Anne L. Wilson

Estimating the potential public health impact of seasonal malaria chemoprevention in African children

Seasonal malaria chemoprevention, previously known as intermittent preventive treatment in children, is highly effective in areas with a short malaria transmission season. Here we assess seasonality in malaria incidence data and define a predictor of seasonality based on rainfall. We then use spatial rainfall, malaria endemicity and population data to identify areas likely to have highly seasonal malaria incidence, and estimate the population at risk and malaria burden in areas where seasonal malaria chemoprevention would be appropriate. We estimate that in areas suitable for seasonal malaria chemoprevention, there are 39 million children under 5 years of age, who experience 33.7 million malaria episodes and 152,000 childhood deaths from malaria each year. The majority of this burden occurs in the Sahelian or sub-Sahelian regions of Africa. Our data suggest that seasonal malaria chemoprevention has the potential to avert several million malaria cases and tens of thousands of childhood deaths each year if successfully delivered to the populations at risk.

A Systematic Review and Meta-Analysis of the Efficacy and Safety of Intermittent Preventive Treatment of Malaria in Children (IPTc)

Background Intermittent preventive treatment of malaria in children less than five years of age (IPTc) has been investigated as a measure to control the burden of malaria in the Sahel and sub-Sahelian areas of Africa where malaria transmission is markedly seasonal. Methods and Findings IPTc studies were identified using a systematic literature search. Meta-analysis was used to assess the protective efficacy of IPTc against clinical episodes of falciparum malaria. The impact of IPTc on all-cause mortality, hospital admissions, severe malaria and the prevalence of parasitaemia and anaemia was investigated. Three aspects of safety were also assessed: adverse reactions to study drugs, development of drug resistance and loss of immunity to malaria. Twelve IPTc studies were identified: seven controlled and five non-controlled trials. Controlled studies demonstrated protective efficacies against clinical malaria of between 31% and 93% and meta-analysis gave an overall protective efficacy of monthly administered IPTc of 82% (95%CI 75%–87%) during the malaria transmission season. Pooling results from twelve studies demonstrated a protective effect of IPTc against all-cause mortality of 57% (95%CI 24%–76%) during the malaria transmission season. No serious adverse events attributable to the drugs used for IPTc were observed in any of the studies. Data from three studies that followed children during the malaria transmission season in the year following IPTc administration showed evidence of a slight increase in the incidence of clinical malaria compared to children who had not received IPTc. Conclusions IPTc is a safe method of malaria control that has the potential to avert a significant proportion of clinical malaria episodes in areas with markedly seasonal malaria transmission and also appears to have a substantial protective effect against all-cause mortality. These findings indicate that IPTc is a potentially valuable tool that can contribute to the control of malaria in areas with markedly seasonal transmission.

Are topical insect repellents effective against malaria in endemic populations? A systematic review and meta-analysis

BackgroundRecommended vector control tools against malaria, such as long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS), mainly target mosquitoes that rest and feed on human hosts indoors. However, in some malaria-endemic areas, such as Southeast Asia and South America, malaria vectors primarily bite outdoors meaning that LLINs and IRS may be less effective. In these situations the use of topical insect repellents may reduce outdoor biting and morbidity from malaria. A systematic review and meta-analysis was conducted to assess the efficacy of topical insect repellents against malaria.MethodsStudies were identified using database searches (MEDLINE, EMBASE, Web of Science and clinical trials registers), as well as reference list searches and contact with researchers. Randomized and non-randomized controlled trials were included that assessed the effect of topical repellents (all active ingredients and concentrations) on Plasmodium falciparum or Plasmodium vivax malaria or infection in malaria-endemic populations. Meta-analysis of clinical data was conducted in order to generate summary risk ratios.ResultsTen trials met the inclusion criteria. Studies varied in terms of repellent active ingredient and formulation, co-interventions, study population, compliance, and follow-up period. Topical repellents showed an 18% protective efficacy against P. falciparum malaria, although this was not significant (95% CI: -8%, 38%). Similarly, the average protective efficacy of topical repellents against P. vivax malaria did not reach significance (protective efficacy: 20%, 95% CI: -37%, 53%). Exclusion of non-randomized trials from the meta-analysis did not alter the findings.ConclusionsAlthough topical repellents can provide individual protection against mosquitoes, the results of this meta-analysis indicate that topical repellents are unlikely to provide effective protection against malaria. However, there was substantial heterogeneity between studies included and the relatively small number of studies meant that this heterogeneity could not be fully explored in the analysis. Further well-designed trials of topical repellents at appropriate doses and alternative modes of repellent delivery, such as spatial repellents and long-lasting insecticide-treated clothing, are required.

