Background: Understanding the factors which determine a household's or individual's risk of malar... more Background: Understanding the factors which determine a household's or individual's risk of malaria infection is important for targeting control interventions at all intensities of transmission. Malaria ecology in Tanzania appears to have reduced over recent years. This study investigated potential risk factors and clustering in face of changing infection dynamics. Methods: Household survey data were collected in villages of rural Muheza district. Children aged between six months and thirteen years were tested for presence of malaria parasites using microscopy. A multivariable logistic regression model was constructed to identify significant risk factors for children. Geographical information systems combined with global positioning data and spatial scan statistic analysis were used to identify clusters of malaria. Results: Using an insecticide-treated mosquito net of any type proved to be highly protective against malaria (OR 0.75, 95% CI 0.59-0.96). Children aged five to thirteen years were at higher risk of having malaria than those aged under five years (OR 1.71, 95% CI 1.01-2.91). The odds of malaria were less for females when compared to males (OR 0.62, 95% CI 0.39-0.98). Two spatial clusters of significantly increased malaria risk were identified in two out of five villages. Conclusions: This study provides evidence that recent declines in malaria transmission and prevalence may shift the age groups at risk of malaria infection to older children. Risk factor analysis provides support for universal coverage and targeting of long-lasting insecticide-treated nets (LLINs) to all age groups. Clustering of cases indicates heterogeneity of risk. Improved targeting of LLINs or additional supplementary control interventions to high risk clusters may improve outcomes and efficiency as malaria transmission continues to fall under intensified control.
*<p>Superscript letter indicates statistical significance of blood-feeding inhibition in tr... more *<p>Superscript letter indicates statistical significance of blood-feeding inhibition in treatment arm as compared to the control arm; a = <i>P</i><0.001, b = <i>P</i><0.01, c = <i>P</i><0.05, d = <i>P</i>>0.05.</p
<p>Map showing the location of the field stations, in Moshi and Muheza, north-eastern Tanza... more <p>Map showing the location of the field stations, in Moshi and Muheza, north-eastern Tanzania.</p
*<p>Superscript letter indicate statistical significance as compared to the control arm; a ... more *<p>Superscript letter indicate statistical significance as compared to the control arm; a = <i>P</i><0.001, b = <i>P</i><0.01, c = <i>P</i><0.05, d = <i>P</i>>0.05.</p
An experimental hut evaluation of Olyset ® nets against anopheline mosquitoes after seven years u... more An experimental hut evaluation of Olyset ® nets against anopheline mosquitoes after seven years use in Tanzanian villages
Background: Despite considerable reductions in malaria achieved by scaling-up long-lasting insect... more Background: Despite considerable reductions in malaria achieved by scaling-up long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS), maintaining sustained community protection remains operationally challenging. Increasing insecticide resistance also threatens to jeopardize the future of both strategies. Non-pyrethroid insecticidetreated wall lining (ITWL) may represent an alternate or complementary control method and a potential tool to manage insecticide resistance. To date no study has demonstrated whether ITWL can reduce malaria transmission nor provide additional protection beyond the current best practice of universal coverage (UC) of LLINs and prompt case management.
Long-lasting insecticidal nets (LN) are an effective tool for malaria prevention. The World Healt... more Long-lasting insecticidal nets (LN) are an effective tool for malaria prevention. The World Health Organization Pesticide Evaluation Scheme has established evaluation criteria to facilitate registration for public use. A household randomised trial was conducted in Tanzania according to WHOPES Phase III procedures to evaluate the alpha-cypermethrin coated Interceptor® LN (BASF) over three years' use. Outcomes were calibrated against results of Phase II experimental hut trials. Interceptor LN (200 mg/m(2) alpha-cypermethrin) and conventionally treated nets CTN (40 mg/m(2) alpha-cypermethrin) were randomly distributed to 934 households. At 6-monthly intervals, household surveys recorded net use, durability, adverse effects, user acceptance and washing practices. Concurrently, 30 nets of each type were collected and tested for knock-down and kill of Anopheles gambiae mosquitoes in cone and tunnel bioassays. Alpha-cypermethrin content of nets was assessed annually. At 12 months 97 % ...
