Strengthening capacity, collaboration and quality of clinical research in Africa: EDCTP Networks of Excellence

Developing countries bear 90% of the global disease burden, but only access about 10% of globally available health research funding. Weak south-south networking hampers effective use of limited resources, production of critical mass of quality scientists, career opportunities and incentives to retain the few available scientists. The south must urgently act strategically to accelerate generation of talented scientists, create enabling environment and incentives to retain scientists and attract back those in diaspora. The creation of strong networks of excellence for clinical research among southern academic and research institutions is a novel strategic approach championed by European and Developing Countries Clinical Trials Partnership to achieve the aforementioned goals and mitigate the high disease burden. It will promote strong collaboration, resource sharing and cross-mentorship allowing each partner to grow with complementary capacities that support each other rather than compete negatively. It will enable the south and Africa in particular to participate actively and own the means for solving its own health problems and raise the professional quality and capacity of southern institutions to forge better and equal partnership with northern institutions.

Biological and haematological safety profile of oral amodiaquine and chloroquine in healthy volunteers with or without Plasmodium falciparum infection in northeast Tanzania

Amodiaquine (AQ), an effective antimalarial drug for uncomplicated malaria, has been greatly restricted after cases of life-threatening agranulocytosis and hepatic toxicity during prophylactic use. We conducted a hospital based open-label randomised clinical trial in 40 indigenous semi-immune healthy adult male volunteers with and without malaria parasites. The objective was to collect data on biological and haematological safety, tolerability, and parasitological efficacy to serve as baseline in the evaluation of the effectiveness of AQ preventive intermittent treatment against malaria morbidity in infants. Volunteers were stratified according to parasitaemia status and randomly assigned 20 participants each arm to three days treatment with either AQ or chloroquine (CQ). The level of difference of selected haematological and hepatological values pre-and post-trial were marginal and within the normal limits. Clinical adverse effects mostly mild and transient were noticed in 33.3% CQ treated-aparasitaemic, 23.8% of CQ treated-parasitaemic, 28.6% ofAQ-treated parasitaemic and 14.3% of aparasitaemic receiving AQ. Amodiaquine attained 100% parasitological clearance rate versus 70% in CQ-treated volunteers. The findings indicate that there was no agranulocytosis or hepatic toxicity suggesting that AQ may pose no public health risk in its wide therapeutic dosage uses. Larger studies are needed to exclude rare adverse effects.

Smokeless tobacco use among adolescents in Ilala Municipality, Tanzania

Smokeless tobacco use is a significant part of the overall world tobacco problem. When the habit is introduced early in life, it increases the chance for permanent addiction and primes adolescents for use of harder drugs, exposing them to higher risk of oral cancer and other adverse effects of tobacco. This baseline study aimed at providing descriptive information on smokeless tobacco knowledge and use among adolescents at a time just before the ban on such products was enforced nationally on 1st December 2006. Six out of 101 primary and four out of 11 secondary schools were randomly selected in Ilala Municipality, Tanzania. A total of 1011 students were randomly selected and interviewed; boys (mean age = 14.5 years) accounted for 50.7% and girls (mean age = 13.6 years) 49.3%. The prevalence of tobacco use was 5.9% (boys = 9%; girls = 2.4%). Prevalence of smokeless tobacco use was 3.6%, about half of all who have ever smoked. Most popular brand of smokeless tobacco reported was Kuberi (44.8%) followed by Gutka (6.9%). Twelve (41%) of the smokeless tobacco users were using the products almost everyday. Among the reasons reported for smokeless tobacco use were pleasure (27.6%), smell (17.2%) and taste (6.9%). However, 48.3% of the users did not know why they used the product for the first time. Smokeless tobacco products were branded as nutritional supplements with different tastes and strengths, ideal for enticing the curiosity of adolescents. Given the crafty practice of the tobacco industry and salesmen, there is need for monitoring of availability of these products in circulation and enforcement of the ban nationally and globally to institute measures for effective elimination of this harmful practice.

