Effect of fly control on trachoma and diarrhoea

The causative agent of trachoma, Chlamydia trachomatis, has been found on flies fed on heavily infected laboratory culture media. Findings are presented from an assessment of the effect of domestic fly control upon the prevalence of trachoma and associated cases of childhood diarrhea in 2 pairs of Gambian villages. 1 pair of villages was studied in the 1997 wet season and the second pair in the 1998 dry season. For each pair, deltamethrin was sprayed for 3 months to control flies in 1 village, while the other village was used as a control. Fly populations were monitored with traps. The prevalence of trachoma was measured at baseline and at 3 months, and data were collected daily on diarrhea in children aged 3 months to 5 years. Fly control decreased the numbers of muscid flies by approximately 75% in the intervention villages compared with controls. While the prevalence of trachoma was similar at baseline between study and control villages, after 3 months of fly control there were 75% fewer new cases of trachoma in the intervention villages. There was 22% and 26% less childhood diarrhea in the wet and dry seasons, respectively, compared with controls. These findings demonstrate that muscid flies are important vectors of trachoma and childhood diarrhea in The Gambia, and that the use of deltamethrin spray can help to reduce the prevalence of both trachoma and associated diarrhea cases.     

DDT indoor residual spray, still an effective tool to control Anopheles fluviatilis-transmitted Plasmodium falciparum malaria in India

This study from two districts of Orissa State which are endemic for Plasmodium falciparum transmitted by Anopheles fluviatilis and A. culicifacies investigated the impact of dichlorodiphenyl trichloroethane (DDT) indoor residual spraying, in view of the ongoing discussion on phasing out DDT in India. Based on their high annual parasite incidence and logistical considerations, 26 villages in Malkangiri and 28 in Koraput district were selected for DDT spraying. For comparison, six and four unsprayed villages were chosen from the same districts. In each district, the prevalence of malaria infection and incidence of malaria fever, indoor resting density and parous rate of the vectors, and their susceptibility to DDT were monitored in six and three villages selected randomly from the sprayed and unsprayed groups respectively. Anopheles fluviatilis was susceptible to DDT while A. culicifacies was resistant. DDT residual spraying with 1 g/m(2), was carried out in October-November 2001. Spraying 74-86% of human dwellings and 100% of cattle sheds brought down the indoor resting density of A. fluviatilis by 93-95%. This was associated with a significant reduction of incidence of malaria fever as well as prevalence of malaria infection from November to February in both districts. The spraying also seemed to impact on vector longevity, and a residual effect of DDT on the sprayed walls was observed up to 10-12 weeks despite re-plastering. Hence DDT spraying can still be an effective tool for controlling fluviatilis-transmitted malaria. Although this species is exophilic, its nocturnal resting behaviour facilitates its contact with the sprayed surfaces. DDT is still useful for residual spraying in India, particularly in areas where the vectors are endophilic and not resistant.     

Indoor residual spraying with alphacypermethrin controls malaria in Pakistan: a community-randomized trial

We conducted a community-randomized controlled trial in Pakistan to determine the efficacy of indoor residual spraying with alphacypermethrin ('Fendona', Cyanamid, NJ, USA), applied at 25 mg/m2, to prevent falciparum and vivax malaria. Wettable powder (WP) and suspension concentrate (SC) formulations were tested against an unsprayed control in an irrigated rice-growing area of Sheikhupura district, Punjab province. The study area of 180 km2 was divided into nine sectors, which were assigned at random to control, WP, or SC treatments in replicates of 3. Sentinel villages were selected from each sector for entomological and disease monitoring. Malaria was monitored by fortnightly active case detection (ACD) and by cross- sectional parasite surveys on schoolchildren. Mosquito populations were monitored by space spraying of rooms and by cattle-landing catches. The spray campaign took place in June 1997 and covered 96% of compounds. During the 7 months after spraying, the incidence of falciparum malaria was 95% lower and that of vivax malaria 80% lower in WP-sprayed than unsprayed sectors. Similar results were obtained for sectors sprayed with the SC formulation. Cross-sectional surveys gave estimates of efficacy comparable to those obtained by ACD. Anopheles culicifacies was 80% less abundant and A.stephensi, the predominant anopheline, was up to 68% less abundant in sprayed areas over the 7-month period. Reductions in anopheline parous rates indicated that the single-spray treatment was effective for the entire transmission season. Sprayed surfaces lacked odour, which contributed to the popularity of the campaign. Alphacypermethrin is a promising insecticide for the control of malaria in Pakistan and South Asia generally.     

