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Quantifying the impact of decay in bed-net efficacy on malaria transmission.

Ngonghala CN, Del Valle SY, Zhao R, Mohammed-Awel J - J. Theor. Biol. (2014)

Bottom Line: The potential impact of ITNs on reducing malaria transmission is limited due to inconsistent or improper use, as well as physical decay in effectiveness.We develop a model for malaria spread that captures the decrease in ITN effectiveness due to physical and chemical decay, as well as human behavior as a function of time.These analyses show that the basic reproduction number R0, and the infectious human population are most sensitive to bed-net coverage and the biting rate of mosquitoes.

View Article: PubMed Central - PubMed

Affiliation: Department of Global Health and Social Medicine, Harvard Medical School, Boston, MA 02115, USA; National Institute for Mathematical and Biological Synthesis, Knoxville, TN 37996-1527, USA. Electronic address: Calistus_Ngonghala@hms.harvard.edu.

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Simulation results for three ITN efficacy levels and two mosquito biting rates. The top panels show the scenario when the ITNs’ lifespan coincides with the replacement period. The bottom panels show the case when the ITNs’ lifespan is shorter than or equal to the replacement period. Figures (a) and (b) suggest that in both, moderately and highly endemic malaria regions, rapid replacement of ITNs can play an important role in malaria control, while graphs (c) and (d) indicate that when the ITNs’ lifespan is shorter than the replacement period, it will be harder to control malaria.
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Figure 6: Simulation results for three ITN efficacy levels and two mosquito biting rates. The top panels show the scenario when the ITNs’ lifespan coincides with the replacement period. The bottom panels show the case when the ITNs’ lifespan is shorter than or equal to the replacement period. Figures (a) and (b) suggest that in both, moderately and highly endemic malaria regions, rapid replacement of ITNs can play an important role in malaria control, while graphs (c) and (d) indicate that when the ITNs’ lifespan is shorter than the replacement period, it will be harder to control malaria.

Mentions: The top panels of Fig. 6 show the basic reproduction number for different ITN lifespans. In this case, we assume that the lifespan of the bed-net, T, coincides with the replacement period. Fig. 6(a) shows the results when βmax = 0.5, which represents a low mosquito biting rate. The solid brown line shows that if nets are replaced every six months, approximately 45% ITN coverage is required to control malaria. The dash-dotted red line shows that if nets are replaced on a yearly basis, about 48% coverage will be required. The dashed dark green line shows that if nets are replaced every two years, about 54% coverage will be required. The solid blue line shows that if nets are replaced every three years, 58% ITN coverage will be required. The dashed light green line shows that if nets are replaced every four years, 60% ITN protection may be required to control the disease. The biological implication of these results is that for areas where malaria prevalence is low (or mosquito-biting rates are low), the sooner ITNs are replaced, the lower the coverage that will be required to control malaria. However, there will be a cost associated with the replacement of ITNs. Thus, continuous replacement may not be possible in many malaria endemic areas. Fig. 6(b) shows the results when βmax = 1.0. The results suggest that in areas where malaria prevalence is high (or mosquito-biting rates are high), controlling malaria transmission will require a higher ITN coverage. For example, even if ITNs were replaced every six months, more than 89% coverage will be required to bring malaria under control. In other words, control becomes more difficult when the replacement period is longer.


Quantifying the impact of decay in bed-net efficacy on malaria transmission.

Ngonghala CN, Del Valle SY, Zhao R, Mohammed-Awel J - J. Theor. Biol. (2014)

Simulation results for three ITN efficacy levels and two mosquito biting rates. The top panels show the scenario when the ITNs’ lifespan coincides with the replacement period. The bottom panels show the case when the ITNs’ lifespan is shorter than or equal to the replacement period. Figures (a) and (b) suggest that in both, moderately and highly endemic malaria regions, rapid replacement of ITNs can play an important role in malaria control, while graphs (c) and (d) indicate that when the ITNs’ lifespan is shorter than the replacement period, it will be harder to control malaria.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4374367&req=5

Figure 6: Simulation results for three ITN efficacy levels and two mosquito biting rates. The top panels show the scenario when the ITNs’ lifespan coincides with the replacement period. The bottom panels show the case when the ITNs’ lifespan is shorter than or equal to the replacement period. Figures (a) and (b) suggest that in both, moderately and highly endemic malaria regions, rapid replacement of ITNs can play an important role in malaria control, while graphs (c) and (d) indicate that when the ITNs’ lifespan is shorter than the replacement period, it will be harder to control malaria.
Mentions: The top panels of Fig. 6 show the basic reproduction number for different ITN lifespans. In this case, we assume that the lifespan of the bed-net, T, coincides with the replacement period. Fig. 6(a) shows the results when βmax = 0.5, which represents a low mosquito biting rate. The solid brown line shows that if nets are replaced every six months, approximately 45% ITN coverage is required to control malaria. The dash-dotted red line shows that if nets are replaced on a yearly basis, about 48% coverage will be required. The dashed dark green line shows that if nets are replaced every two years, about 54% coverage will be required. The solid blue line shows that if nets are replaced every three years, 58% ITN coverage will be required. The dashed light green line shows that if nets are replaced every four years, 60% ITN protection may be required to control the disease. The biological implication of these results is that for areas where malaria prevalence is low (or mosquito-biting rates are low), the sooner ITNs are replaced, the lower the coverage that will be required to control malaria. However, there will be a cost associated with the replacement of ITNs. Thus, continuous replacement may not be possible in many malaria endemic areas. Fig. 6(b) shows the results when βmax = 1.0. The results suggest that in areas where malaria prevalence is high (or mosquito-biting rates are high), controlling malaria transmission will require a higher ITN coverage. For example, even if ITNs were replaced every six months, more than 89% coverage will be required to bring malaria under control. In other words, control becomes more difficult when the replacement period is longer.

Bottom Line: The potential impact of ITNs on reducing malaria transmission is limited due to inconsistent or improper use, as well as physical decay in effectiveness.We develop a model for malaria spread that captures the decrease in ITN effectiveness due to physical and chemical decay, as well as human behavior as a function of time.These analyses show that the basic reproduction number R0, and the infectious human population are most sensitive to bed-net coverage and the biting rate of mosquitoes.

View Article: PubMed Central - PubMed

Affiliation: Department of Global Health and Social Medicine, Harvard Medical School, Boston, MA 02115, USA; National Institute for Mathematical and Biological Synthesis, Knoxville, TN 37996-1527, USA. Electronic address: Calistus_Ngonghala@hms.harvard.edu.

Show MeSH
Related in: MedlinePlus