Michael Coleman

Using the SaTScan method to detect local malaria clusters for guiding malaria control programmes

BackgroundMpumalanga Province, South Africa is a low malaria transmission area that is subject to malaria epidemics. SaTScan methodology was used by the malaria control programme to detect local malaria clusters to assist disease control planning. The third season for case cluster identification overlapped with the first season of implementing an outbreak identification and response system in the area.MethodsSaTScan™ software using the Kulldorf method of retrospective space-time permutation and the Bernoulli purely spatial model was used to identify malaria clusters using definitively confirmed individual cases in seven towns over three malaria seasons. Following passive case reporting at health facilities during the 2002 to 2005 seasons, active case detection was carried out in the communities, this assisted with determining the probable source of infection. The distribution and statistical significance of the clusters were explored by means of Monte Carlo replication of data sets under the null hypothesis with replications greater than 999 to ensure adequate power for defining clusters.Results and discussionSaTScan detected five space-clusters and two space-time clusters during the study period. There was strong concordance between recognized local clustering of cases and outbreak declaration in specific towns. Both Albertsnek and Thambokulu reported malaria outbreaks in the same season as space-time clusters. This synergy may allow mutual validation of the two systems in confirming outbreaks demanding additional resources and cluster identification at local level to better target resources.ConclusionExploring the clustering of cases assisted with the planning of public health activities, including mobilizing health workers and resources. Where appropriate additional indoor residual spraying, focal larviciding and health promotion activities, were all also carried out.

Insecticide resistance and the future of malaria control in Zambia.

Background In line with the Global trend to improve malaria control efforts a major campaign of insecticide treated net distribution was initiated in 1999 and indoor residual spraying with DDT or pyrethroids was reintroduced in 2000 in Zambia. In 2006, these efforts were strengthened by the Presidents Malaria Initiative. This manuscript reports on the monitoring and evaluation of these activities and the potential impact of emerging insecticide resistance on disease transmission. Methods Mosquitoes were captured daily through a series of 108 window exit traps located at 18 sentinel sites. Specimens were identified to species and analyzed for sporozoites. Adult Anopheles mosquitoes were collected resting indoors and larva collected in breeding sites were reared to F1 and F0 generations in the lab and tested for insecticide resistance following the standard WHO susceptibility assay protocol. Annual cross sectional household parasite surveys were carried out to monitor the impact of the control programme on prevalence of Plasmodium falciparum in children aged 1 to 14 years. Results A total of 619 Anopheles gambiae s.l. and 228 Anopheles funestus s.l. were captured from window exit traps throughout the period, of which 203 were An. gambiae malaria vectors and 14 An. funestus s.s.. In 2010 resistance to DDT and the pyrethroids deltamethrin, lambda-cyhalothrin and permethrin was detected in both An. gambiae s.s. and An. funestus s.s.. No sporozoites were detected in either species. Prevalence of P. falciparum in the sentinel sites remained below 10% throughout the study period. Conclusion Both An. gambiae s.s. and An. funestus s.s. were controlled effectively with the ITN and IRS programme in Zambia, maintaining a reduced disease transmission and burden. However, the discovery of DDT and pyrethroid resistance in the country threatens the sustainability of the vector control programme.

Insecticide Resistance in Anopheles funestus (Diptera: Culicidae) from Mozambique

Malaria control in southern Mozambique is currently by indoor residual carbamate insecticide treatment, with pyrethroid-treated bed-nets distributed to pregnant women and children under five in northern Mozambique. The susceptibility of Anopheles funestus s.s. to pyrethroid, carbamate, organochlorine, and organophosphorus insecticides was determined by World Health Organization adult mosquito susceptibility tests at 19 localities in Mozambique, from March 2000 to July 2002. Biochemical assays were carried out on mosquitoes from the same families to detect shifts in the quantity or activity of enzyme families involved in insecticide detoxification. An. funestus from all localities remained fully susceptible to DDT and the organophosphorus insecticide malathion. A high level of pyrethroid resistance was detected in An. funestus populations in southern Mozambique. An. funestus outside Maputo province were still susceptible to pyrethroids. An. funestus from six localities also were resistant to carbamate insecticides propoxur and bendiocarb. Both pyrethroid and carbamate resistance occurred in five of these six localities. Mosquitoes from five of the localities with elevated p450 estimates, compared with the insecticide-susceptible Durban strain, were pyrethroid-resistant. The only exception to this trend was Mozal, which had elevated p450 estimates but full pyrethroid susceptibility by bioassay. The lack of cross-resistance between pyrethroids and DDT in Mozambican An. funestus suggests that a kdr-type target site resistance mechanism has not been selected. Low levels of insecticide-insensitive acetylcholinesterase, the target site for carbamates and organophosphates, were found in all populations tested. The high level of metabolically based pyrethroid resistance has implications for current malaria control programs in Mozambique.

