Distribution of anopheline mosquitoes in Eritrea

The spatial distribution of anopheline mosquito species was studied throughout Eritrea during the 1999-2001 malaria transmission seasons from October to December for the highlands and western lowlands and February to April for the coastal region. Of the 302 villages sampled, 59 were visited in both the first and second year. Overall, 13 anopheline species were identified, with the Anopheles gambiae complex predominating during the first year (75.6%, n = 861) and the second year (91.9%, n = 1,262). Intrazonal variation accounted for 90% of the total variation in mosquito distribution. Polymerase chain reaction results indicated that 99% (n = 1,309) of the An. gambiae s.l. specimens were An. arabiensis, indicating that this was the only member of the gambiae complex present. There was a high degree of aggregation of anophelines within zones and villages, with more than 80% of the total anophelines being collected from less than 20% of the villages and from only 10% of the houses sampled. At least 80% of the anopheline mosquitoes were collected from grass-thatched Agudo-type housing. Vector abundance showed an inverse relationship with elevation, with highest densities in the low-lying western lowlands. Multiple regression analysis of log-transformed mean density of An. arabiensis with rainfall and the normalized difference vegetation index (NDVI) (average NDVI, minimum NDVI, and maximum NDVI) showed that these independent variables were not significantly associated with mosquito densities (R2 = 0.058). Our study contributes to the basic understanding of the ecology and distribution of malaria vectors with respect to species composition and spatial heterogeneities both that could be used to guide vector control operations in Eritrea.     

Field evaluation of an enzyme-linked immunosorbent assay (ELISA) for Plasmodium falciparum sporozoite detection in anopheline mosquitoes from Kenya

An enzyme-linked immunosorbent assay (ELISA) using a monoclonal antibody that recognizes a repetitive epitope on the circumsporozoite protein of Plasmodium falciparum was used in Kenya to assess malaria infections in Anopheles gambiae s.l. and An. funestus. The ELISA confirmed that 88% of 44 sporozoite-positive gland dissections were P. falciparum. The ELISA infection rate of 18.6% (n = 736) for individually tested mosquitoes for both species was significantly higher than the 10.4% (n = 537) salivary gland sporozoite rate determined by dissection. This difference was due to ELISA detection of medium and large sized oocysts on the midguts of infected mosquitoes which did not contain salivary gland sporozoites. From a series of 379 Anopheles that were cut at the thorax, ELISA tests on "head" and "body" portions showed that 29.5% of 95 positive mosquitoes contained circumsporozoite antigen in the body portion in the absence of salivary gland infections. This field evaluation demonstrates that the ELISA can most accurately be used to estimate sporozoite rates by cutting mosquitoes at the thorax and testing anterior portions.     

Interrupting malaria transmission by genetic manipulation of anopheline mosquitoes

Malaria ranks among the deadliest infectious diseases that kills more than one million persons every year. The mosquito is an obligatory vector for malaria transmission. In the mosquito, Plasmodium undergoes a complex series of developmental events that includes transformation into several distinct morphological forms and the crossing of two different epithelia--midgut and salivary gland. Circumstantial evidence suggests that crossing of the epithelia requires specific interactions between Plasmodium and epithelial surface molecules. By use of a phage display library we have identified a small peptide-SM1--that binds to the surfaces of the mosquito midgut and salivary glands. Transgenic Anopheles stephensi mosquitoes expressing a SM1 tetramer from a blood-inducible and gut-specific promoter are substantially impaired in their ability to sustain parasite development and transmission. A second effector gene, phospholipase A2, also impairs parasite transmission in transgenic mosquitoes. These findings have important implications for the development of new strategies for malaria control.     