Tolerance of house fly, Musca domestica L. (Diptera: Muscidae) to dichlorvos (76% EC) an insecticide used for fly control in the tsunami-hit coastal villages of southern India

The Directorate of Public Health (DPH), Tamil Nadu, in southern India employed spraying of dichlorvos (76% EC) for quick elimination of fly concentrations in the tsunami-hit coastal villages at the concentration of 304g (a.i.)/10,000m(2). However, nuisance of house flies remained high particularly in temporary shelters and centralized relief kitchens. Susceptibility of house fly, Musca domestica to dichlorvos was determined in the laboratory to provide information for an effective management of this pest. Various concentrations of dichlorvos (76% EC) viz., 0.1, 0.2, 0.4, 0.6 and 0.8microg (a.i.) per fly, were tested using topical application against F(1) progenies of house flies collected 12 months after insecticide applications from different habitats in the tsunami-hit coastal villages. Fly mortality was recorded at 24h post treatment. Parallel controls were maintained for comparison. Mortality of the house flies varied between 17.5% and 100% and increased with an increase in dosage of the insecticide. Mortality was >80% at 0.6 and 0.8microg (a.i.) per fly. The LD(50) of dichlorvos tested against flies collected from different villages varied from 0.218microg (a.i.) to 0.235microg (a.i.) per fly and the LD(90) varied from 0.574microg (a.i.) to 0.639microg (a.i.) per fly. House flies collected from a rural village, Thirukanur that had never been exposed for insecticide treatment in the past one decade, when tested, the mortality varied between 92.5% and 100% and increased with concentration of dichlorvos. Mortality was >90% from 0.2microg (a.i.) per fly and the LD(50) was 0.0399microg (a.i.)/fly, while the LD(90) was 0.1604microg (a.i.)/fly. The LD(90) values of the flies collected from the tsunami-hit villages were 3.5-3.9 times higher than that of the flies collected from Thirukanur. Fly abundance remained high in tsunami-hit villages with no marked reduction, suggesting that the flies had developed tolerance to dichlorvos. It is suggested that for an effective management of these resistant populations changing insecticides, application of unrelated insecticide, together with an appropriate environmental sanitation measure is necessary to keep the population under check.     

The Indian and Nepalese programmes of indoor residual spraying for the elimination of visceral leishmaniasis: performance and effectiveness

Although, when applied under controlled conditions in India and Nepal, indoor residual spraying (IRS) has been found to reduce sandfly densities significantly, it is not known if IRS will be as effective when applied generally in these countries, via the national programmes for the elimination of visceral leishmaniasis. The potential benefits and limitations of national IRS programmes for the control of sandflies were therefore evaluated in the districts of Vaishali (in the Indian state of Bihar), Sarlahi (in Nepal) and Sunsari (also in Nepal). The use of technical guidelines, levels of knowledge and skills related to spraying operations, insecticide bio-availability on the sprayed surfaces, concentrations of the insecticide on the walls of sprayed houses, insecticide resistance, and the effectiveness of spraying, in terms of reducing sandfly densities within sprayed houses (compared with those found in unsprayed sentinel houses or control villages) were all explored. It was observed that IRS programme managers, at district and subdistrict levels in India and Nepal, used the relevant technical guidelines and were familiar with the procedures for IRS operation. The performance of the spraying activities, however, showed important deficiencies. The results of bio-assays and the chemical analysis of samples from sprayed walls indicated substandard spraying and suboptimal concentrations of insecticide on sprayed surfaces. This was particularly obvious at one of the Nepali study sites (Sunsari district), where no significant vector reduction was achieved. Sandfly resistance to the insecticide used in India (DDT) was widespread but the potential vectors in Nepal remained very susceptible towards a pyrethroid similar to the one used there. The overall short-term effectiveness of IRS was found to be satisfactory in two of the three study sites (in terms of reduction in the densities of the sandfly vectors). Unfortunately, the medium-term evaluation, conducted 5 months after spraying, was probably made invalid by flooding or lime plastering in the study areas. Preparation for, and the monitoring of, the IRS operations against sandfly populations in India and Nepal need to be improved.     

