Susceptibility of Aedes aegypti and Aedes albopictus larvae to Ascogregarina culicis and Ascogregarina taiwanensis (Apicomplexa: Lecudinidae) from Florida

The susceptibility of Aedes aegypti to Ascogregarina culicis and Aedes albopictus to Ascogregarina taiwanensis was examined with mosquito and parasite strains from Tampa, FL. When each host was bioassayed with its natural gregarine, the infection intensity indicated that Ae. aegypti was 59% more susceptible to A. culicis (87 gamonts/larva) than Ae. albopictus to A. taiwanensis (47 gamonts/larva). Infections in single and mixed host populations exposed to 100 oocysts/larva of one and both parasites demonstrated that Ae. aegypti harbors higher A. culicis gamont loads than Ae. albopictus of A. taiwanensis. In dual gregarine exposures of single host populations, the A. culicis infection intensity in Ae. aegypti was reduced by approximately 50%. A. taiwanensis exhibited the same capability of infecting Ae. albopictus in single and dual exposures. In mixed host populations there were no cross infections, but A. taiwanensis in Ae. albopictus produced an infection intensity of approximately 70% lower than that of A. culicis in Ae. aegypti.     

Prevalence and seasonality of Ascogregarina culicis (Apicomplexa: Lecudinidae) in natural populations of Aedes aegypti (Diptera: Culicidae) from temperate Argentina

Ascogregarina infections from South America were recently documented in Brazil and Argentina. The aim of this study was to report our recent findings on the prevalence and seasonality of Ascogregarina culicis in Aedes aegypti adults from temperate Argentina. Between December 2003 and May 2005, 391 females of Ae. aegypti were captured in two areas of Greater Buenos Aires. Overall prevalence of A. culicis was 21.2% (83/391), and a significant difference was observed between both areas (28.4% vs. 8%). Infected Ae. aegypti were found from November to May, with highest values in March (24-37%). Parasite prevalence and host abundance showed similar seasonal patterns. Our observations suggest a widespread infestation of A. culicis among Ae. aegypti populations from temperate Argentina.     

Role of gregarine parasite Ascogregarina culicis (Apicomplexa: Lecudinidae) in the maintenance of Chikungunya virus in vector mosquito

Ascogregarina culicis and Ascogregarina taiwanensis are common gregarine parasites of Aedes aegypti and Aedes albopictus mosquitoes, respectively. These mosquito species are also known to transmit dengue and Chikungunya viruses. The sporozoites of these parasites invade the midgut epithelial cells and develop intracellularly and extracellularly in the gut to complete their life cycles. The midgut is also the primary site for virus replication in the vector mosquitoes. Therefore, studies were carried out with a view to determine the possible role of these gregarines in the vertical transmission of dengue and Chikungunya viruses from larval to adult stage. Experiments were performed by exposing first instar mosquito larvae to suspensions containing parasite oocysts and viruses. Since Ascogregarina sporozoites invade the midgut of first instar larvae, the vertical transmission was determined by feeding the uninfected first instar larvae on the freshly prepared homogenates from mosquitoes, which were dually infected with viruses and the parasite oocysts. Similarly, the role of protozoan parasites in the vertical transmission of viruses was determined by exposing fresh first instar larvae to the dried pellets of homogenates prepared from the mosquitoes dually infected with viruses and the parasite oocysts. Direct vertical transmission and the vertical transmission of CHIK virus through the oocyst of the parasites were observed in the case of Ae. aegypti mosquitoes. It is suggested that As. culicis may have an important role in the maintenance of CHIK virus during the inter-epidemic period.     

Differential identification of Ascogregarina species (Apicomplexa: Lecudinidae) in Aedes aegypti and Aedes albopictus (Diptera: Culicidae) by polymerase chain reaction

