Polymerase Chain Reaction Used To Describe Larval Habitat Use by Anopheles gambiae Complex (Diptera: Culicidae) in the Environs of Ifakara, Tanzania

Larvae of the Anopheles gambiae complex were collected in and around the town of Ifakara, southern Tanzania during the wet season of 1994 and identified to species by polymerase chain reaction. All but 1 surface pool contained mixed populations of An. gambiae and An. arabiensis larvae. The 2 species varied among locations rather than types of water. An. arabiensis predominated in pools close to cattle. The numbers of identified early instars of both species were similar, but more An. gambiae 4th instars were identified, perhaps indicating that An. gambiae were able to survive heavy rainfall better than A. arabiensi

Gene flow and cross-mating in Plasmodium falciparum in households in a Tanzanian village

The diversity of the genes encoding 2 merozoite surface proteins (MSP-1 and MSP-2) of Plasmodium falciparum has been examined in parasites infecting members of 4 households in a village in Tanzania. The polymerase chain reaction (PCR) was used to characterize allelic variants of these genes by the sizes and sequences of regions of tandemly repeated bases in each gene. In each household extensive polymorphism was detected among parasites in the inhabitants and in infected mosquitoes caught in their houses. Similar frequencies of the alleles of these genes were observed in all households. Capture-recapture data indicated that both Anopheles gambiae and A.funestus freely dispersed among households in the hamlet. The results confirm that cross-mating and gene flow occur extensively among the parasites, and are discussed within the context of spatial clustering of natural populations of P. falciparu

Absence of relationships between selected human factors and natural infectivity of Plasmodium falciparum to mosquitoes in an area of high transmission

The effects of sex, age of the human host, patency of asexual and sexual stages and seasonality on infectiousness of Plasmodium falciparum to mosquitoes were investigated in a rural village in southern Tanzania between 1992 and 1994. Villagers from randomized subgroups of households were surveyed for malaria parasites. Gametocyte and trophozoite prevalences were age dependent and fluctuated without any clear pattern of seasonality. A sample of 107 participants, selected to include an excess of gametocyte carriers, slept under bednets with holes cut into the sides for 3 weeks. A total of 3837 Anopheles gambiae s.l. and 5403 A. funestus recovered from these bednets, was examined for all oocysts 5-7 days after feeding or for oocysts less than 17·5 µn in diameter 2-3 days after feeding. Additional blood slides from participants were taken twice weekly. The 5-7 day oocyst rates were 12·1% in A. gambiae s.l. and 10·9% in A. funestus and 2-3 day rates were 3·6 and 4·9%, respectively. The higher rates using the former method were attributed to previous infection. There were strong correlations in the levels of infection in both vectors when they fed on the same hosts. However, patent gametocytaemia was only weakly associated with the development of oocysts in the mosquito. Infectiousness was not related to host age, sex, or the seaso

An Estimation of the Entomological Inoculation Rate for Ifakara: A Semi-Urban Area in a Region of Intense Malaria Transmission in Tanzania.

An entomological study on vectors of malaria and their relative contribution to Plasmodium falciparum transmission in the semi-urban area of Ifakara, south-eastern Tanzania, was conducted. A total of 32 houses were randomly sampled from the area and light trap catches (LTC) performed in one room in each house every 2 weeks for 1 year. A total of 147 448 mosquitoes were caught from 789 LTC; 26 134 Anopheles gambiae s.l., 615 A. funestus, 718 other anophelines and 119 981 culicines. More than 60% of the total A. gambiae s.l. were found in five (0.6%) LTCs, with a maximum of 5889 caught in a single trap. Of 505 A. gambiae s.l. speciated by polymerase chain reaction, 91.5% were found to be A. arabiensis. Plasmodium falciparum sporozoite enzyme-linked immunosorbent assay tests were performed on 10 108 anopheles mosquitoes and 39 (0.38%) were positive. Entomological inoculation rate (EIR) estimates were generated using a standard method and an alternative method that allows the calculation of confidence intervals based on a negative binomial distribution of sporozoite positive mosquitoes. Overall EIR estimates were similar; 31 vs. 29 [95% confidence interval (CI): 19, 44] infectious bites per annum, respectively. The EIR ranged from 4 (95% CI: 1, 17) in the cool season to 108 (95% CI: 69, 170) in the wet season and from 54 (95% CI: 30, 97) in the east of the town to 15 (95% CI: 8, 30) in the town centre. These estimates show large variations over short distances in time and space. They are all markedly lower than those reported from nearby rural areas and for other parts of Tanzania

Atividade crepuscular de Chlorotabanus inanis (Fab.) e Cryptotylus unicolor (Wied.) (Diptera : Tabanidae)

Utilizing an adult horse for attraction of horse flies. Chlorotabanus inanis (Fab.) and Cryptotylus unicolor (Wied.) demonstrate flight activity for feeding only below 1,500 lux. During the day they present biphasic activityone in the morning between 5:20 and 5:50 a.m. and the other in the ofternoon between 5:45 and 6:20 p.m., coinciding with both the rising and setting of the sun

Idade fisiológica, variação sazonal e periodicidade diurna de quatro populações de Tabanidae (Diptera) no Campus Universitário, Manaus, Brasil ()