防制中华白蛉对控制内脏利什曼病的效果追踪

目的　观察灭蛉与家犬药浴措施后对内脏利什曼病流行的影响。　方法　在四川省南坪县野外洞穴用奋斗呐(50mg/m2)滞留喷洒灭蛉和药浴 (2.5%溴氰菊脂可湿性粉剂250mg/L)家犬防治中华白蛉措施后,逐年进行野外洞穴白蛉密度观察和当地内脏利什曼病的流行病学调查。　结果　野外洞穴白蛉密度得到有效控制。家犬药浴和白蛉密度降低后,对控制内脏利什曼病起到一定作用。　结论　在内脏利什曼病流行区,采取家犬药浴和野外洞穴药物滞留喷洒灭蛉措施,对预防和阻断内脏利什曼病传播具有重要作用。     

Effect of Aerial Insecticide Spraying on West Nile Virus Disease—North-Central Texas, 2012

During 2012, four north-central Texas counties experienced high West Nile virus (WNV) disease incidence. Aerial insecticide spraying was conducted in two counties. To evaluate the effect of spraying on WNV disease, we calculated incidence rate ratios (IRRs) in treated and untreated areas by comparing incidence before and after spraying; for unsprayed areas, before and after periods were defined by using dates from a corresponding sprayed area. In treated areas, WNV neuroinvasive disease incidence before and after spraying was 7.31/100,000 persons and 0.28/100,000 persons, respectively; the IRR was 26.42 (95% confidence interval [CI]: 12.42–56.20). In untreated areas, the before and after incidence was 4.80/100,000 persons and 0.45/100,000 persons, respectively; the IRR was 10.57 (95% CI: 6.11–18.28). The ratio of IRRs was 2.50 (95% CI: 0.98–6.35). Disease incidence decreased in both areas, but the relative change was greater in aerial-sprayed areas.     

A comparison of use of a pyrethroid either for house spraying or for bednet treatment against malaria vectors

In an intensely malarious area in north-east Tanzania, microencapsulated lambdacyhalothrin was used in four villages for treatment of bednets (provided free of charge) and in another four villages the same insecticide was used for house spraying. Another four villages received neither intervention until the end of the trial but were monitored as controls. Bioassays showed prolonged persistence of the insecticidal residues. Light traps and ELISA testing showed reduction of the malaria vector populations and the sporozoite rates, leading to a reduction of about 90% in the entomological inoculation rate as a result of each treatment. Collections of blood fed mosquitoes showed no diversion from biting humans to biting animals. Incidence of re-infection was measured by weekly monitoring of cohorts of 60 children per village, after clearing pre-existing infection with chlorproguanil-dapsone. The vector control was associated with a reduction in probability of re-infection per child per week by 54–62%, with no significant difference between the two vector control methods. Cross-sectional surveys for fever, parasitaemia, haemoglobin and weight showed association of high parasitaemia with fever and anaemia and beneficial effects of each intervention in reducing anaemia. However, passive surveillance by resident health assistants showed no evidence for reduced prevalence of fever or parasitaemia. Net treatment consumed only about one sixth as much insecticide as house spraying and it was concluded that the former intervention would work out cheaper and nets were actively demanded by the villagers, whereas spraying was only passively assented to.     

