Limits...
Modeling the interruption of the transmission of soil-transmitted helminths by repeated mass chemotherapy of school-age children.

Truscott J, Hollingsworth TD, Anderson R - PLoS Negl Trop Dis (2014)

Bottom Line: For a given rate of drug use, sexual reproduction dictates that less frequent, higher coverage treatment is more effective.Our work suggests that for models to capture the dynamics of parasite burdens in populations under regular treatment as elimination is approached, they need to include the effects of sexual reproduction among parasites and the dynamics infectious material in the reservoir.The interaction of these two mechanisms has a strong effect on optimum treatment strategies, both in terms of how frequently to treat and for how long.

View Article: PubMed Central - PubMed

Affiliation: London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, Faculty of Medicine, Imperial College London, St Marys Campus, Norfolk Place, London, United Kingdom.

ABSTRACT

Background: The control or elimination of neglected tropical diseases has recently become the focus of increased interest and funding from international agencies through the donation of drugs. Resources are becoming available for the treatment of soil-transmitted helminth (STH) infection through school-based deworming strategies. However, little research has been conducted to assess the impact of STH treatment that could be used to guide the design of efficient elimination programs.

Methodology: We construct and analyse an age-structured model of STH population dynamics under regular treatment. We investigate the potential for elimination with finite rounds of treatment, and how this depends on the value of the basic reproductive number R0 and treatment frequency.

Principal findings: Analysis of the model indicates that its behaviour is determined by key parameter groupings describing the basic reproduction number and the fraction of it attributable to the treated group, the timescale of material in the environment and the frequency and efficacy of treatment. Mechanisms of sexual reproduction and persistence of infectious material in the environment are found to be much more important in the context of elimination than in the undisturbed baseline scenario. For a given rate of drug use, sexual reproduction dictates that less frequent, higher coverage treatment is more effective. For a given treatment coverage level, the lifespan of infectious material in the environment places a limit on the effectiveness of increased treatment frequency.

Conclusions: Our work suggests that for models to capture the dynamics of parasite burdens in populations under regular treatment as elimination is approached, they need to include the effects of sexual reproduction among parasites and the dynamics infectious material in the reservoir. The interaction of these two mechanisms has a strong effect on optimum treatment strategies, both in terms of how frequently to treat and for how long.

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Related in: MedlinePlus

Dependence of growth rate, k, on A) R0 and effective treatment, γ; B) contribution of children to parasite reproduction, rc, and effective treatment; C) relative reservoir timescale, ε, and effective treatment.D) Extinction point for parasite for different values of ε. [For C, R0 = 2.5 and D, rc = 1].
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pntd-0003323-g002: Dependence of growth rate, k, on A) R0 and effective treatment, γ; B) contribution of children to parasite reproduction, rc, and effective treatment; C) relative reservoir timescale, ε, and effective treatment.D) Extinction point for parasite for different values of ε. [For C, R0 = 2.5 and D, rc = 1].

Mentions: In Figure 2, we examine how the resilience of the model to treatment, as expressed by q, depends on these key parameters. Figures 2 A and 2B illustrate the impact of treatment efficacy on Re as a function of R0 and rc, respectively. Figure 2A shows that the effect of treatment on q is approximately linear for the range of R0 which we are considering. Fully effective treatment reduces q by about 40%. Extinction of the parasite is only possible for low R0 (around 1.5) and the highest levels of effective treatment coverage (close to 100% with efficacy of 70%).


Modeling the interruption of the transmission of soil-transmitted helminths by repeated mass chemotherapy of school-age children.

Truscott J, Hollingsworth TD, Anderson R - PLoS Negl Trop Dis (2014)

Dependence of growth rate, k, on A) R0 and effective treatment, γ; B) contribution of children to parasite reproduction, rc, and effective treatment; C) relative reservoir timescale, ε, and effective treatment.D) Extinction point for parasite for different values of ε. [For C, R0 = 2.5 and D, rc = 1].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4256169&req=5

pntd-0003323-g002: Dependence of growth rate, k, on A) R0 and effective treatment, γ; B) contribution of children to parasite reproduction, rc, and effective treatment; C) relative reservoir timescale, ε, and effective treatment.D) Extinction point for parasite for different values of ε. [For C, R0 = 2.5 and D, rc = 1].
Mentions: In Figure 2, we examine how the resilience of the model to treatment, as expressed by q, depends on these key parameters. Figures 2 A and 2B illustrate the impact of treatment efficacy on Re as a function of R0 and rc, respectively. Figure 2A shows that the effect of treatment on q is approximately linear for the range of R0 which we are considering. Fully effective treatment reduces q by about 40%. Extinction of the parasite is only possible for low R0 (around 1.5) and the highest levels of effective treatment coverage (close to 100% with efficacy of 70%).

Bottom Line: For a given rate of drug use, sexual reproduction dictates that less frequent, higher coverage treatment is more effective.Our work suggests that for models to capture the dynamics of parasite burdens in populations under regular treatment as elimination is approached, they need to include the effects of sexual reproduction among parasites and the dynamics infectious material in the reservoir.The interaction of these two mechanisms has a strong effect on optimum treatment strategies, both in terms of how frequently to treat and for how long.

View Article: PubMed Central - PubMed

Affiliation: London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, Faculty of Medicine, Imperial College London, St Marys Campus, Norfolk Place, London, United Kingdom.

ABSTRACT

Background: The control or elimination of neglected tropical diseases has recently become the focus of increased interest and funding from international agencies through the donation of drugs. Resources are becoming available for the treatment of soil-transmitted helminth (STH) infection through school-based deworming strategies. However, little research has been conducted to assess the impact of STH treatment that could be used to guide the design of efficient elimination programs.

Methodology: We construct and analyse an age-structured model of STH population dynamics under regular treatment. We investigate the potential for elimination with finite rounds of treatment, and how this depends on the value of the basic reproductive number R0 and treatment frequency.

Principal findings: Analysis of the model indicates that its behaviour is determined by key parameter groupings describing the basic reproduction number and the fraction of it attributable to the treated group, the timescale of material in the environment and the frequency and efficacy of treatment. Mechanisms of sexual reproduction and persistence of infectious material in the environment are found to be much more important in the context of elimination than in the undisturbed baseline scenario. For a given rate of drug use, sexual reproduction dictates that less frequent, higher coverage treatment is more effective. For a given treatment coverage level, the lifespan of infectious material in the environment places a limit on the effectiveness of increased treatment frequency.

Conclusions: Our work suggests that for models to capture the dynamics of parasite burdens in populations under regular treatment as elimination is approached, they need to include the effects of sexual reproduction among parasites and the dynamics infectious material in the reservoir. The interaction of these two mechanisms has a strong effect on optimum treatment strategies, both in terms of how frequently to treat and for how long.

Show MeSH
Related in: MedlinePlus