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Ascaris lumbricoides
Abstract
In the context of the current unprecedented momentum and commitment to control neglected tropical diseases, and the increased advocacy of anthelmintic mass drug administration (MDA), there are renewed calls for research and development into the epidemiology and population biology of helmintic parasites to be embedded at the core of intervention strategies. This review of the epidemiology of Ascaris lumbricoides – one of the three neglected soil-transmitted helminth infections of greatest public health importance – includes discussion on diagnostic methods and their limitations; patterns of transmission within communities, including heterogeneities in infection and reinfection following curative treatment; the geographical distribution of infection, and the role of environmental, climatic and socio-economic co-variables. Special emphasis is placed on the mathematical approaches that underpin contemporary parasite epidemiology. In particular, statistical models – for analyzing highly variable, overdispersed, zero-inflated and hierarchically or spatially structured data – and dynamic models of infection and transmission. Deterministic, stochastic and hybrid dynamic models are discussed in the context of their application in elucidating the interplay between the parasite frequency distribution and density-dependent population processes; the dynamics of reinfection following curative treatment; the sustainability of parasite populations at low densities; theoretical threshold densities (transmission breakpoints) for elimination; and the potential spread of anthelmintic resistance. The review highlights the public health relevance of mathematical models and analytical methods, and concludes by focusing on recent insights into the epidemiology of A. lumbricoides which are particularly germane to the effective implementation of MDA-based control.
... After adjusting for other covariates, infection by A. lumbricoides was found to be significantly associated with the prevalence of anaemia and the prevalence of both lowand moderate/high-severity anaemia. The biological ability of A. lumbricoides to produce c.200,000 eggs/day [44], causing inflammation in the intestinal tract, may result in increased prevalence of anaemia and explain the trend evident in our models. In fact, A. lumbricoides eggs in tissue incite granulomatous inflammation, and larvae migrating through the host's lungs stimulate an inflammatory infiltrate with abundant eosinophilic leukocytes. ...
Background:
Childhood anaemia affects 1.8 billion people globally. Little is known about the long-term impact of mass drug administration (MDA) for the control of soil-transmitted helminthiases (STH) on the spatiotemporal variation of anaemia prevalence and severity. We describe the long-term spatiotemporal impact of a 5-year STH MDA programme (2007-2011) on the prevalence of anaemia and anaemia severity in school-aged children (SAC) in Burundi.
Methodology/principal findings:
We used annual haemoglobin concentration and STH data collected during 2007-2011 in 31 schools in Burundi. Spatial dependence in prevalence and severity of anaemia was assessed using semivariograms. Bayesian geostatistical models were developed to (a) quantify the role of STH (adjusted for other anaemia determinants) in the spatiotemporal distribution of anaemia prevalence/severity, and (b) predict the geographical variation of both outcomes across Burundi. Adjusted population data were used to estimate the geographical distribution of the number of SAC at risk of anaemia and with low and moderate/severe anaemia. Infections with Ascaris lumbricoides and Trichuris trichiura were positively and significantly associated with childhood anaemia; hookworm infections were not. A significant decrease in anaemia prevalence, from 40-50% (2008) to 10-20% (2011) was predicted in western areas. The predicted prevalence of low-severity anaemia decreased from 40-50% (2008) to <20% (2011) in southern and eastern areas. Moderate/high-severity anaemia was concentrated in western regions of Burundi, with pockets of moderate/high-severity anaemia in central and northern regions in 2008. The overall number of predicted anaemic children decreased from 443,657 (2008) to 232,304 (2011), with a resurgence after MDA disruption in 2010 (to 480,605). Prevalence of low- and moderate-severity anaemia was higher in boys than in girls.
Conclusions/significance:
Despite ongoing MDA, the prevalence of anaemia in SAC remained high and increased in certain parts of the country. It is recommended that MDA programmes targeting STH are complemented with specific anaemia interventions.
... The high prevalence of helminths in developing countries, high rates of reinfection and resistance to anthelmintics and current unavailability of vaccines against these parasites, stress the need to focus research into elucidating the mechanisms involved in these interactions and thus identify essential aspects pertaining the design of new strategies to control the spread of these helminths as well as novel therapeutic alternatives. In this review, we have included the nematodes Trichuris and Ascaris since they exhibit the highest prevalence and level of endemicity in low and middleincome countries, as well as to their notorious impact on animal health and the swine industry (Sayasone et al., 2011;Walker et al., 2013;Ojha et al., 2014;Pullan et al., 2014;Dunn et al., 2016;Corteś et al., 2019;Hernańdez et al., 2019;Sobotkováet al., 2019;Else et al., 2020;Gordon et al., 2020). ...
