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.

Due to the presence of artefacts in stool samples, the copromicroscopic diagnosis of Ascaris lumbricoides is not always straightforward, particularly in the case of fertilized decorticated eggs. A total of 286 stool samples from 115 schoolchildren in India and 171 adult immigrants in Italy were screened for the presence of A. lumbricoides eggs by both Kato-Katz thick smear and Mini-FLOTAC. If the outer layer of A. lumbricoides eggs was absent, two aliquots of each stool sample were preserved: one for coproculture to identify larvae after development and one to compose a pool of stool for molecular analysis. A total of 64 stool samples (22.4%) were positive for A. lumbricoides using the Kato-Katz thick smear; 36 (56.3%) of these showed mammillated A. lumbricoides eggs, 25 (39.1%) showed elements resembling fertilized decorticated eggs, while three samples (4.7%) showed both mammillated and decorticated eggs. By Mini-FLOTAC, 39 stool samples (13.6%) were positive, while decorticated A. lumbricoides-like eggs were identified as artefacts. These results were confirmed by negative coprocultures and quantitative polymerase chain reaction. Mini-FLOTAC can be used for a reliable diagnosis of A. lumbricoides, thanks to the flotation and translation features which allow a clearer view, resulting in the correct identification of A. lumbricoides eggs.

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.

The soil-transmitted helminth Ascaris lumbricoides infects ~800 million people worldwide. Some people are heavily infected, harbouring many worms, whereas others are only lightly infected. The mechanisms behind this difference are unknown. We used a mouse model of hepatic resistance to Ascaris, with C57BL/6J mice as a model for heavy infection and CBA/Ca mice as a model for light infection. The mice were infected with the porcine ascarid, Ascaris suum or the human ascarid, A. lumbricoides and immune cells in their livers and spleens were enumerated using flow cytometry. Compared to uninfected C57BL/6J mice, uninfected CBA/Ca mice had higher splenic CD4+ and γδ T cell counts and lower hepatic eosinophil, Kupffer cell and B cell counts. Infection with A. suum led to expansions of eosinophils, Kupffer cells, monocytes and dendritic cells in the livers of both mouse strains and depletions of hepatic natural killer (NK) cells in CBA/Ca mice only. Infection with A. lumbricoides led to expansions of hepatic eosinophils, monocytes and dendritic cells and depletions of CD8+, αβ, NK and NK T cells in CBA/Ca mice, but not in C57BL/6J mice where only monocytes expanded. Thus, susceptibility and resistance to Ascaris infection are governed, in part, by the hepatic immune system.

Ascariasis is a neglected tropical disease, caused by Ascaris lumbricoides, affecting 800 million people worldwide. Studies focused on the early stage of parasite infection, occurring in the gut, liver and lungs, require the use of a mouse model. In these models, the porcine ascarid, Ascaris suum, is often used. The results obtained from these studies are then used to draw conclusions about A. lumbricoides infections in humans. In the present study, we sought to compare larval migration of A. suum and A. lumbricoides in mouse models. We used a previously developed mouse model of ascariasis, which consists of two mouse strains, where one mouse strain – C57BL/6J – is a model for relative susceptibility and the other – CBA/Ca – for relative resistance. Mice of both strains were infected with either A. suum or A. lumbricoides. The larval burden was assessed in two key organs, the liver and lungs, starting at 6 h post infection (p.i.) and ending on day 8 p.i. Additionally, we measured the larval size of each species (μm) at days 6, 7 and 8 p.i. in the lungs. We found that larval burden in the liver is significantly higher for A. lumbricoides than for A. suum. However, the inverse is true in the lungs. Additionally, our results showed a reduced larval size for A. lumbricoides compared to A. suum.

Ascariasis is one of the most common parasitic diseases in both humans and pigs. It has been shown to cause growth deficits in both species and to impair cognitive development in children. Notwithstanding its substantial impact on pig economy and public health, diagnosis of ascariasis has mostly relied on the detection of eggs in stool and further development of novel, more sensitive methods has been limited or non-existent. Here, we discuss the currently available techniques for the diagnosis of ascariasis in pigs, their caveats, and the implications of a new serological detection technique for the evaluation of both pig and human ascariasis.

