Malaria Journal - Latest articles

Background: The current status of insecticide resistance and the underlying resistance mechanisms were studied in the major vector of malaria, Anopheles culicifacies, and the secondary vector, Anopheles subpictus in five districts (Anuradhapura, Kurunegala, Moneragala, Puttalam and Trincomalee) of Sri Lanka. Eight other anophelines, Anopheles annularis, Anopheles barbirostris, Anopheles jamesii, Anopheles nigerrimus, Anopheles peditaeniatus, Anopheles tessellatus, Anopheles vagus and Anopheles varuna from Anuradhapura district were also tested. Methods: Adult females were exposed to the WHO discriminating dosages of DDT, malathion, fenitrothion, propoxur, lambda-cyhalothrin, cyfluthrin, cypermethrin, deltamethrin, permethrin and etofenprox. The presence of metabolic resistance by esterase, glutathione S-transferase (GST) and monooxygenase-based mechanisms, and the sensitivity of the acetylcholinesterase target site were assessed using synergists, and biochemical, and metabolic techniques. Results: All the anopheline species had high DDT resistance. All An. culicifacies and An. subpictus populations were resistant to malathion, except An. culicifacies from Kurunegala, where there was no malathion carboxylesterase activity. Kurunegala and Puttalam populations of An. culicifacies were susceptible to fenitrothion. All the An. culicifacies populations were susceptible to carbamates. Both species were susceptible to the discriminating dosages of cypermethrin and cyfluthrin, but had different levels of resistance to other pyrethroids. Of the 8 other anophelines, only An. nigerrimus and An. peditaeniatus were resistant to all the insecticides tested, probably due to their high exposure to the insecticides used in agriculture. An. vagus showed some resistance to permethrin. Esterases, GSTs and monooxygenases were elevated in both An. culicifacies and An. subpictus. AChE was most sensitive to insecticides in Kurunegala and Trincomalee An. culicifacies populations and highly insensitive in the Trincomalee An. subpictus population. Conclusions: The complexity of the resistance segregating in these field populations underlines the need for new molecular tools to identify the genomic diversity, differential upregulation and different binding specificities of resistance conferring genes, and the presence of different subspecies with different vectorial capacities.

Background: Malaria control is currently receiving significant international commitment. As part of this commitment, Rwanda has undertaken a two-pronged approach to combating malaria via mass distribution of insecticide-treated bed nets and distribution of antimalarial medications by community health workers. This study attempted to measure the impact of these interventions on paediatric hospitalizations for malaria and on laboratory markers of disease severity. Methods: A retrospective analysis of hospital records pre- and post-community-based malaria control interventions at a district hospital in rural Rwanda was performed. The interventions took place in August 2006 in the region served by the hospital and consisted of mass ITN distribution and community health workers antimalarial medication disbursement. The study periods consisted of the December-February high transmission seasons pre- and post-rollout. The record review examined a total of 551 paediatric admissions to identify 1) laboratory-confirmed malaria, defined by thick smear examination, 2) suspected malaria, defined as fever and symptoms consistent with malaria in the absence of an alternate cause, and 3) all-cause admissions. To define the impact of the intervention on clinical markers of malaria disease, trends in admission peripheral parasitaemia and haemoglobin were analyzed. To define accuracy of clinical diagnoses, trends in proportions of malaria admissions which were microscopy-confirmed before and after the intervention were examined. Finally, to assess overall management of febrile illnesses antibiotic use was described. Results: Of the 551 total admissions, 268 (48.6%) and 437 (79.3%) were attributable to laboratory-confirmed and suspected malaria, respectively. The absolute number of admissions due to suspected malaria was smaller during the post-intervention period (N=150) relative to the pre-intervention period (N=287), in spite of an increase in the absolute number of hospitalizations due to other causes during the post-intervention period. The percentage of suspected malaria admissions that were laboratory-confirmed was greater during the pre-intervention period (80.4%) relative to the post-intervention period (48.1%, prevalence ratio [PR]: 1.67; 95% CI: 1.39 - 2.02; chi-squared p-value<0.0001). Among children admitted with laboratory-confirmed malaria, the risk of high parasitaemia was higher during the pre-intervention period relative to the post-intervention period (age-adjusted PR: 1.62; 95% CI: 1.11 - 2.38; chi-squared p-value=0.004), and the risk of severe anaemia was more than twofold greater during the pre-intervention period (age-adjusted PR: 2.47; 95% CI: 0.84 - 7.24; chi-squared p-value=0.08). Antibiotic use was common, with 70.7% of all children with clinical malaria and 86.4% of children with slide-negative malaria receiving antibacterial therapy. Conclusions: This study suggests that both admissions for malaria and laboratory markers of clinical disease among children may be rapidly reduced following community-based malaria control efforts. Additionally, this study highlights the problem of over-diagnosis and over-treatment of malaria in malaria-endemic regions, especially as malaria prevalence falls. More accurate diagnosis and management of febrile illnesses is critically needed both now and as fever aetiologies change with further reductions in malaria.