Background: Malaria prevalence and transmission intensity in Tanzania is heterogeneous with spati... more Background: Malaria prevalence and transmission intensity in Tanzania is heterogeneous with spatial and temporal variations between geographical areas and ecological systems. The objective of this study was to determine the prevalence of malaria, anaemia and nutritional status in relation to livelihoods, ecosystem and health systems in Kilosa District in central Tanzania. Methods: This study was conducted in four villages, two characterised by rice irrigation ecosystem and the other two by dry savannah ecosystem and pastoral livelihoods. In each ecosystem, one of the villages had a healthcare facility. Schoolchildren were screened for malaria infection using malaria rapid diagnostic test (mRDT) and microscopy and they were assessed for their anaemia and nutritional statuses. Results: A total of 1,019 school children (age = 4-16 years) were screened for malaria infection. The overall prevalence of Plasmodium falciparum infection was 10.6 % and 4.5 % by mRDT and microscopy, respectively. Children from pastoral villages had lower (2.9 %) prevalence of malaria than their counterparts (18.2 %) in the rice irrigation villages. A significantly high risk of malaria was observed among children in rice irrigation than in the pastoral ecosystem (OR: 0.13; 95%CI 0.07, 0.23). Children living in areas with health care facilities had a low odd of malaria infection by 45 % (OR: 0.55; 95 % CI = 0.35, 0.86). Overall, the prevalence of anaemia in the district was 43.4 % (n = 775); and 58.3 % of those with severe anaemia were among children from the pastoral villages. Anaemia was significantly higher among children not using mosquito nets (p = 0.049); and among those with malaria infection (p <0.001). The majority (96 %) of the children had Body Mass Index less than 18.5 kg/m 2 which indicate high proportion of underweight. Conclusion: There are significant variations in the risk of acquiring malaria infection between different ecosystems and livelihoods. These findings suggest that malaria control programmes must take into account ecosystems and livelihoods of the targeted population through an integrated management of malaria and nutrition approach.
Insecticide-treated nets are the primary method of preventing malaria. To remain effective, the p... more Insecticide-treated nets are the primary method of preventing malaria. To remain effective, the pyrethroid insecticide must withstand multiple washes over the lifetime of the net. ICON® Maxx is a 'dip-it-yourself' kit for long-lasting treatment of polyester nets. The twin-sachet kit contains a slow-release capsule suspension of lambda-cyhalothrin plus binding agent. To determine whether ICON Maxx meets the standards required by the World Health Organization Pesticide Evaluation Scheme (WHOPES), the efficacy and wash fastness of ICON Maxx was evaluated against wild, free-flying anopheline mosquitoes. ICON Maxx was subjected to bioassay evaluation and experimental hut trial against pyrethroid-susceptible Anopheles gambiae, Anopheles arabiensis and Anopheles funestus. Mosquito mortality, blood feeding inhibition and personal protection were compared between untreated nets, conventional lambda-cyhalothrin treated nets (CTN) washed either four times (cut-off threshold) or 20 time...
Tropical Medicine & International Health, 2008
SummaryObjective To determine the efficacy of chlorfenapyr against Anopheles arabiensis and Cule... more SummaryObjective To determine the efficacy of chlorfenapyr against Anopheles arabiensis and Culex quinquefasciatus in East Africa and to identify effective dosages for net treatment in comparison with the commonly used pyrethroid deltamethrin.Methods Chlorfenapyr was evaluated on bed nets in experimental huts against A. arabiensis and C. quinquefasciatus in Northern Tanzania, at application rates of 100–500 mg/m2.Results In experimental huts, mortality rates in A. arabiensis were high (46.0–63.9%) for all dosages of chlorfenapyr and were similar to that of deltamethrin‐treated nets. Mortality rates in C. quinquefasciatus were higher for chlorfenapyr than for deltamethrin. Despite a reputation for being slow acting, >90% of insecticide‐induced mortality in laboratory tunnel tests and experimental huts occurred within 24 h, and the speed of killing was no slower than for deltamethrin‐treated nets.Conclusions Chlorfenapyr induced low irritability and knockdown, which explains th...
