Preventive chemotherapy in human helminthiasis: theoretical and operational aspects.

Preventive chemotherapy (PC), the large-scale distribution of anthelminthic drugs to population groups at risk, is the core intervention recommended by the WHO for reducing morbidity and transmission of the four main helminth infections, namely lymphatic filariasis, onchocerciasis, schistosomiasis and soil-transmitted helminthiasis. The strategy is widely implemented worldwide but its general theoretical foundations have not been described so far in a comprehensive and cohesive manner. Starting from the information available on the biological and epidemiological characteristics of helminth infections, as well as from the experience generated by disease control and elimination interventions across the world, we extrapolate the fundamentals and synthesise the principles that regulate PC and justify its implementation as a sound and essential public health intervention. The outline of the theoretical aspects of PC contributes to a thorough understanding of the different facets of this strategy and helps comprehend opportunities and limits of control and elimination interventions directed against helminth infections.

Elimination of neglected tropical diseases in the South-East Asia Region of the World Health Organization.

The neglected tropical diseases (NTDs), which affect the very poor, pose a major public health problem in the South-East Asia Region of the World Health Organization (WHO). Although more than a dozen NTDs affect the region, over the past five years four of them in particular - leprosy, lymphatic filariasis, visceral leishmaniasis (kala-azar) and yaws - have been targeted for elimination. These four were selected for a number of reasons. First, they affect the WHO South-East Asia Region disproportionately. For example, every year around 67% of all new leprosy cases and 60% of all new cases of visceral leishmaniasis worldwide occur in countries of the region, where as many as 850 million inhabitants are at risk of contracting lymphatic filariasis. In addition, several epidemiological, technological and historical factors that are unique to the region make each of these four diseases amenable to elimination. Safe and effective tools and interventions to achieve these targets are available and concerted efforts to scale them up, singly or in an integrated manner, are likely to lead to success. The World Health Assembly and the WHO Regional Committee, through a series of resolutions, have already expressed regional and global commitments for the elimination of these diseases as public health problems. Such action is expected to have a quick and dramatic impact on poverty reduction and to contribute to the achievement of the Millennium Development Goals. This paper reviews the policy rationale for disease control in the WHO South-East Asia Region, the progress made so far, the lessons learnt along the way, and the remaining challenges and opportunities.

Giardia and Cryptosporidium join the 'Neglected Diseases Initiative'.

Giardia and Cryptosporidium are ubiquitous enteric protozoan pathogens that infect humans, domestic animals and wildlife worldwide. Both pathogens are significant causes of diarrhea and nutritional disorders in institutional and community settings. They are also significant waterborne pathogens. In developing regions of the world, Giardia and Cryptosporidium constitute part of the complex group of parasitic, bacterial and viral diseases that impair the ability to achieve full potential and impair development and socio-economic improvements. All diseases included in the WHO Neglected Diseases Initiative have a common link with poverty and, as the current view is to take a comprehensive approach to all these diseases, both Giardia and Cryptosporidium were included in 2004. Our current state of knowledge of Giardia and Cryptosporidium is summarized here, and some important questions are raised that need to be addressed if control strategies are to be effective.

Soil-transmitted helminths and haemoglobin status among Afghan children in World Food Programme assisted schools.

In recent years there have been major socio-economic changes within Afghanistan such that the present public health burden of soil-transmitted helminths (STH), especially that within school-aged children, remains to be determined. A baseline parasitological survey was therefore carried out in four defined areas of Afghanistan to better assess the distribution, prevalence and intensity of STH infections prior to a nationwide de-worming campaign beginning within World Food Programme assisted schools. A cross-sectional examination of 1001 children aged between 8 and 15 years old revealed that approximately half (47.2%) were infected with at least one STH. Infections with Ascaris lumbricoides were most widespread (40.9%) and elevated prevalences were detected in urban environments; for example, schoolchildren in Kabul were more likely to be infected (OR=2.2, 95% CI 1.6-3.0) than elsewhere and these infections were often of higher intensity (OR=7.6, 95% CI 4.9-11.8). Trichuris trichiura (9.9%) and hookworms (0.7%), previously unknown from Afghanistan, were encountered. The blood haemoglobin concentration of surveyed children was also assessed: 4% resulted to be anaemic (Hb<11 g dl(-1)), and 0.4% to be severely anaemic (Hb<7 g dl(-1)).

The WHO dose pole for the administration of praziquantel is also accurate in non-African populations.

In 2001, WHO developed a pole for the administration of praziquantel without the use of weighing scales, with encouraging results in African populations. In the present study, the pole was tested on height/weight data from 9354 individuals from 11 non-African countries. In more than 98% of the individuals (95% CI 97.8-98.4) the pole estimated an acceptable dosage (30-60 mg/kg), a performance statistically similar to that observed in African populations. Reproducing the present pole in the form of a strip of paper and including it in each container of praziquantel would greatly facilitate the administration of the drug in large-scale interventions.

Progress in the prevention and control of schistosomiasis and soil-transmitted helminthiasis.

In the last two decades important progress has been made in the understanding the epidemiology and the disease burden of schistosomiasis and soil-transmitted nematodes infection. In addition, practical tools for disease control have been developed and a strategy for the prevention and control of morbidy of schistosomaisis and soil-transmitted nematodes infection has been endorsed by the World Health Organization. This paper presents the recent progress in the prevention and control of these infections: the estimates of chronic and subtle morbidity in high risk groups and the evidence that these chronic and severe sequelae of infections can be reversed by appropriate treatment; the use of anthelminthic drugs during pregnancy and lactation; the relevance to control morbidity due to these infections also in pre-school children; the efficacy of anthelminthic drugs and the possible threat of drug resistance; price, quality and accessibility of treatment by delivering drugs through the school system and ways of reaching also non-enrolled school-age children. Finally, the strategy, targets and recommendations of the World Health Organization for the control of schistosomiasis and soil-transmitted nematodes infection are described.