The effects of larval stages of Ascaris lumbricoides on human blood clotting was studied in vitro. Extracts and excretory/secretory products of third-stage larvae (L3) and late third-stage larvae (LL3) cultured from ova obtained from infected patients were analysed for anti-coagulant activity. Prothrombin time (PT) was prolonged by the addition of either whole extract of L3/LL3 or ES products of L3/LL3 as compared to controls. Partial thromboplastin time with kaolin (PTTK) was also prolonged on the addition of either extracts of ES products of L3/LL3. The prolongation of PTTK was significantly higher with extracts/ES products of L3 when compared to the extracts/ES products of LL3 (p<0.005). Thrombin time (TT) was prolonged by extracts of L3/LL3 and their ES products.

The importance of larval viability in relation to the success of recovery techniques and to the interpretation of histological and migration studies was tested using mice infected with Toxocara pteropodis, T. canis and T. cati. Little difference was found in total numbers of viable larvae recovered from tissues incubated for 18 hours in 0·85% saline, 2% trypsin or 1% pepsin, but the rates of larval egress did vary. The recovery of dead larvae by digestion techniques was much lower. Larvae migrated in tissues undergoing fixation, which influenced histological findings. Larvae of T. canis did not undergo significant peritoneal migration in acutely-infected mice, but did penetrate their intestinal walls in large numbers within 4 hours of death. The implications of these findings in experimental studies are discussed.

In order to determine the prevalence of intestinal parasites among labourers from Thailand in Taiwan, the stool samples from 1364 Thai labourers were examined by the formalin-ether concentration method and 18·0% were found to be infected with one or more parasites. The infection rates of hookworm, Opisthorchis viverrini, Strongyloides stercoralis, Enterobius vermicularis, Ascaris lumbricoides, Hymenolepis nana, Capillaria philippinensis, Schistosoma japonicum, Echinostoma sp., Entamoeba coli, Giardia lamblia, and Entamoeba histolytica, were 7·6%, 7·0%, 3·2%, 0·5%, 0·3%, 0·1%, 0·1%, 0·l%,0·l%, 0·4%, 0·2%, and 0·1% respectively. The prevalence was highest among the 21–25 age group (24·8%). Among the 245 infected persons, 91% were infected with one parasite, 8% with two parasites and 1% with three parasites. The finding that parasitic infections are prevalent among Thai labourers demonstrates the need for control measures in foreign labourers in Taiwan and further studies to determine the susceptibility of O. viverrini to the snail hosts of Clonorchis sinensis.

Two cases of intestinal obstruction due to Ascaris lumbricoides infection are reported from Ishaka Adventist Hospital, in south western Uganda. One was a male aged two and a half years and another was a female aged twenty. They were both treated surgically with good results. A review of the literature also revealed that intestinal obstruction due to A. lumbricoides is a common complication, though other surgical and nutritional complications also seem to be common, they are less reported.

Fifty children aged 6 to 13 years and infected with Ascaris lumbricoides were selected for the study. The number of eggs laid daily by a female Ascaris increased with increase in its length, weight and diameter. Female worms became mature and started laying eggs when they reached a length of 118 mm. Adult female worms measuring 3·7 mm or more in diameter were found to be mature. The minimum weight of a worm producing eggs was 1·1 g. On average the number of eggs produced by the female decreased with increase in the worm load.

Human helminthiases are common in China, especially in rural areas where sanitation conditions are poor. Soil-transmitted helminths (STHs) are predominantly found in the southern provinces. Schistosoma japonicum is also endemic to southern China. Here we review the prevalence of helminth infections and polyparasitism in China, and discuss the interactions between helminth parasites in the co-infected host. It is clear that STHs are more prevalent in rural China than previously suggested emphasizing the need for systematic control of STHs. Further, the need for improved sanitation and hygiene conditions to prevent parasite transmission is highlighted. We provide supporting evidence for human genetic susceptibility to both single helminth infection and polyparasitism, and suggest that susceptibility to helminths infections may not be independent of one or the other. We demonstrate an association between single nucleotide polymorphism (SNP) variants in IL-5 and symptomatic S. japonicum infection and discuss the potential role of IL-5 in other helminth infections. Fundamental to disease and morbidity control is adequate and effective diagnosis and surveillance of disease. We discuss the role of sICAM-1 and TNFR-I and -II as candidate markers for schistosome-induced hepatomegaly and fibrosis, and their potential for assessing disease stage and progression in schistosomiasis.

