Background wet deposition of mercury in Great Britain.

Precipitation samples have been collected on a monthly basis from a network of 10 sites in Great Britain (GB) in order to estimate background mercury (Hg) deposition in the rural environment. Collection started in February 2005 and results presented here cover the period up to June 2009. The annual volume-weighted mean (AVWM) Hg concentrations range from 1.0 ng L(-1) at Cockley Beck in the Lake District in 2006 to 8.8 ng L(-1) at Heigham Holmes on the Norfolk Coast England in 2008. The largest validated solution concentrations were 33.7 ng L(-1) Hg measured at Cockley Beck in May 2008. The large difference in rainfall amount between sites means that the remote site at Cockley Beck has both the lowest long-term AVWM concentration (1.6 ng L(-1)) and the greatest annual flux is greatest at 43 mg ha(-1) yr(-1). Predicted deposition tends to be much greater in western Britain where the greater rainfall occurs. Because some observations are very close to the analytical detection limit (1.0 ng L(-1)), rigorous cleaning procedures, the use of replicate samplers to monitor contamination, and the inclusion of 'bottle blanks' are required to obtain valid measurements of Hg in the bulk deposition. Deposition in rural sites is equivalent to about 10% of the estimated magnitude of known emissions in GB.

Travel as a risk factor for uncomplicated Plasmodium falciparum malaria in the highlands of western Kenya.

In the 1980s, highland malaria returned to the tea estates of western Kenya after an absence of nearly a generation. In order to determine the importance of travel for the spread of malaria in this region, we prospectively collected blood films and travel, demographic and geographic information on well persons and outpatients on tea estates near the western rim of the Rift Valley. Risk factors for malaria asexual parasitaemia included: tribal/ethnic group, home province and home district malaria endemicity. Travel away from the Kericho tea estates within the previous two months showed an odds ratio (OR) for parasitaemia of 1.59 for well persons and 2.38 for outpatients. Sexual stages of malaria parasites (gametocytes) had an OR of 3.14 (well persons) and 2.22 (outpatients) for those who had travelled. Increased risk of malaria parasitaemia with travel was concentrated in children aged <5 years. An increase in population gametocytaemia is possibly due to increased chloroquine resistance and suppressed infections contracted outside of the tea estates.

Anthelmintics. A comparative review of their clinical pharmacology.

Virtually all the important helminth infections in humans can be treated with one of 5 anthelmintics currently in use: albendazole, mebendazole, diethylcarbamazine, ivermectin and praziquantel. These drugs are vital not only for the treatment of individual infections, but also useful in controlling transmission of the more common infections. This article reviews briefly the pharmacology of these 5 drugs, and then discusses current issues in the use of anthelmintics in the treatment and/or control of soil-transmitted nematode infections, filariasis, onchocerciasis, schistosomiasis (and other trematode infections), neurocysticercosis and hydatidosis. Mebendazole and albendazole are most effective against intestinal nematodes, but are contraindicated during the first trimester of pregnancy. The efficacy of prolonged therapy with these 2 drugs for treatment of larval cestode infections has not yet been established. Diethylcarbamazine is widely used to treat and control lymphatic filariasis, but adverse effects related to death of microfilariae or damage to adult worms may be marked. While ivermectin has been used in the treatment of patients with onchocerciasis, it is also undergoing investigation against lymphatic filariae. Praziquantel, used to treat schistosome infections, is also effective in other trematode infections and adult cestode infections.

Different approaches to modeling the cost-effectiveness of schistosomiasis control.

The limited economic resources available for health care in developing countries necessitates the involvement of cost analysis in the planning of any control intervention. A number of studies have undertaken cost-effectiveness analysis of schistosomiasis control, and the methodologies utilized in both cost and effectiveness evaluation are discussed. In attempting to relate cost to effectiveness, most studies have utilized static models expressing effectiveness in terms of coverage (drug delivery) or cure rate (infection prevalence reduction). These immediate output measures do not consider the long-term impact of control nor the effect on disease. An alternative approach is to use a model of the transmission dynamics of the parasite to permit evaluation of the long-term impact of control. An example of a population dynamic approach to cost-effectiveness analysis that can assess the impact of treatment on infection and disease due to the intestinal nematodes is presented to illustrate the potential of this approach in modeling the cost-effectiveness of schistosomiasis control.