We report 2 polymerase chain reaction (PCR)-based methods for distinguishing morphologically similar gregarine species based on amplification of variable regions of the internal transcribed spacer region of ribosomal DNA. The gregarines we investigated were Ascogregarina barretti (Vavra), A. culicis (Ross), and A. taiwanensis (Lien and Levine), parasites of the mosquitoes Ochlerotatus triseriatus (Say), Aedes aegypti (Linnaeus), and Ae. albopictus (Skuse), respectively. These 3 important vector mosquitoes often utilize the same container habitats, where larval development and infection by the parasite occurs, leaving ample opportunity for cross-species gregarine infection. Because previous studies have shown that the parasites A. culicis and A. taiwanensis variably affect fitness in both normal and abnormal mosquito hosts, distinguishing parasite infection and species is important. The task is complicated by the fact that these 2 parasite species are virtually identical in morphology, whereas A. barretti is morphologically distinct. Of the 2 PCR-based assays reported here, the first provides a rapid, sensitive, and straight-forward means of general ascogregarine detection based on a single PCR amplification. The second method provides a means of differentiation between A. culicis and A. taiwanensis based on a species-specific PCR assay. Together, these assays allow whole mosquitoes to be tested for the presence of Ascogregarina species as well as identification of both A. culicis and A. taiwanensis singly or in dual infections.     

Laboratory susceptibility of Wyeomyia smithii (Diptera: Culicidae) to Ascogregarina taiwanensis (Apicomplexa: Lecudinidae)

Gregarines in the genus Ascogregarina are not known to develop in sabethine mosquitoes, but we successfully infected larvae of Wyeomyia smithii with Ascogregarina taiwanensis in the laboratory. Ascogregarina taiwanensis is a natural parasite of the exotic Asian tiger mosquito, Aedes albopictus. Only 18% to 70% of the W. smithii larvae had visible trophozoites, with a range of 1-92 per larva. Trophozoites persisted in the midgut for more than 37 d, and one adult female W. smithii had gametocysts in its Malphigian tubules, which indicated that A. taiwanensis might fully develop in W. smithii. After 50 d, gregarines were not found in W. smithii larvae.     

Comparison of the morphology of oocysts and the phylogenetic analysis of four Ascogregarina species (Eugregarinidae: Lecudinidae) as inferred from small subunit ribosomal DNA sequences

This study on the ultrastructure of the oocysts of four isolated species of Ascogregarina (A. taiwanensis (Lien and Levine) (Eugregarinidae: Lecudinidae) from Aedes albopictus (Skuse), A. culicis (Ross) (Eugregarinidae: Lecudinidae) from Aedes aegypti (L.), A. armigerei (Eugregarinidae: Lecudinidae) from Armigeres subalbatus (Coquillet), and Ascogregarina sp. (Eugregarinidae: Lecudinidae) from Ochlerotatus japonicus japonicus (Theobald)) using a scanning electron microscope revealed significant differences in size and in surface structure. The average length of the oocyst was greatest in A. armigerei (13.2+/-0.2 microm) (mean+/-SD) and least in A. culicis (8.8+/-0.4 microm). Oocysts were of moderate length in A. taiwanensis (9.9+/-0.6 microm) and in Ascogregarina sp. (10.7+/-1.1 microm) isolated from O. j. japonicus. The ultrastructure of the surface of the A. culicis oocyst was rough in texture with numerous dense spots and was easily distinguishable from the oocysts of the other three Ascogregarina spp. The maximum likelihood tree inferred from small subunit ribosomal DNA (SSU rDNA) sequences indicated that the four Ascogregarina spp. form a monophyletic cluster among other gregarine parasites. Within the Ascogregarina clade, A. culicis, A. taiwanensis, and Ascogregarina sp. from O. j. japonicus showed a close relationship, whereas A. armigerei was a distantly related species.     

Proteome of Aedes aegypti larvae in response to infection by the intracellular parasite Vavraia culicis

We report on the modification of the Aedes aegypti larval proteome following infection by the microsporidian parasite Vavraia culicis. Mosquito larvae were sampled at 5 and 15 days of age to compare the effects of infection when the parasite was in two different developmental stages. Modifications of the host proteome due to the stress of infection were distinguished from those of a more general nature by treatments involving hypoxia. We found that the major reaction to stress was the suppression of particular protein spots. Older (15 days) larvae reacted more strongly to infection by V. culicis (46% of the total number of spots affected; 17% for 5 days larvae), while the strongest reaction of younger (5 days) larvae was to hypoxia for pH range 5-8 and to combined effects of infection and hypoxia for pH range 3-6. MALDI-TOF results indicate that proteins induced or suppressed by infection are involved directly or indirectly in defense against microorganisms. Finally, our MALDI-TOF results suggest that A. aegypti larvae try to control or clear V. culicis infection and also that V. culicis probably impairs the immune defense of this host via arginases-NOS competition.     