This study was carried out to understand the role social determinants and health seeking behavior... more This study was carried out to understand the role social determinants and health seeking behavior among rice farming and pastoral communities in Kilosa District in central Tanzania. The study involved four villages; two with rice farming communities while the other two with pastoral communities. In each village, heads of households or their spouses were interviewed to seek information on livelihoods activities, knowledge and practices on malaria and its preventions. A total of 471 individuals (males=38.9%; females=61.1%) were interviewed. Only 23.5% of the respondents had adequate knowledge on malaria. Fifty-six percent of the respondents could not associate any livelihood activity with malaria transmission. Majority (79%) of the respondents believed that most of fevers were due to malaria; this was higher among the pastoral (81.7%) than rice farming communities (76.1%) (p=0.038). Cases of fever were significantly higher in households with non-educated (31.2%) than educated responde...
Tropical Medicine & International Health, 2014
ObjectiveInsecticide resistance molecular markers can provide sensitive indicators of resistance ... more ObjectiveInsecticide resistance molecular markers can provide sensitive indicators of resistance development in Anopheles vector populations. Assaying these makers is of paramount importance in the resistance monitoring programme. We investigated the presence and distribution of knock‐down resistance (kdr) mutations in Anopheles gambiae s.l. in Tanzania.MethodsIndoor‐resting Anopheles mosquitoes were collected from 10 sites and tested for insecticide resistance using the standard WHO protocol. Polymerase chain reaction‐based molecular diagnostics were used to genotype mosquitoes and detect kdr mutations.ResultsThe An. gambiae tested were resistance to lambdacyhalothrin in Muheza, Arumeru and Muleba. Out of 350 An. gambiae s.l. genotyped, 35% were An. gambiae s.s. and 65% An. arabiensis. L1014S and L1014F mutations were detected in both An. gambiae s.s. and An. arabiensis. L1014S point mutation was found at the allelic frequency of 4–33%, while L1014F was at the allelic frequency 6–4...
Three insecticides -the pyrethroid deltamethrin, the carbamate carbosulfan and the organophosphat... more Three insecticides -the pyrethroid deltamethrin, the carbamate carbosulfan and the organophosphate chlorpyrifos-methyl -were tested on mosquito nets in experimental huts to determine their potential for introduction as malaria control measures. Their behavioural effects and efficacy were examined in Anopheles gambiae Giles s.s. (Diptera: Culicidae) and Anopheles funestus Giles s.s. in Muheza, Tanzania, and in Anopheles arabiensis Patton and Culex quinquefasciatus Say in Moshi, Tanzania. A standardized dosage of 25 mg/m 2 plus high dosages of carbosulfan (50 mg/m 2 , 100 mg/m 2 and 200 mg/m 2 ) and chlorpyrifos-methyl (100 mg/m 2 ) were used to compare the three types of insecticide. At 25 mg/m 2 , the rank order of the insecticides for insecticide-induced mortality in wild An. gambiae and An. funestus was, respectively, carbosulfan (88%, 86%) > deltamethrin (79%, 78%) > chlorpyrifos-methyl (35%, 53%). The rank order of the insecticides for blood-feeding inhibition (reduction in the number of blood-fed mosquitoes compared with control) in wild An. gambiae and An. funestus was deltamethrin > chlorpyrifos-methyl > carbosulfan. Carbosulfan was particularly toxic to endophilic anophelines at 200 mg/m 2 , killing 100% of An. gambiae and 98% of An. funestus that entered the huts. It was less effective against the more exophilic An. arabiensis (67% mortality) and carbamate-resistant Cx quinquefasciatus (36% mortality). Carbosulfan deterred anophelines from entering huts, but did not deter carbamate-resistant Cx quinquefasciatus. Deltamethrin reduced the proportion of insects engaged in blood-feeding, probably as a consequence of contact irritancy, whereas carbosulfan seemed to provide personal protection through deterred entry or perhaps a spatial repellent action. Any deployment of carbosulfan as an individual treatment on nets should be carried out on a large scale to reduce the risk of diverting mosquitoes to unprotected individuals. Chlorpyrifos-methyl was inferior to deltamethrin in terms of mortality and blood-feeding inhibition and would be better deployed on a net in combination with a pyrethroid to control insecticide-resistant mosquitoes.