The biotin-streptavidin system in a two-site ELISA for the detection of plasmodial sporozoite antigen in mosquitoes

A two-site ELISA has been designed for the detection of sporozoite antigen in mosquitoes. Biotin-labelled monoclonal antibodies against sporozoites and a streptavidin-biotin-peroxidase complex were used to visualize the antigen. Evaluation of the sensitivity and specificity of the procedure was carried out and background levels of reactivity on the basis of negative mosquitoes were calculated. The test has been deliberately kept as simple as possible for use in the tropics and was designed using Anopheles stephensi infected with in vitro cultivated Plasmodium falciparum gametocytes. A minimum of about 100-350 sporozoites could be detected in mature salivary gland infections; in addition sporozoite antigen was detected in mosquitoes several days before the entry of sporozoites into the salivary glands. No reaction was demonstrable either with bloodstage or ookinete antigens of P. falciparum, or with mosquitoes carrying sporozoites of other plasmodial species. The number of sporozoites in positive mosquitoes and the generating capacity of a single oocyst could be assessed by the use of a calibration curve based on dilution data of a known sporozoite suspension. It was found that a single oocyst can produce about 10,000 sporozoite equivalents.     

Ingestion of Plasmodium falciparum sporozoites during transmission by anopheline mosquitoes.

We investigated the process of sporozoite transmission during blood feeding for Anopheles gambiae and An. stephensi experimentally infected with Plasmodium falciparum. When infective mosquitoes were fed 22-25 days postinfection on an anesthetized rat, sporozoites were detected in the midgut of 96.5% of 57 An. gambiae (geometric mean [GM] = 32.5, range 3-374) and in 96.2% of 26 An. stephensi (GM = 19.5, range 1-345). There were no significant differences between species either in salivary gland sporozoite loads or in the number of ingested sporozoites. There was a significant linear relationship between sporozoite loads and the numbers of ingested sporozoites for both An. gambiae (r = 0.38) and An. stephensi (r = 0.69). Subsequently, An. gambiae were tested for sporozoite transmission by allowing them to feed individually on a suspended capillary tube containing 10 microliters of blood. A total of 83.3% of 18 infective mosquitoes transmitted a GM of 5.9 (range 1-36) sporozoites. The same mosquitoes contained a GM of 23.4 (range 2-165) ingested sporozoites. The number of ingested sporozoites was related to sporozoite loads (r = 0.42) but not to the number of sporozoites ejected into capillary tubes. Ingested sporozoites remained in the midgut up to 10 hr after feeding. The comparable numbers of sporozoites ingested by infective mosquitoes in both experiments indicates that the actual number of sporozoites transmitted to the vertebrate host during blood feeding is significantly reduced by the blood ingestion process.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reappraisal on anopheline mosquitoes of Garhwal region, Uttarakhand, India

BACKGROUND & OBJECTIVES: The study examines occurrence of anopheline mosquitoes in seven districts--Dehradun, Pauri, New Tehri, Hardwar, Rudraprayag, Chamoli and Uttarkashi of Garhwal region in Uttarakhand state, India. METHODS: The methodological approach comprised sampling and processing of adult/immature mosquitoes, data compilation, meteorological information and parasitological survey. RESULTS: A total of 87 localities covering 24 tehsils/blocks were surveyed during January 2000 to December 2005 for mosquito sampling. The study encountered 18 species of anophelines including three malaria vectors namely Anopheles culicifacies, An. fluviatilis and An. stephensi collected from Kalsi, Dehradun City, Sahaspur, Hardwar town, Roorkee, New Tehri town and Kotdwar localities. An. pallidus has been recorded for the first time from the Garhwal region. All the collected species have been presented with particular reference to their both adult and immature distribution, brief account of bionomics and some ecological notes. INTERPRETATION & CONCLUSION: Out of 18 collected anopheline species, 15 were non-vectors and they were found to create nuisance to the inhabitants. As far as the species distribution was concerned the diversity was more at elevation between 150 and 1000 m above the mean sea level, while the immature of some species were not recovered from those localities where their adults were collected. Certain species of Anopheles were climate determined and their distribution was localized while some others were cosmopolitan.     

Ookinete rates in Afrotropical anopheline mosquitoes as a measure of human malaria infectiousness.

