SciCombinator

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Concept: Parasitic animals

173

Understanding the global limits of transmission of soil-transmitted helminth (STH) species is essential for quantifying the population at-risk and the burden of disease. This paper aims to define these limits on the basis of environmental and socioeconomic factors, and additionally seeks to investigate the effects of urbanisation and economic development on STH transmission, and estimate numbers at-risk of infection with Ascaris lumbricoides, Trichuris trichiura and hookworm in 2010.

Concepts: Disease, Infection, Nematodes, Whipworm, Hookworm, Parasitic worm, Parasitic animals, Ascaris lumbricoides

165

BACKGROUND: The prevalence of infection with the three common soil-transmitted helminths (i.e. Ascaris lumbricoides, Trichuris trichiura and hookworm) in Bolivia is among the highest in Latin America. However, the spatial distribution and burden of soil-transmitted helminthiasis are poorly documented. METHODS: We analysed historical survey data using Bayesian geostatistical models to identify determinants of the distribution of soil-transmitted helminth infections, predict the geographical distribution of infection risk, and assess treatment needs and costs in the frame of preventive chemotherapy. Rigorous geostatistical variable selection identified the most important predictors of A. lumbricoides, T. trichiura and hookworm transmission. RESULTS: Results show that precipitation during the wettest quarter above 400 mm favours the distribution of A. lumbricoides. Altitude has a negative effect on T. trichiura. Hookworm is sensitive to temperature during the coldest month. We estimate that 38.0%, 19.3% and 11.4% of the Bolivian population is infected with A. lumbricoides, T. trichiura and hookworm, respectively. Assuming independence of the infections, 48.4% of the population is infected with any soil-transmitted helminth. Empirical-based estimates, according to treatment recommendations by the World Health Organization, suggest a total of 2.9 million annualised treatments for the control of soil-transmitted helminthiasis in Bolivia. CONCLUSIONS: We provide estimates of soil-transmitted helminth infections in Bolivia based on high-resolution spatial prediction and an innovative variable selection approach. However, the scarcity of the data suggests that a national survey is required for more accurate mapping that will govern spatial targeting of soil-transmitted helminthiasis control.

Concepts: Infection, Prediction, Transmission and infection of H5N1, Nematodes, Whipworm, Hookworm, Parasitic worm, Parasitic animals

137

Trichuris trichiura (whipworm) is one of the four major soil-transmitted helminth infections of man, affecting an estimated 465 million people worldwide. An effective vaccine that induces long-lasting protective immunity against T. trichiura would alleviate the morbidity associated with this intestinal-dwelling parasite, however the lack of known host protective antigens has hindered vaccine development. Here, we show that vaccination with ES products stimulates long-lasting protection against chronic infection in male C57BL/6 mice. We also provide a framework for the identification of immunogenic proteins within T. muris ES, and identify eleven candidates with direct homologues in T. trichiura that warrant further study. Given the extensive homology between T. muris and T. trichiura at both the genomic and transcriptomic levels, this work has the potential to advance vaccine design for T. trichiura.

Concepts: Immune system, Vaccine, Vaccination, Immunology, Nematodes, Whipworm, Parasitic animals, Trichuris

93

Infection with intestinal helminths results in immunological changes that influence co-infections, and might influence fecundity by inducing immunological states affecting conception and pregnancy. We investigated associations between intestinal helminths and fertility in women, using 9 years of longitudinal data from 986 Bolivian forager-horticulturalists, experiencing natural fertility and 70% helminth prevalence. We found that different species of helminth are associated with contrasting effects on fecundity. Infection with roundworm (Ascaris lumbricoides) is associated with earlier first births and shortened interbirth intervals, whereas infection with hookworm is associated with delayed first pregnancy and extended interbirth intervals. Thus, helminths may have important effects on human fertility that reflect physiological and immunological consequences of infection.

Concepts: Intestinal parasite, Fertility, Nematodes, Hookworm, Parasitic worm, Parasitic animals, Pinworm, Ascaris lumbricoides

59

We created a mobile phone microscope and assessed its accuracy for the diagnosis of soil-transmitted helminths compared with conventional microscopy. Mobile phone microscopy has a sensitivity of 69.4% for detecting any helminth egg and sensitivities of 81.0%, 54.4%, and 14.3% for the diagnosis of Ascaris lumbricoides, Trichuris trichiura, and hookworm, respectively.