Background: Understanding the factors which determine a household's or individual's risk of malar... more Background: Understanding the factors which determine a household's or individual's risk of malaria infection is important for targeting control interventions at all intensities of transmission. Malaria ecology in Tanzania appears to have reduced over recent years. This study investigated potential risk factors and clustering in face of changing infection dynamics. Methods: Household survey data were collected in villages of rural Muheza district. Children aged between six months and thirteen years were tested for presence of malaria parasites using microscopy. A multivariable logistic regression model was constructed to identify significant risk factors for children. Geographical information systems combined with global positioning data and spatial scan statistic analysis were used to identify clusters of malaria. Results: Using an insecticide-treated mosquito net of any type proved to be highly protective against malaria (OR 0.75, 95% CI 0.59-0.96). Children aged five to thirteen years were at higher risk of having malaria than those aged under five years (OR 1.71, 95% CI 1.01-2.91). The odds of malaria were less for females when compared to males (OR 0.62, 95% CI 0.39-0.98). Two spatial clusters of significantly increased malaria risk were identified in two out of five villages. Conclusions: This study provides evidence that recent declines in malaria transmission and prevalence may shift the age groups at risk of malaria infection to older children. Risk factor analysis provides support for universal coverage and targeting of long-lasting insecticide-treated nets (LLINs) to all age groups. Clustering of cases indicates heterogeneity of risk. Improved targeting of LLINs or additional supplementary control interventions to high risk clusters may improve outcomes and efficiency as malaria transmission continues to fall under intensified control.
*<p>Superscript letter indicates statistical significance of blood-feeding inhibition in tr... more *<p>Superscript letter indicates statistical significance of blood-feeding inhibition in treatment arm as compared to the control arm; a = <i>P</i><0.001, b = <i>P</i><0.01, c = <i>P</i><0.05, d = <i>P</i>>0.05.</p
<p>Map showing the location of the field stations, in Moshi and Muheza, north-eastern Tanza... more <p>Map showing the location of the field stations, in Moshi and Muheza, north-eastern Tanzania.</p
*<p>Superscript letter indicate statistical significance as compared to the control arm; a ... more *<p>Superscript letter indicate statistical significance as compared to the control arm; a = <i>P</i><0.001, b = <i>P</i><0.01, c = <i>P</i><0.05, d = <i>P</i>>0.05.</p
An experimental hut evaluation of Olyset ® nets against anopheline mosquitoes after seven years u... more An experimental hut evaluation of Olyset ® nets against anopheline mosquitoes after seven years use in Tanzanian villages
Background: Despite considerable reductions in malaria achieved by scaling-up long-lasting insect... more Background: Despite considerable reductions in malaria achieved by scaling-up long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS), maintaining sustained community protection remains operationally challenging. Increasing insecticide resistance also threatens to jeopardize the future of both strategies. Non-pyrethroid insecticidetreated wall lining (ITWL) may represent an alternate or complementary control method and a potential tool to manage insecticide resistance. To date no study has demonstrated whether ITWL can reduce malaria transmission nor provide additional protection beyond the current best practice of universal coverage (UC) of LLINs and prompt case management.
Long-lasting insecticidal nets (LN) are an effective tool for malaria prevention. The World Healt... more Long-lasting insecticidal nets (LN) are an effective tool for malaria prevention. The World Health Organization Pesticide Evaluation Scheme has established evaluation criteria to facilitate registration for public use. A household randomised trial was conducted in Tanzania according to WHOPES Phase III procedures to evaluate the alpha-cypermethrin coated Interceptor® LN (BASF) over three years' use. Outcomes were calibrated against results of Phase II experimental hut trials. Interceptor LN (200 mg/m(2) alpha-cypermethrin) and conventionally treated nets CTN (40 mg/m(2) alpha-cypermethrin) were randomly distributed to 934 households. At 6-monthly intervals, household surveys recorded net use, durability, adverse effects, user acceptance and washing practices. Concurrently, 30 nets of each type were collected and tested for knock-down and kill of Anopheles gambiae mosquitoes in cone and tunnel bioassays. Alpha-cypermethrin content of nets was assessed annually. At 12 months 97 % ...
