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Control of endophagic Anopheles mosquitoes and human malaria in Guinea Bissau, West Africa by permethrin-treated bed nets.

We compared the anti-mosquito and antimalarial potentialities of placebo-treated versus permethrin-impregnated bed nets in north-western Guinea Bissau. Baseline, pre-intervention entomological and parasitological data were collected during the rainy season of 1990 and bed nets were distributed shortly before the rainy season of 1991. Pairs of 3 ethnically different villages were investigated. The villages in each pair were at least 2 km apart but belonged to the same ethnic group in an ecologically similar area. After one year permethrin-treated bed nets were provided to all people in one village of each pair and placebo-treated bed nets to the other villages. About 98% of mosquitoes caught in bedrooms belonged to Anopheles gambiae and A. melas, which we consider to be the main malaria vectors in the study villages. Mean Plasmodium falciparum sporozoite rate in A. gambiae (9.6%) and A. melas (12.4%) was highest during October-November. The Plasmodium index in children 2-9 years old in the 6 villages, at the end of the rainy season 1990, ranged between 44% and 79%. Of these, 98% were identified as P. falciparum, 1% as P. malariae and 1% as mixed infections of these species. Significant reductions of Anopheles indoor resting densities and malaria parasite rates in humans were recorded in villages which had received permethrin-treated nets, but not in the control villages. The mean number of P. falciparum-infective mosquito bites received indoors in untreated villages during the rainy season was estimated to be about 4 per child and 20 per adult. This inoculation rate was reduced by at least 78% by the use of permethrin-impregnated bed nets. The malaria parasite rates and proportions of people experiencing 'disease with fever' decreased significantly in villages provided with permethrin-treated nets but not in the control villages. Impregnated nets may be an important tool to reduce disease and death due to malaria in Guinea Bissau.

Adolescent↗

Life-table analysis of Anopheles malaria vectors: generational mortality as tool in mosquito vector abundance and control studies.

BACKGROUND & OBJECTIVES: Vector control will for sometime remain a primary weapon in the war against vector borne diseases. Malaria is of paramount importance in this with its associated high morbidity and mortality especially in sub-Saharan Africa. This study on generational mortality associated factors in Anopheles mosquitoes life-table analysis was designed to investigate the fecundity, levels of mortality and mortality associated factors at the aquatic stages of anopheline malaria vectors. METHODS: Mortality associated factors were investigated at the eggs, I and II instar larval, III and IV instar larval and pupal stages of two anopheline species--Anopheles pseudopunctipennis (Theobald) and An. gambiae life-cycles in screen cages. Adult male and female mosquitoes were membrane filter-fed and algae in culture medium formed the bulk of food substances for the larval stage. Environmental temperature of culture media, pH and some associated physio-chemical factors were also determined. RESULTS: Results showed significant mortality rates at various aquatic stages. Infertility, cannibalism and environmental factors were the major factors responsible for mortality at the egg, larval and pupal stages respectively. INTERPRETATION & CONCLUSION: The aquatic stages of Anopheles mosquito mortality factor K and the mortality factors at the various stages investigated k1, k2, k3 and k4 are discussed. Our recommendations include further studies on the possible genetic modification of predacious An. pseudopunctipennis larvae and/or its modification for the production of sterile/infertile eggs as possible alternatives in the reduction and control of anopheline malaria burden.

Animals↗

[Preliminary study on the biological control of dengue vectors by fish in Liouchyou Prefecture, Pingtung County, Taiwan].

An investigation made in May 1989 with questionnaires to 2,480 families in Liouchyou Prefecture, Pingtung County, showed that there were about 6,533 water containers in the whole village, of which 49.83% were used to store water for drinking, and the remaining 50.17% were used for washing clothes and watering plants. 32.42% of the residents volunteered to rear fish in the family water containers to control the mosquito population. During the period from April to October 1989, there was a total approximately 17,600 Gambusia affinis, Poecilia reticulata, Tilapia mossambica, and Sarotherodon niloticus released into the household water containers in the Liouchyou areas to control dengue vectors--Aedes aegypti and Aedes albopictus. One month after the release, a comparison of the container index of Aedes larvae showed that among 530 containers with fish in them, the positive container index was 3.58; among the 3,219 containers without fish in them, it was 25.97. Furthermore, the positive container index without fish was as high as 97.32 in May 1989, and dropped to as low as 18.00 at the end of September 1989. This indicats that rearing fish to control household mosquitoes yielded significant results in the initial stage. Also, in some water containers Gambusia affinis and Porcilia reticulata lived longer than five months, and Gambusia affinis could eat 31.33 Aedes larvae/0.4078g fish per day on the average. It appears that the biological control of dengue vectors by fish in the Liouchyou areas would be advantageous.