Background: Each year, several thousand cases of malaria occur in south-central Vietnam. Evidence from elsewhere suggests that malaria can have an economic impact on the household as the illness prevents households from completing their normal, physically demanding, productive duties such as tending crops and animals. The economic impact of malaria on households was explored within the Raglay ethnic minority living in the montainous and forested area of south-central Vietnam (Ninh Thuan Province). Methods: Two-hundred fifty-one malaria patients were identified and interviewed in an exit survey at Community Health Centres. The same patient sample was then re-interviewed in a household survey two to four weeks later. Survey data were complemented by approximately 40 informal discussions with health workers, vendors, patients, and community leaders. Results: Each episode of malaria was estimated to cost the patient's household an average of 11.79USD (2005 prices), direct costs for travel and treatment representing 6% of the total while the remainder was loss in annual income. Conclusions: Whilst government provision of malaria treatment keeps the direct costs relatively low, the overall loss in income due to illness can still be significant given the poverty amongst this population, especially when multiple cases of malaria occur annually within the same household.

Background: To combat malaria, the Kenya Ministry of Health and nongovernmental organizations (NGOs) have distributed insecticide-treated nets (ITNs) for use over beds, with coverage for children under five years of age increasing rapidly. Nevertheless, residents of fishing villages have started to use these bed nets for drying fish and fishing in Lake Victoria. This study investigated the extent of bed net misuse in fishing villages. Methods: Seven fishing villages along the lake were surveyed to estimate how widely bed nets were being used for fishing and drying fish. Villagers were asked why they used the bed nets for such purposes. Results: In total, 283 bed nets were being used for drying fish. Of these, 239 were long-lasting insecticidal bed nets (LLIN) and 44 were non-long-lasting insecticidal bed nets (NLLIN). Further, 72 of the 283 bed nets were also being used for fishing. The most popular reasons were because the bed nets were inexpensive or free and because fish dried faster on the nets. LLINs were preferred to NLLINs for fishing and drying fish. Conclusion: There is considerable misuse of bed nets for drying fish and fishing. Many villagers are not yet fully convinced of the effectiveness of LLINs for malaria prevention. Such misuses may hamper the efforts of NGOs and governmental health organizations.

Background: The Zambian Malaria Control Programme with the Roll Back Malaria (RBM) partners have developed the current National Malaria Strategic Plan (NMSP 2006-2011) which focuses on prevention based on the Integrated Vector Management (IVM) strategy. The introduction and implementation of an IVM strategy was planned in accordance with the World Health Organization (WHO) steps towards IVM implementation namely Introduction Phase, Consolidation Phase and Expansion Phase. Achievements IVM has created commitment for Legal and Regulatory policy review, monitoring, Research and a strong stewardship by the chemical suppliers. It has also leveraged additional resources, improved inter-sectoral collaboration, capacity building and enhanced community participation which facilitated a steady scaling up in coverage and utilisation of key preventive interventions. Thus, markedly reducing malaria incidence and case fatalities in the country. Conclusion: Zambia has successfully introduced, consolidated and expanded IVM activities. Resulting in increased coverage and utilization of interventions and markedly reducing malaria-related morbidity and mortality while ensuring a better protection of the environment.

