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A comparison of two mathematical models of the impact of mass drug administration on the transmission and control of schistosomiasis.

ABSTRACT: The predictions of two mathematical models describing the transmission dynamics of schistosome infection and the impact of mass drug administration are compared. The models differ in their description of the dynamics of the parasites within the host population and in their representation of the stages of the parasite lifecycle outside of the host. Key parameters are estimated from data collected in northern Mozambique from 2011 to 2015. This type of data set is valuable for model validation as treatment prior to the study was minimal. Predictions from both models are compared with each other and with epidemiological observations. Both models have difficulty matching both the intensity and prevalence of disease in the datasets and are only partially successful at predicting the impact of treatment. The models also differ from each other in their predictions, both quantitatively and qualitatively, of the long-term impact of 10 years' school-based mass drug administration. We trace the dynamical differences back to basic assumptions about worm aggregation, force of infection and the dynamics of the parasite in the snail population in the two models and suggest data which could discriminate between them. We also discuss limitations with the datasets used and ways in which data collection could be improved.

SUBMITTER: Truscott JE

PROVIDER: S-EPMC5340850 | biostudies-literature | 2017 Mar

REPOSITORIES: biostudies-literature

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A comparison of two mathematical models of the impact of mass drug administration on the transmission and control of schistosomiasis.

Truscott J E JE Gurarie D D Alsallaq R R Toor J J Yoon N N Farrell S H SH Turner H C HC Phillips A E AE Aurelio H O HO Ferro J J King C H CH Anderson R M RM

Epidemics 20170301

The predictions of two mathematical models describing the transmission dynamics of schistosome infection and the impact of mass drug administration are compared. The models differ in their description of the dynamics of the parasites within the host population and in their representation of the stages of the parasite lifecycle outside of the host. Key parameters are estimated from data collected in northern Mozambique from 2011 to 2015. This type of data set is valuable for model validation as t ...[more]

PMID: 28279453

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Project description:BackgroundSchistosomiasis is a neglected tropical disease, targeted by the World Health Organization for reduction in morbidity by 2020. It is caused by parasitic flukes that spread through contamination of local water sources. Traditional control focuses on mass drug administration, which kills the majority of adult worms, targeted at school-aged children. However, these drugs do not confer long-term protection and there are concerns over the emergence of drug resistance. The development of a vaccine against schistosomiasis opens the potential for control methods that could generate long-lasting population-level immunity if they are cost-effective.MethodsUsing an individual-based transmission model, matched to epidemiological data, we compared the cost-effectiveness of a range of vaccination programmes against mass drug administration, across three transmission settings. Health benefit was measured by calculating the heavy-intensity infection years averted by each intervention, while vaccine costs were assessed against robust estimates for the costs of mass drug administration obtained from data. We also calculated a critical vaccination cost, a cost beyond which vaccination might not be economically favorable, by benchmarking the cost-effectiveness of potential vaccines against the cost-effectiveness of mass drug administration, and examined the effect of different vaccine protection durations.ResultsWe found that sufficiently low-priced vaccines can be more cost-effective than traditional drugs in high prevalence settings, and can lead to a greater reduction in morbidity over shorter time-scales. MDA or vaccination programmes that target the whole community generate the most health benefits, but are generally less cost-effective than those targeting children, due to lower prevalence of schistosomiasis in adults.ConclusionsThe ultimate cost-effectiveness of vaccination will be highly dependent on multiple vaccine characteristics, such as the efficacy, cost, safety and duration of protection, as well as the subset of population targeted for vaccination. However, our results indicate that if a vaccine could be developed with reasonable characteristics and for a sufficiently low cost, then vaccination programmes can be a highly cost-effective method of controlling schistosomiasis in high-transmission areas. The population-level immunity generated by vaccination will also inevitably improve the chances of interrupting transmission of the disease, which is the long-term epidemiological goal.