Animals↗

Anopheles culicifacies: effects of age on the male reproductive system and mating ability of virgin adult mosquitoes.

Under controlled laboratory conditions of 28-30 degrees C and 16:8 L:D photoperiod, an attempt was made to develop an age-grading technique for Anopheles culicifacies males. Mating activity was maximal when females were 5-12 days old males were 5-7 days old. The numbers of total and mature spermatocysts declined significantly with age, and the proportion of the testes occupied by the sperm reservoir increased as virgin males grew older. Mating resulted in the loss of spermatozoa and accessory gland substance from the reproductive system. Loss of mating ability of older virgin males seemed to be age-related, because the reproductive system contained ample supplies of accessory gland substance and spermatozoa. Morphological changes of the reproductive system, due to mating and age, were used to infer the age and reproductive history of unknown males in a laboratory evaluation.

Aging↗

Efficacy of Australian quarantine procedures against the mosquito Aedes aegypti.

Methods employed by Australian quarantine officers to control Aedes mosquitoes in containers were tested against all stages of Aedes aegypti. Saltwater emersion killed all larvae but not pupae or eggs that were briefly exposed. Swimming pool chlorine, methyl bromide fumigation, and permethrin (2% active ingredient) spray provided 100% mortality of eggs, larvae, and pupae. Aerosol sprays incorporating synthetic pyrethrins are practical and also provide effective control of adults.

Aedes↗

Immune responses to mosquito saliva in 14 individuals with acute systemic allergic reactions to mosquito bites.

BACKGROUND: Mosquito bite-induced acute systemic allergic reactions are an increasing clinical concern and have not been optimally characterized immunologically. OBJECTIVE: We wanted to study the immunologic basis of these reactions. METHODS: Sera were received from 14 individuals with a history of acute systemic allergic reactions to mosquito bites, defined as the presence of one or more of the following: urticaria, angioedema, wheezing, dyspnea, hypotension, and decrease or loss of consciousness. Ten individuals were from the United States and one each was from Canada, Germany, Japan, and Switzerland. An indirect ELISA was developed to measure specific IgE and IgG antibodies to saliva from 5 common mosquito species with different geographic distributions: Aedes aegypti, Aedes vexans, Aedes albopictus, Anopheles sinensis, and Culex quinquefasciatus. Twenty-nine individuals with negative bite test results from laboratory-reared mosquitoes served as control subjects. RESULTS: Mosquito saliva-specific IgE levels to all 5 species were significantly increased in the individuals with systemic allergic reactions compared with the control subjects ( P < .061 for Aedes vexans and P < .008 for the remaining 4 species). By using the mean of the control subjects plus 1 SD as a cut-off level, 11 individuals had positive results to Aedes albopictus and up to 4 additional species; 3 individuals had positive results to only one species. Saliva-specific IgG levels were not significantly increased in the individuals with systemic allergic reactions compared with levels seen in the control subjects ( P > .05). CONCLUSION: Acute systemic allergic reactions to mosquito bites involve mosquito saliva-specific IgE and can be characterized immunologically. Aedes albopictus is the most common species associated with systemic allergic reactions to mosquito bites.

Acute Disease↗

The effectiveness of ultra-low-volume applications of malathion at a rate of 3 US fluid ounces per acre in controlling Aedes aegypti in Thailand.

Ultra-low-volume (ULV) aerial applications of malathion at a rate of 3 US fl oz per acre (219 ml/ha) for the control of Aedes aegypti and Culex pipiens fatigans were evaluated in 2 areas near Bangkok, Thailand. A housing project of the Royal Thai Air Force received 2 applications a week apart while the village of Bang Khen received 1 application. Bioassays, oil-sensitive red dye cards, landing-rate counts, ovitraps, and light-traps were used to evaluate the effects of the treatment. A comparison of pre- and post-treatment indices indicated good control of A. aegypti following all treatments. The results of these tests when compared with those of an earlier study using 6 US fl oz/acre (438 ml/ha) showed that the higher rate of application rate was more effective. Only fair control of C. p. fatigans was obtained. A comparison of light-trap collections before and after treatment demonstrated fairly good over-all control of other species of mosquitos for 3-4 days following each of the 2 treatments on the Air Force housing area.

