Lymphatic Filariasis Transmission Assessment Survey Research Articles

Impact assessment of onchocerciasis through lymphatic filariasis transmission assessment surveys using Ov-16 rapid diagnostic tests in Sierra Leone.

Onchocerciasis is endemic in 14 of Sierra Leone's 16 districts with high prevalence (47-88.5%) according to skin snips at baseline. After 11 rounds of mass treatment with ivermectin with good coverage, an impact assessment was conducted in 2017 to assess the progress towards eliminating onchocerciasis in the country. A cluster survey was conducted, either integrated with lymphatic filariasis (LF) transmission assessment survey (TAS) or standalone with the LF TAS sampling strategy in 12 (now 14) endemic districts. Finger prick blood samples of randomly selected children in Grades 1-4 were tested in the field using SD Bioline Onchocerciasis IgG4 rapid tests. In total, 17,402 children aged 4-19years in 177 schools were tested, and data from 17,364 children aged 4-14years (14,230 children aged 5-9years) were analyzed. Three hundred forty-six children were confirmed positive for Ov-16 IgG4 antibodies, a prevalence of 2.0% (95% CI 1.8-2.2%) in children aged 4-14years with prevalence increasing with age. Prevalence in boys (2.4%; 95% CI 2.1-2.7%) was higher than in girls (1.6%; 95% CI 1.4-1.9%). There was a trend of continued reduction from baseline to 2010. Using data from children aged 5-9years, overall prevalence was 1.7% (95% CI 1.5-1.9%). The site prevalence ranged from 0 to 33.3% (median prevalence = 0.0%): < 2% in 127 schools, 2 to < 5% in 34 schools and ≥ 5% in 16 schools. There was a significant difference in average prevalence between districts. Using spatial analysis, the Ov-16 IgG4 antibody prevalence was predicted to be < 2% in coastal areas and in large parts of Koinadugu, Bombali and Tonkolili Districts, while high prevalence (> 5%) was predicted in some focal areas, centered in Karene, Kailahun and Moyamba/Tonkolili. Low Ov-16 IgG4 antibody prevalence was shown in most areas across Sierra Leone. In particular, low seroprevalence in children aged 5-9years suggests that the infection was reduced to a low level after 11 rounds of treatment intervention. Sierra Leone has made major progress towards elimination of onchocerciasis. However, attention must be paid to those high prevalence focal areas.

Lymphatic Filariasis Transmission Assessment Survey in Burkina Faso in Connection with 4 Districts

RésuméObjectifDans le cadre d'une étude d'impact de la chimiothérapie préventive contre la filariose lymphatique au Burkina Faso, le Programme national de lutte contre les maladies tropicales négligées (PNMTN) a conduit une enquête d'évaluation de la transmission dans les districts sanitaires de Léo, Sapouy, Boromo et Dédougou. L'objectif principal était d'évaluer le niveau de transmission de la filariose lymphatique dans ces 4 districts sanitaires répartis en 2 unités d'évaluation (UE) (Boucle du Mouhoun 3 et du Centre-Ouest 2) après au moins 9 ans de traitement médicamenteux de masse.MéthodologieIl s'est agi d'une enquête transversale à visée descriptive réalisée en milieu communautaire sur un échantillon d'enfants de 6 à 7 ans sélectionnés par sondage en grappe.RésultatsSur 1649 enfants enquêtés dans l'UE Centre-Ouest 2, quatre étaient positifs au Filariasis Test Strip (FTS), soit une proportion de porteurs d'antigène filarien circulant (signant la présence de stades adultes vivant de Wuchereria bancrofti ) de 0,24%. Dans l'UE BMH3, aucun des 1716 enfants enquêtés n'était positif au FTS.ConclusionCes résultats montrent que la transmission de la filariose lymphatique est interrompue dans ces districts sanitaires, où les traitements de masse à l'albendazole et l'ivermectine peuvent donc être interrompus.

Simulating a Transmission Assessment Survey: An evaluation of current methods used in determining the elimination of the neglected tropical disease, Lymphatic Filariasis

