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The basic strength of the AMCA family is the wide range of expertise and "can do" attitude of its diverse membership. The AMCA is currently experiencing problems with federal legislation and fiscal stability because we have not fully utilized member strengths to reevaluate the association's direction and set new goals to address change. However, the AMCA Board of Directors and many committee chairpersons met, reevaluated direction and clarified goals, and initiated major changes to meet the challenges facing the association and its members. Members of the AMCA are encouraged to contribute their individual talents to ensure that the association prosper and serve the needs of the mosquito and vector control family.
A review of the filariasis control programme in Tahiti from November 1967 to January 1968.
District filariasis surveys in Tahiti in the years after the Second World War yielded the highest microfilaria rates in the South Pacific area, ranging from 25% to 44%; the mean elephantiasis rate was 5% and microfilaria densities (MfD(50)) ranged from 18 to 31. A co-operative filariasis research programme was begun and a control programme was inaugurated in 1953, using diethylcarbamazine therapy supported by mosquito larvae control measures. By 1959 fifteen districts had received mass treatment. Re-examination after 12 months showed that the mean microfilaria rate had dropped from 31% to 3% and the MfD(50) from 23 to 4. Subsequently, only positives were re-treated and by 1964 the microfilaria rate had risen to 6.8%. The increase caused concern and the significance of this reservoir of infection was investigated.Administration of diethylcarbamazine in periodic mass treatments only in American Samoa began in 1963 and was accompanied by a drop in the microfilaria rate to less than 1%, leading to interruption of transmission in some areas.
Enhanced gametocyte formation by Plasmodium chabaudi in immature erythrocytes: pattern of production, sequestration, and infectivity to mosquitoes.
The objective of this study was to investigate the chronobiology and infectivity of the gametocytes of Plasmodium chabaudi chabaudi. In order to increase the production of gametocytes, mice were treated with phenylhydrazine to induce a hyper-reticulocytosis. The authors observed an important stimulation of gametocytogenesis. Gametocytes were seen as soon as the second day postinoculation and were produced periodically at each schizogony, every 24 hr. The gametocytic developmental cycle lasted 60 hr and consisted of 4 successive stages: stage 0 at 36 hr, from merozoite invasion, stage I at 42 hr, stage II at 48 hr, and stage III at 54 hr. An important fraction of stage II was sequestered in small peripheral capillaries. The numbers of oocysts in the mosquitoes fed on phenylhydrazine-treated mice were larger than in controls. When mosquitoes were fed at different times of the day, circadian differences in the oocyst counts were not statistically significant. However, stage II was considered to be probably the most infective stage because, like the infective gametocyte stage of other species of murine malaria, it is sequestered in the peripheral capillaries. In contrast with Plasmodium vinckei, there is no peak of infectivity at the time of sequestration of the infective stage; this is probably due to the inhibitory effect of the schizogony occurring at this time.
Repellency of two controlled-release formulations of deet against Anopheles quadrimaculatus and Aedes taeniorhynchus mosquitoes.
Two experimental controlled-release repellent formulations containing 35% (3M) and 44% (Biotek) deet, respectively, were compared with a 75% standard formulation of deet used by the military. The military repellent was equal to or significantly better than the formulations in duration of protection against 2 mosquito species in laboratory and field tests, but the formulations contained only 47-59% the amount of deet in the military repellent. In all cases high levels of protection (greater than 95%) were measured, but because of high densities of biting mosquitoes in field tests, this level did not necessarily indicate few bites. In terms of mean bites/test/day by Anopheles quadrimaculatus in caged tests, the military repellent had fewest (2) and Biotek had most (41).
Vertebrate safety of Clostridium bifermentans serovar malaysia, a new larvicidal agent for vector control.
The safety of bacterial cells of Clostridium bifermentans serovar malaysia, which is highly toxic to mosquito larvae, was tested on mice, guinea pigs, rabbits, and goldfish. Inoculations of at least 1 x 10(8) cells per animal by routes recommended by World Health Organization (subcutaneous, percutaneous, inhalation, force-feeding, intraperitoneal, intravenous) and tests of subacute toxicity, anaphylactic shock, persistence in heart blood, and virulence by successive passages, were performed on mice, guinea pigs, or both. Growth was monitored for 1 mo before necropsy. Ocular irritation and skin scarification were tested with rabbits. C. bifermentans serovar malaysia did not induce any mortality or abnormal reactions in mammals at a dose 1,000 times higher than the level established by W.H.O. for the demonstration of safety. Bacterial cells are not toxic to goldfish at a dose 1,000 times higher than the LD50 for the target-mosquito larvae. We conclude that C. bifermentans serovar malaysia bacterial cells are safe for laboratory mammals and goldfish.
Expression of mosquitocidal toxin genes in a gas-vacuolated strain of Ancylobacter aquaticus.
A series of plasmids bearing the binary toxin genes of Bacillus sphaericus 2297 or 2317.3, the 100-kDa toxin gene of B. sphaericus SSII-1, or the 130-kDa (cryIVB) toxin gene of Bacillus thuringiensis subsp. israelensis were constructed and introduced into Ancylobacter aquaticus by electroporation. The transformed A. aquaticus cells exhibited significant toxicity towards mosquito larvae, demonstrating a potential use of recombinant A. aquaticus for biological control of mosquitoes.
