Trial of pyrethroid impregnated bednets in an area of Tanzania holoendemic for malaria. Part 4. Effects on incidence of malaria infection.

Groups of about 30 children in each of five villages were given pyrimethamine-sulfadoxine to clear their malaria parasitaemia, and they were followed up with fortnightly blood slides. Parasitaemia returned rapidly in the absence of vector control, but more slowly when pyrethroid impregnated nets were in use or the houses had been sprayed with DDT. Variation between the incidence of malaria infection in these cases seemed to depend more on ecological or social factors than on the particular form of vector control adopted.     

Trial of pyrethroid impregnated bednets in an area of Tanzania holoendemic for malaria. Part 3. Effects on the prevalence of malaria parasitaemia and fever.

Children aged 1-10 in five villages were contacted fortnightly. Their axillary temperatures, reports of fevers and blood slides were taken. Following the introduction of permethrin impregnated nets into two estate villages the slide positivity for falciparum malaria declined markedly. In traditional villages the introduction of impregnated nets had less convincing effects than in the estate villages and DDT spraying had no perceptible effect on malaria. Over all villages there was a clear relationship between axillary temperature greater than 37.4 degrees C, reports of fever and high parasitaemia. We defined malaria fever in this way, and found in some cases significant reductions in occurrence of such fever following some time after introduction of permethrin impregnated nets. No such effects were found with lambdacyhalothrin nets or with DDT spraying.     

Trial of pyrethroid impregnated bednets in an area of Tanzania holoendemic for malaria. Part 1. Operational methods and acceptability.

In five Tanzanian villages, nets impregnated with permethrin or lambdacyhalothrin were given out. The people received them enthusiastically and brought their nets for re-impregnation at six monthly intervals. Bioassays showed that the insecticidal power of permethrin impregnated nets remained adequate for six months unless the nets were washed. Nets with 30 mg lambdacyhalothrin/m2 retained high insecticidal power despite washing, but this dose caused temporary cold-like symptoms in those sleeping under freshly treated dry nets. Methods by which durable bednets might be made affordable by Tanzanian villagers are discussed.     

Deltamethrin-impregnated bednets as an operational tool for malaria control in a hyper-endemic region of Burundi: impact on vector population and malaria morbidity

Within the framework of the National Malaria Control Programme Burundi, impregnated bednets were promoted through health care facilities, schools and local administration in Nyanza Lac district. The decision to buy a bednet was left to the inhabitants and, as a result, coverage rates between 6 and 65% were observed at sub-district level. Three intervention regions were specified based on the intervention start date. From November 1992 until March 1995, bi-monthly parasitological and entomological surveys were carried out in two areas each of Region 1 and Region 2. After introduction of impregnated bednets in Region 1 the proportions of children under 5 with high parasitaemia were reduced by 42 and 53% in the 2 parasitological survey areas, where the average bednet coverages were 55 and 44% respectively. In the survey areas of Region 2 (control) no significant change occurred during the same period. During the second part of the intervention from September 1994, when intervention was also operational in Region 2, significant decreases in the proportion of high parasitaemia (63 and 42%) among children under 5 years were obtained in both parasitological survey areas of Region 2 (average coverages of 51 and 29%). The positive output of the intervention was maintained and even reinforced in the survey areas of Region 1. Bednets as a tool for malaria control entail specific problems such as coverage, daily use, reimpregnation, and renewal of old and torn nets. Further evaluation has to point out the possible shift of the clinical spectrum and the age-specific admission of malaria cases to assess the long-term benefit of this control method.     

Maternal influence on the use of impregnated bednets in the protection of infantile malaria

A cross-sectional survey of 184 mothers or caretakers was undertaken to investigate the effect of socio-behavioral background on decision making in relation to the use of impregnated bednets to prevent malaria for their children in Ratchaburi Province, Thailand. It was found that most mothers had knowledge of the cause, transmission and prevention of malaria. They perceived susceptibility and severity of malaria as a risk to their children, which might even cause death. They also perceived and had positive attitudes toward impregnated bednets as a protection for their children. Three-quaters (76.4%) of them used impregnated bednets regularly to protect their children whereas one-quarter (23.6%) used infrequently and few never used. Bivariate analysis showed that the use of impregnated bednets was significantly related to the factors such as knowledge of malaria prevention, perception of benefits of the use, the receipt of information about the impregnated bednets from malaria workers.     