Insecticide Resistance in Anopheles arabiensis and Anopheles gambiae from Mozambique

Abstract Malaria control in the southern part of Mozambique is currently by indoor residual spraying with a carbamate insecticide and by pyrethroid-treated bed-nets distributed to pregnant women and children under five in northern Mozambique. The susceptibility of Anopheles gambiae s.s. and Anopheles arabiensis Patton to pyrethroid, carbamate, organochlorine, and organophosphorus insecticides was determined by World Health Organization adult mosquito susceptibility tests at 17 localities in Mozambique, from March 2000 to July 2002. Biochemical assays were carried out on mosquitoes from the same families to detect shifts in the quantity or activity of enzyme families involved in insecticide detoxification. An. gambiae s.s. from all localities remained fully susceptible to DDT and the organophosphorus insecticide malathion. A low level of pyrethroid resistance was detected in populations in southern Mozambique. Populations outside Maputo province were still susceptible to pyrethroids. Low level resistance to the carbamate propoxur also was detected in An. arabiensis from two localities. Mosquitoes from five of the localities had elevated p450 estimates, compared with the insecticide susceptible Durban strain. The lack of cross-resistance between pyrethroids and DDT in Mozambican populations suggests that a kdr-type target site resistance mechanism has not been selected. Increased frequencies of insecticide insensitive acetylcholinesterase, the target site for carbamates and organophosphates, were found in 16 of the populations tested. Although vector control with bendiocarb is not being compromised by the presence of the acetylcholinesterase mechanism alone, the high level of insensitive acetylcholinesterase unless sensibly managed may have long-term implications for malaria control programs in Mozambique.

Impact of pyrethroid resistance on operational malaria control in Malawi

The impact of insecticide resistance on insect-borne disease programs is difficult to quantify. The possibility of eliminating malaria in high-transmission settings is heavily dependent on effective vector control reducing disease transmission rates. Pyrethroids are the dominant insecticides used for malaria control, with few options for their replacement. Their failure will adversely affect our ability to control malaria. Pyrethroid resistance has been selected in Malawi over the last 3 y in the two major malaria vectors Anopheles gambiae and Anopheles funestus, with a higher frequency of resistance in the latter. The resistance in An. funestus is metabolically based and involves the up-regulation of two duplicated P450s. The same genes confer resistance in Mozambican An. funestus, although the levels of up-regulation differ. The selection of resistance over 3 y has not increased malaria transmission, as judged by annual point prevalence surveys in 1- to 4-y-old children. This is true in areas with long-lasting insecticide-treated nets (LLINs) alone or LLINs plus pyrethroid-based insecticide residual spraying (IRS). However, in districts where IRS was scaled up, it did not produce the expected decrease in malaria prevalence. As resistance increases in frequency from this low initial level, there is the potential for vector population numbers to increase with a concomitant negative impact on control efficacy. This should be monitored carefully as part of the operational activities in country.

Use of Google Earth to strengthen public health capacity and facilitate management of vector-borne diseases in resource-poor environments.