Capacity of healthcare facilities in the implementation of direct observed treatment strategy for tuberculosis in Arumeru and Karatu districts, Tanzania

Directly Observed Treatment Short course strategy (DOTS) has proved to have potential improvement in tuberculosis (TB) control in Tanzania. The objective of this cross sectional study was to assess the capacity of health facilities in implementing DOTS, in Arumeru and Karatu districts, Tanzania. Information sought included the capacity to offer TB service and availability of qualified staff and equipment for TB diagnosis. Information on availability and utilization of TB registers and treatment outcome for the year 2004 were also collected. A total of 111 health facilities were surveyed, 86 (77.5%) in Arumeru and 25 (22.5%) in Karatu. Only 23.4% (26/111) facilities were offering TB treatment services in the two districts. Majority 17/26 (65.38%) of them were government owned. Thirty eight (44.7%) facilities were offering TB laboratory services. All facilities with TB services (TB laboratory investigation and treatment) had TB registers. Seventy two (85.0%) of health facilities which do not provide any TB services had qualified clinical officers and at least a microscopy. Of the 339 cases notified in Arumeru in 2004, 187 (60.7%) had treatment outcome available, 124 (66.3%) were cured and 55 (29.4%) completed treatment. In Karatu 638 cases were notified in 2004, 305 (47.8%) had treatment outcome available, 68 (22.3%) cured and 165 (54.1%) completed treatment. In conclusion, the overall capacity for implementing DOTS among the facilities surveyed is found only in about 20% and 30% for clinical and laboratory components of DOTS, respectively. The capacity to provide TB diagnosis and treatment in Karatu district was relatively lower than Arumeru. It is important that capacity of the facilities is strengthened concurrently with the planned introduction of community-based DOTS in Tanzania.

Hospital-based safety and tolerability study to assess efficacy of oral doxycycline in the treatment of Wuchereria bancrofti infection in north-eastern Tanzania

A hospital based open-label clinical trial of 19 apparently healthy adult males with microfilaraemia was conducted to assess safety, tolerability and efficacy of doxycycline on Wuchereria bancrofti. Study individuals were assigned 8 weeks treatment with doxycycline 200 mg daily. The results of different selected tests showed that, the haematological, hepatic, renal and clinical parameters pre-and post-drug administrations were within the normal range for all treated individuals. Clinical adverse events were mild, transient, tolerable and reported in 7/19 (36.8%) of the study cohort. The mf clearance rate was 100% at 12 months post treatment for the 13 individuals who completed the follow up. These findings indicate that, although the drug was administered for a long period, there was no evidence of toxicity to the myocardium, hepatocytes, renal, bone marrow and blood cells, suggesting that an 8-week course of 200 mg/day doxycycline is a safe and tolerable regime for the treatment of Wuchereria bancrofti infections.

The quality of sputum smear microscopy diagnosis of pulmonary tuberculosis in Dar es Salaam, Tanzania

This study was carried out to determine the rate of agreement or disagreement of microscopy reading and culture positivity rate among smear positixe and negative specimens between peripheral tuberculosis diagnostic centres (PDCs) and Central Reference luberculosis laboratory (CTRL). In this study 13 PDCs in Dar es Salaam, Tanzania were involved. Lot Quality Assurance Sampling (LQAS) method was used to collect 222 sputum smear slides. A total of 190 morning sputum specimens with corresponding slides were selected for culture. First readings were done by technicians at PDCs and thereafter selected slides and specimens were sent to CTRL for re-examination and culture. Culture results were used as a gold standard. Of 222 slides selected, 214 were suitable for re-examination. Percentage of agreement of smear reading between PDCs and CTRL was 42.9% and 100% for positive and negative slides, respectively. Measure of agreement (Kappa statistic) was 0.5, indicating moderate agreement. Of 190 samples cultured, percentage of agreement between smear reading from PDCs and CTRL was 37% and 88.9% for smear positive and negative slides, respectively. Kappa statistic was 0.3 indicating poor-fair agreements. Comparison of smear reading from PDCs with culture showed sensitivity of 36.9% and specificity of 88.9%. Comparison of smear readings from CTRL with culture results showed sensitivity of 95.6% and specificity of 98.6%. In conclusion there was inadequate performance in diagnosis of TB using smear microscopy among peripheral diagnostic centres in Dar es Salaam. This calls for immediate and rigorous measures to improve the quality of smear microscopy. It is therefore important to strengthen the capacity of laboratory personnel in smear microscopy techniques through supportive supervision and training.