Evidence-based vector control? Improving the quality of vector control trials

Vector-borne diseases (VBDs) such as malaria, dengue, and leishmaniasis cause a high level of morbidity and mortality. Although vector control tools can play a major role in controlling and eliminating these diseases, in many cases the evidence base for assessing the efficacy of vector control interventions is limited or not available. Studies assessing the efficacy of vector control interventions are often poorly conducted, which limits the return on investment of research funding. Here we outline the principal design features of Phase III vector control field studies, highlight major failings and strengths of published studies, and provide guidance on improving the design and conduct of vector control studies. We hope that this critical assessment will increase the impetus for more carefully considered and rigorous design of vector control studies.

Benefit of insecticide-treated nets, curtains and screening on vector borne diseases, excluding malaria: a systematic review and meta-analysis

Introduction Insecticide-treated nets (ITNs) are one of the main interventions used for malaria control. However, these nets may also be effective against other vector borne diseases (VBDs). We conducted a systematic review and meta-analysis to estimate the efficacy of ITNs, insecticide-treated curtains (ITCs) and insecticide-treated house screening (ITS) against Chagas disease, cutaneous and visceral leishmaniasis, dengue, human African trypanosomiasis, Japanese encephalitis, lymphatic filariasis and onchocerciasis. Methods MEDLINE, EMBASE, LILACS and Tropical Disease Bulletin databases were searched using intervention, vector- and disease-specific search terms. Cluster or individually randomised controlled trials, non-randomised trials with pre- and post-intervention data and rotational design studies were included. Analysis assessed the efficacy of ITNs, ITCs or ITS versus no intervention. Meta-analysis of clinical data was performed and percentage reduction in vector density calculated. Results Twenty-one studies were identified which met the inclusion criteria. Meta-analysis of clinical data could only be performed for four cutaneous leishmaniasis studies which together showed a protective efficacy of ITNs of 77% (95%CI: 39%–91%). Studies of ITC and ITS against cutaneous leishmaniasis also reported significant reductions in disease incidence. Single studies reported a high protective efficacy of ITS against dengue and ITNs against Japanese encephalitis. No studies of Chagas disease, human African trypanosomiasis or onchocerciasis were identified. Conclusion There are likely to be considerable collateral benefits of ITN roll out on cutaneous leishmaniasis where this disease is co-endemic with malaria. Due to the low number of studies identified, issues with reporting of entomological outcomes, and few studies reporting clinical outcomes, it is difficult to make strong conclusions on the effect of ITNs, ITCs or ITS on other VBDs and therefore further studies be conducted. Nonetheless, it is clear that insecticide-treated materials such as ITNs have the potential to reduce pathogen transmission and morbidity from VBDs where vectors enter houses.

Risk and Control of Mosquito-Borne Diseases in Southeast Asian Rubber Plantations.

Unprecedented economic growth in Southeast Asia (SEA) has encouraged the expansion of rubber plantations. This land-use transformation is changing the risk of mosquito-borne diseases. Mature plantations provide ideal habitats for the mosquito vectors of malaria, dengue, and chikungunya. Migrant workers may introduce pathogens into plantation areas, most worryingly artemisinin-resistant malaria parasites. The close proximity of rubber plantations to natural forest also increases the threat from zoonoses, where new vector-borne pathogens spill over from wild animals into humans. There is therefore an urgent need to scale up vector control and access to health care for rubber workers. This requires an intersectoral approach with strong collaboration between the health sector, rubber industry, and local communities.