IntroductionThe World Health Organization (WHO) recommends Transmission Assessment Surveys (TAS) to determine when an evaluation unit (EU) (a designated population survey area) has achieved elimination of transmission of the vector-borne macroparasitic disease Lymphatic Filariasis (LF). These determinations are based on combining data from multiple survey units within an EU; it is unclear how underlying cluster-level variation influences the outcome of the TAS at EU level. We simulate LF infection distribution in an EU and compare three methods for assessing whether LF elimination has occurred based on currently recommended decision thresholds and sampling methods. MethodsWe simulate an EU divided into clusters of varying size and disease prevalence. We produce 1000 samples according to LF TAS examples and WHO guidelines and compare three decision-making approaches: lot quality assurance sampling (LQAS) (recommended by WHO), one-sided interval estimate (CI), and nth order statistic (MAX). Summary statistics demonstrating the “pass” rate for the EU under different disease transmission conditions are generated using a versatile SAS® macro. ResultsAs the prevalence of LF decreases, the LQAS and CI approaches produce increased likelihood of a pass outcome for an EU while some cluster units may still have a high likelihood of transmission. The MAX provides an alternative that increases the likelihood of determining a pass only once the whole area has a low likelihood of transmission. LQAS and CI approaches designed to estimate the LF prevalence in the EU miss hotspots that will continue to transmit infection while the MAX approach focuses on identifying clusters with high risk of transmission. ConclusionsThe current TAS methodology has a flaw that may result in false predictions of LF transmission interruption throughout an EU. Modifying the TAS methodology to address results from extreme clusters rather than being based on mean prevalence over an EU will result in greater success for global elimination of LF.

A first nation-wide assessment of soil-transmitted helminthiasis in Fijian primary schools, and factors associated with the infection, using a lymphatic filariasis transmission assessment survey as surveillance platform.

BackgroundSoil-transmitted helminthiasis (STH) is endemic in Fiji but its prevalence is not known and likely to have changed after a decade of mass drug administration (MDA) for lymphatic filariasis (LF). By linking with LF transmission assessment surveys (LF-TAS), we undertook the first nation-wide assessment of STH in Fijian primary schools, as well as an analysis of factors associated with STH infections.Methodology/Principal findingsA cross-sectional assessment for STH was conducted in all four Divisions of Fiji from 2014 to 2015. In the Western, Central, and Northern Divisions, schools were sub-sampled after LF-TAS, while, in the Eastern Division, schools were selected via simple random sampling. For the diagnosis of STH, stool samples were examined by coproscopy with a single Kato-Katz thick smear (KK) and the formol-ether-acetate concentration technique, except for the samples from the Eastern Division where only KK was used. Mean prevalence of any STH among class 1–2 students at the national level was 10.5% (95% CI: 6.9–15.5). Across the three Divisions via LF-TAS, the prevalence levels for ascariasis were 8.7% (95% CI: 4.3–16.6), hookworm 3.9% (95% CI: 2.3–6.6) and trichuriasis 0%. In the Eastern Division, ascariasis prevalence was 13.3% (95% CI: 6.4–25.6), and hookworm 0.7% (95% CI: 0.2–2.5), with one case of trichuriasis. Among class 3–8 students, ascariasis prevalence was lower. Lower risk of any STH was associated with wearing shoes (adjusted OR 0.54, 95% CI: 0.32–0.90) and having piped water from the Fiji Water Authority at home (adjusted OR 0.48, 95% CI: 0.25–0.92).ConclusionsAfter a decade of community-based LF-MDA, STH in school-age children in Fiji is now close to 10%, but localities of endemicity remain. Preventive chemotherapy should be maintained in areas with elevated STH prevalence alongside targeted delivery of integrated WASH interventions. LF-TAS has provided an opportunity to develop future public health surveillance platforms.

Island-Wide Surveillance of Gastrointestinal Protozoan Infection on Fiji by Expanding Lymphatic Filariasis Transmission Assessment Surveys as an Access Platform.

.As part of lymphatic filariasis (LF) transmission assessment surveys (TAS) on Fiji, an island-wide assessment of gastrointestinal protozoan infection was performed by inspection of a concomitant stool sample collection to investigate the distribution of parasitic protozoa. All grade 1 and 2 students of 69 schools on the two main islands were targeted in two phases (one in the Western Division and the other in the Central and Northern Divisions, except Taveuni sub-Division of Northern), where fecal samples of 1,800 students were available for coproscopy using formalin-ether-acetate concentration. The overall prevalence of Giardia infection was 1.6%, having 2.2% in Western and 0.8% in Central/Northern Divisions (P = 0.094). The school-level prevalence of giardiasis ranged from 0% to 15.4%, and hotspot analysis using the Getis-Ord Gi* method detected spatial heterogeneity of giardiasis prevalence in schools around Lautoka (Z-score = 3.36, P value < 0.05), an area affected by Cyclone Kofi in February 2014. Any protozoan infection prevalence was 4.9% in Western and 4.4% in Central/Northern Divisions (P = 0.825). Real-time polymerase chain reaction analysis to confirm the findings from a parasitological examination of a 10% stool archive in 95% ethanol from Western Division revealed an elevated prevalence of giardiasis up to 22.4%, the presence of Entamoeba histolytica, and the absence of Cryptosporidium parvum. Obtaining stool samples alongside LF TAS is a convenient access platform for cosurveillance of gastrointestinal protozoan infection and has pinpointed hitherto unknown hotspots of giardiasis in urban city centers of Fiji. This calls for greater attention to apply tailored water, sanitation and hygiene measures for the control of these parasites.

