Can anything be done to maintain the effectiveness of pyrethroid-impregnated bednets against malaria vectors?
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Pyrethroid-treated bednets are the most promising available method of controlling malaria in the tropical world. Every effort should be made to find methods of responding to, or preventing, the emergence of pyrethroid resistance in the Anopheles vectors. Some cases of such resistance are known, notably in An. gambiae in West Africa where the kdr type of resistance has been selected, probably because of the use of pyrethroids on cotton. Because pyrethroids are irritant to mosquitoes, laboratory studies on the impact of, and selection for, resistance need to be conducted with free-flying mosquitoes in conditions that are as realistic as possible. Such studies are beginning to suggest that, although there is cross-resistance to all pyrethroids, some treatments are less likely to select for resistance than others are. Organophosphate, carbamate and phenyl pyrazole insecticides have been tested as alternative treatments for nets or curtains. Attempts have been made to mix an insect growth regulator and a pyrethroid on netting to sterilize pyrethroid-resistant mosquitoes that are not killed after contact with the netting. There seems to be no easy solution to the problem of pyrethroid resistance management, but further research is urgently needed. (+info)
Chagas disease vector control through different intervention modalities in endemic localities of Paraguay.
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In a field study carried out in three rural communities in Paraguay in a zone endemic for Chagas disease, we implemented three different vector control interventions--spraying, housing improvement, and a combination of spraying plus housing improvement--which effectively reduced the triatomine infestation. The reduction of triatomine infestation was 100% (47/47) in the combined intervention community, whereas in the community where housing improvement was carried out it was 96.4% (53/55). In the community where fumigation alone was used, the impact was 97.6% (40/41) in terms of domiciliary infestation. In all the houses where an intervention was made, an 18-month follow-up showed reinfestation rates of less than 10%. A serological survey of the population in the pre- and post-intervention periods revealed a shift in positive cases towards older age groups, but no significant differences were observed. The rate of seroconversion was 1.3% (three new cases) in the community with housing improvement only, but none of these cases could have resulted from vector transmission. The most cost-effective intervention was insecticide spraying, which during a 21-month follow-up period had a high impact on triatomine infestation and cost US$ 29 per house as opposed to US$ 700 per house for housing improvement. (+info)
Chemical control of Haematobia irritans with 0.5% topical ivermectin solution in cattle.
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A field trial was conducted to evaluate the efficacy of a topical formulation of ivermectin administered at the dose of 500 micrograms/kg against horn flies (Haematobia irritans) in cattle. Eighty-eight cattle in four herds naturally exposed to horn flies were used in the trial. Replicates were formed of two herds. Within replicates, one herd was randomly allocated to the untreated control and the other to the ivermectin treatment group. Horn fly counts were taken on the treatment day (Day 0) and on Days 7, 14, 21, 28, and 35 post-treatment. There were no horn flies on any cattle in the treatment group, whereas all the control cattle were continuously infested by horn flies on each examination day. (+info)
Genomic and evolutionary analysis of Feilai, a diverse family of highly reiterated SINEs in the yellow fever mosquito, Aedes aegypti.
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Five short interspersed repetitive elements (SINEs) were found fortuitously in the introns of a steroid hormone receptor AaHR3-2 gene of the yellow fever mosquito, Aedes aegypti, constituting a novel family of tRNA-related SINEs named Feilai. In addition, nine other Feilai elements were found in currently available sequences in Ae. aegypti, six of which were also near genes. Approximately 5.9 x 10(4) copies of Feilai were present in Ae. aegypti, equivalent to 2% of the entire genome. An additional 35 Feilai elements were isolated from a genomic library. Of the total 49 Feilai elements, 20 were full-length. Sequence comparisons and phylogenetic analyses of the full-length elements strongly suggest that there are at least two subfamilies within the Feilai family. There is a high degree of conservation within the two subfamilies. However, sequence divergence between the subfamilies, along with the presence of highly degenerate Feilai elements, suggests that Feilai is likely a diverse family of SINEs that has existed in Ae. aegypti for a long time. Many Feilai elements were closely associated with other transposons, especially with fragments of non-LTR retrotransposons and miniature inverted-repeat transposable elements. The 500-bp sequences immediately flanking a Feilai element were highly A + T-rich, which is consistent with the fact that no Feilai has been found in the coding regions of genes. It is likely that the highly reiterated and interspersed Feilai elements are partially responsible for the pattern of short-period interspersion of the Ae. aegypti genome. The evolutionary relationship between Feilai and the Ae. aegypti genome is likely complex. (+info)
Environmental controls in reducing house dust mites and nasal symptoms in patients with allergic rhinitis.
