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PubMed2002

Hazard assessment of resmethrin: I. Effects and fate in aquatic systems.

A comparative aquatic hazard assessment of resmethrin was conducted to investigate the need for its restricted use classification by the US. EPA as an adult mosquito control agent. This paper describes the environmental fate and aquatic toxicity of resmethrin. The following paper compares resmethrin to the alternative insecticides. Environmental fate studies indicate that resmethrin has a short photolytic half-life in water (<1 h). Furthermore, it is immobile in soil and biodegradable (half-life = 36.5 d) under aerobic conditions. Laboratory studies with constant 48- to 96-h exposures show it is acutely toxic to fish and invertebrates in the 0.22-15.0 microg/L range. Daphnia magna, pink shrimp (Penaeus duorarum) and rainbow trout (Oncorhynchus mykiss) are the most sensitive and mollusks are the least sensitive species. Chronic laboratory studies indicate that the maximum acceptable toxicant concentrations (MATCs) for resmethrin and D. magna, Pimephales promelas, O. mykiss, and Cyprinodon variegatus are 0.58, 0.52, 0.43, and 10.3 microg/L, respectively. The acute-to-chronic ratios (1.1-7.3) for all species studied indicate that chronic toxicity will not be an issue for resmethrin. Furthermore, the characteristics of acute exposures (48- to 96-h) used in the laboratory will not occur under field conditions because of the short half-life of resmethrin in fresh- and salt-water.

Animals↗
PubMed2006

Two chemosensory receptors together mediate carbon dioxide detection in Drosophila.

Blood-feeding insects, including the malaria mosquito Anopheles gambiae, use highly specialized and sensitive olfactory systems to locate their hosts. This is accomplished by detecting and following plumes of volatile host emissions, which include carbon dioxide (CO2). CO2 is sensed by a population of olfactory sensory neurons in the maxillary palps of mosquitoes and in the antennae of the more genetically tractable fruitfly, Drosophila melanogaster. The molecular identity of the chemosensory CO2 receptor, however, remains unknown. Here we report that CO2-responsive neurons in Drosophila co-express a pair of chemosensory receptors, Gr21a and Gr63a, at both larval and adult life stages. We identify mosquito homologues of Gr21a and Gr63a, GPRGR22 and GPRGR24, and show that these are co-expressed in A. gambiae maxillary palps. We show that Gr21a and Gr63a together are sufficient for olfactory CO2-chemosensation in Drosophila. Ectopic expression of Gr21a and Gr63a together confers CO2 sensitivity on CO2-insensitive olfactory neurons, but neither gustatory receptor alone has this function. Mutant flies lacking Gr63a lose both electrophysiological and behavioural responses to CO2. Knowledge of the molecular identity of the insect olfactory CO2 receptors may spur the development of novel mosquito control strategies designed to take advantage of this unique and critical olfactory pathway. This in turn could bolster the worldwide fight against malaria and other insect-borne diseases.

Animals↗
PubMed2024

Mosquitoes provide a transmission route between possums and humans for Buruli ulcer in southeastern Australia.

Buruli ulcer, a chronic subcutaneous infection caused by Mycobacterium ulcerans, is increasing in prevalence in southeastern Australia. Possums are a local wildlife reservoir for M. ulcerans and, although mosquitoes have been implicated in transmission, it remains unclear how humans acquire infection. We conducted extensive field survey analyses of M. ulcerans prevalence among mosquitoes in the Mornington Peninsula region of southeastern Australia. PCR screening of trapped mosquitoes revealed a significant association between M. ulcerans and Aedes notoscriptus. Spatial scanning statistics revealed overlap between clusters of M. ulcerans-positive Ae. notoscriptus, M. ulcerans-positive possum excreta and Buruli ulcer cases, and metabarcoding analyses showed individual mosquitoes had fed on humans and possums. Bacterial genomic analysis confirmed shared single-nucleotide-polymorphism profiles for M. ulcerans detected in mosquitoes, possum excreta and humans. These findings indicate Ae. notoscriptus probably transmit M. ulcerans in southeastern Australia and highlight mosquito control as a Buruli ulcer prevention measure.