Health research agenda for East Africa in the new millennium: looking ahead

The Regional East African Health Research agenda was presented as a keynote speech during the first East African Health and Scientific Conference, held in Kampala, Uganda from 28th to 30th March 2007. The agenda was developed through a critical analysis of the global, African and Regional East African health challenges and mitigating strategies, taking into account the Millennium Development Goals (MDG), the Abuja declaration and the New Partnership for African Development as background environment, within which the agenda will operate. It is proposed to establish a joint mechanism for research coordination, promotion and regulation; establish stronger collaborative mechanisms for research and training; create a joint Regional East African Community health research and development fund; create joint intellectual property rights protection mechanism; enhance patenting and link research to industry; create a mechanism to enhance translation of research to policy and practice; strengthen clinical research capacities; and strengthen innovation and discovery research capacities. Effective implementation of this agenda will greatly raise the profile and quality of research in the region and improve the health status of the East African populations.

Quality of HIV laboratory testing in Tanzania: a situation analysis

Tanzania is scaling up prevention, treatment, care and support of individuals affected with HIV. There is therefore a need for high quality and reliable HIV infection testing and AIDS staging. The objective of this study was to assess laboratories capacities of services in terms of HIV testing and quality control. A baseline survey was conducted from December 2004 to February 2005 in 12 laboratories which were conveniently selected to represent all the zones of Tanzania. The questionnaires comprised of questions on laboratory particulars, internal and external quality control for HIV testing and quality control of reagents. Source and level of customer satisfaction of HIV test kits supply was established. Of 12 laboratories, nine used rapid tests for screening and two used rapid tests for diagnosis. In the 12 laboratories, four used double ELISA and five used single ELISA and three did not use ELISA. Confirmatory tests observed were Western Blot in three laboratories, DNA PCR in two laboratories, CD4 counting in seven laboratories, and viral load in two laboratories. Although all laboratories conducted quality control (QC) of the HIV kits, only two laboratories had Standard Operating Procedures (SOPs). Internal and external quality control (EQC) was done at varied proportions with the highest frequency of 55.6% (5/9) for internal quality control (IQC) for rapid tests and EQC for ELISA, and the lowest frequency of 14.3% (1/ 7) for IQC for CD4 counting. None of the nine laboratories which conducted QC for reagents used for rapid tests and none of the five which performed IQC and EQC had SOPs. HIV kits were mainly procured by the Medical Store Department and most of laboratories were not satisfied with the delay in procurement procedures. Most of the laboratories used rapid tests only, while some used both rapid tests and ELISA method for HIV testing. In conclusion, the survey revealed inadequacy in Good Laboratory Practice and poor laboratory quality control process for HIV testing reagents, internal and external quality control.