Impact of residual spraying of Reldan against Anopheles culicifacies in selected villages of District Ghaziabad (Uttar pradesh), India

BACKGROUND & OBJECTIVES: Indoor residual spraying of Reldan 40% EC @ 0.5 and 1 g/m2 was done in Tatarpur and Chauna villages, respectively in Dhaulana PHC, Distt. Ghaziabad (U.P.) to evaluate its impact against Anopheles culicifacies and malaria incidence. Results were compared with that of Piyawali village which was taken as control area. METHODS: Four rounds of spray were done from 1999--2000 in human dwellings and cattlesheds in experimental villages. Entomological parameters--man hour density, parity rate, sporozoite rate, etc. were monitored using standard procedures. Epidemiological indicators such as SPR, SFR, cases/000, Pf/000 were also calculated. Cone bioassays as per WHO method were also carried out to assess the persistence of the insecticide on different surfaces. RESULTS: Entomological results revealed that spraying of reldan @ 0.5 g/m2 resulted in significant reduction in adult densities of An. culicifacies in sprayed villages over the control village. Spraying also resulted in reduction of percent parous females, reduction in malaria incidence (p < 0.05). INTERPRETATION & CONCLUSION: Reldan showed high efficacy @ 0.5 g/m2 in controlling the densities of An. culicifacies and malaria incidence. However, double dosage of reldan @ 1 g/m2 can be used for comprehensive vector control provided > 95% spray coverage is achieved.     

Effects of partial housing improvement and insecticide spraying on the reinfestation dynamics of Triatoma infestans in rural northwestern Argentina

The long-term effects on domiciliary reinfestation by Triatoma infestans of smoothing the plaster of indoor walls prior to insecticide application (in Amamá village) relative to only insecticide application (in Trinidad-Mercedes villages) were evaluated in rural northwestern Argentina from 1992 to 1997. All domestic and peridomestic areas of each house were sprayed with 2.5% suspension concentrate deltamethrin at 25 mg/m(2) in October 1992, and infestations were assessed by various methods every 6 months. Domiciliary infestation decreased from 72-88% in 1992 to 6-17% in late 1995, to increase moderately thereafter without returning to baseline rates. Peridomestic sites were the first in becoming reinfested, and reached more abundant T. infestans populations than domiciliary areas. Domiciliary infestation rates and bug abundances were not significantly different between communities during surveillance. Domiciliary infestation rates in well-plastered houses were very low (5-9%) and approximately stable until 1996, but in houses with regular or bad plaster they consistently increased from 5 to 19-21% in both communities. Logistic multiple regression analysis showed that the likelihood of domestic infestation assessed through householders' collections was significantly and positively associated with the occurrence of an infested peridomestic site in the respective house, the occurrence of high-density domestic infestations before interventions, and well-plastered walls in 1996. Combining insecticide spraying and partial improvement of walls controlled domestic infestations and transmission of Trypanosoma cruzi effectively, but was not sufficient to eliminate T. infestans from the study area or increase the effectiveness of careful chemical control.     

Indoor spray and windows screens effects on dengue vector density after space spraying in a field trial

Objective: To demonstrate the effect of indoor spraying and window screens on Aedes aegypti mosquito density after space spraying.Methods: A total of 141 households(the study houses) in six communities of Songkhla City, located in Songkhla Province of southern Thailand, were randomly selected and the adult Ae. aegypti populations were assessed pre-and post-insecticide spraying from March to October, 2014. Houses close to(within a 20 m radius) the study houses were analyzed using spatial analysis tools. The Aedes aegypti density in the study houses and house density index were compared with the density in the neighbouring houses, based on three spraying conditions:(i) unsprayed(ii) only outdoor sprayed and(iii) indoor plus outdoor sprayed. Results: Only spraying houses indoors was the most effective(P0.05). There was insufficient evidence that the source of the increase in the number of mosquitoes in unsprayed houses was due to their migration from neighbouring houses which had been sprayed. However, the study houses without screens on their windows were found to have a likely higher dengue vector population after spraying, but the difference was not significant.Conclusions: In dengue endemic areas, all houses should be fully screened and the number of houses ultra-low volume sprayed indoor plus outdoor should be increased with the cooperation of householders and communities during epidemics.     