Animals↗
PubMed1984

Bancroftian filariasis in Kenya. V. Mass treatment given by members of the local community.

Diethylcarbamazine citrate was given for a total of 13 days to all people above one year of age in the following areas: (1) Mambrui, a town with a population of about 1300; (2) Jaribuni, a rural area with a population of about 1500; (3) The towns and villages on the islands off the north coast of Kenya with a population of over 20 000. The people were not weighed, but the daily dose was calculated according to age, being approximately 6 mg kg-1; drug taking was not supervised. The drug was mainly distributed by local people who also treated the side-effects; a doctor remained available in the background for consultation and advice. In Mambrui and Jaribuni, where baseline data had been collected, the number of infective larvae per 1000 vector-mosquitoes had decreased by more than 90% in the six to 12 months period after the campaign. Two years after the campaign, the microfilaria rate in Mambrui had dropped by 75%; in Jaribuni, a reduction of 75% was recorded in men, but in women it was only 48%. The overall rates after the mass treatment were 5.3 and 9.3% in Mambrui and Jaribuni, respectively. On the islands to the north, particularly good results were obtained in the village of Siyu, where the highest elephantiasis rate had been recorded; three years after the campaign, the microfilaria rate there had fallen to 3.6%, while none of 48 children under ten were found infected. The spectacular results in Lamu town may have been partly due to excellent mosquito control in preceding years. However, no control was achieved on the remote island of Ndau, probably because the treatment team left before the side-effects had disappeared, causing many people to stop the course of tablets. Thus, on the East African coast it is possible and cheap to control Bancroftian filariasis by mass treatment campaigns carried out by local, non-medical personnel.

Adolescent↗
PubMed2006

Factors affecting the geographic distribution of West Nile virus in Georgia, USA: 2002-2004.

The distribution of West Nile virus (WNV) is dependent on the occurrence of both susceptible avian reservoir hosts and competent mosquito vectors. Both factors can be influenced by geographic variables such as land use/landcover, elevation, human population density, physiographic region, and temperature. The current study uses geographic information systems (GIS) and logistic regression analyses to model the distribution of WNV in the state of Georgia based on a wild bird indicator system, and to identify human and environmental predictor variables that are important in the determination of WNV distribution. A database for Georgia was constructed that included (1) location points of all the avian samples tested for WNV, (2) local land use classifications, including temperature, physiographic divisions, land use/landcover, and elevation, (3) human demographic data from the U.S. Census, and (4) statistics summarizing land cover, elevation, and climate within a 1-km-radius landscape around each sample point. Logistic regression analysis was carried out using the serostatus of avian collection sites as the dependent variable. Temperature, housing density, urban/suburban land use, and mountain physiographic region were important variables in predicting the distribution of WNV in the state of Georgia. While weak, the positive correlation between WNV-antibody positive sites and the urban/suburban environment was consistent throughout the study period. The risks associated with WNV endemicity appear to be increased in urban/ suburban areas and decreased in the mountainous region of the state. This information may be used in addressing regional public health needs and mosquito control programs.

Animals↗
PubMed1992

Ecology of mosquitoes and St. Louis encephalitis virus in the Los Angeles Basin of California, 1987-1990.

St. Louis encephalitis (SLE) virus has become established in the Los Angeles Basin of California, where it most likely is maintained by horizontal transmission among Culex tarsalis Coquillet and passerine birds in park-riparian habitat. Viral transmission also was detected at low levels in residential habitat by the infrequent seroconversion of sentinel chickens. SLE virus activity was documented in all months except March and April. Cx. tarsalis was incriminated as the primary vector, based on elevated field infection rates (0.17 infected females per 1,000 tested), population abundance concomitant in time and space with increased SLE virus activity, vector competence, and vectorial capacity. Culex stigmatosoma Dyar also may be important in the horizontal maintenance of SLE virus because this species was an efficient laboratory vector, fed frequently on passeriform birds, and had field infection rates (0.15 females per 1,000) comparable with Cx. tarsalis. However, difficulty in trapping adult females precluded the assessment of Cx. stigmatosoma because abundance may have been underestimated and comparatively few females were tested for virus. Although Cx. quinquefasciatus Say was the most abundant species in residential habitats (greater than 85% of total catch at CO2 traps) where it occasionally fed on humans (0.6% of total tested), this species was considered to be of secondary importance because field infection rates were low (0.03 females per 1,000) and few females became infected and transmitted SLE virus in laboratory vector competence experiments. Although Culex erythrothorax Dyar fed on humans in marsh habitat (5% of total tested), this species infrequently fed on birds (12%) and was refractory to SLE virus infection in vector competence experiments; therefore, it was not considered a vector of SLE virus. Future SLE virus surveillance and mosquito control programs should be directed toward Cx. tarsalis populations.