Anopheles gambiae s.1. and An. funestus were sampled for Plasmodium spp. ookinetes in two P. falciparum-endemic sites in western Kenya. Since the ookinete is a transitional stage of short duration, occurring after fertilization and before oocyst development, only females in the half-gravid and gravid stages of blood digestion were examined. Preparations of homogenized midguts were spotted onto microslides and examined microscopically after staining with Giemsa. Overall, ookinetes were detected in 4.4% of 1,079 anophelines examined over an eight-month period. Anopheles funestus had higher ookinete rates than An. gambiae s.1., and ookinete rates were higher in half-gravid than in gravid An. gambiae s.1. Geometric mean numbers of ookinetes per infected female were less than five for each species at the two sites, and the maximum number observed was only 12. The low frequencies and numbers of ookinetes were sufficient to produce sporozoite rates of 4-18% in the vector populations. The intense transmission of P. falciparum in these two sites is maintained by anthropophilic vectors where only one in 23 blood meals initiates an infection of generally less than five ookinetes. Relationships between human malaria infectiousness and vector infectivity are dependent upon the high efficiency of the developmental transition from the ookinete to the subsequent oocyst and sporozoite stages.     

Comparative susceptibility of anopheline mosquitoes in Rondonia, Brazil to infection by Plasmodium vivax

Seven anopheline species from Costa Marques, Rondonia, Brazil were compared with Anopheles darlingi for susceptibility to infection by Plasmodium vivax. Laboratory-reared F1 progeny of field-collected An. darlingi and the test anopheline species were fed at the same time on the same patients, all of whom had gametocytes in peripheral blood before treatment. Mosquitoes were dissected on day 8 after infection for oocysts and on days 14-16 after infection for sporozoites. The mean numbers of P. vivax oocysts and the percent of salivary gland infections for An. darlingi and An. deaneorum were similar and far exceeded those found in the other anopheline species tested. Anopheles albitarsis and An. mediopunctatus were less susceptible to infection by oocyst measurements than An. darlingi. However, for oocyst-infected An. albitarsis and An. mediopunctatus, the percent of mosquitoes with salivary gland infections and the numbers of sporozoites in the salivary glands were similar to An. darlingi. Anopheles triannulatus and An. oswaldoi were both susceptible to P. vivax infection, but the sporozoite infection rates and the numbers of sporozoites observed in the salivary glands were very low. Anopheles braziliensis and An. benarrochi both developed oocysts, but were never observed to have sporozoites in the salivary glands. These studies implicate some anopheline species as potential malaria vectors, but also show that species previously incriminated by ELISA techniques are not vectors of malaria parasites in Costa Marques, Rondonia, Brazil.     

Breeding point and larval association of anopheline mosquitoes of northwest Mindoro, Philippines

A larval survey of stream breeding Anopheles was conducted in the foothills of northwest Mindoro Island, Philippines. Eleven species were collected with An. ludlowae constituting 27.9% of the total. The three malaria vectors in the area, An. flavirostris, An. maculatus and An. mangyanus, made up 25.2, 5.1 and 3.8% of the collection, respectively. Breeding point induces were used to identify optimum habitat and larval association analyses. An. annularis and An. ludlowae had high positive association index with An. flavirostris, while An. mangyanus and An. filipinae appeared to have poor association within the breeding point.     

按蚊中肠细菌及其应用的研究进展

按蚊中肠细菌能够在控制传疟按蚊种群数量和抑制疟原虫在按蚊体内的发育等方面发挥重要作用。本文从细菌与按蚊的食物关系、按蚊幼虫和成蚊中肠细菌及其应用、细菌在按蚊体内的经发育期传递、细菌与按蚊成蚊的免疫反应,以及利用细菌防控疟疾流行的可行性等方面进行综述。     

Dusk to dawn activity patterns of anopheline mosquitoes in West Timor and Java, Indonesia

