Seasonally timed treatment programs for Ascaris lumbricoides to increase impact-An investigation using mathematical models

A prevalence-based transmission model for the study of the epidemiology and control of soil-transmitted helminthiasis

Much effort has been devoted by the World Health Organization (WHO) to eliminate soil-transmitted helminth (STH) infections by 2030 using mass drug administration targeted at particular risk groups alongside the availability to access water, sanitation and hygiene services. The targets set by the WHO for the control of helminth infections are typically defined in terms of the prevalence of infection, whereas the standard formulation of STH transmission models typically describe dynamic changes in the mean-worm burden. We develop a prevalence-based deterministic model to investigate the transmission dynamics of soil-transmitted helminthiasis in humans, subject to continuous exposure to infection over time. We analytically determine local stability criteria for all equilibria and find bifurcation points. Our model predicts that STH infection will either be eliminated (if the initial prevalence value, y(0), is sufficiently small) or remain endemic (if y(0) is sufficiently large), with the two stable points of endemic infection and parasite eradication separated by a transmission breakpoint. Two special cases of the model are analysed: (1) the distribution of the STH parasites in the host population is highly aggregated following a negative binomial distribution, and (2) no density-dependent effects act on the parasite population. We find that disease extinction is always possible for Case (1), but it is not so for Case (2) if y(0) is sufficiently large. However, by introducing stochastic perturbation into the deterministic model, we discover that chance effects can lead to outcomes not predicted by the deterministic model alone, with outcomes highly dependent on the degree of worm clumping, k. Specifically, we show that if the reproduction number and clumping are sufficiently bounded, then stochasticity will cause the parasite to die out. It follows that control of soil-transmitted helminths will be more difficult if the worm distribution tends towards clumping.

Daily patterns in parasite processes: diel variation in fish louse transcriptomes

Parasites, similar to all other organisms, time themselves to environmental cues using a molecular clock to generate and maintain rhythms. Chronotherapeutic (timed treatment) techniques based on such rhythms offer great potential for improving control of chronic, problematic parasites. Fish lice are a key disease threat in aquaculture, with current control insufficient. Assessing the rhythmicity of fish lice transcriptomes offers not only insight into the viability of chronotherapy, but the opportunity to identify new drug targets. Here, for the first known time in any crustacean parasite, diel changes in gene transcription are examined, revealing that approximately half of the Argulus foliaceus annotated transcriptome displays significant daily rhythmicity. We identified rhythmically transcribed putative clock genes including core clock/cycle and period/timeless pairs, alongside rhythms in feeding-associated genes and processes involving immune response, as well as fish louse drug targets. A substantial number of gene pathways showed peak transcription in hours immediately preceding onset of light, potentially in anticipation of peak host anti-parasite responses or in preparation for increased feeding activity. Genes related to immune haemocyte activity and chitin development were more highly transcribed 4 h post light onset, although inflammatory gene transcription was highest during dark periods. Our study provides an important resource for application of chronotherapy in fish lice; timed application could increase efficacy and/or reduce dose requirement, improving the current landscape of drug resistance and fish health while reducing the economic cost of infection.

How modelling can help steer the course set by the World Health Organization 2021-2030 roadmap on neglected tropical diseases

The World Health Organization recently launched its 2021-2030 roadmap, Ending the Neglect to Attain the Sustainable Development Goals , an updated call to arms to end the suffering caused by neglected tropical diseases. Modelling and quantitative analyses played a significant role in forming these latest goals. In this collection, we discuss the insights, the resulting recommendations and identified challenges of public health modelling for 13 of the target diseases: Chagas disease, dengue, gambiense human African trypanosomiasis (gHAT), lymphatic filariasis (LF), onchocerciasis, rabies, scabies, schistosomiasis, soil-transmitted helminthiases (STH), Taenia solium taeniasis/ cysticercosis, trachoma, visceral leishmaniasis (VL) and yaws. This piece reflects the three cross-cutting themes identified across the collection, regarding the contribution that modelling can make to timelines, programme design, drug development and clinical trials.

How modelling can help steer the course set by the World Health Organization 2021-2030 roadmap on neglected tropical diseases

The World Health Organization recently launched its 2021-2030 roadmap, Ending the Neglect to Attain the Sustainable Development Goals , an updated call to arms to end the suffering caused by neglected tropical diseases. Modelling and quantitative analyses played a significant role in forming these latest goals. In this collection, we discuss the insights, the resulting recommendations and identified challenges of public health modelling for 13 of the target diseases: Chagas disease, dengue, gambiense human African trypanosomiasis (gHAT), lymphatic filariasis (LF), onchocerciasis, rabies, scabies, schistosomiasis, soil-transmitted helminthiases (STH), Taenia solium taeniasis/ cysticercosis, trachoma, visceral leishmaniasis (VL) and yaws. This piece reflects the three cross-cutting themes identified across the collection, regarding the contribution that modelling can make to timelines, programme design, drug development and clinical trials.