Background: Malaria prevalence and transmission intensity in Tanzania is heterogeneous with spati... more Background: Malaria prevalence and transmission intensity in Tanzania is heterogeneous with spatial and temporal variations between geographical areas and ecological systems. The objective of this study was to determine the prevalence of malaria, anaemia and nutritional status in relation to livelihoods, ecosystem and health systems in Kilosa District in central Tanzania. Methods: This study was conducted in four villages, two characterised by rice irrigation ecosystem and the other two by dry savannah ecosystem and pastoral livelihoods. In each ecosystem, one of the villages had a healthcare facility. Schoolchildren were screened for malaria infection using malaria rapid diagnostic test (mRDT) and microscopy and they were assessed for their anaemia and nutritional statuses. Results: A total of 1,019 school children (age = 4-16 years) were screened for malaria infection. The overall prevalence of Plasmodium falciparum infection was 10.6 % and 4.5 % by mRDT and microscopy, respectively. Children from pastoral villages had lower (2.9 %) prevalence of malaria than their counterparts (18.2 %) in the rice irrigation villages. A significantly high risk of malaria was observed among children in rice irrigation than in the pastoral ecosystem (OR: 0.13; 95%CI 0.07, 0.23). Children living in areas with health care facilities had a low odd of malaria infection by 45 % (OR: 0.55; 95 % CI = 0.35, 0.86). Overall, the prevalence of anaemia in the district was 43.4 % (n = 775); and 58.3 % of those with severe anaemia were among children from the pastoral villages. Anaemia was significantly higher among children not using mosquito nets (p = 0.049); and among those with malaria infection (p <0.001). The majority (96 %) of the children had Body Mass Index less than 18.5 kg/m 2 which indicate high proportion of underweight. Conclusion: There are significant variations in the risk of acquiring malaria infection between different ecosystems and livelihoods. These findings suggest that malaria control programmes must take into account ecosystems and livelihoods of the targeted population through an integrated management of malaria and nutrition approach.
Insecticide-treated nets are the primary method of preventing malaria. To remain effective, the p... more Insecticide-treated nets are the primary method of preventing malaria. To remain effective, the pyrethroid insecticide must withstand multiple washes over the lifetime of the net. ICON® Maxx is a 'dip-it-yourself' kit for long-lasting treatment of polyester nets. The twin-sachet kit contains a slow-release capsule suspension of lambda-cyhalothrin plus binding agent. To determine whether ICON Maxx meets the standards required by the World Health Organization Pesticide Evaluation Scheme (WHOPES), the efficacy and wash fastness of ICON Maxx was evaluated against wild, free-flying anopheline mosquitoes. ICON Maxx was subjected to bioassay evaluation and experimental hut trial against pyrethroid-susceptible Anopheles gambiae, Anopheles arabiensis and Anopheles funestus. Mosquito mortality, blood feeding inhibition and personal protection were compared between untreated nets, conventional lambda-cyhalothrin treated nets (CTN) washed either four times (cut-off threshold) or 20 time...
Tropical Medicine & International Health, 2008
SummaryObjective To determine the efficacy of chlorfenapyr against Anopheles arabiensis and Cule... more SummaryObjective To determine the efficacy of chlorfenapyr against Anopheles arabiensis and Culex quinquefasciatus in East Africa and to identify effective dosages for net treatment in comparison with the commonly used pyrethroid deltamethrin.Methods Chlorfenapyr was evaluated on bed nets in experimental huts against A. arabiensis and C. quinquefasciatus in Northern Tanzania, at application rates of 100–500 mg/m2.Results In experimental huts, mortality rates in A. arabiensis were high (46.0–63.9%) for all dosages of chlorfenapyr and were similar to that of deltamethrin‐treated nets. Mortality rates in C. quinquefasciatus were higher for chlorfenapyr than for deltamethrin. Despite a reputation for being slow acting, >90% of insecticide‐induced mortality in laboratory tunnel tests and experimental huts occurred within 24 h, and the speed of killing was no slower than for deltamethrin‐treated nets.Conclusions Chlorfenapyr induced low irritability and knockdown, which explains th...