OBJECTIVE Novel, inexpensive solutions are needed for improved management of vector-borne and other diseases in resource-poor environments. Emerging free software providing access to satellite imagery and simple editing tools (e.g. Google Earth) complement existing geographic information system (GIS) software and provide new opportunities for: (i) strengthening overall public health capacity through development of information for city infrastructures; and (ii) display of public health data directly on an image of the physical environment. METHODS We used freely accessible satellite imagery and a set of feature-making tools included in the software (allowing for production of polygons, lines and points) to generate information for city infrastructure and to display disease data in a dengue decision support system (DDSS) framework. FINDINGS Two cities in Mexico (Chetumal and Merida) were used to demonstrate that a basic representation of city infrastructure useful as a spatial backbone in a DDSS can be rapidly developed at minimal cost. Data layers generated included labelled polygons representing city blocks, lines representing streets, and points showing the locations of schools and health clinics. City blocks were colour-coded to show presence of dengue cases. The data layers were successfully imported in a format known as shapefile into a GIS software. CONCLUSION The combination of Google Earth and free GIS software (e.g. HealthMapper, developed by WHO, and SIGEpi, developed by PAHO) has tremendous potential to strengthen overall public health capacity and facilitate decision support system approaches to prevention and control of vector-borne diseases in resource-poor environments.

Developing an Evidence-Based Decision Support System for Rational Insecticide Choice in the Control of African Malaria Vectors

Abstract The emergence of Anopheles species resistant to insecticides widely used in vector control has the potential to impact directly on the control of malaria. This may have a particularly dramatic effect in Africa, where pyrethroids impregnated onto bed-nets are the dominant insecticides used for vector control. Because the same insecticides are used for crop pests, the extensive use and misuse of insecticides for agriculture has contributed to the resistance problem in some vectors. The potential for resistance to develop in African vectors has been apparent since the 1950s, but the scale of the problem has been poorly documented. A geographical information system-based decision support system for malaria control has recently been established in Africa and used operationally in Mozambique. The system incorporates climate data and disease transmission rates, but to date it has not incorporated spatial or temporal data on vector abundance or insecticide resistance. As a first step in incorporating this information, available published data on insecticide resistance in Africa has now been collated and incorporated into this decision support system. Data also are incorporated onto the openly available Mapping Malaria Risk in Africa (MARA) Web site (http://www.mara.org.za). New data, from a range of vector population-monitoring initiatives, can now be incorporated into this open access database to allow a spatial understanding of resistance distribution and its potential impact on disease transmission to benefit vector control programs.

How much does malaria vector control quality matter: the epidemiological impact of holed nets and inadequate indoor residual spraying.

Background Insecticide treated nets (ITN) and indoor residual spraying (IRS) are the two pillars of malaria vector control in Africa, but both interventions are beset by quality and coverage concerns. Data from three control programs were used to investigate the impact of: 1) the physical deterioration of ITNs, and 2) inadequate IRS spray coverage, on their respective protective effectiveness. Methods Malaria indicator surveys were carried out in 2009 and 2010 in Bioko Island, mainland Equatorial Guinea and Malawi to monitor infection with P.falciparum in children, mosquito net use, net condition and spray status of houses. Nets were classified by their condition. The association between infection and quality and coverage of interventions was investigated. Results There was reduced odds of infection with P.falciparum in children sleeping under ITNs that were intact (Odds ratio (OR): 0.65, 95% CI: 0.55–0.77 and OR: 0.81, 95% CI: 0.56–1.18 in Equatorial Guinea and in Malawi respectively), but the protective effect became less with increasingly worse condition of the net. There was evidence for a linear trend in infection per category increase in deterioration of nets. In Equatorial Guinea IRS offered protection to those in sprayed and unsprayed houses alike when neighbourhood spray coverage was high (≥80%) compared to those living in areas of low IRS coverage (<20%), regardless of whether the house they lived in was sprayed or not (adjusted OR = 0.54, 95% CI 0.33–0.89). ITNs provided only personal protection, offering no protection to non users. Although similar effects were seen in Malawi, the evidence was much weaker than in Equatorial Guinea. Conclusions Universal coverage strategies should consider policies for repair and replacement of holed nets and promote the care of nets by their owners. IRS programs should ensure high spray coverage since inadequate coverage gives little or no protection at all.