The relationship between malaria parasitaemia and availability of healthcare facility in Mpwapwa district, central Tanzania

A study was carried out in six villages located at different altitudes in Mpwapwa district of central Tanzania to determine malaria parasitaemia and transmission levels in villages with or without health care facilities. A total of 1119 schoolchildren (age = 5.9-12.3 years) were examined for malaria parasitaemia. Plasmodiumfalciparum was the predominant malaria species accounting for 92.8% of all species. The average malaria prevalence rate among schoolchildren was 25.8% (range 1.5-53.8%). The geometric mean parasite densities for P.falciparum was 361 (N = 286). Higher malaria prevalence was observed in villages at lower (< 1000 m) than at intermediate (1000-1500m) or higher (> 1500m) altitudes. Schoolchildren in areas with health care facilities were less at risk of acquiring malaria by 33.4% as compared with those living in areas without health facilities. Mean packed cell volume in schoolchildren was 38.5% (range = 35.2-41.0%). Splenomegaly was observed in 18.1% (0-40.2%) of the schoolchildren examined and it was higher among those in villages without health care facilities. Anopheles gambiae sensu lato was the only malaria vector found in the district and was found in all villages and at all altitudes. Sporozoite rate in An. gambiae s.l. ranged from 0-10.5%, with the lowland villages recording the highest rates. This study indicates that altitude and geographical accessibility to healthcare service are important determinants of malaria infection among rural communities in Tanzania.

Implication of diethylcarbamazine induced morbidity and the role of cellular responses associated with bancroftian filariasis pathologies

Pre and post-diethylcarbamazine treatment clinical expression, microfilaraemia prevalence and cellular responses were investigated in individuals in Tanga, Tanzania. Fifty-seven male individuals (aged = 15 years old) were identified for further studies on IL-4, IL-6, IL-8. IFN-gamma, IL-beta, TNF-alpha and nitric oxide in plasma and hydrocoele fluid. Microfilarial prevalence in the examined individuals was 12% with a geometric mean intensity (GMI) of 838 mff/ml in a community with a population of 1018 individuals. Microfilaraemic hydrocoele stage II and III were the most frequent pathologies observed with prevalence of 17.5% and 42. 1 %, respectively. All study individuals treated with diethylcarbamazine (DEC) standard dose of 6 mg/kg experienced post-treatment adverse events. There was no direct relationship between elevated IL-6 and the occurrence and severity of clinical adverse effects post-treatment. The findings from this study suggests that, blood elevated cytokine profile is not the main etiological factor in the inflammatory responses developing after treatment of bancroftian filariasis infections and pathology with DEC. Plasma levels of cellular (cytokines) responses during treatment revealed a proportion of symptomatic patients. Prior to treatment, patients with hydroecoele had high levels of IL-6 than those without the pathology. In conclusion these findings do not support the hypothesis that pro-inflammatory cytokines are directly responsible for adverse events to DEC chemotherapy in bancroftian filariasis infections and pathologies such as hydrocoele, lymphoedema and elephantiasis.

Malaria epidemics in Tanzania: An overview

Malaria endemicity and epidemiology in Tanzania is changing rapidly as a result of changes in climatological, topographical and vector related factors. Malaria is now prevalent in previously malaria free mountainous areas, such as Muheza, Lushoto, Babati, Hanang and Loliondo Districts where records show dramatic changes in the incidence of and endemicity of malaria in the past five decades. The observed malaria epidemics in Tanzania were also greatly enhanced by a rapid increase in immigrants into and/or from malarious areas and by deforestation. Changes in mosquito host-preference, increased human socio-economic activities, and the wide self medication practices and drug resistance are also likely to have played important roles in malaria epidemics in Tanzania. This overview explores and discusses the contribution of the above-mentioned factors to malaria epidemics in the past five decades.

Apparent tolerance of Plasmodium falciparum in infants in a highly endemic area

The incidence of fever among infants in the village of Idete in the Morogoro region of Tanzania was analyzed in relation to densities of Plasmodium falciparum parasites in the peripheral blood. Parasite densities in both fever cases and in asymptomatic infants, were compared and a Bayesian non-parametric mixture decomposition algorithm was used to estimate the proportion of fevers attributable to malaria and hence the incidence of clinical malaria. Age group-specific densities of peripheral parasitaemia showed little seasonality, but the clinical malaria incidence showed a clear peak in the wet season in children aged less than 9 months. Estimates of the parasitaemia-specific incidence of clinical malaria were used to quantify apparent tolerance of parasites, and indicated that clinical episodes occurred on average at lower parasite densities during the wet season than in the dry season. These patterns could reflect differences in levels of anti-toxic immunity, but the nature of the seasonal differences supports the alternative explanation that the variation in apparent tolerance may be an effect of changes in the ratio of peripheral parasite densities to the sequestered mass.