The epidemiology and burden of Plasmodium falciparum-related anemia among pregnant women in sub-Saharan Africa.

The paucity of precise information on the burden of malaria among pregnant women has hampered effective lobbying for the inclusion of preventative strategies against malaria in Safe Motherhood Initiatives. This article reviews the evidence on the coincidental risks of malaria and anemia in Africa and attempts to estimate the probable burden of malaria-related severe anemia in this susceptible group. Twenty-six studies on hemoglobin levels in all-parity pregnant women throughout this region could be matched with a malaria parasite ratio in children < 15 yr old (a measure of the intensity of transmission). In areas with no malaria, the mean hemoglobin levels were markedly higher than those found in areas with stable malaria transmission, though changes with increasing intensity of transmission were unclear. Eighteen studies from areas with stable malaria transmission in sub-Saharan Africa suggested that the median prevalence of severe anemia in all-parity pregnant women is approximately 8.2%. Assuming that 26% of these cases are due to malaria, it is suggested that as many as 400,000 pregnant women may have developed severe anemia as a result of infection with malaria in sub-Saharan Africa in 1995.

Assessing the public health importance of Schistosoma mansoni in different endemic areas: attributable fraction estimates as an approach.

Assessment of the public health importance of schistosomiasis mansoni is hampered by the nonspecificity of many of its disease symptoms. Parasitologic, clinical, and anamnestic data from two areas in Burundi were used to obtain estimates of the attributable fractions for different disease symptoms at both the population level and within different age strata. A large proportion of individuals had symptoms commonly associated with Schistosoma mansoni infection that were not attributable to this parasite. The clinical indicator with the best test efficiency was shown to be bloody diarrhea. At the population level, 35% of bloody diarrhea cases were attributable to S. mansoni, compared with only 9% of diarrhea cases without blood. The attributable fractions were age-dependent, and in the case of diarrhea (with and without blood), children had a higher proportion of cases attributable to S. mansoni infection than adults. The association between infection and disease symptoms also increased with the intensity of infection. The prevalence of morbidity attributable to S. mansoni was similar for all symptoms, and higher in children than adults. The estimation of attributable fractions provides a simple approach to quantify S. mansoni-related morbidity, which could also be extended to both S. haematobium and S. japonicum. Attributable fraction estimates for these three schistosome species in different endemic areas would greatly aid in the assessment of the health burden of this parasite and the effectiveness of control programs.

Dynamic models of schistosomiasis morbidity.

Previous attempts to assess the health impact of schistosomiasis control programs on community morbidity have been limited by a lack of a theoretical framework that describes the dynamic relationships between infection and morbidity. In this paper, a model of schistosomal morbidity is developed and parameterized. Morbidity is divided into that due to current heavy infection, and early and late stages of chronic disease. The model was parameterized using data showing resolution of disease after treatment, correlations between prevalence of disease and intensity of infection and using age-morbidity profiles. The fitted parameters suggest that early manifestations of disease such as hepatomegaly in Schistosoma mansoni and S. japonicum infections would resolve relatively quickly following treatment whereas later forms of disease such as liver fibrosis resolve very slowly or not at all. Similar general conclusions were obtained with data on early and late forms of urinary tract morbidity in S. haematobium.

Estimating prevalence of community morbidity due to intestinal helminths: prevalence of infection as an indicator of the prevalence of disease.

The rational design of helminth control programmes for endemic areas requires that the limited resources be focused on the communities in greatest need. The process of locality-targetting would be facilitated by a simple, inexpensive method of assessing morbidity at the community level. This paper describes how a simple model of the distribution of infection in human populations can use infection prevalence data to predict the proportion of heavy, and potentially clinically significant, infections in a community. Analysis of observed data for Ascaris lumbricoides indicates that the risk of clinical ascariasis increases non-linearly with the prevalence of infection. The predicted prevalence of morbidity is low up to approximately 60% prevalence of infection, but increases very rapidly thereafter. Analyses of data for Trichuris trichiura, Schistosoma mansoni, S. haematobium and the hookworms suggests qualitatively similar patterns. The application of the model in predicting resource requirements for control is illustrated using infection prevalence data for A. lumbricoides in Brazil.

