Albendazole

Individual adult Brugia malayi female worms (TRS Labs Inc., Athens, GA) were assayed in RPMI-1640 (25 mM HEPES, 2 g/L , Antibiotic/Antimycotic, 5% HI FBS) in 24-well tissue culture plates (1 worm/well). 30 mM stock solutions of albendazole (methyl 5-(propylthio)-2-benzimidazolecarbamate, Sigma), ivermectin (22,23-dihydroavermectin B1, Sigma) and fenbendazole (methyl 5-(phenylthio)-2-benzimidazolecarbamate, Sigma) were prepared with DMSO (Sigma) and serially diluted in media into concentrations of , , , , . DMSO was used as the control and each concentration was run in triplicate. Plates were maintained in a 37 C 5% incubator for 48 hours. data were calculated using Microsoft Excel (Microsoft Corp.) and Prism 5 (GraphPad Software, Inc.).

The description of the study population, design, and methods of the original study are detailed in prior publications [19 (link),20 (link)]. Briefly, a double-blind, randomized, placebo-controlled trial was conducted in four semi-urban villages situated near Ile-Ife, in Osun State, Nigeria. The goal of the study was to investigate the impact of repeated antihelminthic therapy with albendazole on Plasmodium infection in children between 12 and 60 months of age. Children were randomized to receive either placebo or albendazole every four months during the study period. Stool specimens were examined for the presence of helminth infections. Eggs per gram (epg) of faeces was used to estimate parasite intensity. Finger-prick blood specimens were taken for analysis of Plasmodium infection via malaria rapid diagnostic testing (RDT) (Parascreen, Zephyr Biomedicals, Verna Industrial Estate, Verna Goa, India) and microscopic examination for malaria parasites. Haemoglobin levels were determined using a haemoglobinometer (Accuscience, Ireland). Children suffering from a malaria attack were treated with artemether-lumefantrine.The study was approved by the Ethics and Research Committee, Obafemi Awolowo University Teaching Hospital’s Complex, Ile-Ife, Nigeria. Informed consent was obtained from the mother of each child included in this study.
This study utilized the available data from the baseline, four-month, and eight-month time points. At each time point, only those patients with a result for haemoglobin, malaria testing, and stool microscopy for helminths were included. Mild anaemia was defined as haemoglobin (Hb) level between 10.0 and 10.9 g/dl, moderate anaem ia was defined as 7.0 g/dL≤ Hb <10 g/dL, and severe anaemia was defined as Hb <7.0 g/dL [21 ].

The mathematical model used describes the evolution of the parasite distribution in different host age groups and the impact of periodic chemotherapy on host burdens, incorporating the key epidemiological and biological processes influencing transmission. Building on past research
[15 (link),16 ], it includes the observed features of sexual reproduction by the dioecious helminths, heterogeneity in exposure to infection by host age, variation in the intensity of transmission in different human communities, aggregated distributions of worm numbers per host and a decline in fecundity as a function of worm burden (density dependence)
[16 -18 (link)]. The dynamics of transmission under repeated rounds of treatment is examined for the three main intestinal nematodes, Ascaris lumbricoides, Trichuris trichuria and hookworms (Necator americanus and Ancylostoma duodenale). The model is described in detail in the Additional file
1 available online.
Although a full age distribution is embedded in the model, we employ the key age groupings described above to define intervention coverage levels and illustrate their effect. These are infants (0–1 years of age) who cannot be treated under current licensure of the main anthelmintic drugs in wide use (e.g. albendazole and mebendazole), pre-school aged children (pre-SAC, 2–4 years of age), school aged children (SAC, 5–14 years of age) and adults (15+ years of age). Varying combinations of the fraction treated in each age grouping, treatment frequency and duration of treatment are explored. The fraction in each grouping effectively treated is a product of the fraction given treatment and drug efficacy (defined as the proportion of worms expelled). Within the current model, these two aspects of treatment are inseparable, and coverage of the population is represented as a proportion of worms treated. Drug efficacy is typically in the region of 90% or more for Ascaris and hookworms, but somewhat less for Trichuris[19 (link)-22 (link)]. It should be noted that the fraction treated is effectively chosen at random from the subpopulation. This model does not address systematic non-compliance.
The life cycles of these parasites involve free living stages that are passed in the faeces of the human host and mature to infective stages in the external habitat (eggs for Ascaris and Trichuris and larvae for hookworms). The infective stages of the parasite in the environment are represented in the model by a common pool of infectious material. The life span of these stages is typically weeks to months under favourable environmental conditions, and they are excreted in very large numbers
[23 -26 (link)]. Although this duration is short by comparison with adult worm life expectancies in the human host, infectious material in the environment acts as a reservoir which is unaffected by chemotherapy and can play a significant role in the dynamics of treatment. Dynamics of a range of parasites within the host population can be represented by the same model, with distinct parameter ranges for different species (See Additional file
1: Table S1).
Different age groups are thought to both contribute to, and be exposed to, this infective pool to varying degrees. An indication of this is provided by the changes in the intensity of infection by age; the patterns are typically convex for Ascaris and Trichuris, but continue to rise for hookworms as individuals age
[27 (link)-29 (link)] (Figure 
2). The respective roles of age related exposure to infection versus acquired immunity remains uncertain, but rapid re-infection by all three parasites post treatment points to the former as the main driver of age-intensity of infection profiles. On this basis, MCMC methods
[30 ] are employed to fit the model to these age related patterns of infection, to estimate both transmission intensity (measured by the basic reproductive number R₀ - the average number of offspring produced by one female worm that survive to reproductive maturity) and age related exposure. We have endeavoured to choose typical or characteristic infection profiles for the parasite species investigated in the hope that our results will be broadly applicable.