Antibodies against Plasmodium falciparum vaccine candidates in infants in an area of intense and perennial transmission: relationships with clinical malaria and with entomological inoculation rates

Serum immunoglobulin (Ig)G1, IgG3 and total IgG were assessed by immunoabsorbent assay in 198 infants from a Tanzanian village highly endemic for Plasmodium falciparum. Antibodies were measured against epitopes of the circumsporozoite protein (the repetitive epitope (NANP)50 and a construct of the flanking regions (CS27IC)), the malaria vaccine SPf66, and two constructs of the merozoite surface protein-1 (MSP-1), a 19-kDa fragment from the C-terminal domain (MSP-119) and an N-terminal fragment spanning blocks 1-6 (H6-p190 M-1/6-H6). IgG1 and total IgG titres showed similar age profiles, all decreasing for the first 2 months of life. Anti-(NANP)50 titres remained very low throughout the first year of life, while anti-CS27IC antibody appeared to peak around 7 months of age. Only a slight tendency to increase with age was observed for levels of the other antibodies studied. IgG3 titres except for H6-p190(1/6), were very low initially and remained very low throughout the first year of life. Clinical malaria incidence at the village dispensary was analysed prospectively in relation to antibody. No IgG1 or total IgG titre showed protective effects, but low IgG3 against p190(1/6) appeared to be a risk factor in some age groups. Given the large number of antibodies tested, this single indication of possible protection could merely be chance. There were no strong associations between antibody titres and entomologically assessed sporozoite exposure suggesting that transmission-reducing interventions may have little effect on antibody levels in such children.

Evaluation of the SPf66 vaccine for malaria control when delivered through the EPI scheme in Tanzania

BACKGROUND

Malaria control programmes need to protect young children, who bear the brunt of malaria disease and death in Africa. The development of a vaccine is a priority if improved and sustained malaria control is to be achieved. The best use of a vaccine in Africa will be achieved if it can be delivered through the expanded programme of immunization (EPI). We conducted a trial designed to evaluate the efficacy of SPf66 vaccine for malaria control when delivered through the EPI scheme in Tanzania.

METHODS

The study was a two-arm, double blind, individually randomized placebo controlled trial involving 1207 infants. The primary objective of the trial was to estimate the efficacy of three doses of SPf66 given at 1, 2 and 7 months of age in preventing clinical episodes of malaria. These were documented through a health facility-based passive case detection system.

RESULTS

Among 1207 randomized children, overall compliance for third dose was 91%. SPf66 was safe, immunogenic and did not interfere with the humoral immune responses to EPI vaccines. There were 294 children among SPf66 recipients and 288 among placebo recipients with at least one malaria episode, yielding a vaccine efficacy estimate of 2% (95% CI: -16, 16; P = 0.84).

CONCLUSION

This has been the first trial of a malaria vaccine among very young infants. It provides information on the safety of peptide vaccines administered at this early age as well as their capacity to induce immune responses without negatively interacting with EPI vaccines. Given the modest protection previously documented in older age groups and the lack of efficacy in younger infants, this vaccine in its current alum-based formulation does not appear to have a role in malaria control in sub-Saharan Africa. The lack of efficacy found in this trial also raises concerns about potential difficulties of inducing protective immune responses against malaria through immunization in infants.