Proguanil daily or chlorproguanil twice weekly are efficacious against falciparum malaria in a holoendemic area of Tanzania

The prophylactic efficacy of proguanil 100 mg (Paludrine) daily was compared to that of chlorproguanil 20 mg (Lapudrine) twice weekly in school children from Nyamisathi village, in a coastal area of Tanzania, 160 km south of Dar es Salaam. A total of 80 children were randomly allocated to three groups after radical treatment with a curative dose of mefloquine (Lariam). Seventy-six children were then followed up with daily prophylaxis and/or placebo for 13 weeks. All children in the group taking placebo prophylaxis were reinfected within 10 weeks whereas no parasites were detected in the children taking proguanil or chlorproguanil for prophylaxis. We conclude that both regimens were efficacious and that chlorproguanil represents an important alternative for chemoprophylaxis if taken at least twice weekly instead of the recommended once weekly regimen.     

Introducing insecticide impregnated bednets in an area of low bednet usage: an exploratory study in north-east Ghana

To find out the acceptability of the use of insecticide impregnated bednets before launching a large‐scale trial to evaluate their impact on child mortality, 96 permethrin impregnated bednets were distributed in 4 communities within the Kassena Nankana district of the Upper East Region of Ghana, where previously only 4% of the people had owned a mosquito net. The nets were readily accepted and used by the recipients. The major benefit perceived by the users was the reduction of the nuisance effect of mosquitoes and other insects. The people in the study area normally sleep on mats in either an open courtyard or a sleeping room depending on the weather but this did not deter them from using the nets. The white nets distributed for this study became dirty with use, and users thought they needed to be washed. In order to discourage this, it is recommended that dark coloured nets be used in the main intervention trial. After having used the nets for a year, the community members expressed willingness to buy the nets if they were made available after the harvest season when they had sold their crops and had enough money to pay for them. The results of this study have been used to plan and conduct a large intervention trial.     

Perception of chloroquine efficacy and alternative treatments for uncomplicated malaria in children in a holoendemic area of Tanzania: implications for the change of treatment policy

Prior to policy change from chloroquine (CQ) to sulphadoxine/pyrimethamine (S/P; Fansidar) we assessed the perception of CQ efficacy and the alternative treatment options for malaria in children among parents/guardians (N=527) of under-fives attending first level health facilities on account of fever. It was hypothesized that the long experience with CQ and its antipyretic effect (lacking in S/P) might impede acceptance of S/P for wider use as first-line drug. Malarial fevers in children were most commonly treated with CQ (92.8%), followed by quinine (60.7%) and S/P (28.7%). A 63.2% knew the reasons for non-response to antimalarial treatment, and only 50% were aware that CQ could fail to treat malaria, and 57.1% knew alternative treatment options, namely quinine (52.2%) and S/P (20.5%). Generally, decreased efficacy of CQ had been noticed, and quinine was prescribed for both suspected and proven CQ failures in first level health facilities and the district hospital. S/P was judged to be more effective than quinine, but too strong for children, and was the least known drug in the study area. All formulations of S/P cost more per dose for a child and an adult than CQ. The implications of these findings on the change of malaria treatment policy are discussed.     

Towards a rational malaria management at district hospital level: exploratory case series of febrile adult patients in a holoendemic area of Tanzania

One hundred and sixty eight febrile adult outpatients were investigated at St Francis Designated District Hospital in fakara, a holoendemic area in Tanzania. We wanted to assess the potential anamnestic and clinical risk indicators for malaria and to establish a rational strategy for malaria management. Blood slide investigations showed that 14% of all patients were positive for P. falciparum. All the positive cases were found during the rainy season. No reliable criteria for malaria were found in the history taking and physical examinations. Signs and symptoms of respiratory tract infection such as difficulties during breathing, sore throat, chest pain, cough, pathological findings in lung auscultation and combinations of these were negatively associated with malaria parasitaemia.The same was true for lymph node swelling and a clinical diagnosis other than malaria. Quality control of blood slide results from the hospital revealed a sensitivity of 55%, a specificity of 72%, and positive and negative predictive values of 24% and 91%. The main recommendations for malaria management in adults were to improve the quality of blood slide examinations and to use a different diagnostic strategy during the dry and rainy seasons. During the dry season blood slides of febrile adult patients should only be performed if there is a suspicion of malaria and antimalarial drugs should only be administered if blood slide results are positive. During the rainy season all febrile adults without obvious cause of fever other than malaria should be treated with antimalarials without previous blood slide examination.     