The LF MDA campaign functions both as a treatment delivery and data collection platform. For the LF treatment campaign considered in this study, community drug distributors (CDDs) responsible for administering the correct dose of albendazole and ivermectin also record the number of persons treated on a paper tally sheet. After, or in some cases during the MDA, this number is aggregated up through intermediate administrative levels (e.g., supervisory area, chiefdom, health area) to the health district, hereafter synonymous with implementation unit (IU). The total number of LF treatments in each treated district is reported to the national NTD program.
Population data were provided by the national NTD programs for each district conducting LF MDA. The data were provided each year, accounting for population growth, and were typically based on a national census. In certain years, a minority of the NTD programs included opted to use NTD-specific population estimates for (e.g., a pre-MDA community census conducted by the CDDs themselves). This was done in cases of population movement or where the national census was considered unreliable or too old to be accurate.
Treatment and population data were considered exactly as reported to implementing partners following the MDA and national validation. All treatment and population data were recorded for the district level along with the month and calendar year of the MDA start. All treatment, population, and calendar data were sourced directly from the USAID NTD database for countries currently participating in USAID’s Act to End NTDs | West program. District geographic boundary data (i.e. shapefiles) was also shared by the ten ministries of health to implementing partners during the course of implementation.

Interventions were modeled by using the SIR-selected parameter vectors/models for simulating the impacts of both currently used as well as proposed MDA-based intervention strategies in reducing the observed baseline LF prevalence in each site to below either the global TAS (1% mf prevalence) or site-specific 95% EP thresholds. When simulating these interventions, the observed MDA regimens and coverages followed in each site were used (Supplementary Table 2), while MDA was assumed to target all residents aged 5 years and above. While the drug-induced mf kill rate and the duration of adult worm sterilization were fixed among the models (Supplementary Table 1), the worm kill rate was left as a free parameter to be estimated from the post-intervention data to account for uncertainty in this drug efficacy parameter. For making mf prevalence forecasts beyond the observations made in each site, predictions arising from the impacts of MDA simulated with and without vector control were carried out for 5 years and 20 years after the stoppage of MDA in each site. Three different MDA regimens: (i) annual MDA with ivermectin and albendazole (IVM+ALB) or diethylcarbamazine and ivermectin (IVM+DEC) as applied in each site, (ii) biannual MDA with the above regimens, and (iii) annual triple drug MDA (IDA: combined ivermectin, diethylcarbamazine and albendazole) were modeled with and without vector control in this study to provide a comparison of the effectiveness of these drug regimens for affecting LF elimination. In these simulations, MDAs are stopped after achieving either the 1% mf TAS threshold or the model-predicted 95% EP threshold in each modeled site but simulations of subsequent changes in mf prevalence with or without VC for the next 20 years were continued to evaluate the probability of LF elimination and the risk of recrudescence of the infection respectively over both the shorter 5-year TAS period and over the longer-term 20 years period (using the assessment methods for calculating the occurrence of either of these events described above). VC is modeled in terms of the impact of long-lasting insecticidal nets (LLINs) with 65% coverage following the equation given in ref. ^{9 (link)}. The specific details concerning the different MDA-based scenarios investigated are as listed in Tables 1 and 2.
Note that the estimated 95% EP mf prevalence threshold at ABR was used when carrying out simulations of durations or timelines to break transmission by MDA alone strategies while the corresponding and comparatively higher 95% EP thresholds (obtaining at TBR) for this indicator was employed when modeling the impact of including VC into MDA programs^{9 (link)}. The MDA plus MDA and vector control model formulations, parameters and functions used to carry out these simulations are as described previously and provided in Supplementary Information.

Study participants received albendazole 400mg as part of the MDA campaign following the national and WHO MDA guideline [29 ]. MDA was administered to all children attending the study schools regardless of their STH infection status as scheduled by the Rwanda Ministry of Health [17 (link)]. The study team had no role in the MDA planning or administering the drug. Children participating in the study were provided a light snack before albendazole administration. Three weeks after albendazole MDA, the enrolled school-age children followed-up for efficacy outcome measurement.