Incidence of Plasmodium falciparum infection in infants in relation to exposure to sporozoite-infected anophelines

The relationship of the incidence of Plasmodium falciparum infection to entomologic inoculation rates (EIRs) was studied in 163 children less than one year of age in a Tanzanian village to determine likely effects of transmission-reducing interventions on infection incidence. A total of 66,727 Anopheles gambiae s.l. and 17,620 An. funestus mosquitoes were caught in 1,056 light trap collections from 139 houses over a period of more than two years. Time period-specific human biting rates were estimated for 11 village neighborhoods. Sporozoites were detected by ELISA in 4.4% of the An. funestus and 2.5% of the An. gambiae s.l. Eight hundred seventeen pairs of blood slides with approximately two-week intervals between slides were used to estimate incidence of parasitemia by fitting reversible catalytic models to parasite positivity data. Estimated EIRs during the four weeks preceding each intersurvey interval averaged 1.6 (SD = 2.1) per adult per night. Parasites were present at the end of 31% of the 443 intervals that commenced with a parasite-negative slide. Attack rates were comparable with those in western Kenya, and the proportion of bites resulting in human infections was strongly dependent on mosquito density. Incidence of infection increased with the EIR up to approximately one bite from a sporozoite-carrying mosquito per adult per night. However, higher levels of transmission observed locally in the wet season did not result in a correspondingly higher incidence. These data suggest that transmission-reducing measures cannot be expected to reduce incidence of infection at the highest levels of EIR.

Relationships of malaria morbidity with exposure to Plasmodium falciparum in young children in a highly endemic area

To study incidence of clinical Plasmodium falciparum malaria in relation to exposure to parasites, attendance of children less than eighteen months old at a village dispensary in a highly endemic area of Tanzania was recorded. Entomologic inoculation rates (EIRs), estimated as a function of time period and place of residence, exceeded one sporozoite positive bite per adult per night in some village neighborhoods during the wet season. Incidence of clinical P. falciparum malaria, defined either as fever with parasitemia or as fever with hyperparasitemia, increased with the EIR over the whole range of exposures. Each 10-fold increase in the EIR corresponded to a 1.6-fold increase in incidence of fever plus parasitemia (95% confidence interval = 1.4-2.0). Therefore reduction of human-vector contacts will probably reduce morbidity incidence even at very high exposures. Incidence showed little relationship to estimated cumulative numbers of inoculations since birth, but decreased steeply with estimated cumulative time infected with trophozoites. This suggests that clinical immunity depends mainly on the extent of exposure to blood-stage antigens, not on the diversity of inocula seen, and thus temporary reductions in human-vector contacts are unlikely to result in subsequent increases in morbidity.

Immune responses to Plasmodium falciparum antigens during a malaria vaccine trial in Tanzanian children

Among Tanzanian children living in an area of intense and perennial malaria transmission, prevalence of naturally acquired IgG antibodies that recognize SPf66, NANP, p190 and a 19 kDa fragment of the merozoite surface protein-1 (MSP-1) is high and increases with age. This possibly reflects the high level of natural exposure of the children to P. falciparum. The prevalences of IgG antibodies that recognize the three putative merozoite derived sequences contained in the malaria vaccine SPf66 (83.1, 55.1 and 35.1) is low but also show some age dependence. Three doses of the SPf66 vaccine induce a strong IgG antibody response against both the SPf66 construct, NANP and the three individual peptides. Vaccination with SPf66 did not result in an increase of anti19 kDa fragment antibodies. This reflects the specificity of the humoral immune response induced by the SPf66 construct. Among vaccinated children, antibody titres against SPf66 decreased over time following the third dose. However, 18 months after the third dose, SPf66 recipients still had significantly higher IgG titres and stimulation indices of peripheral blood mononuclear cells (PBMC) than placebo recipients. Within the vaccine group, there is a trend for increasing anti-SPf66 IgG titre to be associated with decreasing risk of clinical malaria but this was not statistically significant. Results also show the difficulties of establishing whether antibody responses are related to protection in field trials in endemic areas.