Enduring toxicity of transgenic Anabaena PCC 7120 expressing mosquito larvicidal genes from Bacillus thuringiensis ssp. israelensis.
Persistence of biological control agents against mosquito larvae was tested under simulated field conditions. Mosquito larvicidal activity of transgenic Anabaena PCC 7120 expressing cry4Aa, cry11Aa and p20 from Bacillus thuringiensis ssp. israelensis was greater than B. thuringiensis ssp. israelensis primary powder (fun 89C06D) or wettable powder (WP) (Bactimos products) when either mixed with silt or exposed to sunlight outdoors. Reduction of Bactimos primary powder toxicity was at least 10-fold higher than Anabaena's after mixing with silt. In outdoors experiments, Bactimos WP remained toxic (over 30% mortality of 3rd instar Aedes aegypti larvae) for 2-4 days only, while transgenic Anabaena's toxicity endured 8-21 days.
Mass treatment with ivermectin for filariasis control in Papua New Guinea: impact on mosquito survival.
Field studies were carried out to determine the impact of mass human treatment with ivermectin on the survival of anthropophagic mosquitoes of the Anopheles punctulatus complex (Diptera: Culicidae), the vectors of lymphatic filariasis and malaria in Papua New Guinea. In a village where mass treatment had been given, using 400 microg/kg ivermectin plus 6 mg/kg diethylcarbamazine citrate (DEC), we performed pre- and post-treatment collections of freshly blood-engorged mosquitoes from the same nine bedrooms. All blood-fed mosquitoes collected less than 4 days after mass treatment died within 9 days, whereas 67% of those collected before treatment survived for >9 days. Comparison (using the log-rank test) of the survival curves for mosquitoes collected (i) before treatment, (ii)<4 days after treatment, and (iii) 28 days after treatment, showed the survival rate of group (ii) to be significantly lower than the other two (chi2=176, df=2, P<0.0001). Pre- and post-treatment all-night landing catches showed no reduction in human biting rates in the experimental village. In another village, where people were mass treated with ivermectin (400 microg/kg) only, the survival rates of freshly blood-engorged An. punctulatus collected from bedroom resting-sites less than 1 day after treatment, were compared to similar collections carried out at the same time in a nearby village where people were not treated with ivermectin. The 48-h survival rate for the ivermectin-treated village was 31% compared to 94% for the other; this difference was highly significant (chi2=32.42, df=1, P<0.0001). Mosquitoes fed 2 months post-treatment with DEC or collected 38 days post-treatment with ivermectin had normal survival rates. We conclude that the duration of the systemic lethal effect of ivermectin on mosquitoes is insufficient to be of epidemiological significance in filariasis control programmes that are based on biannual and annual single-dose treatments, but might reduce vectorial capacity sufficiently to block epidemics of dengue or even malaria.
A novel association between clustered NF-kappaB and C/EBP binding sites is required for immune regulation of mosquito Defensin genes.
A comparative analysis identified key cis-acting regulatory elements responsible for the temporal control of mosquito Defensin gene expression. The promoters of Anopheles gambiae Defensin 1 and two isoforms of Aedes aegypti Defensin A are up-regulated by immune challenge. This stimulated activity depends upon a cluster of three NF-kappaB binding sites and closely associated C/EBP-like motifs, which function as a unit for optimal promoter activity. Binding of NF-kappaB and C/EBP like transcription factors is confirmed by electrophoretic mobility shift assay, including supershifts with antibodies to C/EBP. KappaB-like motifs are abundant within antimicrobial peptide gene promoters and most are very closely associated with putative C/EBP binding sites. This novel association between NF-kappaB and C/EBP binding sites may, therefore, be of widespread significance.
Comparison of dry ice-baited centers for disease control and New Jersey light traps for measuring mosquito abundance in California.
Mosquito catch in New Jersy light traps (NJLTs) has been declining in recent years, compromising the sensitivity of the California mosquito monitoring program. Centers for Disease Control traps (CDCTs) operated without light and augmented with dry ice have been considered for replacement or augmentation. To provide information on comparative sensitivity and ability to measure abundance over time and space, catch of mosquitoes in NJLTs was compared to catch in CDCTs operated concurrently at 8-10 sites within the Coachella Valley, Kern, San Joaquin County, and Sacramento-Yolo Mosquito and Vector Control Districts. The CDCTs always collected more female mosquitoes than did NJLTs; however, differences in sensitivity varied markedly over time and space precluding the calculation of a universal conversion factor. Regressions of the catch of female Culex tarsalis in CDCTs as a function of catch in NJLTs within districts indicated that the slopes varied markedly, again precluding the derivation of a universal function. Therefore, we recommend that mosquito surveillance programs replace or supplement NJLTs with systematically operated CDCTs to enhance sampling sensitivity for females of most mosquito species. However, both trap types should be operated concurrently at several sites within each district to derive regression functions to convert historical relative abundance data from NJLTs to equivalent counts in CDCTs for retrospective analyses.
