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The potential contribution of mass treatment to the control of Plasmodium falciparum malaria.

Okell LC, Griffin JT, Kleinschmidt I, Hollingsworth TD, Churcher TS, White MJ, Bousema T, Drakeley CJ, Ghani AC - PLoS ONE (2011)

Bottom Line: We also estimate the effects of using gametocytocidal treatments such as primaquine and of restricting treatment to parasite-positive individuals.In conclusion, mass treatment needs to be repeated or combined with other interventions for long-term impact in many endemic settings.The benefits of mass treatment need to be carefully weighed against the risks of increasing drug selection pressure.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious Disease Epidemiology, MRC Centre for Outbreak Analysis and Modeling, Imperial College London, London, United Kingdom. l.okell@imperial.ac.uk

ABSTRACT
Mass treatment as a means to reducing P. falciparum malaria transmission was used during the first global malaria eradication campaign and is increasingly being considered for current control programmes. We used a previously developed mathematical transmission model to explore both the short and long-term impact of possible mass treatment strategies in different scenarios of endemic transmission. Mass treatment is predicted to provide a longer-term benefit in areas with lower malaria transmission, with reduced transmission levels for at least 2 years after mass treatment is ended in a scenario where the baseline slide-prevalence is 5%, compared to less than one year in a scenario with baseline slide-prevalence at 50%. However, repeated annual mass treatment at 80% coverage could achieve around 25% reduction in infectious bites in moderate-to-high transmission settings if sustained. Using vector control could reduce transmission to levels at which mass treatment has a longer-term impact. In a limited number of settings (which have isolated transmission in small populations of 1000-10,000 with low-to-medium levels of baseline transmission) we find that five closely spaced rounds of mass treatment combined with vector control could make at least temporary elimination a feasible goal. We also estimate the effects of using gametocytocidal treatments such as primaquine and of restricting treatment to parasite-positive individuals. In conclusion, mass treatment needs to be repeated or combined with other interventions for long-term impact in many endemic settings. The benefits of mass treatment need to be carefully weighed against the risks of increasing drug selection pressure.

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Related in: MedlinePlus

Model-estimated combined impact of MDA and vector control and the potential for elimination.(A) Vector control is scaled up in year 0, with or without 2 rounds of MDA during the first year. B), C) & D) Probabilities of local elimination in an isolated population of (B) 1000, (C) 10,000 or (D) 500,000 using vector control alone or in combination with MDA. Transmission is moderately seasonal and MDA is given prior to the transmission season.
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pone-0020179-g004: Model-estimated combined impact of MDA and vector control and the potential for elimination.(A) Vector control is scaled up in year 0, with or without 2 rounds of MDA during the first year. B), C) & D) Probabilities of local elimination in an isolated population of (B) 1000, (C) 10,000 or (D) 500,000 using vector control alone or in combination with MDA. Transmission is moderately seasonal and MDA is given prior to the transmission season.

Mentions: Scaling up vector control together with MDA raises the probability of elimination above what would be achieved with either strategy alone. We assume that a scaled-up vector control programme would approximately halve slide-prevalence of infection 2 years after its introduction in most scenarios when used alone (simulations suggest this could be achieved by raising insecticide-treated net coverage to 80%, see Text S1). MDA can speed up the reduction in slide-prevalence (Figure 4A) and while it does not in the long-term produce a lower prevalence than would be achieved by vector control alone, prevalence can be brought to low levels for a period of time which raises the chance of elimination. For example in a population of 1000, estimated probabilities of elimination of >40% could be achieved in settings of up to 25% baseline slide-prevalence by 5 rounds of MDA together with simultaneous scale-up of vector control (Figure 4B). However in a larger population of 10,000, the probabilities using the same strategies would be considerably lower (Figure 4C) and would approach zero in a population of 500,000 (Figure 4D).


The potential contribution of mass treatment to the control of Plasmodium falciparum malaria.

Okell LC, Griffin JT, Kleinschmidt I, Hollingsworth TD, Churcher TS, White MJ, Bousema T, Drakeley CJ, Ghani AC - PLoS ONE (2011)

Model-estimated combined impact of MDA and vector control and the potential for elimination.(A) Vector control is scaled up in year 0, with or without 2 rounds of MDA during the first year. B), C) & D) Probabilities of local elimination in an isolated population of (B) 1000, (C) 10,000 or (D) 500,000 using vector control alone or in combination with MDA. Transmission is moderately seasonal and MDA is given prior to the transmission season.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3101232&req=5

pone-0020179-g004: Model-estimated combined impact of MDA and vector control and the potential for elimination.(A) Vector control is scaled up in year 0, with or without 2 rounds of MDA during the first year. B), C) & D) Probabilities of local elimination in an isolated population of (B) 1000, (C) 10,000 or (D) 500,000 using vector control alone or in combination with MDA. Transmission is moderately seasonal and MDA is given prior to the transmission season.
Mentions: Scaling up vector control together with MDA raises the probability of elimination above what would be achieved with either strategy alone. We assume that a scaled-up vector control programme would approximately halve slide-prevalence of infection 2 years after its introduction in most scenarios when used alone (simulations suggest this could be achieved by raising insecticide-treated net coverage to 80%, see Text S1). MDA can speed up the reduction in slide-prevalence (Figure 4A) and while it does not in the long-term produce a lower prevalence than would be achieved by vector control alone, prevalence can be brought to low levels for a period of time which raises the chance of elimination. For example in a population of 1000, estimated probabilities of elimination of >40% could be achieved in settings of up to 25% baseline slide-prevalence by 5 rounds of MDA together with simultaneous scale-up of vector control (Figure 4B). However in a larger population of 10,000, the probabilities using the same strategies would be considerably lower (Figure 4C) and would approach zero in a population of 500,000 (Figure 4D).

Bottom Line: We also estimate the effects of using gametocytocidal treatments such as primaquine and of restricting treatment to parasite-positive individuals.In conclusion, mass treatment needs to be repeated or combined with other interventions for long-term impact in many endemic settings.The benefits of mass treatment need to be carefully weighed against the risks of increasing drug selection pressure.

View Article: PubMed Central - PubMed

Affiliation: Department of Infectious Disease Epidemiology, MRC Centre for Outbreak Analysis and Modeling, Imperial College London, London, United Kingdom. l.okell@imperial.ac.uk

ABSTRACT
Mass treatment as a means to reducing P. falciparum malaria transmission was used during the first global malaria eradication campaign and is increasingly being considered for current control programmes. We used a previously developed mathematical transmission model to explore both the short and long-term impact of possible mass treatment strategies in different scenarios of endemic transmission. Mass treatment is predicted to provide a longer-term benefit in areas with lower malaria transmission, with reduced transmission levels for at least 2 years after mass treatment is ended in a scenario where the baseline slide-prevalence is 5%, compared to less than one year in a scenario with baseline slide-prevalence at 50%. However, repeated annual mass treatment at 80% coverage could achieve around 25% reduction in infectious bites in moderate-to-high transmission settings if sustained. Using vector control could reduce transmission to levels at which mass treatment has a longer-term impact. In a limited number of settings (which have isolated transmission in small populations of 1000-10,000 with low-to-medium levels of baseline transmission) we find that five closely spaced rounds of mass treatment combined with vector control could make at least temporary elimination a feasible goal. We also estimate the effects of using gametocytocidal treatments such as primaquine and of restricting treatment to parasite-positive individuals. In conclusion, mass treatment needs to be repeated or combined with other interventions for long-term impact in many endemic settings. The benefits of mass treatment need to be carefully weighed against the risks of increasing drug selection pressure.

Show MeSH
Related in: MedlinePlus