Axel Kroeger

Towards a global dengue research agenda.

Dengue is the most rapidly advancing vector-borne disease with an estimated 50 million dengue infections occurring annually. As a result of major demographic changes rapid urbanization on a massive scale global travel and environmental change the world - particularly the tropical world - faces enormous challenges from emerging infectious diseases. Dengue epitomizes these challenges. In the early years of the 21st century we are collectively failing to meet the threat posed by dengue as the disease spreads unabated and almost 40% of the worlds population now live at risk of contracting it. Because of the rapidly increasing public health importance of dengue the 2002 World Health Assembly Resolution (WHA55.17) urged greater commitment among Member States and WHO to dengue control; of particular significance is the 2005 Revision of the International Health Regulations (WHA58.3) which includes dengue fever as an example of a disease that may constitute an international public health emergency. (excerpt)

Editorial: Towards a global dengue research agenda

Dengue is the most rapidly advancing vector-borne disease with an estimated 50 million dengue infections occurring annually. As a result of major demographic changes rapid urbanization on a massive scale global travel and environmental change the world - particularly the tropical world - faces enormous challenges from emerging infectious diseases. Dengue epitomizes these challenges. In the early years of the 21st century we are collectively failing to meet the threat posed by dengue as the disease spreads unabated and almost 40% of the worlds population now live at risk of contracting it. Because of the rapidly increasing public health importance of dengue the 2002 World Health Assembly Resolution (WHA55.17) urged greater commitment among Member States and WHO to dengue control; of particular significance is the 2005 Revision of the International Health Regulations (WHA58.3) which includes dengue fever as an example of a disease that may constitute an international public health emergency. (excerpt)

Dengue: setting the global research agenda

The global incidence of dengue has increased exponentially over past decades. Fuelled by conditioning factors such as rapid urbanisation demographic change large-scale migration and travel the disease is now endemic in most countries of the tropics and about 925 million people now live in urban areas that are at risk of dengue infection. The increasing incidence intensity and geographical expansion of dengue epidemics pose a growing threat to the health and economic well-being of populations living in endemic areas where the introduction of new virus strains to regions affected by existing serotypes is a risk factor for outbreaks and severe disease. Dengue is a major international public-health concern as expressed in World Health Assembly resolution WHA 55.17 and in the 2005 revision of the International Health Regulations (WHA 58.3). We do have strategies methods and guidelines with which we can greatly reduce dengue case-fatality rates and virus transmission but weak implementation of these plans and an inability to respond effectively to conditioning factors (such as those mentioned above) outside the health sector is causing concern. (excerpt)

Ecological, biological and social dimensions of dengue vector breeding in five urban settings of Latin America: a multi-country study

BackgroundDengue is an increasingly important public health problem in most Latin American countries and more cost-effective ways of reducing dengue vector densities to prevent transmission are in demand by vector control programs. This multi-centre study attempted to identify key factors associated with vector breeding and development as a basis for improving targeted intervention strategies.MethodsIn each of 5 participant cities in Mexico, Colombia, Ecuador, Brazil and Uruguay, 20 clusters were randomly selected by grid sampling to incorporate 100 contiguous households, non-residential private buildings (businesses) and public spaces. Standardized household surveys, cluster background surveys and entomological surveys specifically targeted to obtain pupal indices for Aedes aegypti, were conducted in the dry and wet seasons.ResultsThe study clusters included mainly urban low-middle class populations with satisfactory infrastructure and –except for Uruguay- favourable climatic conditions for dengue vector development. Household knowledge about dengue and “dengue mosquitoes” was widespread, mainly through mass media, but there was less awareness around interventions to reduce vector densities. Vector production (measured through pupal indices) was favoured when water containers were outdoor, uncovered, unused (even in Colombia and Ecuador where the large tanks used for household water storage and washing were predominantly productive) and –particularly during the dry season- rainwater filled. Larval infestation did not reflect productive container types. All productive container types, including those important in the dry season, were identified by pupal surveys executed during the rainy season.ConclusionsA number of findings are relevant for improving vector control: 1) there is a need for complementing larval surveys with occasional pupal surveys (to be conducted during the wet season) for identifying and subsequently targeting productive container types; 2) the need to raise public awareness about useful and effective interventions in productive container types specific to their area; and 3) the motivation for control services that-according to this and similar studies in Asia- dedicated, targeted vector management can make a difference in terms of reducing vector abundance.