Larval competition alters susceptibility of adult Aedes mosquitoes to dengue infection

Dengue, the most important human arboviral disease, is transmitted primarily by Aedes aegypti and, to a lesser extent, by Aedes albopictus. The current distributions of these invasive species overlap and are affected by interspecific larval competition in their container habitats. Here we report that competition also enhances dengue infection and dissemination rates in one of these two vector species. We determined the effects of competition on adult A. aegypti and A. albopictus, comparing their susceptibility to infection with a Southeast Asian strain of dengue-2 virus. High levels of intra- or interspecific competition among larvae enhanced the susceptibility of A. albopictus to dengue virus infection and potential for transmission, as indicated by disseminated infections. Doubling the number of competing larvae (A. albopictus or A. aegypti), led to a significant (more than 60%) increase in the proportion of A. albopictus with disseminated dengue-2 infection. Competition-enhanced vector competence appears to result from a reduction in 'barriers' (morphological or physiological) to virus infection and dissemination and may contribute to the importance of A. albopictus in dengue transmission. Similar results for other unrelated arboviruses suggest that larval competition, common in mosquitoes, should be considered in estimates of vector competence for pathogens that infect humans.     

The first report of Aedes (Stegomyia) albopictus in Haiti

Aedes albopictus was found in six of the 10 departments of Haiti and in 14 of the 35 communes surveyed. The survey found the larvae of Ae. albopictus in 13 different types of containers. Used tires and tins were by far the most common breeding sites used by this mosquito species. At the breeding sites, Ae. albopictus was associated with other mosquito species, such as Aedes aegypti, Culex nigripalpus and Aedes mediovittatus. The highest proportion of association was with Ae. aegypti. This study represents the first report of Ae. albopictus in Haiti.     

Ovitrap surveys of dengue vector mosquitoes in Chiang Mai, northern Thailand: seasonal shifts in relative abundance of Aedes albopictus and Ae. aegypti

Aedes aegypti (L.) and Aedes albopictus (Skuse) were surveyed using ovitraps in residential areas in Chiang Mai, northern Thailand. Egg populations (both species inclusive) remained low in the dry season, but increased/decreased exponentially during the first/latter half of the rainy season, respectively. This seasonal pattern was similar to the seasonal distribution of dengue haemorrhagic fever cases in the area. During the dry season (November-March) Ae.aegypti was dominant in urban and indoor ovitraps. With onset of the rainy season in April, relative abundance of Ae.albopictus increased in rural and outdoor ovitraps. Ae.albopictus displaced Ae.aegypti in the latter half of the rainy season in the rural area. Possible mechanisms to account for this seasonal decline of Ae.aegypti and reciprocal fluctuations in relative abundance of Ae.albopictus are discussed in relation to food availability for larvae in container habitats.     

Distribution of dengue vectors in neighborhoods with different urbanization types of Manaus, state of Amazonas, Brazil

Aedes aegypti and Ae. albopictus are vectors of dengue viruses, which cause endemic disease in the city of Manaus, capital of the state of Amazonas, Brazil. More than 53 thousand cases have been registered in this city since the first epidemic in 1998. We evaluated the hypothesis that different ecological conditions result in different patterns of vector infestation in Manaus, by measuring the infestation level in four neighborhoods with different urbanization patterns, during the rainy (April), dry (August), and transitional (November) seasons. Ae. aegypti predominated throughout the study areas and sampling periods, representing 86% of all specimens collected in oviposition traps. High frequencies of houses positive for both species were observed in all studied sites, with Ae. aegypti present in more than 84% of the houses in all seasons. Ae. albopictus, on the other hand, showed more spatial and temporal variation in abundance. We found no association between infestation level and house traits. This study highlights the homogeneity of dengue vector distribution in Manaus.     

Effects of temperature and diet on development and interspecies competition in Aedes aegypti and Aedes albopictus

We asked whether climate change might affect the geographic distributions of Aedes aegypti (L.) and Aedes albopictus (Skuse) (Diptera: Culicidae). We tested the effects of temperature, diet and the presence of congeneric species on the performance of immature stages of these two aedine species in the laboratory. Mosquitoes in three different species-density combinations were reared at four constant temperatures (20 °C, 25 °C, 30 °C, 35 °C) on low- or high-level diets. Of the four temperatures tested, mortality increased only at 35 °C in both species. Mortality was higher on the high-level diet than on the low-level diet at 35 °C, but not at other temperatures. The presence of congeneric species had a significant positive effect on mortality in Ae. albopictus, but not in Ae. aegypti. Both species developed more quickly at higher temperatures within the range of 20-30 °C; development was not enhanced at 35 °C. Population growth of Ae. albopictus was more stable, regardless of diet and temperature; that of Ae. aegypti varied more according to these two factors. These species-specific attributes may help to explain the latitudinal distribution of the mosquitoes and degree of species dominance where they are sympatric.     