Helminth infections remain a global public health issue, particularly in low- and middle-income countries, where roundworms from theTrichuris and Ascaris genera are most prevalent. These geohelminths not only impact human health but most importantly also affect animal well-being, in particular the swine industry. Host-helminth parasite interactions are complex and at the same time essential to understand the biology, dynamics and pathophysiology of these infections. Within these interactions, the immunomodulatory capacity of these helminths in the host has been extensively studied. Moreover, in recent years a growing interest on how helminths interact with the intestinal microbiota of the host has sparked, highlighting how this relationship plays an essential role in the establishment of initial infection, survival and persistence of the parasite, as well as in the development of chronic infections. Identifying the changes generated by these helminths on the composition and structure of the host intestinal microbiota constitutes a field of great scientific interest, since this can provide essential and actionable information for designing effective control and therapeutic strategies. Helminths like Trichuris and Ascaris are a focus of special importance due to their high prevalence, higher reinfection rates, resistance to anthelmintic therapy and unavailability of vaccines. Therefore, characterizing interactions between these helminths and the host intestinal microbiota represents an important approach to better understand the nature of this dynamic interface and explore novel therapeutic alternatives based on management of host microbiota. Given the extraordinary impact this may have from a biological, clinical, and epidemiological public health standpoint, this review aims to provide a comprehensive overview of current knowledge and future perspectives examining the parasite-microbiota interplay and its impact on host immunity.
... Similar to other macroparasites, one of the defining parameters that contribute to our understanding of Ascaris epidemiology is the intensity of infection (Walker et al., 2013). Macroparasite intensity is not distributed randomly among hostsbut manifests itself as an aggregated distribution (Holland et al., 1989;Holland and Boes, 2002) whereby few hosts carry the majority of the worms and most hosts remain uninfected or carry light infections. ...
Ascaris lumbricoides and Ascaris suum are helminth parasites of humans and pigs, respectively. The life cycle of Ascaris sets it apart from the other soil-transmitted helminths because of its hepato-tracheal migration. Larval migration contributes to underestimated morbidity in humans and pigs. This migration, coupled with a lack of a murine model in which the Ascaris parasite might complete its life cycle, has undoubtedly contributed to the neglected status of the ascarid. Our knowledge of the epidemiology of adult worm infections had led us to an enhanced understanding of patterns of infection such as aggregation and predisposition; however, the mechanisms underlying these complex phenomena remain elusive. Carefully controlled experiments in defined inbred strains of mice – with enhanced recovery of larvae in tandem with measurements of cellular, histopathological and molecular processes – have greatly enhanced our knowledge of the early phase of infection, a phase crucial to the success or failure of adult worm establishment. Furthermore, the recent development of a mouse model of susceptibility and resistance, with highly consistent and diverging Ascaris larval burdens in the murine lungs, represents the extremes of the host phenotype displayed in the aggregated distribution of worms and provides an opportunity to explore the mechanistic basis that confers predisposition to light and heavy Ascaris infection. Certainly, detailed knowledge of the cellular hepatic and pulmonary responses at the molecular level can be accrued from murine models of infection and, once available, may enhance our ability to develop immunomodulatory therapies to elicit resistance to infection.
... Capillaria spp., though look like Trichuris, are critical in goats and share a wide range of herbivores including man (Rehbein and Haupt 1994;Fakae 1990;Odermatt et al. 2010). Notably, our reports of Ascaris spp. in 1% of the sample may suggest that these nematodes are successfully matured and established in the goats (Rajamohan et al. 1970;Martin 1926). The high prevalence of these nematodes might be attributed to their usual favorable transmission via ingestion of infective egg or larval stages and or transmission via udder milk and larval penetration. ...
Gastrointestinal (GI) parasites in goats are predominant around the world. They may be the underlying cause of the pathological and immunological consequences leading to significant economic losses of the goat industry. The main aim of the current research was to reveal the prevalence of gastrointestinal parasites, including protozoa, trematodes, and nematodes in the fecal samples of goats in the goat market in Kathmandu, Nepal. A total of 400 goat fecal specimens were purposively collected from the goat market, and they were processed by direct wet mount, sedimentation, floatation techniques, and acid-fast staining, and were observed under the compound microscope. Out of a total 400 fecal samples, 349 (87.25%) were found to be infected with GI parasites among which Eimeria (80.75%), Strongyle (59.25%), Trichuris (29.75%), Strongyloides (28.75%), Moniezia (21.75%), Entamoeba (20%), Fasciola (10.25%), Balantidium (7.75%), Cryptosporidium (4%), Capillaria (1.75%), Trichomonas (1.25%), Ascaris (1.0%), Cyclospora (1%), Blastocystis (0.75%), Giardia (0.5%), and Paramphistomum (0.5%) were reported. GI parasites like protozoa and helminthes were widely distributed in the goats brought for the meat purposes in Kathmandu Valley, showing a high proportion of the goats were having higher risks of morbidity and mortality around the country.