The future of malaria research and control: An African perspective

A century after Sir Ronal Ross' discovery of the malaria parasite in the mosquito gut, unveiling the mode of malaria transmission, 40 per cent of the global population is still exposed to the disease. The exposed population lives in the tropical world. Africa bears the heaviest burden of the disease estimated at 31.6 million DALYs equivalent to 62.1 DALYs per 1,000 population. Children and pregnant women are the most affected groups. Control methods of source reduction which were effective in Europe and America using DDT spraying, larviciding and drainage of swamps and stagnant waters were not effective in the tropics. The complexity of the disease, the parasite' life cycle and the tropical environment within which it thrives calls for a new approach to malaria control, multilateral collaboration and funding an d above all commitment from the south and south-south collaboration. The long-term challenge lies on the discovery of better methods for malaria control. However, Africa cannot wait. Better utilization of existing tools exploiting their synergistic effect will save millions of lives.

Randomised placebo-controlled trial of iron supplementation and malaria chemoprophylaxis for prevention of severe anaemia and malaria in Tanzanian infants

BACKGROUND

Malaria and anaemia, especially that due to iron deficiency, are two leading causes of morbidity worldwide. Little is known about the relative contribution of Plasmodium falciparum infection and iron deficiency to the aetiology of anaemia in malaria-endemic areas. We undertook a randomised comparison of different strategies for control of anaemia and malaria in infants, including an assessment of the effect of iron supplementation on malaria susceptibility.

METHODS

832 infants born at one hospital in a malaria-hyperendemic area of Tanzania between January and October, 1995, were randomly assigned to group DI, receiving daily oral iron (2 mg/kg daily) plus weekly Deltaprim (3.125 mg pyrimethamine plus 25 mg dapsone); group IP, receiving iron plus weekly placebo; group DP, receiving daily placebo plus weekly Deltaprim; or group PP. supplementation was given from 8 to 24 weeks of age, and the weekly chemoprophylaxis from 8 to 48 weeks. The frequency of severe anaemia (packed-cell volume < 25%) and malaria episodes was assessed through a combination of passive case detection and cross-sectional surveys.

FINDINGS

The groups that received iron supplementation had a lower frequency of severe anaemia than those that did not receive iron (0.62 vs 0.87 cases per person-year; protective efficacy 28.8% [95% CI 6.3-45.8). Iron supplementation had no effect on the frequency of malaria (0.87 vs 1.00 cases per person-year; protective efficacy 12.8% [-12.8 to 32.5]). The groups that received malaria prophylaxis had lower frequencies of both severe anaemia (0.45 vs 1.04 episodes per person-year; protective efficacy 57.3% [43.0-67.9]) and malaria (0.53 vs 1.34 episodes per person-year; protective efficacy 60.5% [48.2-69.9]) than the groups that did not receive prophylaxis. After the end of the intervention period, children who had received malaria chemoprophylaxis had higher rates of severe anaemia and malaria than non-chemoprophylaxis groups (relative risks 2.2 [1.3-3.7] and 1.8 [1.3-2.6]).

INTERPRETATION

Malaria chemoprophylaxis during the first year of life was effective in prevention of malaria and anaemia but apparently impaired the development of natural immunity. Iron supplementation was effective in preventing severe anaemia without increasing susceptibility to malaria. Our findings support iron supplementation of infants to prevent iron-deficiency anaemia, even in malaria-endemic areas.