Project description:IntroductionSchistosomiasis is one of the neglected tropical diseases targeted for elimination in Uganda through the Mass Drug Administration (MDA) programme. Praziquantel has been distributed using community resource persons in fixed sites and house-to-house visits; however the uptake is still below target coverage. In 2011/2012 MDA exercise, uptake stood at 50% yet WHO target coverage is 75% at community level. We assessed the uptake of MDA and the associated factors in Koome Islands, Central Uganda.MethodsIn March 2013, we conducted a mixed methods cross sectional study in 15 randomly selected villages. We interviewed a total of 615 respondents aged 18 years and above using semi structured questionnaires and five key informants were also purposively selected. Univariate and multivariate analysis was done. MDA uptake was defined as self reported swallowing of praziquantel during the last (2012) MDA campaign. We conducted key informant interviews with Ministry of Health, district health personnel and community health workers.ResultsSelf reported uptake of praziquantel was 44.7% (275/615), 95% confidence interval (CI) 40.8-48.7%. Of the 275 community members who said they had swallowed praziquantel, 142 (51.6%) reported that they had developed side effects. Uptake of MDA was more likely if the respondent was knowledgeable about schistosomiasis transmission and prevention (adjusted odds ratio [AOR] 1.85, 95% CI 1.22-2.81) and reported to have received health education from the health personnel (AOR 5.95, 95% CI 3.67-9.65). Service delivery challenges such as drug shortages and community health worker attrition also influenced MDA in Koome Islands.ConclusionsUptake of MDA for schistosomiasis control in Koome was sub optimal. Lack of knowledge about schistosomiasis transmission and prevention, inadequate health education and drug shortages are some of the major factors associated with low uptake. These could be addressed through routine health education and systematic drug supply for the successful elimination of schistosomiasis on the islands.

Project description:BackgroundMass drug administration is one of the key interventions recommended by WHO to control certain NTDs. With most support from donors, health workers distribute antihelminthic drugs annually in Malawi. Mean community coverage of MDA from 2018 to 2020 was high at 87% for praziquantel and 82% for albendazole. However, once donor support diminishes sustaining these levels will be challenging. This study intended to compare the use of the community-directed intervention approach with the standard practice of using health workers in delivery of MDA campaigns.MethodsThis was a controlled implementation study carried out in three districts, where four health centres and 16 villages in each district were selected and randomly assigned to intervention and control arms which implemented MDA campaigns using the CDI approach and the standard practice, respectively. Cross-sectional and mixed methods approach to data collection was used focusing on quantitative data for coverage and knowledge levels and qualitative data to assess perceptions of health providers and beneficiaries at baseline and follow-up assessments. Quantitative and qualitative data were analyzed using IBM SPSS software version 26 and NVivo 12 for Windows, respectively.ResultsAt follow-up, knowledge levels increased, majority of the respondents were more knowledgeable about what schistosomiasis was (41%-44%), its causes (41%-44%) and what STH were (48%-64%), while knowledge on intermediate host for schistosomiasis (19%-22%), its types (9%-13%) and what causes STH (15%-16%) were less known both in intervention and control arm communities. High coverage rates for praziquantel were registered in intervention (83%-89%) and control (86%-89%) communities, intervention (59%-79) and control (53%-86%) schools. Costs for implementation of the study indicated that the intervention arm used more resources than the control arm. Health workers and community members perceived the use of the CDI approach as a good initiative and more favorable over the standard practice.ConclusionsThe use of the CDI in delivery of MDA campaigns against schistosomiasis and STH appears feasible, retains high coverages and is acceptable in intervention communities. Despite the initial high costs incurred, embedding into community delivery platforms could be considered as a possible way forward addressing the sustainability concern when current donor support wanes.Trial registrationPan-African Clinical Trials Registry PACTR202102477794401, date: 25/02/2021.

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A comparison of two mathematical models of the impact of mass drug administration on the transmission and control of schistosomiasis.

Publications

A comparison of two mathematical models of the impact of mass drug administration on the transmission and control of schistosomiasis.

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