Essential oils as potential adulticides against two populations of Aedes aegypti, the laboratory and natural field strains, in Chiang Mai province, northern Thailand.
Essential oils derived from five plant species, celery (Apium graveolens), caraway (Carum carvi), zedoary (Curcuma zedoaria), long pepper (Piper longum), and Chinese star anise (Illicium verum), were subjected to investigation of adulticidal activity against mosquito vectors. Two populations of Aedes aegypti, the laboratory and natural field strains, collected in Chiang Mai province, northern Thailand were tested in pyrethroid-susceptibility bioassays. The results revealed that the natural field strain of A. aegypti was resistant to permethrin, with mortality rates ranging from 51 to 66%. A mild susceptibility, with mortality rates ranging from 82 to 88%, was observed in the natural field strain of A. aegypti exposed to lambdacyhalothrin, which suggested that this strain was tolerant and might be resistant to this insecticide. However, laboratory-reared A. aegypti exposed to discriminating dosages of permethrin and lambdacyhalothrin induced 100% mortality in all cases, thus indicating complete susceptibility of this strain to these insecticides. The adulticidal activity determined by topical application revealed that all five essential oils exerted a promising adulticidal efficacy against both laboratory and natural field strains of A. aegypti. Although the laboratory strain was slightly more susceptible to these essential oils than the natural field strain, no statistically significant difference was observed. Moreover, comparison of the adulticidal activity indicated that the performance of these essential oils against the two strains of A. aegypti was similar. The highest potential was established from caraway, followed by zedoary, celery, long pepper, and Chinese star anise, with an LC(50) in the laboratory strain of 5.44, 5.94, 5.96, 6.21, and 8.52 microg/mg female, respectively, and 5.54, 6.02, 6.14, 6.35, and 8.83 microg/mg female, respectively, in the field strain. These promising essential oils are, therefore, an alternative in developing and producing mosquito adulticides as an effective measure used in controlling and eradicating mosquito vectors.
Control of arthropods of medical and veterinary importance.
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Gas-propelled aerosols and micronized dusts for control of insects in aircraft. 5. Effectiveness against insects of public health importance.
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Insecticide resistance issues in vector-borne disease control.
Vector-borne diseases are an increasing cause of death and suffering worldwide. Efforts to control these diseases have been focused on the use of chemical pesticides, but arthropod resistance (whether physiological, biochemical, or behavioral) to pesticides is now an immense practical problem. The pharmacokinetic interactions of pesticides with arthropods, mechanisms of resistance, and the strengths and shortcomings of different resistance test methods are briefly reviewed. Using malaria control as an example, the differences between the efficacy of insecticide-sprayed houses in reducing malaria transmission, and the actual effect of such treatments on vectors are discussed. Reduced malaria transmission as a result of spraying house walls occurs through some combination of killing vectors that land on sprayed walls (insecticidal effect) and by preventing vectors from entering or remaining inside long enough to bite (behavioral effects). Both insecticidal and behavioral effects of insecticides are important, but the relative importance of one versus the other is controversial. Field studies in Africa, India, Brazil, and Mexico provide persuasive evidence for strong behavioral avoidance of DDT by the primary vector species. This avoidance behavior, exhibited when malaria vectors avoid insecticides by not entering or by rapidly exiting sprayed houses, should raise serious questions about the overall value of current physiological and biochemical resistance tests. The continued efficacy of DDT in Africa, India, Brazil, and Mexico, where 69% of all reported cases of malaria occur and where vectors are physiologically resistant to DDT (excluding Brazil), serves as one indicator that repellency is very important in preventing indoor transmission of malaria. This experience with DDT has implications for future control efforts because pyrethroids also stimulate avoidance behaviors in arthropods. Each chemical should be studied early (before broad-scale use) to define types of action against vector species by geographic area, especially for impregnated bed net applications. The problems for vector control created by use of insecticides in agriculture and the potential for management of resistance in both agriculture and vector-borne disease control are discussed.
[Toward integrated dengue control ].
Dengue is the most important arthropod-borne viral disease, it is characterized by mild symptoms to hemorrhagic manifestations and shock syndrome (DHF/DSS). Dengue and DHF/DSS have become major public health problems worldwide. In the urban areas of tropical and subtropical regions approximately 50 million infections occur annually. In Venezuela the situation is similar to the rest of the Americas. The impact of dengue points out the necessity of very organized and effective control programs. The emergency measures to combat the epidemics have had limited effects. There is not a specific management of dengue infections, no vaccine is commercially available and vector control is one of the alternatives to stop the spread of the disease, but an integral control program is needed, with each population's particularities and the state of epidemic risk in that it is. In the practice, it is to combine the environmental reparation with the changes in the human behavior taken place by the sanitary education and the necessary laws for it, integrated with the biological fight against the vector in the way and more appropriate moment and the chemical control in epidemic situations. This last aspect is fundamental as message of change toward an active attitude and of conscience, without which we can affirm with all security that doesn't exist government neither system of health able to solve this problem.
Malaria control program in Sri Lanka.
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New international convention allows use of DDT for malaria control.
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