Soil-transmitted helminths, such as Ascaris lumbricoides, are the most prevalent parasites globally. Optimal anthelmintic treatment for A. lumbricoides in endemically infected communities is challenged by several host-related and environmental factors influencing infection acquisition. We assessed the risk of A. lumbricoides (re)infection after treatment in a Venezuelan rural community. Individual merthiolate-iodine-formaldehyde-fixed faecal samples were collected from 224 persons before a single-dose pyrantel treatment and at 1, 3, 6, 9 and 15 months after treatment. Effects of age, sex and socioeconomic status (SES) on A. lumbricoides prevalence, eggs/gram faeces (EPG) and infection (re)acquisition were assessed using both generalised linear mixed-effects models and survival analysis. Pre-treatment A. lumbricoides prevalence was 39.7%. Higher prevalence was associated with younger age and lower SES. Higher EPG values were observed among young children. Median time to A. lumbricoides infection was six months after treatment: at 1, 3, 6, 9 and 15 months post-treatment, cumulative incidence was 6.7%, 18.9%, 34.6%, 42.2%, and 52.6%, respectively. Younger age, lower SES, and pre-treatment A. lumbricoides infection status showed significantly elevated hazard ratios. Mass drug administration protocols would benefit from considering these factors in selective treatment strategies and possibly more than just annual or biannual treatments in the target population.
Reuse of faecal sludge in agriculture has many potential benefits, but also poses risks to human health. To better understand the potential risks, Quantitative Microbial Risk Assessment (QMRA) was performed for three population groups in Kampala, Uganda: wastewater and faecal sludge treatment plant workers; farmers using faecal sludge; and consumers of faecal sludge-fertilised vegetables. Two models were applied for farmers and consumers, one based on pathogen concentrations from field sampling of sludge, soils and vegetables, and one based on theoretical pathogen contribution from the last sludge application, including decay and soil to crop transfer of pathogens. The risk was evaluated for two pathogens (enterohaemorrhagic E. coli (EHEC) and Ascaris lumbricoides). The field data on sludge, soil and vegetables indicated that the last application of faecal sludge was not the sole pathogen source. Correspondingly, the model using field data resulted in higher risks for farmers and consumers than the theoretical model assuming risk from sludge only, except when negligible for both. For farmers, the yearly risk of illness, based on measured concentrations, was 26% from EHEC and 70% from Ascaris, compared with 1.2% and 1.4%, respectively, considering the theoretically assumed contribution from the sludge. For consumers, the risk of illness based on field samples was higher from consumption of leafy vegetables (100% from EHEC, 99% from Ascaris) than from consumption of cabbages (negligible for EHEC, 26% from Ascaris). With the theoretical model, the risk of illness from EHEC was negligible for both crops, whereas the risk of illness from Ascaris was 64% and 16% for leafy vegetables and cabbage, respectively. For treatment plant workers, yearly risk of illness was 100% from EHEC and 99.4% from Ascaris. Mitigation practices evaluated could reduce the relative risk by 30-70%. These results can help guide treatment and use of faecal sludge in Kampala, to protect plant workers, farmers and consumers.
Polymerase chain reactions are helpful diagnostic methods to accurately quantitate the intensities of infections of various soil-transmitted helminths, especially in the low-intensity infection samples. Method of DNA extraction hugely impacts the outcomes of the diagnostic method. Trichuris trichiura is one of the three major helminths prevalent world-wide and accurate estimation of their loads in stool is affected by the method of DNA extraction. We meta-analyze two studies by dividing them into all together 6 sub-studies. The objectives of the meta-analysis required the two studies to be divided into sub-studies as the different methods of DNA extractions could not be combined. We found that the inclusion of the bead-beating step during DNA extraction significantly increases the sensitivity of the test.