Efficacy of mebendazole and levamisole alone or in combination against intestinal nematode infections after repeated targeted mebendazole treatment in Zanzibar.

OBJECTIVE: To evaluate the efficacy of and resistance to mebendazole (500 mg) and levamisole (40 or 80 mg), alone or in combination, for the treatment of Ascaris lumbricoides, Trichuris trichiura and hookworm infections on Pemba Island - an area exposed to periodic school-based mebendazole treatment since 1994. METHODS: A randomized, placebo-controlled trial was carried out in 914 children enrolled from the first and fifth grades of primary schools. Stool samples collected at baseline and 21 days after treatment were examined by the Kato-Katz technique to assess the prevalence and intensity of helminth infection. FINDINGS: Efficacies of mebendazole and levamisole as single treatments against intestinal nematode infections were comparable with those in previous trials, but mebendazole treatment of hookworm infections gave significantly lower cure (7.6%) and egg reduction (52.1%) rates than reported in a study undertaken before the beginning of periodic chemotherapy (cure rate, 22.4%; egg reduction rate, 82.4%). Combined treatment with mebendazole and levamisole had a significantly higher efficacy against hookworm infections (cure rate, 26.1%; egg reduction rate, 88.7%) than either drug given alone. No difference in mebendazole efficacy was found in children who had been treated repeatedly compared with those who had not been treated previously. CONCLUSION: The overall efficacy of mebendazole against hookworm infections after periodic chemotherapy is reduced. The efficacy of benzimidazoles in chemotherapy-based control programmes should be monitored closely. Combined treatment with mebendazole and levamisole may be useful as a tool to delay the development of benzimidazole resistance.

Clinical signs and household characteristics associated with human fascioliasis among rural population in Egypt: a case-control study.

The symptomatology associated with human fascioliasis has been studied mostly in hospitalised subjects. Very little is known about clinical signs and symptoms associated with infections in human endemic zones, as well as on possible new ways of transmission which might be responsible for the increased number of human cases reported in recent years. This information is of great importance to facilitate diagnosis and plan effective control measures. With the objective to identify clinical signs, blood tests, household characteristics and hygienic habits associated with human fascioliasis, a cross-sectional case-control study was implemented among the rural population of three endemic foci in the Nile Delta, Egypt. Clinical history was collected from 53 cases of fascioliasis and the same number of individually matched controls. They received a complete clinical examination and a range of blood tests was performed on them. Information on socio-economic conditions, dietary and hygienic habits was also collected. The most important complaints, associated with the infection, were right abdominal pain (Odds Ratio 20, P = 0.005), epigastric burning (o.r. 16, P = 0.007) and nausea (o.r. 8, P = 0.05). Blood analyses reported a marked increase in blood eosinophils (o.r 1.3, P = 0.001) among cases. The presence of cows (o.r 3.2), buffaloes (o.r 3.0) and goats (o.r 2.6) in the household was closely associated with the infection together with the habit to bring those animals to the canal for bathing and/or drinking (o.r. 3.2). Among dietary habits investigated, eating raw seeds was more common in cases than controls (o.r. 9, P = 0.03) and emerged as a possible new way of infection.

Field test of the 'dose pole' for praziquantel in Zanzibar.

A graduated pole for height measurement, estimating the number of praziquantel tablets needed for treatment, was field-tested on 1289 children in Zanzibar. A bathroom-type scale performed better than the dose pole in delivering the optimal dose (40-60 mg/kg) and the 2 methods performed similarly in delivering a dose considered appropriate (30-60 mg/kg).

The global epidemiological situation of schistosomiasis and new approaches to control and research.

While the distribution of schistosomiasis has changed over the last 50 years and there have been successful control programmes, the number of people estimated to be infected or at risk of infection has not been reduced. Today, 85% of the number of infected people are estimated to be on the African continent where few control efforts are made. In terms of disease burden, there is therefore a growing discrepancy between sub-Saharan Africa and the rest of the world. WHO has now developed a dual strategy for the control of schistosomiasis: a strategy for morbidity control adapted to the public health context in high burden areas, and a strategy to consolidate control in areas where a low endemic level has been reached and elimination may be feasible. Related to this new vision, some research needs are pointed out.

Soil-transmitted nematode infections and mebendazole treatment in Mafia Island schoolchildren.

In August 2000, a cross-sectional study was performed to assess the prevalence and intensity of soil-transmitted nematode infections in schoolchildren on Mafia Island. Hookworm infection was widespread (72.5% prevalence) whereas Trichuris trichiura was less prevalent (39.7%) and Ascaris lumbricoides was present at a low prevalence (4.2%), mainly in urban areas. In a subsample of the study population, both Necator americanus and Ancylostoma duodenale were found, although N. americanus was more prevalent. This survey was followed by a parasitological evaluation of mebendazole treatment using a single, 500-mg dose. The data on outcome were used for comparison with those from recent studies of similar treatment regimens in the neighbouring island of Pemba, Zanzibar, where periodic chemotherapy with mebendazole to schoolchildren has been implemented as part of a helminth-control programme since 1994. A higher efficacy of mebendazole against hookworm infection was found in Mafia Island (where a cure 'rate' of 31.3% and an egg-reduction 'rate' of 78.1% were recorded) when compared with that observed in Pemba Island, possibly indicating that hookworms may be developing mebendazole resistance on Pemba Island as a result of intense exposure to the drug there.