The potential for malaria control with the biological larvicide Bacillus thuringiensis israelensis (Bti) in Peru and Ecuador

A study on the efficacy of Bti spraying in mosquito breeding places was undertaken in the Pacific coast of Peru and Ecuador and in the Amazon area of Peru. It was shown that Bti is a powerful larvicide for Anopheles larvae, although it sinks quickly, whereas Anopheles larvae feed at the water surface. The duration of its effect was less than 7 days with the exception of the Amazon area of Peru, where it was approximately 10 days. In two study areas, Bti was sprayed weekly over periods of 10 and 7 weeks, respectively, and the adult mosquito densities were monitored. The Anopheles adult density (bites per person per hour on human baits) was reduced by an average of 70% in one area and by up to 50% in the other. This means that Bti spraying can potentially be an important component of a modified malaria control strategy.

WASH RESISTANCE OF INSECTICIDE – TREATED MATERIALS

The effectiveness of insecticide-treated materials (ITMs) for malaria control is reduced by washing them. This research in Colombia and Bolivia investigated the resistance of different insecticide formulations and, in particular, a commercially available impregnated bednet (PermaNet) which provides chemical protection for the insecticide. The fabrics studied were all polyester; the pyrethroids used for impregnation were deltamethrin (tablet and suspension concentrate both at 25 mg/m2 target dose), lambdacyhalothrin (capsule suspension at 15 mg/m2; laboratory study only), alphacypermethrin (suspension concentrate at 40 mg/m2) and, in the case of PermaNet, deltamethrin (55 mg/m2). The indicator of wash resistance was Anopheles spp. mortality (using the bioassay cone method) before and after different numbers and intensities of washing. When the fabrics were washed under controlled conditions, gently with water and a bar of soap, the wash resistance of all formulations was good (100% Anopheles mortality after 3 washes). However, when the impregnated nets were soaked for 30-60 min and washed with soap powder and tap water by local women in the usual way, the mortality after 4 washes declined considerably (43.5% and 41.3% for deltamethrin tablets and liquid respectively when washing every second day). Alphacypermethrin showed slightly better results after 3 washes every 7th day compared to deltamethrin tablets (63.8% and 43.3% mortality, respectively). The wash resistance offered by PermaNet was much better and longer lasting: Anopheles mortality after 4 washes was 92.6%, after 10 washes 83.7% and after 20 washes 87.1%. The limitations of commercially available wash-resistant nets are, however, their limited accessibility and the difficulty of replacing all existing bednets with a new product.

Operational aspects of bednet impregnation for community-based malaria control in Nicaragua, Ecuador, Peru and Colombia

Community intervention projects with pyrethroid (permethrin and lambdacyhalothrin) impregnated bednets and an accompanying community education programme were carried out in 6 malaria endemic areas on the Pacific coast of Nicaragua, Ecuador, Peru and Colombia as well as in the Peruvian Amazon basin. In this paper the operational aspects are analysed: bednet coverage, results of promotional activities for increased bednet use, the sale of low‐cost bednets, techniques and difficulties with impregnation, acceptance of the programme (including washing of impregnated nets), side‐effects, residual concentrations of the chemical in the nets, costs of the impregnation programme and insecticide resistance of the malaria vectors.

