Cost-sharing strategies combining targeted public subsidies with private-sector delivery achieve high bednet coverage and reduced malaria transmission in Kilombero Valley, southern Tanzania

Background: Cost-sharing schemes incorporating modest targeted subsidies have promoted insecticide-treated nets (ITNs) for malaria prevention in the Kilombero Valley, southern Tanzania, since 1996. Here we evaluate resulting changes in bednet coverage and malaria transmission. Methods: Bednets were sold through local agents at fixed prices representing a 34% subsidy relative to full delivery cost. A further targeted subsidy of 15% was provided to vulnerable groups through discount vouchers delivered through antenatal clinics and regular immunizations. Continuous entomological surveys (2,376 trap nights) were conducted from October 2001 to September 2003 in 25 randomly-selected population clusters of a demographic surveillance system which monitored net coverage. Results: Mean net usage of 75 % (11,982/16,086) across all age groups was achieved but now-obsolete technologies available at the time resulted in low insecticide treatment rates. Malaria transmission remained intense but was substantially reduced: Compared with an exceptionally high historical mean EIR of 1481, even non-users of nets were protected (EIR [fold reduction] = 349 infectious bites per person per year [×4]), while the average resident (244 [×6]), users of typical nets (210 [×7]) and users of insecticidal nets (105 [×14]) enjoyed increasing benefits. Conclusion: Despite low net treatment levels, community-level protection was equivalent to the personal protection of an ITN. Greater gains for net users and non-users are predicted if more expensive long-lasting ITN technologies can be similarly promoted with correspondingly augmented subsidies. Cost sharing strategies represent an important option for national programmes lacking adequate financing to fully subsidize comprehensive ITN coverage

Genome-Wide Patterns of Gene Expression during Aging in the African Malaria Vector Anopheles gambiae

The primary means of reducing malaria transmission is through reduction in longevity in days of the adult female stage of the Anopheles vector. However, assessing chronological age is limited to crude physiologic methods which categorize the females binomially as either very young (nulliparous) or not very young (parous). Yet the epidemiologically relevant reduction in life span falls within the latter category. Age-grading methods that delineate chronological age, using accurate molecular surrogates based upon gene expression profiles, will allow quantification of the longevity-reducing effects of vector control tools aimed at the adult, female mosquito. In this study, microarray analyses of gene expression profiles in the African malaria vector Anopheles gambiae were conducted during natural senescence of females in laboratory conditions. Results showed that detoxification-related and stress-responsive genes were up-regulated as mosquitoes aged. A total of 276 transcripts had age-dependent expression, independently of blood feeding and egg laying events. Expression of 112 (40.6%) of these transcripts increased or decreased monotonically with increasing chronologic age. Seven candidate genes for practical age assessment were tested by quantitative gene amplification in the An. gambiae G3 strain in a laboratory experiment and the Mbita strain in field enclosures set up in western Kenya under conditions closely resembling natural ones. Results were similar between experiments, indicating that senescence is marked by changes in gene expression and that chronological age can be gauged accurately and repeatedly with this method. These results indicate that the method may be suitable for accurate gauging of the age in days of field-caught, female An. gambiae

Non-destructive determination of age and species of Anopheles gambiae s.l. using near-infrared spectroscopy

Determining malaria vector species and age is crucial to measure malaria risk. Although different in ecology and susceptibility to control, the African malaria vectors Anopheles gambiae sensu stricto and An. arabiensis are morphologically similar and can be differentiated only by molecular techniques. Furthermore, few reliable methods exist to estimate the age of these vectors, which is a key predictor of malaria transmission intensity. We evaluated the use of near-infrared spectroscopy (NIRS) to determine vector species and age. This non-destructive technique predicted the species of field-collected mosquitoes with approximately 80% accuracy and predicted the species of laboratory-reared insects with almost 100% accuracy. The relative age of young or old females was predicted with approximately 80% accuracy, and young and old insects were predicted with ≥ 90% accuracy. For applications where rapid assessment of the age structure and species composition of wild vector populations is needed, NIRS offers a valuable alternative to traditional methods. Copyright © 2009 by The American Society of Tropical Medicine and Hygiene

Interdependence of domestic malaria prevention measures and mosquito-human interactions in urban Dar es Salaam, Tanzania