Animals↗
PubMed1993

Effect of salt marsh drainage on the distribution of Tabanus nigrovittatus (Diptera: Tabanidae).

Immature stages of Tabanus nigrovittatus Macquart inhabit salt marsh sod. A study of the distribution of larvae in relation to the presence or absence of surface water showed that larval densities were higher in salt marsh areas that appeared well drained. Late instars remained above the sod surface more frequently in laboratory conditions mimicking high water-table levels. The development of anaerobic conditions in sod at high water levels probably deterred larvae from burrowing into the sod. Therefore, mosquito control ditches, constructed to augment interstitial drainage inadvertently may have created optimal tabanid larval habitat.

Animals↗
PubMed1997

Ross River virus in mosquitoes (Diptera:Culicidae) during the 1994 epidemic around Brisbane, Australia.

During the summer 1994 outbreak of epidemic polyarthritis in suburban Brisbane, 29,931 adult female mosquitoes were collected by octenol-CO2 light traps and tested for virus by species in pools of approximately 20 using an in situ enzyme-linked immunoassay. Overall, 63 isolations of Ross River (RR) virus were made from 7 different mosquito species, including 23 from freshwater-breeding Culex annulirostris Skuse, 13 from peridomestic Aedes notoscriptus (Skuse), 4 from Aedes procax (Skuse), 12 from the brackish water-breeding Aedes funereus (Theobald), 9 from saltmarsh Aedes vigilax (Skuse), and 1 each from Culex sitiens Wiedemann and Aedes alternans (Westwood). The RR virus minimum infection rate in mosquitoes ranged from 1.6 to 2.5/1,000 from March to June 1994. This study implicates freshwater and brackish water mosquitoes as important suburban vectors of RR virus and indicates the need for refocusing mosquito control priorities.

Aedes↗
PubMed1997

Distribution of organophosphate and carbamate resistance in Culex pipiens quinquefasciatus (Diptera: Culicidae) in West Africa.

The distribution of organophosphate and carbamate resistance was investigated in 33 samples of Culex pipiens quinquefasciatus Say from 25 cities in Côte d'Ivoire and Burkina Faso. Organophosphate resistance levels were higher in Côte d'Ivoire than in Burkina Faso. Chlorpyrifos resistance ratios at LC95 ranged from 4 to 30 times in Côte d'Ivoire and from 3 to 6 times in Burkina Faso. For temephos, ratios ranged from 3 to 18 and from 1 to 2, respectively. Of 27 samples from Côte d'Ivoire, 25 also displayed cross resistance to carbamates as shown by a mortality plateau in bioassays with propoxur and carbosulfan (similar to chlorpyrifos). Cross resistance to organophosphates and carbamates was caused by an insensitive acetylcholinesterase allele (AceR). This gene was absent from Burkina Faso, except in Niangoloko near the Côte d'Ivoire border. Organophosphate resistance also was associated with the presence of A2-B2 overproduced esterases which had higher frequencies in Côte d'Ivoire (75-100%) than in Burkina Faso (40-50%). Two other esterases with the same electrophoretic mobility as C2 from Puerto Rico and B1 from California were identified for the 1st time in West Africa. "C2" was widespread, whereas "B1" was present in only a few mosquitoes from Côte d'Ivoire. These differences in resistance patterns should be taken into consideration in planning urban mosquito control strategies within 2 countries.

Africa, Western↗
PubMed1975

Epidemic Venezuelan equine encephalitis in North America in 1971: vertebrate field studies.