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A randomized comparison group pretest-posttest experimental design was used to quantitatively determine the effects of environmental control measures on patients with allergic rhinitis. Environmental controls included wrapping the mattress with a vinyl cover, washing the top bedding cover with 55 degrees C hot water every two weeks, removal of soft furniture, and wet cleaning of the bedroom floor every day. Thirty subjects were randomly assigned to experimental and control groups. The amount of house dust mites in dust samples collected from the bedroom floor, bedding and mattress, as well as the nasal symptoms of patients, were measured twice at one-month intervals. A significant decrease in house dust mites in dust samples and relief in patients' nasal symptoms were observed in the experimental group who had environmental controls. (+info)
Short report: entomologic inoculation rates and Plasmodium falciparum malaria prevalence in Africa.
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Epidemiologic patterns of malaria infection are governed by environmental parameters that regulate vector populations of Anopheles mosquitoes. The intensity of malaria parasite transmission is normally expressed as the entomologic inoculation rate (EIR), the product of the vector biting rate times the proportion of mosquitoes infected with sporozoite-stage malaria parasites. Malaria transmission intensity in Africa is highly variable with annual EIRs ranging from < 1 to > 1,000 infective bites per person per year. Malaria control programs often seek to reduce morbidity and mortality due to malaria by reducing or eliminating malaria parasite transmission by mosquitoes. This report evaluates data from 31 sites throughout Africa to establish fundamental relationships between annual EIRs and the prevalence of Plasmodium falciparum malaria infection. The majority of sites fitted a linear relationship (r2 = 0.71) between malaria prevalence and the logarithm of the annual EIR. Some sites with EIRs < 5 infective bites per year had levels of P. falciparum prevalence exceeding 40%. When transmission exceeded 15 infective bites per year, there were no sites with prevalence rates < 50%. Annual EIRs of 200 or greater were consistently associated with prevalence rates > 80%. The basic relationship between EIR and P. falciparum prevalence, which likely holds in east and west Africa, and across different ecologic zones, shows convincingly that substantial reductions in malaria prevalence are likely to be achieved only when EIRs are reduced to levels less than 1 infective bite per person per year. The analysis also highlights that the EIR is a more direct measure of transmission intensity than traditional measures of malaria prevalence or hospital-based measures of infection or disease incidence. As such, malaria field programs need to consider both entomologic and clinical assessments of the efficacy of transmission control measures. (+info)
Surveillance for acute pesticide-related illness during the Medfly eradication program--Florida, 1998.
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The Mediterranean fruit fly (Medfly) (Ceratitis capitata, Wiedemann) is an exotic insect that can damage approximately 250 fruit and vegetable plant species and is a serious threat to domestic agriculture. During the spring and summer of 1998, pesticides were used by federal and state agriculture authorities to eradicate Medfly infestations that had been detected in portions of five Florida counties (Table 1). This report summarizes surveillance data, describes probable and possible cases of illness associated with the eradication effort, and provides recommendations for future Medfly-eradication programs. (+info)
Pathology and epizootiology of Entomophaga maimaiga infections in forest Lepidoptera.
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The insect-pathogenic fungal pathogen Entomophaga maimaiga is endemic to northeastern Asia and was first found in North America in 1989. Due to repeated epizootics and spread within populations of the major forest defoliator in northeastern North America, the gypsy moth (Lymantria dispar), this pathogen has gained much notoriety. Although this pathogen was purposely introduced to North America for biological control of L. dispar in 1910 to 1911, it is questionable whether it became established at the time of release and then remained at innocuous levels until relatively recently. Alternatively, the fungal strain present in North America today could be a more recent accidental introduction. DNA analysis demonstrates that this pathogen differs significantly from North American members of the same species complex (the Lepidoptera-specific Entomophaga aulicae species complex), and, to date, isolates of this introduced pathogen display little heterogeneity in North America. Nonsusceptible lepidopteran larvae have been identified, and either E. maimaiga is unable to penetrate the cuticle or the fungus cannot survive within the hemocoel. In the latter case, although E. maimaiga grows as protoplasts lacking cell walls in the host hemolymph, glycoproteins on plasma membranes of the protoplasts could lead to host recognition. Epizootiological studies demonstrate a clear association between fungal activity and environmental moisture but little association with host density under hypothesized conditions of high fungal density. Prediction of the occurrence of epizootics is not yet possible. E. maimaiga is easily established in new areas by releasing azygospores, but the ability to use this pathogen further for biological control will depend, in large part, on the development of mass production systems. (+info)