Malaria in pregnancy as an indirect cause of infant mortality in sub-Saharan Africa.

Although randomized controlled trials of interventions to reduce malaria in pregnancy have demonstrated an increase in the birthweight of the newborn in primigravidae, the subsequent impact on infant mortality in all-parities has not been assessed. The aim of this paper was to model the possible impact of placental malarial infection on infant mortality through reduced birthweight. An extensive literature search was undertaken to define a series of parameters describing the associations between placental infection, birthweight and premature mortality in sub-Saharan Africa. It was shown that a baby is twice as likely to be born of low birthweight if the mother has an infected placenta at the time of delivery (all-parities: 23% vs 11%, primigravidae only: 32% vs 16%), and that the probability of premature mortality of African newborns in the first year of life is 3 times higher in babies of low birthweight than in those of normal birthweight (16% vs 4.6%). Assuming 25% of pregnant women in malaria-endemic areas of Africa harbour placental malarial infection, it is suggested that 5.7% of infant deaths in malarious areas could be an indirect cause of malaria in pregnancy. This would imply that, in 1997, malaria in pregnancy could have been responsible for around 3700 infant deaths under the diverse epidemiological conditions in Kenya. Placental infection with Plasmodium falciparum appears to have a more significant role in infant survival in Africa than has been previously assumed. This may explain the high reduction in infant mortality rates from interventions aimed at reducing transmission, over and above that expected from a decline in direct malaria-specific mortality alone.

Cost analysis of schistosomiasis.

Cost analysis of schistosomiasis is important both in assessing the economic impact of the disease and in identifying the most cost-effective approaches to control. Economic impact has been examined both within and without the health sector, but there is a lack of measurement of the effects of disease, or the threat of disease, on patterns of production and community development. The cost-effectiveness of control approaches has been examined empirically and by using static models. Future analyses require a stronger epidemiological basis incorporating realistic demography and the temporal dynamics of reinfection, and assessment of outcomes in terms of disease rather than infection.

A population dynamic approach to the cost-effectiveness analysis of mass anthelmintic treatment: effects of treatment frequency on Ascaris infection.

This study examines the cost-effectiveness of different frequencies of mass chemotherapy in reducing helminth infection and morbidity at the community level. The cost-effectiveness framework utilities a dynamic model of helminth transmission which permits the effectiveness of treatment to be expressed as some long-term reduction in infection and disease. Cost analysis is incorporated into this framework using an itemized cost menu and cost data from an actual control programme. The cost-effectiveness of mass treatment is investigated using epidemiological measures considered appropriate to Ascaris lumbricoides infection in both a high and low transmission area. The optimal strategy for control is shown to be dependent on the control objectives, the rate of transmission, and existing budget constraints. The analysis suggests that if the aim of control is to reduce morbidity due to ascariasis and mass treatment is the approach selected, then it is more cost-effective to intervene in a high transmission area than in a low transmission area, and that relatively long intervals between treatments offer the most cost-effective strategy.

Morbidity and mortality due to Ascaris-induced intestinal obstruction.

We examined epidemiological aspects of Ascaris-induced intestinal obstruction (AI-IO) through analysis of published reports on the subject. In 9 studies of > or = 100 patients admitted to hospital due to ascariasis, intestinal obstruction was the single most common complication and accounted for 38-87.5% of all complications (weighted mean 72%). The proportion of intestinal obstruction caused by ascariasis was identified in 14 studies from 7 countries with varying degrees of endemic ascariasis. Using relevant data on the duration of the study, the number of beds in the reporting hospital, and the number of hospital beds/1000 population in the area, the number of cases of AI-IO/year/1000 population was estimated from 11 studies. Both the proportion of AI-IO (range 0-0.71) and the number of cases of AI-IO/year/1000 population (range 0-0.25) were significantly related, in a non-linear manner, to the local prevalence of ascariasis (range 0.01-0.92). In 12 studies of > or = 30 patients with AI-IO, the case fatality rates ranged from 0 to 8.6% (weighted mean 5.7%). The mean age of patients with AI-IO was < or = 5 years in 6 of 7 studies in which age was specified.