The four populations studied, Tabanus dorsiger var. dorsovittatus, T. d. var. modestus, T. importunus and Phaeotabanus cajennensis, presented low seasonal parity. The duration of the gonotrophic cycle was uniform, attaining Christopher's stage V in 120 hours after a complete blood meal. The majority of captured females that arrived to feed on an animal had stage II follicles. Only P. cajennensis was not registered throughout the year, not occuring from December to the deginning of February, at the start of the rainy season Flight activity was greates in the afternoon, and differences in activity between nulliparous and parous females was not significant (x2>0,05).", 'enAs quatro populações estudadas, Tabanus dorsiger var. dorsovitattus, T. d. var. modestus, T. importunus e Phaeotabanus cajennensis, apresentaram baixa oniparidade sazonal. A duração do ciclo gonotrófico foi uniforme, atingindo estádio V de Christophers em 120 horas, após um repasto sangüíneo completo. A maioria das fêmeas capturadas que chegavam para alimentação tinha o folículo em estádio II. Apenas P. cajennensis não foi registrada durante todo ano, deixando de ocorrer de dezembro a princípio de fevereiro, no início da estação chuvosa. A atividade de vôo foi maior no período da tarde e diferenças de atividade entre fêmeas nulíparas e oníparas não foram significativas (x2>0,05)

Métodos de determinar a idade fisiológica em Diptera de importância médica. Uma revisão com especial referência aos vetores de doenças na América do Sul.

Physiological age grading methods for bloodsucking Diptera of medical importance which shows gonotrophic concordance are reviewed. In the first part the changes which occur in mosquitoes following a blood meal are outlined and the theretical basis for age determination discussed. In the second part the methods applicable to Culicidae, Simuliidae, Phlebotomidae, Ceratopogonidae and Tabanidae are given. Extensive use of photographic material is made where this is a useful diagnostic aid in the interpretation of ovarian dissection.Os métodos de determinar a idade fisiológica em Diptera hematófagos de importância médica, que mostram concordância gonotrófica, são revisados. Na primeira parte, são delineadas as mudanças que ocorrem no inseto, após o repasto sangüíneo e discutida a base teórica para determinação da idade fisiológica. Na segundo parte, são dados os métodos aplicáveis a Culicidae, Simuliidae, Phlebotomidae, Ceratopogonidae e Tabanidae. Amplo uso de material fotográfico é adotado, dando proveitoso auxílio na interpretação da dissecação do ovário

'Nature or nurture': survival rate oviposition interval, and possible gonotrophic discordance among South East Asian anophelines

Background: Mosquito survival, oviposition interval and gonotrophic concordance are important determinants of vectorial capacity. These may vary between species or within a single species depending on the environment. They may be estimated by examination of the ovaries of host-seeking mosquitoes. Methods: Landing collections, Furvela tent-trap and CDC light-trap collections were undertaken sequentially in four locations in Cambodia between February 2012 and December 2013 and samples from the collected mosquitoes were dissected to determine parity, sac stage (indicative of time spent prior to returning to feed) and egg stage. Results: A total of 27,876 Anopheles from 15 species or species groups were collected in the four locations and 2883 specimens were dissected. Both the density and predominant species collected varied according to location and trapping method. Five species were dissected in sufficient numbers to allow comparisons between locations. Estimated oviposition interval differed markedly between species but less within species among different locations. Anopheles aconitus had the shortest cycle, which was 3.17 days (95 % CI 3–3.64), and Anopheles barbirostris had the longest cycle, which took four days (95 % CI 3.29–4). Anopheles minimus had a higher sac rate in weeks leading up to a full moon but there was apparently little effect of moon phase on Anopheles dirus. Despite the fact that many of the species occurred at very low densities, there was no evidence of gonotrophic dissociation in any of them, even during sustained hot, dry periods. The principal Cambodian malaria vector, An. dirus, was only common in one location where it was collected in miniature light-traps inside houses. It did not appear to have an exceptional survival rate (as judged by the low average parous rate) or oviposition cycle. Conclusions: Differences in the oviposition interval were more pronounced among species within locations than within species among ecologically diverse locations. A nationwide survey using CDC light-traps for the collection of An. dirus inside houses may help in determining patterns of malaria transmission in Cambodia

Assessement of Malaria Transmission in an Area with Very Low Mosquito Density

The increase in world travel in recent years, especially to and from areas where vector-borne diseases are endemic, has resulted in a substantial rise in imported cases of those diseases. In particular, malaria is a cause of concern. In those countries at the edge of its distribution, it can be difficult to distinguish between autochthonous and imported cases. However, distinguishing between the two is important because of the different allocation of resources to combat the disease that each requires. In general, observation of the various stages of parasite development in wild-caught female mosquitoes is considered evidence of autochthonous transmission. Observation of oocysts in the mosquito mid-gut testifies that mosquitoes are susceptible to infection but conclusions cannot be reached about their ability to complete the transmission cycle. Perhaps the best indication of autochthonous transmission is microscopic observation of sporozoites in mosquito salivary glands, since this detects parasites ready to be inoculated (BELER et al., 1990). Detection of circumsporozoite protein (CSP)(BURKOT, WILLIAMS & SCHNEIDER, 1984) in dry mosquito thoraxes, by Enzyme Linked Immunosorbent Assay (ELISA) is also widely used to determine transmission, especially when large numbers of mosquitoes need to be processed. Such assays provide information about the parasite species infecting the mosquito (BURKOT & WIRTZ, 1986; WIRTZ et al., 1987; BELER et al., 1990)