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How effective is integrated vector management against malaria and lymphatic filariasis where the diseases are transmitted by the same vector?

Stone CM, Lindsay SW, Chitnis N - PLoS Negl Trop Dis (2014)

Bottom Line: Transmission of both diseases was most sensitive to vector mortality and biting rate.Simulating different levels of coverage of long lasting-insecticidal nets (LLINs) and larval control confirms the effectiveness of these interventions for the control of both diseases.When LF was maintained near the critical density of mosquitoes, minor levels of vector control (8% coverage of LLINs or treatment of 20% of larval sites) were sufficient to eliminate the disease.

View Article: PubMed Central - PubMed

Affiliation: Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.

ABSTRACT

Background: The opportunity to integrate vector management across multiple vector-borne diseases is particularly plausible for malaria and lymphatic filariasis (LF) control where both diseases are transmitted by the same vector. To date most examples of integrated control targeting these diseases have been unanticipated consequences of malaria vector control, rather than planned strategies that aim to maximize the efficacy and take the complex ecological and biological interactions between the two diseases into account.

Methodology/principal findings: We developed a general model of malaria and LF transmission and derived expressions for the basic reproductive number (R0) for each disease. Transmission of both diseases was most sensitive to vector mortality and biting rate. Simulating different levels of coverage of long lasting-insecticidal nets (LLINs) and larval control confirms the effectiveness of these interventions for the control of both diseases. When LF was maintained near the critical density of mosquitoes, minor levels of vector control (8% coverage of LLINs or treatment of 20% of larval sites) were sufficient to eliminate the disease. Malaria had a far greater R0 and required a 90% population coverage of LLINs in order to eliminate it. When the mosquito density was doubled, 36% and 58% coverage of LLINs and larval control, respectively, were required for LF elimination; and malaria elimination was possible with a combined coverage of 78% of LLINs and larval control.

Conclusions/significance: Despite the low level of vector control required to eliminate LF, simulations suggest that prevalence of LF will decrease at a slower rate than malaria, even at high levels of coverage. If representative of field situations, integrated management should take into account not only how malaria control can facilitate filariasis elimination, but strike a balance between the high levels of coverage of (multiple) interventions required for malaria with the long duration predicted to be required for filariasis elimination.

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Related in: MedlinePlus

A) Proportion of mosquitoes infectious with LF when malaria is removed from the co-endemic equilibrium; B) the proportion of mosquitoes infectious with malaria when LF is removed from the co-endemic equilibrium.The negative effect of LF on malaria is due to the increased mortality associated with harbouring W. bancrofti larvae, while the effect of malaria on LF is a balance between the additional death rate on humans, increasing the mosquito∶human ratio, and the Plasmodium-induced mosquito mortality.
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pntd-0003393-g003: A) Proportion of mosquitoes infectious with LF when malaria is removed from the co-endemic equilibrium; B) the proportion of mosquitoes infectious with malaria when LF is removed from the co-endemic equilibrium.The negative effect of LF on malaria is due to the increased mortality associated with harbouring W. bancrofti larvae, while the effect of malaria on LF is a balance between the additional death rate on humans, increasing the mosquito∶human ratio, and the Plasmodium-induced mosquito mortality.

Mentions: Potential positive or negative side effects associated with disease control methods that target a single parasite only (for instance, due to treatment of humans) can be investigated by simulating the artificial removal of either parasite from the co-endemic equilibrium state. The effects on the proportion of infectious mosquitoes of either disease (i.e. harbouring sporozoites or third-stage larvae) after setting all human and mosquito infections to zero for the other disease are shown (Fig. 3). When malaria is removed, LF transmission intensity is expected to initially increase, before decreasing, eventually to a slightly lower equilibrium. The initial rise in the proportion of infectious mosquitoes can be ascribed to the removal of Plasmodium-induced mosquito mortality. Over a much longer period this is balanced by the adjustment in human population size following the removal of malaria-induced human deaths. The implications or removing LF on malaria transmission, based on our model, are more straightforward as transmission will increase in intensity due to the absence of filarial-induced vector mortality.