The emergence of insecticide resistance in central Mozambique and potential threat to the successful indoor residual spraying malaria control programme

BackgroundMalaria vector control by indoor residual spraying was reinitiated in 2006 with DDT in Zambézia province, Mozambique. In 2007, these efforts were strengthened by the Presidents Malaria Initiative. This manuscript reports on the monitoring and evaluation of this programme as carried out by the Malaria Decision Support Project.MethodsMosquitoes were captured daily through a series of 114 window exit traps located at 19 sentinel sites, identified to species and analysed for sporozoites. Anopheles mosquitoes were collected resting indoors and tested for insecticide resistance following the standard WHO protocol. Annual cross sectional household parasite surveys were carried out to monitor the impact of the control programme on prevalence of Plasmodium falciparum in children aged 1 to 15 years.ResultsA total of 3,769 and 2,853 Anopheles gambiae s.l. and Anopheles funestus, respectively, were captured from window exit traps throughout the period. In 2010 resistance to the pyrethroids lambda-cyhalothrin and permethrin and the carbamate, bendiocarb was detected in An. funestus. In 2006, the sporozoite rate in An. gambiae s.s. was 4% and this reduced to 1% over 4 rounds of spraying. The sporozoite rate for An. funestus was also reduced from 2% to 0 by 2008. Of the 437 Anopheles arabiensis identified, none were infectious. Overall prevalence of P. falciparum in the sentinel sites fell from 60% to 32% between October 2006 and October 2008.ConclusionBoth An. gambiae s.s. and An. funestus were controlled effectively with the DDT-based IRS programme in Zambézia, reducing disease transmission and burden. However, the discovery of pyrethroid resistance in the province and Mozambiques policy change away from DDT to pyrethroids for IRS threatens the gains made here.

DDT-based indoor residual spraying suboptimal for visceral leishmaniasis elimination in India

Significance Visceral leishmaniasis (VL), also known as kala-azar, is a major parasitic disease on the Indian subcontinent, with 85% of the disease incidence in India. As with malaria, indoor residual spraying (IRS) can be used to control and, ultimately, eliminate VL as a public health problem. However, in India, widespread resistance to dichlorodiphenyltrichloroethane (DDT), the insecticide used, combined with poor quality assurance (QA) of IRS and limited entomological surveillance, is hindering the VL elimination effort. Here, we present entomological abundance and insecticide resistance data and data arising from QA of IRS to explore these issues and establish an evidence base for improving the Indian VL elimination program. Unless these issues are addressed, the South Asian VL elimination effort will fail. Indoor residual spraying (IRS) is used to control visceral leishmaniasis (VL) in India, but it is poorly quality assured. Quality assurance was performed in eight VL endemic districts in Bihar State, India, in 2014. Residual dichlorodiphenyltrichloroethane (DDT) was sampled from walls using Bostik tape discs, and DDT concentrations [grams of active ingredient per square meter (g ai/m2)] were determined using HPLC. Pre-IRS surveys were performed in three districts, and post-IRS surveys were performed in eight districts. A 20% threshold above and below the target spray of 1.0 g ai/m2 was defined as “in range.” The entomological assessments were made in four districts in IRS and non-IRS villages. Vector densities were measured: pre-IRS and 1 and 3 mo post-IRS. Insecticide susceptibility to 4% DDT and 0.05% deltamethrin WHO-impregnated papers was determined with wild-caught sand flies. The majority (329 of 360, 91.3%) of pre-IRS samples had residual DDT concentrations of <0.1 g ai/m2. The mean residual concentration of DDT post-IRS was 0.37 g ai/m2; 84.9% of walls were undersprayed, 7.4% were sprayed in range, and 7.6% were oversprayed. The abundance of sand flies in IRS and non-IRS villages was significantly different at 1 mo post-IRS only. Sand flies were highly resistant to DDT but susceptible to deltamethrin. The Stockholm Convention, ratified by India in 2006, calls for the complete phasing out of DDT as soon as practical, with limited use in the interim where no viable IRS alternatives exist. Given the poor quality of the DDT-based IRS, ready availability of pyrethroids, and susceptibility profile of Indian sand flies, the continued use of DDT in this IRS program is questionable.