Malaria is a serious health issue in Indonesia. We investigated the dusk to dawn anopheline mosquito activity patterns, host-seeking and resting locations in coastal plain, hilly and highland areas in West Timor and Java. Adult mosquitoes were captured landing on humans or resting in houses or animal barns. Data analyzed were: mosquito night-time activities; period of peak activity; night-time activity in specific periods of time and for mosquito resting locations. Eleven species were recorded; data were sparse for some species therefore detailed analyses were performed for four species only. In Java Anopheles vagus was common, with a bimodal pattern of high activity. In West Timor, its activity peaked around midnight. Other species with peak activity around the middle of the night were An. barbirostris and An. subpictus. Most species showed no biting and resting preference for indoors or outdoors, although An. barbirostris preferred indoors in West Timor, but outdoors in Java. An. aconitus and An. annularis preferred resting in human dwellings; An. subpictus and An. vagus preferred resting in animal barns. An. barbirostris preferred resting in human dwellings in West Timor and in animal barns in Java. The information is useful for planning the mosquito control aspect of malaria management. For example, where mosquito species have peak activity at night indoors, bednets and indoor residual spraying should reduce malaria risk, but where mosquitoes are most active outdoors, other options may be more effective.     

Feeding pattern of anopheline and culicine mosquitoes in relation to biotopes and seasons in Delhi and environs

In the studies to know the feeding pattern of various species of mosquitoes, a total of 7461 specimens comprising of Anopheles culicifacies (150), An. stephensi (61), An. subpictus (990), An. annularis (572), Culex quinquefasciatus (5217) and C. vishnui group (471) of mosquitoes were collected from different biotopes of selected localities in Delhi and environs during all the months of the year. The mosquito blood samples were processed by Gel diffusion technique to know the source of blood meal. Results of study revealed that the mosquito species tested in the study were by and large zoophilic and opportunistic feeders. The feeding behaviour was found to be highly influenced by biotopes from where the mosquitoes were collected, village and areas, different climatic seasons, sleeping behaviour of human beings and availability of alternative hosts particularly animal population. Overall anthropophilic index was found to be 24.66% for An. culicifacies, 20.96% for An. stephensi, 16.93% for An. subpictus, 9.96% for An. annularis, 26.33% for C. quinquefasciatus and 36.39% for C. vishnui group of mosquitoes. Feeding behaviour towards other animals viz: bovine, goat, dog, pig and bird for all these mosquito species in different months and biotopes e.g. human dwellings, cattle sheds and mixed dwellings; in different months and seasons of the year have been presented.     

海南岛按蚊的鉴定和迷走按蚊的进化研究

目的 阐明海南岛某些按蚊的分类地位,探讨迷走按蚊与其近缘种的亲缘关系. 方法 对采自海南岛8个地点的按蚊依据形态和分子特征进行鉴别研究,应用的分子特征包括核糖体DNA(ribosomal DNA,rDNA)第2内转录间隔区(second internal transcribed spacer,ITS2)和28S第3编码区(third domain,D3)序列,综合分析迷走按蚊及其近缘种的ITS2和D3序列,构建系统发育树. 结果 本研究共鉴定按蚊407只,其中84.9％的成蚊分子鉴定与依据形态鉴定的结果一致.在228条迷走按蚊的ITS2序列中,部分个体在2个位点存在单碱基套峰(G/A),出现的频率分别为57.9％、64.8％,同时有两个套峰的占样本数的57.0％,其他位点保守.迷走按蚊的D3序列,在种内无碱基差异.结合本研究和文献的迷走按蚊及其近缘种ITS2序列构建的ML树,显示迷走按蚊与浅色按蚊MC/D亲缘关系近,与另一支的浅色按蚊B、圣代克按蚊复合体的亲缘关系较远.关于未订名种NBC (Anophelessp.NBG)的分类地位,依据分子特征鉴定其为浅色按蚊B,可能是圣代克按蚊复合体新的成员种.结论 鉴定形态在个体间变异大的种类时,客观的分子特征更具重要性,迷走按蚊与浅色按蚊MC/D具较近的亲缘关系.