Concepts: Nematodes, Mobile phone, Whipworm, Hookworm, Parasitic worm, Parasitic animals

27

Solid evidence regarding the epidemiology of intestinal helminth infections in Tajikistan is currently lacking. As such information is essential for the evidence-based design, implementation and evaluation of control interventions, a national intestinal helminth survey was conducted with the following objectives: i) to assess the prevalence of intestinal helminth infections among school-aged children nationally and stratified by region; ii) to identify locally relevant risk factors for infection; and iii) to better understand the children’s knowledge and perception of intestinal helminth infections, and asses their haemoglobin status. Standard field and laboratory procedures including the Kato-Katz thick smear and tape test were employed. Complete data was obtained for 1642 children from 33 randomly selected primary schools from different parts of the country. Across the country, prevalences of E. vermicularis, A. lumbricoides, H. nana and T. trichiura were 26.5%, 16.9%, 15.5% and 2.7% respectively. The prevalence of common soil-transmitted helminth (A. lumbricoides and T. trichiura) infections was 19.4%. No hookworm infections were detected, and prevalences of various infections differed significantly between administrative districts (all P<0.05). Hand washing after toilet usage (OR=0.78; P=0.047) and handling animals (OR=0.66; P=0.009) were identified as significant protective factors against E. vermicularis infections. H. nana infection was associated with a 2.85g/L decrease in haemoglobin levels (P<0.001) despite already low average haemoglobin levels. The proportions of children with knowledge about intestinal helminths and protective hygiene practices varied significantly between regions (both P<0.001). Mass albendazole administration to school-aged children and women of child-bearing age against intestinal helminths has now been initiated in Tajikistan, to be followed by mass albendazole and praziquantel distribution to school-aged children. In the longer term, an integrated approach including chemotherapy, provision of safe water and proper sanitation as well as targeted health education will be necessary to achieve sustainable control.

Concepts: Disease, Intestinal parasite, Hygiene, Hookworm, Parasitic worm, Parasitic animals, Pinworm, Helminthology

15

Quantifying the burden of parasitic diseases in relation to other diseases and injuries requires reliable estimates of prevalence for each disease and an analytic framework within which to estimate attributable morbidity and mortality. Here we use data included in the Global Atlas of Helminth Infection to derive new global estimates of numbers infected with intestinal nematodes (soil-transmitted helminths, STH: Ascaris lumbricoides, Trichuris trichiura and the hookworms) and use disability-adjusted life years (DALYs) to estimate disease burden.

Concepts: Disease, Infection, Intestinal parasite, Nematodes, Hookworm, Parasitic worm, Parasitic animals, Pinworm

11

Soil-transmitted helminth (STH) infections (i.e., Ascaris lumbricoides, hookworm, and Trichuris trichiura) affect more than a billion people. Preventive chemotherapy (i.e., repeated administration of anthelmintic drugs to at-risk populations), is the mainstay of control. This strategy, however, does not prevent reinfection. We performed a systematic review and meta-analysis to assess patterns and dynamics of STH reinfection after drug treatment.

Concepts: Drug, Nematodes, Whipworm, Anthelmintic, Parasitic animals, Ascaris lumbricoides

5

The human helminth infections include ascariasis, trichuriasis, hookworm infections, schistosomiasis, lymphatic filariasis (LF) and onchocerciasis. It is estimated that almost 2 billion people worldwide are infected with helminths. Whilst the WHO treatment guidelines for helminth infections are mostly aimed at controlling morbidity, there has been a recent shift with some countries moving towards goals of disease elimination through mass drug administration, especially for LF and onchocerciasis. However, as prevalence is driven lower, treating entire populations may no longer be the most efficient or cost-effective strategy. Instead, it may be beneficial to identify individuals or demographic groups who are persistently infected, often termed as being “predisposed” to infection, and target treatment at them.

Concepts: Epidemiology, Disease, Demography, Parasitic diseases, Neglected diseases, Hookworm, Parasitic worm, Parasitic animals

2

Recommendations for soil-transmitted helminth (STH) control give a key role to deworming of school and pre-school age children with albendazole or mebendazole; which might be insufficient to achieve adequate control, particularly against Strongyloides stercoralis. The impact of preventive chemotherapy (PC) against STH morbidity is still incompletely understood. The aim of this study was to assess the effectiveness of a community-based program with albendazole and ivermectin in a high transmission setting for S. stercoralis and hookworm.

Concepts: Strongyloidiasis, Strongyloides stercoralis, Hookworm, Parasitic worm, Parasitic animals, Pinworm