Epidemic Venezuelan equine encephalitis in North America in 1971: vertebrate field studies. Am J Epidemiol 101:36-50, 1975.-In June 1971, epidemic Venezuelan equine encephalitis (VEE) invaded the lower Rio Grande Valley in south Texas. The Boca Chica area of Cameron County was selected as a study site to investigate vertebrate involvement in the natural cycle of epidemic VEE on the basis of considerable evidence of VEE virus activity there in equines, humans, and mosquito vectors. Only one VEE virus isolation was made from 4739 wild and domestic non-equine vertebrates, although numerous equine and human VEE virus isolations were made in concurrent studies. Serologic studies indicated that VEE virus activity was far greater in large domestic animals than in wild birds, wild mammals, or reptiles. Apparently epidemic VEE virus failed to establish itself in a wild vertebrate cycle in south Texas, since VEE antibody was found only in rabbits in 1972. Eventual cessation of VEE transmission in south Texas has been attributed 1) to the elimination of equines as a source of VEE virus by death, naturally acquired antibodies, or vaccination, 2) to quarantines, 3) to mosquito control, and 4) to the failure of epidemic VEE virus to become established in the wild vertebrate population. Equines emerge as the most important vertebrate host in the amplification and spread of virus during an epidemic of VEE.

Animals↗
PubMed2004

Outbreak of dengue in Mumbai and predictive markers for dengue shock syndrome.

An alarming rise of dengue has been seen in Mumbai during the post-monsoon season. We undertook this prospective study in the pediatric wards and pediatric intensive care unit of B. J. Wadia Hospital for Children between 27 August 2003 and 10 October 2003 to determine the clinical features, laboratory abnormalities, and outcome of children affected with dengue and to determine the predictive markers for dengue shock syndrome. Fifty-one suspected dengue cases were tested for positivity of dengue by determination of dengue IgM antibodies by ELISA test. These positive cases were analysed for common clinical features, laboratory derangements, and outcome. Patients were subdivided into three subgroups: dengue fever (DF), dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS) as per WHO classification. Predictive markers for DSS were also determined. Thirty-nine patients had a positive dengue IgM titre, 20 patients had DHF, 18 patients had DSS, and one patient had DF The mean age of presentation was 4.9 years. Fever, hepatomegaly, vomiting, bleeding tendencies, erythematous rash, thrombocytopenia, elevated liver enzymes, and deranged PT and PTT were the predominant clinical and laboratory features. Predictive markers for DSS were younger age at onset, altered sensorium, paralytic ileus, and significantly deranged PT. Patients with DSS also had a longer recovery period and required more supportive management in the form of component therapy and ionotropic support. All three patients who died belonged to the DSS subgroup with case fatality rate for DSS being 16.6 per cent. None of the patients in the DHF or DF subgroup died. Endemicity of dengue fever is on the rise in Mumbai with increased incidence among children. Appropriate investigations, strict monitoring and prompt supportive management can reduce mortality in dengue. Predictive markers of DSS can reduce the mortality if promptly treated. Also prevention of transmission by mosquito control and maintaining water sanitation is required to effectively control this epidemic.

Analysis of Variance↗
PubMed1990

Application of polar-orbiting, meteorological satellite data to detect flooding of Rift Valley Fever virus vector mosquito habitats in Kenya.

Measurements of green-leaf vegetation dynamics recorded by the advanced very high resolution radiometer instruments onboard National Oceanic and Atmospheric Administration satellites 7 and 9 were used to derive ground moisture and rainfall patterns in Kenya and monitor resultant flooding of mosquito larval habitats (dambos) likely to support Rift Valley Fever virus vector mosquitoes (Aedes and Culex spp.). Satellite-derived data from mid-1981 to December 1988 have been analysed with corresponding rainfall, flooding and vector population data as they relate to Rift Valley Fever virus ecology. Single (7 x 7 km) and multiple grid-cell image analysis (200 x 300 km) in small localized areas and large geographical regions, respectively, of vegetation data were used to quantify the potential for flooding of mosquito breeding habitats. The ability to detect accurately parameters, such as ground moisture, that determine flooding could provide local officials with sufficient warning to allow for implementation of specific mosquito control measures before a disease outbreak.

