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      Gonotrophic discordance in Culex quinquefasciatus (Diptera: Culicidae) in the city of São Paulo, Brazil

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          Abstract

          INTRODUCTION:

          This study aimed to assess the occurrence of gonotrophic discordance in females of Culex quinquefasciatus in São Paulo, Brazil.

          METHODS:

          Resting females were collected monthly for 8 months. Females of Cx. quinquefasciatus were identified, and their midgut and ovaries were dissected.

          RESULTS:

          Two hundred females were dissected, out of which, 27.5% were nulliparous and 57% were parous. Most females had no blood in the midgut, but gonotrophic discordance was found in 21% females.

          CONCLUSIONS:

          Females of Cx. quinquefasciatus showed a high parity rate and gonotrophic discordance, which could favor the vector capacity of this species.

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          Most cited references 10

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          Dirofilariosis in the Americas: a more virulent Dirofilaria immitis?

          Dirofilarioses are widespread diseases caused by filarioid nematodes (superfamily Filarioidea) of the genus Dirofilaria, which are transmitted by a plethora of mosquito species. The principal agent of canine dirofilariosis in the Americas is Dirofilaria immitis, which may also occasionally infest humans, resulting in pulmonary nodules that may be confounded with malignant lung tumours. Because human cases of dirofilariosis by D. immitis are relatively frequent in the Americas and rare in Europe and other eastern countries, where Dirofilaria repens is the main causative agent, the existence of a more virulent strain of D. immitis in the Americas has been speculated. Recently, a case of human ocular infestation by Dirofilaria sp. was diagnosed in Pará State, northern Brazil, where canine heartworm dirofilariosis is endemic. The nematode was shown to be morphologically and phylogenetically related to D. immitis but it was genetically distinct from reference sequences, including those of D. immitis infesting dogs in the same geographical area. This finding raised questions regarding the aetiology of human dirofilariosis in the Americas, since information on the genetic makeup of filarioids infesting dogs and humans is meagre. Further studies would be needed to better characterize filarioids infesting dogs, wild animals, and humans in the Americas and to assess the existence of a more virulent D. immitis strain in this continent. Finally, the competence of different culicid species/strains from Europe and the Americas as vectors of Dirofilaria species should be investigated. Such studies would help us to understand possible variations in transmission patterns and even to predict possible scenarios that may emerge in the future, with the introduction of non-endemic Dirofilaria species/strains in free areas through importation of infested animals, vectors, or both.
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            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.
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              Mosquito abundance and bionomics in residential communities in Orange and Los Angeles Counties, California.

              Mosquito abundance and bionomics were studied intensively during summer and spring at two residential communities of contrasting economic status. Culex quinquefasciatus was the most abundant adult and immature mosquito collected in both communities, followed by Culiseta incidens, Culex stigmatosoma, and Culex tarsalis. Cx. stigmatosoma and Cx. tarsalis were more abundant in CO2 traps hung in tree canopy than at ground level and fed most frequently on birds. Cx. quinquefasciatus was abundant in both ground level and tree canopy CO2 traps and fed on both mammals and birds. Cs. incidens was collected most frequently by ground level CO2 traps and fed primarily on dogs. Cx. quinquefasciatus and Cs. incidens readily exploited peridomestic breeding sources, and resting adults were aggregated at houses with positive breeding sources. Although Cx. stigmatosoma and Cx. tarsalis larvae were collected primarily at peripheral breeding sources, the dispersion of resting adults was still clumped at houses within both communities. Mosquitoes were most abundant in the more affluent community due to an increased number of breeding sites created by automatic watering devices and poorly managed peripheral drainage channels. Resident opinion of recent mosquito annoyance was not related to the presence of mosquito breeding sources or the abundance of either resting or host-seeking mosquitoes.
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                Author and article information

                Journal
                Rev Soc Bras Med Trop
                Rev. Soc. Bras. Med. Trop
                rsbmt
                Revista da Sociedade Brasileira de Medicina Tropical
                Sociedade Brasileira de Medicina Tropical - SBMT
                0037-8682
                1678-9849
                20 December 2019
                2020
                : 53
                Affiliations
                [1 ]Universidade de São Paulo, Faculdade de Saúde Pública, Laboratório de Entomologia em Saúde Pública, São Paulo, SP, Brasil.
                [2 ]Universidade de São Paulo, Faculdade de Saúde Pública, Departamento de Epidemiologia, São Paulo, SP, Brasil.
                Author notes
                Corresponding author: Dra. Tamara Nunes Lima-Camara e-mail: limacamara@ 123456usp.br

                Conflict of interest: The authors declare that there is no conflict of interest.

                Article
                00614
                10.1590/0037-8682-0277-2019
                7083354
                31859951
                4104c36d-a676-4103-b3a0-db9114ed1b6e

                This is an open-access article distributed under the terms of the Creative Commons Attribution License

                Page count
                Figures: 1, Tables: 1, Equations: 0, References: 15
                Categories
                Short Communication

                vector, culex, parity, ovaries

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