Effects of temperature, pH and salinity on the infection of Leptolegnia chapmanii Seymour (Peronosporomycetes) in mosquito larvae

The effects of temperature, pH, and NaCl concentrations on the infectivity of zoospores of Leptolegnia chapmanii (Argentine isolate) were determined for Aedes aegypti and Culex pipiens under laboratory conditions. Zoospores of L. chapmanii were infectious at temperatures between 10 and 35 degrees C but not at 5 or 40 degrees C. At the permissive temperatures, mortality rates in young instars were much higher than in older instars and larvae of Ae. aegypti were more susceptible to L. chapmanii than larvae of Cx. pipiens. At 25 degrees C, Ae. aegypti larvae challenged with L. chapmanii zoospores resulted in 100% infection at pH levels ranging from 4 to 10. Larvae of Cx. pipiens exposed to similar pH and zoospore concentrations resulted in increasing mortality rates from 62% to 99% at pH 4 to 7, respectively, and then decreased to 71% at pH 10. Aedes aegypti larvae exposed to L. chapmanii zoospores in NaCl concentrations ranging from 0 to 7 parts per thousand (ppt) at 25 degrees C resulted in 100% mortality while mortality rates for Cx. pipiens decreases from 96% in distilled water to 31.5% in water with 6 ppt NaCl. Control Cx. pipiens larvae died when exposed at a NaCl concentration of 7 ppt. Vegetative growth of L. chapmanii was negatively affected by NaCl concentrations. These results have demonstrated that the Argentinean isolate of L. chapmanii tolerated a wide range of temperatures, pH, and salinity, suggesting that it has the potential to adapt to a wide variety of mosquito habitats.     

Parity and ovarian development of Aedes aegypti and Ae. albopictus (Diptera: Culicidae) in metropolitan Rio de Janeiro.

Vector blood-feeding frequency, parity, and ovarian development are important factors that can influence pathogen transmission. Parity rates of the dengue vectors Aedes aegypti and Ae. albopictus were determined from females collected from August 2002 to July 2004 in metropolitan Rio de Janeiro. A high frequency of parous Ae. aegypti (92.9%, n = 550) and Ae. albopictus (99.1%, n = 320) females suggested high survivorship of both species. A total of 69% of wild-caught Ae. aegypti females had blood in the midgut compared to 19% of Ae. albopictus. For Ae. aegypti, red-colored midgut contents were associated with ovaries in early stages of development, and brown-colored midguts were associated with ovaries in late stages of maturation. Ovaries of Ae. aegypti females without blood in the midgut were most frequently in stages I and V of Christophers.     

Comparative efficacy of existing surveillance tools for Aedes aegypti in Western Kenya

All traditional surveillance techniques for Aedes aegypti have been developed for the cosmopolitan domestic subspecies Ae. aegypti aegypti, and not the sylvatic subspecies, Ae. aegypti formosus. The predominant form in Western Kenya is Ae. aegypti formosus that is rarely associated with human habitations but is linked to transmission of sylvatic dengue virus strains. We compared five surveillance methods for their effectiveness in sampling Ae. aegypti formosus with the goal of determining a sustainable surveillance strategy in Kenya. The methods included larval and pupal surveys, oviposition trapping, BG‐Sentinel trapping, resting boxes, and backpack aspirations. Larval and pupal surveys collected the highest number of Ae. aegypti formosus (51.3%), followed by oviposition traps (45.7%), BG‐Sentinel traps (3.0%), and zero collected with either backpack aspiration or resting box collections. No Ae. aegypti formosus larvae or pupae were found indoors. The results indicate that oviposition traps and outdoor larval and pupal surveys were better surveillance methods for Ae. aegypti formosus in Western Kenya.     