采用加强传染源防治结合健康教育的新对策控制海南山区疟疾的试点研究

目的：探索与当前的流行病学条件相适应,并符合现代医学模式以及费用－效益原则的新的疟疾防治对策。方法：新的防治对策以高危村和高危人群为重点,结合健康教育和行为干预的综合性措施,包括：在高危村进行健康教育,对高危村和曾在山上住宿的高危人群进行集体药物治疗,对疟疾病例进行追踪治疗,但不采用传统的杀虫剂喷洒或浸泡蚊帐。结果：采取新的防治对策措施后群众的疟疾知识、蚊帐使用率和治疗依从性有所提高,各项疟疾指数迅速下降至较低水平。全乡的年疟疾带虫发病率从１９９４年的３．５％下降至１９９６年的１．１％和１９９７年的０．８％;恶性疟带虫发病率从１．０％分别下降至０．３％和０．３％;疟原虫率从１９９５年５月的７．２％下降至１９９６年１１月的２．１％和１９９７年１０月的１．２％,其中恶性疟原虫率则从１．２％下降至０．１％;没有疟疾病例的村比例从１８．６％上升到５４．２％,发病率大于５％的高危村从１４个减少至２个;费用－效益比率１９９５～１９９６年为１∶２．４,１９９７年为１∶４．４。结论：试点研究达到了预期效果,从而为进一步控制海南山区的疟疾提供了新的经验     

Spatio-temporal analysis of reinfestation by Triatoma infestans (Hemiptera: Reduviidae) following insecticide spraying in a rural community in northwestern Argentina

The spatio-temporal reinfestation patterns by Triatoma infestans following a blanket insecticide spraying in the rural community of Amama in northwestern Argentina were analyzed using a geographic information system, satellite imagery, and spatial statistics. Domestic and peridomestic reinfestation by triatomine bugs was monitored from 1993 to 1997. Triatoma infestans was detected at least once in 75% of 2,110 sites evaluated. The prevalence of sites positive at least once for T. infestans during the study period increased sharply from 1993-1995 (0.6-2.9%) to November 1997 (32%). The initial source of T. infestans was a pig corral in southern Amama one year post-spraying. Subsequent infestations were clustered around this initial focus at a distance of approximately 400 meters starting in 1995. In 1996, clustering was maximized in sites within the same or in neighboring compounds at distances of 25-175 meters. An effective control program on the community level will be based on the spraying of actual epicenters and sites within 450 meters of these epicenters to prevent the propagation of T. infestans.     

Distribution and ecological aspects of sand flies(Diptera:Psychodidae) species in Northeastern Iran

Objective:To determine both the distribution and the ecological characteristics of sand flies in Golestan Province,northeast of Iran in 2016.Methods:In this study,34 villages were selected based on their geographical conditions.Sticky paper traps were used for collecting the sand flies.Sampling was carried out in each of villages from May to November.In each village,60 traps for indoors and 60 for outdoors were monthly installed.The species of all collected sand flies were determined using approved morphological keys.Pearson coefficient correlation was used to find the relationship between the number of collected Phlebotomus papatasi from different villages and incidence rate of zoonotic cutaneous leishmaniasis as well as the number of positive cases of the disease.The altitude of the studied villages was extracted from digital elevation model of the area using GIS and vegetation cover density index of the province was extracted from Modis satellite imagery and distribution map of sand flies drown up.Results:Overall,5 428 sand flies were collected and identified,belonging to 18 species.Phlebotomus wenyoni was reported for the first time from the area in this study.The frequency of sand flies in the villages located in northeast of the Golestan province(the plateau area,lower altitude,arid and semi-arid climates,and lower vegetation cover density),were more than other villages in this province.There was a significant correlation between the number of collected Phlebotomus papatasi and incidence rate of the zoonotic cutaneous leishmaniasis cases in different villages(r=0.837,P=0.019) as well as the number of positive cases of the disease(r=0.688,P0.001).Conclusions:In the northeaster areas of Golestan Province which is known as the endemic foci of zoonotic cutaneous leishmaniasis,the abundance of sand flies were more and the conditions for their growth and development were more appropriate.     