Background: Successful malaria vector control depends on understanding behavioural interactions between mosquitoes and humans, which are highly setting-specific and may have characteristic features in urban environments. Here mosquito biting patterns in Dar es Salaam, Tanzania are examined and the protection against exposure to malaria transmission that is afforded to residents by using an insecticide-treated net (ITN) is estimated. Methods: Mosquito biting activity over the course of the night was estimated by human landing catch in 216 houses and 1,064 residents were interviewed to determine usage of protection measures and the proportion of each hour of the night spent sleeping indoors, awake indoors, and outdoors. Results: Hourly variations in biting activity by members of the Anopheles gambiae complex were consistent with classical reports but the proportion of these vectors caught outdoors in Dar es Salaam was almost double that of rural Tanzania. Overall, ITNs confer less protection against exophagic vectors in Dar es Salaam than in rural southern Tanzania (59% versus 70%). More alarmingly, a biting activity maximum that precedes 10pm and much lower levels of ITN protection against exposure (38%) were observed for Anopheles arabiensis, a vector of modest importance locally, but which predominates transmission in large parts of Africa. Conclusions: In a situation of changing mosquito and human behaviour, ITNs may confer lower, but still useful, levels of personal protection which can be complemented by communal transmission suppression at high coverage. Mosquito-proofing houses appeared to be the intervention of choice amongst residents and further options for preventing outdoor transmission include larviciding and environmental management

Crude biting rate estimates for mosquitoes (B) and monthly rainfall measurements in the Kilombero Valley during the study period

<p><b>Copyright information:</b></p><p>Taken from "Cost-sharing strategies combining targeted public subsidies with private-sector delivery achieve high bednet coverage and reduced malaria transmission in Kilombero Valley, southern Tanzania"</p><p>http://www.biomedcentral.com/1471-2334/7/121</p><p>BMC Infectious Diseases 2007;7():121-121.</p><p>Published online 25 Oct 2007</p><p>PMCID:PMC2211306.</p><p></p> Thin solid line: ; thick solid line: ; thin dotted line: species

Relationship between reported net usage (proportion of people sleeping under nets) and net ownership (number of nets per person)

<p><b>Copyright information:</b></p><p>Taken from "Cost-sharing strategies combining targeted public subsidies with private-sector delivery achieve high bednet coverage and reduced malaria transmission in Kilombero Valley, southern Tanzania"</p><p>http://www.biomedcentral.com/1471-2334/7/121</p><p>BMC Infectious Diseases 2007;7():121-121.</p><p>Published online 25 Oct 2007</p><p>PMCID:PMC2211306.</p><p></p

The frequency distribution of the age of nets in houses sampled for mosquitoes () and () a 15-year old polyethylene net still in use in Namwawala village, July 2004

<p><b>Copyright information:</b></p><p>Taken from "Cost-sharing strategies combining targeted public subsidies with private-sector delivery achieve high bednet coverage and reduced malaria transmission in Kilombero Valley, southern Tanzania"</p><p>http://www.biomedcentral.com/1471-2334/7/121</p><p>BMC Infectious Diseases 2007;7():121-121.</p><p>Published online 25 Oct 2007</p><p>PMCID:PMC2211306.</p><p></p> This net was verified to still be in use at the time of publication, 18 years after initial distribution

Relationship between reported net usage (proportion of people sleeping under nets) and Entomological Inoculation Rate (EIR) experienced by non users and net usage (open circles: ; open squares: ; solid diamonds: Total)

<p><b>Copyright information:</b></p><p>Taken from "Cost-sharing strategies combining targeted public subsidies with private-sector delivery achieve high bednet coverage and reduced malaria transmission in Kilombero Valley, southern Tanzania"</p><p>http://www.biomedcentral.com/1471-2334/7/121</p><p>BMC Infectious Diseases 2007;7():121-121.</p><p>Published online 25 Oct 2007</p><p>PMCID:PMC2211306.</p><p></p

The distribution of sex and physiological status of mosquitoes caught in CDC light traps during the course of the study

<p><b>Copyright information:</b></p><p>Taken from "Cost-sharing strategies combining targeted public subsidies with private-sector delivery achieve high bednet coverage and reduced malaria transmission in Kilombero Valley, southern Tanzania"</p><p>http://www.biomedcentral.com/1471-2334/7/121</p><p>BMC Infectious Diseases 2007;7():121-121.</p><p>Published online 25 Oct 2007</p><p>PMCID:PMC2211306.</p><p></p