Malaria control reinvented: health sector reform and strategy development in Colombia

The consequences of health sector reforms on control of malaria were analysed using Colombia as an example. One of the most complex health sector reform programmes in Latin America took place in the 1990s; it included transferring the vertical vector‐borne disease control (VBDC) programme into health systems at state and district levels. A series of studies was undertaken in 1998–2000 at the national level (Ministry of Health Study), at the state level (Departamento Study) and at the health district level (District Study) using formal and informal interviews among control staff and document analysis as data collection tools. A government‐financed national training programme for VBDC staff – which included direct observation of control operations – was also used to analyse health workers performance in the postreform period (longitudinal study). The results showed that some shortcomings of the old vertical system, such as the negative aspects of trade union activity, have not been overcome while some positive aspects of the old system, such as capacity building, operational planning and supervision have been lost. This has contributed to a decrease in control activity which, in turn, has been associated with more malaria cases. Malaria control had to be reinvented at a much larger scale than anticipated by the reformers caused by a whole series of problems: complex financing of public health interventions in the new system, massive staff reductions, the difficulty of gaining access to district and state budgets, redefining entire organizations and – in addition to the reforms – introducing alternative strategies based on insecticide‐treated materials and the growth of areas of general insecurity in many parts of Colombia itself. However, positive signs in the transformed system include: the strengthening of central control staff (albeit insufficient in numbers) when transferred from the Ministry of Health to the National Institute of Health, the opportunities offered by the Basic Health Plan (PAB) for new planning initiatives and intersectoral co‐operation and the integration of malaria diagnosis and treatment into the general health services (associated with a decrease of malaria mortality). The potentials of the new system have not yet been fully exploited: capacity building, communication and management skills need to be improved and it require guidance from the national level.

Inadequate drug advice in the pharmacies of Guatemala and Mexico: the scale of the problem and explanatory factors.

A study of urban pharmacies in Guatemala and in Chiapas, southern Mexico, was undertaken to analyse the scale of the inadequate drug advice provided, and to identify the contributing factors. The estimate of the scale of the problem was based on the results of 969 approaches to 191 pharmacies by magic clients (i.e. researchers pretending to be looking for treatment for relatives who had one of three tracer diseases), interviews with 4469 pharmacy users as they left the same 191 pharmacies, and a comparison of the quality of advice offered by public and private pharmacies in Guatemala (based on exit interviews with 150 users). The contributing factors were explored using a provider survey (interviews with 166 pharmacy supervisors and 371 drug vendors), an in-depth study analysing large-chain and independent Mexican pharmacies, and a review of the national drug policies in both countries. Although only about 11% of all drug treatments were recommended in pharmacies (the rest being prescribed by physicians or recommended by kin-groups), this still represents large numbers of treatments. Overall, 501 individuals who visited the 191 study pharmacies over 2 days of observation received drugs recommended by pharmacy staff. Much of the pharmacy advice was revealed to be poor: > 80% of the treatments recommended to the magic clients for diarrhoeal disease or acute respiratory infection included unnecessary or dangerous drugs. Few of those who worked in the pharmacies based their advice on careful case histories. Drug advice in pharmacies was much more likely to be of poor quality than that from physicians or even kin-groups. The factors behind this poor advice were identified as a lack of knowledge about standard treatments and legal regulations, incompetence among pharmacy staff, commercial pressures (particularly in the large-chain pharmacies of Mexico), and a failure to implement the existing regulations covering the drug market and its retail practices. It is recommended that: (1) pharmacy owners and drug vendors be made more aware that the selling of drugs should involve provision of healthcare (as well as reasonable profit-making); (2) existing drug-related legislation be reinforced (through consensus-building rather than coercion); and (3) mass training of pharmacy supervisors and drug vendors, in the standard treatment of common diseases, be undertaken. This process will be challenging and slow.

Combined field and laboratory evaluation of a long-term impregnated bednet, PermaNet®

For how long does the insecticidal effect of long-lasting nets achieve high Anopheles mortality? Four PermaNets tested previously in Colombia for wash resistance were bioassayed again after 3 years of use and 23 washes. The tests were done both in Colombia and a reference laboratory in Indonesia. Additionally the residual concentration of deltamethrin on the nets was chemically analysed. The results showed high Anopheles mortality and a mean deltamethrin concentration of 9.6 mg/m2. Discrepancies with other studies are discussed.