Aedes↗

[Current malaria stratification in China].

During the past 30 years since 1958 when malaria stratification was first made, a great change in malaria situation has occurred. The original stratification can not represent the current status of malaria distribution. Therefore, it needs to be redivided so as to provide basis for future malaria control work. Taking species of mosquito vector and malaria incidence as the main indices and making reference to the natural geographical division, the current malaria endemic area in China can be divided into four regions, i.e. (1) Western region: it is mostly a natural non-endemic area, except some limited areas with sporadic cases in Xinjiang Autonomous Region; (2) Northern region: the whole north-eastern and partial northern China belong to the areas where malaria has been basically eliminated; but sporadic occurrence still exist in most part of the northern China; (3) Central region: it is mostly a hypo-endemic area, only a small part has meso-endemicity; (4) Southern region: nearly 50% has meso-endemicity and the other 50% has hypo-endemicity. The demarcation line of natural non-endemic areas and the areas where malaria has been basically eliminated has been defined.

Animals↗

Surveillance of above- and below-ground mosquito breeding habitats in a rural midwestern community: baseline data for larvicidal control measures against West Nile Virus vectors.

BACKGROUND: Mosquitoes in the genus Culex are thought to play a major role as vectors in the transmission cycle of West Nile virus (WNV) and other arboviruses in the United States. Effective control of mosquitoes through larviciding and adulticiding is expensive for communities and should be guided by reliable surveillance data on the distribution of mosquito breeding habitats. However, few small to medium sized cities in rural areas of the midwestern United States have this type of baseline information available. OBJECTIVE: During the summer of 2004, we investigated the characteristics of Culex and other mosquito-breeding habitats in a rural central Wisconsin community with a population of approximately 19,000. Such baseline information will aid in the development of rational strategies to control mosquito populations and prevent human exposure to WNV and other mosquito-transmitted viruses. METHODS: Mosquito larvae were collected and identified weekly from 14 below-ground storm water catch basins and 10 above-ground standing water sites distributed throughout the community. Collection began June 4, 2004 and continued through September 24, 2004. For each collection site the primary and adjacent land use patterns were determined. RESULTS: Over the study period, 1,244 larvae were collected from catch basins; 94% were Culex species. Breeding activity was first detected in early July. Peak breeding was observed during a period of several weeks when average daily temperatures were at the maximum observed and rainfall had declined. Organically enriched catch basins in low intensity urban sites adjacent to forests and wetlands were found to be more productive breeding habitats compared to catch basins having little organic debris located in isolated high intensity urban sites. Above-ground standing water sites produced 1,504 larvae; 66% of which were Culex species. Flood control ditches and permanent wetlands with stagnant water were most productive, while ditches with moving water were least productive habitats. Larvae were produced earlier in the season by above-ground sites than were produced by catch basins. However, larvae production was more variable in above-ground sites since half the sites became dry at some point during the study period. CONCLUSION: The observed differences in Culex larvae production based on the variables of habitat-type, temperature, and precipitation support the need for ongoing surveillance in communities to guide public health officials in planning for and prioritizing mosquito control efforts.

Animals↗

Transgenic mosquitoes and malaria transmission.

As the malaria burden persists in most parts of the developing world, the concept of implementation of new strategies such as the use of genetically modified mosquitoes to control the disease continues to gain support. In Africa, which suffers most from malaria, mosquito vector populations are spread almost throughout the entire continent, and the parasite reservoir is big and continuously increasing. Moreover, malaria is transmitted by many species of anophelines with specific seasonal and geographical patterns. Therefore, a well designed, evolutionarily robust and publicly accepted plan aiming at population reduction or replacement is required. The task is twofold: to engineer mosquitoes with a genetic trait that confers resistance to malaria or causes population suppression; and, to drive the new trait through field populations. This review examines these two issues, and describes the groundwork that has been done towards understanding of the complex relation between the parasite and its vector.

Africa↗