Indication of pyrethroid resistance in the main malaria vector, Anopheles stephensi from Iran

ObjectiveTo investiagte insecticide resistance in target species for better insecticide resistance managemnet in malaria control programs.MethodsThe status of insecticide resistance to different imagicides in Anopheles stephensi (An. stephensi) including DDT 4%, lambdacyhalothrin 0.50%, deltamethrin 0.05%, permethrin 0.75%, cyfluthrin 0.15% and etofenprox 0.50% was performed according to WHO standard method.ResultsThe mortality rate to lambdacyhalothrin, permethrin, cyfluthrin, deltamethrin, etofenprox and DDT was (88.0±3.2), (92.0±2.7), (52.0±5.0), (96.0±2.2), (90.0±3.0) and (41.0±5.7) percent, respectively at diagnostic dose for one hour exposure time followed by 24 h recovery period.ConclusionsThese results showed first indication of pyrethroid resistance in An. stephensi in a malarious area, from southern Iran. There is widespread, multiple resistances in the country in An. stephensi to organochlorine and some report of tolerance to organophosphate insecticides and recently to pyrethroids. However, results of this paper will provide a clue for monitoring and mapping of insecticide resistance in the main malaria vector for implementation of any vector control.     

Plasmodium falciparum clinical malaria in Dielmo, a holoendemic area in Senegal: no influence of acquired immunity on initial symptomatology and severity of malaria attacks.

Six hundred eighty-nine Plasmodium falciparum malaria attacks were observed during a three-year period among 226 inhabitants of the village of Dielmo, Senegal, an area of high malaria transmission. Malaria attacks were defined as clinical episodes with fever (body temperature > or = 38.0 degrees C) or reporting of fever or headache or vomiting, associated with a parasite:leukocyte ratio above an age-dependent pyrogenic threshold identified in this population. The symptom frequencies were tested against age, gender, and parasite density using a random-effect logistic regression model and the study of distinguishable clinical presentations was carried out by multi-correspondence analysis. There was little difference between the severity of symptoms during the initial course of attacks in young children and adults, and this severity was not correlated with the duration of the pathologic episode. It was not possible to distinguish objectively different malaria attack types according to the severity of clinical manifestations. In contrast, the duration of fever, symptoms, and parasite clearance were significantly longer among the youngest children than among the oldest children and adults. These findings suggest that of the two components of protective immunity, anti-parasite immunity and anti-toxic immunity, only the first would play a major role as age increases. They suggest also that the initial clinical presentation of malaria attacks is not predictive of the level of protective immunity.     

Trial of deltamethrin impregnated bed nets for the control of malaria transmitted by Anopheles sinensis and Anopheles anthropophagus

In 1985-1987, a field trial of malaria control using deltamethrin impregnated mosquito nets was carried out with 4,450 people in the Buji district, Bao'an County, Guangdong Province, China. The vectors were exophilic Anopheles sinensis (80%) and the endophilic and anthropophilic An. anthropophagus (20%). The first impregnation of the nets was in June 1985 and the second in April 1986. About 87% of the population slept under treated nets. The indoor vector density decreased by 93% and remained at the same level during the second year. During the second year the average monthly malaria incidence was 1.3% for January-June, a decrease of 74.6% as compared with pretreatment data, and 0.85% from July to December, a decrease of 92.7%. In April 1986 and April 1987, the treatment was extended to the whole Buji District, which has a total population of approximately 40,000. The average monthly malaria incidence (April-December 1986 and 1987) was 0.54% and 0.17%, a decrease of 64.7% and 89% respectively as compared with the same period for the previous year.     