上海闵行区2005～2008年蝇密度监测结果分析

采用笼诱法对闵行区2005~2008年蝇密度及其种群分布进行调查。闵行区蝇密度为0.32只/笼;优势蝇种为家蝇,构成比为41.63%;季节消长呈现5、9月两个季节高峰;农贸市场和小饭店以家蝇密度最高,居民小区和大型绿化以麻蝇密度最高。闵行区蝇密度呈现季节和区域分布特征。     

The impact of vector control on Triatoma dimidiata in the Guatemalan department of Jutiapa

In 2000, a national control operation against the triatomine vectors of Trypanosoma cruzi, based on house spraying with residual pyrethroid insecticides, was initiated in Guatemala. The impact of the operation against Triatoma dimidiata in the most heavily infested department, Jutiapa, was evaluated by pre- and post-spraying surveys of the vector populations. Of the houses checked for Tri. dimidiata in the baseline surveys, 18.3% were found to be infested with the bug, and in 12.1% of the villages investigated more than half of the houses were found to be infested. The later survey was conducted after 24,250 houses and their associated peridomestic structures (in the 336 villages in which >5% of the houses had been found infested in the pre-spraying survey) had been sprayed. As a result of just this one round of spraying, the mean percentage of houses found infested in each of the villages surveyed twice fell from 36.0% to 8.9%. After the spraying, the percentage of houses infested in each sprayed village was never >50%, and the houses in 35.2% of the sprayed villages that were re-surveyed appeared to have been completely cleared of triatomine bugs. Re-infestation and colonization were mainly observed inside the houses, probably indicating that some indoor bugs survived the spraying round. If the department of Jutiapa is to be freed and kept free from domestic infestation, the efficacy of the insecticide spraying needs to be improved, spraying techniques need to be reviewed, and insecticides need to be re-applied at regular intervals. An effective vector-surveillance system (preferably one in which community participation is encouraged) is also essential.     

Susceptibility to chemical insecticides of two Brazilian populations of the visceral leishmaniasis vector Lutzomyia longipalpis (Diptera: Psychodidae)

Objectives  To investigate the insecticide susceptibility of two geographically separated Lutzomyia longipalpis populations (Lapinha and Montes Claros) with different histories of insecticide exposure (i.e. no exposure and repeated exposure, respectively).
Methods  (i) Bioassay monitoring of sand fly survival over time when exposed to a range of insecticides; and (ii) analysis of the level of insecticide detoxification enzymes in individual sand flies caught at both study sites. Insecticides tested were the organophosphates malathion and fenitrothion and the pyrethroids λ-cyhalothrin, permethrin and deltamethrin.
Results  Survival analyses showed that whilst there was no overall significant difference in susceptibility of both populations to organophosphates, Lapinha sand flies were significantly more susceptible to pyrethroids than those from Montes Claros. Multiple regression analyses also showed that insecticide susceptibility in both locations varied with sand fly sex. The relative susceptibilities of the two sand fly populations to tested insecticides were also compared. Thus, Montes Claros sand flies were most susceptible to malathion, followed by fenitrothion, deltamethrin and permethrin. Those from Lapinha were most susceptible to λ-cyhalothrin, followed by malathion, permethrin, deltamethrin and fenitrothion. Biochemical analyses demonstrated that Montes Claros sand flies had significantly lower insecticide detoxification enzyme activity than Lapinha sand flies.
Conclusions  Our results are the first record of significantly reduced susceptibility to the insecticides used in control of wild populations of Lu. longipalpis. They demonstrate the importance of evaluating chemicals against this species by conventional bioassay and microplate assays before and during spraying programmes.     

