengue virus type 2 in Aedes aegypti, Aedes albopictus, and Aedes scutellaris from the Torres Strait, Australia

To determine their relative roles in transmission of dengue virus (DENV) in the Torres Strait region of northern Australia, we examined infection and dissemination of a sympatric strain of dengue virus type 2 (DENV-2) in Aedes scutellaris, Ae. albopictus, and Ae. aegypti. In experiments using membrane feeders for virus exposure, infection rates were 83% and 43% for Ae. scutellaris and Ae. aegypti, respectively. Salivary gland infection rates for both species were 43%. In experiments using pledgets for virus exposure, infection rates for Ae. aegypti, Ae. scutellaris, and Ae. albopictus were 68%, 55%, and 37%, respectively. Aedes albopictus exhibited the greatest barriers to infection with only 7% tested developing a salivary gland infection, compared to 42% and 24% of Ae. aegypti and Ae. scutellaris, respectively. These results suggest that Ae. scutellaris may have been responsible for DENV transmission on Torres Strait islands, where Ae. aegypti does not occur. In contrast, Ae. albopictus may not be an important vector of DENV-2 from the Torres Strait.     

Distribution of Aedes aegypti and dengue in the State of Maranh?o, Brazil]

Dengue and Aedes aegypti are widespread in the State of Maranh?o. During 1995, 87 of the 136 of the State's counties, including 176 towns and 480,687 households, were studied, of which 30 counties (34. 4%), 118 towns (67.0%) and 10,357 households (2.1%) were positive for Aedes aegypti. The positive counties are distributed as follow: 3 on S?o Luís Island, 7 in the Amazonia of Maranh?o, 12 in the southern zone of the cerrados or savannas, and 5 in the mixed forest/savanna/palm grove zone. One positive county for Ae. aegypti was located in each of the following: alluvial fields, forest/palm grove, and sand dune/shoals areas. The Ae. aegypti-positive household rates were higher in the Amazonia of Maranh?o (3.5%) and on S?o Luís Island (2.5%), because they are the most heavily traveled migratory and trade routes between Maranh?o and neighboring states and are also the State's main economic centers. Household infestation rates for Ae. aegypti and reported dengue case rates were higher during the rainy season, showing the importance of rain in forming prime breeding sites for Aedes and spreading dengue.     

Age-dependent bloodfeeding of Aedes aegypti and Aedes albopictus on artificial and living hosts

In order to quantify age-dependent acquisition of a bloodmeal, we compared bloodfeeding patterns of Aedes aegypti and Aedes albopictus starting from the time of first responsiveness to a bloodmeal up to 15 days postemergence. In separate experiments, cohorts of Ae. aegypti and Ae. albopictus of known age were offered their first bloodmeal from a silicon-membrane system or a restrained chicken. For cohorts ranging from 3 to 15 days old, the proportions feeding were significantly affected by species, age, feeding protocol, and the age x feeding protocol interaction. For both feeding protocols, a higher proportion of Ae. aegypti than Ae. albopictus, on average, consumed blood. Regressions of proportion feeding versus age indicated significantly positive slopes for Ae. albopictus and Ae. aegypti on the membrane system, and no significant relationship was observed for either species on the restrained chicken. Additionally, slopes for Aedes, as a group, fed on the membrane system were significantly different from those fed on the living host. For both Aedes species fed on the restrained chicken and for Ae. aegypti fed on the membrane system, the proportions feeding exhibited periodic patterns, with peaks approximately 2 days apart, suggesting possible control by endogenous rhythms.     

Long-term surveillance data and patterns of invasion by Aedes albopictus in Florida

We used geographic information system (GIS) and long-term mosquito surveillance data from Lake, Pasco, Manatee, and Sarasota Counties, FL, to look at patterns of invasion by Aedes albopictus and concurrent changes in resident Ae. aegypti. We investigated environmental factors associated with population changes in these species with the use of satellite climate data. Aedes aegypti densities attenuated rapidly following the arrival of Ae. albopictus in most counties, yet both species persisted in equilibrium in Manatee County. We discuss the relative importance of rainfall, habitat, and proximity to urban areas in the population dynamics of these species in sympatry.     