Ascaris lumbricoides, the human roundworm, is a remarkably infectious and persistent parasite. It is a member of the soil-transmitted helminths or geohelminths and infects in the order of 1472 million people worldwide. Despite, its high prevalence and wide distribution it remains along with its geohelminth counterparts, a neglected disease. Ascariasis is associated with both chronic and acute morbidity, particularly in growing children, and the level of morbidity assessed as disability-adjusted life years is about 10·5 million. Like other macroparasite infections, the frequency distribution of A. lumbricoides is aggregated or overdispersed with most hosts harbouring few or no worms and a small proportion harbouring very heavy infections. Furthermore, after chemotherapeutic treatment, individuals demonstrate consistency in the pattern of re-infection with ascariasis, described as predisposition. These epidemiological phenomena have been identified, in a consistent manner, from a range of geographical locations in both children and adults. However, what has proved to be much more refractory to investigation has been the mechanisms that contribute to the observed epidemiological patterns. Parallel observations utilizing human subjects and appropriate animal model systems are essential to our understanding of the mechanisms underlying susceptibility/resistance to ascariasis. Furthermore, these patterns of Ascaris intensity and re-infection have broader implications with respect to helminth control and interactions with other important bystander infections.

Antibody responses to Ascaris lumbricoides worm antigens were examined by ELISA in a case-control study of 2 groups of Bangladeshi children, one of which had been shown over a period of 12 months to be consistently lightly infected (controls) and the other consistently heavily infected (cases). The children showed a wide range in intensity of infection; children identified as cases were on average 4 times more heavily infected than the controls. There were no significant differences in weight, height, mid-upper arm circumference and skinfold thickness between the case or control subjects at the time blood samples for analyses by ELISA were collected. Children with repeatedly heavy infections with A. lumbricoides had higher concentrations of antibody isotypes to the antigens of A. lumbricoides than children who are repeatedly lightly infected. IgG1, IgG4 and IgE to worm antigens occurred in significantly higher concentrations in heavily infected subjects. This suggests that these antibody responses simply reflect the intensity of infection and may not play a significant role in protecting against heavy infections.

The distribution of Ascaris lumbricoides within a community was examined at an initial mass anthelmintic treatment programme (January 1984) and following an 11-month period of reinfection (November 1984). Similar patterns of the negative binomial parameter k (an inverse measure of parasite aggregation) and the proportion of parasites within the most heavily infected quartile of the community were recorded at the two dates. The pattern of parasite aggregation within individuals, measured by parameter k, appears to be a stable characteristic of this host-parasite relationship. Significant variation in the intensity of infection was observed between households in the community. The number of family members living in the house strongly influenced the mean Ascaris burden and proportion of relatively heavy infections within adults and children. This finding suggests that the density of people in a house positively influences the frequency of exposure to infective stages of Ascaris, which in turn plays a major role in determining which individuals will harbour heavy infections. Positive correlations were recorded between the initial and reinfection burdens of individuals, relative to others in the community. The correlations were strongest in the youngest and oldest age groups and were more frequently significant among age-stratified groups of females, compared to males. A comparative examination of hypothetical treatment strategies suggests that for Ascaris infections in this community, targetting age groups with anthelmintic treatment would probably be more cost-effective in the long term in reducing the abundance of this parasite than selective treatment of individually identified heavy infections.

An epidemiological survey of intestinal helminthiases was conducted on 766 primary school children aged 5–16 years from Ile-Ife, Nigeria. On the basis of stool examinations, the prevalence of Ascaris lumbricoides, Trichuris trichiura, hookworm and Strongyloides stercoralis was 88·5, 84·5, 33·1 and 3% respectively. Intensity of infection was measured indirectly by egg counts for each species of helminth and also by counting worms passed after chemotherapy in the case of A. lumbricoides. The influence of host age and sex on infection levels was assessed. Relationships between the intensities of A. lumbricoides, T. trichiura and hookworm in individual children were identified. After anthelmintic treatment with levamisole, the frequency distribution of A. lumbricoides per host and the relationship between parasite fecundity and worm burden were investigated.