Epidemiology of acute filarial episodes caused by Wuchereria bancrofti infection in two rural villages in Tamil, Nadu, south India.

This year-long study investigated the epidemiology of acute filarial episodes due to Wuchereria bancrofti in 2 rural villages in south India. The annual incidence of 96.5 episodes/1000 population was significantly higher in males (108.5) than females (84.1) an strongly age dependent. First occurrence of acute disease was observed in 0.86% of the population, and the average duration of each episode was 3.6 +/- 2.0 d. Although more than half (63.5%) of the affected individuals suffered only 1 episode, a few experienced as many as 8 over the one-year period. Individuals with chronic disease were more prone to acute attacks, with 82.9% of the total episodes occurring in this group. No seasonal pattern was observed in the frequency of episodes. Probit analysis showed that the number of episodes per affected person was dependent on sex and chronic condition. Swelling of lymph nodes in the inguinal region and fever were the most common symptoms of acute disease. The high incidence and resulting debility observed in this study suggest that acute episodes are a significant health problem associated with lymphatic filariasis. There is clearly a need for more studies on this acute form of filarial disease to aid the understanding of the aetiology and epidemiology of acute episodes, in planning appropriate control interventions, and in evaluating the resulting health burden.

Geohelminth infection of children from rural plantations and urban slums in Malaysia.

This study compares levels of geohelminth infection in children living in rural estates and urban slum areas of Malaysia. The statistical characteristics of geohelminth infection in 1499 children from birth up to 15 years of age, living in rural estates, were analysed according to age, sex and ethnic origin and compared with the same statistics for 1574 slum-dwelling children of similar age groups and ethnic origins. The prevalence and intensity of ascariasis and trichuriasis were significantly higher among children from the urban slums. Slum-dwelling ethnic Indians and Malays had higher levels of infection with Ascaris lumbricoides and Trichuris trichiura than their rural counterparts, but the infection status of the ethnic Chinese in the 2 areas was similar. Hookworm infection was similar in both areas, indicating that hookworm infection is neither necessarily nor solely a rural disease. These results suggest that urban slum children are at greater risk of ascariasis and trichuriasis than their rural counterparts.

Control of Ascaris infection by chemotherapy: which is the most cost-effective option?

Cost-effectiveness analysis is used to predict the optimal design of mass chemotherapy strategies in controlling Ascaris lumbricoides infection. The question of who to treat, how many to treat, and how often to treat are addressed using a population dynamic model of helminth transmission that assesses effectiveness in terms of disease reduction, combined with cost data from an actual control programme. Child-targeted treatment can be more cost-effective than population treatment in reducing the number of disease cases. The model also implies that, in the circumstances described here, enhancing coverage is a more cost-effective approach than increasing frequency of treatment.

Patterns of concurrent hookworm infection and schistosomiasis in schoolchildren in Tanzania.

A cross-sectional study of 6897 schoolchildren in 59 out of the 155 primary schools in Magu District on the shores of Lake Victoria, Tanzania, was undertaken in 1997 to determine the prevalence of single- and multiple-species helminth infection. Schistosoma haematobium, hookworm (primarily Necator americanus) and S. mansoni were the most common helminth species infecting schoolchildren in the district. The prevalences of Ascaris lumbricoides and Trichuris trichiura were negligible (< 1%). Anaemia and stunting were highly prevalent and widespread. Hookworm and S. mansoni occurred more frequently in multiple infections with other helminths than as single-species infections, but triple-species infection was rare. Analysis of the frequency distribution of infection amongst schools showed that prevalences of S. haematobium and hookworm tended to be normally distributed, with medians 75% and 45%, respectively, while the distribution of S. mansoni was markedly skewed such that only 17% schools had a prevalence greater than 20%. An inverse association between S. mansoni and S. haematobium was observed. Geographical information system (GIS) analysis indicated that S. mansoni infection was highly prevalent only along the shore of Lake Victoria, whilst S. haematobium was homogeneously prevalent everywhere except the lakeshore. This pattern appears to reflect the distribution of schistosome species-specific snail intermediate hosts. The results imply that joint treatment for hookworm infection and schistosomiasis would be beneficial throughout the district.

