Global Epidemiology, Ecology and Control of Soil-Transmitted Helminth Infections

Abstract

Soil-transmitted helminth (STH) infections are among the most prevalent of chronic human infections worldwide. Based on the demonstrable impact on child development, there is a global commitment to finance and implement control strategies with a focus on school-based chemotherapy programmes. The major obstacle to the implementation of cost-effective control is the lack of accurate descriptions of the geographical distribution of infection. In recent years considerable progress has been made in the use of geographical information systems (GIS) and remote sensing (RS) to better understand helminth ecology and epidemiology, and to develop low cost ways to identify target populations for treatment. This chapter explores how this information has been used practically to guide large-scale control programmes. The use of satellite-derived environmental data has yielded new insights into the ecology of infection at a geographical scale that has proven impossible to address using more traditional approaches, and has in turn allowed spatial distributions of infection prevalence to be predicted robustly by statistical approaches. GIS/ RS have increasingly been used in the context of large-scale helminth control programmes, including not only STH infections but also those focusing on schistosomiasis, filariasis and onchocerciasis. The experience indicates that GIS/RS provides a cost-effective approach to designing and monitoring programs at realistic scale. Importantly, the use of this approach has begun to transition from being a specialist approach of international vertical programs to become a routine tool in developing public sector control programs. GIS/RS is used here to describe the global distribution of STH infections and to estimate the number of infections in school age children in sub-Saharan Africa (89.9 million) and the annual cost of providing a single anthelmintic treatment using a school-based approach (US$5.0-7.6 million). These are the first estimates at a continental scale to explicitly include the fine spatial distribution of infection prevalence and population, and suggest that traditional methods have overestimated the situation. The results suggest that continent-wide control of parasites is, from a financial perspective, an attainable goal.

Rapid Re-Infection with Soil-Transmitted Helminths after Triple-Dose Albendazole Treatment of School-Aged Children in Yunnan, People's Republic of China

“…16 The high egg production and long survival of the infective stage (the ova) of A. lumbricoides in the environment could explain the quick re-infection wherever permissive hygiene and behavioral conditions coincide and no measures to prevent re-infection have been implemented. 6 Recent publications have highlighted the low efficacy of albendazole against T. trichiura infections. [40][41][42][43] A single oral dose of 400 mg of albendazole was reported to give a cure rate of 28% in a meta-analysis.…”

“…Specifically, they are still common among the world's poorest populations in the Americas, Asia, and sub-Saharan Africa that lack access to clean water and improved sanitation, and where hygiene is poor. 6,7 Children and pregnant women are most vulnerable to the detrimental effects of soil-transmitted helminth infections, among them anemia, nutritional deficiencies, and impairments in cognitive and physical development. [8][9][10][11] Preventive chemotherapy, i.e., the periodic administration of anthelmintic drugs to entire populations or high-risk groups (e.g., school-aged children), is the hallmark of the control strategy currently advocated by the World Health Organization (WHO).…”

Point-of-care mobile digital microscopy and deep learning for the detection of soil-transmitted helminths and Schistosoma haematobium

“…A majority of these diseases are caused by parasitic worms, of which the most common species affect more than 500 million people in sub-Saharan Africa [2,3]. The vast majority of NTDs here are caused by the soil-transmitted helminths Ascaris lumbricoides, Trichuris trichiura and hookworms, and the trematode Schistosoma haematobium .…”

FLOTAC: a new sensitive technique for the diagnosis of hookworm infections in humans

“…The collective burden of soil-transmitted helminthiases may be as high as 39 million disability-adjusted life-years, similar to that due to malaria or tuberculosis (Hotez et al, 2006a;WHO, 2002). Fortunately, local, regional and global commitments to control soil-transmitted helminthiases and other so-called neglected tropical diseases have grown recently, with efforts getting underway to harness potential synergies through the integration of control programmes targeting multiple neglected tropical diseases simultaneously (Brady et al, 2006;Brooker et al, 2006;Fenwick, 2006;Lammie et al, 2006;Molyneux et al, 2005). The main thrust of the new helminth control initiatives is that safe, efficacious and inexpensive drugs are available to reduce the burden caused by these diseases (Hotez et al, 2006a).…”

“…An infection with hookworm can cause abdominal pain and diarrhoea, but the main clinical consequence is iron deficiency anaemia caused by intestinal blood loss resulting from the haematophagy of these worms and from areas of microhaemorrhages on the gut mucosa when the worms detach (Bethony et al, 2006;Brooker et al, 2006;Stoltzfus et al, 1996). The definitive diagnosis of a hookworm infection rests on microscopic visualisation of eggs in stool.…”