Background: SINEs (Short INterspersed Elements) are homoplasy-free and co-dominant genetic markers which are considered to represent useful tools for population genetic studies, and could help clarifying the speciation processes ongoing within the major malaria vector in Africa, Anopheles gambiae s.s. Here, we report the results of the analysis of the insertion polymorphism of a nearly 200 bp-long SINE (SINE200) within genome areas of high differentiation (i.e. speciation islands ) of M and S A. gambiae molecular forms. Methods: A SINE-PCR approach was carried out on thirteen SINE200 insertions in M and S females collected along the whole range of distribution of A. gambiae s.s. in sub-Saharan Africa. Ten specimens each for Anopheles arabiensis, Anopheles melas, Anopheles quadriannulatus A and 15 M/S hybrids from laboratory crosses were also analysed. Results: Eight loci were successfully amplified and were found to be specific for A. gambiae s.s.: 5 on 2L chromosome and one on X chromosome resulted monomorphic, while two loci positioned respectively on 2R (i.e. S200 2R12D) and X (i.e. S200 X6.1) chromosomes were found to be polymorphic. S200 2R12D was homozygote for the insertion in most S-form samples, while intermediate levels of polymorphism were shown in M-form, resulting in an overall high degree of genetic differentiation between molecular forms (Fst=0.46 p<0.001) and within M-form (Fst=0.46 p<0.001). The insertion of S200 X6.1 was found to be fixed in all M- and absent in all S-specimens. This led to develop a novel easy-to-use PCR approach to straightforwardly identify A. gambiae molecular forms. This novel approach allows to overcome the constraints associated with markers on the rDNA region commonly used for M and S identification. In fact, it is based on a single copy and irreversible SINE200 insertion and, thus, is not subjected to peculiar evolutionary patterns affecting rDNA markers, e.g. incomplete homogenization of the arrays through concerted evolution and/or mixtures of M and S IGS-sequences among the arrays of single chromatids. Conclusions: The approach utilized allowed to develop new easy-to-use co-dominant markers for the analysis of genetic differentiation between M and S-forms and opens new perspectives in the study of the speciation process ongoing within A. gambiae.

Background: Malaria is endemic in the low-altitude areas of the northern and eastern parts of South Africa with seasonal transmission. The aim of this descriptive study is to give an overview of the malaria incidence and mortality in Limpopo Province for the seasons 1998-1999 to 2006-2007 and to detect trends over time and place. Methods: Routinely collected data on diagnosed malaria cases and deaths were available through the provincial malaria information system. In order to calculate incidence rates, population estimates (by sex, age and district) were obtained from Statistics South Africa. The Chi squared test for trend was used to detect temporal trends in malaria incidence over the seasons, and a trend in case fatality rate (CFR) by age group. The Chi squared test was used to calculate differences in incidence rate and CFR between both sexes and in incidence by age group. Results: In total, 58,768 cases of malaria were reported, including 628 deaths. The mean incidence rate was 124.5 per 100,000 person-years and the mean CFR 1.1% per season. There was a decreasing trend in the incidence rate over time (p < 0.001), from 173.0 in 1998-1999 to 50.9 in 2006-2007. The CFR was fairly stable over the whole period. The mean incidence rate in males was higher than in females (145.8 versus 105.6; p < 0.001); the CFR (1.1%) was similar for both sexes. The incidence rate was lowest in 0-4 year olds (78.3), it peaked at the ages of 35-39 years (172.8), and decreased with age from 40 years (to 84.4 for those [greater than or equal to] 60 years). The CFR increased with increasing age (to 3.8% for those [greater than or equal to] 60 years). The incidence rate varied widely between districts; it was highest in Vhembe (328.2) and lowest in Sekhukhune (5.5). Conclusions: Information from this study may serve as baseline data to determine the course and distribution of malaria in Limpopo province over time. In the study period there was a decreasing trend in the incidence rate. Furthermore, the study addresses the need for better data over a range of epidemic-prone settings.

Background: During erythrocytic schizogony, Plasmodium falciparum interacts with the human erythrocyte membrane when it enters into, grows within and escapes from the erythrocyte. An interaction between the P. falciparum M18 aspartyl aminopeptidase (PfM18AAP) and the human erythrocyte membrane protein spectrin was recently identified using phage display technology. In this study, recombinant (r) PfM18AAP was characterized and the interaction between the enzyme and spectrin, as well as other erythrocyte membrane proteins, analyzed. Methods: rPfM18AAP was produced as a hexahistidine-fusion protein in Escherichia coli and purified using magnetic bead technology. The pI of the enzyme was determined by two-dimensional gel electrophoresis and the number of subunits in the native enzyme was estimated from Ferguson plots. The enzymatic activity over a pH and temperature range was tested by a coupled enzyme assay. Blot overlays were performed to validate the spectrin-PfM18AAP interaction, as well as identify additional interactions between the enzyme and other erythrocyte membrane proteins. Sequence analysis identified conserved amino acids that are expected to be involved in cofactor binding, substrate cleavage and quaternary structure stabilization. Results: rPfM18AAP has a molecular weight of ~67 kDa and the enzyme separated as three entities with pI 6.6, 6.7 and 6.9. Non-denaturing gel electrophoresis indicated that rPfM18AAP aggregated into oligomers. An in vitro coupled enzyme assay showed that rPfM18AAP cleaved an N-terminal aspartate from a tripeptide substrate with maximum enzymatic activity at pH 7.5 and 37C. The spectrin-binding region of PfM18AAP is not found in Homo sapiens, Saccharomyces cerevisiae and other Plasmodium species homologues. Amino acids expected to be involved in cofactor binding, substrate cleavage and quaternary structure stabilization, are conserved. Blot overlays with rPfM18AAP against spectrin and erythrocyte membrane proteins indicated that rPfM18AAP binds to spectrin, as well as to protein 4.1, protein 4.2, actin and glyceraldehyde 3-phosphate dehydrogenase. Conclusions: Studies characterizing rPfM18AAP showed that this enzyme interacts with erythrocyte spectrin and other membrane proteins. This suggests that, in addition to its proposed role in haemoglobin digestion, PfM18AAP performs other functions in the erythrocyte host and can utilize several substrates, which highlights the multifunctional role of malaria enzymes.