Prevalence of soil-transmitted helminthes and its association with water, sanitation, hygiene among schoolchildren and barriers for schools level prevention in technology villages of Hawassa University: Mixed design

BACKGROUND

Soil-transmitted helminths (STH) remain one of the most common causes of morbidity among children in Ethiopia. Assessment of the magnitude of STH and its association with water, sanitation, and hygiene (WASH) and identify barriers for school-level prevention assist public health planners to prioritize promotion strategies and is a basic step for intervention. However, there is a lack of evidence on the prevalence of STH and its association with WASH and barriers for school-level prevention among schoolchildren.

OBJECTIVE

To assess the prevalence of STH and its association with WASH and identify barriers for school level prevention in technology village of Hawassa University; 2019.

METHODS

An institution-based analytical cross-sectional study was conducted on a sample of 1080 schoolchildren from September 5 to October 15, 2019. A two-stage cluster and purposive sampling technique were used to draw the study participants. A pretested, structured questionnaire, observation checklist, and in-depth interview were used to collect the data. Two grams of stool samples were collected from each study participant and examined using direct wet mount and Kato-Katz technique. Data were entered into Epi Info version 7 and analyzed using SPSS version 25. Both bi-variable and multivariable logistic regression analyses were done. Qualitative data were analyzed using thematic content analysis method by Atlas-Ti software and presented in narratives.

RESULTS

The overall prevalence of STHs was 23.1% (95% CI = 21.4, 27.6). The identified predictors of STHs were large family size (AOR = 2.03; 95% CI = 1.53-3.99), absence of separate toilet room for male and female (AOR = 3.33; 95% CI = 1.91-5.79), toilet not easy to clean (AOR = 2.17; 95% CI = 1.44-3.33), inadequate knowledge about STHs (AOR = 2.08; 95% CI = 1.07-3.44) and children who had travelled greater than 100 meters to access toilet (AOR = 3.45; 95% CI = 2.24-8.92). These results were supported by the individual, institutional, socio-economic and cultural qualitative results.

CONCLUSION

The STHs was moderate public health concerns. Reinforcing the existing fragile water, sanitation and hygiene programs and regular deworming of schoolchildren may support to reduce the burden of STHs. Also, increasing modern family planning methods utilization to decrease family size is recommended.

The high prevalence of intestinal parasitic infections is associated with stunting among children aged 6-59 months in Boricha Woreda, Southern Ethiopia: a cross-sectional study

Background

Prior studies reported controversial results about the association between intestinal parasitic infections and childhood under-nutrition. We investigated the association of intestinal parasitic infections with under-nutrition among children aged 6–59 months in Boricha Woreda, Southern Ethiopia.

Methods

This community-based prospective cross-sectional study was carried out from January 1–30, 2019 among 622 children aged 6–59 months. A two-stage stratified sampling procedure was used. Data were collected using a structured, face-to-face interviewer-administered questionnaire and standard anthropometric measurements. The stool specimens were collected using standard technique and examined for the existence and species of intestinal parasites using direct wet mount, Kato Katz and staining technique. We have entered data using Epi Data 3.1 and WHO Anthro software and all analyses were conducted using SPSS version 20. The descriptive analyses were done to find descriptive measures for the socio-demographic and other important variables. Multivariable logistic regression analysis was used to identify factors associated with under-nutrition. Adjusted odds ratios (AORs) with a 95% confidence interval (CI) were computed to assess the presence and strength of associations.

Results

The total prevalence of intestinal parasitic infection was 48.7% (95% CI, 44.77–52.62). Approximately one-fourth (22%) of the children were infected with moderate intensity infections. Prevalence of stunting, underweight, wasting were 39.3, 24 and 11.6%, respectively. The prevalence of stunting among children infected with the intestinal parasite (59.4%) was significantly higher than the prevalence in non-infected children (20.6%) (p < 0.001). The absence of sanitation facility, living in medium and large family size, lack of shoes wearing practice, consuming raw vegetables and fruits were positively associated with intestinal parasitic infections. The presence of intestinal parasitic infections was positively associated with stunting (AOR = 2.18, 95% CI: 1.36–3.50) but not with wasting (AOR = 0.58, 95% CI: 0.3–1.13) and underweight (AOR: 0.92, 95% CI = 0.55–1.54).

Conclusions

Under-nutrition and intestinal parasitic infections were serious public health concerns. Consolidating the prevailing water, sanitation and hygiene packages and routine deworming of children aged 6–59 months may aid to decrease the burden of both stunting and intestinal parasitic infection in children. Also, improving modern contraceptive methods utilization to reduce family size is recommended.