How effective is integrated vector management against malaria and lymphatic filariasis where the diseases are transmitted by the same vector?

Stone CM, Lindsay SW, Chitnis N - PLoS Negl Trop Dis (2014)

A) Proportion of mosquitoes infectious with LF when malaria is removed from the co-endemic equilibrium; B) the proportion of mosquitoes infectious with malaria when LF is removed from the co-endemic equilibrium.The negative effect of LF on malaria is due to the increased mortality associated with harbouring W. bancrofti larvae, while the effect of malaria on LF is a balance between the additional death rate on humans, increasing the mosquito∶human ratio, and the Plasmodium-induced mosquito mortality.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4263402&req=5

pntd-0003393-g003: A) Proportion of mosquitoes infectious with LF when malaria is removed from the co-endemic equilibrium; B) the proportion of mosquitoes infectious with malaria when LF is removed from the co-endemic equilibrium.The negative effect of LF on malaria is due to the increased mortality associated with harbouring W. bancrofti larvae, while the effect of malaria on LF is a balance between the additional death rate on humans, increasing the mosquito∶human ratio, and the Plasmodium-induced mosquito mortality.
Mentions: Potential positive or negative side effects associated with disease control methods that target a single parasite only (for instance, due to treatment of humans) can be investigated by simulating the artificial removal of either parasite from the co-endemic equilibrium state. The effects on the proportion of infectious mosquitoes of either disease (i.e. harbouring sporozoites or third-stage larvae) after setting all human and mosquito infections to zero for the other disease are shown (Fig. 3). When malaria is removed, LF transmission intensity is expected to initially increase, before decreasing, eventually to a slightly lower equilibrium. The initial rise in the proportion of infectious mosquitoes can be ascribed to the removal of Plasmodium-induced mosquito mortality. Over a much longer period this is balanced by the adjustment in human population size following the removal of malaria-induced human deaths. The implications or removing LF on malaria transmission, based on our model, are more straightforward as transmission will increase in intensity due to the absence of filarial-induced vector mortality.

Bottom Line: Transmission of both diseases was most sensitive to vector mortality and biting rate.Simulating different levels of coverage of long lasting-insecticidal nets (LLINs) and larval control confirms the effectiveness of these interventions for the control of both diseases.When LF was maintained near the critical density of mosquitoes, minor levels of vector control (8% coverage of LLINs or treatment of 20% of larval sites) were sufficient to eliminate the disease.

View Article: PubMed Central - PubMed

Affiliation: Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.

ABSTRACT

Background: The opportunity to integrate vector management across multiple vector-borne diseases is particularly plausible for malaria and lymphatic filariasis (LF) control where both diseases are transmitted by the same vector. To date most examples of integrated control targeting these diseases have been unanticipated consequences of malaria vector control, rather than planned strategies that aim to maximize the efficacy and take the complex ecological and biological interactions between the two diseases into account.

Methodology/principal findings: We developed a general model of malaria and LF transmission and derived expressions for the basic reproductive number (R0) for each disease. Transmission of both diseases was most sensitive to vector mortality and biting rate. Simulating different levels of coverage of long lasting-insecticidal nets (LLINs) and larval control confirms the effectiveness of these interventions for the control of both diseases. When LF was maintained near the critical density of mosquitoes, minor levels of vector control (8% coverage of LLINs or treatment of 20% of larval sites) were sufficient to eliminate the disease. Malaria had a far greater R0 and required a 90% population coverage of LLINs in order to eliminate it. When the mosquito density was doubled, 36% and 58% coverage of LLINs and larval control, respectively, were required for LF elimination; and malaria elimination was possible with a combined coverage of 78% of LLINs and larval control.

Conclusions/significance: Despite the low level of vector control required to eliminate LF, simulations suggest that prevalence of LF will decrease at a slower rate than malaria, even at high levels of coverage. If representative of field situations, integrated management should take into account not only how malaria control can facilitate filariasis elimination, but strike a balance between the high levels of coverage of (multiple) interventions required for malaria with the long duration predicted to be required for filariasis elimination.

Show MeSH
Related in: MedlinePlus