Long Distance Trade and the Luba Lomami Empire

The kingdom of Luba Lomami was enlarged and strengthened by the conquest of Kalala Ilunga at an unknown date before the end of the sixteenth century. It became a large but not dominant state. The expansion of Luba Lomami is generally considered to have occurred in the early eighteenth century, as a delayed consequence of the Kalala Ilunga conquest. In this it is said to have been paralleled by the expansion of Lunda. Unlike Lunda, however, it is supposed to have suffered from severe structural deficiencies. These, it has been argued, inhibited its further expansion and, in the mid-nineteenth century, caused it to disintegrate. It is suggested here, however, that the expansion of Luba Lomami did not occur until the late eighteenth or early nineteenth century. This expansion coincided with the extension of the Bisa trading system into the chiefdoms south-east of Luba Lomami and was designed to capture this trade. Later conquests in the south may have been related to the development of Nyamwezi and Bihe trading systems. However, the principal motive for further expansion was the need to capture new sources of ivory and, to a lesser extent, slave-yielding lands. Luba Lomamis success can be attributed to its proximity to the Bisa trade route, its relatively centralized political structures, the availability of viable areas of expansion, and the existence of suitable mechanisms to incorporate the conquered chiefdoms. In the first half of the nineteenth century Luba Lomami subjected most of the area between the Lubilash and Lake Tanganyika and between the forest and the copper belt. In about 1870 the terms of the long-distance trade turned against Luba Lomami. New traders arrived carrying guns. Luba Lomami could not match the new techniques for it no longer had the resources with which to purchase guns. Its own resources of ivory and slaves were exhausted. It could no longer obtain supplies by expansion, for the traders were carving out new states on its periphery, and it was itself becoming subject to slave raids and encroachment. This external pressure weakened the political structures. Rival brothers sought the aid of mercenary traders to promote their cause. The ideological basis of the state was undermined. In a desperate attempt to obtain guns the emperors began to raid for slaves amongst their own people. The empire disintegrated and, in about 1890, the rump of the state became tributary to the trader-state of Msiri.

The contemporary distribution of Trypanosoma cruzi infection in humans, alternative hosts and vectors.

This corrects the article DOI: 10.1038/sdata.2017.50.

Improving the Built Environment in Urban Areas to Control Aedes Aegypti-Borne Diseases

The vector Aedes aegypti is now present in nearly every tropical and sub-tropical region in the world and poses a threat to health globally. The mosquito can transmit several viruses that cause diseases, such as dengue fever, chikungunya, yellow fever and Zika virus infection. Recent outbreaks of Ae. aegypti-borne diseases have shown that urban areas are particularly vulnerable because the built environment provides ideal conditions for mosquito proliferation and contact with humans. Unless the global public health community takes a coordinated, pre-emptive approach to controlling the Ae. aegypti population, these outbreaks will become more common and widespread as urban populations expand and movement of people and their goods increase. Improving the built environment would contribute to a long-term solution to reducing the threat of Ae. aegypti-bome diseases. Our ability to deal with Ae. Aegypti-borne viral epidemics is limited. Apart from supportive care, specific treatments for vector-borne viral diseases are lacking. No commercial vaccines for Zika or chikungunya are available, the only licensed dengue vaccine is partially protective (1) and globally the yellow fever vaccine is in short supply. (2) Although current vector control programmes are often poorly resourced and under-used, (3) historically, vector control was the main method for controlling mosquito-borne diseases. By using container inspections, oiling of breeding sites and later perifocal spraying of DDT (dichlorodiphenyltrichloroethane) in water containers and on nearby walls, Ae. aegypti, yellow fever and dengue fever were successfully eliminated from much of South America in the 1960s. (4) In the 1970s and 1980s in Singapore and in the 1980s and 1990s in Cuba, controlling adult and larval Ae. aegypti reduced dengue transmission. In the future, new methods of vector control, such as novel delivery systems for insecticides with new modes of action and release of Wolbachia-infected or genetically-modified mosquitoes, may contribute to the control or elimination of mosquito-borne diseases. (5) Affected towns and cities, however, already have several options to reduce Ae. aegyptibome diseases and these options should be built into future planning strategies. Current Ae. aegypti control focuses on reducing densities of immature and adult mosquitoes with larvicides or adult insecticides. While these interventions can be effective, continued reliance on these single-intervention control programmes is resource-intensive and threatened by insecticide resistance. The World Health Organization (3,6) and other major international organizations7 have recommended an intersectoral approach to achieve more effective and sustainable vector control. Governments, however, have often overlooked such approaches when designing vector control programmes. An underutilized aspect of integrated vector management is improving the urban built environment to reduce Ae. aegypti populations and their contact with humans. (8) The built environment in many urban areas provides abundant habitats for the immature stages of Ae. aegypti, and high human population densities create the potential for large outbreaks of Aedes-borne diseases. More than half of the worlds population currently lives in urban areas and by 2050 it is estimated that 70% of the population will live in cities. (9) This urban expansion will increase the frequency and intensity of Aedes-borne outbreaks. However, developing urban areas that minimize human contact with mosquitoes could enable sustainable and cost-effective prevention of mosquito-borne diseases. Several aspects of urban planning can be targeted to reduce human contact with Ae. aegypti. Reducing the availability of small plastic containers around homes and improving solid waste management will remove habitats for Ae. aegypti larvae development. Provision of constant piped water will reduce the need to store water in containers in and around homes, since water-filled containers are known to be favoured habitats for Ae. …