Evaluating the Evidence for Lymphatic Filariasis Elimination

In the global drive for elimination of lymphatic filariasis (LF), 15 countries have achieved validation of elimination as a public health problem (EPHP). Recent empirical evidence has demonstrated that EPHP does not always lead to elimination of transmission (EOT). Here we show how the probability of elimination explicitly depends on key biological parameters, many of which have been poorly characterized, leading to a poor evidence base for the elimination threshold. As more countries progress towards EPHP it is essential that this process is well-informed, as prematurely halting treatment and surveillance programs could pose a serious threat to global progress. We highlight that refinement of the weak empirical evidence base is vital to understand drivers of elimination and inform long-term policy.

Prevalence of intestinal parasitic infection and its association with anemia among pregnant women in Wondo Genet district, Southern Ethiopia: a cross-sectional study

Background

Previous studies reported contradicting findings about the association between intestinal parasitosis and maternal anemia. In this study we aimed to determine the prevalence of intestinal parasitic infection and its association with anemia among pregnant women in Wondo Genet district, Southern Ethiopia.

Methods

This facility-based cross-sectional study was conducted in June and July 2018. Pregnant women (n = 352) were randomly drawn from five health centers using antenatal care follow-up lists. Trained data collectors administered the questionnaire. Capillary blood was collected and analyzed for hemoglobin using the HemoCue method. Stool sample was collected following standard procedure and analyzed for the presence and types of intestinal parasites using direct microscopy with Formalin-ether concentration technique. Association between intestinal parasitosis and anemia was measured using multivariable binary logistic regression analysis. The outputs are presented using adjusted odds ratio (AOR) with 95% confidence intervals (CI).

Results

The overall prevalence of intestinal parasitic infection was 38.7% (95% CI: 33.6–43.8%). One-tenth (9.7%) of the pregnant women were infected with polyparasites. Ascaris lumbricoides was the predominant infection encountered in 24.9% of the women. The other infections identified were: hookworms (11.2%), Giardia lamblia (5.4%), Entamoeba histolytica (3.4%), Trichuris trichiura (2.9%) and Schistosoma mansoni (2.3%). The mean (± standard deviation) hemoglobin concentration was 12.3 (±1.9) g/dl and 31.5% (95% CI: 26.6–36.4%) women were anemic (hemoglobin < 11 g/dl). The prevalence of anemia among women infected with intestinal parasite (55.6%) was substantially higher than the prevalence in their counterparts (16.4%) (p <  0.001). In a multivariable model adjusted for multiple potential confounders including socio-economic status indicators, the odds of anemia were six times increased (AOR = 6.14, 95% CI: 2.04–18.45) among those affected by at least one intestinal parasite.

Conclusion

Strengthening the existing water, sanitation and hygiene programs and routine deworming of pregnant mothers may help to reduce the burden of both intestinal parasitic infection and anemia in pregnant women.

Electronic supplementary material

The online version of this article (10.1186/s12879-019-4135-8) contains supplementary material, which is available to authorized users.

Soil-transmitted helminth reinfection four and six months after mass drug administration: results from the delta region of Myanmar

BACKGROUND

Mass drug administration (MDA), targeted at school-aged children (SAC) is the method recommended by the World Health Organization for the control of morbidity induced by soil-transmitted helminth (STH) infection in endemic countries. However, MDA does not prevent reinfection between treatment rounds and research suggests that only treating SAC will not be sufficient to bring prevalence to low levels and possibly interrupt transmission of STH. In countries with endemic infection, such as Myanmar, the coverage, who is targeted, and rates of reinfection will determine how effective MDA is in suppressing transmission in the long-term.

METHODS/PRINCIPAL FINDINGS

In this paper, data from an epidemiological study on STH, comprising three surveys conducted between June 2015 and June 2016 in the delta region of Myanmar, are analysed to determine how STH prevalence and intensity in the study community changes over the course of a year, including reinfection after two MDA rounds in which the whole study sample (all age groups, n = 523) were treated with albendazole. Prevalence in the first survey (August 2015) was 27.92% for any STH, 5.54% for Ascaris lumbricoides, 17.02% for Trichuris trichiura and 9.75% for hookworm. Over the year (survey one to survey three), prevalence of any STH decreased by 8.99% (P < 0.001) and mean EPG significantly decreased for T. trichiura (P < 0.01) and hookworm (P < 0.001). Risk ratios (RRs) for a four-month reinfection period (August to December) were statistically significant and were below one, indicating that STH prevalence had not bounced back to the prevalence levels recorded immediately prior to the last round of treatment (any STH RR = 0.67, 95% CI 0.56-0.81; A. lumbricoides RR = 0.31, 95% CI 0.16-0.59; T. trichiura RR = 0.70, 95% CI 0.55-0.88; hookworm RR = 0.69, 95% CI 0.50-0.95). The only statistically significant RR for the six-month reinfection period (December to June) was for A. lumbricoides infection in SAC (RR = 2.67, 95% CI 1.37-5.21). All six-month RRs were significantly higher than four-month RRs (P < 0.05). Evidence of predisposition to infection (low and high), as measured by the Kendall Tau-b statistic, was found for all species overall and within most age groups stratifications, except for hookworm infection in preschool-aged children.