An overview of progress towards Neglected Tropical Disease Control i Sierra Leone

Synergy exists between infectious diseases that target the poor and perpetuate poverty. Common strategies of mass drug administration (MDA) have enabled the control and possible elimination of the five previously neglected tropical diseases (NTDs) to help alleviate poverty. Mapping of five NTDs from 2003-2009 in Sierra Leone found lymphatic filariasis (LF) endemic in all 14 districts, soil transmitted helminthiasis (STH) endemic in all 14 districts with moderate or high prevalence, onchocerciasis endemic in 12 districts and schistosomiasis in 7 (non-coastal) districts, while trachoma was below public health interventio====n significance (<5%). Coordinating with MDA, a national integrated NTD program began in 2008 with funding from United States Agency for International Development and donated or procured medicines. The goal was to eliminate LF and control STH, schistosomiasis and onchocerciasis by year 2020. The program reached full geographic coverage in 2010 with effective programme coverage for all four NTDs each year. By 2016-2018, despite one round of MDA missing due to the Ebola outbreak, LF transmission had been interrupted in 9 districts as shown by LF transmission assessment surveys (TAS), STH and schistosomiasis prevalence had decreased to low or moderate levels in all endemic districts with prevalence of moderate/heavy infection of below 1% and 2% respectively. The burden of onchocerciasis had also decreased significantly, i.e. at baseline the microfilaridermia prevalence (in population of 1 year old and above) using the skin snip biopsy was 53%, while a recent impact assessment using OV16 rapid diagnostic tests showed an antibody prevalence of 2% in children of 5-9 years of age using the LF TAS sampling methodology. Despite the health sectors in Sierra Leone having been severely damaged during the war (1991-2002), with adequate and consistent funding, technical support and drug supplies, Sierra Leone has made remarkable progress towards the control/elimination of four targeted NTDs.

Partnering for impact: Integrated transmission assessment surveys for lymphatic filariasis, soil transmitted helminths and malaria in Haiti.

BackgroundSince 2001, Haiti’s National Program for the Elimination of Lymphatic Filariasis (NPELF) has worked to reduce the transmission of lymphatic filariasis (LF) through annual mass drug administration (MDA) with diethylcarbamazine and albendazole. The NPELF reached full national coverage with MDA for LF in 2012, and by 2014, a total of 14 evaluation units (48 communes) had met WHO eligibility criteria to conduct LF transmission assessment surveys (TAS) to determine whether prevalence had been reduced to below a threshold, such that transmission is assumed to be no longer sustainable. Haiti is also endemic for malaria and many communities suffer a high burden of soil transmitted helminths (STH). Heeding the call from WHO for integration of neglected tropical diseases (NTD) activities, Haiti’s NPELF worked with the national malaria control program (NMCP) and with partners to develop an integrated TAS (LF-STH-malaria) to include assessments for malaria and STH.Methodology/Principle findingsThe aim of this study was to evaluate the feasibility of using TAS surveys for LF as a platform to collect information about STH and malaria. Between November 2014 and June 2015, TAS were conducted in 14 evaluation units (EUs) including 1 TAS (LF-only), 1 TAS-STH-malaria, and 12 TAS-malaria, with a total of 16,655 children tested for LF, 14,795 tested for malaria, and 298 tested for STH. In all, 12 of the 14 EUs passed the LF TAS, allowing the program to stop MDA for LF in 44 communes. The EU where children were also tested for STH will require annual school-based treatment with albendazole to maintain reduced STH levels. Finally, only 12 of 14,795 children tested positive for malaria by RDT in 38 communes.Conclusions/SignificanceHaiti’s 2014–2015 Integrated TAS surveys provide evidence of the feasibility of using the LF TAS as a platform for integration of assessments for STH and or malaria.

Successful Control of Soil-Transmitted Helminthiasis in School Age Children in Burkina Faso and an Example of Community-Based Assessment via Lymphatic Filariasis Transmission Assessment Survey.