Insecticide-treated bednets for the prevention of Plasmodium falciparum malaria in Cambodia: a cluster-randomized trial

OBJECTIVES: To validate and quantify the impact of insecticide-treated bednets (ITN) on malaria morbidity and mortality in Cambodia. METHODS: A paired, cluster-randomized trial of ITN was conducted in Rattanakiri, North East Cambodia. Thirty-four villages with a total population of 10,726 were randomized to receive deltamethrin-impregnated bednets or to control (no net provision). Cross-sectional surveys measured Plasmodium falciparum prevalence at baseline and 10 months after ITN distribution. Village malaria volunteers in control and intervention villages treated dipstick-positive P. falciparum cases with artesunate and mefloquine. The resulting passive surveillance data were used as an estimate of the incidence of clinical P. falciparum infections. RESULTS: There was a protective efficacy of 28% in P. falciparum incidence (adjusted rate ratio 0.72, 95% CI 0.47-1.08) and 9% in P. falciparum prevalence (adjusted prevalence ratio 0.91, 95% CI 0.65-1.28) in ITN relative to control villages; however, neither of these estimates reached statistical significance. Individual-level analysis indicated a greater reduction in P. falciparum prevalence among under 5-year-olds (adjusted OR = 0.63, 95% CI 0.26-1.53) compared to older individuals (interaction P = 0.042). The protective efficacy of 35% (95% CI -28, 67%) with respect to clinical P. falciparum incidence in under 5-year-olds was more pronounced than the corresponding estimates for prevalence but was again not significant. CONCLUSIONS: Lack of statistical significance in the results is likely to be due to a lack of power. The analysis provides further evidence for ITN effectiveness in South East Asia, particularly among individuals under 5 years of age.     

Dynamics of insecticide resistance in the malaria vector Anopheles gambiae s.l. from an area of extensive cotton cultivation in Northern Cameroon

Objective To explore temporal variation in insecticide susceptibility of Anopheles gambiae s.l. populations to the four chemical groups of insecticides used in public health and agriculture, in close match with the large‐scale cotton spraying programme implemented in the cotton‐growing area of North Cameroon. Methods Mosquito larvae were collected in 2005 before (mid June), during (mid August) and at the end (early October) of the cotton spraying programme. Larvae were sampled in breeding sites located within the cotton fields in Gaschiga and Pitoa, and in Garoua, an urban cotton‐free area that served as a control. Insecticide susceptibility tests were carried out with 4% DDT (organochlorine), 0.4% chlorpyrifos methyl (organophosphate), 0.1% propoxur (carbamate), 0.05% deltamethrin and 0.75% permethrin (pyrethroids). Results Throughout the survey, An. gambiae s.l. populations were completely susceptible to carbamate and organophosphate, whereas a significant decrease of susceptibility to organochlorine and pyrethroids was observed during spraying in cotton‐growing areas. Tolerance to these insecticides was associated with a slight increase of knockdown times compared to the reference strain. Among survivor mosquitoes, the East and West African Kdr mutations were detected only in two specimens of An. gambiae s.s. (n = 45) and not in Anopheles arabiensis (n = 150), suggesting metabolic‐based resistance mechanisms. Conclusions Environmental disturbance due to the use of insecticides in agriculture may provide local mosquito populations with the enzymatic arsenal selecting tolerance to insecticides.     

Antibodies to Plasmodium falciparum in an indigenous population from a malaria endemic area of Malaysia

Indirect fluorescent antibody (IFA) tests and enzyme-linked immunosorbent assays (ELISA) were used to measure antibodies to Plasmodium falciparum in an indigenous population in an area of Malaysia with high malaria prevalence. The results of three surveys were analyzed to examine the relation of these serologic measures with age, parasite rate, and spleen size. For children 0-4 years old, increasing spleen size was associated with an increasing likelihood of malaria parasitemia, while for 5-9 year olds the two variables were unrelated. Parasite rate declined with age and ELISA titre increased with age in all surveys; IFA titre was consistently high and did not vary with age. Neither antibody measure was significantly correlated with either the presence or the actual density of parasitemia. These antibody measures are most useful as adjuncts to the more traditional techniques of malaria assessment.