The epidemiology of hookworm infection and its contribution to anaemia among pre-school children on the Kenyan coast.

Intestinal nematode infections are recognized as a major public health problem, and helminth control is currently being directed towards school-aged children who are known to harbour the heaviest infections and are most likely to suffer from associated morbidity. However, few data are available for the epidemiology of intestinal nematodes in pre-school children in Africa, and the contribution of hookworm infection to the aetiology and severity of anaemia among pre-school children remains poorly understood. This paper investigates the epidemiology of parasitic infections in 460 pre-school children who were part of a larger case-control study of severe malaria in Kilifi on the Kenyan coast. Almost one-third (28.7%) were infected with hookworm, 20.2% with Ascaris lumbricoides and 15.0% with Trichuris trichiura. Infection prevalence of each species rose with age, and the prevalence of heavy infection with hookworm and mean intensity of hookworm were markedly age-dependent. One-third (34.3%) of children had malaria. Overall, 76.3% of children were anaemic (haemoglobin < 110 g/L), with the prevalence decreasing with age. Anaemia was significantly worst in children with heavy hookworm infection (> 200 eggs per gram). This relationship held for all ages, both sexes, and was independent of socioeconomic factors. The application of attributable morbidity methods confirmed the contribution of hookworm infection to anaemia.

Desirable characteristics of a schistosomiasis vaccine: some implications of a cost-effectiveness analysis.

This paper investigates some of the characteristics which a vaccine for schistosomiasis would require to be more cost-effective than chemotherapy. The impact of a variety of possible vaccination scenarios are assessed in terms of the discounted years of heavy infection prevented in children, and the cost-effectiveness of these approaches are compared with annual mass treatment. The analyses demonstrate that the three critical parameters determining whether a vaccine would ever be more cost-effective than mass chemotherapy are price, duration of protection and efficacy. If the vaccine had sufficient duration of protection to be delivered through the regular childhood immunization programmes (EPI), it could be more cost-effective than annual chemotherapy. The necessary condition is that adding the vaccine to EPI must not cost more than $4.30 per person in excess of one round of chemotherapy. For a shorter duration of vaccine protection, the schistosomiasis vaccine could not exceed the cost (including delivery costs) of one round of annual chemotherapy by more than approximately $3.50.

The cost effectiveness of mass drug therapy for intestinal helminths.

This article reviews the principles involved in establishing the cost effectiveness of mass drug therapy for the major intestinal nematodes and the intestinal form of schistosomiasis, as well as the extent to which the available studies have provided definitive answers. For governments or agencies that have decided to introduce a control programme, there is considerable evidence about the comparative cost effectiveness of different types of delivery strategies. For example, mass treatment is more cost effective than selective treatment (treatment after individual screening) in high prevalence areas and at observed prices. Mass treatment targeted at known high risk groups, such as schoolchildren, for the major intestinal helminths (apart from hookworm) can be more cost effective than population-based mass treatment. However, this raises the question whether any form of mass anthelmintic chemotherapy is an efficient use of scare health resources in view of the competing demands for scarce public funds, and for the scarce resources of other funders of healthcare including donors, nongovernmental organisations and missions. Some evidence that it is an efficient use of resources is available; this article concludes by outlining the type of information that is required to strengthen the argument for mass therapy.

The effects of sex and age of responders on the reliability of self-diagnosed infection: a study of self-reported urinary schistosomiasis in Tanzanian school children.

Self-reported schistosomiasis has been proven to be a reliable estimation of the prevalence of infection in school children. For the first time, this paper presents an investigation into the use of self-reported schistosomiasis to estimate the prevalence of urinary schistosomiasis, due to Schistosoma haematobium, in school children with particular emphasis on whether the age and sex of respondents influences the reliability of diagnosis. It is shown first, that the prevalence and intensity of infection vary with sex; infection in boys is always more prevalent and more intense than in girls of the same age and second, that age and sex influence the reliability of self-reported schistosomiasis as a diagnostic method. Age and sex are factors that should be considered when implementing control measures in endemic areas.