白纹伊蚊和埃及伊蚊对基孔肯雅病毒的易感性和传播性的研究

用４株基孔肯雅病毒经口感染白纹伊蚊和埃及伊蚊,进行了易感性和传播性的研究。结果表明,这两种蚊虫对基孔肯雅病毒易感。无论白纹伊蚊或埃及伊蚊,感染后第５－６天即可通过吸血将病毒传播给乳鼠,至第８－１３天,传播率可高达５５．５５％－１００％。感染蚊亦可经叮咬将病毒传播给小鸡。埃及伊蚊的易感性和传播率高于白纹伊蚊。实验还发现,不同来源毒株之间存在一定差异,如分离自云南白纹伊蚊的Ｍ８１株的感染率和传播率均高于其它毒株。这些结果表明,白纹伊蚊和埃及伊蚊在基孔肯雅病毒的保存和传播中起重要作用。     

State‐wide survey of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Florida

Aedes aegypti and Aedes albopictus are invasive mosquito species with geographic ranges that have oscillated within Florida since their presence was first documented. Local transmission of dengue, chikungunya, and Zika viruses serves as evidence of the public health importance of these two species. It is important to have detailed knowledge of their distribution to aid in mosquito control efforts and understand the risk of arbovirus transmission to humans. Through a partnership involving the University of Florida Institute of Food and Agricultural Sciences Cooperative Extension Service and the Florida Medical Entomology Laboratory; the Florida Department of Health; and mosquito control agencies throughout Florida, a container mosquito surveillance program involving all life stages was launched in the summer of 2016 to detect the presence of Ae. aegypti and Ae. albopictus. Results from this survey were mapped to provide a picture of the current known distribution of Ae. aegypti and Ae. albopictus in Florida. Aedes aegypti and/or Ae. albopictus were detected in the 56 counties that were part of the survey. Only Aedes albopictus was detected in 26 counties, primarily in the panhandle region of Florida. The results of this work underscore the importance of maintaining container mosquito surveillance in a state where chikungunya, dengue, and Zika viruses are present and where there is continued risk for exotic arbovirus introductions.     

Productivity of natural and artificial containers for Aedes polynesiensis and Aedes aegypti in four American Samoan villages

Six mosquito species were identified in a survey of containers associated with 347 households in four villages in American Samoa. Aedes polynesiensis Marks (Diptera: Culicidae) and Aedes aegypti (L) were the most abundant species, representing 57% and 29% of the mosquitoes identified. Culex quinquefasciatus (Say), Culex annulirostris (Skuse), Aedes oceanicus (Belkin) and Toxorhynchites amboinensis (Doleschall) were also found. Aedes aegypti and Ae. polynesiensis showed distinct differences in their use of containers, preferring large and small containers, respectively. By contrast with previous studies, Ae. polynesiensis utilized domestic and natural containers with equal frequency, whereas Ae. aegypti continued to be found predominantly in domestic containers. Only 15% of containers holding immature mosquitoes included pupae and fewer than 10 Aedes spp. pupae were found in most containers with pupae. An estimated 2289 Ae. polynesiensis and 1640 Ae. aegypti pupae were found in 2258 containers. The presence of both species in the same container did not affect the mean density of either species for larvae or pupae. Glass jars, leaf axils, tree holes and seashells produced few Aedes spp. pupae in any of the study villages. Overall, 75% of Ae. polynesiensis pupae were found in buckets, ice-cream containers and tyres, with <7% being produced in natural containers, whereas 82% of Ae. aegypti pupae were found in 44-gallon (US) drums ( approximately 166L), buckets and tyres. Source reduction efforts targeting these container types may yield significant reductions in both Ae. polynesiensis and Ae. aegypti populations in American Samoa.     

Ultrastructure of Infection, Development and Gametocyst Formation of Ascogregarina taiwanensis (Apicomplexa: Lecudinidae) in Its Mosquito Host, Aedes albopictus (Diptera: Culicidae)

ABSTRACT. The life history of the protozoan parasite Ascogregarina taiwanensis in mosquito larvae ( Aedes albopictus , collected in southern Taiwan) was shown to consist of two consecutive stages—intracellular and extracellular. Light microscopy showed that most trophozoites moved into the Malpighian tubules and developed into giant trophozoites during the first day pupa. The locomotion may be associated with bristle-like ridges of the trophozoite. The stage for sexual reproduction, i.e. the gamete, was then formed by segmentation of the giant trophozoite and twisting off the anucleate extremities of the body. Sexual reproduction occurred via fertilization by fusion of two resulting gametes, presumably two opposed sexes. The fused gametes finally generate the formation of the gametocyst, within which oocysts develop by budding from the cytoplasmic mass. This type of sexual reproduction has not been reported previously in any gregarine protozoa. We here proposed it as a new hypothesis for further elucidation of the protozoan reproduction.