Weight and length profiles are presented of 3505 Ascaris worms recovered after mass anthelmintic treatment of a human community in January 1984 and, after an 11 month period of reinfection, in November 1984. Male and female worms recovered after reinfection were significantly heavier and longer than those expelled after initial treatment (P < 0·0001). Multiple regression models were employed to examine variability in parasite size. A positive influence of host body weight on the weight of parasites recovered in January, but not in November, was observed. No negative relationship was recorded at either date between worm size and the total number of worms harboured, even after controlling for host weight. Striking host age-related variability was observed in the distribution profile of weights and lengths of individual worms recovered in January. Children harboured predominantly smaller worms before initial treatment, while adults expelled mainly heavy worms. In contrast, worms expelled by both children and adults after reinfection were heavier and more homogeneous in size, particularly within the relatively heavily infected group. These patterns argue against a primary role for density- dependent or acquired resistance mechanisms in determining the size of Ascaris in humans. However, the results are consistent with a hypothesis initially suggested by Jung (1954) that established worms may inhibit the development of newly acquired Ascaris larvae, perhaps regulating their own abundance.

Appetite and growth were studied in primary schoolboys (6–10 years) infected with Ascaris lumbricoides (86%) and Trichuris trichiura (100%) who received a single dose of pyrantel pamoate (which has little or no effect on Trichuris trichiura ) or a placebo. Boys were examined, allocated at random by descending Ascaris egg count to pyrantel (PR, n = 36) or placebo (PL, n = 36) groups, treated, and re-examined 3 and 7 weeks later. The 2 groups did not differ significantly before treatment in helminth infections, appetite, or growth. Three and 7 weeks after treatment, the PR group exhibited significantly greater increases than did the PL group in weight (0·2 kg and 0·4 kg more, respectively) and percentage weight-for-age (0·6% and 1·7% points more, respectively). Appetite increased significantly in the PR group at 3 and 7 weeks (P < 0·0005 and P < 0·01, respectively) but not in the PL group. The prevalence and intensity of A. lumbricoides infection were greatly reduced in the PR group at 3 and 7 weeks (both P < 0·0001) but not in the PL group. We conclude that treatment with pyrantel pamoate may improve appetite and growth in schoolchildren in areas where A. lumbricoides infections and poor growth are highly prevalent.

Observed field data from a range of geographically distinct human communities suggest a consistent non-linear relationship between prevalence and mean intensity of Ascaris lumbricoides infection. Utilizing the negative binomial distribution as a description of observed aggregation, maximum-likelihood analysis reveals that the degree of aggregation is a negative linear function of mean worm burden. The factors responsible for this relationship in human populations require further study but may involve some combination of (i) density-dependent reduction in worm numbers within individuals, (ii) density-dependent parasite-induced host mortality or (iii) self-treatment by heavily infected hosts. Variability in the degree of aggregation appears dependent on the level of infection in a community and independent of geographical differences in the host or parasite populations.

Programmes to control Ascaris lumbricoides, Trichuris trichiura and hookworm infections have often been targeted at each infection separately, but the advent of benign and broad-spectrum anthelmintics suggests that combined control ma be feasible. The extent to which the infections co-occur in communities will determine the need for, and potential benefits of, such a combined approach. This paper examines the comparative distribution of the three geohelminths in different geographical areas and shows that A. lumbricoides and T. trichiura have closely related distributions, while hookworm infection is largely independent of the other two. These results indicate that many communities are at risk of disease from infection by more than one species of helminth. The similar distributions and epidemiological characteristics of A. lumbricoides and T. trichiura suggest that simultaneous control of these two parasites by the same strategy would be feasible and highly beneficial to communities. Multiple species control strategies which aim to control hookworm infection may require a more complicated protocol with more precise locality targeting.