This study was carried out to understand the role social determinants and health seeking behavior... more This study was carried out to understand the role social determinants and health seeking behavior among rice farming and pastoral communities in Kilosa District in central Tanzania. The study involved four villages; two with rice farming communities while the other two with pastoral communities. In each village, heads of households or their spouses were interviewed to seek information on livelihoods activities, knowledge and practices on malaria and its preventions. A total of 471 individuals (males=38.9%; females=61.1%) were interviewed. Only 23.5% of the respondents had adequate knowledge on malaria. Fifty-six percent of the respondents could not associate any livelihood activity with malaria transmission. Majority (79%) of the respondents believed that most of fevers were due to malaria; this was higher among the pastoral (81.7%) than rice farming communities (76.1%) (p=0.038). Cases of fever were significantly higher in households with non-educated (31.2%) than educated responde...
Tropical Medicine & International Health, 2014
ObjectiveInsecticide resistance molecular markers can provide sensitive indicators of resistance ... more ObjectiveInsecticide resistance molecular markers can provide sensitive indicators of resistance development in Anopheles vector populations. Assaying these makers is of paramount importance in the resistance monitoring programme. We investigated the presence and distribution of knock‐down resistance (kdr) mutations in Anopheles gambiae s.l. in Tanzania.MethodsIndoor‐resting Anopheles mosquitoes were collected from 10 sites and tested for insecticide resistance using the standard WHO protocol. Polymerase chain reaction‐based molecular diagnostics were used to genotype mosquitoes and detect kdr mutations.ResultsThe An. gambiae tested were resistance to lambdacyhalothrin in Muheza, Arumeru and Muleba. Out of 350 An. gambiae s.l. genotyped, 35% were An. gambiae s.s. and 65% An. arabiensis. L1014S and L1014F mutations were detected in both An. gambiae s.s. and An. arabiensis. L1014S point mutation was found at the allelic frequency of 4–33%, while L1014F was at the allelic frequency 6–4...
Three insecticides -the pyrethroid deltamethrin, the carbamate carbosulfan and the organophosphat... more Three insecticides -the pyrethroid deltamethrin, the carbamate carbosulfan and the organophosphate chlorpyrifos-methyl -were tested on mosquito nets in experimental huts to determine their potential for introduction as malaria control measures. Their behavioural effects and efficacy were examined in Anopheles gambiae Giles s.s. (Diptera: Culicidae) and Anopheles funestus Giles s.s. in Muheza, Tanzania, and in Anopheles arabiensis Patton and Culex quinquefasciatus Say in Moshi, Tanzania. A standardized dosage of 25 mg/m 2 plus high dosages of carbosulfan (50 mg/m 2 , 100 mg/m 2 and 200 mg/m 2 ) and chlorpyrifos-methyl (100 mg/m 2 ) were used to compare the three types of insecticide. At 25 mg/m 2 , the rank order of the insecticides for insecticide-induced mortality in wild An. gambiae and An. funestus was, respectively, carbosulfan (88%, 86%) > deltamethrin (79%, 78%) > chlorpyrifos-methyl (35%, 53%). The rank order of the insecticides for blood-feeding inhibition (reduction in the number of blood-fed mosquitoes compared with control) in wild An. gambiae and An. funestus was deltamethrin > chlorpyrifos-methyl > carbosulfan. Carbosulfan was particularly toxic to endophilic anophelines at 200 mg/m 2 , killing 100% of An. gambiae and 98% of An. funestus that entered the huts. It was less effective against the more exophilic An. arabiensis (67% mortality) and carbamate-resistant Cx quinquefasciatus (36% mortality). Carbosulfan deterred anophelines from entering huts, but did not deter carbamate-resistant Cx quinquefasciatus. Deltamethrin reduced the proportion of insects engaged in blood-feeding, probably as a consequence of contact irritancy, whereas carbosulfan seemed to provide personal protection through deterred entry or perhaps a spatial repellent action. Any deployment of carbosulfan as an individual treatment on nets should be carried out on a large scale to reduce the risk of diverting mosquitoes to unprotected individuals. Chlorpyrifos-methyl was inferior to deltamethrin in terms of mortality and blood-feeding inhibition and would be better deployed on a net in combination with a pyrethroid to control insecticide-resistant mosquitoes.
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