BackgroundBurkina Faso is endemic with soil-transmitted helminth infections. Over a decade of preventive chemotherapy has been implemented through annual lymphatic filariasis (LF) mass drug administration (MDA) for population aged five years and over, biennial treatment of school age children with albendazole together with schistosomiasis MDA and biannual treatment of pre-school age children through Child Health Days. Assessments were conducted to evaluate the current situation and to determine the treatment strategy for the future.Methodology/Principal FindingsA cross-sectional assessment was conducted in 22 sentinel sites across the country in 2013. In total, 3,514 school age children (1,748 boys and 1,766 girls) were examined by the Kato-Katz method. Overall, soil-transmitted helminth prevalence was 1.3% (95% CI: 1.0–1.8%) in children examined. Hookworm was the main species detected, with prevalence of 1.2% (95% CI: 0.9–1.6%) and mean egg counts of 2.1 epg (95% CI: 0–4.2 epg). Among regions, the Centre Ouest region had the highest hookworm prevalence of 3.4% (95% CI: 1.9–6.1%) and mean egg counts of 14.9 epg (95% CI: 3.3–26.6 epg). A separate assessment was conducted in the Centre Nord region in 2014 using community-based cluster survey design during an LF transmission assessment survey (TAS). In this assessment, 351 children aged 6–7 years and 345 children aged 10–14 years were examined, with two cases (0.6% (95% CI: 0.2–2.1%)) and seven cases (2.0% (95% CI: 1.0–4.1%)) of hookworm infection was identified respectively. The results using both age groups categorized the region to be 2% to <10% in STH prevalence according to the pre-defined cut-off values.Conclusions/SignificanceThrough large-scale preventive chemotherapy, Burkina Faso has effectively controlled STH in school age children in the country. Research should be conducted on future strategies to consolidate the gain and to interrupt STH transmission in Burkina Faso. It is also demonstrated that LF TAS provides one feasible and efficient platform to assess the STH situation for post LF MDA decision making.

Factors associated with the performance and cost-effectiveness of using lymphatic filariasis transmission assessment surveys for monitoring soil-transmitted helminths: a case study in Kenya.

Transmission assessment surveys (TAS) for lymphatic filariasis have been proposed as a platform to assess the impact of mass drug administration (MDA) on soil-transmitted helminths (STHs). This study used computer simulation and field data from pre- and post-MDA settings across Kenya to evaluate the performance and cost-effectiveness of the TAS design for STH assessment compared with alternative survey designs. Variations in the TAS design and different sample sizes and diagnostic methods were also evaluated. The district-level TAS design correctly classified more districts compared with standard STH designs in pre-MDA settings. Aggregating districts into larger evaluation units in a TAS design decreased performance, whereas age group sampled and sample size had minimal impact. The low diagnostic sensitivity of Kato-Katz and mini-FLOTAC methods was found to increase misclassification. We recommend using a district-level TAS among children 8–10 years of age to assess STH but suggest that key consideration is given to evaluation unit size.

Lymphatic filariasis transmission assessment survey in schools three years after stopping mass drug treatment with albendazole and ivermectin in the 7 endemic districts in Togo

The aim of this study is to verify the level of transmission of lymphatic filariasis three years after stopping mass drug treatment in the 7 endemic districts in Togo. The survey was conducted in 2012 in Togo's 7 endemic districts grouped into four evaluation units (EU) using the WHO-recommended transmission assessment survey (TAS) protocol. Children aged 6-7 years were screened for Wuchereria bancofti antigen using the immunochromatographic card (ICT) method. A cluster sampling method was used to select eligible children in schools as the net primary-school enrolment ratio is greater than or equal to 75% in each of the four EUs. The number of children and schools to be selected in each EU, the randomization list for the selection of these children and the critical cut-off number of positive cases not to exceed were automatically generated using the Survey Sample Builder (SSB) tool, (NTD Support Center, Atlanta, Ga, USA). For confirmation, positive cases were subsequently tested for microfilaremia using nocturnal thick blood smear and for filarial antigen using Og4C3 antigen ELISA (TropBio ELISA Kit®, Townsville, Queensland, Australia). An EU is considered to have passed the test successfully (it is assumed that transmission can no longer be sustained), when the number of positive cases is below the critical cut-off number set by the SSB, which is roughly equivalent to 2% prevalence. Of the 1 706 children surveyed in Kpendjal-Tone's EU, 1 549 in Binah-Doufelgou's EU, 1 550 in Kozah's EU and the 1 575 in Amou-Haho's EU, 8 (0.46%), 1 (0.08%), 0 (0.00%) and 4 (0.25%) ICT positive cases respectively were detected. The number of positive ICT tests was well below 18, the critical cut number for each of the 4 EUs. All 13 ICT positive cases tested negative for nocturnal microfilaremia and Og4C3 ELISA. We conclude that all four EU passed the TAS with success, and the transmission of Wuchereria bancrofti is no longer likely to be sustained in the 7 endemic districts in Togo 3 years after stopping the MDA. A new TAS will be carried out in 2015, after which, if the results are still good, the country will submit a dossier to WHO for verification of the elimination of lymphatic filariasis.