Possible dengue sequential infection: dengue spread in a neighbourhood during the 1996/97 dengue-2 epidemic in French Polynesia

A DEN-2 epidemic occurred in French Polynesia from August 1996 to April 1997 after 7 years of DEN-3 circulation. The susceptible population constituted all expatriates and Polynesians under 21. In August 1996, two successive DEN-2 cases occurred in Teroma, a Tahitian neighbourhood close to the international airport of Tahiti. A serological prospective study of persons < 21 years living in Teroma was conducted. The study population was bled in September 1996, October 1996 and June 1997. Analysis of dengue spread in Teroma confirmed that dengue transmission occurs primarily in the house, thus vector control campaigns should incorporate focal insecticide spraying and systematic daily use of insecticide in houses. The evolution in time of the disease demonstrated that among a susceptible population, prevalence and incidence rates are related to the time of exposure, and consequently to age. Comparison of dengue incidence or dengue prevalence between populations therefore requires adjusted age rates. Most studies did not adjust for age, leading to the conclusion that DHF is more frequent during secondary than during primary dengue infection. Prospective studies taking into account the time of dengue exposure are necessary to confirm the sequential infection hypothesis.     

Acceptability and perceived side effects of insecticide indoor residual spraying under different resistance management strategies

OBJECTIVE:To assess household acceptability and perceived side effects of residual indoor pyrethroid (PYR), carbamate and organophosphate insecticides sprayed by annual rotation (ROT), spatial mosaic (MOS), and a single insecticide (DDT or PYR) in communities of the coastal plain of Chiapas, Mexico. MATERIAL AND METHODS: A questionnaire to assess the acceptability and perceived side effects of indoor insecticides was administered to one member of 30% of the families in eight villages of Chiapas. The association of different insecticide treatments with their responses was evaluated (Chi-square).The intensity of side effects indicated under different treatments was compared in an ordered logistic model, using a severity index as the response variable. RESULTS: Insecticide spraying as a probable cause of symptoms was identified by 2.1% of interviewees. A significantly high percentage of persons with blurred vision, dizziness, sneezing, coughing, numbness, watery eyes, and itching lived in villages under MOS and ROT and a high severity index was significantly associated with ROT treatment. Reduction of mosquito bites and cockroaches were the perceived main benefits, and most villagers that perceived no benefits lived in DDT treated villages. Most of the interviewees welcomed spraying (83.7%), but the smell and having to remove furniture from houses were the main arguments against it. CONCLUSIONS: Acceptability correlated with insecticide spray coverage, although the most frequent suggestion for improvement was to increase the understanding of the objectives of spraying in the communities. The frequency of side effects was low, but higher in localities where a combination of insecticides was applied. This is a limitation for the use of this type of resistance management strategy in public health.     

The use of aerial spraying to eliminate tsetse from the Okavango Delta of Botswana

In Botswana, 16,000 km(2) of the Okavango Delta were aerial sprayed five times with deltamethrin, applied at 0.26-0.3g/ha, to control Glossina morsitans centralis Machado (Diptera: Glossinidae) over a period of approximately 8 weeks. The northern half of the Delta (7180 km(2)) was sprayed in June-September 2001 and the southern half (8720 km(2)) in May-August 2002. A barrier (mean width approximately 10 km) of 12,000 deltamethrin-treated targets was deployed at the interface of these two blocks to prevent tsetse from invading from the southern to the northern block. Prior to spraying, the mean catches of tsetse from man fly-rounds were 44.6 round/day in the northern block and 101 in the southern. Between September 2002 and November 2005, surveys ( approximately 820 daily fly-rounds and approximately 2050 trap-days) in the northern and southern blocks failed to detect tsetse. Simulations of tsetse populations suggest that while spraying operations can reduce tsetse populations to levels that are difficult to detect by standard survey techniques, such populations will recover to densities >100 tsetse/km(2) after 1000 days, at which density there is a very high probability (>0.999) that the survey methods will catch at least one fly. Since none was caught, it is argued that tsetse have been eliminated from the Delta. The particular success of this operation in comparison to the 18 aerial spraying operations conducted in the Delta prior to 2001 is attributed to the application of an adequate dose of insecticide, the use of a GPS-based navigation system to ensure even application of insecticide, and the large size and spatial arrangement of the spray blocks coupled with the use of a barrier of targets which prevented tsetse from re-invading the northern sprayed block before the southern one was treated.