A catalogue, based on both examined specimens and the published literature, of all the ascaridoid nematodes recorded in China is presented. A total of 95 recognised species, representing 26 genera in five families, are reported. Detailed information on the type-host, type-locality, original reference, synonyms, annotated subsequent references of taxonomic importance, other host records, site of infection, location of type-specimens and distribution are listed for each recognised species. Additional comments on the taxonomic status of some species are also given. Moreover, some nomenclatural changes are proposed: (i) Toxascaris selenarctis Wang, 1965 and T. ailuri Wu, He & Hu, 1987 are placed in synonymy with Baylisascaris transfuga (Rudolphi, 1819); (ii) Raphidascaris lophii Wang & Wu, 1991 is a secondary homonym of R. lophii (Wu, 1949) and a replacement name, R. wangi nom. nov., is proposed for the former species; (iii) Aliascaris
aetoplatea Luo, 2001 is transferred to Terranova Leiper & Atkinson, 1914, as T. aetoplatea (Luo, 2001) n. comb., and should be considered a species inquirenda; (iv) Ophidascaris orientalis (Wang, 1965) is resurrected as a valid species; (v) Phocascaris longispiculum Wang & Wu, 1991 and Ophidascaris agkistrodontis Wang, 1979 are treated as incertae sedis; and (vi) Hysterothylacium
sauridae Li, Xu & Zhang, 2008 is listed as a nomen nudum.
More than thirty years ago Stoll (1947) noted that helminth parasites were amongst the most prevalent of all human infections within many tropical, subtropical and temperate regions of the world. Today the global pattern of infection has changed little. World Health Organization statistics, for example, suggest that approximately one billion people are currently infected with the directly transmitted nematode Ascaris lumbricoides (roundworms). The picture is similar for other nematode parasites such as Trichuris trichiura (whipworms), Enterobius vermicularis (pinworms) and the hookworms Ancylostoma duodenale and Necator americanus (Table 3.1).
The present paper presents new models for the trans mission of microparasites and macroparasites, which take into account the change of the age structure of the host population due to parasite-induced mortality. The equilibrium density or prevalence of parasites is positive if and only if the basic reproductive rate, H, of the parasites is greater than ~t is suggested that this condition is not sufficient to determine the critical community size, N*, required to maintain an endem ic parasite population. Formulas will be derived which will allow us to estimate N* on the basis of R and on the duration of the immunity induced by an infection.
In the analysis of data it is often assumed that observations y1, y2, …, yn are independently normally distributed with constant variance and with expectations specified by a model linear in a set of parameters θ. In this paper we make the less restrictive assumption that such a normal, homoscedastic, linear model is appropriate after some suitable transformation has been applied to the y's. Inferences about the transformation and about the parameters of the linear model are made by computing the likelihood function and the relevant posterior distribution. The contributions of normality, homoscedasticity and additivity to the transformation are separated. The relation of the present methods to earlier procedures for finding transformations is discussed. The methods are illustrated with examples.
In recent years much new information has been obtained about the epidemiology, population biology and public health significance of infections of Ascaris lumbricoides in humans. Results from experimental infections of A. suum in pigs have helped to elucidate the observations made in the community on human ascariasis. The main purpose of the review is to see how new information may contribute to further acceptance of ascariasis as a serious contributor to ill-health and so to the design and implementation of sustainable control programmes intended to reduce the morbidity due to infection with A. lumbricoides. Eradication is neither a realistic nor prudent aim given the current shortage of appropriate sanitation in many countries where ascariasis is endemic. A substantial body of evidence shows that for the four common species of soil-transmitted nematode, including A. lumbricoides, regular administration of broad-spectrum anthelminthic drugs to children attending primary schools is a cost-effective means of controlling the infections. Anthelminthic drugs must be of proven quality and efficacy and health professionals should be prepared to detect and manage drug resistance should that emerge. Despite a deeper understanding of the immune response of a variety of hosts to infections with either A. lumbricoides or A. suum there is at present little prospect of an effective vaccine against ascariasis. The relationship between A. lumbricoides and A. suum is addressed, particularly since both species, if they are indeed separate species, occur in people and their pigs in many communities.
Intestinal helminths—including hookworm, roundworm, whipworm, and schistosomiasis—infect more than one-quarter of the world's population. Studies in which medical treatment is randomized at the individual level potentially doubly underestimate the benefits of treatment, missing externality benefits to the comparison group from reduced disease transmission, and therefore also underestimating benefits for the treatment group. We evaluate a Kenyan project in which school-based mass treatment with deworming drugs was randomly phased into schools, rather than to individuals, allowing estimation of overall program effects. The program reduced school absenteeism in treatment schools by one-quarter, and was far cheaper than alternative ways of boosting school participation. Deworming substantially improved health and school participation among untreated children in both treatment schools and neighboring schools, and these externalities are large enough to justify fully subsidizing treatment. Yet we do not find evidence that deworming improved academic test scores.