埃及伊蚊监测

埃及伊蚊清除后，从１９９３年开始在旧发生区分别采用诱卵器诱测、面上定期检查及定期检查从疫区来的到港船只等３种方法进行系统监测。已查诱卵器２８２０个次，查出白纹伊蚊阳性容器８６８个次，容器指数为２６．３１；库蚊类阳性容器１１８个次，容器指数为４．１８。面上调查５１７４户次，检查积水容器１０５５６个次，查出白纹伊蚊７４０个次，容器指数为７．０１；库蚊类阳性容器５９６个次，容器指数为５．６５。检查到港船只７０４艘次，船上积水容器１８７５个次，未查出携带蚊子。３种监测方法均未查到埃及伊蚊。用诱卵器法查到的白纹伊蚊容器指数，比面上的调查高２．７５倍，两者在统计学上存在显著差异（Ｐ＝５．４５９．Ｐ０．５＝２．７７６，Ｐ０．０１＝８．６１）。目前对到港船只进行全面检查尚存在一定困难，故坚持在旧发生区布放诱卵器诱测及定期作好面上调查，就有可能及时发现新传入的埃及伊蚊，可作为目前埃及伊蚊监测的重要手段。     

Microhabitats of Aedes albopictus (Skuse) in the region of the Paraiba Valley, S?o Paulo State, Brazil]

The objective of this study was the determination of extent of the spatial distribution of Aedes albopictus in the Paraíba River Valley, State S. Paulo, Brazil. Thus, collections of larvae and pupae mosquitoes were carried out at six sites distributed along a transection with a 10-km extension. The target was the tree-holes but artificial containers were also used in this investigation. Aedes terrens and Ae. albopictus were the only species of genus Aedes present in the tree-holes mentioned. The segregation of seven species of the tree-hole community was undertaken in the light of macrohabitat and microhabitat features. Thus, the distribution of Ae. albopictus was found to cover the rural, rural-urban and urban zones, but the rural-urban held the preference. Ae. albopictus never present in the residual and primary forest. The favorable factor to infestation with Ae. albopictus in the Paraíba Valley seems to have been the large number of natural niches made vacant by human influence. The rain has been important in the production of larvae and pupae, but the rainfall period does not coincide with the maximum production on them. The tree-holes whose volume exceeded 600 ml were the most productive breeding places. The abundance of these two stages occurs in the summer and autumn. However, the highest peak was observed in the months of March and April. These seasonal variations were found to be common in both the bamboo trap and the artificial container. The temperature data suggest a limit of from 17 to 23 degrees C for the best development of larvae. In the light of this, the strain of Ae. albopictus studied seems to have originated in tropical Asia. Just as happened with Ae. aegypti it may become an important epidemiological vector for the dengue fever and provide links for yellow fever transmission in Brazil.     

Interspecific mating between Louisiana strains of Aedes albopictus and Aedes aegypti in the field and laboratory

Interspecific mating between Aedes albopictus males and Ae. aegypti females was detected in the field using mark-release-recapture techniques. By 3 days after the release of virgin Ae. aegypti females into a field site containing only Ae. albopictus, 100% of the captured females were inseminated. Laboratory investigations indicated that male Ae. albopictus were very proficient at inseminating Ae. aegypti females and that Ae. aegypti males rarely inseminated Ae. albopictus females, especially if Ae. aegypti females were available. Most of the Ae. aegypti females inseminated by Ae. albopictus males contained only small amounts of dead sperm in their spermathecae, while inseminated females from the converse interspecific mating and from intraspecific matings contained only large amounts of live sperm. The results are discussed in relation to the decline in Ae. aegypti densities observed since the introduction of Ae. albopictus into the southern USA.     

Susceptibility of adult field strains of Aedes aegypti and Aedes albopictus in Singapore to pirimiphos-methyl and permethrin

The susceptibilities of field strains (Fl) of Aedes aegypti and Ae. albopictus adult females to pirimiphos-methyl and permethrin were investigated and compared with a susceptible laboratory strain (S) by using a filter paper (12 x 15 cm) impregnation method. The resistance ratio between the 50% lethal concentration values (RR50) of the Fl and the S strains shows that the RR50 of Fl Ae. aegypti for pirimiphos-methyl was 1.5 and the RR50 of Fl Ae. aegypti for permethrin was 12.9. The RR50 of Fl Ae. albopictus for pirimiphos-methyl was 1.4, and that for permethrin was 1.8. This indicates that the field strain Ae. aegypti, but not Ae. albopictus, has developed resistance to permethrin. However, both species are still susceptible to pirimiphos-methyl. Therefore, control with pirimiphos-methyl will still be effective.     