Field trials of malaria vaccines

Malaria due to Plasmodium falciparum is probably the most important infectious disease in the tropical world. About 2000 million people live in areas exposed to malaria and 300 million individuals are infected every year. In Africa south of the Sahara alone, over 1 million children die annually as a result of malaria. It is a difficult parasitic disease both to diagnose and control. It does not provide sterile immunity even after long exposure periods. However, acquisition of partial immunity allows over 60 per cent of individuals with long exposure to carry the parasite in their blood without symptoms, posing difficulties for case definition, malaria attributable morbidity and deaths. Further, it is extremely difficult to establish the extent to which malaria has influence over the adverse outcome of other infectious disease like measles and malnutrition. The complex life cycle of the parasite involving human and vector mosquitos as well as its allelic diversity and antigenic variations makes the development and implementation of effective malaria control intervention problematic. It is now becoming evident that multi-intervention approach may be the most appropriate way of combating malaria in view of the increasing resistance of the parasite to antimalarial drugs as well as vector mosquitoes to insecticides. Malaria vaccines will therefore play a major role in future malaria interventions. New malaria vaccine candidates will require testing in malaria endemic countries. Sufficient sites for testing potential malaria vaccines must be prepared. In this paper we discuss the necessary preparations required for field testing of malaria vaccines in tropical countries.

The role of low level Plasmodium falciparum parasitaemia in anaemia among infants living in an area of intense and perennial transmission

Children under one year of age in an area of intense and perennial Plasmodium falciparum transmission were followed up for one year to establish to what extent chronic, low parasitaemia was associated with severe anaemia. There was a significant increase in the prevalence of anaemia (PCV < or = 25%) with increase in parasite density. PCV levels were related not only to concurrent parasite density but also decreased with densities measured one month previously. At any point in time, the mean PCV level in infants with low parasitaemia (< 1000 parasites/microliter) was higher than that of infants with intermediate (1000-9999/microliter) and high parasite densities (> or 10000/microliter). After the age of 7 months, infants with low parasite densities tend to recover, probably as a result of developing immunity. At the age of 12 months, they have similar PCV levels to infants with no detectable parasitaemia by microscopy. The maintenance of low parasite density appears crucial to the survival of infants in malaria endemic areas. The findings suggest that interventions which lower parasite densities in areas of intense transmission reduce the development of severe malarial anaemia and thus malaria-related mortality and morbidity in infants.

Plasmodium falciparum malaria in the first year of life in an area of intense and perennial transmission

A longitudinal study of Plasmodium falciparum malaria in infants in Idete village, south-eastern Tanzania, was conducted over a period of 14 months in order to determine the incidence of P. falciparum infection and clinical malaria in the first year of life. Of 1356 blood slides from cross-sectional surveys, 52.1% were positive for asexual stages of P. falciparum. There were marked increases in P. falciparum prevalence, parasite densities, overall fever incidence and the incidence of malaria fevers with age for the first 6 months of life. The average attack rate, estimated from a reversible catalytic model, was 0.029 per day with a slight increase with age but there was no initial period of protection against infection in neonates. Estimated average duration of infections was 64 days, with infections in older infants lasting much longer than those contracted during the first 2 months of life. These results support the hypotheses that the main effect of passively transferred maternal immunity to malaria is in the control of asexual stage parasites, and that the level of clinical immunity depends upon the extent of recent exposure to parasites. Infants as young as 4 months of age are at high risk of clinical attacks. Intervention programmes against malaria in areas of the highest transmission should therefore be designed to include this group.

Duration of protection and age-dependence of the effects of the SPf66 malaria vaccine in African children exposed to intense transmission of Plasmodium falciparum

The SPf66 synthetic vaccine is safe and partly efficacious against Plasmodium falciparum malaria among children 1-5 years old. The estimated vaccine efficacy [VE] for all clinical episodes over a period of 18 months after the third dose is 25% (95% confidence interval [CI], 1%-44%; P = .044). The observed temporal variations in efficacy could have been due to chance (likelihood ratio chi 2 = 13.8, 8 df; P = .086). Efficacy against clinical malaria did not vary significantly with age (chi 2 = 1.07, 4 df; P = .90). Overall parasite density was 21% lower in vaccine recipients than in the placebo group (95% CI, 0%-38%; P = .044). Further development of SPf66 may require trials to evaluate safety, immunogenicity, and efficacy when administered in the first year of life, together with other vaccines contained in the Expanded Programme of Immunization schedule.