CONCLUSIONS/SIGNIFICANCE

This study demonstrates that, for certain demographic groups, a six-month gap between MDA in these communities is enough time for STH infection to return to STH prevalence levels recorded immediately before the previous MDA round, and that on average the same individuals are being consistently infected between MDA rounds.

The impact of seasonality on the dynamics and control of Ascaris lumbricoides infections

Intestinal nematode infections affect a huge proportion of the world's population. Increasingly these infections, particularly amongst the poorest communities, are controlled through mass drug treatment programs. Seasonal variations of climate and behaviour in these regions can be significant, but their impact on the dynamics of infection and implications for the effectiveness of any mass drug treatment program (a pulsed reduction in worm burden in hosts) is not clearly understood. Here the effect of seasonality on the dynamics of the soil-based helminth, Ascaris lumbricoides, is investigated using a reformulated version of the Anderson-May model for macro-parasitic infections. Explicit analytical expressions are obtained for the stable oscillatory solution over the annual cycle, which provides a means of relating times of peak numbers of eggs, larvae and mature worms to seasonal variations. Numerical and analytical techniques are then used to consider the impact of seasonality on the optimal timing of drug treatment. Our results show that there is a relatively large window for the timing of optimal treatment, and the impact of repeated annual mass drug treatments can be substantially improved if they are timed to coincide with the months when the number of eggs and larvae are at their lowest - minimising reinfection. In terms of a more measurable quantity, in our example this corresponds to the months when the seasonal temperature is highest. Multiple annual treatments at (or close to) the optimal time each year are predicted to achieve local elimination in the community, whereas treatment at other times has a more limited impact. A key finding is that even for pronounced seasonality, perturbations in mean worm burden, and hence seasonal variation in observed egg output, may be small, potentially explaining why seasonal effects have been overlooked. Taken together these results suggest that seasonality of soil-transmitted helminths requires further experimental, field and mathematical study if the impact for mass drug administration programs is to be exploited.

100 Years of Mass Deworming Programmes: A Policy Perspective From the World Bank's Disease Control Priorities Analyses

For more than 100 years, countries have used mass drug administration as a public health response to soil-transmitted helminth infection. The series of analyses published as Disease Control Priorities is the World Bank's vehicle for exploring the cost-effectiveness and value for money of public health interventions. The first edition was published in 1993 as a technical supplement to the World Bank's World Development Report Investing in Health where deworming was used as an illustrative example of value for money in treating diseases with relatively low morbidity but high prevalence. Over the second (2006) and now third (2017) editions deworming has been an increasingly persuasive example to use for this argument. The latest analyses recognize the negative impact of intestinal worm infection on human capital in poor communities and document a continuing decline in worm infection as a result of the combination of high levels of mass treatment and ongoing economic development trends in poor communities.

Testing for soil-transmitted helminth transmission elimination: Analysing the impact of the sensitivity of different diagnostic tools

In recent years, an increased focus has been placed upon the possibility of the elimination of soil-transmitted helminth (STH) transmission using various interventions including mass drug administration. The primary diagnostic tool recommended by the WHO is the detection of STH eggs in stool using the Kato-Katz (KK) method. However, detecting infected individuals using this method becomes increasingly difficult as the intensity of infection decreases. Newer techniques, such as qPCR, have been shown to have greater sensitivity than KK, especially at low prevalence. However, the impact of using qPCR on elimination thresholds is yet to be investigated. In this paper, we aim to quantify how the sensitivity of these two diagnostic tools affects the optimal prevalence threshold at which to declare the interruption of transmission with a defined level of confidence. A stochastic, individual-based STH transmission model was used in this study to simulate the transmission dynamics of Ascaris and hookworm. Data from a Kenyan deworming study were used to parameterize the diagnostic model which was based on egg detection probabilities. The positive and negative predictive values (PPV and NPV) were calculated to assess the quality of any given threshold, with the optimal threshold value taken to be that at which both were maximised. The threshold prevalence of infection values for declaring elimination of Ascaris transmission were 6% and 12% for KK and qPCR respectively. For hookworm, these threshold values are lower at 0.5% and 2% respectively. Diagnostic tests with greater sensitivity are becoming increasingly important as we approach the elimination of STH transmission in some regions of the world. For declaring the elimination of transmission, using qPCR to diagnose STH infection results in the definition of a higher prevalence, than when KK is used.