Anthropophilic activity of Aedes aegypti and of Aedes albopictus in area under control and surveillance

OBJECTIVE: To describe the hematophagous activity of Ae. aegypti and Ae. albopictus in an area under control and surveillance. METHODS: The study was conducted during 18 months, from April, 1993 to October, 1994, in Cosmopolis, Sao Paulo state, Brazil. Human baits were used to collect mosquitoes. The number of females captured is presented monthly by area of the city and local in the household. The rainfall was measured and indices are presented without model adjustment. RESULTS: The presence of females of both species was observed in 83% (Ae albopictus) and 61% (Ae. aegypti) of the period studied. The months of January, February and March presented the highest rates of activity for females of both species, with Ae. albopictus being more frequently captured than Ae. aegypti. Both species were captured in central and peripheral areas of the city, during the day from 9 to 12 am and from 4 to 7 pm. By a Poisson regression, it was observed that Ae. albopictus females were more frequently captured in the peri-housed area, in an independent way considering the area of the city. CONCLUSIONS: It has been identified difference on the hematophagous activity only for Ae. albopictus, being of importance the outside area of the house.     

Differences in the larval alarm reaction in populations of Aedes aegypti and Aedes albopictus

The time spent submerged during the larval alarm reaction was measured for several strains of Aedes aegypti and Ae. albopictus from different locations. Differences between the 2 species were not significant. Differences in strains within the species were highly significant. Greater differences were seen among strains of Ae. albopictus than among strains of Ae. aegypti. These differences represent an additional indication of extensive local differentiation in Ae. albopictus.     

Vector competence of Brazilian Aedes aegypti and Ae. albopictus for a Brazilian yellow fever virus isolate

Because the potential urban yellow fever (YF) mosquito vectors Aedes aegypti and Ae. albopictus are at historical highs in Brazil, both in terms of density and geographical range, we assessed the risk of an urban YF epidemic in Brazil. We evaluated and confirmed in a laboratory setting the vector competence of Brazilian Ae. aegypti for a currently circulating strain of YF virus, and investigated the potential for Brazilian Ae. albopictus to transmit YF.     

Aedes albopictus in the United States: current status and prospects for further spread.

Since its initial discovery in the continental USA in 1985, the Asian tiger mosquito, Aedes albopictus, has spread rapidly throughout the eastern part of the country. Infestations of Ae. albopictus now have been reported to the Centers for Disease Control and Prevention from 919 counties in 26 states in the continental USA. This species is believed to be established in 911 counties in 25 states. Single individuals or small numbers of Ae. albopictus have been intercepted and destroyed in 3 additional states (California, New Mexico, and Washington). Five states (Florida, Georgia, North Carolina, South Carolina, and Tennessee) have reported infestations in all of their counties. The current reported distribution of Ae. albopictus was compared to ecoregions of the U.S. Environmental Protection Agency's Level III ecoregion map. Several areas are identified as probable candidates for extension of this species based on ecological characteristics of the landscape. In other areas, populations seem likely to become locally abundant in urban or suburban oases that do not reflect the native ecology of the region. The ability of Ae. albopictus to transmit a variety of pathogens of human and veterinary public health importance, coupled with its ability to colonize diverse ecological settings makes continued surveillance an important issue.     

The significance of the introduction of Aedes albopictus into the southeastern United States with implications for the Caribbean, and perspectives of the Pan American Health Organization

The introduction and apparent infestation of Aedes albopictus into the Gulf States of Texas and Louisiana in the United States is viewed as the most singular medical entomological happening of this decade in the Americas. The implications for the Caribbean and other countries southward are serious, as the habitat described for this Stegomyia cousin of Ae. aegypti, is amply available in the Windward and Leeward islands of the Antilles. Studies from the Pacific and regions of Southeast Asia indicate that Ae. albopictus competes for the same peridomestic niches as Ae. aegypti and it has been found to be a competent vector of several dengue serotypes. In this presentation, a call is issued to the mosquito control and abatement programs in the Gulf States to take stringent measures to eliminate this new dengue vector before it becomes thoroughly established and spreads to other states as well as into countries of the Americas and into the West Indies.     

Past, present and future of Aedes albopictus in the United States

Aedes albopictus was first detected in Houston, Texas, in 1985. Since then it has spread to 17 states and 122 counties. This exotic species from Asia appears to have arrived in the U.S. in imported used tire casings. Public health concerns have been raised regarding the potential of this species to serve as a vector of arboviruses indigenous to the U.S., such as La Crosse encephalitis, and also for imported dengue. The Division of Vector-Borne Viral Diseases, Centers for Disease Control, has actively pursued a program to determine the distribution of Ae. albopictus in the U.S., monitor the spread of the species and implement procedures that would eliminate the risk of further importation of exotic mosquitoes in used tire casings. The latter goal was achieved in large measure in 1988 with a 98% reduction in imported used tires containing water. The ultimate consequences of establishment of Ae. albopictus in the U.S. is unknown; however, because of its biologic characteristics and broad viral susceptibility, it seems likely that this species will eventually become involved as an arbovirus vector in the U.S.