Concept of vectors with special reference to resurgence of malaria
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Background
Considerable declines in malaria have accompanied increased funding for control since the year 2000, but historical failures to maintain gains against the disease underscore the fragility of these successes. Although malaria transmission can be suppressed by effective control measures, in the absence of active intervention malaria will return to an intrinsic equilibrium determined by factors related to ecology, efficiency of mosquito vectors, and socioeconomic characteristics. Understanding where and why resurgence has occurred historically can help current and future malaria control programmes avoid the mistakes of the past.
Methods
A systematic review of the literature was conducted to identify historical malaria resurgence events. All suggested causes of these events were categorized according to whether they were related to weakened malaria control programmes, increased potential for malaria transmission, or technical obstacles like resistance.
Results
The review identified 75 resurgence events in 61 countries, occurring from the 1930s through the 2000s. Almost all resurgence events (68/75 = 91%) were attributed at least in part to the weakening of malaria control programmes for a variety of reasons, of which resource constraints were the most common (39/68 = 57%). Over half of the events (44/75 = 59%) were attributed in part to increases in the intrinsic potential for malaria transmission, while only 24/75 (32%) were attributed to vector or drug resistance.
Conclusions
Given that most malaria resurgences have been linked to weakening of control programmes, there is an urgent need to develop practical solutions to the financial and operational threats to effectively sustaining today’s successful malaria control programmes.
Background
The gains achieved against malaria in the past decade have no parallel since the Global Malaria Eradication Programme (GMEP), which ended in 1969 [1]. Increased funding since 2000 has allowed scale-up of effective interventions, and malaria has declined considerably in many previously highly endemic parts of the world [2]. While these successes confirm that well-funded anti-malaria interventions can have enormous impact, the global increase in malaria burden that occurred in the aftermath of the GMEP [3] underscores the potential fragility of such gains. In 1972, when malaria was on the rise after cessation of the GMEP, Bruce-Chwatt suggested the term “resurgence” to refer to “the reappearance of new infections in significant numbers after malaria has subsided owing to the measures applied to reduce or interrupt its transmission” [4]. Nájera later clarified, “A malaria resurgence is actually the return to a state of equilibrium which has been disturbed” [5] by malaria control efforts.
Resurgence is the result of the fact that there is a certain intrinsic potential for malaria in an area, mathematically described by the basic reproduction number R0[6]. Although malaria can be reduced from that baseline by implementation of effective control measures, in the absence of active suppression malaria will return to a prevalence level determined by R0. This intrinsic potential for malaria transmission may evolve slowly as a function of socioeconomic development or environmental change. Such structural changes may eventually result in sufficiently low potential that active measures are not required to suppress transmission, but the malaria baseline will usually be unaffected by commonly implemented malaria control activities [7]. The concept of resurgence as a return towards a baseline level of malaria is distinct from that of “rebound” [8], which is used to describe a hypothetical overshoot that could occur in populations that have lost their immunity.
Today, the threat of resurgence again looms as constrained global funding and competing priorities threaten the sustainability of successes [9,10]. Brief increases in malaria incidence in countries including Rwanda and Zambia have raised fears about whether recent gains against malaria can be sustained and extended
Background
Considerable declines in malaria have accompanied increased funding for control since the year 2000, but historical failures to maintain gains against the disease underscore the fragility of these successes. Although malaria transmission can be suppressed by effective control measures, in the absence of active intervention malaria will return to an intrinsic equilibrium determined by factors related to ecology, efficiency of mosquito vectors, and socioeconomic characteristics. Understanding where and why resurgence has occurred historically can help current and future malaria control programmes avoid the mistakes of the past.
Methods
A systematic review of the literature was conducted to identify historical malaria resurgence events. All suggested causes of these events were categorized according to whether they were related to weakened malaria control programmes, increased potential for malaria transmission, or technical obstacles like resistance.
Results
The review identified 75 resurgence events in 61 countries, occurring from the 1930s through the 2000s. Almost all resurgence events (68/75 = 91%) were attributed at least in part to the weakening of malaria control programmes for a variety of reasons, of which resource constraints were the most common (39/68 = 57%). Over half of the events (44/75 = 59%) were attributed in part to increases in the intrinsic potential for malaria transmission, while only 24/75 (32%) were attributed to vector or drug resistance.
Conclusions
Given that most malaria resurgences have been linked to weakening of control programmes, there is an urgent need to develop practical solutions to the financial and operational threats to effectively sustaining today’s successful malaria control programmes.
Background
The gains achieved against malaria in the past decade have no parallel since the Global Malaria Eradication Programme (GMEP), which ended in 1969 [1]. Increased funding since 2000 has allowed scale-up of effective interventions, and malaria has declined considerably in many previously highly endemic parts of the world [2]. While these successes confirm that well-funded anti-malaria interventions can have enormous impact, the global increase in malaria burden that occurred in the aftermath of the GMEP [3] underscores the potential fragility of such gains. In 1972, when malaria was on the rise after cessation of the GMEP, Bruce-Chwatt suggested the term “resurgence” to refer to “the reappearance of new infections in significant numbers after malaria has subsided owing to the measures applied to reduce or interrupt its transmission” [4]. Nájera later clarified, “A malaria resurgence is actually the return to a state of equilibrium which has been disturbed” [5] by malaria control efforts.
Resurgence is the result of the fact that there is a certain intrinsic potential for malaria in an area, mathematically described by the basic reproduction number R0[6]. Although malaria can be reduced from that baseline by implementation of effective control measures, in the absence of active suppression malaria will return to a prevalence level determined by R0. This intrinsic potential for malaria transmission may evolve slowly as a function of socioeconomic development or environmental change. Such structural changes may eventually result in sufficiently low potential that active measures are not required to suppress transmission, but the malaria baseline will usually be unaffected by commonly implemented malaria control activities [7]. The concept of resurgence as a return towards a baseline level of malaria is distinct from that of “rebound” [8], which is used to describe a hypothetical overshoot that could occur in populations that have lost their immunity.
Today, the threat of resurgence again looms as constrained global funding and competing priorities threaten the sustainability of successes [9,10]. Brief increases in malaria incidence in countries including Rwanda and Zambia have raised fears about whether recent gains against malaria can be sustained and extended
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