Background: Introduction of artemisinin combination therapy (ACT) has boosted interest in parasite-based malaria diagnosis, leading to increased use of rapid diagnostic tests (RDTs), particularly in rural settings where microscopy is limited. With donor support, national malaria control programmes are now procuring large quantities of RDTs. The scarcity of health facilities and trained personnel in many sub-Saharan African countries means that limiting RDT use to such facilities would exclude a significant proportion of febrile cases. RDT use by volunteer community health workers (CHWs) is one alternative, but most sub-Saharan African countries prohibit CHWs from handling blood, and little is known about CHW ability to use RDTs safely and effectively. This Zambia-based study was designed to determine: (i) whether Zambian CHWs could prepare and interpret RDTs accurately and safely using manufacturer's instructions alone; (ii) whether simple, mostly pictorial instructions (a job aid ) could raise performance to adequate levels; and (iii) whether a brief training programme would produce further improvement. Methods: The job aid and training programme were based on formative research with 32 CHWs in Luangwa District. The study team then recruited three groups of CHWs in Chongwe and Chibombo districts. All had experience treating malaria based on clinical diagnosis, but only six had prior RDT experience. Trained observers used structured observation checklists to score each participant's preparation of three RDTs. Each also read 10 photographs showing different test results. The first group (n=32) was guided only by manufacturer's instructions. The second (n=21) used only the job aid. The last (n=26) used the job aid after receiving a three-hour training. Results: Mean scores, adjusted for education, age, gender and experience, were 57% of 16 RDT steps correctly completed for group 1, 80% for group 2, and 92% for group 3. Mean percentage of test results interpreted correctly were 54% (group 1), 80% (group 2), and 93% (group 3). All differences were statistically significant (p<0.05). Conclusions: Manufacturer's instructions like those provided with the RDTs used in this study are insufficient to ensure safe and accurate use by CHWs. However, well-designed instructions plus training can ensure high performance. More study is underway to determine how well this performance holds up over time.

Background: Maps of malaria distribution are vital for optimal allocation of resources for anti-malarial activities. There is a lack of reliable contemporary malaria maps in endemic countries in sub-Saharan Africa. This problem is particularly acute in low malaria transmission countries such as those located in the horn of Africa. Methods: Data from a national malaria cluster sample survey in 2005 and routine cluster surveys in 2007 were assembled for Somalia. Rapid diagnostic tests were used to examine the presence of Plasmodium falciparum parasites in finger-prick blood samples obtained from individuals across all age-groups. Bayesian geostatistical models, with environmental and survey covariates, were used to predict continuous maps of malaria prevalence across Somalia and to define the uncertainty associated with the predictions. Results: For analyses the country was divided into north and south. In the north, the month of survey, distance to water, precipitation and temperature had no significant association with P. falciparum prevalence when spatial correlation was taken into account. In contrast, all the covariates, except distance to water, were significantly associated with parasite prevalence in the south. The inclusion of covariates improved model fit for the south but not for the north. Model precision was highest in the south. The majority of the country had a predicted prevalence of < 5%; areas with [greater than or equal to] 5% prevalence were predominantly in the south. Conclusions: The maps showed that malaria transmission in Somalia varied from hypo- to meso-endemic. However, even after including the selected covariates in the model, there still remained a considerable amount of unexplained spatial variation in parasite prevalence, indicating effects of other factors not captured in the study. Nonetheless the maps presented here provide the best contemporary information on malaria prevalence in Somalia.