Animals↗
PubMed1991

Pathogenicity of Spiroplasma taiwanense for larval Aedes aegypti mosquitoes.

Helical replicative forms, but not the persistent non-replicative forms, of Spiroplasma taiwanense Abalain-Colloc et al. (isolated from the mosquito Anopheles sinensis Wiedemann in Taiwan) were shown to reduce significantly the survival of Aedes aegypti (L.) mosquito larvae reared in 10 ml of water with 0.3 ml of S.taiwanense suspensions added on days 0 and 3. The suspensions contained, respectively, helical forms at a concentration of 10(9) Colour Change Units (CCU)/ml and persistent forms at 10(6) CCU/ml. It is suggested that S.taiwanense, or toxins produced from it, are potentially useful for use in integrated mosquito control programmes.

Aedes↗
PubMed1991

Evaluation of the water fern Azolla microphylla for mosquito population management in the rice-land agro-ecosystem of south India.

The floating water fern Azolla microphylla Kaulfess was evaluated as a biocontrol agent against mosquitoes breeding in rice fields in Tamil Nadu, South India. Anopheles subpictus Grassi, Culex pseudovishnui Colless and Culex tritaeniorhynchus Giles were the predominant species of mosquitoes, with peak densities of late instar larvae and pupae occurring during the second week after transplantation of rice seedlings of short-term (c. 80 days from transplantation to harvest) or medium-term (c. 95 days) varieties. Immature mosquito populations were reduced by mats of Azolla microphylla covering more than 80% of the water surface. However, since 80% coverage by Azolla was achieved only 13-14 days after rice transplantation, its usefulness for mosquito control was limited. Azolla may have a greater potential in an integrated control programme, or in areas where long-term varieties of rice are predominantly grown.

Agriculture↗
PubMed1992

Saliva activated transmission (SAT) of Thogoto virus: relationship with vector potential of different haematophagous arthropods.

Tick saliva (or salivary gland extract) potentiates the transmission of Thogoto (THO) virus to uninfected ticks feeding on a non-viraemic guinea-pig. This phenomenon has been named saliva activated transmission (SAT). To investigate the potential of different haematophagous arthropods to mediate SAT, guinea-pigs were infested with uninfected R.appendiculatus Neumann nymphs and inoculated with THO virus and salivary gland extract (SGE) derived from a range of ixodid (metastriate and prostriate) or argasid ticks, or mosquitoes; control guinea-pigs were inoculated with virus alone. Enhancement of THO virus transmission was observed only when SGE was derived from metastriate ticks. Comparison with the vector potential of these various arthropod species revealed that enhancement of THO virus transmission was specific for ticks which were competent vectors of the virus. The data indicate a correlation between vector competence and the ability of haematophagous arthropods to mediate SAT of THO virus.

Aedes↗
PubMed1993

Changes in malathion and pyrethroid resistance after cypermethrin selection of Culex quinquefasciatus field populations of Cuba.

Use of the organophosphorus insecticide malathion for mosquito control in Cuba, for 7 years up to 1986, selected elevated non-specific esterase and altered acetylcholinesterase (AChE) resistance mechanisms in Culex quinquefasciatus. In central Havana space-spraying of malathion was replaced by the pyrethroid cypermethrin in 1987: alternate cycles of malathion and cypermethrin were applied in some of the more rural areas of Havana district during 1987-91. Consequently, populations of Cx quinquefasciatus in the central area of Havana developed resistance to cypermethrin, but there is no evidence of pyrethroid resistance in the outlying areas. Malathion resistance levels declined significantly after 1986, measured both by bioassay and the frequency of the elevated esterase resistance mechanism, and then stabilized with no measurable decline during 1990 in any of the populations tested. These populations had less than 10% frequency of susceptible homozygotes for both the esterase and AChE resistance mechanisms, indicating that organophosphate resistance is still prevalent in Cuban Cx quinquefasciatus. These two mechanisms appear to be in linkage equilibrium, suggesting that current selection for double resistance is not strong. In the central Havana region, pirimiphos-methyl, an organophosphorus insecticide unaffected by the two common malathion resistance mechanisms, is now being used in a resistance management strategy designed to avoid pyrethroid resistance spreading.

Animals↗